The invention relates to an ultrasound device and a method for operating an ultrasound device, in particular a HIFU device, ac cording to the independent claims.

Ultrasound devices and in particular HIFU (High Intensity Fo cussed Ultrasound) devices are well known in the art. An example of such a device is described in EP 2 504 063 of the applicant.

Ultrasound device are commonly used for the non-invasive treat ment of tissue, mainly based on two effects, thermal ablation and cavitation.

According to the general use of ultrasound and in particular HI FU devices, the probe head is approximately placed over the ob ject (i.e. a patient) to be treated. Then precise positioning of the focus with respect to the target is done under imaging guid ance provided by the associated imaging device (B-mode, MRI, etc.) with mechanical motion of the probe head (e.g. if mounted on a robot) or using electronic focusing. Generally, the probe head contains a coupling liquid which ensures the acoustic cou pling to the object. To contain the coupling liquid, the probe head is closed by a coupling balloon on its distal end. The cou pling liquid may be circulated by a set of pumps. Since the bal loon is in contact with the object, part of the fluid pressure is transmitted to the object. In this context, the balloon and the fluid pressure play an important role in the targeting: a change in the fluid pressure in the balloon will tend to offset the focus away from the target. High pressure will tend to com press a soft object, not only the superficial layers but also to certain extent the deeper structures. For example, by applying pressure to a tissue of a patient by means of the coupling liq- uid pressure inside the balloon and/or by pressing the probe head with the balloon against the tissue, an underlying vein may be partially or totally collapsed.

In order to maintain a high targeting accuracy, some systems control the pressure of the fluid within the balloon.

For example, a "constant pressure system" (i.e. capable of main taining a constant pressure in the balloon) uses a pressure sen sor in the probe head. A controller unit with a feedback loop which receives information from the pressure sensor acts on a fluid control system so as to ensure a constant pressure of the coupling liquid in the balloon. This enables the device to com ply with the object characteristics such as shape, size, contact surface with the balloon, etc. by maintaining contact when the probe head is moved away from the object by increasing the cou pling liquid volume within the balloon (inflation) and by avoid ing too high mechanical stress on the object when the treatment head is moved towards the object by decreasing the fluid volume within the balloon (deflation) or by applying a constant pres sure on the object (e.g. for partially or totally collapsing a vein) . In other systems, the volume of the fluid is kept con stant .

In the course of these adjustments by an operator, a "constant pressure system" will adjust the quantity of coupling liquid in the balloon to maintain a constant pressure of the balloon onto the object. However, a delay is introduced by the feedback mech anism. For example, the length of the tubes in which the cou pling liquid flows may causes a delay in the increase of pres sure in the balloon. Accordingly, it can take up to a few sec onds for the balloon to reach the set pressure value. In the context of the operation, this leads to the following un wanted sequence of events: In a first phase, the operator manu ally compresses and/or moves the object (i.e. a patient tissue) or the probe head to bring the target onto focus. The pressure feedback loop detects an abrupt increase in fluid pressure, and starts deflating the balloon. The beginning of the deflation is quite quick due to the high pressure value reached, which ena bles the operator to place the target at focus without too much effort .

However, when the operator reaches proper positioning, the pres sure has not yet fully reached its set value. Therefore, in the following seconds, the balloon slowly deflates and the target slowly drifts away from the focus. The operator would generally compensate that drift manually, forcing the operator to maintain its potentially uncomfortable position for several seconds and slowing down the procedure.

Although those phases are described separately to illustrate the feeling of the operator, in reality, there is a continuous shift from the fast adjustment phase to the slow adjustment phase along with the decrease (or increase) in pressure towards its set value.

Increasing the gain parameter in the feedback loop makes the system more reactive to pressure changes but can lead to insta ble regimes where the balloon is continuously inflating and de flating, thus leading to an unwanted oscillation of the focus position .

According to existing techniques for the treatment of veins as disclosed in US 7,921,854 B2 or US 6,752,803 B2, a tourniquet for reducing or stopping the blood flow upstream of the target area is used. Other techniques comprise placing the patient in the Trendelenburg position in order to decrease the blood flow or tumescent anesthesia, where liquid is injected around the target area (preferably in a fascia surrounding the vein) , which reduces the vein diameter. Mechanical compression with bandages is also used.

When a vein is collapsed, the problem arises that the vein is not visible anymore in commonly used imaging devices. For exam ple, a fully collapsed vein is not visible using B-mode ultra sound imaging. Similarly, in colour Doppler imaging, stopping the blood flow will render the vein downstream (that means the vein without blood stream) invisible, even if the vein is not collapsed .

It is therefore an aim of the present invention to provide an ultrasound device and a method for operating an ultrasound de vice for the treatment of tissue and in particular of veins, which avoids the drawbacks of the prior art and in particular allows reliable and fast variation of the compression of the ob ject necessary to optimally perform different tasks/steps during operation .

This aim is solved by a device and a method according to the in dependent claims of the present invention.

