Magnetic resonance imaging in acute and subacute mediastinal bleeding.

The appearance of intracranial hematoma on magnetic resonance (MR) images has been described. However, the appearance of hematoma on ECG-gated spin-echo images, which are used for cardiac imaging, has not been described previously. Accordingly a retrospective analysis of nine consecutive patients with acute and subacute mediastinal bleeding imaged with ECG-gated spin-echo MR images was done. The time interval between the incipient event and the date of the MR study was determined, and the signal appearance of the hemorrhage was evaluated relative to striated muscle and fat. MR findings were corroborated by other imaging modalities and surgical findings. Acute hematomas showed medium to high signal intensity, whereas subacute hematomas had areas of high signal intensity on images acquired with ECG gating to every heart beat (repetition time = R-R interval) and a short echo time (30 msec). The characteristic signal intensities of blood on ECG-gated MR images are usually distinct in comparison to other pericardial and mediastinal fluid collections. The ability of MR to specifically identify blood within the first few hours after hemorrhage was not tested in this study.