Image registration and modeling of Ga-68 EDTA for determination of BBB permeability changes induced by pharmacological intervention (RMP7) in tumor patients

To study the effects of RMP7, an bradykinin analog, on BBB permeability changes in brain tumor patients, Ga-68 EDTA PET was used for quantitative determination of tumor tissue permeability, two dynamic Ga-68 EDTA PET scans (with and without RMP7) were performed for each patient. Changes between the results of the two scans were used to assess the effect of the drug. MRI was also performed to provide the anatomical information. Patient movement during the dynamic PET studies were corrected by frame-to-frame PET image registration. Due to different orientation among PET and MRI images, all PET images were co-registered to the MRI images of the corresponding patient. All frames of a dynamic scan were summed before registering to the MRI images. The main features for registration were boundaries of skull and tumor. After registration, region of interest (ROI) was defined on MRI images and was copied to registered PET dynamic images. The whole tumor radioactivity was calculated based on each plane's tumor ROI. The transport constant from plasma to tissue (Ki) that is related to BBB permeability was estimated by a two-compartmental model. The PET-MRI registration method developed by Lin et al was found to work well for Ga-68 PET-MRI image registration. Estimated whole tumor K _i was 0.0002 ± 0.0019 (s.d.)ml/min/g for the baseline study and was increased by 46 ± 42 (s.d.)% with RMP7.