in accordance with one preferred embodiment of the invention , a volume of tissue is imaged using a modified conventional b - mode ultrasound imager wherein the probe , as shown in fig1 comprises a spheroidal piezoelectric element 26 ( hereinafter &# 34 ; therapy transducer &# 34 ;) with a phased - array imaging transducer 28 , comprising a multiplicity of piezoelectric elements , mounted in the center . the probe is mounted in a mechanical positioning system ( not shown ) having three or more axes of motion in a container of an acoustic medium , e . g ., water . in particular , therapy transducer 26 can be moved to focus on different locations in the patient . the therapy transducer is focused onto the tumor tissue , avoiding bone or air in the path of the ultrasound beam , and pulsed to selectively heat the tumor tissue at the focal point f of the therapy transducer . the phased - array transducer 28 constitutes part of a conventional ultrasound imaging system . such transducers typically comprise an array of ultrasonic transducer elements which transmit an ultrasound beam and then receive reflected ultrasound from an object or target region being studied . for ultrasound imaging , the array typically is made up of a plurality of transducer elements arranged in a line and driven with separate voltages . by selecting the time delay ( or phase ) and amplitude of the applied voltages , the individual transducer elements can be controlled to produce ultrasonic waves which combine to form a composite or net ultrasonic wave that travels along a preferred vector direction and is focused at a selected point along the beam . multiple firings may be used to acquire data representing the same anatomical information . the beamforming parameters of each of the firings may be varied to provide a change in maximum focus or otherwise change the content of the received data for each firing , e . g ., by transmitting successive beams along the same scan line with the focal point of each beam being shifted relative to the focal point of the previous beam . by changing the time delay and amplitude of the applied voltages , the focal point of the beam can be moved in a plane to scan the target region . the same principles apply when the transducer is employed to receive the reflected sound ( receive mode ). the voltages produced at the receiving transducer elements are summed so that the net signal is indicative of the ultrasound reflected from a single focal point in the object . as with the transmission mode , this focused reception of the ultrasonic energy is achieved by imparting separate time delay ( and / or phase shifts ) and gains to the signal from each receiving transducer element . ultrasound beam scanning as described above comprises a series of measurements in which the steered ultrasonic wave is transmitted , the system switches to its receive mode after a brief time interval , and the reflected ultrasonic wave is received and stored . typically , transmission and reception are steered in the same direction during each measurement to acquire data from a series of points along an acoustic beam or scan line . the receiver is dynamically focussed at a succession of ranges along the scan line as the reflected ultrasonic waves are received . the positioning system for moving the focal point f of the probe to a desired location allows multiple two - dimensional b - mode images to be acquired by a work - station as a registered set of image slices representing a tissue volume . the imaging volume can then be reformatted as necessary to obtain the views desired . since the registration of the object ( i . e ., patient ) is fixed to the mechanical positioning system , the probe can be registered to the positioning system . this provides a known mechanical relationship between the probe and the patient . the system operator can then prescribe the tissue volume to be treated by outlining tissue boundaries on a set of ultrasound image slices describing a tissue volume including the tissue volume to be treated . the combined imaging and therapy probe can then be moved by the positioning system to locations within the prescribed outline to deliver treatment to the desired area of each image slice . at each treatment location , prior to delivery of the therapy , verification of the therapy beam location is accomplished by way of ultrasound b - mode imaging using therapy transducer 26 as the ultrasound emitter and phased - array imaging transducer 28 as the detector . in a transmit mode , therapy transducer 26 is pulsed to produce a transmit field 32 which is focused at point f . in a receive mode , the elements of phased - array imaging transducer 28 are time - delayed to form successive receive beams 34 . this provides a b - mode image wherein the only area in the image to be significantly illuminated is at the focus f of therapy transducer 26 . this yields an image with an elliptical artifact 30 related to the position and amplitude of the pulse applied to the therapy element . these image frames can then be interleaved with , or superimposed on , normal b - mode imaging frames where both transmit and receive functions are performed using only phased - array imaging transducer 28 . once the therapy treatment location has been verified in this manner , therapy can be delivered by applying higher - power , longer - duration excitation to the large therapy element 26 . the intended use for the invention is to provide a system and method for identifying and localizing tissue volumes to be treated , prescribing tissue to be treated , and applying significant thermal energy to a localized tissue region due to ultrasonic absorption , while verifying each position to avoid errors due to reflection , refraction , or mechanical positioning errors . in the alternative preferred embodiment depicted in fig2 instead of the phased - array imaging transducer being incorporated into the therapy transducer , a spheroidal therapy transducer 26 &# 39 ; and a phased - array imaging transducer 28 &# 39 ; are rigidly mounted on a positioning system 38 in fixed relationship , one laterally displaced from the other . in this embodiment , the b - mode imaging field for phased - array transducer 28 &# 39 ; is designated 36 , the transmit field for therapy transducer 26 &# 39 ; is designated 32 , and the receive beam for phased - array transducer 28 &# 39 ; when therapy transducer 26 &# 39 ; is used as the transmitter is designated 34 . using therapy transducer 26 &# 39 ; to transmit and phased - array imaging transducer 28 &# 39 ; to receive yields an image with an elliptical artifact 30 related to the position and amplitude of the pulse applied to the therapy transducer . as described previously , these image frames can then