BACKGROUND ART Sonic transducer arrays can be used, for example, in ultrasonic imaging; in ultrasonic lithotripsy; and in high intensity focused ultrasound ("HIFU") heating of tissues within a human or animal subject. Such heating can be used, for example, to kill tissues such as abnormal tissues. Techniques of this type, also referred to as hyperthermia treatment or ablation are disclosed, for example, in U. S. Patents and 5,247,935. Improvements in hyperthermia and related techniques and apparatus are disclosed in the copending, commonly assigned PCT International Publication W098/52465. Ultrasonic energy may be applied by a transducer disposed outside of the body or, as described United States Patent Application 09/496,988 filed February 2,2000, by transducer arrays disposed inside the body.

Ultrasonic transducer arrays as described in the aforementioned commonly assigned documents typically include a set of piezoelectric elements disposed at spaced-apart locations on a support. The piezoelectric elements may be formed as separate pieces of piezoelectric material such as a crystal or a polymer such as polyvinylidene fluoride. Electrodes overlie opposite sides of each piezoelectric element. One electrode on each piece of piezoelectric material is connected to ground or other constant potential. The opposite electrode on each piece of piezoelectric material is referred to as the signal input electrode or"hot electrode".

Individual actuation signals are applied to the hot electrodes, so that each piece of piezoelectric material is subjected to an individual, time-varying potential and vibrates in accordance with such potential. By controlling the individual actuation signals, the ultrasonic output of the array can be controlled so as to provide a phased set of ultrasonic vibrations which reinforce one another at a selected focal point. This focal point can be moved by adjusting the individual actuation signals. The transducer array must provide for individual signal connections to the hot electrode associated with each piece of piezoelectric material.

In a variant of this approach also described in the aforementioned commonly assigned documents, a transducer array may include a continuous sheet of piezoelectric material such as a polyvinylidene fluoride film. Pairs of electrodes are provided on opposite sides of the sheet, in separate regions of the sheet. Each region of the sheet constitutes a separate piezoelectric element. Here again, individual, time-varying signals must be applied to at least one electrode associated with each region of the sheet, and hence individual connections must be provided for each hot electrode.

As described in certain embodiments of the aforementioned International Publication W098/52465, the transducer array may have a dome-like or other curved shape. The transducer array may be in the form of a deformable strip, dome or other shape, so that the properties of the array may be adjusted by deforming the array.

As described in further detail in commonly assigned United States Patent Application 09/532,614, transducer arrays may be fabricated using flexible printed circuit panels associated with the piezoelectric material or formed from the piezoelectric material. A piezoelectric polymer sheet may be provided with conductive electrodes arranged in pairs on opposite sides of the sheet, so that the region of the polymer sheet disposed between each such pair of electrodes acts as a piezoelectric element controlled by the voltages applied to the electrodes.

Also, the piezoelectric elements may be stacked in multiple layers with electrodes disposed between the layers. The electrodes in each stack desirably are arranged in an alternating sequence of ground and signal electrodes. With such stacked piezoelectric elements, the displacements contributed by the various elements in the stack are combined, so that substantial sonic power output can be achieved at reasonable signal voltages.

DISCLOSURE OF THE INVENTION The present invention provides further improvements in transducer arrays.

One aspect of the invention provides a focused sonic emitter for use in applying sonic energy to a subject. The emitter according to this aspect of the invention desirably includes a frame and a set of sonic transducers mounted to the frame, each transducer being adapted to emit sonic waves. One or more of the transducers are movable transducers. Preferably, many or all of the individual transducers are movable transducers. The movable transducers are provided in groups, each such group including one transducer or more than one transducer.

Each group of movable transducers is mounted to the frame so that the group of transducers is

movable with respect to the frame over a range of dispositions, independently of movement of other groups. The emitter desirably includes an actuator associated with each group of movable transducers, each such actuator being connected between the associated group of movable transducers and the frame, each such actuator being operative to position the associated group of transducers at any disposition within its range of dispositions. The transducers, frame and ranges of dispositions being selected so that sonic waves from the transducers can be directed into a first focal region by positioning the movable transducers at a first set of dispositions relative to the frame and so that sonic waves from the transducers can be directed into a second focal region different from the first focal region by positioning the movable transducers at a second set of dispositions relative to the frame.

Stated another way, the emitted sonic beam can be"steered"relative to the frame by moving the movable transducers. This steering action can be used in addition to, or in lieu of, beam steering by adjusting the phases of the signals supplied to the individual transducers.

Steering by moving the individual transducers avoids or mitigates the problems associated with steering only by adjusting the phases of the signals, such as reduction in power at the steered focal region and creation of additional focal regions or"side lobes". Moreover, because the groups of transducers constitutes a small mass with relatively low inertia, and because substantial steering can be accomplished with relatively small movements of the transducer groups, the focal region can be moved rapidly. Most preferably, each group of movable transducers includes only one transducer or a small number of transducers.

Preferably, the movable transducers are pivotably mounted to said frame. Some or all of the groups of movable transducers can be mounted to the frame for pivoting movement relative to the frame about two non-parallel axes. The actuators used to move the transducers may be piezoelectric actuators; magnetic actuators; thermally-responsive actuators, fluid-drive actuators or other conventional devices for imparting mechanical movement.

A related aspect of the invention provides methods of applying energy to a subject.

