Abstract
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Objectives Integrated PET and MRI hold great promise for disease characterization as they enable the simultaneous measurement of complementary molecular and anatomical information on disease. However, the high cost of integrated PET/MRI has limited its availability. To address this issue, we are developing an RF-penetrable PET insert that can be inserted into any existing MR system, using the built-in body coil for RF transmission. We include measurements from an RF-penetrable PET ring integrated with a custom RF receive coil and inserted into a 3T MR system.
Methods The RF-penetrable PET system consists of 16 PET modules in a ring pattern with 1mm gaps and a 6.5cm long custom 16-channel birdcage RF receive coil. By using electro-optical coupling, the PET insert is electrically floating relative to the MRI RF ground, which enables the RF field to uniformly transmit from the body coil through the gaps. The resulting MR RF signal is received by the RF receive coil. MR performance was evaluated by measuring the uniformity and the SNR of a gradient echo MR image of a standard MR agar phantom. We compared these results with those acquired using the body coil as the receiver and with no PET insert present.
Results The MR images acquired for 3 cases (1) PET insert + custom receive coil, (2) PET insert + body coil (TX/RX), and (3) no PET insert, resulted in SNR values of 131.4, 35.6, 49.6, respectively, and uniformity (%) values of 50.6, 70.8, 74.5, respectively. The custom receive coil showed the best SNR, but reduced uniformity due to its short length.
Conclusions We have shown that the SNR of the MR image acquired with the custom PET/MR receive coil is significantly better than that acquired with the body coil (TX/RX) and no PET insert present. The uniformity of this custom PET/MR receive coil will likely be improved by extending the length of the custom receive coil.