According to the present invention, an ultrasound treatment de vice, in particular a HIFU treatment device comprises a probe head comprising an ultrasound transducer for delivering treat ment ultrasound waves focused onto a target within an object.

The device may include an imaging device for imaging of the ob- j ect . The device further comprises a compression device for applying a compression force to at least some parts of the object located near the target and the probe head an in particular to apply a compression force to the target area to be treated.

As it will become more clear from the description below, the compression device may be in a preferred embodiment the balloon itself, where the pressure of the coupling liquid is used to ap ply a compression force to the object. Alternatively, the com pression device may be a moving mechanism of the probe head, where the probe head is pressed towards the object to apply a compression force (e.g. by clamping the object between the probe head and an abutment) . The compression device may also be a sep arated device, in particular attached to the probe head and ar ranged near the contact point of the balloon with the object, which can be moved and or inflated/deflated in order to apply a compression force to the object.

Further, a controller unit the probe head and the compression device is present.

The device is adapted to switch between at least two operating modes .

In a first operating mode the compression force applied to the object by the compression means is maintained at a first com pression force value.

In a second operating mode the compression force applied to the object by the compression unit is maintained at a second com pression force value which is preferably higher than the first compression force value. The compression force is in particular induced by a pressure or a volume of a coupling liquid arranged in a cavity of a coupling balloon of a probe head.

A coupling balloon may be arranged at a target side of the probe head, wherein a cavity between the probe head and the coupling balloon is filled or tillable with a coupling liquid. The bal loon may be a deformable balloon.

The cavity of the balloon is preferably in fluid connection with a coupling fluid reservoir.

The device may further comprise a pressure measurement unit for determining the pressure of the coupling liquid in the cavity, and a fluid control system for controlling the pressure or the volume of the coupling liquid in the cavity.

The pressure measurement unit preferably comprises a pressure sensor. Alternatively, the pressure may be determined using oth er criteria such as the volume of coupling liquid in the cavity or in a part/subsection of the cavity (taking the density of the coupling liquid into consideration and using gravity) .

The fluid control system may preferably comprise a pump and at least one valve or at least two pumps. Coupling liquid can therefore be circulated within the balloon and in particular be tween the balloon and the fluid reservoir. The coupling liquid may be additionally kept to a constant temperature, in particu lar cooled by means of a heat exchanger.

In the first operating mode, the controller unit preferably con trols the device in order to perform imaging of the object, while in the second operating mode, in particular when the sec- ond compression force is higher than the first compression force, the controller unit preferably controls the device in or der to emit at least one pulse of treatment ultrasound waves.

According to a preferred embodiment of the present invention, the controller unit is connected at least to the pressure meas uring unit, the fluid control system, the probe head and the compression device.

In the first operating mode the pressure of the coupling liquid is maintained at a first pressure value and/or maintained at a first volume value and/or controlled according to a first con trol rule.

In the second operating mode the pressure of the coupling liquid is maintained at a second pressure value, preferably higher than the first pressure value or the volume of the liquid in the cav ity is kept constant at a second volume value and/or the pres sure is controlled according to a second control rule different from the first control rule. As an example, in the second oper ating mode, if a fluid control system comprising two pumps is used, the speed of the pumps may be controlled by the controller unit, in particular to keep the volume constant to the second volume value. It must be noted that in this case, if the speed of the pumps is equal, a slight drift in the volume value may be exist and may be compensated by adjusting the speed of one of the pumps from time to time.

A control rule is in particular a defined control loop mecha nism. The first control rule may e.g. differ from the second control rule in that the pressure is controlled in a more de layed way as according to the second rule. The first operating mode is preferably a positioning and/or im aging mode. In particular, the first pressure value or the first volume value is suitable for the tasks of positioning the probe head onto the object and/or imaging the object and in particular the target area of the object and/or roughly focusing the probe head on the target.

The second operating mode is preferably a treatment mode. In particular, the second pressure value or the second volume value is suitable for the tasks of displacing the object, in particu lar the soft tissue of a patient, in order to bring and keep fo cus into the target area and/or treating the target by means of emitting at least one pulse of treatment ultrasound waves.

In this regard, the second operating mode is preferably adapted for partial or total collapsing of a vein and/or stop blood flow for the treatment of varicose veins. Partial collapsing accord ing to the present invention is defined as the lumen of the vein still visible by means of the imaging device, wherein the lumen section area is smaller than a reference (i.e. when a patient is standing) wherein totally collapsing of the vein is defined by the vein being totally compressed and therefore the lumen of the vein being not more visible by means of the imaging device.

For the treatment of veins, both thermal and cavitation effects can be used, alone or in combination. In particular, two main principles are used, namely stopping the blood flow and/or col lapsing (partially or totally) the vein.

