Introduction: Dedicated carotid radiofrequency (RF) coils allow high-resolution carotid vessel wall imaging. An RF MRI coil in PET field of view introduces attenuation, which can result in a bias in PET quantification. In this study, we compare the performance of a newly developed dedicated PET/MRI carotid coil against a model designed for MRI-only use, in a phantom and patient study.
Methods: A 3.0T Siemens Biograph mMR PET/MRI scanner was used to test the performance of 2 coils: PACC-SB30 (PET/MRI coil) and PACC-ST30 (MRI-only coil), i.e. 4-channel bilateral carotid coils (Machnet BV, Roden, The Netherlands).

Phantom Study: A cylindrical phantom filled with an aqueous solution of 18F-fluorodeoxyglucose (18F-FDG) was scanned without dedicated coils (baseline), with the PET/MRI coil (Figure 1A) and with the MRI-only coil.

Patient Studies: Three patients directly following the clinical exam, were scanned for 10 minutes with the PET/MRI coil, the MRI-only coil and without a dedicated coil.  
Results: In the phantom study, the PET/MRI coil demonstrates only a slight decrease (3-4%) at the position of the coil. The MRI-only coil shows a more substantial decrease (up-to 10%) in this region (Figure 2). In patients, SUVs acquired with the PET/MRI coil were significantly higher than with the MRI-only coil (p=0.039) (Figure 3). The SUVmax of the lesion visible in a patient with oropharyngeal cancer acquired with the PET/MRI coil was 6.1, while 5.8 without a dedicated coil.
Conclusion: The phantom study clearly demonstrates less attenuation by the dedicated PET/MRI coil as compared to the MRI-only coil. Initial data from three patients show similar findings.

04 - EVALUATION OF ATTENUATION REDUCTION OF A DEDICATED CAROTID PET/MRI COIL FOR CAROTID PLAQUE IMAGING