Image quality evaluation of virtual monoenergetic spectral images obtained in two types of dual energy CT based on noise level / 中华放射学杂志

ABSTRACT

Objective To investigate the image quality difference of the virtual monochromatic spectral(VMS) images synthesized from fast kilovoltage switching and dual-source dual-energy CT for a given radiation dose. Methods A plurality of disposable syringes containing 15 mg/ml iodine contrast agent and saline were placed on the surface of the male anthropomorphic phantom consisting ofhead neck and torso, GE HD750 gemstone spectral imaging and Siemens Somatom Definition Flash dual energy CT protocols were performed on the phantom for a same dose(volume CT dose index 6.52 mGy), and VMS images (40, 60, 70, 80, 100, 120, 140 keV) were reconstructed and obtained(VMSkV switching and VMSdual-source image), respectively. The objective image noise, iodine signal noise ratio(SNR), iodine contrast noise ratio (CNR) and CT values were measured. The results were analyzed using the paired t test and ANOVA. Results 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 100 keV,while most VMSdual-source iodine CT values were highest on chest(P<0.05). VMSdual-source and VMSkV switching image noise were highest at 40 keV and successively raised from the head, chest , abdomen. VMSkV switching image noise gradually decreased with the increase of keV in the range of 40 to 70 keV , gradually increased up to the trough after 70 keV from 80 keV gradually decreased, while VMSdual-source image noise was lowest at 70 keV or 80 keV , and then with the keV increased gradually increased. Image noise on VMSkV switching images in the range of 40 to 100 keV were higher than that on VMSdual-source images and lower in the range of 100 to 140 keV at most part(P<0.05). VMSdual-source and VMSkV switching iodine SNR were highest at 40 keV or 60 keV,SNR on VMSdual-source images are greater than on VMSkV switching images except 40 keV images on head and abdomen(P<0.05) . VMSdual-source and VMSkV switching iodine CNR were highest at 60 keV,CNR on VMSdual-source images are greater than on VMSkV switching images except 40 keV images on head 100 keV and 120 keV on abdomen(P<0.05).SNR and CNR decreased from the head, chest, abdomen (P<0.05). Conclusion 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.