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Browsing by Subject "HIFU"

Now showing 1 - 4 of 4
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    HIFU Monitoring and control With dual-mode ultrasound arrays
    (2013-11) Casper, Andrew Jacob
    The biological effects of high-intensity focused ultrasound (HIFU) have been known and studied for decades. HIFU has been shown capable of treating a wide variety of diseases and disorders. However, despite its demonstrated potential, HIFU has been slow to gain clinical acceptance. This is due, in part, to the difficulty associated with robustly monitoring and controlling the delivery of the HIFU energy. The non-invasive nature of the surgery makes the assessment of treatment progression difficult, leading to long treatment times and a significant risk of under treatment. This thesis research develops new techniques and systems for robustly monitoring HIFU therapies for the safe and efficacious delivery of the intended treatment. Systems and algorithms were developed for the two most common modes of HIFU delivery systems: single-element and phased array applicators. Delivering HIFU with a single element transducer is a widely used technique in HIFU therapies. The simplicity of a single element offers many benefits in terms of cost and overall system complexity. Typical monitoring schemes rely on an external device (e.g. diagnostic ultrasound or MRI) to assess the progression of therapy. The research presented in this thesis explores using the same element to both deliver and monitor the HIFU therapy. The use of a dual-mode ultrasound transducer (DMUT) required the development of an FPGA based single-channel arbitrary waveform generator and high-speed data acquisition unit. Data collected from initial uncontrolled ablations led to the development of monitoring and control algorithms which were implemented directly on the FPGA. Close integration between the data acquisition and arbitrary waveform units allowed for fast, low latency control over the ablation process. Results are presented that demonstrate control of HIFU therapies over a broad range of intensities and in multiple in vitro tissues. The second area of investigation expands the DMUT research to an ultrasound phased-array. The phased-array allows for electronic steering of the HIFU focus and imaging of the acoustic medium. Investigating the dual-mode ultrasound array (DMUA) required the design and construction of a novel ultrasound-guided focused ultrasound (USgFUS) platform. The platform consisted of custom hardware designed for the unique requirements of operating a phased-array in both therapeutic and imaging modes. The platform also required the development of FPGA based signal processing and GPU based beamforming algorithms for online monitoring of the therapy process. The results presented in this thesis represent the first demonstration of a real-time USgFUS platform based around a DMUA. Experimental imaging and therapy results from series of animal experiments, including a 12 animal GLP study, are presented. In addition, in vitro control results, which build upon the DMUT work, are presented.
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    Optimized pulsing of high-intensity focused ultrasound for enhanced therapeutic window
    (2010-03) Al-Qaisi, Muhammad K.
    High intensity focused ultrasound (HIFU) provides a unique modality to perform non-invasive surgeries. The thermal ablation technique relies on focusing the non-ionizing acoustic wave within soft tissues to produce a small lesion. HIFU operations are typically attempted by continuous-wave (CW) applications of the beam intervened by wait periods to allow surrounding tissue to cool down. Large contiguous lesions are produced by raster-scanning the beam over the volume of the tumor; a procedure that requires up to three hours for a 2-cm diameter tumor. This is one of the main limitations of HIFU thermal therapy. As part of the ongoing research to accelerate the procedure, we investigate the role of pulsed-HIFU (pHIFU) parameters in the enhancement of the therapeutic gain within the HIFU focus. A therapeutic gain is observed when high duty cycle pHIFU is pulsed at the mechanical resonance of the medium. Up to 50% increase in temperature was measured in lab-prepared tissue mimicking phantoms. The therapeutic gain achieved by pHIFU over cwHIFU is attractive as no modifications on the currently used applicators are required.
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    Real-time imaging of thermal and mechanical tissue response to focused ultrasound.
