[0001] This application incorporates by reference and claims priority to U.S. Provisional Patent Application 63/370,991 , filed August 10, 2022.

TECHANICAL FIELD

[0002] The invention relates to endovascular treatment of stenosis and chronic total occlusions of a patient’s peripheral arteries, particularly the navigation of crossing devices used to connect a vein and an artery in a percutaneous femoral popliteal bypass.

BACKGROUND

[0003] Peripheral artery disease has been associated with significant morbidity and mortality. Critical limb ischemia, the late stage and worst form of peripheral artery disease, is characterized by multilevel and multivessel arterial stenoses, and an increasing risk for limb loss, and death.

[0004] Peripheral artery disease affects 200 million people worldwide, and 20 million people in the United States. Further, it is estimated that 25- 30 million people worldwide and greater than 3 million in the United States alone are burdened with critical limb ischemia. Moderate to severe calcium is present in 50% of peripheral artery disease patients with severe claudication (cramping pain in the leg is induced by exercise), and the numbers are even higher (greater than 65%) in critical limb ischemia patients.

[0005] Calcification is a hallmark of advanced atherosclerotic disease and is often hard to treat. Stenosis and chronic total occlusions are encountered frequently in patients with both coronary and peripheral artery disease. These occlusions are associated with a higher risk of adverse events, decreased quality of life, worse procedural success and treatment outcomes, and increased healthcare costs. Angioplasty, stenting, surgical bypass, and endovascular treatment strategies are all therapies that have been employed to treat occlusions.

[0006] Endovascular treatment strategies are less invasive than bypass surgery and have evolved to increasingly become the revascularization methods of choice for patients with severe peripheral artery disease and critical limb ischemia. Successful revascularization significantly reduces the need for amputations.

[0007] Although the endovascular approach is the first-choice treatment in patients suffering from peripheral artery disease and artery occlusions, standard endoluminal revascularization fails in treating occlusions in about 20% of cases. Subintimal revascularization is an alternative solution, but it fails in 25% of cases as well. Percutaneous intentional extraluminal revascularization has been employed as an ancillary technique, to cross chronic total occlusions when standard subintimal revascularization does not work or risks to occlude important collateral vessels.

[0008] Although progress has been made in avoiding invasive bypass surgery, many occlusions remain hard to treat because treatment requires crossing the occlusion with the therapeutic catheter. In these cases, percutaneous extraluminal bypass is a promising option. Percutaneous intentional extraluminal revascularization (PIER) is a percutaneous technique used in interventional radiology for limb salvage in patients with lower limb ischemia due to long superficial femoral artery occlusions. During PIER a guide wire is intentionally introduced in the subintimal space, after which balloon dilatation is performed to create a new lumen for the blood to flow through e.g. between the layers of the arterial wall. However, as are all procedures that require reentry of the true arterial lumen, the rotation of the reentry device can cause misplacement of the penetration needle or a mismatch between the needle's exit point and the radiological markers with subsequent unsuccessful punctures. [0009] One recently introduced approach that avoids surgically bypassing an “uncrossable” occlusion includes a fully percutaneous femoral-popliteal bypass. Using fluoroscopic guidance, a series of stent grafts are deployed from the popliteal artery into the femoral vein, and from the femoral vein into the superficial femoral artery in a continuous, overlapping fashion through two independent anastomoses. The intended result is a large lumen, endograft bypass that delivers unobstructed, pulsatile flow from the femoral artery to the popliteal artery. This approach is described in U.S. patent 1 1 ,090,177; the entire content of which is incorporated herein by reference. Percutaneous femoral popliteal bypass (also known as PQ Bypass) is marketed as DETOUR System by PQ Bypass, Milpitas, California for the percutaneous bypass of long-segment femoropopliteal occlusive disease. While successful, the percutaneous femoral popliteal bypass remains a challenging procedure that may require more time and skill to perform than desired.

[0010] In particular, since percutaneous femoral popliteal bypass performs a penetration from a relatively larger and very elastic vein into a relatively smaller arterial lumen (around 4 mm) the penetration maneuver can be a challenge for the operator. For percutaneous femoral popliteal bypass procedures involving the femoral artery and vein, the challenges of the penetration maneuver can be further exacerbated by the fact that near the knee vascular and nerve structures condense and the space becomes crowded. It is also noted that veins can be easily moved and distorted when a relatively stiff tool is inserted into a veinous lumen, and that fluoroscopy provides a two-dimension (2D) projection instead of a three- dimensional (3D) map for the procedure with no way to obtain a view that is cross sectional to both artery and vein. In addition, the radiocontrast dye used to assist fluoroscopy is nephrotoxic and there is a general need to reduce use of X-ray to limit radiation exposure and to reduce the use of nephrotoxic dye to limit its exposure to the patient’s kidneys. As a result of poor alignment, multiple punctures may be needed to place the exchange wire across from the vein lumen to the artery lumen.

[001 1 ] This challenge is not only present for the femoral artery and vein but is also present in any procedure that involves crossing from one blood vessel into another to joining a vein and an artery in an extremity or a body trunk such as during the creation of arteriovenous fistula for dialysis, percutaneous venous arterialization, or percutaneous coronary bypass.

[0012] Another challenge is that the existing procedures are complex, require high degree of skill, and take a long time to complete (e.g., up to three hours). In addition, although intravascular ultrasound devices are effective, they are expensive and require capital equipment purchases and significant maintenance and training. They also require an external console that is cumbersome, takes valuable Cath lab space and is also expensive. A simpler artery to vein and particularly vein to artery crossing procedure that requires less skill and less time to complete the percutaneous femoral popliteal bypass is desired. SUMMARY

[0013] Inventors propose a system and a method that solves the problems discussed above.

[0014] In one aspect of the technology, an apparatus for enabling safe crossing is a crossing catheter that comprises a hollow needle, a shaft with a distal ultrasound transducer aligned with the lumen of the hollow needle, and a waveform generator operatively connected to the ultrasound transducer and configured to energize the ultrasound transducer to produce a pulsed ultrasound pressure wave of predetermined duration. A signal receiver is electronically connected to the ultrasound transducer, while a signal processor that is a microcontroller and incudes internal or external memory is connected to the receiver and a storage medium such as an electronic storage that contains command code and received data. The signal processor is configured to record, in the storage medium, magnitudes of Doppler frequency changes of ultrasonic waves reflected from one or more predetermined sample volumes at respective predetermined distances from the ultrasound transducer in a selected ultrasound-transmissive medium. Settings relevant to these parameters may be entered by the user using user interface such as knobs, buttons or separate tablet in communication with the electronics inside the catheter handle assembly.

[0015] In another configuration, the apparatus further comprises an electro-acoustic transducer operatively connected to the signal processor to generate an audible signal, a haptic signal or a visual signal feedback varying with Doppler magnitude as dependent on a direction of propagation of the pulsed ultrasound pressure wave in the selected ultrasound-transmissive blood and tissue.

[0016] The predetermined tissue examination sample volume of the apparatus is typically has a depth of several millimeters or tens of millimeters, chosen so that blood flow is detectable in the volume corresponding to the length of the extended penetration needle.

[0017] The waveform generator may be operatively connected to the signal processor for transmitting the selected waveform to the ultrasound transducer, in response to a control signal from the signal processor, a pulsed electrical signal inducing the ultrasound transducer to produce the pulsed ultrasound pressure wave of the predetermined amplitude, frequency and duration. The signal receiver and the signal processor are configured to process Doppler frequency changes of incoming reflected pressure waves arriving at a predetermined interval after termination of the pulsed ultrasound pressure wave, whereby size and location of the predetermined sample volume of tissue may be preselected to contain the targeted blood vessel within the volume.

[0018] The apparatus may additionally comprise a power source such as battery to power electronics. That entire electronics assembly including the battery may be supplies sterile for single use.

[0019] The apparatus may additionally comprise communication hardware for near field or mid field radio communication such as Bluetooth communication with an external display or controller with expanded user interface capable of storing images such as a smart phone or a tablet. [0020] The apparatus may additionally comprise a shaft configured to transmit torque such as a braided polymer coated shaft and an ergonomic handle attached to the distal end of the shaft for steering or orienting a distal end portion of the hollow needle and/or the Doppler transducer to thereby adjust a direction of propagation of the pulsed ultrasound pressure wave towards location locations of the sample volume that contains the targeted vessel.

[0021] In addition, in some embodiments the apparatus may include advanced mechanical features to assist the operator in crossing from one vessel into the targeted vessel. The handle electronics may comprise an electromechanical locking mechanism, such as a solenoid latch, designed to lock the needle release spring loaded mechanism until the correct target volume is identified by the Doppler targeting electronics. This latch mechanism may be a solenoid release pin operating as a trigger safety of a firing pin of a firearm.

