Functional and Structural Synergy for Resolution Recovery and Partial Volume Correction in Brain PET

Objectives: Positron Emission Tomography (PET) has the unique capability of measuring brain function but its clinical potential is affected by low resolution and lack of morphological detail. The purpose of this study is to evaluate a wavelet synergistic approach that combines functional and structural information from a number of sources (CT, MRI and anatomical frequency-based atlases1) for the accurate quantitative recovery in PET imaging. When the method is combined with anatomical frequency-based atlases, the outcome is a functional volume corrected for partial volume effects of all the selected regions.\nMethods: The proposed method is based on the multiresolution property of the wavelet transform2. First, the target PET image and the corresponding anatomical image are decomposed into several resolution elements. Secondly, high-resolution components of the PET image are replaced, in part, with those of the anatomicalimage after appropriate scaling. The amount of structural input is weighted by the relative high frequency signal content of the two modalities. Anatomical information was provided either by CT and MRI volumes or by a frequency-based anatomical atlas1 whose regional intensity values were obtained by averaging the PET data for each ROI. Accurate simulations of a brain [18F]FDG dataset based on Zubal brain phantom3 were conducted to evaluate the accuracy of ROI values after resolution recovery. As anatomical information, three images (the measured MRI, CT and the segmented image) were used. The resolution-recovered images were compared with the true image of 10 ROIs. The proposed method was also applied to two clinical datasets from an Alzheimer disease patient with moderate atrophy ([18F]FDG) and a young normal volunteer ([11C]raclopride). Static images of these datasets were processed using both MRI and the Hammersmith frequency-based Atlas1,and the results were compared.\nResults: Simulation studies showed that resolution recovery with CT images, which contain minimum amount of tissue anatomy, did not improve resolution. The use of MRI images brought significant improvements in PET image resolution but improvements were maximized when atlas-based segmented images as anatomicalreferences were used (Fig-1A). These results were replicated in the clinical data sets (Fig-1B).\nConclusions: The synergistic use of functional and structural data, and the incorporation of anatomical information in particular, generate morphologically corrected PET images of exquisite quality.\nReference:[1] Hammers A, 2003, Hum Brain Mapp, 19, 224-47.[2] Boussion N, 2006, Phys Med Biol, 51, 1857-76.[3] Tsoumpas C, 2008, Med Phys, 35, 1299-309.[pic_01] Fig.1 (A) ROI comparisons of the simulated FDG images against true image (B) Original andresolution recovered images of a [18F]FDG and [11C]raclopride studies.Brain\u2709 & BrainPET\u270