Formalin-fixed, paraffin embedded (FFPE) tissue is the most abundant, accessible, and versatile tissue sample type available for genetic research and clinical applications. However, FFPE DNA extraction presents unique challenges and requires lengthy incubation periods, which can be impractical for certain applications. Here, we propose the use of focused ultrasound extraction (FUSE) technology for improved DNA extraction from FFPE tissue. FUSE generates a dense bubble cloud of acoustic cavitation capable of ablating tissue into an acellular lysate. FUSE treatment was applied to de-paraffinized porcine pancreas FFPE scrolls, followed by heated incubation for formaldehyde-induced DNA-protein crosslink reversal. When applied for 30 minutes, FUSE was found to successfully extract DNA from FFPE tissue as defined by increased DNA yield and improved purity ratios compared to conventional methods. DNA extracted via FUSE showed comparable fragmentation to conventional methods, and three out of four samples successfully amplified via PCR, indicating suitability for downstream analysis. These findings suggest that FUSE has the potential to increase the efficiency and effectiveness of DNA extraction from FFPE tissue. Further development and optimization of this protocol could develop a streamlined, easy to use extraction method that would simplify FFPE DNA extraction methods and address the primary time constraints which currently make FFPE DNA extraction time-consuming and impracticable for high-throughput applications. / Master of Science / Formalin-fixed, paraffin embedding (FFPE) has historically been the most popular method of biological tissue preservation, as it allows tissue to remain shelf stable for decades. As such, FFPE tissue is the most abundant, accessible, and versatile tissue sample type available for genetic research applications. Here, we propose the use of focused ultrasound extraction (FUSE) technology for improved DNA extraction from FFPE tissue. FUSE treatment applies rapid, focused ultrasound waves to tissue, resulting in the mechanical breakdown of cells and subsequent release of DNA. FUSE treatment was applied to pig pancreatic FFPE samples. When applied for 30 minutes, FUSE was found to successfully extract DNA from FFPE tissue as defined by increased DNA yield and improved purity compared to conventional methods. Three out of four DNA samples extracted via FUSE were successfully amplified, and DNA fragment lengths were comparable between FUSE and conventional methods, showing that FUSE did not fragment DNA beyond useful fragment lengths. These findings suggest that FUSE has the potential to increase the efficiency and effectiveness of DNA extraction from FFPE tissue. Further development and optimization of this protocol could develop a streamlined, easy to use extraction method that would simplify FFPE DNA extraction methods and address the primary time constraints which currently make FFPE DNA extraction time-consuming and impracticable for high-throughput applications.

Histotripsy is a noninvasive mechanical ablation method that uses focused ultrasound to disintegrate target tissues into acellular homogenate through the generation of acoustic cavitation and is currently being developed for numerous clinical applications. Histotripsy uses high-pressure (>10 MPa), short-duration (<15 cycles) pulses to cause the rapid expansion and collapse of nuclei at the focus resulting in large applied stress and strain in the adjacent tissue. At a sufficiently high pressure above the target medium's intrinsic cavitation threshold and an adequate number of applied pulses, cavitation "bubble clouds" create precise lesions with high fidelity to the region of the focus. Despite advances in histotripsy, additional research is still needed to better understand the acoustic cavitation nucleation process and its effects on therapies using focused ultrasound. This understanding is critical to better predict and control pulse dose for more rapid and efficient ablation procedures, to reduce off-target cavitation events for safer focused ultrasound therapies, and to localize ablation for high-precision procedures near critical structures or treatments without active imaging guidance. In this dissertation, I investigate the nucleation and dynamics of ultrasonically generated acoustic cavitation for novel applications of focused ultrasound. My Ph.D. thesis focuses on (1) investigating the effect of histotripsy pulsing parameters on bubble cloud cavitation nucleation, bubble dynamics, and ablation efficiency, (2) investigating the effect of nuclei characteristics on the threshold for cavitation nucleation and resulting bubble dynamics for therapeutic applications, and (3) developing methods alter select characteristics and dynamics of acoustic cavitation by adjusting pulsing parameters to optimize ablation efficiency in conventional and nanoparticle-mediated histotripsy. The culmination of this thesis will advance our understanding of the nucleation and behavior of acoustic cavitation from pulsed focused ultrasound and develop innovative systems to improve the efficacy, efficiency, and safety of clinical focused ultrasound therapies. / Doctor of Philosophy / Histotripsy is a noninvasive focused ultrasound method that precisely destroys target tissues