Using the modified Dixon technique to evaluate incidental adrenal lesions on 3T MRI

To use the mDIXON-Quant sequence to quantify the fat fraction of adrenal lesions discovered incidentally on CT studies. To analyze the relation between the signal loss between in-phase and out-of-phase T1-weighted sequences and the fat fraction in mDIXON-Quant. To compare the sensitivity and specificity of the two methods for characterizing adrenal lesions.

This prospective descriptive study included 31 patients with incidentally discovered adrenal lesions evaluated with 3T MRI using in-phase and out-of-phase T1-weighted sequences and mDIXON-Quant; the fat fraction of the adrenal lesions was measured by mDIXON-Quant and by calculating the percentage of signal loss between in-phase and out-of-phase T1-weighted sequences.

The percentage of signal loss was significantly higher in the group of patients with adenoma (61.3% ± 20.4% vs. 5.1% ± 5.8% in the group without adenoma, p<0.005). The mean fat fraction measured by mDIXON-Quant was also higher for the adenomas (26.9% ±10.8% vs. 3.4% ± 3.0%, p<0.005).The area under the ROC curve was 0.99 (0.96 - 1.00) for the percentage of signal loss and 0.98 (0.94 - 1.00) for the fat fraction measured by mDIXON-Quant. The cutoffs obtained were 24.42% for the percentage of signal loss and 9.2% for the fat fraction measured by mDIXON-Quant. The two techniques had the same values for diagnostic accuracy: sensitivity 96% (79.6 - 99.9), specificity 100% (39.8 - 100.0), positive predictive value 100% (85.8 - 100.0), and negative predictive value 80% (28.4 - 99.5).

The fat fraction measured by the modified Dixon technique can differentiate between adenomas and other adrenal lesions with the same sensitivity and specificity as the percentage of signal loss between in-phase and out-of-phase T1-weighted sequences.