K

SI = 29

Fig. 2. Left adrenal adenoma in a patient with lung cancer. Chemical-shift MRI shows significant signal decrease on opposed phase (b), compared to the in-phase image (a)

Fig. 2. Left adrenal adenoma in a patient with lung cancer. Chemical-shift MRI shows significant signal decrease on opposed phase (b), compared to the in-phase image (a)

tent. The spleen has been shown to be the most reliable internal standard, although this might also be affected by iron overload [21].

To calculate the adrenal lesion to spleen ratio (ASR), regions of interest are used to acquire the SI within the adrenal mass and the spleen from in-phase and out-of-phase images. The ASR reflects the percentage signal drop-off within the adrenal lesion compared with the spleen and it can be calculated as follows:

SI lesion (out-of-phase) / SI spleen (out-of-phase) SI lesion (in-phase) / SI spleen (in-phase)

x 100

An ASR ratio of 70 or less has been shown to be 100% specific for adenomas but only 78% sensitive [21-23].

Simple visual assessment of relative signal intensity loss is just as accurate, but quantitative methods might be useful in equivocal cases. A signal intensity loss within an adrenal mass on out-of-phase images of greater than 20% is diagnostic of an adenoma [24].

The combination of spin-echo signal characteristics, gadolinium enhancement and CSI is currently 85-90% accurate in distinguishing adenomas from non-adenomas.

There are few direct comparisons between CT and MRI. Evidence from one histological study showed that because both non-contrast CT alone and CSI rely upon the same property of adenomas, namely their lipid content, the techniques correlate.

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