Abstract:
An ultrasound therapy transducer head comprises an ultrasound source emitting ultrasonic radiation, the ultrasound source comprising a plurality of transducer elements, integrated driving electronics coupled to the transducer elements, the electronics generating at least one output ultrasound waveform and driving at least some of the transducer elements independently based on the at least one output ultrasound waveform and temperature control structure providing cooling for the electronics.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/397,984, filed Mar. 4, 2009, which claims the benefit of U.S. Provisional Application No. 61/095,171 filed on Sep. 8, 2008 entitled “Ultrasound Transducer Head and Ultrasound Therapy System Incorporating the Same”, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to ultrasound therapy and in particular, to an ultrasound therapy transducer head and to an ultrasound therapy system incorporating the same. 
       BACKGROUND OF THE INVENTION 
       [0003]    Ultrasound therapy uses high-frequency sound waves to produce heat that can reduce some types of acute and chronic pain and is often employed during physical, occupational or manipulation therapy to treat conditions such as musculoskeletal injuries, arthritis and fibromyalgia. Therapeutic ultrasound is typically delivered at frequencies between about 200 to about 10000 kHZ. Lowering the frequency of therapeutic ultrasound provides for deeper penetration of the sound waves. Sound waves penetrating the tissue of the subject cause molecules in the tissue to vibrate, producing heat and mechanical energy allowing for deep heating of tissues such as muscles, tendons, ligaments, joint capsules and bone. As is well known, therapeutic ultrasound differs from diagnostic ultrasound, which uses less-intense sound waves to create images of internal structure. 
         [0004]    In the case of diagnostic ultrasound systems, compact electronics have been developed. For example, U.S. Pat. No. 5,924,993 to Hadjicostis et al. discloses an ultrasound mixed signal multiplexer/pre-amplifier application specific integrated circuit (ASIC) for supplying voltages to a group of transducer elements of an ultrasound array, receiving voltages from the same or another group of transducer elements of the ultrasound array, and amplifying the received voltages for transmission to external circuitry. The transmit and receive groups of transducer elements are shifted to provide accurate visual images with a minimal number of transmit and receive cycles. 
         [0005]    U.S. Pat. No. 6,497,664 to Randall et al. discloses a medical diagnostic ultrasound receive beamformer including an upsampler upstream of both a time delay device and a summer, and a smoothing filter downstream of both the time delay device and the summer The receive beamformer is automatically programmed into a gate array as a single-beam, dynamic-focus receive beamformer when the user selects B-mode and as a dual-beam, fixed-focus receive beamformer when the user selects color flow mode. 
         [0006]    U.S. Pat. No. 6,969,352 to Chiang et al. discloses a hand-held ultrasound system including integrated electronics within an ergonomic housing. The integrated electronics include control circuitry, beamforming circuitry and transducer drive circuitry. The integrated electronics communicate with a host computer using an industry standard high speed serial bus. The ultrasound system is operable on a standard, commercially available, user computing device such as a personal computer (PC) without specific hardware modifications, and is adapted to interface with an external application without modification to the ultrasound system. This allows a user to gather ultrasonic data on the standard user computing device, and employ the data so gathered via the external application without requiring a custom system, expensive hardware modifications, or system rebuild. An integrated interface program allows such ultrasonic data to be invoked by a variety of external applications having access to the integrated interface program via a standard, predetermined platform such as Visual Basic or C++. 
         [0007]    U.S. Pat. No. 7,169,108 to Little et al. discloses a continuous wave Doppler beam former application specific integrated circuit (CW-ASIC). The beam former may be a transmit or receive beam former. In one mode, the CW-ASIC is used in a diagnostic medical ultrasound system comprising a plurality of channels forming a CW analog receive path, wherein each channel is connected with a digital beam former. The plurality of channels are mixed down in quadrature to base band using a mixer and a local oscillator (LO) generator in quadrature. The outputs of the mixer are summed and wall/high pass filtered to provide a beam formed base band signal. A sub circuit provides a digital serial control function to interface to a real time control bus providing per channel enable/disable of the mixer and the LO generator, and LO delay as well as global local oscillator frequency select. The digital serial control function also has an external delay enable signal to start the LO generator and synchronize all the internal LO delays. 
