Attenuation correction in [18F] FDG-PET imaging using modified CT data matching emission data

Abstract

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Objectives: Heart-beating and respiration can cause emission-transmission misregistration during attenuation correction in cardiac PET imaging, and this may lead to erroneous myocardial perfusion defects. Because radiotracer uptake is through cardiac or other soft tissues, other authors has suggested an approach to correct attenuation by using transmission scans that were modified by adding CT voxels to the tracer uptake spot. This study will evaluate the effects of these modified transmission scans using a phantom study. Methods: After acquiring an emission and CT scan of a 9cm cylinder filled with 1.5L of water and 2mCi [F-18] FDG, the cylinder was moved 1cm(11% of diameter), 2cm(22%), 3cm(33%) sideways and CT scan was taken again. After attenuation correction of the CT data acquired from these various positions, the changes of SUV at the center of the cylinder and at the misregistration area were calculated. Voxels of soft tissue attenuation values are added to the CT data in the area of misregistration area. This modified transmission data was then used for attenuation correction. Finally, the SUV changes at the corrected area and at center of cylinder were calculated. Results: In cases where attenuation was corrected without the modified CT data, the SUV values of each misregistration area were reduced by 14%, 48% and 49%. When using the modified CT data, the reduced SUV data in the misregistration area was recovered with minimal over-correction by 2%, 3%, 5%, and at the cylinder center there was an overcorrection by 5%, 8%, and 12%. Conclusions: Use of modified CT data matching emission data will correct erroneously-calculated SUV at the misregistration area. However, if misregistration area is large, SUV at the cylinder center will tend to become over-corrected. When the misregistration area is not very large compared to cardiac PET imaging, attenuation correction using modified CT data can be a good approach to correct pseudo-lesions induced by misregistration.