| Purpose:Dual Energy CT can acquire a certain photon energy (keV) virtual monochromatic spectral images. This study aim to quantitative analysis image quality and related factors of virtual monochromatic spectral images.Methods:DECT and conventional polychromatic single-energy CT were performed on the male anthropomorphic phantom which including head neck and torso. Sinogram affirmed iterative reconstruction (SAFIRE level3) algorithm and filtered back projection (FBP) algorithm were used, and 70 keV/FBP,70 keV/Safire(3),120 kVp/FBP,120 kVp/Safire(3) images were reconstructed and obtained, respectively. The objective image noises and CT values were measured. The results were analyzed using the paired t-test and mixed-effects model with Bonferroni correction. A plurality of containing 15mg(I)/ml iodine contrast agent and saline disposable syringe were placed on the surface of the male anthropomorphic phantom which including head neck and torso, GE HD750 GSI and Siemens Somatom Definition Flash DECT protocols were performed on the phantom for a same dose (CTDIvol6.52mGy), and VMS 40keV,60keV,70keV, 80keV,100keV,120keV,140keV images were reconstructed and obtained, respectively. The objective image noise, iodine SNR, iodine CNR and CT values were measured. The results were analyzed using the paired t-test and ANOVA.Results:Regardless of reconstruction algorithm, the CT values between 70 keV and 120 kVp images in thalamus, the air outside skull, gall bladder, liver, spleen, prostate were considered no statistical significant differences (all P>0.0083), while the CT values of 70 keV images in lateral ventricle, cerebellum, thymus, heart, lung, the stomach and the air inside rectum were lower than that of 120 kVp images, while the CT values of 70 keV images in mandibular, thoracic vertebra, lumbar spine, central part of femoral head were higher than that of 120 kVp images (all P<0.006). The objective image noises between 70 keV and 120 kVp images with the same reconstruction algorithm were considered no statistical significant differences (all P>0.0083), but the 70 keV or 120 kVp images with SAFIRE Ievel3 and FBP algorithm were considered statistical significant differences (all P<0.0083), the images noises of 70 keV and 120 kVp with SAFIRE Ievel3 algorithm were reduced about 25.29±9.39% and 27.93±8.39% compared with FBP algorithm. All VMS iodine CT values were gradually decreased with the increasing of keV, and iodine CT values on VMSdual-source images were greater than on VMSkv switching images(P<0.05), VMSkv switching iodine CT values in descending order from the head, chest, abdomen at less than 100keV,while most VMSdual-source iodine CT values were highest on chest(P<0.05). VMSdual-source and VMSkv switching image noise were highest at 40keV and successively raised from the head, chest, abdomen(P<0.05). VMSkv switching image noise gradually decreased with the increase of keV in the range of 40-70keV, gradually increased up to the trough after 70keV from 80keV gradually decreased, while VMSdual-source image noise was lowest at 70keV or 80keV, and then with the keV increased gradually increased. Image noise on VMSkv switching images in the range of 40-100 keV were higher than that on VMSdual-source images and lower in the range of 100-140keV at most part(P<0.05). VMSdual-source and VMSkv switching iodine SNR were highest at 40keV or 60keV, SNR on VMSdual-source images are greater than on VMSkv switching images except 40keV images on head and abdomen(P<0.05). VMSdual-source and VMSkv switching iodine CNR were highest at 60keV, CNR on VMSdual-source images are greater than on VMSkv switching images except 40keV images on head 100keV and 120keV on abdomen(P<0.05).SNR and CNR decreased from the head, chest, abdomen (P<0.05).Conclusion:In parts of the tissues and organs, the CT values between 70 keV and 120 kVp images were not equivalent. The objective image noises between 70 keV and 120 kVp images were equivalent. DECT and conventional polychromatic single-energy CT with iterative algorithm can significantly reduce the image noise and enhance image quality. VMS images synthesized from fast kilovoltage switching and dual-source dual-energy CT have different image quality performance at most keV and body parts, but VMS imaging at approximately 70 keV yielded lower image noise, and at approximately 60 keV yielded highest SNR and CNR... |
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