A Method to Locate Radio-Frequency Coils Using a CT-Based Template for a More Accurate Photon Attenuation Correction in PET/MRI

Abstract

In simultaneous positron emission tomography and magnetic resonance (PET/MR) imaging, MR radio-frequency (RF) coils are placed on the top of the patient to receive the MR signal. These coils can produce an undesirable photon attenuation of the PET signal by as much as 17% in certain local regions of a reconstructed PET cylindrical phantom. Currently, photon attenuation of RF body coils is not typically accounted for in the attenuation correction (AC) procedure in commercial PET/MR systems. To correct for this coil attenuation, the position of the coils and their most attenuating components, such as the preamplifier housings must be accurately determined. This work proposes a simple and effective solution to this problem by using three optical cameras placed just outside the field-of-view (FOV) of the PET/MR system. The cameras are used to determine the positions of markers attached to the RF coils. An average marker location error of 7.7 mm was achieved over eight markers placed on a flexible RF coil draped over a cylindrical PET phantom. Quantification of reconstructed PET signal error due to inaccurate assessment of flexible RF coil location on a phantom is presented. Given the coil location accuracy of this method, the PET signal attenuation error is reduced from 17% to less than 3%. Our method can also be extended to correct for other attenuating objects in the FOV of the PET/MR system.