Purpose The objective of this paper was to evaluate the performance of the built-in MR-based attenuation correction method (MRAC) included in the combined whole-body Ingenuity TF PET/MR scanner and compare it to Dexmedetomidine HCl the gold standard CT-based Dexmedetomidine HCl attenuation correction (CTAC). by an experienced clinician was also reported. Results Body mass index (BMI) and lung density showed significant differences between and groups. Right group (with coils) presented higher MRAC PET values than the group when compared to the CTAC (group (with coils) Dexmedetomidine HCl showed increased overall PET quantification as well as increased variability when compared to the group (no coils). PET reconstructed with MRAC showed some differences when compared to PET reconstructed with CTAC mostly due to air pockets metallic implants and attenuation differences in big bone areas (such as pelvis and spine) due to the segmentation limitation of the MRAC method. group including only subjects who did not have any MR coils during their PET/MR image acquisition and the group including subjects who had MR coils during PET/MR image acquisition. The group (N=14) was composed of 7 males and 7 females aged 61±11 (mean±SD). The group (N=12) was composed of 7 males and 5 females aged 64±10. See table 1 for a summary of the patient details and imaging times post-FDG injection. The study was approved by the Institutional Review Board of the Mount Sinai School of Medicine. All patients gave written informed consent. TABLE 1 Summary of the patient details. Dexmedetomidine HCl The same patient supports for head and legs were used in both scanners in order to place the patient in the same position during both scans and therefore facilitating image coregistration of CT and PET/MR images. These holders were however outside the analysed PET FOV (from pelvis to shoulders) and therefore did not contribute to photon attenuation. CT Imaging CT Images were obtained from the combined PET/CT images (16 slices multidetector CT) scanner (GE Discovery LS Waukesha WI). A non-contrast low dose CT was acquired. The final matrix size of the CT images was 512×512 voxels in-plane with 1.37×1.37×3.75 mm3 voxel size. PET/MR Scanner Immediately after their PET/CT session patients were taken to the PET/MR facility. PET/MR images were acquired on the combined whole-body PET/MR system Ingenuity TF PET/MR (Philips Healthcare Cleveland) [16]. PET images were acquired in 3D mode using TOF information standard for this system. Whole-body and partial-body protocols were acquired on the PET/MR: 2 to 3 3 minutes per bed position (159.4±59.7 sec) 7 to 11 bed positions with 45 slices per bed and a 55% overlap between Dexmedetomidine HCl beds (standard for this system). Images IMPG1 antibody were reconstructed with a matrix size of 144×144 with 4×4×4 mm3 voxel size using a TOF list-mode blob-based OSEM algorithm with 3 iterations and 33 subsets using corrections for normalization dead time attenuation scatter random coincidences sensitivity and decay. PET/MR attenuation correction MRAC Since the objective of this study was to compare the manufacturer built-in MRAC method with the gold standard CTAC all PET images followed the built-in method for attenuation correction implemented on the Ingenuity TF PET/MR (v3.7). Full details of this method are provided in [1]. Briefly a specific MR sequence (called atMR for MR attenuation correction) was run prior to any PET acquisition. The atMR sequence acquired only with the integrated body coil of the MR scanner matches the PET dimensions and allows both anatomical detail and attenuation correction similarly to Dexmedetomidine HCl a low-dose CT image in a standard PET/CT camera. The atMR image was segmented into 3 tissue classes air soft tissue and lungs and pre-determined LACs were assigned to each class (0 0.095 and 0.022 cm?1 respectively). An attenuation template of the patient table and of those MR coils for which the manufacturer provides an attenuation template were incorporated into the attenuation map in order to correct for their attenuation. As the objective of this study was to evaluate the global effect of the presence of clinical MR coils in the PET FOV 4 different coils were used on the group: Cardiac coil (32 channel) Torso Sense XL (16 elements) Neuro-Vascular Sense (16 elements) and Sense Spine coil (15 elements). The built-in MRAC method developed by the manufacturer provided templates for both fix-positioned coils Neuro-Vascular and Spine coils however by default the standard procedure of the PET/MR scanner does not provide an attenuation template for the flexible coils (cardiac and torso). While the posterior parts of these flexible coils remain on the patient table the standard procedure requires.