Comparative evaluation between external phased array coil at 3 T and endorectal coil at 1.5 T: preliminary results

Abstract

Objective: The aim of this study was to compare the image quality and the diagnostic accuracy of endorectal coil 1.5 T MRI (erMRI) and phased-array coil 3 T MRI (3-T MRI) in the pretherapeutic staging of prostate cancer.

Methods: Twenty-nine consecutive patients, with pathological proven prostate cancer, have been examined in the same week with both erMRI and 3-T MRI. Two radiologists independently evaluated the image quality focusing on the following points: cancer tissue conspicuity, capsular infiltration and tumor involvement of seminal vesicles, neuro-vascular bundles, and apex. The radiologists assigned to each one of the above findings an image-quality score ranging from 1 to 5 (with 1 meaning "not visible," 2 "poorly visible," 3 "fairly visible," 4 "well visible with some artifacts," and 5 "clearly visible without artifacts".) Afterwards a comparative evaluation of the mean score obtained respectively by erMRI and 3 T MRI was done. Twenty-two of these 29 patients underwent radical prostatectomy. Assuming as gold standard the pathological report from the resected specimen, we compared the diagnostic accuracy of 3TMRI and erMRI in differentiating between tumors confined within the prostate gland (stage<or=T2) and tumors extending through the prostatic capsule (stages T3 and T4).

Results: erMRI's image quality was found to be statistically significantly better than 3 T MRI's in evaluating tumor conspicuity, capsular infiltration, and seminal vesicles involvement. On the other hand, considering apex and NVB involvement no statistically significant difference was found between the 2 techniques. On the diagnosis of intracapsular or extracapsular tumor spread 3 T MRI and erMRI showed a comparable performance of sensitivity (75% vs. 83%), specificity (90% vs. 90%), positive predictive value (90% vs. 90%), and negative predictive value (75% vs. 81%).

Conclusions: During preoperative prostate cancer staging, 3 T MRI, despite a slightly worse image quality, can provide comparable diagnostic information to erMRI.