Methods according to this aspect of the invention desirably include the steps of positioning a frame having a plurality of transducers thereon adjacent to the subject; actuating the transducers to direct sonic energy into a focal spot within the subject; and moving at least some of the transducers with respect to said frame so as to move said focal spot within the subject.

The step of moving at least some of said transducers typically includes the step of moving some of said transducers to a different extent than others of said transducers.

A further aspect of the invention provides a sonic emitter which preferably includes an array of sonic transducers, the transducers having emitting surfaces facing towards a focal region ; and directing elements associated with at least some of the transducers. Each directing element projects forwardly from the emitting surface of the associated transducer. The directing elements desirably are arranged so as to guide sonic waves emitted from said transducers toward said focal region. For example, at least some of the directing elements may define tubular guides projecting forwardly from the emitting surfaces of the associated transducers toward said focal region. The directing elements may be formed integrally with the frame. Alternatively, where the transducers are movable relative to the frame as discussed above, the directing elements may be mounted for movement relative to the frame so that each directing element moves with the associated transducer.

A sonic emitter according to yet another aspect of the invention includes a plurality of sonic transducers having emitting surfaces facing towards a focal region; at least one thermal sensor in thermal communication with one or more of the sonic transducers. The thermal sensor can detect the temperature of one or more of said transducers. Preferably, the at least one thermal sensor includes a plurality of thermal sensors, and each sensor is associated with one transducer or with a small group of transducers adjacent to one another. For example, the emitter may include thermally conductive temperature control blocks in thermal communication with said transducers, the temperature sensors and temperature control elements being mounted to the temperature control blocks. Typically, one transducer or a small group of transducers is mounted to each temperature control block, and a thermal sensor is mounted in thermal communication with each temperature control block. The emitter according to this aspect of the invention may further include individually adjustable temperature control elements, such as thermoelectric elements or electrical resistance heaters, in thermal communication with one or more individual transducers. Where temperature control blocks are employed, the individual temperature control elements may be arranged to control the temperature of each block individually. The apparatus desirably further includes array cooling means for cooling all of said transducers as, for example, a coolant channel in thermal communication with said transducers.

A related aspect of the invention provides methods of operating a sonic emitter to provide a focused sonic wave at a focal region. The method according to this aspect of the invention may include the steps of applying electrical excitation signals to a plurality of transducers having emitting surfaces facing towards a focal region so that said transducers emit sonic waves and the sonic waves from said transducers mutually reinforce one another within said focal region; monitoring the temperature of a plurality of said transducers during the applying step; and separately actuating individual temperature control devices each associated with one or more of said transducers so that each such temperature control device tends to maintain the associated transducer or transducers at a fixed set point temperature.

Alternatively or additionally, the method may include the step of adjusting one or more characteristics of one or more of the electrical excitation signals based upon the temperature or temperatures detected in said monitoring step so as to maintain mutual reinforcement in said focal region. For example, where the amplitude or phase relationship between the sonic emission from an individual transducer and the electrical signal applied to that transducer varies with the temperature of that transducer, the amplitude or phase of the electrical signal can be adjusted to compensate for such variation.

Yet another aspect of the invention provides a disposable sonic energy application unit comprising a plurality of sonic transducers and a non-volatile, machine-readable memory containing information pertinent to the unit, such as data defining properties of the transducers or a serial number which can be used to access a database having such data therein. The data desirably includes individualized data obtained by actual test or measurement of said transducers, and may include data representing a phase relationship for each said transducer; an amplitude relationship or power relationship, or both, for each transducer, or for groups of transducers. The memory may be any device capable of storing the desired information in a machine-readable form as, for example, an electronic memory such as a PROM (programmable read-only memory); EEPROM (electronically erasable programmable read-only memory); a magnetic memory element such as a magnetic strip; or an optically-readable memory element such as, for example, a bar code. A related method of applying focused sonic energy desirably includes the steps of providing a reusable system incorporating an excitation system; providing a plurality of disposable units, each such unit including a plurality of sonic transducers and a nonvolatile memory having stored therein data defining one or more characteristics of the

transducers in that unit; temporarily connecting each of the disposable units to the reusable system. While a particular one of the disposable units is connected to the excitation system, the excitation system is operated apply drive signals to the transducers of the disposable unit and to select at least one characteristic of the drive signals based at least in part on the data in the memory of that disposable unit.

Emitters and methods according to these aspects of the invention can provide compensation for differing characteristics of the transducers in the disposable units. This facilitates production of the desired sonic emissions despite variability in the characteristics of the individual transducers, which reduces the need for extremely tight tolerances in manufacture of the disposable units. The methods may further include the step of automatically altering the memory associated with each disposable unit at or before termination of the temporary connection between that unit and the reusable system, and automatically disabling the excitation system if a newly-connected unit has such alteration. This prevents reuse of the disposable device.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic perspective view depicting a transducer array in accordance with one embodiment of the invention.

Figure 2 is a fragmentary perspective view depicting certain components used in the array of Fig. 1.

Figure 3 is a fragmentary, diagrammatic sectional view of the array of Fig. 1.

Figure 4 is a diagrammatic view, partially in section and partially in block form, depicting a disposable transducer array according to a further embodiment of the invention, together with portions of a reusable system.

Figure 5 is a fragmentary sectional view depicting a portion of the transducer array of Fig. 4.

Figure 6 is a view similar to Fig. 4 but depicting a reusable system and disposable transducer array in accordance with a further embodiment of the invention.