such as tumors through the acoustic generation of cavitation and is currently being developed for numerous clinical applications. Histotripsy uses high-pressure, short-duration pulsed soundwaves to cause the bubbles to rapidly expand and collapse within a precise region called the focus. This rapid cavitation results in large mechanical strain in the targeted tissue. With increasingly higher pressure, numerous bubbles form in the shape of cavitation "bubble clouds" that create lesions, closely matching their shape, in the target tissue after a sufficient number of pulses have been applied. Despite advances in histotripsy, additional research is still needed to better understand the initiation of the acoustic cavitation process in histotripsy and its effects on focused ultrasound therapies. This understanding is critical to better predict and control ablation procedures, improve procedure efficiency, reduce off-target cavitation events for safer focused ultrasound therapies, and further increase ablation precision for procedures near critical structures or treatments without active image guidance. In this dissertation, I investigate the initiation, growth, and collapse of ultrasonically generated acoustic cavitation for novel applications of focused ultrasound. My Ph.D. thesis focuses on (1) investigating the effect of histotripsy pulsing parameters on bubble cloud cavitation initiation, bubble growth and collapse, and treatment efficiency, (2) investigating the effect of particle characteristics on the threshold for cavitation initiation and resulting bubble behavior for therapeutic applications, and (3) adjusting pulsing parameters to optimize ablation efficiency in conventional and particle mediated histotripsy. The culmination of this thesis will advance our understanding of the initiation and behavior of acoustic cavitation from pulsed focused ultrasound and develop innovative systems to improve the efficacy, efficiency, and safety of clinically focused ultrasound therapies.

Tendinopathy is a common pathology of tendons characterized by pain and a decrease in function resulting from changes in the tissue's structure and/or composition due to injury. Diagnosis of tendinopathy is determined by the qualitative analysis of a trained physician usually with assistance from an imaging modality. Although physicians can often identify tendinopathy, there are no quantitative metrics to evaluate tendon fatigue, damage, or healing. Physical therapy (PT) is a common treatment for patients with tendinopathy, and recent studies have investigated Focused Ultrasound (FUS) for its treatment of tendons. Developments in the use of FUS as a therapeutic have led to studies of the underlying mechanisms by which it operates. Digital Image Correlation (DIC) is a non-contact method of quantifying tissue displacements and strains of a deforming material using high resolution imaging DIC programs can evaluate and interpolate strain data by applying statistical image processing algorithms and solid continuum mechanics principles using a set of sequential image frames capturing the mechanical deformation of the specimen during testing. The studies presented in this thesis investigate methodologies for using DIC with ultrasound imaging of mouse Achilles tendons to characterize strains resulting from FUS therapies. The first method is based upon an orthogonal configuration of therapy and imaging transducers while the second investigates a coaxial experimental configuration. This work explores DIC as a viable means of quantifying the mechanical stimulation caused by FUS therapies on tendon tissue through ultrasound imaging to better understand the underlying mechanisms of FUS therapy. / Master of Science / Tendinopathy is a common injury that many people will experience in their lifetime. Pain and swelling are common symptoms and can make daily actions uncomfortable to perform. Physical therapy (PT) is one of the most common ways to help relieve the symptoms of this condition. A therapy being investigated to help treat tendinopathy utilizes Focused Ultrasound (FUS) technology to help the healing process. PT can be difficult and painful for those experiencing tendinopathy, but if a therapeutic like FUS could mimic the effects of PT, then some patients would not need to perform these physically demanding tasks. To understand if this treatment is viable, we need to better understand the underlying mechanisms by which it operates. Therefore, we are investigating the mechanical stimulation that FUS imparts on tendons because it is believed that the mechanical stimulations from exercise are a primary contributor to healing. Specifically, we want to evaluate the kind of strains applied by FUS therapies to inform decisions about dosage. One method uses Digital Image Correlation (DIC). DIC is a method of evaluating displacements and strains using non-contact high resolution imaging. DIC works using statistically motivated algorithms to calculate the deformation between subsequent video frames in a given material undergoing a state of stress. Using this technology along with ultrasound imaging, this work gives a preliminary exploration of using DIC as a means of quantifying strain to better understand the underlying mechanisms of the mechanical stimulations caused by FUS therapy.

