Patient-Specific 3-Dimensional Model for High-Intensity Focused Ultrasound Treatment Through the Rib Cage: A Preliminary Study.

Abstract

The purpose of this study was to develop a patient-specific 3-dimensional model for high-intensity focused ultrasound (HIFU) treatment through the rib cage using patient data. Experimental testing to derive parameters used in defining the amount of energy and alteration needed in treatment protocols for upper abdominal disorders under the rib cage was performed. Reconstructed rib cage models based on patient data, tissue-mimicking material phantoms, and magnetic resonance imaging-guided HIFU using a multielement phased array transducer were used in the experiments. Changes in the focal temperature, acoustic power, and acoustic pressure distribution were investigated with and without the presence of the rib cage model. An ExAblate system (InSightec Ltd, Tirat Carmel, Israel) was used to sonicate phantoms by varying the target phantom or rib cage model location. The effect of the rib cage on the acoustic pressure distribution and acoustic power was closely related to the anatomic structures of the ribs. Thermometry revealed that heating at the focus could be controlled by changing either the power or duration of HIFU application to improve the focal temperature change. The focal temperature change was found to be related to the distance between the rib cage model and focus and the shadow area on the transducer elements covered by the rib cage model in the beam path. Experimental results suggest that the rib cage model is a valuable and useful tool that can provide realistic human anatomic structures and properties for evaluating the effects of the rib cage on ultrasound propagation.