Differentiation of volume averaging and mass on magnetic resonance images of the mediastinum.

Volume averaging of high intensity mediastinal fat and low intensity flowing blood in mediastinal vessels can mimic a mediastinal mass on magnetic resonance (MR) images of the chest. However, when different repetition times (TR) are used to perform two imaging sequences, volume averaging can be distinguished from true disease, since the ratio of intensities of mediastinal fat, which is volume averaged, to nonvolume-averaged fat will remain relatively constant on a pair of images obtained using different TR times. Mediastinal masses, on the other hand, will exhibit predictable alterations in intensity relative to fat with changing TR.