Voxel-Based Analysis of Dual-Time-Point ¹⁸F-FDG PET Images for Brain Tumor Identification and Delineation

Abstract

We have investigated dual-time-point ¹⁸F-FDG PET for the detection and delineation of high-grade brain tumors using quantitative criteria applied on a voxel basis. Methods: Twenty-five patients with suspected high-grade brain tumors and inconclusive MRI findings underwent ¹¹C-methionine PET and dual-time-point ¹⁸F-FDG PET. Images from each subject were registered and spatially normalized. Parametric maps of standardized uptake value (SUV) and tumor–to–normal gray matter (TN) ratio for each PET image were obtained. Tumor diagnosis was evaluated according to 4 criteria comparing standard and delayed ¹⁸F-FDG PET images: any SUV increase, SUV increase greater than 10%, any TN increase, and TN increase greater than 10%. Voxel-based analysis sensitivity was assessed using ¹¹C-methionine as a reference and compared with visual and volume-of-interest analysis for dual-time-point PET images. Additionally, volumetric assessment of the tumor extent that fulfills each criterion was compared with the volume defined for ¹¹C-methionine PET. Results: The greatest sensitivity for tumor identification was obtained with any increase of TN ratio (100%), followed by a TN increase greater than 10% (96%), any SUV increase (80%), and an SUV increase greater than 10% (60%). These values were superior to visual analysis of standard ¹⁸F-FDG (sensitivity, 40%) and delayed ¹⁸F-FDG PET (sensitivity, 52%). Volume-of-interest analysis of dual-time-point PET reached a sensitivity of only 64% using the TN increase criterion. Regarding volumetry, voxel-based analysis with the TN ratio increase as a criterion, compared with ¹¹C-methionine PET, detected 55.4% of the tumor volume, with the other criteria detecting volumes lower than 20%. Nevertheless, volume detection presented great variability, being better for metastasis (78%) and glioblastomas (56%) than for anaplastic tumors (12%). A positive correlation was observed between the volume detected and the time of acquisition of the delayed PET image (r = 0.66, P < 0.001), showing volumes greater than 75% when the delayed image was obtained at least 6 h after ¹⁸F-FDG injection. Conclusion: Compared with standard ¹⁸F-FDG PET studies, quantitative dual-time-point ¹⁸F-FDG PET can improve sensitivity for the identification and volume delineation of high-grade brain tumors.