American Journal of Neuroradiology, Vol 17, Issue 9 1675-1680, Copyright © 1996 by American Society of Neuroradiology
ARTICLES |
Reverse enhancement of hemorrhagic brain lesions on postcontrast MR: detection with digital image subtraction
HP Gaul, CJ Wallace and AP Crawley
Department of Radiological Sciences and Diagnostic Imaging, Foothills Hospital, Calgary, Alberta, Canada.
PURPOSE: To investigate the decrease in signal intensity on T1 - weighted MR images of some hemorrhagic intracranial lesions after administration of contrast material. METHODS: Postprocessing digital image subtraction was performed in 16 MR studies (13 patients) of lesions that showed hyperintensity on noncontrast T1-weighted images. Repetition time and echo time were identical for all precontrast and postcontrast studies. Regions of interest were measured in each lesion, contralateral white matter, and background (before and after contrast enhancement). RESULTS: In six of 16 MR studies, a significant net decrease in signal intensity was seen within the hemorrhagic lesion after contrast enhancement (reverse enhancement). All the lesions were hematomas within residual or recurrent malignant tumors. CONCLUSIONS: Digital image subtraction confirms the existence of reverse enhancement. This phenomenon is due to the combined T2-shortening effects of two paramagnetic substances, methemoglobin and gadolinium, which cause the signal reduction produced by the T2 effects to occur at lower concentrations of gadolinium.
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