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The objective of this study is to investigate the feasibility of elastographic monitoring of High Intensity Focused Ultrasound (HIFU) therapy of prostate cancer. Elastography is an imaging technique based on strain estimation in soft tissues under quasi-static compression. Since pathological tissues and HIFU-induced lesions exhibit different elastic properties than normal tissues, elastography is potentially able to achieve these goals. An ultrasound scanner was connected to a PC to acquire RF images. This setup is compatible with a HIFU device used for prostate cancer therapy by transrectal route. The therapy transducer and the biplane-imaging probe are covered with a balloon filled with a coupling liquid. Compression of the prostate is applied by inflating the balloon, while imaging sector scans of the prostate. In-vivo elastograms of the prostate were acquired before HIFU treatment. Problems inherent to in-vivo acquisitions are reported, such as undesired tangential displacements during the radial compression. This study shows the potential for in-vivo elastogram acquisition of HIFU-induced lesions in the human prostate.

One technique of elasticity imaging, elastography, uses cross- correlation between two ultrasound A-lines to obtain an axial strain image of a sample. Usually, great care is taken with respect to the assumption that the response of the sample is elastic (lossless). In this paper, we relax this assumption and extend elastography to estimate the time-varying displacement and strain status of small samples (of the order of 1 mm). Results are presented for gel phantoms and articular cartilage samples, and they are consistent with the current theories of poroelastic materials. For example, an effective Poisson's ratio of approximately 0.5 obtained at ramp completion indicates volume conservation since the ramp time was much shorter than the characteristic relaxation time of the material. Subsequent reduction in effective Poisson's ratio coincident with stress-relaxation confirms poroelastic mechanisms whereby fluid exudation dissipates internal fluid pressurization. Observed slower relaxation of strain at the center of the sample is also compatible with these types of models. Preliminary data obtained with articular cartilage also shows valuable potential of this technique to investigate tissue biomechanics.