NI-85DELAYED CONTRAST MRI FOR DIFFERENTIATING TUMOR/NON-TUMOR TISSUES IN BRAIN TUMOR PATIENTS - HISTOLOGICAL VALIDATION AND COMPARISON WITH DSC/DCE

BACKGROUND: Conventional MRI is unable to differentiate tumor/non-tumoral enhancing tissues on conventional T1-MRI (radionecrosis/pseudoprogression). We have applied delayed contrast MRI for calculating high resolution (1mm3) treatment response assessment maps (TRAMs) clearly differentiating tumor/non-tumoral tissues in brain tumor patients and validated the TRAMs histologically. We further assessed the sensitivity and positive predictive value (PPV) of rCBV/KTrans (DSC/DCE MRI) to tumor. METHODS: 162 patients with primary/metastatic tumors were recruited/followed on study. The maps were validated by comparing pre-surgical maps of 51 patients with histology. Histological evaluation consisted of blinded pathological reports and non-blinded evaluation of 62 biopsies and 8 en-block samples. The sensitivity/PPV of rCBV to tumor was studied for 46 resected patients, where rCBV was compared with histology. The sensitivity/PPV of rCBV/KTranse was studied separately for 49/42 non-resected patients where these parameters were compared with the TRAMs. RESULTS: Histological validation confirmed that regions of contrast agent-clearance > 1hr post contrast injection represent morphologically active tumor while regions of contrast accumulation represent non-tumor tissues. Based on the blinded histological reports, the TRAMs showed sensitivity/PPV to active tumor of 100%/92%. The addition of the non-blinded data resulted in sensitivity/PPV of 99%/95%. Significant correlation was found between tumor volumes in the TRAMs and in the en-block samples (r2 = 0.84, p < 0.0001). Comparison of rCBV with histology resulted in sensitivity/PPV of 51%/96%. When comparing rCBV/KTrans to the TRAMs we found a sensitivity of 23%/24% and PPV of 100%/90% to tumor regions in the TRAMs. The lower sensitivity of rCBV to tumor in the non-resected patients may be attributed to the larger percentage of smaller metastatic tumors that tend towards lower perfusion. CONCLUSIONS: Despite the high PPV of rCBV/KTrans to tumor, the low sensitivity suggests that 49%-76% of the tumors will remain undetected. Our data suggest that the TRAMs provide both high PPV and high sensitivity to tumor tissues.