Determination of the optimal delay between sonications during focused ultrasound surgery in rabbits by using MR imaging to monitor thermal buildup in vivo.
OBJECTIVE
To use magnetic resonance (MR) imaging to monitor thermal buildup and its effects in treated tissues during sequentially delivered sonications in vivo to optimize the intersonication delay for any set of ultrasound and tissue parameters.


METHODS
Sequential sonications were delivered next to each other in both thighs in 10 male New Zealand white rabbits. The time between sonications was 11-60 seconds. Phase-difference MR imaging was used to monitor temperature rise, which was used to estimate the thermal dose delivered to the tissue. T2-weighted and contrast agent-enhanced T1-weighted imaging were used to gauge the extent of tissue coagulation.


RESULTS
With a short intersonication delay (11-40 seconds), the estimated temperature rise and the extent of tissue coagulation increased dramatically in subsequent sonications. However, when the delay was long (50-60 seconds), the size and shape of the destroyed tissue with subsequent sonications was uniform, and the temperature buildup was substantially lower.


CONCLUSIONS
MR imaging can be used to monitor thermal buildup and its effects due to sequential, neighboring sonications in vivo to produce evenly shaped regions of tissue coagulation. The temperature information obtained from the monitoring can be used to optimize the intersonication delay for any set of ultrasound and tissue parameters.
McDannold
N J
NJ
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Jolesz
F A
FA
Hynynen
K H
KH
D000818:Animals; D008279:Magnetic Resonance Imaging; D008297:Male; D011817:Rabbits; D013010:Sonication; D013997:Time Factors; D014464:Ultrasonic Therapy / Q000379:methods*