IMG-60. Comparative evaluation of standardized relative cerebral blood volume (sRCBV) and fractional tumor burden (FTB) for predicting histologic diagnosis in brain tumors

BACKGROUND Contrast-enhanced MRI is the standard method by which the neurosurgical biopsy site is chosen even though tumor and non-tumor/necrosis appear similar. This limitation may result in underdiagnosis. Alternatively, previously validated standardized relative cerebral blood volume (sRCBV) thresholds can be used to create fractional tumor burden (FTB) maps that spatially distinguish regions of contrast-enhancing tumor from non-tumor and provide potentially more informative biopsy targets. This study evaluates the accuracy of sRCBV and FTB maps for this purpose. METHODS All patients provided written, informed consent to participate in this prospective HIPAA-compliant and IRB-approved study. Using Imaging Biometrics (Elm Grove, WI) software, FTB maps were generated by applying sRCBV thresholds to the contrast-enhancing regions defined on calibrated (dT1) difference maps. FTB maps were uploaded to a surgical navigation system where surgical trajectory placement was recorded during tissue biopsy. Classifications based on median sRCBV (≥/<1) and FTB (≥/<50%) were compared to the pathologic diagnosis for each biopsy sample. Accuracy was assessed along with Fisher’s exact test (p<.05), sensitivity and specificity, and positive and negative predictive values. RESULTS 21 biopsy samples were collected from 14 patients (7 male/7 female). MRI was performed a mean of 5 (1-8) days prior to biopsy. Histologic diagnoses of the biopsy samples included WHO 2021 grade 4 astrocytoma (N=1), glioblastoma with (N=3) and without (N=8) radiation effect, reactive changes without evidence of tumor (N=7), and metastatic disease (N=2). FTB (p<.0001) and sRCBV (p=.0055) were significantly associated with histologic outcome (Fisher’s exact test). Diagnostic accuracy was 95.2% (FTB) and 85.7% (sRCBV). Sensitivity/specificity were 92.9%/100% (FTB) and 92.9%/71.4% (sRCBV), with positive/negative predictive values of 100%/87.5% (FTB) and 86.7%/83.3% (sRCBV). CONCLUSION These initial results support the use of FTB and sRCBV to guide surgical biopsy, with FTB outperforming sRCBV. Future studies will assess both metrics in a larger cohort.