[0022] In another configuration the electromechanical mechanism can be used to rotate the shaft inside the handle such as worm drive or a gear drive. The gear mechanism may be designed to rotate the shaft inside the handle and the blood vessel slowly to achieve alignment of the penetration needle with the target vessel based on the Doppler signal strength.

[0023] In yet another aspect of the technology, a method for crossing from artery to vein and from vein to artery to create a fully percutaneous bypass of an occluded artery segment in a mammalian subject comprises, in accordance with the present invention, providing a crossing catheter having a Doppler ultrasound transducer and a directionally advanceable puncture needle at a distal end thereof aligned with the transducer, inserting a distal end portion of the crossing catheter into a lumen of a vein, manipulating the shaft to align the hollow needle and the transducer to position the Doppler ultrasound transducer in the direction facing towards the targeted artery of the mammalian subject while that the distal end portion of the needle is retracted and thereafter actuating the Doppler transducer to transmit pulsed Doppler signals to scan blood flow velocity within a predetermined sample volume located at the predetermined distance from the transducer corresponding to the length of the extended and deployed needle of the mammalian subject and deploying the needle when the Doppler return signal is strongest and indicates that the needle is pointing to the artery located within the anticipated range at the crossing distance, advancing the hollow needle through a side opening of the steerable shaft through the wall of the vein predetermined distance so that a distal end portion of the needle is located in the targeted artery within the targeted volume of the mammalian subject and so that the distal end portion of the shaft remains in the vein.

[0024] The actuating of the Doppler transducer typically includes inducing the Doppler transducer to produce a pulsed ultrasound pressure wave of a predetermined duration. The method further comprises monitoring incoming reflected pressure waves arriving a predetermined interval after termination of the pulsed ultrasound pressure wave, whereby size and location of the predetermined sample volume may be preselected to be located within the distance of the puncture needle, and inserting the distal end portion of the hollow needle into the extravascular tissue in the direction of the artery occurs only after detection of blood flow velocity of a predetermined desired characteristic such as intensity, velocity, pulsatility and directionality that can be expected in an artery or a vein being targeted.

[0025] The method may further comprise steering, torquing, or orienting a distal end portion of the shaft to thereby adjust a direction of propagation of the pulsed ultrasound pressure wave and at least partially location of the sample volume.

[0026] Pursuant to further features of the invention, penetration by the hollow needle is followed by the insertion of a wire that creates a continuous track between two vessels that can be dilated and made an anastomosis. The method comprises activating an electro-acoustic transducer to generate an audible signal, a visual signal, a haptic signal varying with Doppler frequency shift magnitude in accordance with direction of propagation of the pulsed ultrasonic pressure wave from the ultrasound transducer into the tissue and performing a surgical procedure known as “DETOUR” procedure currently marketed by PQ Bypass or venous arterialization or other peripheral vascular procedure that requires temporary or permanent connection of the lumens of an artery and a vein to facilitate flow of blood in a patient with PAD.

[0027] Yet another aspect of the technology includes the integration of purpose-built optimized Doppler guided electronics into the shaft and handle of the “crossing catheter”. The user does not need to visualize the needle and the artery on the screen as in prior art to direct and deploy the needle. The system is designed to be automatically aligned and to target the volume of tissue where the targeted segment of a target artery that can be popliteal artery is expected to be, based on peri-operative X-ray imaging. User can receive feedback in real time from the same handle that is used to manipulate the catheter and deploy the needle while keeping their eyes on the primary real time X-ray imaging (fluoroscopy) where the catheter, the artery and the vein are visualized as a two-dimensional projection. [0028] Veins have thinner walls compared to arteries, which may be easier to puncture with the puncture needle. Veins are distensible and flexible and a change in conformation may be achieved by applying force from inside or outside the vessel which may be advantageous for positioning the catheter or accessing a target crossing site. Veins have no atherosclerotic or arteriosclerotic disease and blood flows away from the brain eliminating a risk of causing a brain embolism.

[0029] Accordingly, in one configuration, an endovascular ultrasonic catheter is configured to aim ultrasonic energy at an artery from inside a vein and may include limited and specialized ultrasound detection capabilities. The ultrasound detection may include Doppler to detect blood flow. The catheter may be rotated within the vein using Doppler feedback to identify when it is aimed at a targeted artery that is expected to be in the defined target zone. Such a targeted artery lumen may be 5 to 15 mm from the vein.

[0030] In some embodiments a guided crossing catheter such as a self-contained sensor guided crossing catheter includes at least one targeting transducer (e.g., an ultrasound targeting transducer), which can be a diagnostic ultrasound transducer, a magnetometer, or other type of sensor or transducer to assist alignment. The transducer is positioned on the catheter relative to the penetration needle in such a way that when the targeting transducer is aligned with a vasculature landmark, the needle is also aligned with a target vascular landmark, which can be a reconstituted popliteal artery (PA) distal of the occlusion. Vasculature landmark as used herein includes an artery, a vein, a calcification, a blood flow stream, or a fiducial marker placed in the artery or vein such as an echogenic guidewire, a magnetic guidewire, or an echogenic contrast agent (e.g., echogenic liquid or gas bubbles).

[0031] The invention may be embodied as a method of crossing from a vein into an adjacent artery with a hollow needle, the method comprising: inserting a crossing catheter with the hollow needle into the vein of the patient; advancing the crossing catheter through the vein to position the hollow needle at a target location for crossing back into the artery; emitting an ultrasonic beam from a transducer on the crossing catheter; and rotating the crossing catheter to align the hollow needle based on a characteristic of reflected sound waves received by the transducer, wherein a sample volume of the transducer is limited to a deployment range of the hollow needle.

[0032] The vein and artery may be in the leg of a patient. The crossing catheter may be inserted into the vein at the patient’s groin area and advanced below the knee of the patient.

[0033] The deployment range of the hollow needle and the sample volume of the transducer may be 5 to 15 mm. The sample volume of the transducer may be a near field of the transducer.

[0034] The transducer and hollow needle may be incorporated into a distal end of catheter.

[0035] A drop in intensity of the reflected waves may indicate that the hollow needle is oriented at the target site.

[0036] The catheter may comprise a handle and the rotation of the catheter is controlled by manipulating the handle. Feedback based on the characteristic of reflected sound waves received by the transducer may be generated in the handle. The feedback may be audible, visual, or haptic signal. The feedback in the handle may be continuous. [0037] The invention may be embodied as an endovascular ultrasonic catheter system configured to connect a vein to an adjacent artery, the catheter system includes: a catheter body; a hollow needle incorporated into the catheter body; an ultrasound transducer incorporated into the catheter body and aligned with the hollow needle so that a penetration zone of the ultrasound transducer overlaps with a deployment zone of the hollow needle; and a handle positioned at an end of the catheter body, the handle being configured to generate tangible feedback to a user in response to a characteristic of reflected sound waves received by the transducer, wherein the sample volume of the transducer is limited to the deployment range of the hollow needle.

[0038] The deployment range of the hollow needle and the sample volume of the transducer may be 5 to 15 mm. The transducer and hollow needle may be incorporated into a distal end of catheter.

[0039] The may be configured to generate a feedback signal indicative of the hollow needle being oriented toward the artery in response to a drop in intensity of the reflected waves received by the transducer. The feedback signal may audible, visual, or haptic signal, issuing from the handle and may be continuous. The feedback signal may be proportional to the intensity of the reflected waves received by the transducer. The may be configured to control the rotation of the catheter.

[0040] The invention may be embodied as a method of crossing from a vein into an adjacent artery with a hollow needle, the method comprising: inserting a crossing catheter with the hollow needle into the vein of the patient; advancing the crossing catheter through the vein to position the hollow needle at a target location for crossing back into the artery; emitting an ultrasonic beam from a Doppler transducer on the crossing catheter; and rotating the crossing catheter to align the hollow needle based on an intensity of reflected sound waves received by the transducer, wherein the Doppler transducer is optimized to detect blood flow in the artery at a depth that is the same as a deployment range of the hollow needle.

[0041 ] The deployment range of the hollow needle may be 5 to 15 mm. The transducer and hollow needle may be incorporated into a distal end of catheter.

[0042] A maximum Doppler signal from arterial blood flow may be used to indicate that the hollow needle is oriented at the target site.

[0043] The vein and the artery may be in a leg of the patient. The crossing catheter may inserted into the vein at the patient’s groin area and advanced below the knee of the patient.

[0044] The catheter may comprise a handle and the rotation of the catheter is controlled by manipulating the handle.

[0045] Feedback based on the intensity of the Doppler signal from the arterial blood flow may be generated in the handle. The feedback may be audible, visual, or haptic signal issuing at the handle, and may issue continuously.