         [0008]    Although considerable attention has been paid to diagnostic ultrasound imaging systems, the same cannot be said as regards ultrasound therapy systems. The technologies described above relating to diagnostic ultrasound imaging systems are not applicable to therapeutic ultrasound delivery mainly due to the longer ultrasound bursts and higher time average power requried. As a result, there are still numerous barriers to the construction of fully electronically steerable, focused ultrasound devices for therapy including the number of transducer array elements, interconnects and driving and monitoring electronics that are required. As will be appreciated, further improvements in the design of ultrasound therapy systems are desired. 
         [0009]    It is therefore an object of the present invention to provide a novel ultrasound therapy transducer head and ultrasound therapy system incorporating the same. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, in one aspect there is provided an ultrasound therapy transducer head comprising an ultrasound source emitting ultrasonic radiation, said ultrasound source comprising a plurality of transducer elements; integrated driving electronics coupled to said transducer elements, said electronics generating at least one output ultrasound waveform and driving at least some of said transducer elements independently based on said at least one output ultrasound waveform; and temperature control structure providing cooling for said electronics. 
         [0011]    In one embodiment, the electronics drive each of the transducer elements independently. The transducer elements are arranged in groups and wherein circuitry is provided for each group of transducer elements. The circuitry comprises digital and analog circuit components. For each group, the digital circuit comprises digital memory storing a digital waveform for each transducer element of the group and at least one digital to analog converter to convert each digital waveform output by the digital memory to an analog signal. The analog circuit comprises at least one amplification stage receiving the analog signal output of the at least one digital to analog converter and provides a variable driving signal to each transducer element of the group. The digital circuit and analog circuit for each group may be implemented on one integrated circuit chip or on separate integrated circuit chips. 
         [0012]    According to another aspect there is provided an ultrasound therapy transducer head comprising an ultrasound source comprising at least one transducer element for generating an ultrasound beam; and an acoustic power sensing arrangement through which said ultrasound beam passes, said acoustic power sensing arrangement sensing the acoustic power of the ultrasound beam generated by said at least one transducer element. 
         [0013]    In one embodiment, the ultrasound source comprises an array of transducer elements and wherein the acoustic power sensing arrangement senses the acoustic power of the ultrasound beam generated by each transducer element. The acoustic power sensing arrangement comprises a pressure sensitive layer and an electrode pair generally aligned with each transducer element. The electrodes of each electrode pair are positioned on opposite sides of the pressure sensitive layer. In one form, the pressure sensitive layer is a piezoelectric membrane and wherein each electrode pair develops a potential voltage between the electrodes thereof generally proportional to the power of the ultrasound beam generated by the associated transducer element. Readout circuitry electively reads out the potential voltages developed by the electrode pairs. Control circuitry communicates with the readout circuitry and the ultrasound source. The control circuitry provides feedback to the ultrasound source based on the potential voltages readout by the readout circuitry. 
         [0014]    According to yet another aspect there is provided an ultrasound therapy transducer head comprising an ultrasound source comprising at least one transducer element for generating an ultrasound beam; and temperature control structure to control temperature within said ultrasound therapy transducer head. 
