Evaluation of referenceless thermometry in MRI-guided focused ultrasound surgery of uterine fibroids.
OBJECTIVE
To clinically assess a previously described method (Rieke et.al., Magn Reson Med 2004) to produce more motion-robust MRI-based temperature images using data acquired during MRI-guided focused ultrasound surgery (MRgFUS) of uterine fibroids.


METHODS
The method ("referenceless thermometry") uses surface fitting in nonheated regions of individual phase images to extrapolate and then remove background phase variations that are unrelated to temperature changes. We tested this method using images from 100 sonications selected from 33 patient MRgFUS treatments. Temperature measurements and thermal dose contours estimated with the referenceless method were compared with those produced with the standard phase-difference technique. Fitting accuracy and noise level were also measured.


RESULTS
In 92/100 sonications, the difference between the two measurements was less than 3 degrees C. The average difference in the measurements was 1.5 +/- 1.4 degrees C. Small motion artifacts were observed in the phase-difference imaging when the difference was greater than 3 degrees C. The method failed in two cases. The mean absolute error in the surface fit in baseline images corresponded to a temperature error of 0.8 +/- 1.4 degrees C. The noise level was approximately 40% lower than the phase-difference method. Thermal dose contours calculated from the two methods agreed well on average.


CONCLUSIONS
Based on the small error when compared with the standard technique, this method appears to be adequate for temperature monitoring of MRgFUS in uterine fibroids and may prove useful for monitoring temperature changes in moving organs.
McDannold
Nathan
N
Department of Radiology, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA. njm@bwh.harvard.edu
Tempany
Clare
C
Jolesz
Ferenc
F
Hynynen
Kullervo
K
D000465:Algorithms; D001831:Body Temperature; D005260:Female; D006801:Humans; D007889:Leiomyoma / Q000601:surgery*; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods*; D013817:Thermography / Q000379:methods*; D016896:Treatment Outcome; D014464:Ultrasonic Therapy / Q000379:methods*; D014594:Uterine Neoplasms / Q000601:surgery*