Summary

This lecture will address two primary challenges for PET/MR in relation to body imaging: specifically, the limitations of MR-based attenuation correction (MRAC) as well as strategies necessary to enable motion-robust simultaneous imaging. Despite the aforementioned challenges, 18F-FDG PET/MR has been shown to be at least as effective as PET/CT in most oncologic applications, with great future potential to extend this capability utilizing the multi-parametric imaging capabilities of advanced MRI techniques and non-FDG PET tracers. While it is well-known that current MRAC approaches can yield underestimation or overestimation of standardized uptake values (SUV), by up to 20% in bone or up to 5% in soft tissue, the shortcomings of less quantitatively accurate PET do not appear to limit diagnostic utility of the modality. Furthermore, MRAC errors are expected to be systematic, and thus repeatable within subjects and populations, which provides interesting ramifications for imaging of treatment response and usage for clinical trials, particularly when juxtaposed with other PET uncertainties. An additional challenge in PET/MR relates to the management of patient motion (typically respiratory). While PET has traditionally been performed under free breathing at rest, MRI in the body usually requires multiple breath-holds per acquisition, creating a general incompatibility and workflow limitation between the two modalities (with potential significant image artifacts). Furthermore, given the limited time per PET bed position for feasible whole body PET/MR imaging (e.g., 3-6 minutes per bed), the development of rapid, motion-robust MR acquisitions is a necessary step to realize the full potential of MRI. This lecture will discuss current approaches for MRAC and motion management, examine their impact on clinical workflow, and provide an assessment and outlook for future approaches.

Acknowledgements

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References

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