Quantification of serial tumor glucose metabolism

We developed a method to improve the quantitative precision of FDG-PET scans in cancer patients. The total-lesion evaluation method generates a correlation coefficient (r) constrained Patlak parametric image of the lesion together with three calculated glucose metabolic indices: (a) the total- lesion metabolic index (ml/min/lesion); (b) the total-lesion voxel index (voxels/lesion); and (c) the global average metabolic index (ml/min/voxel). Methods: The glucose metabolic indices obtained from conventional region of interest (ROI) and multiplane evaluation were used as standards to evaluate the accuracy of the total-lesion evaluation method. Computer simulations and four patients with metastatic melanoma before and after chemotherapy were studied. Results: Computer simulations showed that the total-lesion evaluation method has improved precision (%s.d. < 0.6%) and accuracy (~10% error) compared with the conventional ROI method (%s.d. ~5%; ~25% error). The indices from human FDG-PET studies using the total-lesion evaluation method showed excellent correlations with the corresponding values obtained from the conventional ROI methods and multiplane evaluation (r ~ 1.0) and CT lesion volume measurements. Conclusion: This method is a simple but reliable way to quantitatively monitor tumor FDG uptake. The method has several advantages over the conventional ROI method: (a) less sensitive to the ROI definition, (b) no need for image registration of serial scan data and (c) includes tumor volume changes in the global tumor metabolism.