Stopping blood flow mainly aims at avoiding its cooling effect on the vein wall. Collapsing the vein can bring more of the vein wall within the focus, thus considerably decreasing treatment time and/or increasing treatment efficacy. Stopping blood flow can be done by compressing the vein distally or proximally to the targeted zone. A distal compression may however not be efficient since, if a tributary branch to the vein is present between the compression point and the targeted area, it will bring some flow to the vein. Conversely, proximal compression is more efficient in stopping the flow but blood will tend to accumulate within the vein, thus inflating it. Me chanical compression just above the targeted area is difficult to perform with existing devices.

Alternatively, ultrasound emission may be performed with some blood still present in the vein (partial collapsing of the vein) in order to treat the vein wall by cavitation.

It must be noted at this point that according to this preferred embodiment, if in the first operating mode the pressure is main tained to the first pressure value, in the second operating mode the controlled parameter must not necessarily be the pressure, but may also be the volume (second volume value) and vice-versa.

The controller unit is preferably adapted to monitor the pres sure of the coupling liquid determined by the pressure measure ment unit and to detect a change and in particular an increase of the pressure of the coupling liquid in the cavity when the device is in the first operating mode and the coupling balloon is arranged on the object.

The controller unit is further preferably adapted to switch from the first operating mode to the second operating mode upon de tection of a switch signal.

In particular, if a compression force is applied to the object by the compression device or by an operator, in the second mode, the balloon is not, as known from the prior art, deflated in or der to keep the pressure constant, but is only deflated to a second pressure value higher than the first pressure value or the volume is set and then kept constant to a second volume val ue in order to avoid the slow shifting of the target position during the slow adjustment phase as described in the introduc tion.

When the device is in the second operating mode, the device can trigger the emission of at least one pulse of treatment ultra sound waves and in particular of a treatment sequence comprising a plurality of treatment ultrasound wave pulses.

Preferably, the balloon may be shaped such that deformation of the balloon mainly occurs in a direction toward the focus. This may be achieved by providing a balloon with lateral stiff walls and a flexible membrane on the part facing the ultrasound trans ducer. Alternatively, cover members may be applied to conven tional balloons in order to constrain lateral deformation.

Therefore, the pressure of the coupling liquid may be better controlled when applying pressure to the object.

The device is further adapted to switch back from the second op erating mode to the first operating mode after the emission of at least one pulse of treatment ultrasound waves.

The device may preferably comprise a manual switch for switching between the first operating mode and the second operating mode. In this case, the switching signal is generated by actuating the manual switch.

Preferably, a delay is introduced between activation of the man ual switch and generation of the switching signal in order to allow an operator to perform other tasks, e.g. compress the ob ject manually or by means of the compression device.

In particular, in the cases where switching from the first oper ating mode to the second operating mode is automatic, as com pression of the tissue is complex and requires several trials to find the right position of the hands or of the compression de vice, the operator has the possibility to switch to a "training mode" where he can freely test the compression without generat ing the switching signal, while checking the effect of his com pression by means of the imaging device.

Optionally, when the operator is satisfied by the position of his hands, the operator can switch to a "learning mode", where the operator successively performs his compression manoeuvre one to several times (preferably, the number of compression manoeu vres is pre-defined) . During this phase, the device analyses the pressure curve in order to determine the appropriate first pres sure threshold value. For example, if the operator performs the compression one time, the first threshold value can be set to e.g. 80% of the maximum pressure reached.

A manual switch according to the present invention must not nec essarily be activated by the hand of an operator, but can also be voice activated or a foot or a leg switch.

Alternatively, the controller unit is further adapted to switch from the first operating mode to the second operating mode when the detected pressure increase is above a threshold value. In this case, the switching signal is generated automatically by the controller unit when the detected pressure increase is above the threshold value. This is in particular advantageous when the object compression is performed with the compression device or manually by an operator.

Preferably, the threshold value is greater (e.g. tenfold) than the standard variation of the pressure value measured during the first operating mode to avoid untimely switching. Other control terms such as the rate of change of the pressure value (D-term) may be used for generating the switching signal and therefore switch the operating mode from the first to the second operating mode .

Preferably, if the controller unit is further adapted to switch from the first operating mode to the second operating mode when the detected pressure increase is above a threshold value, the switching signal is generated with a delay.

In particular, after the pressure value has reached a value above the first threshold value, the controller unit first con trols the pressure in the balloon in order to lower it to the second pressure value. When the pressure in the balloon has reached a second pressure threshold value and drops below this second pressure threshold value, the switching signal is gener ated .

Preferably the controller unit is further adapted to switch from the second operating mode to the first operating mode when the detected pressure decrease is below a pressure threshold value. In this case, the switching signal is generated automatically by the controller unit when the detected pressure decrease is below the pressure threshold value. This is in particular advantageous when the object compression is performed with the compression device or manually by an operator and the compression is lowered after the emission of the ultrasound treatment waves. The device preferably further comprises at least one force sen sor, preferably a finger force sensor for a device operator, connected to the controller unit and preferably arranged or ar- rangeable on the object, and the controller unit is further adapted to compare a force determined by the force sensor with a force threshold value and to switch the device to the second op erating mode when the force determined by the force sensor is above the force threshold value and is preferably kept constant for a pre-determined amount of time.