Figures 7 is a diagrammatic sectional view depicting a transducer arrays in accordance with further embodiments of the invention.

Figure 8 is a fragmentary, diagrammatic perspective view of a disposable unit in accordance with a further embodiment of the invention.

Figure 9 is a fragmentary, partially sectional, partially block form view depicting the disposable unit of Fig. 8 in conjunction with a reusable system.

Figure 10 is a diagrammatic view depicting the system and unit of Figs. 8 and 9 during operation.

MODES FOR CARRYING OUT THE INVENTION A transducer array according to one embodiment of the invention, as schematically illustrated in Fig. 1, includes a frame 10 having a plurality of individual transducer elements mounted to the frame. The particular frame illustrated in Fig. 1 is generally dome-like, and is in the form of a portion of a generally spherical shell having a radius R. The frame defines a central axis 14. Transducers 12 are mounted to the frame so that each transducer is aimed generally towards the central axis, into a focal region 15 surrounding the central axis. Thus, as seen in Fig. 3, each transducer 12 is mounted on the interior side of frame 10. Each transducer is pivotable relative to frame 10 about 2 mutually orthogonal axes. For example, transducer 12a is pivotable about axes 16a and 18a (Fig. 2) relative to frame 10.

Transducers 12 may be formed on a flexible circuit panel 20 (Figs. 2 and 3). Each transducer 12 includes one or more layers of piezoelectric material and two or more electrodes, the electrodes being connected to one another and to a plug or coupler for connection to external circuitry by traces 22 (Fig. 2) extending along the flexible circuit 20. Although flexible circuit 20 is illustrated as a single layer of flexible circuitry, in practice the flexible circuit may include more than one layer. The electrodes of each transducer are arranged so that each layer of piezoelectric material lies between a signal electrode and a ground electrode.

Preferably, the layers of piezoelectric material and the electrodes are arranged so that ground electrodes are disposed on the outside surfaces of the each transducer, whereas active, signal- applying electrodes are disposed within the transducer. The piezoelectric material desirably is a polymeric piezoelectric material, such as polyvinylidene fluoride (PVDF) and co-polymers of PVDF. Copolymers of PVDF and trifluoroethylene (TrFE) are particularly preferred.

Although transducers 12 are depicted separately for clarity of illustration, the piezoelectric layers of multiple transducers may be formed by portions of continuous sheets of piezoelectric polymer coextensive with the flexible circuit 20, as further discussed below with reference to Fig. 5. Each transducer is provided with a rigid backing element 24 (Fig. 3) disposed between

the piezoelectric material of the transducer 12 and frame 10. For example, backing element 24 may be formed from alumina, glass, metal or other relatively rigid material.

A set of four thermally operated actuators 26 such as bimetallic elements or shape memory elements with heating devices are mounted between the backing element 24 of each transducer 12 and frame 10. As best appreciated with reference to Fig. 2, the actuators associated with the backing element 24 of each transducer are disposed adjacent to corners of the backing element. Actuators 26 have ground and operating connections connected to additional traces 23 on flex circuit 22. Although only a few such additional traces 23 are depicted in Fig. 2, it should be appreciated that individual operating traces desirably are provided for each actuator 26 so that each such actuator may be operated independently to expand or contract by applying appropriate current through the heating device of the actuator so as to heat the actuator. Additional traces 23 are connected to controllable current drivers (not shown) in the reusable system when the transducer array is connected to the reusable system. The current drivers, in turn, are controlled by a control computer or other control circuit in the reusable system. Although only single actuators are illustrated in Figs. 2 and 3, each actuator 26 may incorporate a stack of multiple devices. By applying appropriate currents through the actuators associated with an individual backing element 24 and transducer 12, that backing element and transducer can be pivoted relative to the frame. For example, the backing element 24 and transducer 12a depicted in Fig. 2 can be caused to pivot about axis 16a or axis 18a. If movement elements 26a and 26b are expanded whereas elements 26c and 26d are allowed to cool and contract, the backing element, and hence the ultrasonic transducer 12a, will pivot around axis 18a. If elements 26a and 26c are expanded whereas elements 26b and 26d are contracted, backing element 24, and hence transducer 12a, will pivot around axis 16a. The reverse motions and combinations of these motions can be performed. To facilitate movement of the individual transducers 12 and backing elements, flex circuit 20 may be formed as a main sheet with a hole or cut-out 30 surrounding each transducer and with flexible curved beam portions 32 extending from the main sheet to the individual transducer 12.

In operation, the individual transducers can be actuated to apply ultrasonic energy at a focal point 34 within focal region 15 as by applying ultrasonic driving signals to the transducer 12 in the conventional manner. Also in the conventional manner, the location of focal point 34 can be changed, for example to location 34'or 34", by altering the relative phases and

amplitudes of the drive signals applied to the various transducers. For example, the control computer in the reusable system can select appropriate phases and amplitudes for the drive signals, and can command the drive signal generators in the reusable system to apply the desired signals to individual Alternatively or additionally, the focal point can be moved by actuating movement elements 26 so as to turn the individual transducers relative to frame 10, thereby aiming the sonic energy emitted by each transducer along a slightly different path.

