Virtual monochromatic spectral imaging with fast kilovoltage switching: Improved image quality as compared with that obtained with conventional 120-kVp CT

Purpose: To compare image quality obtained in phantoms with virtual monochromatic spectral (VMS) imaging with that obtained with conventional 120-kVp computed tomography (CT) for a given radiation dose. Materials and Methods: Three syringes were filled with a diluted contrast medium (each syringe contained a contrast medium with a different iodine concentration [5, 10, or 15 mg of iodine per milliliter]), and a fourth syringe was filled with water. These syringes were placed in a torso phantom meant to simulate the standard human physique. The phantom was examined with a CT system and use of the fast kilovoltage switching (80 and 140 kVp) and conventional (120 kVp) modes. Image noise and contrast-to-noise (CNR) ratio were analyzed on VMS images and 120-kVp CT images. Results: Image noise on VMS images in the range of 67-72 keV was significantly lower than that on the 120-kVp CT images (P < .014). Image noise was lowest at 69 keV and was 12% lower when compared with that on 120-kVp CT images. CNR on the VMS images was highest at 68 keV. CNR on the VMS images obtained at 68 keV in the syringes filled with diluted contrast material (5, 10, and 15 mg of iodine per milliliter) was 28%, 31%, and 30% higher, respectively, compared with that on the 120-kVp CT images (P < .001). Conclusion: VMS imaging at approximately 70 keV yielded lower image noise and higher CNR than did 120-kVp CT for a given radiation dose. VMS imaging has the potential to replace 120-kVp CT as the standard CT imaging modality, since optimal VMS imaging may be expected to yield improved image quality in a patient with standard body habitus.