The force sensor may be arranged on a glove worn by an operator. Alternatively, the force sensor may be adapted to determine a compression force applied by the compression device to the ob- j ect .

The force sensor is preferably used for detecting the force ap plied by an operator or by the compression device onto the ob ject, which object may be soft and deformable. Therewith it may be possible to determine if the operator or the compression de vice is trying to keep the target in the focus zone of the probe head. Switching to the second mode is preferably performed when the force measured remains stable at a high value for a short duration compared to a characteristic time of the slow adjust ment phase (typically, from 0.1 to 1 seconds) .

The controller unit is further preferably adapted to switch from the second operating mode to the first operating mode after the emission of at least one pulse of treatment ultrasound waves when the force determined by the force sensor is below a second threshold value and preferably remains constant for a pre determined amount of time. In particular, the force measurement may be used to abort the emission of ultrasounds by just decreasing the force applied to the object (e.g. by removing the hands from the object or reduc ing the compression force applied to the object) .

The controller unit is further preferably adapted to automati cally trigger the emission of and emit at least one pulse of treatment ultrasound waves after activation of the second oper ating mode.

In this preferred embodiment, the device is able to determine that the target has been correctly located within a focus of the probe head and therefore an emission of ultrasounds can be auto matically performed.

It must be noted at this point that throughout the present de scription, the terms "triggering the emission of at least one pulse of treatment ultrasound waves" and "emitting at least one pulse of treatment ultrasound waves" art used. Triggering the emission of at least one pulse of treatment ultrasound waves means that the device is in a state where he is actually ready to emit the treatment ultrasound waves, while the emission of the waves may be delayed. In particular, the emission of the treatment ultrasound waves is performed only if supplementary criteria are met.

Alternatively, the device may further comprise a manual switch for triggering the emission of at least one pulse of treatment ultrasound waves by an operator, wherein switching from the first operating mode to the second operating mode is performed automatically after triggering the emission of at least one pulse of treatment ultrasound waves, in particular if compres sion of the object is to be performed by means of the balloon. According to this preferred embodiment, the operator can agree with the device emitting the ultrasounds before the target has been properly focused. The device can then automatically switch from the first operating mode to the second operating mode as described in the present application. Interruption of the proce dure may be possible at any time (e.g. by removing the hands from the object) .

In order to correctly place the focus with respect the target, the device preferably further comprises time measuring means for delaying the emission of at least one pulse of treatment ultra sound waves by a pre-determined amount of time after the second operating mode has been activated.

According to this preferred embodiment, the emission of ultra sounds is delayed in order to allow an operator to focus the target. The pre-determined amount of time may be chosen by the operator manually or may be determined automatically based on operator' s related data such as the time normally needed for fo cusing the target according to an activity register etc.

The time measuring means may be preferably further adapted to automatically switch from the second operating mode to the first operating mode with a delay of a pre-determined amount of time after emission of the treatment ultrasound waves.

The controller unit is preferably further adapted to determine the position of the target based on the images captured by the imaging device and to switch to the second operating mode auto matically when the position of the target is stable over a pre determined amount of time. As cited above, imaging of the target is usually performed in order to properly focus the target. Known image processing algo rithms may be used to determine if the target position is kept within an allowable target zone for a pre-determined amount of time .

The controller unit may be further adapted to switch to at least a third operating mode where the compression force applied to the object by the compression unit is maintained at a third com pression force value, preferably higher than the second compres sion force value, and in particular the pressure of the coupling liquid is maintained at a third pressure value, preferably high er than the second pressure value, or the volume of the coupling liquid in the cavity is maintained at a third volume value.

Switching to the third mode is preferably performed just before and during ultrasound emission, to apply a higher pressure to the vein to further reduce the vein section or totally collapse the vein.

Also in this case it must be noted that according to this pre ferred embodiment, if in the first or second operating mode the pressure is maintained to the first or second pressure value, in the third operating mode the controlled parameter must not nec essarily be the pressure, but may also be the volume (third vol ume value) and vice-versa.

Preferably, the controller unit is adapted to switch from the third operating mode to the second operating mode during treat ment ultrasound emission, such that at least one pulse of treat ment ultrasound waves is emitted with a vein totally collapsed and at least one pulse of treatment ultrasound waves is emitted with the vein in a partially collapsed. After the emission of the treatment ultrasound waves, the con trolling unit is preferably adapted to reduce the pressure of the coupling liquid in the cavity so that vein may be visible again by means of the imaging device.

Therefore, the device may be switched back to the first or to the second operating mode.

The controller unit may then be adapted to move the focus to the next location to be treated. Alternatively, the operator may move the focus to the next location.

Alternatively, the focus may be moved to the next location and the device may be then switched back to the first or second op erating mode.