[0046] The invention may be embodied as an endovascular ultrasonic catheter system configured to connect a vein to an adjacent artery, the catheter system comprising: a catheter body; a hollow needle incorporated into the catheter body; a Doppler transducer incorporated into the catheter body and aligned with the hollow needle, the Doppler transducer being optimized to detect blood in the artery at a depth that is the same as a deployment range of the hollow needle; and a handle positioned at an end of the catheter body, the handle being configured to generate tangible feedback to a user in response to an intensity of a Doppler signal from the arterial blood flow.

[0047] The invention may be embodied as a method for aiming an ultrasonic beam generated by an ultrasonic transducer positioned at an end of a catheter with a puncture needle, the method comprising: positioning the catheter in a vein adjacent to a target artery with an occlusion so that the transducer is positioned adjacent to part of the target artery that is downstream of the occlusion; actuating the transducer to emit an ultrasonic beam toward a target zone in the artery; receiving a reflection of the ultrasonic beam; selectively generating a feedback signal indicative of an intensity of the reflected ultrasonic beam; and rotating, pivoting, and or translating the transducer in response to the feedback signal, wherein a detection range of the transducer is limited to a natural focus distance or a near field transition of the transducer.

[0048] The transducer and the needle may be aligned so that the needle and the transducer are aimed at the target zone. The ransducer may be a Doppler transducer. The method may detect a Doppler shift between a master oscillator and the reflected ultrasonic beam. The feedback signal is generated based on the detected Doppler shift. The feedback signal may vary in response to changes in the intensity of the reflected ultrasonic beam.

[0049] The near field transition distance and/or the natural focus distance of the transducer may be 5 to 10 mm.

[0050] The feedback signal may include at least one of light, sound, and vibration. The feedback signal may include a vibration that waxes when the intensity of the reflected ultrasonic beam increases, and wherein the vibration wanes when the intensity of the reflected ultrasonic beam decreases. The feedback signal may include a light that blinks at a frequency that increases with an increasing intensity of the reflected ultrasonic beam and decreases with a decreasing intensity of the reflected ultrasonic beam. The feedback signal may include a light that changes color as the intensity of the reflected ultrasonic beam changes; or a sound that increases in frequency with an increasing intensity of the reflected ultrasonic beam and decreases in frequency with a decreasing intensity of the reflected ultrasonic beam.

[0051] The needle may have an integrated acoustic sensor that detects the acoustic beam transmitted by the transducer.

[0052] The feedback signal may be indicative of a flow of arterial blood in the target zone.

[0053] An angle at which the transducer and the needle are oriented relative to a central longitudinal axis of the catheter may be within a range of 15 to 45 degrees.

[0054] The method may include introducing echogenic materials into the target artery.

[0055] The invention may be embodied as an endovascular ultrasonic catheter system comprising: a hollow tubular body; a hollow needle extending from a side of the tubular body; an ultrasonic transducer located at an end of the tubular body and configured to emit an ultrasonic beam; an ultrasonic receiver configured to receive a reflection of the ultrasonic beam; and a feedback signal generator configured to generate a feedback signal indicative of an intensity of the reflected ultrasonic beam, wherein the transducer and the needle are aligned so that the needle and the transducer are aimed at the same target area, and wherein a detection range of the transducer is limited to a natural focus distance or a near field transition of the transducer.

[0056] The transducer and the needle may be oriented relative to a central longitudinal axis of the catheter at an angle that is within a range of 15 to 45 degrees. The transducer may be independently rotatable relative to the tubular body. The end of the tubular body with the transducer may be pivotable and the transducer is movable with the pivotable end. The transducer may be pivotable relative to the tubular body.

[0057] The transmission face of the transducer may be convex.

[0058] The invention may be embodied as a method for aiming an ultrasonic beam generated by an ultrasonic transducer positioned at an end of a catheter with a puncture needle, the method comprising: positioning the catheter in a vein adjacent to a target artery with an occlusion so that the transducer is positioned adjacent to part of the target artery that is downstream of the occlusion; actuating the transducer to emit an ultrasonic beam toward a target zone in the artery; receiving a reflection of the ultrasonic beam; selectively generating a feedback signal indicative of an intensity of the reflected ultrasonic beam only when the reflected ultrasonic beam is reflected from within a scanning zone of the transducer; and rotating, pivoting, and or translating the transducer in response to the feedback signal, wherein the scanning zone of the transducer is limited to within a distance from the transducer within which the target artery is predicted.

[0059] An outer limit of the scanning zone may be the transition from the transducer’s near field to the transducer’s far field. An outer limit of the scanning zone may be a predetermined distance from the transition between the transducer’s near field and the transducer’s far field. The predetermined distance corresponds to a distance at which an amplitude of the ultrasonic signal falls below a threshold amplitude.

[0060] The transducer and the needle may be aligned so that the needle and the transducer are aimed at the target zone.

[0061] The transducer may be a Doppler transducer. The method may detect a Doppler shift between a master oscillator and the reflected ultrasonic beam. The feedback signal may be generated based on the detected Doppler shift.

[0062] The transducer may be directionally sensitive.

[0063] The feedback signal may change as the intensity of the reflected ultrasonic beam changes. The feedback signal may includes at least one of light, sound, and vibration. The feedback signal may include a vibration that waxes when the intensity of the reflected ultrasonic beam increases, and wherein the vibration wanes when the intensity of the reflected ultrasonic beam decreases.

[0064] The feedback signal may include a light that blinks at a frequency that increases with an increasing intensity of the reflected ultrasonic beam and decreases with a decreasing intensity of the reflected ultrasonic beam. The feedback signal may include a light that changes color as the intensity of the reflected ultrasonic beam changes. The feedback signal may includes a sound that increases in frequency with an increasing intensity of the reflected ultrasonic beam and decreases in frequency with a decreasing intensity of the reflected ultrasonic beam. The feedback signal may indicate a flow of arterial blood in the target zone.

[0065] The needle may have an integrated acoustic sensor that detects the acoustic beam transmitted by the transducer. The angle at which the transducer and the needle are oriented relative to a central longitudinal axis of the catheter may be within a range of 15 to 45 degrees. [0066] The method may include introducing echogenic materials into the target artery.

SUMMARY OF DRAWINGS

[0067] Fig. 1 is schematic illustration of a patient undergoing a percutaneous bypass procedure.

[0068] Fig. 2 shows cross-sections of the artery and vein that receive the percutaneous bypass device during the percutaneous bypass procedure.

[0069] Fig. 3 is an illustration of a distal end of the device.

[0070] Fig. 4 is an illustration of a handle of the device.

[0071] Fig. 5A is a schematic drawing of the device.

[0072] Fig. 5B is a schematic drawing of electronics in the device.

[0073] Fig. 6 is an illustration of a US guided vein to artery puncture.

[0074] Fig. 7 is an illustration of an alignment of a catheter using a transducer’s near field.

[0075] Fig. 8 is an illustration of Doppler targeting.

[0076] Fig. 9 is another illustration of an alignment of the puncture needle with a target crossing site.

[0077] Fig. 10 is a flow chart showing a method for aligning a puncture needle. DETAILED DESCRIPTION

[0078] Figure 1 illustrates a patient 10 undergoing a percutaneous bypass procedure. The particular procedure illustrated in Fig. 1 involves the femoral and popliteal arteries. However, the percutaneous bypass procedure can be used for other arteries experiencing chronic total occlusions.

[0079] The patient 10 as shown in Fig. 1 has already begun to undergo the percutaneous bypass procedure. As can be seen, a crossover opening 2 has been created between the femoral artery 26 and the femoral vein 16. A crossing catheter 12 has been inserted into the tibial vein 14 by way of the contralateral percutaneous puncture in a groin, femoral artery 26, the cross-over opening 2, and the femoral vein 16. The distal end 52 of the catheter 12 has been positioned adjacent to the popliteal artery distal (on the downstream side) of the occlusion 34.

[0080] At this location (the second or distal crossing site 18), the distal end 52 of the crossing catheter 12 will be used to create a second cross-over opening between the popliteal artery that is normally a downstream continuation of the femoral artery 26 and the femoral vein 16 to complete the bypass pathway as described elsewhere in this disclosure. The intended result after the addition of necessary steps of creating anastomosis and deployment of stent grafts other than the wire is a large lumen, endograft bypass that delivers pulsatile flow from the superficial femoral artery ostium to the popliteal artery. The stent graft system itself may feature a self-expanding composite structure made of a nitinol wire frame encapsulated in expanded polytetrafluoroethylene. Fig. 2 shows a detail cross-section of the patient’s leg including crossing catheter 12, artery 26, and vein 14 at the crossing site 18 as exemplified by the configuration shown in Fig. 1.

[0081] The catheter 12 may include a handle 24 with a user interface 22 and electronics for operating and controlling the catheter 12. It is contemplated that in addition to or instead of the electronics being located in the handle 24, the catheter 12 may be connected by electric or fiberoptic cables, or by a wireless link to a controller that can include an energy generator, a digital processor and another user interface.

