Correlation between high field MR images and histopathological findings of rat transplanted cancer immediately after partial microwave coagulation.
OBJECTIVE
To investigate the immediate effects of microwave coagulation on rat tumors in various magnetic resonance (MR) images at high magnetic field strength using histopathological examinations as reference.


METHODS
Tumors implanted in rat femurs were partially thermocoagulated by microwave. Immediately after, T1- and T2-weighted images, diffusion-weighted images (DWIs), and contrast-enhanced T1 weighted images (CE-T1WIs) were acquired with a 7-tesla MR scanner. After measurements, tumors were examined histopathologically with hematoxylin-eosin (HE) staining and histochemically for acid phosphatase activity.


RESULTS
Without contrast, boundaries of coagulated areas were unclear on MR images, including apparent diffusion coefficient (ADC) maps. CE-T1WIs clearly showed immediate contrast enhancement of untreated areas of tumor, and the area of enhancement gradually enlarged in 5 min. Quantitative analyses were conducted by classifying tumor areas by contrast enhancement results. Signal intensities of the areas in the MR images showed no significant differences, but at the periphery, ADC values were significantly higher in areas with delayed enhancement than those with immediate enhancement. Compared with histopathological findings, with microwave thermocoagulation, increased ADC value seemed to derive from collection of extracellular fluid in the outer zone, where acid phosphatase activity was attenuated.


CONCLUSIONS
ADC values in the areas with delayed enhancement of CE-T1WIs were higher than those in non-affected areas, but MR images could not show areas of coagulation within tumors. Clear detection of the boundaries of coagulated areas required contrast enhancement, even at magnetic field strength of 7T.
Murakami
Koichiro
K
Department of Surgery, Shiga University of Medical Science, Shiga, Japan. emkami@belle.shiga-med.ac.jp
Morikawa
Shigehiro
S
Naka
Shigeyuki
S
Demura
Koichi
K
Sato
Koichiro
K
Shiomi
Hisanori
H
Kurumi
Yoshimasa
Y
Inubushi
Toshiro
T
Tani
Tohru
T
D000818:Animals; D045744:Cell Line, Tumor; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004564:Electrocoagulation / Q000379:methods*; D005266:Femoral Neoplasms / Q000473:pathology* / Q000601:surgery*; D006801:Humans; D006979:Hyperthermia, Induced / Q000379:methods*; D008872:Microwaves / Q000627:therapeutic use*; D051381:Rats; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D016896:Treatment Outcome