Field of Invention This invention relates to sensing apparatus for use with fluid delivery apparatus for use with a system containing or conveying fluid, and a method for determining the position of an elongate insert within the fluid delivery apparatus.

Background to the Invention

The invention is applicable to conduits, pipes or tubes that provide access to regions of a system that would otherwise be difficult to reach, and especially so where wires, cables, tools and the like need to be introduced along such access conduits. The invention is particularly applicable to medical catheters into which elongate inserts, such as guide wires, microcatheters, tools and devices are introduced. In such cases, the system is an organ or the vascular system of a patient's body. If the apparatus of the invention is used in the field of interventional cardiology for the performance of Fractional Flow Reserve (FFR) then the system is the heart or coronary arteries of a patient's body, the access conduit is typically a guide catheter and the insert is typically a guide wire, or more specifically, a pressure wire that contains a miniaturized pressure sensor at or near its distal tip for measuring the local, instantaneous pressure at different locations around the heart and the coronary arteries. During interventional cardiology procedures it is normal practice to collect continuous x-ray images of the heart by means of an x-ray source and a digital image capture device, positioned on opposite sides of the patient. Furthermore, these devices are often mounted on a large C-shaped arm (or C-arm) such that they are in fixed position relative to each other, but can be maneuvered in several degrees of freedom to give the cardiologist the scope to optimize the images of the regions of interest. When a particular artery is being examined or treated it is normal to position the C- arm so that the artery in question is irradiated orthogonally and so is displayed on the monitor with minimal foreshortening. The FFR procedure can involve measuring the pressure drop across a stenosis in a coronary artery by comparing the local pressure downstream of a stenosis with that in the aorta. The latter is normally measured by a proximal sensor located in a fluid line connected to the proximal end of the guide catheter, the distal exit of which is normally located in the aorta.

It will be appreciated that, ordinarily, this proximal pressure measurement can only be made reliably if there is no flow of liquid along the guide catheter. However, a device has recently been developed which connects to the proximal end of a guide catheter and which detects the flow of any liquid, such as a drug, along the same, so that compensation can be made for any change in pressure along the length of the guide catheter due to the same. In an exemplary embodiment, the device includes a differential pressure sensor to measure pressure drop across an internal orifice, a wireless transmitter to communicate the information in real-time to the proximal pressure sensor and/or a display unit and a small battery to power the drive electronics associated with the above. Where patients have one or more stenoses that are distributed along the length of a diseased artery, it can be highly advantageous in the diagnosis to perform a "pullback" procedure whereby the pressure wire is first located downstream of any suspected stenosis and then retracted at a controlled speed such that measurements can be taken along the length of the resulting translation. The results of the pull-back can be displayed to the cardiologist to provide a direct visual indication of the state of stenosis(ses) along the area of interest.

In certain related procedures, such as intra-venous ultrasound (IVUS) imaging or optical coherence tomography (OCT) imaging, a wire device is inserted along the guide catheter and is used to collect data of a form that can be processed into visual images of the interior structure of the arteries, including any diseased regions, which are then displayed to the cardiologist on a monitor. It is also advantageous to perform a translation of an imaging wire, similar to the pullback described above. To automate pullback movements during pressure wire or imaging procedures, Pullback Devices have been developed to control the wire translation. These comprise a motor-driven sled to which the proximal end of the device is attached and which can be programmed to translate the wire at a constant speed over a specific distance, both of which are predetermined and programmed into the unit. In such a way, the cardiologist can effect a carefully controlled movement of the device to capture the data of interest along a specific translation path, and in doing so can "encode" each item of data generated by the device with the corresponding position at which it was captured. It is therefore possible for the captured images to be displayed on the same monitor as the x-ray images, superimposed over the same adjacent the sites of interest to which they correspond. It will be appreciated that to record pressure, calculate FFR values and to correlate these to the translated distance along an artery, it is not essential that a pressure wire translates at constant speed, provided that its relative position is known at any given instant in time. It will also be appreciated that as liquid flows along an artery there is a corresponding pressure drop, and that if any stenoses are present, these will cause more pronounced, possibly very localised, pressure drops than would be seen in a healthy artery. These pronounced, localised, drops in pressure can result in a graph of measured pressure against distance along the artery having a characteristic "staircase" shape, where each step in the curve can correspond to an individual stenosis.

It will further be appreciated that knowledge of certain properties of the guide catheter and the pressure wire, such as their lengths, could be important in the subsequent analysis of the measurements taken.

