Limitations Of Fdg-Pet/Mri In The Detection And Characterization Of Atherosclerosis

1372 Purpose: The recent advent of PET/MRI has introduced a host of new applications for FDG-PET. As interest in this novel hybrid modality steadily grows, the broader community must remain cognizant of its limitations. This study will explore such limitations relating to the imaging of atherosclerotic plaques and arterial inflammation.\n Results: The assessment of small atherosclerotic plaques and related inflammatory foci is hampered by the limited spatial resolution of PET. This inherent limitation leads to “spill-out” and “spill-in” of signal between the target tissues and surrounding structures, degrading image quality and quantitative assessment of PET. Thus, one must be wary of the limitations of the assessment of smaller objects surrounded by active metabolic tissues. As related to the imaging of atherosclerosis, the volume of plaque and of inflammatory lesions in the arteries is sufficiently small to warrant concerns of spill-out. Similarly, FDG uptake in surrounding metabolically active tissue, arterial smooth muscle, and blood pool may lead to spill-in of signal into atherosclerotic plaques. Moreover, cardiac and respiratory motion also contribute to the dispersion of PET-based signals. Although attempts with PET/MRI have been made to mitigate the variability introduced by respiratory motion, the techniques are not yet perfected. The most notable deficiency of PET/MRI lies in the relative inferiority of MR attenuation correction (MRAC) as compared to CT attenuation correction (CTAC), particularly with respect to the attenuation correction of osseous and calcified structures.\n Conclusions: A number of key limitations hamper the ability of PET/MRI to accurately register FDG activity to plaques or lesions. As such, visual inspection and punch biopsy methods of analysis in PET/MRI studies will produce inaccurate qualitative and quantities results. Particular methodologies, such as global assessment, can overcome these barriers and assess the total burden of atherosclerotic inflammation in the arterial walls to accurately monitor disease activity.