Magnetic resonance-guided high-intensity ultrasound ablation of the prostate.
OBJECTIVE
This paper describes our work in developing techniques and devices for magnetic resonance (MR)-guided high-intensity ultrasound ablation of the prostate and includes review of relevant literature.


METHODS
Catheter-based high-intensity ultrasound applicators, in interstitial and transurethral configurations, were developed to be used under MR guidance. Magnetic resonance thermometry and the relevant characteristics and artifacts were evaluated during in vivo thermal ablation of the prostate in 10 animals. Contrast-enhanced MR imaging (MRI) and diffusion-weighted MRI were used to assess tissue damage and compared with histology.


RESULTS
During evaluation of these applicators, MR thermometry was used to monitor the temperature distributions in the prostate in real time. Magnetic resonance-derived maximum temperature thresholds of 52 degrees C and thermal dose thresholds of 240 minutes were used to control the extent of treatment and qualitatively correlated well with posttreatment imaging studies and histology. The directional transurethral devices are selective in their ability to target well-defined regions of the prostate gland and can be rotated in discrete steps to conform treatment to prescribed boundaries. The curvilinear applicator is the most precise of these directional techniques. Multisectored transurethral applicators, with dynamic angular control of heating and no rotation requirements, offer a fast and less complex means of treatment with less selective contouring.


CONCLUSIONS
The catheter-based ultrasound devices can produce spatially selective regions of thermal destruction in prostate. The MR thermal imaging and thermal dose maps, obtained in multiple slices through the target volume, are useful for controlling therapy delivery (rotation, power levels, duration). Contrast-enhanced T1-weighted MRI and diffusion-weighted imaging are useful tools for assessing treatment.
Pauly
Kim Butts
KB
Department of Radiology, Stanford University, Stanford, CA 94305-5488, USA. kimbutts@stanford.edu
Diederich
Chris J
CJ
Rieke
Viola
V
Bouley
Donna
D
Chen
Jing
J
Nau
Will H
WH
Ross
Anthony B
AB
Kinsey
Adam M
AM
Sommer
Graham
G
D000818:Animals; D016477:Artifacts; D001831:Body Temperature; D002404:Catheterization / Q000295:instrumentation; D004285:Dogs; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011467:Prostate / Q000473:pathology*; D036761:Ultrasound, High-Intensity Focused, Transrectal / Q000295:instrumentation* / Q000379:methods*