Compression of the vein may be also maintained during a sequence of ultrasound pulses before compression is released: for exam ple, if several pulses have to be delivered in the same trans verse plane and the displacements are small (e.g. < 5 mm) .

Preferably, in the first operating mode particularly adapted for probe head positioning and imaging, a slight pressure is applied to the object (e.g. 0.5-15 mbar) .

In the second operating mode, which is particularly adapted for targeting (and potentially for cavitation pulses) a moderate pressure, preferably causing partial collapse of the vein, is applied (e.g. 5-40 mbar).

In the third operating mode, which is particularly adapted for pulses relying on thermal effects, a higher pressure causing complete collapse of the vein is applied (e.g. 30-200 mbar) . It must be noted that in the different operating modes, other parameters may be changed by the controller unit. In particular, in the case of a proportional feedback loop, increasing the pressure value to be maintained may require to decrease the gain of the feedback loop to avoid oscillations.

Preferably, the control unit further comprises an input device for manually inputting parameters related to the different oper ating modes. In particular, the pressure values to be maintained during the respective operating modes may be adjusted by an op erator. In addition, the rate of pressure change when switching from one operating mode to the other operating mode may be vari- ated by an operator. In particular, when switching from the first operating mode to the second operating mode and from the second operating mode to the third operating mode, the rate of pressure change is chosen such as to allow an operator and/or an automatic segmentation algorithm implemented in the controller unit to follow a change in the object, e.g. to determine if a vein is partially or totally collapsed.

Compression of the object, especially if it is performed with the balloon, induces some displacement of the object and of the target. Therefore, if the focus was placed on the target before compression, it is likely to be at a wrong position after com pression .

In the case of compression with the balloon, it may be possible to anticipate how the object will deform, in particular how a vein will collapse, due to compression. Therefore, the focus may be placed slightly away from the target with reference to the probe head such that after compression, the deformed object is at focus. As an example, positioning the focus 5 mm under the target with a pressure of 5 mbar in the balloon usually results in the tar get being displaced approximately to the focus when a pressure of 50 mbar is applied.

In particular, the controller unit may be adapted to provide a marker on an image provided by the imaging device indicating the position where the target is presumed to be located after a com pression is applied to the object. This is in particular done by the controller unit being connected or comprising a computing unit with operational instructions stored therein for providing the marker. Preferably, the marker is only displayed during the first operating mode.

The focus positioning may be also performed by means of a trial and error procedure. The device is adapted to increase the pres sure of the balloon to a pressure of the third operating mode. Imaging of the object is performed until the target disappears from the image or reaches a pre-determined level of collapsing (e.g. at 60 mbar), e.g. blood flow has been stopped as assessed by colour Doppler or a vein lumen section area assessed by B- mode imaging has reached a desired value.

At the end of this phase, the target may or may not be visible by means of the imaging device. Therefore, especially if it is intended to become invisible at the end of the phase, the posi tion of the targeted object is followed along compression. Pref erably, a tracking algorithm is used to follow its position as it collapses. Most preferably, its position is still automati cally followed after it has become invisible (e.g. based on its last visible position and a speckle tracking algorithm) . Alter natively, the operator visually follows its position as it col lapses . Then, if the target in the (partial or total) collapsed state is not at the desired position (e.g. with the focus within the vein lumen) , the device is moved by the offset distance to bring the focus on target.

Optionally, the device is further switched to the second operat ing mode where the target is visible by means of the imaging de vice. The position of the focus with respect to the target is then determined and, if the focus is offset, the probe head is moved along the imaging plane. The pressure may be decreased when moving the probe head (the device is switched to the first operating mode) .The procedure is repeated until the focus at the desired location with respect to the target.

As cited above, when the object is compressed, it may be impos sible to see the target by means of the imaging device, e.g. when no blood is flowing through the vein.

By moving the probe head away from the target for a short period of time, this problem can be solved.

The device therefore comprises means for moving the probe head away from the object. The movement shall be of a short duration of time, such that the balloon is not inflated due to the de tected fast pressure decrease, and may be in the range of some millimetres .

Alternatively, the probe head may be displaced manually by an operator to obtain the same results.

Imaging is still performed when moving the probe head away from the target such that the position of the target can be identi- fied clearly without increasing too much the blood flow in the vein .

The device is then adapted to keep the probe head at the new po sition (in this case the pressure would be adjusted back to the pre-determined value where the target is not visible) .

Alternatively, the device may be returned to the original posi tion. Moving the probe head away from the target and then back to the original position is in particular done in a short period of time in order not to activate pressure compensation in the balloon. In particular, moving of the probe head may be per formed in a mode where the volume of the coupling liquid is kept constant by the controller unit (second operating mode) .