Movement of the focal point by turning the individual transducers, rather than by adjusting the signals, offers enhanced steering range and superior focus quality in the steered beam. The ultrasonic beam from an array of transducers comes to focus at a point where the ultrasonic signals from the various transducers reinforce one another, so that the power of the ultrasonic signal applied at such point is much greater than the power at other points. When the focal point is at the geometric center of the transducer (the center of the sphere, for a transducer having the shape of a spherical sector), the ratio between the power at the focal point and the power at other points is very high. Where the beam is steered away from the nominal focal point solely by altering the phases and/or amplitudes of the signals emitted by individual transducers, the power at the steered focal point decreases somewhat, whereas the power at other points, commonly referred to as"side lobes"of the beam, grows. This effect is accentuated the further the focal point is moved from the nominal focal point. Where the beam is steered at least in part by turning the transducers, this effect is suppressed. Therefore, the focal point of the beam can be displaced through a greater range while still maintaining a high ratio of beam power at the desired focal point to beam power in the side lobes. In certain cases, the side lobes may be negligible or nonexistent.

The degree of turning or pivoting motion about pivot axis 16 and 18 need not be particularly large. For example, to displace focal point 34 through a distance of about 10mm transverse to central axis 14 at a distance of about 15cm from array 10, certain transducers may be tilted through an angle of about 4 degrees about one or the other of the pivot axes. For a transducer about 1 cm wide, this corresponds to a displacement at the edge of the transducer of about 350 microns.

The actuators 26 discussed above can be replaced by essentially any device capable of moving the individual transducers relative to the frame in a controlled manner. For example, the thermally activated movement elements can be replaced directly by magnetostrictive

elements. Also, hydraulic, pneumatic or electromechanical actuators such as mechanical screws, linkages or cams driven by electric motors can be used in place of the thermal movement elements.. In the embodiments discussed above, the movement actuators themselves serve to mount the backing elements 24 and transducers 12 to frame 10 for pivoting movement. In other embodiments, separate mechanical linkages such as hinges or ball and socket joints may be used to connect the backing elements to the frame. Also, the transducers need not incorporate backing elements separate from the piezoelectric material. For example, where the transducers are formed from piezoelectric crystalline materials such as quartz, the transducers may be mounted without separate backing elements. In the embodiment discussed above, each individual transducer is movable by itself. Stated another way, each actuator is arranged to move a group of transducers consisting of only one transducer. However, some or all of the transducers may be mounted in larger groups, each such group including a plurality of transducers, and the actuators may be arranged to move each group relative to the frame.

For example, some or all of the groups may include plural transducers which share a common, rigid backing element, and the actuators associated with each such group may move the backing element associated with the group. It is not essential that all of the transducers in a given array be movable relative to the frame. Some of the transducers may be mounted in fixed position relative to the frame, whereas other transducers may be movable relative to the frame.

The transducer array according to this aspect of the invention typically includes all of the accessories commonly provided with transducer arrays as taught in the aforementioned patents and patent applications. For example, the transducer array typically is equipped with a connector for mechanically coupling the frame 10 to a chassis so that the frame can be positioned adjacent to a patient as described in the aforementioned PCT publication WO 98/52465. Likewise, the transducer array typically is provided with cooling devices; as well as an electrical plug for connecting the circuits of the transducer array to a control computer and signal generator. Also, the transducer array typically is used with some sort of transmission medium for coupling the ultrasonic energy developed in the transducers to the body of a subject such as a medical patient. For example, a bag filled with water or other liquid or gel may be provided between the transducer array and the patient's body.

Further, the transducer array can be fabricated in a relatively small size, suitable for operation within the patient's body. The transducer array and associated elements may be provided as a disposable, single-use unit, which may incorporate the transmission medium.

Desirably, the transmission medium is free from bubbles. The transmission medium may be degassed, i. e., freed from dissolved or entrained gasses, during manufacture of the disposable unit, so as to suppress formation of bubbles during storage and use.

According to further embodiments of the invention, the transducer array may be provided with feedback devices for indicating the position of each transducer relative to the frame. For example, strain gauges may be connected between each transducer and the frame and the outputs from the strain gauges may be conveyed to the control computer of the reusable system which operates the array.

A transducer array according to a further aspect of the invention includes multiple transducers 112 mounted having backing elements 124 which are mounted to the frame 110.

As the transducers are fixed relative to the frame, the backing elements may be integral with frame 110. Each transducer is provided with a generally tubular directing element or guide 126 projecting forwardly from transducer 112. The tubular directing elements 126 serve to channel and guide the ultrasonic vibrations emitted by transducers 112 and thus help to concentrate the sonic energy from the transducers at the selected focal point. Where the transducers are mounted on backing elements, the guides 126 may be formed integrally with the backing elements. Alternatively, the guides 126 may be formed integrally with frame 110. Guides 126 need not be tubular. For example, guides 126 may be provided as fins projecting forwardly from the transducer surfaces. The guides typically are formed from relatively rigid materials such as alumina, glass or other ceramics, but may also be formed from polymers.

As shown in Fig. 5, the guides 126'may include multiple layers 101 and 103 having different acoustic impedance so as to form a reflective interface extending along the guide.

Acoustic impedance is the product of the density of a transmission medium and the speed of sound in medium. For example, layer 101 may be formed from a relatively dense material such as a polymer whereas layer 103 may be formed as a space filled with air or another gas, or a layer an open-cell foam composed mainly of air, to form a highly reflective interface.