[0082] X-ray imaging or fluoroscopy is typically relied upon to track the catheter 12 as it is directed through the vein 14. However, fluoroscopy only provides a two dimensional projection for a three dimensional space. In addition, the catheter 12 is prone to rotate and/or twist as it is guided through the vein 14. Thus, a supplemental output is needed to ensure that the puncture needle is located in the radially correct position (i.e., facing the artery 26) when the fluoroscopic image shows the distal end of the catheter 12 being in the linearly correct position (i.e., adjacent to the second crossing site 18). Ultrasound imaging may be used to provide such a supplemental output. However, providing a supplemental image of the space to add a third dimension adds complexity to the feedback provided to the user, which may actually add to the difficulty of aligning the puncture needle with the crossing site 18.

[0083] Fig. 3 shows a distal end 52 of an exemplary catheter 12 that is designed to provide the supplemental output to allow the user to radially align the puncture needle with the artery 26. However, rather than use ultrasound to provide a supplemental image of the overall space that generally necessitates an array of many transducers (e.g., greater than 60), the catheter 12 may be designed to use an ultrasound beam limited to a predetermined range to output an alert or other type of signal that alerts the user as to when the puncture needle is radially aligned with the artery 26. In other words, rather than using ultrasound to provide an image of the overall space and relying on the user to determine the location of the artery 26 relative to the puncture needle based on the user’s analysis of the image, the catheter 12 may be configured as an “artery detector” that uses ultrasound to automatically detect the artery 26 when the puncture needle is radially aligned with the artery 26.

[0084] As can be seen, the distal end 52 may include a puncture needle 28 and an ultrasound transducer 36. The puncture needle 28 may be extendible from a needle exit port 30 on the shaft 44 of the catheter 12. In addition, the puncture needle 28 may include a lumen that terminates at a puncture needle aperture 64.

[0085] A standard guidewire lumen may be located along a central longitudinal axis of the catheter 12 and an exit 68 of the standard guidewire lumen may be located at the terminal end of the catheter 12. The guidewire lumen may be sized to receive a guidewire 66. A second guidewire lumen may extend through the puncture needle 28 along the central longitudinal axis of the puncture needle 28 and may terminate at the puncture needle aperture 64 and further advanced into the artery to serve as a rail upon which the dilation balloons and stents are introduced to complete the bypass.

[0086] The ultrasound transducer 36 may be an emitter and a receiver of ultrasound energy or a combination of an emitter and a receiver. It is contemplated that the ultrasound transducer 36 may be integrated and built into the distal end 52 of the catheter 12 and aligned with the puncture needle 28 (i.e., the emitting face of the transducer 36 is aligned with the puncture needle 28 so that the direction in which sound waves are emitted from the transducer 36 is the same as the direction in which the puncture needle 28 is ejected or delivered). Alternatively, the ultrasound transducer 36 may be aligned with the shaft of the catheter 12 and moved, rotated or advanced, independently of the catheter 12 and/or the puncture needle 28 while in axial alignment with the shaft of the catheter 12 and/or the puncture needle 28. The alignment ensures proper position of the puncture needle 28 when it is advanced out of the catheter 12.

[0087] The transducer 36 may be positioned at a predetermined distance from the needle exit port 30 (e.g., about 5 to about 15 mm) such that the transducer 36 may transmit a signal with a particular signature when the face of the transducer 36 is in linear, radial and angular alignment with the puncture needle 28 and the crossing location 18 on the artery 26. In addition, an acoustic insulator such as stainless steel may be positioned on a backside of the transducer 36 to ensure an ultrasound beam is directed in a direction orthogonal to the front surface (face) of the transducer 36. The reflected and received acoustic signal may generate a user feedback indicative of the materials encountered by the ultrasound beam and material properties (e.g., tissue, blood flow, calcium deposit) reflecting and absorbing ultrasound waves in the transducer's sample volume.

[0088] The catheter 12 may optionally include a deployable structure 32 such as a balloon, cage, mesh or helix positioned on the catheter 12 proximal or distal to the transducer 36. The deployable structure 32 may be used to engage and stabilize the distal portion 52 of the catheter 12 in the vein 14. The deployable structure 32 may deploy to a size suitable to engage and stretch the walls of the vein 14, for example having a diameter of about 4 to about 15 mm. The deployable structure 32 may retract so it can fit in a delivery sheath. Alternatively, the deployable structure 32 may be a part of a delivery sheath.

[0089] Optionally, the catheter 12 may include a deflectable section proximal to the transducer 36 (e.g., between about 5 mm and about 30 mm proximal to the transducer 36) that may be used to direct the angle of the ultrasound beam with respect to the external artery 26, which may be useful to adjust for a variety of vasculature geometries.

[0090] The transducer/sensor enabled catheter 12 may be further adapted to articulate (or deflect) at the distal end 52 (see Fig. 8).

Articulation may facilitate positioning of the transducer 36 in alignment with the target (e.g., the artery 26). For example, the catheter 12 may be controllable so that a length of the distal region 52 (e.g., about 1 to 3 cm) is bent (or deflected) from side to side up to a deflectable distance (e.g., about 0.5 to 3 cm).

[0091] In addition, articulation may be in a plane that is coplanar with the puncture needle 28 and the transducer 36. Controllable deflection may be achieved with pull wires connected to the distal end 52 of the catheter 12 that pass through lumens in the catheter shaft to the proximal region where they may be connected to a deflection actuator on the handle 24 that applies tension to a pull wire to deflect the distal region 52.

[0092] As shown in Fig. 4, the handle 24 and the shaft 44 may be designed to rotate the distal end 52 of the catheter 12. For example, the catheter shaft 44 and/or the handle 24 may include a rotation actuator in addition to the actuation elements that enable advancement and retraction of the puncture needle 28. For example, the handle 24 may include an electromechanical mechanism to rotate the shaft 44 such as a worm drive or a gear drive. The gear mechanism may be designed to rotate the shaft 44 inside the handle and rotate the puncture needle 28 and transducer 36 toward the blood vessel slowly to achieve alignment of the puncture needle 28 with the target vessel 26.

[0093] The handle electronics may also include an electromechanical locking mechanism, such as a solenoid latch, designed to lock the puncture needle 28. A spring loaded mechanism may keep the puncture needle 28 in the retracted state until the correct target volume is identified by the Doppler targeting electronics. This latch mechanism may be a solenoid release pin operating as a trigger safety of a firing pin of a firearm. [0094] In addition, the handle 24 may be equipped with a feedback device that vibrates the handle 24, adjusts a light source, generates a sound, etc. The feedback device may generate one or more of the above feedback signals based on the strength of the electrical signals generated by the echoes impacting the transducer 36 and transmitted back. The handle 24 may also include a user interface 22 such as an electric switch and a needle launch control device. It is contemplated that in addition to or alternatively to the switch, the user interface 22 may include buttons, displays, touch pads, or any other component configured to convey information to a user.

[0095] As can be seen in Figs. 5A and 5B, the handle 24 may contain electronics 70 for operating the catheter 12. The electronics 70 in the handle 24 may include a microcontroller (or processor) 20, the user interface 22, a power source 72, a motor and/or solenoid control 74, an input/output interface 76, a memory 78, and optionally a waveform generator 80 (it is contemplated that the microcontroller 20 may function as the waveform generator). The power source 72 may include one or more batteries or other portable power source. Alternatively, the power source 72 may be a connection to a power cord. The user interface 22 may further include a remote user interface that uses radio frequency (RF) communication via the input/output interface 76 in the handle electronics. [0096] The motor and/or solenoid control 74 may control the movement of the components of the catheter 12. For example, the motor and/or solenoid control 74 may control the deployment of the puncture needle 28, the rotation and/or lateral movement of the shaft 44 and/or the transducer 36, and/or the articulation of the distal end 52 of the catheter 12.

[0097] The input/output interface 76 may be the method of communication between the components of the electronics 70. Accordingly, the input/output interface 76 may facilitate wireless or wired communication. It may also include a communications receptacle and/or antenna for communicating with internal and external components. The input/output interface 76 may include WIFI and/or BlueTooth communication and wired communication. In addition, the memory 78 may be any type of information storage device. In addition, the memory 78 may be permanently positioned within the handle 24 or may be removable. [0098] The microcontroller 20 may process signals received from the transducer 36. In addition, the waveform generator 80 may generate and transmit signals to the transmitter 36.

[0099] It is contemplated that the user may manually rotate the catheter 12, puncture needle 28, and/or the transducer 36 around a common central longitudinal axis by way of the user interface 22 according to the feedback in the handle 24. It is further contemplated that the user may manually trigger the release or deployment of the puncture needle 28 by way of the user interface 22 based on the feedback in the handle 24. Alternatively, the controller 20 may automatically rotate the catheter 12, puncture needle 28, and/or the transducer 36 around the common central longitudinal axis in response to the signals received from the transducer 36. The controller 20 may also automatically release or deploy the puncture needle 28 when the signals received from the transducer 36 indicate that the puncture needle 28 is aligned and facing the target vessel 26.

