Imaging of the Scattering of High-Intensity Focused Ultrasonic Waves at Artificial Bone Replicas
High-intensity focused ultrasound is a technology currently used to treat bodily tissue for various medical purposes. For example, it has been applied for tissue ablation as a treatment for prostate cancer. However, the effective targeting of tissue deeper inside the body remains challenging because bones obstruct and scatter ultrasonic waves, which reduces the energy transmission to the desired location. Thus, understanding wave-scattering effects on focal point location and intensity is crucial for the expansion of the technology. Previous ultrasound visualization studies have not examined these effects in detail, especially for curved bone geometries.
Hence, in this work, the effects of bones on the transmission of focused ultrasound is investigated for hollow and solid cylindrical bone geometries. In laboratory experiments, images of wave fields are captured using shadowgraph techniques. The method uses a pulsed laser synced with a CMOS camera. Ultrasonic waves cause periodic local changes in density of the water, producing bright and dark patterns of laser transmission corresponding to the wave peaks and troughs. Improvements in the experimental setup and image processing compared to previous work allow for an expansion of the field of view with higher contrast. The bone replicas scatter the ultrasonic wave field and the effect of obstruction on ultrasound focal point intensities is quantified using pixel intensity measurements. In addition to visualization, differences in the pressure fields are recorded using a hydrophone and compared to the results obtained from the shadowgraph images. This experimental work provides a reference for future research in medical ultrasound and has the potential to lead to the development of methods that optimize the targeting of tissue deep in the human body.
KeywordsHigh-intensity focused ultrasound Wave scattering Bones Shadowgraphy Hydrophone
The RF amplifier provided by Dr. Ajit Mal (UCLA) is gratefully acknowledged.
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