Patient-specific approach for real-time aberration correction in therapeutic ultrasound

In therapeutic ultrasound, the knowledge of patient-specific tissue properties is one of the challenging problems in planning transcutaneous high-intensity focused ultrasound (HIFU) exposures and aberration correction when focusing through inhomogeneous layers of soft tissues. The aberrations can be corrected using multi-element HIFU arrays by applying time delays to each element to compensate for beam distortions caused by variations in the thickness and sound speed of the tissue layers in the beam path. Various solutions have been proposed to determine these time delays. Here we assess the approach that is based, as the first step, on the preliminary CT scan that provides patient-specific values of acoustic properties of fat, which is the most aberrative soft tissue, and other tissues. The second step is to perform a 3-D ultrasound (US) pulse-echo scan immediately before the therapeutic procedure using the imaging probe combined with a therapeutic transducer. Rapid segmentation of the US scan into the fat/nonfat tissue types and calculation of the required time delays using CT-based acoustic properties enable preliminary correction phases for focusing over the target area. The proposed approach is assessed using an ex vivo porcine body wall embedded in the agarose gel and processed through CT and 3-D ultrasound scans, and simulations using the corresponding CT-based and US-based acoustic models.