An MR-compatible phantom for evaluating the propagation of high intensity focused ultrasound through the skull.

BACKGROUND: In this paper an MR-compatible phantom for evaluating the propagation of high intensity focused ultrasound through the skull is presented. METHODS: The phantom was constructed using the thermoplastic material of ABS. The attenuation of ABS was measured using the transmission-reception method. Knowing the attenuation of human skull, the thickness of the phantom was chosen appropriately so as to achieve the same attenuation effect as in the case of human skull. The phantom was designed using CAD software and then manufactured in a rapid prototyping machine. In order to test the phantom a single element spherically focused transducer of 5 cm diameter, focusing at 10 cm and operating at either 0.5 MHz or 1 MHz was used. Brain tissue was mimicked either using gel phantoms or freshly excised tissue. RESULTS: The measured temperature due to an ultrasonic exposure with the presence of skull and without the skull was measured. It was found that the propagation of ultrasound through the skull was much better with the 0.5 MHz transducer. The skull phantom was tested also inside an MRI scanner, and we were able to detect temperature using the MRI technique of FSPGR indicating that with low frequency ultrasound propagation through the skull is possible. CONCLUSIONS: The skull phantom is a very successful tool for evaluating the propagation of ultrasound during the presence of skull. [ABSTRACT FROM AUTHOR]