Fatty tissue on opposed-phase MR images: paradoxical suppression of signal intensity by paramagnetic contrast agents.

PURPOSE: To evaluate paradoxically decreased signal intensity on gadolinium-enhanced opposed-phase magnetic resonance (MR) images of fatty tissues. MATERIALS AND METHODS: Unenhanced and gadolinium-enhanced axial, opposed-phase, gradient-echo images were analyzed visually and with region-of-interest measurements. Tissues measured included adipose tissue (n = 10), angiomyolipomas (n = 8), and vertebral hemangiomas (n = 7). Additionally, a phantom of mayonnaise, soybean oil, agarose, and water (63% lipid signal) with variable concentrations of gadolinium chelate was imaged with similar technique. RESULTS: After administration of gadolinium chelate, signal intensity reduction averaged 18% for adipose tissue, 34% (72-48 units) for predominately fatty angiomyolipomas, and 39% (85-52 units) for vertebral hemangiomas. Imaging of the phantom showed a maximum of 79% reduction in signal intensity with gadolinium chelate (227-47 units). DISCUSSION: Gadolinium-enhanced opposed-phase images depict a significant loss in signal intensity in tissues with MR signal predominately from lipid. Gadolinium chelate increases the signal of water within fatty tissues, which increases the amount of lipid signal suppression due to destructive interference between water and lipid proton magnetizations.