In fact, they allow to simultaneously acquire both metabolic (through PET imaging) and morphological data with excellent tissue contrast (via MRI). To tackle the problem of lack of visualization of the spinal cord, which hinders evaluation of FDG uptake of the cord in PET/CT, it is now possible to take advantage of the introduction of hybrid PET/MR scanners. Moreover, due to inclusion of the surrounding CSF in the spinal cord ROI sampling in PET/CT, the spinal cord SUVmax, that is assumed to reflect the higher metabolic activity of the cord central gray matter, was usually preferred to SUVmean in PET/CT studies of spinal cord diseases. The other implies measurement of the ratio of SUV to background using the activity of the normal spinal cord, lumbar thecal sac, vertebral marrow, or liver as a reference. One entails measurement of the standardized uptake value (SUV) of the normal or affected spinal cord per se that is usually sampled with a region of interest (ROI) encompassing the entire spinal canal due to lack of the spinal cord definition and taking care to exclude the vertebral bone. The more reliable measurement of FDG uptake in PET/CT studies of normal and diseased spinal cord is uncertain. Studies published so far utilized PET/CT and the metabolic tracer Fluoro-deoxy-glucose (FDG) according to a whole-body or dedicated spinal protocol. Normalization of the SUVmax and SUVmean of the spinal cord to the liver radiotracer uptake could help in multi-institutional comparisons and studies.įunctional imaging of the spinal cord with positron emission tomography (PET) represents a distinctive challenge due to the its small size, the relatively low resolution of PET images, and contamination from vertebral bone marrow. While the observed values show the expected longitudinal distribution, they appear to be higher than those measured in PET/CT. Using a whole-body protocol, we defined the maximum and mean FDG uptake of the normal spinal cord in PET/MRI. However, the average NSUVmax and NSUVmean of the spinal cord were higher (range 21–47%) in PET-MRI than in PET-CT. Comparison with PET-CT data revealed that the average SUVmax and SUVmean of the spinal cord were similar in PET-MRI and PET-CT. The spinal cord FDG-uptake values correlated with the bone marrow uptake at the same level, especially in case of NSUVmax. Using a 9 mm ROI, the highest values were consistently observed at C5 and the lowest at T12 or T6. Using the 3 mm ROI, the highest values of PET-MRI SUVmax, SUVmean, NSUVmax, and NSUVmean were consistently observed at C5 and the lowest at T6. On PET/MRI using the 3 mm ROI, the following average (all level excluding 元) spinal cord median (1st and 3rd quartile) values were measured: SUVmean, 1.68 (1.39 and 1.83) SUVmax, 1.92 (1.60 and 2.14) NSUVmean, 1.18 (0.93 and 1.36) and NSUVmax, 1.27 (1.01 and 1.33). For comparison, the same ROIs were placed in PET-CT images obtained immediately before the PET-MRI acquisition following the same tracer injection. The SUVmax, SUVmean, and the SUVmax and SUVmean normalized (NSUVmax and NSUVmean) to the liver were measured. Using a custom-made software, we placed ROIs of 3 and 9 mm in diameter in the spinal cord, lumbar CSF, and vertebral marrow that were identified on MRI at 5 levels (C2, C5, T6, T12, and 元). Methodsįorty-one patients with lymphoma without clinical or MRI signs of spinal cord or bone marrow involvement underwent simultaneous PET and MRI acquisition using Siemens Biograph mMR after injection of 3.5 MBq/kg body weight of FDG for staging purposes. By exploiting the capability of MRI to precisely outline the spinal cord, we performed a retrospective study aimed to define normal pattern of spinal cord FDG uptake in PET/MRI. The lack of visualization of the spinal cord hinders the evaluation of Fluoro-deoxy-glucose (FDG) uptake of the spinal cord in PET/CT.
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