Focused ultrasound (FUS) is an emerging technology, and it plays an essential role in clinical and contactless acoustic energy transfer applications. These applications have critical criteria for the acoustic pressure level, the creation of complex pressure patterns, spatial management of the complicated acoustic field, and the degree of nonlinear waveform distortion at the focal areas, which have not been met to date. This dissertation focuses on introducing experimentally validated novel numerical approaches, optimization algorithms, and experimental techniques to fill existing knowledge gaps and enhance the functionality of holographic acoustic lenses (HALs) with an emphasis on applications related to biomedical-focused ultrasound and ultrasonic energy transfer. This dissertation also aims to investigate the dynamics of nonlinear acoustic beam shaping in engineered HALs. First, We will introduce 3D-printed metallic acoustic holographic mirrors for precise spatial manipulation of reflected ultrasonic waves. Optimization algorithms and experimental validations are presented for applications like contactless acoustic energy transfer. Furthermore, a portion of the present work focuses on designing holographic lenses in strongly heterogeneous media for ultrasound focusing and skull aberration compensation in transcranial-focused ultrasound. To this end, we collaborated with the Biomedical Engineering and Mechanics Department as well as Fralin Biomedical Research Institute to implement acoustic lenses in transcranial neuromodulation, targeting to improve the quality of life for patients with brain disease by minimizing the treatment time and optimizing the ultrasonic energy into the region of interest. We will also delve into the nonlinear regime for High-Intensity Focused Ultrasound (HIFU) applications, this study is structured under three objectives: (1) establishing nonlinear acoustic-elastodynamics models to represent the dynamics of holographic lenses under low- to high-intensity acoustic fields; (2) validating and leveraging the resulting models for high-fidelity lens designs used in generating specified nonlinear ultrasonic fields of complex spatial distribution; (3) exploiting new physical phenomena in acoustic holography. The performed research in this dissertation yields experimentally proven mathematical frameworks for extending the functionality of holographic lenses, especially in transcranial-focused ultrasound and nonlinear wavefront shaping, advancing knowledge in the burgeoning field of the inverse issue of nonlinear acoustics, which has remained underdeveloped for many years. / Doctor of Philosophy / Ultrasonic waves are sound waves that have frequencies higher than the upper audible limit of human hearing. The versatility and non-invasive nature of ultrasonic waves make them a valuable tool in numerous scientific, medical, and industrial applications. In healthcare, ultrasonic waves are employed in diagnostic imaging techniques, such as ultrasound scans, to create images of internal body structures. Ultrasonic waves are also used for non-destructive testing (NDT) of materials, detecting flaws or cracks within structures without causing any damage. Furthermore, this technology finds applications in the field of material science for the manipulation of particles and in biomedical research for drug delivery systems. Focused ultrasound sound is an emerging non-invasive therapeutic modality that uses focused ultrasound waves to target tissue within the body without damaging the surrounding tissue. This technology allows for precise delivery of ultrasound energy to a specific region, where it can induce various desired therapeutic effects depending on the targeting location and parameters. Therapeutic focused ultrasound has the advantage of being non-invasive, reducing the risks and recovery time associated with traditional surgery. It can be precisely controlled and monitored in real-time with imaging techniques such as ultrasound or MRI, ensuring the targeted treatment of pathological tissues while sparing healthy ones. Applications of therapeutic are broad and include tumor ablation, facilitation of drug delivery across the blood-brain barrier, relief of chronic pain, and treatment of essential tremor and other neurological disorders. The domain of therapeutic focused ultrasound is continually advancing, driven by research that seeks to extend its applications. Recent developments in acoustic engineering and 3D printing have led to the creation of acoustic holograms, or holographic acoustic lenses, which allow for more refined control over the spatial structure of the acoustic field. These technological advancements hold the promise of enhancing FUS by improving the accuracy of acoustic field localization and providing a more cost-effective solution compared to conventional systems like phased array transducers. However, the accuracy and applicability of existing models and techniques are constrained by assumptions, including the uniformity of the propagation medium and the linearity of the acoustic field, which limits the functionality and restricts the potential applications of acoustic holograms. In this dissertation, we present novel numerical techniques, algorithms, and proof-of-concept experiments to fill those knowledge gaps and expand the functionality of acoustic holograms in crucial applications.