Fig. 5 further illustrates a structure for the flexible circuit 137 and transducers 112. A set of signal electrodes 109 and signal leads 108 are provided between two continuous layers of

flexible piezoelectric material 105 and 107. Front surface ground electrodes 111 and ground leads 113 are provided on a front surface of layer 107 in alignment with signal electrodes 109 so that portions of layer 107 are disposed between the signal electrodes and the front surface ground electrodes. Rear surface ground electrodes 115 and ground leads 117 are provided on a rear surface of layer 105 in alignment with the signal electrodes 109 so that portions of piezoelectric layer 105 are disposed between the signal electrodes and ground electrode. Each transducer 112 includes a signal electrode 109, together with the ground electrodes 115 and 111 aligned with such signal electrode and those portions of piezoelectric layers 105 and 107 disposed between such electrodes. The electrodes and leads may be formed on the surfaces of the piezoelectric layers 105 and 107 by techniques similar to those used in forming conventional flexible printed circuits. Rear surface ground electrodes may be thick metallic elements which may also serve as the backing elements for the transducers. The guide elements 126'may be mounted to the front face of the flexible circuit. The flexible circuit may be mounted to a frame 110 as discussed above with reference to Fig. 4.

As shown in Figs. 4 and 5, each transducer 112 is provided with a temperature sensing device 130 such as a thermistor, resistance temperature device or other conventional device for providing an electrical or other indication of temperature. Alternatively, temperature sensors can be formed as parts of circuit panel 137 which carries the signal conductors for the transducers. For example, a thin, high-resistance conductor disposed adjacent a transducer can be connected between a pair of relatively low-resistance auxiliary traces on the same printed circuit. The total resistance between the auxiliary traces is principally related to the resistance of the thin trace. Each thermal sensing device 130 is mounted in close proximity to one of the transducers 112 so that the sensing device is in thermal communication with that particular transducer. As used in this disclosure with reference to two elements or structures, the term "thermal communication"means that there is a low-resistance heat transfer path between the two elements, so that the temperature of the two elements tends to vary together. These devices 130 are connected to conductors (not shown) of the same circuit panel 137 which carries the signals to the transducer. The circuit panel in turn is connected to a plug 138 which is engaged in the mating socket 140 of the reusable system when the transducer array is mounted to the reusable system. Plug 138 and socket 140 connect the conductors associated with the temperature sensing devices 130 to one or more analog-to-digital converters 134 in the

reusable system. The outputs of A/D converters 134 are connected to the control computer 135 of the system which operates the transducer array.

A memory 136 stores data defining the properties of transducers 112. Memory 136 may be a nonvolatile digital memory such as a ROM, PROM or EEPROM, or an array of resistors or other components having resistance values or other parameter values which encode information representing the parameters to be stored by the memory. A machine-readable label, magnetic strip, RF-readable tag or optical device may also be employed as the memory, provided that the reusable unit incorporates an appropriate reading device. Memory 136 is mounted to the array as a part of the disposable unit. For example, where memory 136 is an electrical device, the memory may be electrically connected to the same circuit panel 137 as the ultrasonic transducers, and may be connected to the control computer 135 of the reusable system by the same electrical plug 138 and socket 140. The disposable unit may also include the other components associated with the transducer such as a bag filled with water or gel for coupling the sonic energy to the patient. In this embodiment as well, the frame 110 may form part of the disposable unit or part of the reusable system employed with the disposable unit.

When the disposable unit is engaged with the reusable system, data from the memory is transferred to the control computer 135. The memory may be destroyed or erased upon data transfer, so that the disposable unit cannot be reused. Alternatively, the data stored in the memory may be altered, as by writing information indicating that the disposable unit has been used into the memory or incrementing a usage count stored in the memory. The memory of the disposable unit may also store information useable by the reusable system in operation with the disposable unit. This information may include identification of the disposable unit such as a model number and/or serial number, and may also include parameters such as the maximum drive signal power or maximum drive signal voltage to be applied to individual transducers or to the unit as a whole.

The data included in memory 136 desirably includes one or more parameters which affect a relationship between output amplitude and/or phase and the amplitude and/or phase of the applied drive signal for each transducer at one or more temperatures. For example, a parameter which affects the amplitude relationship may be the conversion efficiency of the transducer; a ratio of output amplitude to drive signal amplitude; or an amplitude correction factor. Parameters which affect the phase relationship include the phase offset relative to the

drive signal and the phase offset between transducers, i. e., the difference in phase between the output signals from the various transducers when all are driven with drive signals of the same phase. This data may be provided as separate parameters for each individual transducer in the particular array; as representative parameters for groups of transducers in the array; or as common parameters representing the properties of all of the transducers in the particular array.

Also, each parameter can be provided as a single value representing performance of the transducer, group or array over its expected operating temperature range, or as data representing variation in such parameter of the transducer, group or array as a function of one or more other variables such as temperature, drive signal frequency, and instantaneous drive power. The data may be individualized data pertaining to a single disposable unit, such as data obtained from actual measurements of the performance of individual transducers included in the particular array at different temperatures. Alternatively, the data may include generic data derived for transducers of the type included in the array. Combinations of individualized data and generic data may be used. For example, the memory may contain individualized data derived from actual test or measurement of the ultrasonic transducers in the array at one temperature; such as at a nominal operating temperature, and this individualized data may be combined with generic data such as data defining the change in amplitude response versus temperature for all transducers of the same type. The use of individualized data pertaining to a particular disposable unit allows the control computer to compensate for differences between units and between transducers within a unit. This reduces the need for precision in manufacture of the disposable units to achieve identical properties in the various transducers.

