Value of subtraction images in the detection of hemorrhagic brain lesions on contrast-enhanced MR images.

Contrast-enhanced T1-weighted MR images are known to improve the detection and conspicuity of CNS lesions; however, lesion enhancement may be indistinguishable from contiguous hemorrhagic areas of intrinsically increased signal intensity. In a series of cranial MR studies in 22 pediatric oncologic patients with evidence of subacute hemorrhage, we found that subtracting the unenhanced from the enhanced T1-weighted images was essential in 14 of the cases to visualize and/or characterize the enhanced tissue in the presence of adjacent hemorrhage. In six patients, a nodular pattern of enhancement suggestive of tumor was detected and/or outlined only after subtraction. In eight patients, linear benign-appearing enhancing margins were seen clearly only after subtraction. In the remaining eight patients, the presence and shape of enhancement was verified with subtraction. Subtraction is a useful, simple, and rapid postprocessing procedure that does not increase scan time or require modification of standard pulse sequences. Subtraction separates the enhanced areas from adjacent bright hemorrhage.