Given the great promise of High Intensity Focused Ultrasound (HIFU) as a therapeutic modality, the aim of the present study is to develop and optimise a technique that uses externally applied focused ultrasound energy and remote, ultrasound-based treatment monitoring to destroy subcutaneous fat safely, effectively and non-invasively. Based on initial cavitation and temperature measurements performed ex vivo in excised porcine fat at four different frequencies (0.5, 1.1, 1.6 & 3.4MHz) over a range of pressure amplitudes and exposure durations, it was concluded that 0.5MHz is the optimal frequency for this application since it is capable of instigating inertial cavitation at relatively modest pressures while enhancing focal heat deposition. Histological assessment of tissue treated above the cavitation threshold at 0.5MHz both ex vivo and in vivo demonstrated damage to adipocytes and connective tissue. Furthermore, a good correlation was identified between the energy of broadband emissions detected by the passive cavitation detector (PCD) and the focal temperature rise at 0.5MHz during ex vivo experimentation, which could be exploited as a tool for non-invasive monitoring of successful treatment delivery. In addition, localisation of cavitation activity by means of passive cavitation detection was achieved and shown to provide a strong indicator of the location of induced histological damage. Based on the specific requirements identified during initial experimentation, an application-specific HIFU transducer, cavitation detector and real-time treatment monitoring software was developed and tested ex vivo. This treatment system was found capable of producing extensive damage to adipocytes and collagen confined to the subcutaneous fat layer at the desired treatment depth, which coincided with the location of cavitation activity as displayed by the real-time treatment monitoring software.

Thesis advisor: Cyril P. Opeil / The physiology of the vasculature in the central nervous system (CNS) which includes the blood-brain-barrier (BBB) and other factors, prevents the transport of most anticancer agents to the brain and restricts delivery to infiltrating brain tumors. The heterogeneous vascular permeability in tumor vessels (blood-tumor barrier; BTB), along with several other factors, creates additional hurdles for drug treatment of brain tumors. Different methods have been used to bypass the BBB/BTB, but they have their own limitations such as being invasive, non-targeted or requiring the formulation of new drugs. Magnetic Resonance Imaging guided Focused Ultrasound (MRIgFUS), when combined with circulating microbubbles, is an emerging noninvasive method to temporarily permeabilize the BBB and BTB. The purpose of this thesis was to use this alternative approach to deliver chemotherapeutic agents through the BBB/BTB for brain tumor treatment in a rodent model to overcome the hinderances encountered in prior approaches tested for drug delivery in the CNS. The results presented in thesis demonstrate that MRIgFUS can be used to achieve consistent and reproducible BBB/BTB disruption in rats. It enabled us to achieve clinically-relevant concentrations of doxorubicin (~ 4.8±0.5 µg/g) delivered to the brain with the sonication parameters (0.69 MHz; 0.55 MPa; 10 ms bursts; 1 Hz PRF; 60 s duration), microbubble concentration (Definity, 10 µl/kg), and liposomoal doxorubicin (Lipo-DOX) dose (5.67 mg/kg) used. The resulting doxorubicin concentration was reduced by 32% when the agent was injected 10 minute after the last sonication. Three weekly sessions of FUS and Lipo-DOX appeared to be safe in the rat brain, despite some minor tissue damage. Importantly, the severe neurotoxicity seen in earlier works using other approaches does not appear to occur with delivery via FUS-BBB disruption. The resuls from three weekly treatments of FUS and Lipo-DOX in a rat glioma model are highly promising since they demonstrated that the method significantly inhibits tumor growth and improves survival. Animals that received three weekly sessions of FUS + Lipo-DOX (N = 8) had a median survival time that was increased significantly (P<0.001) compared to animals who received Lipo-DOX only (N = 6), FUS only (N = 8), or no treatment (N = 7). Median survival for animals that received FUS + Lipo-DOX was increased by 100% relative to untreated controls, whereas animals who received Lipo-DOX alone had only a 16% improvement. Animals who received only FUS showed no improvement. No tumor cells were found in histology in 4/8 animals in the FUS + Lipo-DOX group, and only a few tumor cells were detected in two animals. Tumor doxorubicin concentrations increased monotonically (823±600, 1817±732 and 2432±448 ng/g) in the control tumors at 9, 14 and 17 days respectively after administration of Lipo-DOX. With FUS-induced BTB disruption, the doxorubicin concentrations were enhanced significantly (P<0.05, P<0.01, and P<0.0001 at days 9, 14, and 17, respectively) and were greater than the control tumors by a factor of two or more (2222±784, 3687±796 and 5658±821 ng/g) regardless of the stage of tumor growth. The transfer coefficient Ktrans was significantly (p<0.05) enhanced compared to control tumors only at day 9 but not at day 14 or 17. These results suggest that FUS-induced enhancements in tumor drug delivery for Lipo-DOX are relatively consistent over time, at least in this tumor model. These results are encouraging for the use of large drug carriers, as they suggest that even large/late-stage tumors can benefit from FUS-induced drug enhancement. Corresponding enhancements in Ktrans were found variable in large/late-stage tumors and not significantly different than controls, perhaps reflecting the size mismatch between the liposomal drug (~100 nm) and Gd-DTPA (molecular weight: 938 Da). Overall, this thesis research provides pre-clinical data toward the development of MRIgFUS as a noninvasive method for the delivery of agents such as Lipo-DOX across the BBB/BTB to treat patients with diseases of the central nervous system. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Malignant or benign tumors may be ablated with high‐intensity focused ultrasound (HIFU). This technique, known as focused ultrasound surgery (FUS), has been actively investigated for decades, but slow to be implemented and difficult to control due to lack of real‐time feedback during ablation. Two methods of imaging and monitoring HIFU lesions during formation were implemented simultaneously, in order to investigate the efficacy of each and to increase confidence in the detection of the lesion. The first, Acousto‐Optic Imaging (AOI) detects the increasing optical absorption and scattering in the lesion. The intensity of a diffuse optical field in illuminated tissue is mapped at the spatial resolution of an ultrasound focal spot, using the acousto‐optic effect. The second, Harmonic Motion Imaging (HMI), detects the changing stiffness in the lesion. The HIFU beam is modulated to force oscillatory motion in the tissue, and the amplitude of this motion, measured by ultrasound pulse‐echo techniques, is influenced by the stiffness. Experiments were performed on store‐bought chicken breast and freshly slaughtered bovine liver. The AOI results correlated with the onset and relative size of forming lesions much better than prior knowledge of the HIFU power and duration. For HMI, a significant artifact was discovered due to acoustic nonlinearity. The artifact was mitigated by adjusting the phase of the HIFU and imaging pulses. A more detailed model of the HMI process than previously published was made using finite element analysis. The model showed that the amplitude of harmonic motion was primarily affected by increases in acoustic attenuation and stiffness as the lesion formed and the interaction of these effects was complex and often counteracted each other. Further biological variability in tissue properties meant that changes in motion were masked by sample‐to‐sample variation. The HMI experiments predicted lesion formation in only about a quarter of the lesions made. In simultaneous AOI/HMI experiments it appeared that AOI was a more robust method for lesion detection. / Bernard M. Gordon Center for Subsurface and Imaging Systems (CenSSIS) via the NSF ERC award number EEC‐9986821.

Two issues hindering the clinical application of image-guided transcostal focused ultrasound surgery (FUS) are the organ motion caused by cardiac and respiratory movements and the presence of the ribcage. Intervening ribs absorb and reflect the majority of ultrasound energy excited by an acoustic source, resulting in insufficient energy delivered to the target organs of the liver, kidney, and pancreas. Localized hot spots also exist at the interfaces between the ribs and soft tissue and in highly absorptive regions such as the skin. The aim of this study is to assess the effects of transmitted beam distortion and frequency-dependent rib heating during trans-costal FUS, and to propose potential solutions to reduce the side effects of rib heating and increase ultrasound efficacy. Direct measurements of the transmitted beam propagation were performed on a porcine rib cage phantom, an epoxy rib cage phantom and an acoustic absorber rib cage phantom, in order of their similarities to the human rib cage. Finite element analysis was used to investigate the rib cage geometry, the position of the target tissue relative to the rib cage, and the geometry and operating frequency of the transducer. Of particular importance, frequency-dependent heating at the target and the intervening ribs were estimated along with experimental verification. The ratio of ultrasonic power density at the target and the ribs, the time-varying spatial distribution of temperature, and the ablated focus of each sonication are regarded as key indicators to determine the optimal frequency. Following that, geometric rib-sparing was evaluated by investigating the operation of 2D matrix arrays to optimize focused beam shape and intensity at target. Trans-costal FUS is most useful in treating tumours that are small and near the surface of the abdominal organs, such as the liver, kidney and pancreas. However, for targets deep inside these organs, severe attenuation of acoustic energy occurs, suggesting that pure ultrasound thermal ablation with different heating patterns will have limited effects in improving the treatment efficacy. Results also demonstrate that the optimal ultrasound frequency is around 0.8 MHz for the configurations considered, but that it may shift to higher frequencies with changes in the axial and lateral positions of the tumours. In this work, I aimed to reduce the side effects of rib heating and increase the ultrasound efficacy at the focal point in trans-costal treatment. However, potential advanced techniques need to be explored for further enhanced localized heating in trans-costal FUS.

