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Reverse enhancement of hemorrhagic brain lesions on postcontrast MR: detection with digital image subtraction
H P Gaul1, C J Wallace, A P Crawley
1Department 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.
Insights
Reverse enhancement, a decrease in T1 signal intensity in hemorrhagic lesions after contrast, was observed in MRI studies. This MRI phenomenon occurs in hematomas within malignant tumors due to paramagnetic effects.
Area of Science:
- Neuroradiology
- Magnetic Resonance Imaging (MRI)
- Medical Imaging Analysis
Background:
- Hemorrhagic intracranial lesions can exhibit variable signal intensity on MRI.
- Contrast agents are commonly used to enhance lesion conspicuition and characterization.
Purpose of the Study:
- To investigate the phenomenon of signal intensity decrease in T1-weighted MRI of hemorrhagic intracranial lesions after contrast administration.
- To identify the characteristics of lesions exhibiting this 'reverse enhancement'.
Main Methods:
- Digital image subtraction was employed on 16 MRI studies (13 patients) of lesions with pre-contrast T1 hyperintensity.
- Identical repetition and echo times were used for pre- and post-contrast scans.
- Signal intensity was measured in lesions, contralateral white matter, and background.
Main Results:
- Six out of 16 studies demonstrated a significant decrease in lesion signal intensity post-contrast (reverse enhancement).
- All identified lesions were hematomas associated with residual or recurrent malignant tumors.
Conclusions:
- Digital image subtraction confirms the occurrence of reverse enhancement in specific intracranial lesions.
- This MRI finding is attributed to the synergistic T2-shortening effects of methemoglobin and gadolinium contrast.
- The combined paramagnetic effects lead to signal reduction at lower gadolinium concentrations.