Detection of muscle layer invasion with submillimeter pixel MR images: staging of bladder carcinoma

Conventional magnetic resonance (MR) images used for the pelvic organs generally have a pixel size of 1.3 mm x 1.3 mm. We obtained images with a higher resolution than conventional images, and evaluated the usefulness of this type of image in staging urinary bladder carcinoma. Twenty-six patients having either transurethral resection of bladder tumor (TUR-BT) or cystectomy were retrospectively studied. T2-weighted images of the bladder were acquired with a 20 cm field-of-view, a matrix size of 224 x 224 (pixel size: 0.9 mm x 0.9 mm), and a slice thickness of 7 mm using a 0.5 T system. MR appearances of the carcinoma were divided into the following five categories: no abnormality found on the inner surface of the bladder wall (0), high signal layer or protrusion without breakage of the wall (I), partial disruption of the wall (II), transmural disruption of the wall (III), and complete disruption with mass formations in the perivesicular region (IV). These findings were correlated with the TNM pathologic staging determined from each tissue specimen. A prediction for muscle layer invasion was calculated by selecting pathologic stage pT2 and MR category III as a boundary measure. The accuracy was 96.2%, the sensitivity 100.0%, and the specificity 91.7%. The results obtained indicate that submillimeter pixel MR imaging shows promise as a noninvasive method for the preoperative staging of bladder cancers.