         [0015]    In one embodiment, a coupling fluid reservoir containing coupling fluid is positioned adjacent the ultrasound source through which the ultrasound beam passes before exiting the transducer head. A heat exchanger cools the coupling fluid in response to at least one first sensor monitoring the temperature of the coupling fluid. The heat exchanger also cools the ultrasound source in response to at least one second sensor monitoring the temperature of the ultrasound source. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Embodiments will now be described more fully with reference to the accompanying drawings in which: 
           [0017]      FIG. 1  is a schematic diagram of an ultrasound therapy system comprising an ultrasound transducer head and an external controller; 
           [0018]      FIG. 2  is an enlarged schematic diagram of a portion of the ultrasound transducer head; 
           [0019]      FIGS. 3 and 4  show an acoustic power sensing arrangement, a switching circuit and a voltage measuring circuit forming part of the ultrasound transducer head; 
           [0020]      FIG. 5  is a schematic block diagram of electronics forming part of the ultrasound therapy system of  FIG. 1 ; 
           [0021]      FIG. 6  is a circuit diagram of an analog amplifying stage forming part of the electronics of  FIG. 5 ; 
           [0022]      FIG. 7  is a schematic block diagram of one implementation of the electronics of  FIG. 5 ; and 
           [0023]      FIG. 8  is a schematic block diagram of another implementation of the electronics of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0024]    Turning now to  FIGS. 1 and 2 , a system for ultrasound therapy comprising an ultrasound therapy transducer head  10  coupled to an external controller  11  is shown. As can be seen, ultrasound transducer head  10  comprises a housing  12  that physically supports and protects internal ultrasound therapy source components. An acoustically transparent membrane  13  is provided at one end of the housing  12 . An ultrasound source  14  that emits ultrasonic radiation  15  (i.e. acoustic signals or sound waves) that pass through the membrane  13  for application to a target region  16  of a subject selected for ultrasound therapy is mounted within the housing  12 . The ultrasound source  14  comprises an array of piezoelectric transducer elements  20 , only a small number of which are shown for illustrative purposes only. Each transducer element  20  has an impedance backing  21  thereon comprised of material with different impedance properties than the ultrasonic impendence properties of the associated transducer element  20 . 
         [0025]    A connection layer  22  in the form of a flex circuit or circuit board provides a mechanical mount for the transducer elements  20  and the impendance backing  21  as well as electrical connections between driving electronics  24  and the transducer elements  20 . The driving electronics  24  also communicate with temperature sensing electronics  26  and a heat exchanger  28  disposed within the housing  20  as well as with the external controller  11 . A coupling fluid reservoir  32  filled with a coupling fluid  34  is provided in the housing  12  adjacent the membrane  13 . A temperature sensor  36  is positioned within the coupling fluid reservoir  32  and communicates with the temperature sensing electronics  26 . The distal end of each transducer element  20  extends into the coupling fluid reservoir  32  and is immersed in the coupling fluid  34 . 
         [0026]    An acoustic power sensing arrangement  38  spaced from the array of transducer elements  20  is also disposed in the coupling fluid reservoir  32  and is positioned so that ultrasonic radiation emitted by the transducer elements  20  passes through the acoustic power sensing arrangement  38  before exiting the housing  12  via the membrane  13 . The acoustic power sensing arrangement  38  is connected to a switching circuit  42  which in turn is connected to a voltage measuring circuit  44 . The voltage measuring circuit  44  communicates with the external controller  11 . 
         [0027]    Turning now to  FIGS. 1 to 4 , the acoustic power sensing arrangement  38 , switching circuit  42  and voltage measuring circuit  44  are better illustrated. In this embodiment, the acoustic power sensing arrangement  38  comprises a polarized piezoelectric membrane  40  formed of polyvinylidene fluoride (PVDF). As is known, membranes of this nature are commonly used in hydrophones to measure ultrasound pressure waves in a medium such as water. A set of upper electrodes  40   a  in the form of generally parallel, laterally spaced strips and a set of lower electrodes  40   b  similarly in the form of generally parallel, laterally spaced strips are provided on opposite sides of the piezoelectric membrane  40 . The electrode strips  40   a  of the upper set are generally orthogonal to the electrode strips  40   b  of the lower set. The upper electrode strips  40   a  and the lower electrode strips  40   b  overlap to form electrode pairs, with each electrode pair being aligned with a respective one of the transducer elements  20 . 
         [0028]    Switching circuit  42  comprises a pair of multiplexers  42   a  and  42   b . Each channel of multiplexer  42   a  is connected to a respective one of the upper electrode strips  40   a  and each channel of the multiplexer  42   b  is connected to a respective one of the lower electrode strips  40   b . The multiplexers  42   a  and  42   b  receive address data from the external controller  11  allowing the voltage developed between each electrode pair to be readout. 