Preferably, the controller unit is adapted to switch between a "fast-reaction mode" and a "slow-reaction mode", in particular if the probe head is manually displaced by an operator, wherein in the fast-reaction mode the pressure is adapted quickly enough when a slow movement of the probe head is done, e.g. during probe head positioning, while in the slow reaction mode, pres sure is not adapted quickly when a slow movement of the probe head is done. In particular, during the "slow reaction mode" the pressure is slowly adapted such that a movement of the treatment head towards or away from the target, at a speed which enables imaging of the target, e.g. to control the opening of the vein, does not lead to significant balloon inflation or deflation. For example, the slow reaction mode can be obtained by decreasing the gain of a proportional feedback loop or by switching to a constant volume mode (which corresponds to no reaction) .

In particular, the device comprises a switch for switching be tween the fast reaction mode and the slow reaction mode. As an example, the controller unit may be switched to a slow re action mode when in the third operating mode. Then, the probe head is moved away from the object (e.g. by one to a few milli metres) so the vein becomes visible. Preferably, the displace ment is chosen such that a vein is only slightly opened so the operator and/or the automatic segmentation algorithm can detect it, but only limited blood flow is possible. Then, the probe head is moved back to its initial position. Finally, the con troller unit is switched back to the fast reaction mode. This sequence enables to check the position of the targeted struc ture .

In a preferred embodiment, the ultrasound transducer may be mov- ably arranged with respect to the balloon, wherein after deter mining the correct pressure for the desired treatment, e.g. the vein is collapsed for thermal ablation, the ultrasound transduc er is moved with respect to the probe head and the balloon in order to shift the focus within the target without displacing the target by increasing the pressure of the liquid in the bal loon because of the displacement of the probe head.

The invention further relates to a method for treating a target within an object (tissue of a patient) with an ultrasound de vice, in particular a HIFU device. The device is preferably a device as disclosed above.

The above cited advantages and preferred embodiments of the de vice apply accordingly to the method according to the present invention and vice-versa.

The method comprises the following steps: Placing a probe head comprising an ultrasound transducer for de livering treatment ultrasound waves focused onto a target within an object and applying a first compression force to the object.

In a second step, the compression force applied to the object is increased to a second compression force higher than the first compression force either manually by an operator or by means of a compression unit of the device, and at least one pulse of treatment ultrasound waves is emitted.

Preferably, imaging of the object by means of the imaging device is performed while applying the first compression force to the obj ect .

The method preferably comprises the following steps:

Placing a deformable coupling balloon arranged at a target side of the probe head, wherein a cavity between the probe head and the coupling balloon is filled with a coupling liquid onto the object and activating a first operating mode where the pressure of the coupling liquid is maintained at a first pressure value or the volume of the liquid in the cavity is maintained at a first volume value.

Switching from the first operating mode to a second operating mode, wherein in the second operating mode the pressure of the coupling liquid is maintained to a second pressure value which is preferably higher than the first pressure value or the volume of the cavity is maintained at a second volume value.

Therefore, a compression force may be applied to the object by the coupling liquid pressure only or in addition manually by an operator and/or by means of the compression unit. Also in this case it must be noted that according to this pre ferred embodiment, if in the first operating mode the pressure is maintained to the first pressure value, in the second operat ing mode the controlled parameter must not necessarily be the pressure, but may also be the volume (second volume value) and vice-versa .

Preferably, switching from the fist operating mode to the second operating mode is performed upon detection of a switching sig nal .

Preferably, the pressure of the coupling liquid is monitored by a controller unit connected to a pressure measurement unit and an increase of the pressure of the coupling liquid in the cavity is detected, wherein upon detection of the pressure increase, a switching signal is generated.

Preferably, the pressure of the coupling liquid is monitored by a controller unit connected to a pressure measurement unit an increase of the pressure of the coupling liquid in the cavity is detected, wherein the switching signal is generated if the de tected pressure increase is above a pre-determined first pres sure threshold value and then drops below a second threshold value, preferably within a pre-determined amount of time.

Preferably, the pressure of the coupling liquid is monitored by a controller unit connected to a pressure measurement unit and a decrease of the pressure of the coupling liquid in the cavity below a pressure threshold value is detected, wherein upon de tection of the pressure decrease, a switching signal for switch ing the device from the second operating mode to the first oper ating mode is generated. Preferably, the method comprises the step of switching to a third operating mode from the first or second operating mode, wherein in the third operating mode the pressure of the coupling liquid is maintained at a third pressure value, preferably high er than the second pressure value or the volume of the coupling liquid in the cavity is maintained at a third volume value, .

Also in this case it must be noted that according to this pre ferred embodiment, if in the first or second operating mode the pressure is maintained to the first or second pressure value, in the third operating mode the controlled parameter must not nec essarily be the pressure, but may also be the volume (third vol ume value) and vice-versa.

In a preferred embodiment, a third step, where at least one pulse of treatment ultrasound waves is emitted, is performed.

In a preferred embodiment, a fourth step, where the operating mode is switched from the second operating mode back to the first operating mode, is performed. This fourth step can for ex ample be triggered by a decrease of the measured pressure below another pressure threshold value, which corresponds to the oper ator releasing its compression on the tissue.

