A pre-treatment planning strategy for high-intensity focused ultrasound treatments.

Abstract

High-intensity focused ultrasound (HIFU) therapy is a non-invasive treatment method for uterine fibroids patients. However, there exists focal distortion, due to inhomogeneous tissues, that can divert therapeutic dosage to non-targeted locations. A missing component of current HIFU protocols is a simulated pre-treatment planning, a procedure that can predict the efficiency of ultrasonic energy delivery pathways based on MRI scans using a simulated propagation model. To conduct this study, a 1.502-MHz transducer transmitted HIFU through five ex vivo bovine tissue specimens in an MR-compatible tank setup. A needle hydrophone (aperture = 0.2 mm) scanned the acoustic pressure field orthogonal to the axis of propagation for three different positions of the tissue specimens (0, 4, and 8 deg, about the rotation mounts). To quantify the level of distortion, the distortion index (DI = 1—ratio between local and total acoustic energy fields) were calculated. The data collected confirmed HIFU distortion due to tissue, where 48% of the focal acoustic intensity was redistributed away from the focal field. Focal distortion decreased on average by 7.2% (ranging from 5.6% to 12.3%, SD = 2.8%) upon optimizing the transducer-specimen orientation the default transducer orientation (0 deg). In addition, the propagation simulation model accurately predicted HIFU distortion from a specimen’s MRI data.