Determination of a cutoff attenuation value on single-phase contrast-enhanced CT for characterizing adrenal nodules via chemical shift MRI.

Purpose: This study aims to determine the optimal cutoff attenuation value on single-phase contrast-enhanced CT (CECT) at which chemical shift MRI (CSMRI) yields sufficient accuracy to replace the standard CT adrenal protocol for the diagnosis of adrenal adenomas.

Methods: Between January 2010 and December 2014, a total of 49 patients (age: 20-81 years; 23 men and 26 women) with 60 adrenal tumors (48 adenomas and 12 non-adenomas) who underwent both CECT in portal venous phase and CSMRI were included in the study. Attenuation on portal venous phase CECT, adrenal-to-spleen chemical shift ratio (ASR), and signal-intensity index (SII) were obtained for each adrenal mass.

Results: Among different cutoff values on CECT (from <70 to <120 HU), the diagnostic accuracies for those lesions measuring <80 HU were the highest and most similar to dedicated adrenal CT. The sensitivities and specificities of SII were up to 96% (25/26) and 100% (7/7) for those measuring <80 HU, but reduced to 73% (16/22) and 80% (4/5) for those ≥80 HU. The overall sensitivities and specificities for diagnosing adrenal adenoma using SII vs. ASR were 85% (41/48) and 92% (11/12) vs. 71% (34/48) and 100% (12/12), respectively.

Conclusions: CSMRI may replace CT adrenals in the work-up of patients with adrenal nodules below 80 HU on single-phase CECT, hence reducing radiation exposure and iodinated contrast administration. Adrenal nodules greater than 80 HU cannot be accurately diagnosed by CSMRI. CT adrenal protocol remains the appropriate investigative modality in those cases.