Value of chemical shift subtraction MRI in characterization of adrenal masses

Abstract

OBJECTIVE. ne purpose of this study was to assess the advantages of the image subtraction technique in chemical shift MRI for the differentiation of adrenal adenomas from nonadenomas. SUBJECTS AND METHODS. Thirty-five patients with 42 adrenal masses (eight metastases and 34 nonfunctioning adenomas) underwent chemical shift MRI using a double-echo fast low-angle shot sequence. Subsequently, opposed-phase chemical shift MR images were subtracted from in-phase images, The subtraction images were assessed quantitatively and qualitatively. For quantitative assessment, the signal intensity values of the adrenal masses were measured by one investigator with manually defined regions of interest. Qualitative assessment of the subtraction images was performed independently by two investigators, who reported their confidence in diagnosing adenomas versus nonadenomas based on signal intensity of the adrenal masses on subtraction images. RESULTS. The mean signal intensities were significantly different between adenomas and metastases on subtraction images (213 vs 18: p < 0.0001). There was no overlap in signal intensities between adenomas and metastatic tumors, The accuracy in distinguishing adenomas from metastatic tumors was 100% if the cutoff value of the signal intensity selected was 36-106. Quantitative results corresponding to 100% specificity were also observed, with similar sensitivity. No difference in interpretation between the two investigators occurred. CONCLUSION. Chemical shift subtraction MRI provides a high confidence level in distinguishing adrenal adenomas from adrenal metastases. The image subtraction technique also facilitates quantitative and qualitative evaluation of adrenal masses in chemical shift MRI.