Focal beam distortion and treatment planning for transrib focused ultrasound thermal therapy: a feasibility study...

The purpose of this study is to numerically investigate the feasibility of employing a spherical-section ultrasound phased array for transrib thermal ablation of liver tumors.

Based on CT images, the authors performed a 3D reconstruction of the ribs and the surrounding soft tissues. A 3D pseudospectral time-domain (PSTD) solver was used to assess wave propagation and the distribution of pressure, with the aim of determining the specific absorption rate (SAR) and the resulting thermal doses and dynamics. Phase aberrations caused by the interposed ribs were corrected to assess the efficacy of the device in improving the SAR gain between the ribs and the target positions.

Experimental results supported the usefulness of the PSTD solver for predicting the pressure distribution due to the interfering obstacle. In addition, the method allowed the correction of phase aberrations caused by the ribs, and a significant improvement (176%) in the SAR gain between the ribs and the target points was observed at specific frequencies.

The method allowed successful tissue targeting without causing overheating of the ribs. One main advantage of this approach is the accurate estimation of phase aberration caused by heterogeneously porous ribs and other interposed tissues. This strategy might prove useful to assess the effectiveness and safety of focused ultrasound thermal ablation prior to transrib treatment.