In a preferred embodiment, pressure thresholds values used for triggering a switching signal would take into consideration an hysteresis of the pressure curve.

In addition, the pressure threshold values are preferably used to abort an ultrasound emission step, e.g. if the pressure of the coupling liquid raises above a pre-determined pressure val ue, which may be the first pressure threshold value, or sinks below another pressure value. Preferably, imaging of the object is performed by means of the imaging device while performing the method.

Therefore, the position of the target can be monitored and the probe head may be focused with more accuracy while the method is performed .

A flow of coupling liquid between a reservoir and the cavity is preferably maintained by the pump if the device is equipped with a pump and a coupling liquid reservoir.

Preferably, the method further comprises the step of switching to a third operating mode from the first or second operating mode, wherein in the third operating mode the pressure of the coupling liquid is maintained to a third pressure value higher than the second pressure value.

In particular, the first and the second pressure values are set according to the following method:

The first pressure value is defined so as the vein being visible by means of an imaging device and the second pressure value so as the vein being in the right configuration for treatment (e.g. total col lapse for thermal pulses, partial collapse for cavitation) .

After arranging the probe head on the object, the pressure of the cou pling liquid is gradually increased while imaging of the object is performed. After reaching the highest pressure where the vein is visi ble, the balloon is then deflated and the pressure of the balloon is defined as the first pressure value. Then, to define the second pres sure value, the pressure is increased gradually up to the level where the desired vein shape has been reached. This pressure is then defined as the second pressure value. The pressure values are then preferably stored in a storage unit connected to the control unit and may then be selected automatically or by means of a manual switch. The invention will now be described in more detail by way of non-limiting, exemplary embodiments in connection with the draw ings which show:

Fig. 1 schematically a device according to the present inven tion;

Fig. 2A an exemplary graph showing the coupling liquid pressure development ;

Fig. 2B an exemplary graph showing the coupling liquid pressure development according to an alternative of the method of the present invention;

Fig. 3A a flow diagram of a method according to the present in vention; and

Fig 3B a flow diagram of another method according to the pre sent invention.

In Figure 1 there is shown an embodiment of the device 1 accord ing to the present invention. The device 1 comprises a probe head 2 with a concave HIFU transducer 3 and a B-mode imaging de vice 4. The HIFU waves emitted by the HIFU transducer 3 are fo cused, wherein the focus lies within the imaging plane of the imaging device 4.

The device 1 further comprises a flexible balloon 5 arranged at the distal side of the probe head 2 and defining a cavity 6, which is filled with a coupling liquid 7 . The coupling liquid 7 is drawn from a reservoir 8, which is in fluid connections with the cavity 6 over lines 18 and 19. Coupling liquid is pumped in to the cavity 6 by a pump 11 over the line 18 and exits the cav- ity via the line 19. A valve 12 for regulating the pressure in side the cavity 6 is arranged on the line 19. The pump 11 and the valve 12 therefore build a fluid control system 10 for con trolling the pressure and/or the volume of the coupling liquid 7 in the cavity 6.

Inside the cavity, there is arranged a pressure sensor 9 for de termining the coupling liquid pressure in the cavity 6. The HIFU transducer 2, the pressure sensor 9, the pump 11 and the valve 12 are connected to a controller unit 13 by a connection 20, which may be a wired connection such as a BUS or a wireless con nection .

The controller unit 13 is adapted to control the operation of the device and is further connected to a force sensor 15 ar ranged on an operator's finger 21.

When the device 1 is operated, an object 0 is placed in contact with the balloon 5 and imaging of the object 0 is performed by means of the imaging device 4. A target T to be treated is lo cated within the object 0. An operator moves the probe head 2 and/or the object 0 such that the focus of the HIFU transducer 3 is located within the target T.

A possible curve of the pressure of the coupling liquid during operation is shown in figure 2A. The controller unit 13 keeps the pressure of the coupling liquid 7 in the cavity to a first pressure value PI. During this phase, which is also referred to as the first operating mode I (also shown schematically under the abscissa of the graph of figure 2), the probe head 2 is nor mally oriented such that the target T lies within the imaging plane of the imaging device 4. In order to bring the target T in focus of the HIFU transducer 3, an operator starts compressing the object 0, which is a soft tissue. Starting compression (schematically referred to in fig ure 2 as SC) , however, leads to an undesired increase of the pressure of the coupling liquid 7.

If the pressure increase leads to a pressure value above a threshold value TS1, the controller unit 13 switches the operat ing mode from the first operating mode I to a second operating mode II. After switching to the second operating mode II, the controller unit 13 controls the valve 12 and the pump 11 in or der to decrease the pressure to a second pressure value P2, which is higher than the first pressure value PI kept constant during the first operating mode I.

The second pressure value P2 is then kept constant. Since the second pressure value P2 is higher than the first pressure value PI, the operator does not see the target slowly drift away from the focus as in devices known from the prior art operated with a constant pressure mode.

