CONTRAST-ENHANCED FAST MRI IN DIFFERENTIATING BRAIN TOXOPLASMOSIS ANDLYMPHOMA IN AIDS PATIENTS

Objective: Dynamic contrast-enhanced MRI was used to investigate space -occupying lesions of the brain in 22 AIDS patients without prior neur ologic disease. Final diagnoses were toxoplasmosis in 13 patients (19 lesions), primary lymphoma in 7 patients (9 lesions), and both disease s in two (2 lesions, respectively). Materials and Methods: Dynamic con trast-enhanced MRI was done by using a heavily T1-weighted GE sequence (TRITE 100/5, 80 degrees flip angle) performed before and repeatedly for a period of 15 min after intravenous bolus injection of Gd-DOTA (0 .1 mmol/kg). Signal enhancement of the lesions and normal brain was me asured as the difference of signal intensity before and after intraven ous administration of contrast medium. Results: Lymphomas displayed si gnificantly greater enhancement (mean 67%; SD 18%) than toxoplasmosis did (mean 34%; SD 16%; p < 0.001) on FLASH images. The enhancement rat ios of the two lesions were significantly (p < 0.01) different between 30 and 600 s after injection. The difference between toxoplasmosis (m ean 49%; SD 17%) and lymphoma (mean 69%; SD 26%) enhancement ratios on delayed SE images was less significant(p = 0.04). Conclusion: Prelimi nary evidence suggests that dynamic sequences increase the specificity of MR in distinguishing between toxoplasmosis and lymphoma, and this has important clinical implications.