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A retrospective review of brain tumors examined with magnetic resonance imaging has shown that 12% of tumors or their components do not display evidence of an increase in T1 or T2 when examined with highly T1 dependent inversion recovery of highly T2 dependent spin echo sequences. This was observed in lipid containing tumors, malignant melanomas, tumors containing hemorrhage, acoustic neuromas, meningiomas, hamartomas, a pituitary prolactinoma, astrocytomas (grade I) treated with radiotherapy, pediatric tumors, and cases of unknown cause.
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Mackay et al. (1985) studied this question.
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