acase@tulane.edu / Introduction: High-Intensity Focused Ultrasound (HIFU) is the only noninvasive method available today for thermal ablation of tumors. HIFU-induced rapid heating and mechanical disruption of tissue, not only has a direct destructive effect on tumors, but also provides a noninvasive way for targeted release of chemotherapeutic drugs from drug delivery vehicles such as temperature sensitive liposomes (SfTSLs). The objective of this work was to evaluate the synergistic treatment of Sorafenib-loaded TSLs (SfTSLs) and HIFU via in vitro analysis of cell viability and proliferation using an aggressive human liver cancer cell line and corresponding in vivo analysis of tumor growth and survival using a human xenograft mouse model. Materials and Methods: Liposomes were developed using 70% Dipalmitoylphosphatidylcholine, 20% L-a-Phosphatidylcholinehydrogenated Soy, and 10% Cholesterol using thin film hydration method to encapsulate Sorafenib at 10μM. Pellets of Hep3B human liver cancer cells (100 μl, 2.7 million cells/ml) were placed in a 0.2 ml thin-wall PCR tube to mimic dense tumor aggregation. Cell pellets were then inoculated with HIFU alone, SfTSLs, or exposed to a combination of HIFU and SfTSLs. The focused ultrasound signal was generated by a 1.1 MHz transducer with acoustic power ranging from 4.1 W to 12.0 W. Cell viability and proliferation experiments were conducted to measure cancer cell damage at 24, 48, 72, and 96 h post treatment via Annexin V/PI and WST-8 staining. In our in vivo study, 1.0×106 Hep3B cells in Matrigel were injected into left and right flanks of athymic nude mice. Tumors were allowed to grow to 8-10 mm size and then separated into the following treatment groups: HIFU alone, SfTSLs (50 μl) alone, SfTSLs + HIFU, and sham. Tumor sizes were measured by caliper every day and a diagnostic ultrasound system was used pre-treatment, 5 days, 14 days, and prior to sacrificing. Tumors were grouped and processed at 5 days, 14 days, or placed in a survival study to evaluate whether treatment facilitated longer lifespans. Tumor tissues were collected for H&E staining and evaluated by a blinded pathologist post euthanasia. Results and Discussion: Our in vitro data indicate that Hep3B cells exposed to both SfTSLs and HIFU have a significantly lower viability and proliferation rate than untreated cells or the cells treated with only SfTSLs or HIFU. According to our in vivo study, tumor growth in the SfTSLs + HIFU group was reduced as compared to Sham, SfTSLs only, or HIFU only groups. Conclusions: The results of our in vitro and in vivo experiments clearly indicate that chemotherapeutic drug-loaded SfTSLs and HIFU can be an effective therapy for locally aggressive liver cancer. This combination treatment leads to more cellular damage, reduction in tumor growth, and better survival. / 1 / Gray Halliburton

High Intensity Focused Ultrasound (HIFU) is a promising technique for the treatment of localized cancers. The ability to focus ultrasound precisely on a predetermined volume allows the possibility of selective tissue destruction at this position without damage to surrounding tissues. However, many difficulties remain in the treatment of deep-seated tumors. In this thesis, new therapeutic and monitoring techniques are proposed to address these problems, by using phased arrays of ultrasound transducers. Two monitoring techniques based on the detection of the displacements of the ultrasonic speckle are developed, and allowed us to image the changes in the temperature and the shear modulus during HIFU therapy. In-vitro ultrasound-guided experiments are performed. Secondly, the problem of organs motion during the treatment is addressed. A method for real-time tracking the 3D motion of tissues is combined with a 2D High Intensity Focused Ultrasound multi-channel system in order to correct the respiratory motion during HIFU therapies. In the last section of this thesis, a high power ultrasonic system is developed for transcranial HIFU brain therapy. The skulls aberrations are corrected using a time reversal mirror thanks to an implanted hydrophone. In-vivo experiments are conducted on 22 sheep with minimally invasive surgery. Finally, a non-invasive protocol based on CT scans of the entire skull is developed and allows the prediction of the skulls aberrations and the skull overheating.