RT Journal Article SR Electronic T1 Shine-Through in PET/MR Imaging: Effects of the Magnetic Field on Positron Range and Subsequent Image Artifacts JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 951 OP 954 DO 10.2967/jnumed.114.147637 VO 56 IS 6 A1 Kolb, Armin A1 Sauter, Alexander W. A1 Eriksson, Lars A1 Vandenbrouke, Arne A1 Liu, Chih C. A1 Levin, Craig A1 Pichler, Bernd J. A1 Rafecas, Magdalena YR 2015 UL http://jnm.snmjournals.org/content/56/6/951.abstract AB Simultaneous PET/MR imaging is an emerging hybrid modality for clinical and preclinical imaging. The static magnetic field of the MR imaging device affects the trajectory of the positrons emitted by the PET radioisotopes. This effect translates into an improvement of the spatial resolution in transaxial images. However, because of the elongation of the positron range distribution along the magnetic field, the axial resolution worsens and shine-through artifacts may appear. These artifacts can lead to misinterpretation and overstaging. The aim of this work was to study the relevance of this effect. Methods: Measurements were performed in a 3-tesla PET/MR scanner. A 1-cm2 piece of paper, soaked with a radioisotope and placed in air, was scanned, and the magnitude of the shine-through was quantified from the PET images for various radioisotopes. Additionally, PET/MR and PET/CT images of the lungs and the larynx with trachea of a deceased swine were obtained after injecting a mixture of NiSO4 and 68Ga to simulate hot tumor lesions. Results: For the radioactive paper, shine-through artifacts appeared in the location of the acrylic glass backplane, located 3 cm from the source in the axial direction. The ratio between the activity of the shine-through and the activity reconstructed in the original location ranged from 0.9 (18F) to 5.7 (68Ga). For the larynx-with-trachea images, the magnitude of the artifacts depended on the organ orientation with respect to the magnetic field. The shine-through activity could reach 46% of the reconstructed activity (larynx lesion). The lesion within the trachea produced 2 artifacts, symmetrically aligned with the magnetic field and characterized by artifact-to-lesion volume-of-interest ratios ranging from 21% to 30%. Conclusion: In simultaneous PET/MR imaging, the effect of the magnetic field on positrons may cause severe artifacts in the PET image when the lesions are close to air cavities and high-energy radioisotopes are used. For accurate staging and interpretation, this effect needs to be recognized and adequate compensation techniques should be developed.