Although the individualized data preferably is derived from actual sonic emission testing as discussed below, individualized data also can be provided by measuring, during manufacture of the disposable units, characteristics of individual transducers or arrays which are associated with different sonic emission properties as, for example, thickness of the piezoelectric films or capacitance of the films in particular transducers at a reference temperature. This data can be converted to parameters such as those discussed above based upon relationships between the measured properties and the parameters accumulated through tests of other, similar units.

In the conventional manner, control computer 135 is connected to ultrasonic transducers 112 through appropriate drive circuits (not shown) incorporated in the reusable system so that the control computer can apply the desired signal voltages to the ultrasonic

transducers. However, in this embodiment of the control computer can adjust the phase and/or amplitude of the applied signal voltages so as to produce the desired signal output amplitude and/or phase from each transducer based upon the relationship between signal output and applied drive signal at the actual operating temperature of the ultrasonic transducer 112, as reported by the associated thermal transducer 130.

In a variant of this approach, the parameters referred to above as stored in the memory associated with the disposable unit may be stored in a database within the control computer or accessible to the control computer through a communications channel such as the internet. The memory associated with the disposable unit may include only the serial number or other identification of the disposable unit, and the control computer may retrieve the parameters relevant to a particular disposable unit from the database. Data other than individualized data applying only to individual disposable units may be provided in the database as well. In a further, less preferred variant, the serial number or other identifying data of the disposable unit may be entered manually by the operator based on a human-readable identification.

In a further variant, the individualized transducer performance data provided in the memory may be used to set applied signal amplitudes in a system which does not use thermal monitoring of the transducers. Thus, the individualized transducer performance data incorporated in the memory 136 may define the amplitude and/or phase response of the various transducers of the array at nominal operating temperature, and the control computer may set characteristics such as amplitude and phase of the signals supplied to the individual transducers based on this data.

As an example of the techniques used to derive data for individual disposable units, the transducer array may be placed in a tank of water with an acoustic detector such as a hydrophone disposed at the nominal focal point of the array as, for example, the center of a spherical array. A signal of known phase is applied to a single transducer and the resulting signal at the nominal focal point is detected. The amount by which the phase of the detected signal is delayed relative to an arbitrary zero phase is stored as a difference value in memory 136. The same procedure is repeated for each transducer in the array, using the same arbitrary zero phase for each repetition. A particular transducer in the array is selected arbitrarily as a reference transducer, and the difference value for the reference transducer is subtracted from the difference value for each other transducer in the array, to yield a phase offset for each other

transducer relative to the reference transducer. The reference transducer by definition has zero phase offset. The phase offsets for the individual transducers are stored in memory 136 so that each phase offset is associated with the appropriate transducers. Thus, each phase offset may be stored at an address in memory associated with a particular transducer. Alternatively, the identity of each transducer and the phase offset associated with that transducer can be stored together with one another. In a further alternative, the measured phase differences relative to the drive signal, rather than the phase offsets, may be stored in the memory in the same manner. The phase differences may be measured at a single nominal operating temperature, or else repeat measurements may be made at several different temperatures within a range of operating temperatures, in which case each value of phase difference or phase offset stored in memory is associated with a temperature as well as with the identity of a particular transducer.

In use, the computer associated with the reusable system reads the phase difference or phase offset from the memory and corrects the phase of the signal applied to individual transducers accordingly. For example, where it is desired to drive all of the transducers to apply ultrasonic energy in phase with one another at the nominal focal point, the computer applies drive signals applied to each transducer so that the phase of the drive signal applied to each transducer is advanced by an amount equal to the phase offset associated with that transducer. Alternatively, phase difference or offset values for plural temperatures may be represented as parameters of an equation for such difference value as a function of temperature as, for example, a phase offset value at one temperature and a coefficient representing variation in phase offset value per unit temperature over the expected operating range. In the same, the phase offset value or other parameter affecting the phase relationship may be stored in the same manner as a function of other variables such as instantaneous power and drive frequency.

The calibration procedure may include an amplitude measurement for each transducer as well, and hence amplitude ratios or efficiencies for the transducers may be stored in memory 136 along with the phase data. For example, the ultrasonic signal from a particular transducer is detected by a hydrophone as discussed above with reference to the phase data, and an amplitude correction factor, power conversion efficiency, or other parameter representing the amplitude relationship is calculated by comparing the amplitude or power of the output signal to the amplitude or power of the drive signal applied to the transducer. The resulting parameter is then stored in memory 136 as described above, so that a value of such parameter is

associated with each transducer. In operation, the computer retrieves the parameter representing the amplitude relationship for each transducer and uses such parameter to determine the amplitude of the drive signal to be applied to that transducer. For example, where an amplitude correction factor is used, the computer may simply multiply the nominal amplitude of the signal to be produced by such transducer by the correction factor for that transducer. The amplitude parameter may be provided a representative value for groups of transducers, or for the array as a whole, rather than separate values for each individual transducer. The amplitude parameter may also be provided as a function of one or more other variables such as temperature, drive frequency, or drive power, in the same manner as discussed above with respect to the phase correction data.