         [0029]    The voltage measuring circuit  44  comprises an amplifier  44   a  receiving input from the multiplexers  42   a  and  42   b . The amplifier  44   a  provides output to an analog-to-digital converter  44   b  which in turn provides output to a memory  44   c . Memory  44   c  communicates with the external controller  11 . 
         [0030]    In this embodiment, the transducer elements  20  are arranged in groups with each group comprising forty-eight ( 48 ) transducer elements  20  although this number may be increased or decreased as desired. The driving electronics  24  in this embodiment are formed of discrete components and comprise a digital circuit  50  and an analog circuit  52  for each group of transducer elements  20 .  FIG. 5  better illustrates one of the digital circuits  50  and one of the analog circuits  52 . The digital circuit  50  comprises an address counter  60 , an address counter memory  62 , forty-eight ( 48 ) digital waveform memories  64  (only one of which is shown), forty-eight ( 48 ) waveform digital-to-analog converters (DACs)  66  (only one of which is shown) and a reference voltage DAC  68 . The address counter memory  62 , the digital waveform memories  64  and the reference voltage DAC  68  are connected to the external controller  11  via a 16-bit high speed data bus  70 . The address counter  60  and the waveform DACs  66  are connected to the external controller  11  via OR logic  72  that is driven by a run clock  74 . The address counter  60 , address counter memory  62 , digital waveform memories  64 , waveform DACs  66  and reference voltage DAC  68  also communicate with the external controller  11  via control lines  76 . 
         [0031]    Each digital waveform memory  64  in this embodiment comprises 64K×10 bit static random access memory (RAM) that stores a digital waveform received from the external controller  11  via the high speed data bus  70 . The digital values of the digital waveform at sampled time points are directly and serially loaded into each digital waveform memory  66  via the high speed data bus  70 . The frequencies, amplitudes and phases of digital waveforms loaded into the digital waveform memories  66  by the external controller are selected so that the ultrasonic radiation  15  output by the ultrasound therapy transducer head  10  provides the desired therapeutic ultrasound to the subject. Parallel loading of the digital waveform into each digital waveform memory  64  is also feasible and will reduce the time required for the digital waveform loading procedure. The address counter memory  62  supplies rolling memory addresses to the address counter  60  at 20 MHz as the external controller  11  outputs data onto the high speed data bus  70  which in turn enables the digital waveform memories  64  so that the digital waveform data is stored in the proper digital waveform memories  64 . Each digital waveform memory  64  is also addressed by the address counter  60  to ensure synchronization during output of digital waveforms by the digital waveform memories. 
         [0032]    Once the digital waveform memories  64  have been loaded with the desired digital waveforms, each digital waveform memory is used to provide 10-bit digital waveform data to its associated waveform DAC  66  during the sonication. Each waveform DAC  66  converts the 10-bit digital waveform seen at its input to an analog signal with a dynamic range of 0 to 1 volt. The waveform DAC  66  is fast enough to allow adequate time resolution. During the sonication, the run clock  74  to the address counter  60  and the waveform DACs  66  is switched to a higher frequency oscillator (for example 65 MHz) to allow for adequate time resolution. Each waveform DAC  66  may also have additional features such as power down lines to allow individual channels to be disabled in the event of a channel down condition. Such a channel down condition occurs for example if the channel driving line becomes disconnected from its associated transducer element  20  or if the transducer element  20  is damaged. The reference voltage DAC  68  and its associated latch (not shown) are used to set the reference voltage for all the waveform DACs  66 . This allows the total power level of the ultrasound source  14  to be adjusted in real time during sonication without requiring reloading of the digital waveform memories  66 . 
         [0033]    The analog circuit  52  comprises forty-eight ( 48 ) amplication circuits (only one of which is shown), each of which receives the analog signal output of an associated waveform DAC  66  and outputs a corresponding analog radio frequency (RF) signal that is applied to the channel driving line extending to an associated transducer element  20 . The advantages of having each transducer element  20  connected to its own driving line include the reduction of the driving system size, cost, and power loss when the energy is transmitted from the driving electronics to the transducer element array. 
