MR imaging-guided percutaneous cryoablation of the prostate in an animal model: in vivo imaging of cryoablation-induced tissue necrosis with immediate histopathologic correlation.
OBJECTIVE
To evaluate the feasibility of magnetic resonance (MR) imaging-guided percutaneous cryoablation of normal canine prostates and to identify MR imaging features that accurately predict the area of tissue damage at a microscopic level.


METHODS
Six adult male mixed-breed dogs were anesthetized, intubated, and placed in a 0.5-T open MR imaging system. A receive-only endorectal coil was placed, and prostate location and depth were determined on T1-weighted fast spin-echo (FSE) MR imaging. After placement of cryoprobes and temperature sensors, three freezing protocols were used to ablate prostate tissue. Ice ball formation was monitored with T1-weighted FSE imaging. Tissue necrosis area was assessed with contrast-enhanced weighted MR imaging and compared with histopathologic findings.


RESULTS
A total of 12 cryolesions (mean size, 1.2 cm) were bilaterally created in six prostates. Ice ball formation was oval and signal-free on T1-weighted FSE sequences in all cases. Postprocedural contrast-enhanced MR imaging typically showed a nonenhancing area of low signal intensity centrally located within the frozen area, surrounded by a bright enhancing rim in all cases. On histopathologic examination, two distinct zones were identified within cryolesions. Centrally, a necrotic zone with complete cellular destruction and hemorrhage was found. Between this necrotic zone and normal glandular tissue, a zone of fragmented and intact glands, interstitial edema, and rare acute inflammatory cells was seen. Correlation between nonenhancement on contrast-enhanced weighted MR images and tissue necrosis on pathologic examination was consistent within all six dogs.


CONCLUSIONS
MR imaging-guided cryoablation of the prostate is technically feasible. The nonenhancing area on postablation contrast-enhanced weighted MR imaging accurately predicts the area of cryoablation-induced tissue necrosis on pathologic analysis.
van den Bosch
Maurice A A J
MA
Department of Radiology, Stanford University, 1201 Welch Road, Stanford, CA 94305-5488, USA. maaj.vandenbosch@gmail.com
Josan
Sonal
S
Bouley
Donna M
DM
Chen
Jin
J
Gill
Harcharan
H
Rieke
Viola
V
Butts-Pauly
Kim
K
Daniel
Bruce L
BL
D000818:Animals; D003452:Cryosurgery / Q000379:methods*; D004285:Dogs; D005240:Feasibility Studies; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011467:Prostate / Q000473:pathology* / Q000601:surgery*; D011468:Prostatectomy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000379:methods*