In a further variant (Fig. 6) the reusable system includes an array of temperature control blocks 200. Each temperature control block is equipped with a temperature sensing device 202 and an individually-adjustable temperature controlling element 204 in thermal communication with the temperature control block. The temperature control element may be a Peltier effect refrigeration unit, i. e., a thermocouple which can be actuated to abstract heat from the temperature control block. Desirably, the reusable system also includes a coolant channel 206 in thermal communication with the temperature control blocks. Feedback control systems 208 are provided for adjusting the current flow through the refrigeration unit associated with each temperature control block 200 based on the output from the temperature sensing device 202 associated with that block, so as to maintain the block at a setpoint temperature. The disposable transducer array is positioned so that each ultrasonic transducer 210 overlies one of the temperature control blocks 200. In operation, a coolant such as cold water directed through channel 206 extracts most of the heat generated by the transducers. The controllable refrigeration units extract the remainder of the heat. This arrangement assures that each transducer will remain at its nominal operating temperature over a wide range of operating duty cycles and signal amplitudes.

In a variant of this system, the individual temperature control devices may be resistive heating elements. The coolant temperature and flow rate through channel 206 are selected so that when the transducers 210 are operated at the most severe duty cycle, with maximum heat dissipation, the temperature control blocks tend to reach a temperature below the desired setpoint temperature. The feedback control systems and heaters provide additional heat as

needed to maintain each block at the desired set point temperature. In a further variant, the thermocouples of a Peltier refrigeration unit can be operated either in heating or in cooling as needed to maintain the blocks at the desired setpoint temperatures. In yet another variant, the temperature control blocks and associated elements can be incorporated in the disposable ultrasonic transducer unit. Also, it is not essential to provide temperature control blocks separate from other elements of the transducer array. For example, the temperature sensors may be in direct contact with the transducers or with a rigid backing associated with the transducer elements.

The various aspects of the invention can be used in combination with one another or separately. For example, thermal transducers, memory and the associated control arrangement shown in Fig. 4 can be applied with or without the directing elements. Likewise, the directing elements can be used regardless of whether the thermal transducers and actuators for moving individual transducers are employed. Also, a memory as discussed with reference to Fig. 4 can be used in conjunction with a temperature control arrangement as discussed with reference to Fig. 6.

Although the particular arrays shown in Figs. 1-6 incorporate curved, dome-shaped frames, the same features discussed above can be utilized in generally planar arrays. For example, a planar frame 310 (Fig. 7) has transducers 312 mounted thereon with actuators 326.

Such a flat array typically is employed in conjunction with a focusing lens 301 held in fixed position relative to the frame by structural members (not shown). Such a focusing lens incorporates a material having a different speed of sound than the surrounding medium 303 within the bag 305. The ultrasonic waves from transducers 312 propagates through medium 303 and lens 301, and is focused at a focal spot 334 by refraction. Movement of individual transducers relative to the frame 310 under the influence of actuators 326 moves the focal point 334 in substantially the same way as discussed above with reference to Fig. 1. In the embodiment of Fig. 7, guide elements 305 similar to the guide elements discussed above are mounted with each transducer so that the guide elements associated with each transducer and move relative to the frame in conjunction with that transducer.

Although the frames discussed above are provided in the same disposable unit as the transducer elements and actuators, this is not essential. For example, the frame may form part of the reusable element, and a transducer array including transducers and actuators, with or

without the guide elements and temperature control devices, may be supplied as part of a disposable element which is coupled to the frame so that the individual transducers can be moved relative to the frame by the actuators.

As shown in Figs. 8-10, a disposable unit 400 includes a flexible circuit 402 generally similar to the flexible circuits discussed above with reference to Figs. 2 and 5. Thus, the flexible circuit includes layers of polymeric piezoelectric material 405 and 407; signal electrodes 409 disposed between the piezoelectric layers, and ground electrodes 411 and 415 aligned with the signal electrodes so as to form transducers 412 incorporating regions 406 and 408 of layers 405 and 407. Regions 406 and 408 are free to tilt relative to the remainder of layers 405 and 407. To allow such motion, regions 406 and 408 are separated from the remainder of the layers by gaps 430. Flexible, curved connecting portions 432 integral with layers 405 and 407 extend across gaps 430. Here again, the flexible circuit includes signal leads 421 and ground leads 423 extending along the layers, and extending across the flexible connections to the electrodes of the transducers. Although four connecting portions 432 are depicted for each transducer 412 in Fig. 8, the actual unit may include more or fewer connecting portions. As discussed above, the disposable unit may include a memory and a plug for connecting the flexible circuit to the reusable system.

The rear ground electrodes 415 are thick metallic plates which can act as backing elements for the individual transducers. These plates are provided with locating studs 425 on their rearwardly facing surfaces (the surfaces facing upwardly in Fig. 8). The studs 425 on each plate are precisely located relative to the transducer 412 associated with that plate.

The disposable unit further includes a flexible bag 427 (Fig. 10) filled with a liquid or gel medium 439 having acoustic impedance close to that of body tissue, such as water. The medium is substantially free of bubbles. Preferably, the medium is freed from dissolved gases during manufacture of the disposable unit, and either the bag itself or the package in which the disposable unit is stored and shipped in air-impervious so as to maintain the medium free of dissolved gasses. Bag 427 has a flexible, distensible wall 429 overlying the front face of flexible circuit 402. Wall 429 may extend entirely across the front face of each transducer 412, or may have apertures 440 (Fig. 9) in alignment with the transducers. If the bag wall 429 extends across the transducers, it should have an acoustic impedance close to that of medium 439 to minimize reflection of the energy from the transducer.