         [0034]    One of the amplification circuits is better illustrated in  FIG. 6  and comprises a first Op-Amp stage  80  that provides a voltage gain to the analog signal, and a second Op-Amp stage  82  that provides a high current analog signal output. In this embodiment, the first Op-Amp stage  80  applies a voltage gain of eleven (11) to the DAC analog output signal augmenting the voltage swing from 0 to 11 volts. The Op-Amp stage  80  cuts out high frequencies and can be used to cut the quantization noise frequency. The signal output by the Op-Amp stage  80  is high-pass filtered with a first order resistor-capacitor (RC) circuit  84  to remove DC offset. The second Op-Amp stage  82  employs a high power Op-Amp to amplify the voltage, in this embodiment by a gain of two (2), and provide a high current analog output signal with a maximum peak-to-peak voltage swing of 22 volts. 
         [0035]    The components shown in the shaded region of  FIG. 5  represent the circuitry of the digital and analog circuits  50  and  52  that is repeated for each of the forty-eight ( 48 ) channels. The digital and analog circuits  50  and  52  can be constructed from discrete components or can be constructed using application specific integrated circuit (ASIC) chips. The digital circuit  50  can be combined on one ASIC chip  90  and the analog circuit  52  on another ASIC chip  92  as shown in  FIG. 7 . Alternatively, both the digital and analog circuits  50  and  52  can be combined on one chip  96  using a multiple-chip package (MCP) process as shown in  FIG. 8 . The Op-Amp stages  80  and  82  can be embedded in the module by integrating semiconductor intellectual property (SIP) blocks with ASIC/memories. The chip  90  or  96  may include a line that allows the status of the digital waveform memories  64  to be monitored to assure that each digital waveform is properly loaded. 
         [0036]    The external controller  11  in this embodiment comprises a computing device such as for example, a Microsoft Windows based personal computer (PC) with a NI PCI-6534 (National Instruments, Austin, Tex.), an 80 Mbytes/second data transfer rate, and a 32-bit digital I/O board. The I/O board is controlled through a program executing on the computing device that uses the dynamic link library (DLL) supplied by the I/O board manufacturer. Binary data on thirty-two (32) data lines can be simultaneously transmitted for example at 20 MHz if an 80 Mbytes/s transfer rate is desired. Of the 32 data lines, 16 data lines form the high speed data bus  70  for transmitting digital waveform values, etc. to the driving electronics  24 . The other 16 data lines are used as the control lines  76  for selecting, programming and manipulating different components of the driving electronics  24  and for higher level functions such as powering on and off individual digital circuits  50  and/or individual channels of the digital circuits  50 . 
         [0037]    The analog circuits  52  can be controlled by the external controller  11  for example through a parallel port. The external controller  11  can control electronic components of the ultrasound transducer head  10  via a serial port, universal serial bus (USB) or other suitable communications protocol. Each operation or instruction issued by the external controller  11  is coded with a specific 16-bit word that is used to directly control the appropriate component elements. 16-bit data arguments can be sent by the electronic components to the external controller  11  when required. 
         [0038]    During operation, when the ultrasound transducer head  10  is conditioned to output ultrasonic radiation  15 , the digital waveform data in each digital waveform memory  64  is output to its associated digital waveform DAC  66  and converted into an analog signal. Each analog signal is input to its associated amplification circuit resulting in an output RF signal that is fed to its associated transducer element  20 . In response, each transducer element  20  outputs a beam of ultrasonic radiation corresponding to the digital waveform. 
