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) . 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 . 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.
DNA replication is regulated in response to environmental constraints such as nutrient availability. activity (Wang et al. 2007 Paradoxically primase activity is also directly inhibited by (p)ppGpp (Maciag et al. 2010 Rymer et al. 2012 although decades of classical and modern experiments have not revealed any inhibitory effect of amino acid starvation on replication elongation (Lark and Lark 1966 Billen and Hewitt 1966 Marsh and Hepburn 1980 Levine et al. 1991 Ferullo and Lovett 2008 Tehranchi et al. 2010 This disparity between and results suggests that either (p)ppGpp also inhibits replication elongation in or is conserved in divergent bacteria we quantified genome-wide replication fork progression in cells and discovered that acute amino acid starvation not only inhibited replication initiation but also modestly reduced the rate of replication elongation. We found that (p)ppGpp was both necessary and sufficient to inhibit replication elongation independently of its effect on transcription. We further observed that (p)ppGpp inhibited replication elongation quantitatively in both and cells. We monitored replication fork progression in a synchronized population of cells using genomic microarrays (Khodursky et al. 2000 Tehranchi et al. 2010 Cells carrying a temperature sensitive (Δcells (Figure 1F) indicating that inhibition of replication elongation requires (p)ppGpp induction in cells results in CASIN a modest reduction of replication elongation rate we examined whether further increasing (p)ppGpp concentration inhibits replication elongation more strongly. This can be achieved by deleting (Somerville and Ahmed 1979 (Figure 2A). Using Thin Layer Chromatography (TLC) we confirmed that in Δcells ppGpp was induced by SHX to similar levels as in wild-type cells but pppGpp levels were ~2 fold higher (Figure 2B-D; Table S1). Levels of GTP a precursor of pppGpp and a substrate for primase were reduced similarly in the presence or absence of GppA (Figure 2E; Table S1). Figure 2 Deletion of Results in Higher pppGpp Levels upon Amino Acid Starvation in (Figure 3A-D). While replication elongation rates were not significantly reduced by deletion in untreated cells upon starvation elongation rates were reduced by 35±3% (p < 0.01 Mann-Whitney U test) a 2-3 fold further reduction compared with starved cells (13±2%). Figure 3 Replication Elongation Rates are More Strongly Reduced in Amino Acid-Starved ΔCells To rule CASIN out the possibility that this reduction stems from a synthetic effect between the deletion and the allele we measured CASIN replication rates in Δcells with wild-type by monitoring the incorporation of 3H-thymidine into DNA. While inhibition IMPG1 antibody of replication initiation results in a gradual decrease of 3H-thymidine incorporation over the course of a replication cycle inhibition of elongation results in a rapid decrease of 3H-thymidine incorporation. We observed a rapid decrease in the rate of 3H-thymidine incorporation during amino acid starvation in wild-type cells and found that deletion resulted in a significant further reduction (Figure 3E). It has been shown that (p)ppGpp induction also decreased the uptake of thymidine (Lin-Chao and Bremer 1986 which contributed to the decrease in 3H-thymidine incorporation. However deletion of CASIN did not further decrease thymidine uptake (Figure 3E) suggesting that the difference in thymidine incorporation we observed in SHX-treated Δcells was CASIN due to reduction of DNA replication elongation rates in the presence of wild-type deletion in cells devoid of any (p)ppGpp via removal of both (p)ppGpp synthetases: RelA and SpoT. There was no appreciable reduction of the replication rate in ΔΔΔcells upon SHX treatment (Figure 3F) confirming that the inhibition of replication elongation in the Δmutant resulted from increased pppGpp levels. (p)ppGpp is Sufficient to Slow Replication Elongation in E. coli In (Figure 1-3) and (Wang et al. 2007 the inhibitory effects of (p)ppGpp on replication elongation were revealed only under amino acid starvation. Consequently we wanted to determine whether (p)ppGpp induction only not in combination with amino acid starvation was adequate to reduce replication elongation rates in deletion (Number 4A-C; Table S1). RelA* induction reduced GTP levels to the same extent.