[00100] It is contemplated that all of the electronic components discussed above may be located on one or more printed circuit boards that may be rigid or flexible and positioned within an interior of the handle 24. [00101] Fig. 6 illustrates a basic configuration in which the catheter 12 is aligned with the target vessel 26 (e.g., the femoral artery). The puncture needle 28 maybe extended from the needle exit port 30 on the catheter 12. In addition, the catheter 12 may be placed in the vein 14 adjacent the artery 26 and may be stabilized by the expandable element 32. The expansion of the expandable element 32 may secure the catheter 12 within the vein 14 at a location where the needle exit port 30 is at a desired distance upstream or downstream of the occlusion 34.

[00102] As previously discloses, the transducer 36 may transmit a signal when the transducer 36 is aligned with the puncture needle 28 and the treatment target location 18 on the artery 26. The signal may generate a user feedback indicative of the materials encountered by the ultrasound beam and material properties (e.g., tissue, blood flow, calcium deposit) reflecting and absorbing sound waves in the transducer’s sample volume 38. A mechanism in the handle may be used to adjust the length of a protrusion or penetration of the needle 28 from the catheter 12 to 5 to 15 mm depending on an acoustic signal (e.g., a reflection wave, a time of flight, or a doppler signal) indicating the distance N (see Fig. 7) from the transducer to the targeted lumen of the artery.

[00103] In traditional medical ultrasound imaging, the intensity of the received waves is transformed into brightness (echogenicity or echodensity) on a black and white screen and the time elapsed from sending to reception is depicted as distance from the ultrasonic probe. Water has very low acoustic resistance and ultrasound waves travel with high speed, whereas air and bony structures are almost impenetrable and reflect the ultrasonographic waves almost completely. The processor may be set to the speed of sound (1 ,540 m/sec) in average water containing tissue at 37 °C as the standard for its calculation. Differences from this standard are shown as brightness or darkness. Thus, if a tissue contains a lot of water, the sound waves travel faster and it appears darker. The effect of deeper penetration through fluid is called enhancement. The opposite effect is complete reflection by impenetrable tissues, such as bone or metal. Artificial echogenic materials can be introduced at a known location as so-called fiducial markers to assist the ultrasound guided procedure. [00104] However, for the purpose of detecting an adjacent blood vessel and achieving alignment there is no need to create a full ultrasound image of tissues. The transducer 36 may be a single emitter and receiver with properties matched to the task of detection of an artery within 1-15 mm (the transducer’s near field 40). Alignment may simply be determined by a sudden drop of intensity of the reflected wave indicating that the transducer 36 is aligned with the blood filled vessel (e.g an artery) 26.

Misalignment may be determined by a comparatively higher intensity of the reflection from the same depth of penetration in the adjacent tissues such as muscle or bone or a calcified occlusion.

[00105] The zone of ultrasound penetration 38 can be designed at or around (or limited to) the transducer’s near field transition or natural focus distance (which may be 5-15 mm from the face of the transducer).

In addition, rather than originating from a single point, the ultrasonic beam (or pressure waves) that emanates from the transducer 36 (which may be a piezoelectric transducer) may originate from most of the surface of the piezoelectric element. Round transducers are often referred to as piston source transducers because the ultrasonic beam in the near field resembles a cylindrical mass in front of the transducer. Piston transducers are used in this disclosure as an example and it should be understood that many geometries can be applied because of the design consideration. [00106] As can be seen in Fig. 7, the pressure waves may combine to form a relatively uniform front at the end of the transducer’s near field 40. The area beyond the transducer’s near field is called the transducer’s far field 42. In the far field 42, the beam spreads out in a pattern originating from the uniform front of the near field 40. The transition between the near field 40 and the far field 42 may occur at a distance, N, and is sometimes referred to as the "natural focus" of a flat (or unfocused) transducer 12. The near/far field distance, N, is significant because amplitude variations that characterize the near field change to a smoothly declining amplitude at this point. The area just beyond the near field 40 is where the sound wave is at its maximum strength and signal to noise ratio can be optimal. Therefore, optimal artery detection results can be obtained when transitions in the properties of the investigated tissues occur in this area. [00107] A sweeping motion may be created to search for a landmark, such as the artery 26 by rotationally or translationally moving the shaft of the catheter 12, the internal drive shaft attached to the transducer 36, or by electrically or mechanically manipulating the transducer 36. Feedback from the diagnostic transducer 36 may be transmitted to a processing console and processed into operator feedback such as a graphic display, images, acoustic sounds for room speakers or operator’s headphones, light and color display, waveforms, haptic feedback such as vibration of the catheter handle 24 or electrical signals further integrated into cathlab displays.

[00108] The ultrasound transducer 28 may be operated in the thickness resonance mode, i.e., the frequency of operation is substantially determined by the half wavelength thickness of the piezoelectric transducer element. The transducer element may be made of lead zirconate titanate (PZT) type piezoceramic material. The transducer 28 may be a flat plate, a cylinder, an oval shape cylinder or a toroid.

[00109] Figure 7 illustrates a simple single transducer targeting method. The catheter 12 may be centered in the vein 16. The transducer 36 may emit an ultrasonic beam that can be rotated to seek the artery 26. A transducer aperture and frequency may be selected to maximize the signal to noise ratio in the depth zone of interest 46 where the artery 26 is expected. In addition a bone 48 may be used to help align the catheter 12 since reflection from the bone 48 is much higher than from the blood or tissue and it is virtually impermeable for ultrasound. The face of the transducer 36 can be made convex to further enhance resolution in the zone 46, which approximately corresponds to the transducer’s near field 40. In addition, upon insertion, the puncture needle 28 may be used to reflect ultrasound energy by having a detectable echogenic signature or providing a needle tip integrated acoustic sensor feedback mechanism to a treatment system.

[001 10] The typical size of a prior art transducer of the type illustrated by transducer 36 used for interrogating coronary arteries is about 3 Fr. It is presumed that the catheter 12 may be larger if used in a femoral vein 16. For example, a 6 Fr (2mm) catheter leaves enough room for the use of a 1 .2 mm transducer 36 given as an example to illustrate engineering tradeoffs. At an operating frequency of 30 MHz, the near field transition point 50 may be estimated by taking the square of the transducer diameter and dividing it by four times the sonic wavelength. This is the point at which the beam shape is defined by pressure and velocity vectors that are aligned. The wavelength is dependent upon the propagation speed V in the medium. In blood, and in tissue, V is approximately 1 ,540 m/sec. These ranges of constraints and parameters allows for a transducer 36 that can be fitted into a catheter 12 with the desired “range” or set length of the near field 40 that may be designed to be in the range of 5 to 15 mm from the catheter 12 to approximate the length of the needle 28 in the extended state. Beyond the transducer’s near field 40, energy quickly dissipates and the returning signal will be below the detection threshold calibrated in water. The example shown is that the transducer 36 with an acoustic aperture of approximately 1 to 3 mm can be optimized for the task at the commercially feasible frequency of operation (for example 20 to 40 MHz). There is a potential tradeoff when attempting to increase the working frequency, thereby shortening the wavelength, as frequency dependent attenuation takes place with a “brick wall” (nonlinear) limiting effect at about 40 MHz, caused by a marked increase in ultrasound scattering by RBCs. [001 1 1 ] The effect of the aperture and frequency on the lateral resolution of the transducer is known. For a flat circular piston PZT (set as an example) that is several wavelengths across the best resolution and signal to noise ratio are in the near field. Near field extends from the face of the transducer to a distance approximately calculated as:

N = Near Field Length D = Diameter of the Transducer F = Frequency of the Transducer I = Wavelength (cycles/second) Note: MHz is used in the Java applet for ease of use.