         [0039]    The ultrasound beam transmitted by each transducer element  20  passes through the acoustic power sensing arrangement  38  before exiting the transducer head  10  via the membrane  13 . As each ultrasound beam passes through the acoustic power sensing arrangement, a varying voltage is formed in the piezoelectric membrane  40  between the electrode pair aligned with the transducer element  20  that is outputting the ultrasound beam as a result of the pressure variation created across the piezoelectric membrane  40 . When the controller  11  addresses an electrode pair by enabling the multiplexers  42   a  and  42   b  connected to the upper and lower electrode strips  40   a  and  40   b  forming the electrode pair, the voltage across the piezoelectric membrane  40  between the electrode pair is sensed by the amplifier  44   a . Amplifier  44   a  in turn outputs a voltage signal to the analog-to-digital converter  44   b  which converts the voltage signal to a digital value for storage in the memory  44   c . Since the sensed voltage is proportional to the ultrasound pressure wave, the acoustic power delivered by each transducer element  20  can be measured. These measurements can be relative or they can be calibrated to provide absolute power measurements. 
         [0040]    The generated voltage measurement signal output from the memory  44   c  by the voltage measuring circuit  44  is used by the external controller  11  to assure the proper operation of the transducer elements  20  and/or the driving electronics  24  allowing the ultrasonic radiation  15  output by the ultrasound therapy transducer head  10  to be precisely controlled. The generated voltage measurement signal may also be used to assure proper operation of the software executed by the external controller  11  during generation and loading of digital waveforms, to measure, display and/or control the amplitude of the emitted ultrasound beams, to measure, display and/or control the phase of the emitted ultrasound beams, and as a feedback signal to assure desired operation of the ultrasound therapy transducer head  10  such as by adjusting ultrasound beam amplitudes to stabilize power output. 
         [0041]    The temperature sensing electronics  26  in this embodiment monitor the temperature of the coupling fluid  34  via temperature sensor  36  and the temperature of the driving electronics  24  via another temperature sensor (not shown) and provide output to the heat exchanger  28 . In response to output from the temperature sensing electronics  26 , the heat exchanger cools the coupling fluid  34  and/or the driving electronics  24  by circulating coolant through the housing  12  thereby to control temperature within the housing  12  and assure stable and reliable operation of the ultrasound therapy transducer head  10 . The temperature sensing electronics  26  can signal the heat exchanger  28  so that it operates generally continuously to maintain a desired temperature within the housing or can cycle the heat exchanger  28 . If desired, the temperature sensing electronics  26  may store temperature measurement and control data for transfer to the external controller  11 . 
         [0042]    If desired, the ultrasound therapy transducer head  10  may further comprise a controller to maintain and control the performance of the ultrasound therapy transducer head. Memory may be provided to store sonication, control and/or safety limit data as well as other data generated during ultrasound therapy transducer head monitoring. Additional electronics to enable automatic control and provide enhanced safety may also be included. 
         [0043]    By integrating the array of transducer elements  20  with driving electronics  24  using custom integrated circuits in the transducer housing  12  and by using piezoelectric film technology integrated into the transducer housing  12  to monitor acoustic power output, the manufacturing costs of the ultrasound therapy transducer head  10  are significantly reduced providing for the ability to make ultrasound therapy systems that are not feasible with the current approaches. 
         [0044]    Although the driving electronics  24  are described above as being connected to the array of transducer elements  20  via the connection layer  22 , if desired, the driving electronics  24  may be directly connected to the transducer elements  20  obviating the need for the connection layer. If the connection layer does not provide the mechanical mounting then additional material is used to provide the mechanical mounting for the transducer elements  20 . Also, if desired, the acoustic power sensing arrangement  38  can be positioned directly on the transducer element array face rather than being spaced from it as shown. 
         [0045]    The form of the driving electronics  24  can of course vary from the examples described above and illustrated in the drawings. For example, if desired the amplification circuits may only include the high power Op-Amps. The analog output provided to the amplification circuits may be generated by individual waveform generators. In the example of  FIG. 7 , it is possible to realize only the digital circuits  50  in ASICs while using discrete components for the analog circuits  52 . 
         [0046]    Although embodiments have been described above with reference to the drawings, those of skill in the art will appreciate that variation and modifications may be made without departing from the spirit and scope thereof as defined by the appended claims.