    (2010-08) Liu, Dalong
    The analytic nature of the radio frequency (RF) data from diagnostic pulse-echo ultrasound allows for fine axial displacement and strain estimation through correlation-based speckle tracking techniques. Speckle tracking allows for estimating axial tissue displacements in the sub-micron range with high spatial resolution. This was exploited in the development of ultrasound elastography and thermography. Elastography offers the promise of a higher contrast imaging compared to conventional ultrasound (e.g. in imaging stiff tumors) while thermography offers the promise of guiding and monitoring thermal therapies (e.g. in cancer treatment). At the relatively low frame rates of ultrasound, however, the quality of the speckle tracking may deteriorate (due to loss of correlation between subsequent frame data), which results in noisy displacement field estimates. These, in turn, may render the strain field estimates useless for the intended applications. This thesis research aims at developing a high frame rate pulse-echo ultrasound systems for displacement and strain estimation with application to both elastography and thermography. For elastography, a high frequency ultrasound system has been developed for viscoelastic property measurement of thin tissue samples (e.g. skin and subcutaneous tissue, tissue-engineered cardiovascular valves). A dual-element concave transducer was used for localized application of acoustic radiation force (ARF) pulses and monitoring of the induced axial shift. Synchronous silencing of ARF beam and coded excitation technique were used to allow the capture of the full dynamics of tissue deformation in response to the ARF pulse. A modulation unit was also designed to control the temporal behavior of the ARF beam to allow for the investigation of a variety of modulation schemes. A correlation-based speckle tracking algorithm was used to produce spatio-temporal axial displacement maps. The displacement maps were used as input to an on-line tracking of the viscoelastic properties using an extended Kalman Filter (EKF). The EKF simultaneously estimated the state and parameter values utilizing a second order constitutive model of viscoelastic response with unknown parameters. It also allowed for the incorporation of both input and measurement noise models. The former is significant since local variance in absorption and/or beam distortions cannot be predicted precisely in situ. For thermography, a diagnostic scanner was integrated with high intensity focused ultrasound (HIFU) sources to provide real-time 2D high frame rate data system suitable of performing real-time 2D temperature estimation. The front-end of the system was a commercially available scanner equipped with a research interface, which allowed the control of imaging sequence and access to the RF data in real-time. A high frame-rate 2D RF acquisition mode, M2D, was used to capture the transients of tissue motion/deformations in response to pulsed HIFU. The M2D RF data was streamlined to the back-end of the system, where a 2D temperature imaging algorithm based on speckle tracking was implemented on a graphics processing unit (GPU). The real-time images of temperature change were computed on the same spatial and temporal grid of the M2D RF data, i.e. no decimation. Verification of the algorithm was performed by monitoring localized HIFU-induced heating of a tissue-mimicking elastography phantom. These results clearly demonstrated the repeatability and sensitivity of the algorithm. Furthermore, in vitro results were presented to demonstrate the possible use of this algorithm for imaging changes in tissue parameters due to HIFU-induced lesions. These results clearly demonstrated the value of the real-time data streaming and processing in monitoring and guidance of minimally-invasive thermo-therapy.
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    Refocusing of Dual-mode ultrasound arrays for optimal therapeutic gain.
    (2012-04) Ballard, John Robert
    Dual mode ultrasound arrays (DMUA) have recently been introduced in the field of image-guided noninvasive surgery using high intensity focused ultrasound (HIFU). The goal of this dissertation is to investigate the use of DMUAs for transthoracic targeting of abdominal tumors. DMUAs are capable of operating in both imaging and therapy modes using the same array transducers. The inherent registration between these coordinate systems allows for the use of image feedback in refocusing the DMUA at target point(s) while avoiding critical structures in the path of the HIFU beam. In the #12;rst part of this dissertation, we propose an image-based refocusing algorithm which minimizes the power deposition over critical structures while maintaining or improving the power deposition at the focal location(s) by taking advantage of the available acoustical window. This is of particular importance when targeting abdominal tumors located in the liver or kidneys that are partially obstructed by the rib cage. An optimal weighted minimum-norm least-squares solution is shown to achieve the goal of maintaining desired power level(s) at the target point(s) while minimizing exposure to the ribs. Measurements and simulation results show that the optimal solution channels the ultrasound energy to the target through the intercostals, thus avoiding the ribs. One possible limitation of this approach is the creation of a virtual array in the rib plane, which could result in unacceptably high grating lobes in the target plane. The second part of this dissertation explores the use of a multiple-frequency optimal synthesis approach to mitigate the grating-lobe problem. In addition to the use of simulation and basic measurements in verification, the thesis research includes an extensive investigation of the basic characteristics of HIFU-induced lesions using both single-frequency and multiple-frequency synthesis approaches. Lesion formation experiments using these approaches were performed both in vitro and in vivo using small-animal models. In addition, the synergistic effects of the use of multiple frequency excitation, including enhancement of the thermal rate due to cavitation and increased harmonic generation are discussed.