be interleaved with , or superimposed on , normal b - mode imaging frames where transmit and receive functions are performed using only phased - array imaging transducer 28 &# 39 ;. the position of the transducers can then be adjusted until elliptical artifact 30 is registered with the portion of the displayed b - mode image corresponding to the tissue to be heated . fig3 depicts a focused ultrasound surgery system guided by a phased - array ultrasound imager in accordance with the preferred embodiments of fig1 and fig2 . the ultrasound imaging system includes four main subsystems : a beamformer 2 , a b - mode processor 4 , a scan converter and display controller 6 and a kernel 8 . system control is centered in the kernel , which accepts operator inputs through an operator interface 10 and in turn controls the various subsystems . a master controller 12 performs system level control functions by accepting inputs from the operator via operator interface 10 as well as system status changes ( e . g ., mode changes ) and making appropriate system changes either directly or via a scan control sequencer . a system control bus 14 provides an interface between the master controller and the subsystems . scan control sequencer 16 provides real - time ( acoustic vector rate ) control signals to beamformer 2 including a system timing generator 24 , and to b - mode processor 4 and scan converter 6 . scan control sequencer 16 is programmed by the host with the vector sequences and synchronization options for acoustic frame acquisitions . the scan converter broadcasts the vector parameters defined by the host to the subsystems via scan control bus 18 . the main data path begins with the analog rf ( radio frequency ) input signals to receiver 44 from phased - array imaging transducer 28 &# 39 ;. beamformer 2 produces raw vector data beams that are supplied to b - mode processor 4 , where they are processed and supplied as vector ( beam ) data to scan converter and display processor 6 . the scan converter and display controller accepts the processed vector data and produces video display signals for the image to a color monitor 22 . beamformer 2 is responsible for the transmit and receive beamforming . each transducer includes an array of separately driven transducer elements , each of which produces a burst of ultrasonic energy when energized by a pulsed waveform produced by a transmitter or pulser 42 . the ultrasonic energy reflected back to the transducer array from the patient under study is converted to an electrical signal by each receiving transducer element and applied separately to respective analog receiver channels in receiver 44 through a set of transmit / receive ( t / r ) switches ( not shown ). pulser 42 , receiver 44 and the t / r switches are operated under control of a front end controller ( not shown ) in beamformer 2 . a complete b - mode scan is performed by acquiring a series of echoes in which the t / r switches are set to their transmit positions , pulser 42 is gated on momentarily to energize each transducer element , the t / r switches are then set to their receive positions , and the subsequent echo signals produced by each transducer element are applied to the respective receiver channels of receiver 44 . the location of the focal point of pulsed therapy transducer 26 &# 39 ; is not imaged by conventional b - mode imaging . instead , therapy transducer 26 &# 39 ; is operable in both an imaging mode and a therapy mode so that , in the imaging mode , the therapy transducer is pulsed by pulser 42 to produce a transmitted relatively low - energy beam focused at focal point f ( see fig2 ). phased - array imaging transducer 28 &# 39 ; is then steered to scan the patient &# 39 ; s tissue , thereby acquiring receive beams including ultrasound scattered from the tissue at the focal point of the pulsed therapy transducer . this scattered ultrasound from the tissue at the focal point allows the position of the fixed - focus therapy transducer to be detected and imaged . the image of the focal point can then be superimposed on an image of the tissue to be treated , obtained by conventional b - mode imaging using the phased - array imaging transducer , as previously described . in response to any difference between the detected location of the therapy transducer focal point and the detected location of the tissue to be treated , the position of the probe is adjusted using positioning system 38 which is mechanically coupled to the probe . the necessary adjustment is done automatically under the control of master controller 12 . alternatively , the adjustment can be made by manual operation of the positioning system . when the probe is in the correct position relative to the tissue to be treated , therapy transducer 26 &# 39 ; is switched to the therapy mode by operation of a switch 40 . in the therapy mode , master controller 12 actuates a therapy generator 46 to produce an electrical pulse of energy and duration sufficient to excite the therapy transducer to emit ultrasound having a desired therapeutic level at its focal point . the electrical pulse from therapy generator 46 is amplified by a radio - frequency amplifier 48 and then supplied to the therapy transducer through switch 40 . as a result , ultrasound energy at a therapeutic level is applied at focal point f ( fig2 ) corresponding to the location of the tissue to be treated . while only certain preferred features of the invention have been illustrated and described , many modifications and changes will occur to those skilled in the art . it is , therefore , to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention .
a system employing ultrasound imaging as a method to localize a patient &# 39 ; s tissue volume to be treated prior to applying therapeutic levels of ultrasound energy includes a therapy transducer for producing high - intensity fields that cause necrosis and an imaging transducer for producing high - quality ultrasound images . the therapy transducer is a spheroidal piezoelectric element and the imaging transducer is made up of a plurality of piezoelectric elements mounted in fixed relationship to the therapy transducer . the therapy transducer transmits a beam that is focused at a location in the tissue to be treated . the imaging transducer is then steered to produce successive receive beams which scan the tissue , including the tissue at the focal point of the pulsed therapy transducer . the image of the focal point is then superimposed on an image of the tissue to be treated obtained by b - mode imaging using the imaging transducer to transmit and then receive . proper alignment of the focal point and the tissue to be treated ensures proper positioning of the therapy transducer relative to the patient .