V = Velocity of Sound in the Material

[001 12] At the higher frequency, the depth of resolution is increased and as depth requirements increase, there is less opportunity to increase the operating frequency to preserve resolution. For the exemplary configuration, the transit distance may be up to 5-15 mm (e.g., 8-10 mm), and the transducer 36 can be fine-tuned depending on the catheter size. [001 13] A reference resonance frequency of commercial PZT can be 10 Mhz corresponding to 0.150 mm wavelength, 30 MHz to 0.049 mm and 40 MHz to 0.037 mm. A typical intravenous ultrasound beam transition at 40MHz is 1 .6mm and may not be deep enough for the crossing alignment. The 5-6 Fr 1 mm intravenous ultrasound at 30MHz would have near field of 5.1 mm (4X greater image distance). [001 14] The focusing of the transducer 12 is possible and may be advantageous. It can be achieved by curving the transducer face into a convex shape. It will improve lateral resolution in the near field but does not affect the far field transition which is ultimately determined by the aperture. Thus, a convex transducer may be better suited to focus on the distance to the artery 26 (for example 3 - 30 mm) and achieve better contrast resolution and signal to noise ratio when aligning the catheter 12. [001 15] It is generally desired to position the transducer 36 with the emitter face surface pointing towards the target (e.g., the artery 26 on a distal side of the occlusion 34). The distal assembly containing the ultrasound transducer element 36 may be guided into place, for example adjacent to the artery 26 by using a low intensity of the reflected ultrasound signal or Doppler guidance by the means of sensing blood flow in the artery 26. The sample volume of the pulse wave Doppler along the ultrasound beam axis can be adjustable in length and location. The location of the sample volume along the beam axis is preferably set to cover a range of about 1 to 15 mm (e.g., about 5 mm to 15 mm) from the transducer face. The ultrasound beam may be aligned with the aid of Doppler to align the catheter 12. Once the transducer 36 is determined to be properly aligned, the puncture needle 28 can be advanced in the aligned direction. The puncture needle 28 can be set to advance the selected amount in the 5 to 15 mm range. Ultrasound guidance, such as with or without Doppler, and ultrasound imaging and targeting may be performed with one transducer element, or alternatively with several or a linear array of transducer elements.

[001 16] Figure 8 illustrates the use of Doppler to align the puncture needle 28 (not shown). The Doppler effect or shift is widely used to detect moving fluids, such as the blood stream inside an artery or vein. The Doppler signal is transmitted back to the operator to assist the alignment and targeting of the crossig tool. Ultrasound intensity or Doppler signal feedback to an operator or the computer controlling catheter positioning or needle deployment need not be necessarily an image. It can be an indicator such as a curve, a number, an acoustic signal, an LED bar, a haptic vibration of the device handle, or an indicator light color or intensity. Haptic feedback can be provided using a low energy micromotor such as ones used in mobile phones and smart watches. The intensity or frequency of the signal may grow with better alignment and may diminish with misalignment as the operator rotates the tool. Ultimately, most or all the electronics 70 and user interface 22 can be incorporated in the catheter handle 24 (see Fig. 5) and made a sterile single use device. There is an advantage to this design solution since it avoids cumbersome cables and bulky consoles. It also enables the operator to focus on the patient and the Fluoroscopy image while receiving feedback directly in their hand holding the instrument. After the procedure the instrument can be entirely discarded avoiding potential contamination.

[001 17] It should be understood that Figure 8 is a simplified exemplary design, and many details are omitted for clarity. For example, a single piezoelectric transducer 36 can be used as both the transmitter and the receiver. It is mounted on the deflectable distal tip 52 of the catheter 12 placed in the vein 16. The tip 52 can be deflected towards the wall of the vein 16 at a known 15 to 45 degree deflection angle 9 as measured between a central longitudinal axis 54 of the catheter 12 on a proximal side of the bend and a central longitudinal axis 56 of the catheter 12 on the distal side of the bend. Alternatively, as shown on other figures the transducer face can be angled at a fixed angle to the shaft.

[001 18] The master oscillator frequency of 20 MHz may be pulsed at a repetition frequency of 62.5 KHz. Each transmit pulse 58 may be approximately one microsecond in width and therefore may contain twenty cycles of the master oscillator frequency. These acoustic tone bursts (transmit pulses) may be propagated into the blood or surrounding tissue, where they are reflected by the various structures encountered (blood cells, vessel wall, etc.). The acoustic signals returning to the transducer may be separated in time according to the distance of each reflecting structure. Therefore, by adjusting an electronic time delay called adjustable receiver gate 60, one can select signals reflected from structures a specific distance away from the transducer 12 such as the flow sensing region 62. These reflected signals may be amplified and compared in phase and frequency with a signal from the master oscillator. The result of the processing is the difference in frequency (Doppler shift) between the master oscillator and the signals reflected from the flow sensitive region as defined by the adjustable receiver gate. The relationship between the Doppler shift and absolute velocity is noted in the equation of v (velocity of sound in blood) and f (transmitter frequency) are both constant.

[001 19] Therefore, if the catheter 12 is in a stable position and the angle 9 remains constant, Delta for Doppler shift frequency is linearly related to blood flow velocity (V). For example, the parameters chosen as master oscillator frequency = 20 MHz and pulse repetition frequency = 62.5 KHz allow velocities up to 100 cm/sec to be recorded at a distance up to 1 .2 cm from the catheter tip. The system may be directionally sensitive so that flow reversals are properly displayed, and since zero frequency shift corresponds to zero flow, zero stability can be achieved. In the example of venous to arterial crossing or arterial to venous crossing, these parameters can be fixed and the electronics programmed to register and indicate only the blood flow moving in the desired direction. A control switch can be integrated with the design allowing to set an “artery” or a “vein” search position.

[00120] As described in methods herein, a catheter 12 may be advanced up and down the veing (e.g. femoral or tibial vein) 16 until arterial blood flow is detected distal to the occlusion 34 (See FIG. 1 ). This can be confirmed by a Doppler pulsatile velocity signal or ultrasonic detection. Pulsed Doppler at the preselected depth of 0.5 to 10 mm can be chosen to avoid interference from venous blood flow. A search depth can be settable by the operator based on the pre-exiting image acquisition such as X-ray.

[00121 ] In some embodiments a catheter 12 positioned in a vein 16 may be rotated around its axis until the aperture of the puncture needle 28 is facing the artery 26 to “find” the artery 26 using Doppler feedback. Alternatively, a transducer 36 with a directional emitter can be rotated inside the catheter 12. The Doppler emitter may be part of a core or a part of a sheath. If the Doppler emitter and receiver are located in the distal portion of the catheter 12 placed in a vein 16, certain advantages may be realized by aiming beams at an angle to the direction of the face of the aperture. A vein 16 may be distended and the catheter tip 52 maneuvered into position so that the puncture needle 28 is aimed into the middle (peak) of the strong Doppler signal from the targeted artery 26. A computer algorithm may assist or automate such aiming and may reject signals coming from veins (in the case of venous-arterial crossing) and more distant, not targeted, arteries outside of the targeted zone.

[00122] As described in methods herein, the catheter 12 may be advanced up and down the femoral vein 16 until blood flowing in the artery 26 is clearly detected. If external ultrasound is used, the catheter 12 may be made visible with ultrasound by addition of an echogenic coating. Pulsed Doppler at the preselected depth within the transducer design range of 3 to 15 mm (e.g., 3 to 5 mm or 10 to 15 mm) may be chosen to avoid interference from venous blood flow and other non-targeted structure.

[00123] In some embodiments the catheter 12 (while positioned in the femoral vein 16) may be rotated around its axis until the needle, or transducer aperture is facing the artery 26. Alternatively, a transducer 36 with a directional emitter can be rotated inside the catheter 12. If the Doppler emitter and receiver are in the distal portion of the catheter 12 placed in a femoral vein 16, certain advantages may be realized if the doppler beam is directed at approximately the same exit angle as the puncture needle 28. A concentric PZT material ring may be designed to allow the passage of the puncture needle 28 through the central opening. [00124] A Doppler beam may face the same radial (clockface) direction as the puncture needle aperture. A Doppler signal can then be used for targeting and directing the puncture. The target can be located as a peak of the high blood velocity area between two low velocity areas. [00125] The vein 16 may be distended, and the catheter tip 52 maneuvered and deflected into position so that the high-energy emitter 36 is aimed into the middle of the strong Doppler signal representing the artery 26. A computer algorithm may assist or automate such aiming. The target depth of Doppler emitters and receivers may be configured to enable ultrasound beam shaping and focusing advantages realized when facing substantially different anatomy in the vein 16 and artery 26.

[00126] Combining the electronics illustrated in Fig. 5B with the Doppler transducer illustrated in Fig. 8 may result in a configuration that automatically aligns the puncture needle 28 with the artery 26.

[00127] For example, the waveform generator 80 may transmit a pulsed ultrasonic electrical signal to the transducer 36, thereby energizing the transducer 36 to emit a burst of pulses of one or more ultrasonic frequencies. The burst length, that is, the number of pulses multiplied by the pulse duration, may determine the length L of a sample volume 38 of the transducer 36 (i.e., the volume of space or tissue inside the focal zone of the transducer 36 - see Fig. 9). The gating time (i.e., the interval between the end of a pulse burst and the time when the waveform generator/receiver 82 is switched from generator mode to receiver mode) may determine the depth D of the sample volume 38 or the distance of the sample volume 38 to the transducer 36.