The emission of treatment HIFU waves is then triggered by the operator or automatically. After the emission of the HIFU waves, the operator stops compressing the object 0 (schematically re ferred to in figure 2 as RC) .

The pressure drops below a threshold pressure value TS3, wherein as a response to the pressure drop under the threshold pressure value TS3, the controller unit 13 switches back to the first op erating mode I, where pressure is adjusted to the first pressure value PI and is then kept constant for the preparation of the object for the subsequent emission of HIFU waves. An alternative of the method according to the present invention is shown in figure 2B, which is similar to the method shown in figure 2A with the difference that, when the pressure increase raises above the first threshold value TS1, the controller unit 13 does not switch directly in the second operating mode II. The pressure is controlled by the controller unit 13 and decreased. When the pressure drops below a second threshold value TS2, the controller unit 13 switches to the second operating mode II, and maintains the pressure constant to the second pressure value P2.

By switching to the second operating mode II just before the pressure has reached the second pressure value P2, the operator does not see the target slowly drift away from the focus as in devices known from the prior art operated with a constant pres sure mode, because the slow adjustment phase is reduced or pref erably avoided.

Data from the force sensor 15 may be used additionally or alter natively in order to increase the accuracy of the detection of the pressure changes. As an example, detection of strong com pression by the force sensor 15 may be used to activate the flu id control system 10 for a fast reaction of the pressure adjust ment .

An exemplary method according to the present invention is de scribed hereinbelow with reference to the figure 3A:

The method is performed starting with a patient lying horizon tally on a bed in a first step 100.

The device 1 is activated in the first operating mode I and po sitioned on the patient in a step 110, wherein imaging of the target T is performed by means of the imaging device 4. The probe head 2 is then moved in a step 120 in order to roughly put the focus on the target T.

The device 1 is then switched to the second operating mode II, where the pressure P2 in the balloon is set to a value which in duces a moderate compression on the tissue, which results in a partial collapse of the vein.

The probe head 2 is positioned at the centre of the vein segment to be treated in a step 130. Then, the device 1 is switched in the third operating mode III, causing the total collapse of the vein. The vein therefore becomes invisible.

The position of the focus in step 130 is adjusted based on the trial and error process described in the present invention, which implies switching between the second operating mode II and the operating mode III until the focus is at the desired posi tion.

Then with the device in the third operating mode III, a pulse of treatment ultrasound waves is emitted in a step 140.

After the treatment ultrasound wave emission of step 140 an op erator decides if the treatment is terminated or should be con tinued on the same target T or another target T in a step 150.

In the case the treatment is finished (YES) the method is termi nated in a step 160. Otherwise (NO) the second operating mode II is activated and the pressure is decreased to the second pres sure P2. The probe head 2 is then moved to the next target T ac cording to the step 120. The method is then repeated until the desired tissue volume has been treated. Another method according to the present invention is described herein below with reference to figure 3B:

The method is performed starting with a patient lying horizon tally on a bed in a first step 100.

Then the patient it is placed in the Trendelenburg position to reduce the amount of blood within the vein in a step 110' and the device 1 is activated in the first operating mode I and man ually positioned on the patient, wherein imaging of the target T is performed by means of the imaging device 4. The first pres sure PI in the balloon in step 110' is set to a low value which induces minimal (if any) compression on the tissue and enables easy manual handling of the head.

The probe head 2 is then moved robotically in a step 120 in or der to roughly put the focus on the target T. The device 1 head is positioned at the centre of the vein segment to be treated.

The device 1 is then switched to the second operating mode II, where the pressure P2 in the balloon is set to a value which in duces a moderate compression on the tissue, which results in a partial collapse of the vein.

The probe head 2 is positioned at the centre of the vein segment to be treated in a step 130' . Then, the device 1 is switched in the third operating mode III. In this case the third pressure P3 does not cause the total collapse of the vein.

The vein is totally collapsed by manual pressure application by the operator in step 130'.

The position of the focus is adjusted based on the trial and er ror process described in the present invention in step 130', which implies switching between the second operating mode II and the operating mode III until the focus is at the desired posi tion.

Then, with the device in the third operating mode III and the operator manually compressing the tissue, a pulse of treatment ultrasound waves is emitted in a step 140.

After the treatment ultrasound wave emission, the second operat ing mode II is activated and the pressure is decreased to the second pressure P2 in a step 170.

A pulse of treatment ultrasound waves is emitted again in a step 140' with the vein partially collapsed, therefore inducing dam ages to the tissue by cavitation effects.

After the treatment ultrasound wave emission of step 140' an op erator decides if the treatment of the target is terminated or should be continued on the same target T in a step 180.

In the case the treatment of the target T is not finished (NO) , the method is performed again starting from step 120 on the same target, otherwise (YES) the operator has to decide in a step 150 if the entire treatment is terminated or not.

If the method has to be continued (NO in step 150) the method is performed again starting from step 110' by targeting a new tar get T. The method is then repeated until the desired tissue vol ume has been treated.

Otherwise, the method is terminated in a step 160.