The disposable unit is employed with a reusable unit including a control computer (not shown) similar to those discussed above and also including a generally planar frame 450 plurality of movable elements in the form of metallic plates 452 pivotally mounted to frame 450, as by spherical joints 454 which permit pivoting motion relative to the frame around orthogonal axes. The reusable unit further includes actuators 456, such as solenoids, pneumatic or hydraulic cylinders, or motor driven actuators, connected between the frame 450 and the movable plates 452. The actuators are connected to the control computer of the reusable unit.

Each plate 452 has holes 458 formed in its front face. These holes are arranged to receive the studs 425 on the backing elements or plates 415 of the disposable unit, so as to locate each transducer precisely relative to the plates and hence relative to the frame when the disposable unit is assembled to the reusable unit. Each plate has a gripper 460 such as a spring clip arranged to releasably engage a backing element 415 of the disposable unit, and to hold the backing element firmly in engagement with the plate. The use of studs, holes and spring clips to hold the backing elements in place, and to locate the backing elements, is merely exemplary; any other type of mechanical connection which will releasably hold the backing elements in place and precisely locate them relative to the plates may be used.

The reusable unit further includes a temperature control system incorporating a chiller or other source of coolant 462 a pump 464 and a coolant manifold 466. Each plate or movable element 452 includes a coolant passage 468 having an inlet connected to manifold 466 through an individual temperature control valve 470. Separate valves are provided for each plate 452.

A separate coolant temperature sensor 472 is arranged to monitor the temperature of coolant passing out of the passage 468 in each plate. The plate 452 and the circulating coolant provide a low-resistance thermal path between each transducer 412 and the associated coolant temperature sensor, so that the coolant temperature sensor is in thermal communication with the transducer. A feedback control system 474 controls valve 470 in response to the output from sensor 472, to maintain each plate 452 at a constant temperature. The coolant connections may include flexible hoses so that they do not restrict tilting of the plates.

In use, the disposable unit is mounted on frame 450, so that each transducer 412 is mounted on one movable element or plate 452, so as to provide a generally flat array of transducers, as best seen in Fig. 10. This array is coupled through bag 427 of the disposable

unit to the body of a medical patient or other subject P to be treated. The plates 452 and transducers 412 are tilted relative to the frame, as indicated in solid lines in Fig. 10, so as to point all of the transducers toward the desired focus 480 within the subject's body. The control computer applies signals having the appropriate phases to cause the ultrasound waves emitted by all of the transducers to constructively reinforce one another at focus 480. The focus can be moved a different location 480'by tilting the plates and transducers to different angles, as seen in broken lines in Fig. 10, and adjusting the phases of the signals as required.

The use of a generally flat array with individually movable transducers provides good focusing over a wide range of locations without the need for a lens, and without the cost and complexity associated with forming a curved transducer array. Thus, flexible circuit 402 can be made as a substantially flat unit, and can remain substantially flat in the finished disposable unit. This arrangement provides variable focusing without the need for a lens and without the attenuation of the ultrasonic waves associated with a lens. The separately-movable transducers can provide better focusing over a wide range of positions than can be achieved by focusing ultrasonic waves from a flat array using phase control alone. By providing many of the relatively expensive components, such as the actuators for moving the plates, the temperature sensors and individual temperature control devices as parts of the reusable system, rather than in the disposable unit, the cost of the disposable unit is reduced.

In the embodiments discussed above with reference to Figs. 1-4, the temperatures of individual transducers are monitored by thermal sensors formed separately from the transducers themselves. However, thermal monitoring also can be accomplished in other ways.

For example, an electrical property of each transducer which varies with temperature in a known manner, such as the capacitance or electrical impedance of the piezoelectric material in the transducer, can be monitored by applying electrical signals to such transducer using the same connections and leads normally employed to apply excitation signals to the transducer.

For example, the reusable unit can be programmed to apply test signals between the signal and ground electrodes of the various transducers during operation, to measure the capacitance or impedance of the piezoelectric material. The parameter memory may include data relating the capacitance or impedance to temperature. In a further variant, one or more of the electrodes associated with each transducer may be provided with an auxiliary contact connected to the electrode at a location remote from the connection between the same electrode and the signal or

ground conductor of the printed circuit. The auxiliary contact is connected to an auxiliary conductor of the printed circuit. The reusable unit may apply test voltages between the auxiliary conductor and the signal or ground conductor, and monitor current flow through the electrode so as to determine resistance of the electrode. In a variant of this approach, an electrode may be connected to two auxiliary conductors in addition to the signal or ground conductor. These connections are made through contact pads at locations on the electrode remote from one another, so that the resistance of the electrode can be measured by applying a test voltage between the auxiliary conductors.

For use in therapeutic heating applications, the drive signals applied to the transducers and the resulting sonic vibrations typically are at ultrasonic frequencies, most typically at frequencies above 1 MHz, such as 5-10 MHz. However, similar techniques can be applied to sonic transducers for operation at other frequencies.

As these and other variations and combinations of the features discussed above can be utilized without departing from the present invention, the foregoing description of the preferred embodiments should be taken by way of illustration rather than by way of limitation of the invention.

INDUSTRIAL APPLICABILITY The invention can be applied in medical and veterinary procedures.