Journal of nuclear medicine : official publication, Society of Nuclear Medicine
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Comparative Study
Performance of whole-body integrated 18F-FDG PET/MR in comparison to PET/CT for evaluation of malignant bone lesions.
Because of its higher soft-tissue contrast, whole-body integrated PET/MR offers potential advantages over PET/CT for evaluation of bone lesions. However, unlike PET/CT, PET/MR ignores the contribution of cortical bone in the attenuation map. Thus, the aims of this study were to evaluate the diagnostic performance of whole-body integrated (18)F-FDG PET/MR specifically for bone lesions and to analyze differences in standardized uptake value (SUV) quantification between PET/MR and PET/CT. ⋯ Compared with PET/CT, fully integrated whole-body (18)F-FDG PET/MR is technically and clinically robust for evaluation of bone lesions despite differences in attenuation correction. PET/MR, including diagnostic T1-weighted TSE sequences, was superior to PET/CT for anatomic delineation and allocation of bone lesions. This finding might be of clinical relevance in selected cases--for example, primary bone tumors, early bone marrow infiltration, and tumors with low uptake on PET. Thus, a diagnostic T1-weighted TSE sequence is recommended as a routine protocol for oncologic PET/MR.
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Quantitative PET imaging relies on accurate attenuation correction. Recently, there has been growing interest in combining state-of-the-art PET systems with MR imaging in a sequential or fully integrated setup. As CT becomes unavailable for these systems, an alternative approach to the CT-based reconstruction of attenuation coefficients (μ values) at 511 keV must be found. Deriving μ values directly from MR images is difficult because MR signals are related to the proton density and relaxation properties of tissue. Therefore, most research groups focus on segmentation or atlas registration techniques. Although studies have shown that these methods provide viable solutions in particular applications, some major drawbacks limit their use in whole-body PET/MR. Previously, we used an annulus-shaped PET transmission source inside the field of view of a PET scanner to measure attenuation coefficients at 511 keV. In this work, we describe the use of this method in studies of patients with the sequential time-of-flight (TOF) PET/MR scanner installed at the Icahn School of Medicine at Mount Sinai, New York, NY. ⋯ In conclusion, a transmission-based technique with an annulus-shaped transmission source will be more accurate than a conventional MR-based technique for measuring attenuation coefficients at 511 keV in future whole-body PET/MR studies.