Thermal effects of focused ultrasound on the brain: determination with MR imaging.
OBJECTIVE
To determine the feasibility of the use of temperature-sensitive magnetic resonance (MR) imaging for the detection of local temperature elevations at the focus of a low-power ultrasound beam in the brain.


METHODS
The brains in 28 rabbits were sonicated at acoustic power levels of 3.5-17.5 W. Four to five different locations were sonicated at different acoustic power levels in each rabbit. MR images were obtained 2 hours, 48 hours, 10 days, and 23 days after the sonications, depending on when the animals were sacrificed. Histologic evaluation of whole brain was performed.


RESULTS
Forty of 43 (93%) of the lowest-power (3.5-W) sonications were visible on temperature-sensitive MR images and did not result in any short- or long-term histologic or MR imaging evidence of tissue damage. A contrast-to-noise ratio of approximately 6 and a temperature elevation of 7 degrees-8 degrees C were observed.


CONCLUSIONS
Temperature elevations induced by means of focused ultrasound exposures that do not cause damage in the in vivo rabbit brain can be detected at temperature-sensitive MR imaging.
Hynynen
K
K
Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
Vykhodtseva
N I
NI
Chung
A H
AH
Sorrentino
V
V
Colucci
V
V
Jolesz
F A
FA
D000818:Animals; D001706:Biopsy; D001831:Body Temperature; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000628:therapy*; D004195:Disease Models, Animal; D005240:Feasibility Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008991:Monitoring, Physiologic; D011817:Rabbits; D013997:Time Factors; D014464:Ultrasonic Therapy / Q000379:methods*; D018084:Ultrasonography, Interventional / Q000379:methods*