An Electronic Focusing System For The Treatment Of Ultrasound

In recent years, there is a noticeable shift in the treatment of a num ber of focal diseases including cancer towards m inimally invasive and even fully non-invasive modalities, often known as interventional proc edures. High intensity focused ultrasound(HIFU) has been inves tigated as a non-i nvasive interventional modality and is FDA approved for treatment of uterine fibroids and under clinical trials for bone metastasis and other diseases. The new generatio n of HIFU systems provides m ultiple high p ower channels which, together with a suitably designed therapeutic array transducer, enables electronic steering and focusing of the ultras ound beam. Such systems are challenging to design and build due to high channel count, high power requirement, demanding timing accuracy and, in certain applicatio n, requirement for arbitrary transm it frequency and waveform.In this thesis, a multi-channel HIFU system was des igned, built and tes ted. According to acous tic field theory, a fully functional therapeutic array system would involve up to 1000 channels, whic h is unpractical, especially as a first prototype for our research group.Therefore a reduced channels solution was investigated. It was determined a 128 channel system offers an acceptable com promise between cost and acoustic performance. However, for the future, a higher channel count will be desirable. Therefore, a modular architecture was chosen. A control module(CM) board and a transmission(TX) board were designed.The primary function of the system is the playback and amplification of 128 independent channels of programm ed waveforms. Each channel also incorporates a delay generator to allow focusing and steer ing. A total of 1024 sets of delays can be pre-programmed on the system so that each focal point can be activated as quickly as the highest PRF, without the latency introduced by communication with a PC. Independent waveform memories allow non-standard or advanced sound field to be generated, including simultaneous focusing at multiple focal points. High power amplification was implemented by a 3-level MOSFET driver powered by external high voltage( ±HV) supplies. A maximum sustained power output per channel of 4 W was specified. The output impedance of each channel was specified at 75 ?.A prototype therapeutic array probe was connected to the system and tes ted. Electronic focusing and steering was dem onstrated, proving the delays and waveforms generation was accurate. W aveform fidelity and output p erformance from 1.0 to 10.0 MHz center frequency was excellent. Peak power output was tested on single channels for up to 250 Vpp at 50 ? load and sustained power output ex ceed the specification of 4 W. However, the maximum acoustic output has not yet been tested due to fear of da maging the prototype array. Maximum output will be tested in th e near futu re when a second prototype is available.This thesis reports the design and completion of a 128-ch annels HIFU transmitter system. The system enable research and de velopment of array the rapeutic ultrasound technology, and is ready to suppo rt pre-clinical research. Fu ture extension to up to 1024 channels is possible.