Summary of the Invention

According to the present invention there is provided sensing apparatus for use with fluid delivery apparatus for use with a system for containing or conveying fluid and comprising a fluid delivery conduit, the sensing apparatus comprising an elongate insert for insertion into the fluid delivery conduit, and sensing means for detecting and measuring the movement and position of the insert within the conduit. Preferably the sensing means can detect the linear movement of the insert device by means of a structure introduced into the insert during its manufacturing process. The structure can take the form of an electrical conductor with multiple convolutions, such as those used in handheld digital measurement calipers. Alternatively the structure can be in the form of a regular texturing of the surface, such as circumferential bands, applied to the outer surface of the insert, analogous to an optical encoder. Such bands can be formed, for example, by laser etching, or by printing. In such a way, an optical sensor, such as a photodiode, can detect the difference in intensity of light reflected from the surface of each band against the plain background material. To improve the sensor's ability to discriminate between the bands, the intensity of reflected light can be increased by illuminating them with a light source such as an LED. Such systems are well known, and commonly known as an "opto- pair". The combination of the optical sensor and the marked insert device thus constitutes a simple linear encoder that detects movement of the insert as each band passes through the sensor's field of view. In addition to measuring position, said structure can have information encoded within it, analogous to a 2D barcode. Thus a simple system for including data such as the length and diameter of the insert, can also be incorporated.

The measurement of movement of the device allows its position to be determined at any point in time relative to a specific starting point in the form of a virtual waymark point.

Preferably the access conduit is a guide catheter and the elongate insert is a catheter or microcatheter, guide, pressure or imaging wire.

Preferably, the sensing apparatus is for use in an FFR procedure, which may involve measuring the pressure drop across a stenosis in a coronary artery by comparing the local pressure downstream of a stenosis with that in the aorta. The latter is normally measured by a proximal sensor located in a fluid line connected to the proximal end of the guide catheter, the distal exit of which is normally located in the aorta. However, the sensing apparatus of the present invention may be used in other procedures, such as a coronary flow reserve (CFR) or thermodilution procedure.

In this connection, the fluid delivery apparatus may connect to the proximal end of a guide catheter and detect the flow of any liquid, such as a drug, along the same, so that compensation can be made for any change in pressure along the length of the guide catheter due to the same. In an exemplary embodiment, the fluid delivery apparatus includes a differential pressure sensor to measure pressure drop across an internal orifice, a wireless transmitter to communicate the information in real-time to the proximal pressure sensor and/or a display unit and a small battery to power the drive electronics associated with the above. When the insert device is a pressure or imaging wire, each item of data that it generates can be encoded with the device's position at the time of capture relative to the virtual waymark point. Data is thus generated in pairs, which in the case of a pressure wire, take the form [position, pressure]. By such means multiple data pairs can be presented in the form of a graph on the display monitor.

As described above, such a graphical display of a number of individual stenoses in a diseased artery is likely to have a characteristic "staircase" shape. Each step in the staircase can correspond to an individual stenosis that may need to be treated, with a stent for example. Furthermore the gradient of each step indicates the local rate of pressure drop, and so is a direct indication of the severity of each stenosis. However, the staircase shape is such that it can be difficult for the cardiologist to determine exactly where each of these steps starts and finishes, and hence it can be difficult to decide on the optimum length of stent to be deployed.

By means of differential calculus, the staircase curve can be transformed to show the first derivative of pressure with respect to distance of translation - or dp/dx in mathematical notation, where p is pressure and x is distance of translation from the waymark point. By doing so, the staircase curve is converted into a series of peaks, the height of which provides a direct indication of the severity of each stenosis. Additionally, it can be much easier with the curve of dp/dx to determine the boundaries of each stenosis for the purpose of selecting the optimum length of stent.

Furthermore, if the C-arm x-ray is positioned such that the artery is irradiated in an orthogonal direction, then the linear distance along the artery is displayed without foreshortening. Thus it is feasible, and can be very beneficial, to display the stenosis locations by superimposing the salient features of the graph of on the display of the artery of interest. In this situation, the virtual waymark point becomes important so that the start of the graph can be registered with the location in the artery where data capture commenced. This might be done, for example, by a user interface that allows an operator to position a cursor at the waymark point on a displayed image and corresponding mark.

According to the present invention there is also provided a method for determining the position of an elongate insert within a fluid delivery conduit of fluid delivery apparatus, the method comprising detecting and measuring the movement and position of the insert within the conduit using sensing means. In the method of the present invention, the movement and position of the insert within the conduit are preferably measured and detected using the sensing apparatus according to the present invention.

The method of the present invention provides information on the relative position of the elongate insert from a given starting, datum or waymark point, and may not attempt to provide information about the absolute position of the elongate insert within the fluid delivery conduit. In practice a cardiologist is principally interested in knowing the distance of various features in an artery from a given waymark point that he/she specifies.

Brief Description of the Drawings

By way of illustration only, an embodiment of the present invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 illustrates a typical arrangement in a cardiology catheterisation laboratory.

Figure 2 illustrates a preferred fluid delivery apparatus for use with the sensing apparatus of the present invention.

