Ultrasound Beam Path Research Articles

MRI-guided focused ultrasound surgery in the brain: tests in a primate model.

MRI-guided focused ultrasound was tested in the brains of rhesus monkeys. Locations up to 4.8 cm deep were targeted. Focal heating was observed in all cases with MRI-derived temperature imaging. Subthreshold heating was observed at the focus when the ultrasound beam was targeted with low power sonications, and in the ultrasound beam path during high-power exposures. Lethal temperature values and histologically confirmed tissue damage were confined to the focal zone (e.g., not in the ultrasound beam path), except when the focus was close to the bone. In that case, damage to the neighboring brain tissue was observed. Focal lesions were observed on histological examination and, in some cases, in MR images acquired immediately after the ultrasound exposures. The capabilities demonstrated in this study will be of benefit for clinical ultrasound therapies in the brain.

In situ exposimetry: The ovarian ultrasound examination

We have constructed a specialized in vivo exposimetry system and developed and tested customized software using specially fabricated hydrophones. We placed the hydrophones in the lateral vaginal fornix as close to the ovary as possible (usually 1–2 cm from the ovary) and determined selected first-order and second-order ultrasonic field quantities during a routine ultrasound examination of the ovary. Our sonographic measurements yielded mean ultrasound beam path distances of 7.6 cm. ( n =18) in the presence of a distended bladder and 7.0 cm. ( n = 25) in the presence of an empty bladder with an average group insertion loss of 6.2 dB and 7.3 dB, respectively. Using a Fixed Attenuation Model, the tissue attenuation coefficient value was 2.98 dB/MHz; whereas for the Overlying Tissue Model the value was 0.72 dB/cm-MHz. These data are both specific and unique in that they have been systematically obtained in situ.