[00128] The transducer 36 may also have a zone of penetration corresponding to a zone in which sound waves propagate and are reflected back to the transducer 36. The zone of penetration may contain the sample volume 38, may overlap the sample volume 38, or may coincide with the sample volume 38. [00129] As illustrated in Fig. 9, after the tip of the aperture or the emitting face of the transducer 36 is positioned in the vein 14 of the patient 10, a “wedge-shaped” sample volume 38 of tissue may be located in the adjacent tissue, on the other side of the venous wall where the targeted artery 26 is expected to be. The waveform generator 80 may then transmit a signal to the transducer 36, thereby causing the transducer to emit an ultrasonic beam of energy. The sample volume may be a “tunnel-shaped” beam or a “wedge-shaped” or a combination depending on the design of the transducer as described earlier in this application. The sample volume can be optimized for the task of detecting the targeted artery within the zone of interest.

[00130] The microcontroller 20 may send a signal to the waveform generator 80 to transmit an energization signal to the transducer 36, thereby inducing the transducer 36 to emit a pulsed ultrasound pressure wave 84 of predetermined duration. As discussed above, the duration may determine the length L of the sample volume 38. The pulse train duration may be selectively adjusted by an operator via the user interface 22 and the controller 20. A width W of any given sample volume 38 may be determined by the transducer beam geometry.

[00131] The microcontroller 20 may be configured to process Doppler frequency changes of incoming reflected pressure waves arriving a predetermined time after the termination of a pulsed ultrasound pressure wave output by the transducer 36 so that the distance or range of the sample volume 38 may be selected in addition to length (L) and angular location (azimuth AZ and elevation EL) of the sample volume 38. An operator may modify the distance or range D of the sample volume 38 from the transducer 36 by a sample-volume distance control operatively connected to the microcontroller 20.

[00132] The microcontroller 20 may be operatively connected to an electronic memory storage unit or other storage medium 78 to record therein magnitudes of Doppler frequency changes of ultrasonic waves reflected from one or more predetermined sample volumes 84 at respective predetermined distances D (e.g., at least several millimeters to 10-15 mm) from the ultrasound transducer 36 in a selected ultrasound- transmissive medium such as the blood and heart tissues of a mammalian subject.

[00133] When the transducer 36 and the puncture needle 28 are properly positioned relative to the artery 26, the flow of blood in the artery 26 may be within the sample volume 38. Accordingly, an absorption of the ultrasound beam emitted by the transducer 36 may be minimal due to the reflective properties of the blood flowing in the artery. In response, the controller 20 may generate a feedback signal (e.g., audio signal, blinking light, or handle vibration) notifying the user that a maximal blood flow has been located within the sample volume 38 and that puncture needle 28 has been properly located and can be safely advanced or deployed across the tissue and into the artery 26. With this system, there is no need to create and interpret an image such as an IVUS image or consult an external display or to have separate emitter and receiver transducers coupled together to ensure alignment.

[00134] As depicted in FIGS. 3, 5, 6, and 8, the puncture needle 28 preferably extends longitudinally through a lumen of a steerable shaft 444 of the catheter 12 and exits at an angle favorable for the Doppler detection physics parallel to the central axis of the ultrasound beam (that assumes a substantially conical shape as it travels from the source). In some embodiments the needle may curve to engage the blood vessel lumen and direct the guide wire. This arrangement enables an operator or an automated system to steer or orient a distal end portion of the shaft 44 to thereby adjust a direction of propagation of the pulsed ultrasound pressure wave 82 emitted by the face of the transducer 36.

[00135] This orientation control allows adjustability of the azimuth AZ and elevation EL of sample volume 38 in addition to enabling the accessing of a target structure (e.g., artery or vein parallel to the shaft 44) in accordance with an audible or other feedback Doppler flow signal produced by an electro-acoustic transducer.

[00136] FIG. 9 illustrates the concepts of azimuth (AZ) and elevation (EL) as used in an exemplary embedded software. It should be understood that other ways of defining and tracking target coordinates are possible. The horizontal coordinate system is a commonly used celestial coordinate system that uses the observer's local horizon as the fundamental plane to define two angles: altitude and azimuth.

[00137] The tracking system described below uses the transducer 36 as a local point of observation and can be embedded in the processor memory 78 and executed by the microcontroller 20 in real time.

[00138] Azimuth is the angle of the object around the horizon, usually measured from true north and increasing eastward. In the context of this invention azimuth is a rotational angle of the aligning of the target volume of tissue and the aperture of the catheter shaft 44. The starting point for azimuth angle AZ can be chosen arbitrarily when the transducer 36 starts to emit bursts of ultrasound energy. Azimuth ranges in angles of 0 to 360 degrees from that position. In the context of this invention elevation is the angle at which the ultrasound beam is pointing relative to the axis of the vein 14 in which the shaft 44 is positioned. If the catheter shaft 44 has a fixed design (as opposed to an articulating or deflecting design), this angle is relatively constant. If the shaft distal end 52 can be deflected, it has more freedom and a wider-angle range.

[00139] These terms are used to specify the viewpoint by defining azimuth AZ and elevation EL with respect to the axis origin which can be the transducer 36 acting as a point source relative to the tissue volume (sample volume 38) it is effectively illuminating with sound. Azimuth AZ, for example, is a polar angle in the x-y plane, with positive angles indicating counter-clockwise rotation of the viewpoint. Elevation EL is the angle above (positive angle) or below (negative angle) the x-y plane.

[00140] In addition, the third coordinate can be added to the system which is liner distance (LD) traveled by the transducer 36 along the blood vessel longitudinally, starting from the arbitrarily assigned “xero” point. Unlike angular coordinates, it can be defined as liner distance from the point of origin. Fig. 9 shows the sample volume 38 in a previous location 84 (dashed line) corresponding to a previous location of the transducer 36. Fig. 9 also shows the sample volume 38 (solid line) in a second location 86 after the transducer 36 has been moved a linear distance (LD) to the left (along with the puncture needle 28 and the catheter 12).

[00141] In a medical method as illustrated in the drawings a surgeon or a cardiologist or other operator manipulates the shaft 44 to align the puncture needle 28, typically by steering or maneuvering the handle 24 together with puncture needle 28 and transducer 36 therein, to position the transducer 36 within the effective ultrasound transmission distance of the target artery 26. [00142] With the advent of surgical robotics and automation of common catheter based surgical procedures it is envisioned that the manipulation of the crossing catheter may be performed by a robotic actuator which is motorized and can both advance and retract as well as rotate the shaft 44 in small precise increments guided by the Doppler signal feedback in real time. Such robotic manipulation using feedback controllers such as PID regulators or other integrated motor control algorithms known in the art of motor controls and robotics.

[00143] FIG. 10 illustrates an exemplary algorithm 200 embedded in the microcontroller memory 78 and executed in real time by a motorized catheter shaft 44 that can be a part of a robotic system using Doppler feedback to adjust AZ coordinate and similarly other parameters.

[00144] In the setting of motor-controlled devices, especially automated ones, linear travel, azimuth and elevation allow the controller 20 to optimize and track the position of the transducer 36 in relation to the targeted volume of tissue for the purpose of aligning and advancing the needle into the targeted blood vessel.

[00145] The transducer 36 may be activated to emit pulsed ultrasonic pressure waves configured to monitor blood flow velocities via frequency shifts of return ultrasonic waves reflected at least in part from moving blood in sample volume 38 inside targeted tissues of the subject (e.g. in the leg). The electro-acoustic transducer 36 may be operated to generate a feedback signal varying with Doppler frequency shift and magnitude in accordance with direction of propagation of the pulsed ultrasound pressure waves 82 from the ultrasound transducer 36 into the tissues of the leg such as muscle, bone and blood vessels. [00146] The actuating of the ultrasound transducer 36 during a Doppler procedure entails detecting reflected ultrasound waves 84 via the transducer 36, controlling timing parameters of the emitted pulsed pressure waves 82 and detecting the reflected ultrasound waves 84 to monitor blood flow velocity within sample volume 38 within the leg or a foot of the patient.

[00147] The actuating of the ultrasound transducer 36 further entails energizing the transducer to emit a series of ultrasonic pressure wave pulses 82 having a combined duration predetermined to provide sample volume 36 with length L (FIG. 9).

[00148] In addition, the method 200 may include detecting the reflected ultrasound waves 84 via the transducer 36 after a predetermined time lag or delay after a termination of the series of ultrasonic pressure wave pulses 82, whereby the sample volume 38 is located at a predetermined distance D (range) from transducer 36 mounted on the shaft 44. Distance D may be in the 1 -2 mm range and length L may be in the 10-15 mm range. Width W will depend largely on the design of the transducer 36 but is expected to be wide enough to substantially overlap at least part of an artery of 3-4 mm in diameter at the middle of the targeted tissue volume to maximize the Doppler effect. Some well-defined FEA modeling and acoustic experimentation using hydrophones can enable optimization of the transducer geometry based on available materials, chosen driving frequency and mechanical design of the crossing catheter and its spatial constraints. Similarly the pitch of the mechanical rotation of the mechanism rotating the catheter can be adjusted to achieve planetary motion of the ultrasonic beam in increments or steps that are suitable for the detection of a blood vessel that is 3-4 mm at a distance of 5-15 mm. [00149] It is contemplated that the medical method further includes manipulating the handle 24, launching the puncture needle 28, optimally by steering the shaft 44, to move the distal end portion 52 of the shaft 44 through the cardiac vein 14 in a direction determined in accordance with characteristics of the reflected ultrasound waves 84.

