Self-adaptive ultrasonic beam amplifiers: application to transcostal shock wave therapy

Abstract

Ultrasound shock wave therapy is increasingly used for non-invasive surgery. It requires the focusing of very high pressure amplitude in precisely controlled focal spots. In transcostal therapy of the heart or the liver, the high impedance mismatch between the bones and surrounding tissues gives rise to strong aberrations and attenuation of the therapeutic wavefront, with potential risks of injury at the tissue-bone interface. An adaptive propagation of the ultrasonic beam through the intercostal spaces would be required. Several solutions have been developed so far, but they require a prior knowledge of the patient's anatomy or an invasive calibration process, not applicable in clinic. Here, we develop a non-invasive adaptive focusing method for ultrasound therapy through the ribcage using a time reversal cavity (TRC) acting as an ultrasonic beam amplifier. This method is based on ribcage imaging through the TRC and a projection orthogonally to the strongest identified reflectors. The focal pressure of our device was improved by up to 30% using such self-adaptive processing, without degrading the focal spots size and shape. This improvement allowed lesion formation in an Ultracal phantom through a ribcage without invasive calibration of the device. This adaptive method could be particularly interesting to improve the efficiency and the safety of pulsed cavitational therapy of the heart or the liver.

Four-dimensional computational ultrasound imaging of brain hemodynamics

“…It would be equally feasible to use cUSi with alternative transmission schemes. For example, sequential focusing on each point in the imaging medium via time reversal ( 33 ). While this would result in greater SNR, it would not be compatible with the volume rate necessary for ultrafast imaging of blood flow.…”

“…cUSi falls into the category of computational imaging, which covers techniques across a range of modalities that broadly aim to realize cheaper and/or faster imaging devices in part by shifting the burden of image formation from complex hardware onto computation (24)(25)(26)(27)(28)(29). Within the ultrasound domain, the exploitation of reverberant media to reduce the number of sensors required for imaging has been investigated since the 90s (30)(31)(32)(33). However, the translation of these methods to in vivo imaging has, traditionally, been hindered by challenges in separating backscattered signals from the transducer cross-talk as well as the high-sensitivity of these media to small perturbations (e.g., temperature shifts).…”

Estimation of the Born data in inverse scattering of layered media

“…Although these interactions furnish valuable information, they simultaneously pose considerable challenges to the development and application of inversion methods. To cope with the multiple scattering that leads to nonlinearity, one can either suppress it for a more linear problem [10,11] or fully utilize it for more information [12][13][14].…”