Figure 3 illustrates the fluid delivery apparatus of Figure 2 incorporating sensing apparatus of an embodiment of the present invention in cross-section viewed in a direction perpendicular to the axis of the elongate insert.

Figure 4 illustrates the fluid delivery apparatus incorporating the embodiment of the sensing apparatus of the present invention of Figure 3 in cross-section viewed in a direction parallel to the axis of the elongate insert.

Figure 5 illustrates a characteristic "staircase" curve generated using the data points generated by the sensing apparatus and method of the embodiments of the present invention.

Figure 6 illustrates a graph of the first derivative of pressure with respect to distance (dp/dx) showing the peaks relating to different stenoses. Figure 7 illustrates how these peaks could be superimposed onto an orthogonal X- ray image of an artery of interest. Detailed Description

Figure 1 illustrates a typical arrangement inside a cardiology catheterisation laboratory (1 ) where the patient (2) is positioned on the table (3). The C-arm X-ray system (4) consists of an X-ray source (5), and a digital imaging device (6).

Figure 2 illustrates a preferred fluid delivery apparatus (7) for use with the sensing apparatus of the present invention in cross section. The tapered fitting (8) permits connection to the proximal end of a guide catheter (not shown in this figure). The device entry gland (9) permits a guide, pressure or imaging wire (not shown) to be inserted, and then sealed to prevent the escape of fluid from within the flow paths. The side port (10) allows liquids, such as drugs to be delivered to the patient, or saline to be flushed, prior to insertion into the guide catheter for example. The differential pressure sensor (11) detects difference in pressure across the orifice (12) and hence provides a means to detect the flow rate of any such liquids.

Figure 3 shows an optical sensing means (13) in cross-section within the fluid delivery apparatus (7) connected to a guide catheter (14), viewed in a direction perpendicular to the axis of an insert device (15) with marked bands (16) to act as encoding features circumferentially around its outer surface.

Wires and other devices similar to the insert device described here may have various printed marker bands (for human readability), and these typically have sufficiently different reflective properties to the normal outer surface to be detectable by the optical sensing means described herein. It will be appreciated that, if a light source is directed towards the surface of the insert device (15), then the intensity of light reflecting off the surface will change between two discrete levels as the insert device translates within the fluid delivery apparatus (7). This changing light level can be detected by a light sensitive transducer, such as a photodiode. As an alternative to the reflective marked bands, other features could be applied to the wire in a number of different ways, such as a printed conducting track, similar to the technique used in digital measurement calipers which takes advantage of a capacitive coupling method. However, the precision of measurement required for pull back procedures does not need to be especially high, and the optical method described here is deemed to be adequate. The marked bands could either be applied to the surface of the wire by a printing or deposition technique, or by material removal, such chemical etching or laser ablation. Either of these techniques could produce bands with a width or spacing of less than 1 mm. With particular attention to the method of application, the band width or spacing could be as small as 0.1 mm. However, a total pitch-distance of any feature on one band to the corresponding feature on the adjacent band, of around 0.5mm is adequate to provide a sufficiently fine measurement resolution for the movement of the insert device.

Such a system of translation detection does not attempt to provide information about the absolute position of the insert device (15) within the fluid delivery apparatus (7). Instead it provides information on the relative translation from a given starting, datum or waymark point. In practice the cardiologist is interested only in knowing the distance of various features in an artery from a given waymark point that he/she specifies.

Figure 4 shows an optical sensing means (13), in cross-section within the preferred fluid delivery apparatus (7) viewed in a direction parallel to the axis of the insert device (9) looking in a proximal direction. The two optical devices shown, in the form of a light emitting diode and a photodiode, represent the preferred method for illuminating the insert device and detecting the reflected light.

As the insert device translates and the system reports each increment of movement, a corresponding value of measured pressure can also be recorded. Data pairs in the form of [pressure, distance] that can thereby be collected from the apparatus and method of the present invention. This permits a graphical representation such as that shown in Figure 5, which exhibits a characteristic staircase shape. Each step (17) in the staircase may represent a stenosis since the rapid change in pressure is likely to be caused by a local restriction to blood flow at that particular location. Figure 6 illustrates the appearance of the first derivative of pressure with respect to distance (dp/dx) derived from the same staircase curve after being transformed by differential calculus. It will be apparent that the peaks (18) in the dp/dx curve can provide a clearer indication to the cardiologist of the severity, location and length of different stenoses.

In Figure 7, these peaks (18) are seen superimposed onto an orthogonal X-ray image (19) of an artery of interest. This particular graphical representation is constructed by using values of dp/dx for each value of x generated by the invention and plotting these onto the artery at the corresponding values of x measured from the virtual waymark point. However, the style of graphical representation in Figure 7 could be different if, for example, a different approach, such as a series of shapes of varying size or shape, was easier to assimilate, which are not described here.