[00150] In an additional method, an operator orients a distal end portion of shaft within the leg of the patient to orient same in a desired direction towards an extremum (maximum) of the audible signal (e.g. pitch, frequency or power) produced by transducer X and amplified by the electronics, torques and rotates the steerable shaft in the desired direction and advances a catheter prior to shooting the needle into targeted volume of tissue.

[00151] The method 200 may begin when the catheter 12 and the transducer 36 are deployed within the vein 16 adjacent to the artery 26 at a location downstream of the occlusion 32. This can be confirmed by fluoroscopy (See FIG. 1 ). While the catheter 12 is deployed within the vein 16, the an ultrasound signal transmitted by the transducer 36 may be monitored by a user or the controller 20 (step 210).

[00152] The scannable range of the transducer 36 may be limited to approximately the transducer’s near field 40, the transition from the near field 40 to the far field 42, or just past the transition from the near field 40 to the far field 42 (See FIG 7). In other words, the transducer 36 may be tuned so that only soundwaves reflected from within the limited scannable range of the tissue volume of interest are processed to generate feedback at the user interface 22 and signals coming from outside of the zone of interest are rejected or suppressed. [00153] Upon receiving the reflected soundwave, the transducer 36 may send a signal to the microcontroller 20 where signal is processed or converted into a tangible signal recognizable by the user (step 212). The tangible signal may be visual, audible, and/or tangible. For example, the tangible signal may include (but not limited to) vibrations in the handle 24. The vibrations may change in amplitude and/or frequency. The audible signal may include (but not limited to) a sound that changes in pitch or tone and/or a series of pulses that change in frequency. The visual signal may include (but not limited to) lights that change color, intensity, and/or frequency of pulses. Alternatively, the controller 20 may determine the location and/or orientation of the transducer 36 and the puncture needle 28.

[00154] Upon receiving the tangible signal, the user may advance the catheter 12 with the puncture needle 28 and transducer 36 either linearly (in an axial direction) or rotationally around an axis (step 214). After (or while) the catheter 12 with the puncture needle 28 and transducer 36 has been advanced a predetermined distance or rotated by a predetermined degree, the user may determine whether an amplitude of the “artery finding” sound wave related signal is increasing (step 216). Indicators of increasing amplitude may be increased frequency of light, sound or vibration pulses and/or increased intensity of light, vibrations, sound, and/or sound pitch. Alternatively, the controller 20 may act to automatically advance and/or rotate the puncture needle 28 and the transducer 36.

[00155] If the user (or controller 20) determines that the amplitude of a signal created electronically and digitally by analysis of the reflected sound waves is decreasing (or recognize another signal indicative of the presence of a flow of blood or the blood filled artery 26), the user (or the controller 20) may reverse the motion of the catheter 12 and the transducer 36 (step 218) and then repeat step 216. Alternatively, if the user (or the controller 20) determines that the amplitude of the signal created electronically and digitally by analysis of the reflected sound waves is increasing (or recognizes another signal indicative of the absence of the flow of blood or the blood filled artery), the user (or controller 20) may continue advancing the catheter 12 and the transducer 36 (step 214) and then proceed back to step 216. If the user determines that the amplitude of the sound wave has peaked, the user may halt movement of the catheter 12 and the transducer 36 (step 220). From there, the user (or the controller 20) may unlock and deploy the puncture needle 28. Steps 214, 216 and 218 can be automated and performed in small steps by a motorized controller actuated by a feedback mechanism. Feedback controllers seeking to optimize position of a robotic instrument based on a feedback signal are known and can involve PID regulators and stepper or servo motors.

[00156] For embodiments described herein comprising one or more transducers 36 a fiducial marker may be positioned in the targeted blood vessel 26 to interact with the emitted ultrasound waves to provide a distinguishable aiming artifact on the ultrasound-based image or other user interface that identifies a relative position to the direction of delivery of the puncture needle 28. A fiducial marker may have acoustic properties that are significantly different that the surrounding tissue for example, so echoes are greater (hyperechoic) or less (hypoechoic) than the surrounding tissue. The material or surface of the fiducial marker may be highly reflective or highly absorptive of sound waves relative to surrounding tissue being imaged. A fiducial marker may have a more consistent echo compared to surrounding tissue being imaged. A fiducial marker may be positioned to indicate on an ultrasound-based video the opposite direction of delivery of crossing needle 28.

[00157] Other relative directions or arrangements of fiducial markers may be envisioned. For example, one or more fiducial markers may be positioned along a guidewire placed in the target vessel 26 at a set spacing interval to enable scaling of the positioning.

[00158] To place the fiducial markers in the target artery 26, for example, a popliteal artery (PA), that may be reconstituted distal to the occlusion 32 at an additional vascular access point, which may be established in a suitable artery of the leg such as the tibial or peroneal artery. The access point may be established with a guidewire that is in a standard sheath as small as 4F to accommodate a small vessel size, is in a peel away sheath, or is sheathless. The fiducial markers may be advanced retrograde into the PA to the target anastomosis zone 18 to assist crossing. The fiducial marker can be a guidewire detectable by the sensor on the crossing tool. The catheter 12 can be equipped with the sensor configured to detect the fiducial marker such as ultrasonic detector or magnetometer. The fiducial marker may be magnetic. Electric current may be applied to the fiducial marker to make it easier to detect by the operator rotating the catheter to align the needle with the marker.

[00159] The electrical signals generated by the echoes impacting the transducer and transmitted back to an imaging console may be used to create an image or video that may be displayed on a monitor. For example, the signals may be processed by a computer-executed algorithm and output to a monitor or a video output port on the ultrasound imaging console. [00160] The invention may be embodied as an endovascular ultrasonic catheter system comprising: a hollow tubular body; a hollow needle extending from a side of the tubular body; an ultrasonic transducer located at an end of the tubular body and configured to emit an ultrasonic beam; an ultrasonic receiver configured to receive a reflection of the ultrasonic beam; and a feedback signal generator configured to generate a feedback signal indicative of an intensity of the reflected ultrasonic beam, wherein the transducer and the needle are aligned so that the needle and the transducer are aimed at the same target area, and wherein a detection range of the transducer is limited to a natural focus distance or a near field transition of the transducer.

[00161 ] The scanning zone of the transducer may be limited to within a distance from the transducer within which the target artery is predicted to be.

[00162] An outer limit of the scanning zone may be the transition from the transducer’s near field to the transducer’s far field. The outer limit of the scanning zone may be a predetermined distance from the transition between the transducer’s near field and the transducer’s far field. The predetermined distance corresponds to a distance at which an amplitude of the ultrasonic signal falls below a threshold amplitude.

[00163] The transducer may be a Doppler transducer. The transducer may be configured to detect a Doppler shift between a master oscillator and the reflected ultrasonic beam.

[00164] The feedback signal may indicate a detected Doppler shift. [00165] The near field transition distance and/or the natural focus distance of the transducer may be 5 to 10 mm. [00166] The feedback signal generator may change the feedback signal as the intensity of the reflected ultrasonic beam changes. The feedback signal may include at least one of light, sound, and vibration. The feedback signal may include a vibration that waxes when the intensity of the reflected ultrasonic beam increases, and wherein the vibration wanes when the intensity of the reflected ultrasonic beam decreases.

[00167] The catheter system may include a user interface integrated with the hollow tubular body such as a handle, the user interface comprising the feedback signal generator.

[00168] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or "comprising" do not exclude other elements or steps, the terms "a" or "one" do not exclude a plural number, and the term “or” means either or both, unless the this application states otherwise. Also, the terms “approximately” and “substantially” encompass a range of plus or minus 15%. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise.

Figures and Elements

2 Cross-over opening

10 Patient Catheter

Tibial vein

Femoral vein

Crossing site Controller

User interface

Catheter handle

Femoral artery

Puncture needle Needle exit port Expandable element Occlusion

Transducer

Ultrasound penetration zone Near field

Far field

Shaft

Zone of interest

Bone

Near field transition point Distal end

Central longitudinal axis

Central longitudinal axis Transmit pulse

Receiver gate

Flow sensing region Puncture needle aperture Guidewire

Exit

Electronics

Battery

Motor and solenoid control

Input/output

Memory

Waveform generator

Pressure waves

First location

Second location

Method

Step

Step

Step

Step

Step

Step