Incorporation of Time-of-Flight Information Reduces Metal Artifacts in Simultaneous Positron Emission Tomography/Magnetic Resonance Imaging A Simulation Study

Objectives This study aimed to describe and evaluate the influence of time-of-flight (TOF) information on metal artifact reduction in positron emission tomography (PET) image quality in clinical simultaneous PET/magnetic resonance (MR) scanning. Materials and Methods A total of 7 patients with various malignant tumors were included and underwent a PET/MR examination after standard PET/computed tomography. Baseline TOF and non-TOF PET images were reconstructed. Next, the TOF and non-TOF PET reconstructions were repeated after the introduction of artificial signal voids in the attenuation map to simulate metal artifacts of various sizes in a range of locations. Three different sizes of signal voids were inserted in the attenuation maps for each location of interest: over the maxilla, humeral head, chest, sternum, thoracic and lumbar spine, as well as the femoral head to replicate clinically relevant metal artifacts. The reconstructed images with the artifacts were then compared with the baseline reconstructed images. The mean percentage error in a region of interest surrounding the simulated artifact was used to compare between TOF and non-TOF images. Further comparison between TOF and non-TOF images was performed using histogram analysis. Results In all cases, the mean percentage error in a region of interest surrounding the simulated artifact was reduced when TOF information was included in the reconstruction. The inclusion of TOF also changes the distribution of smaller errors away from the origin of the artifact. In some anatomical regions, an increase in the number of small errors was noted with TOF, although the differences with non-TOF were minimal. Conclusions Positron emission tomographic imaging benefits from the integration of TOF information in simultaneous PET/MR. The inclusion of TOF information in simultaneous PET/MR imaging reduces errors related to metal artifacts at the site of the artifact.