Virtual Monochromatic Spectral Imaging And Non-linear Blending On Solitary Pulmonary Nodules: Phantom Study

PART 1:Virtual monochromatic spectral imaging on solitary pulmonary nodules:phantom studyPurpose: To analyze the relationship of virtual monochromatic spectral(VMS)image to the detection rate of simulated solitary pulmonary nodules and image quality.Methods: The simulated pulmonary nodules [diameter 3,5,8,10 and 12 mm;CT densities-800,-650 and 100 Hounsfield Units(HU)] were randomly placed inside an anthropomorphic chest phantom.The phantom was examined on SOMATOM definition flash with dual mode(80/140 k V).The different levels of VMS image were reconstructed and the detection rate and image quality of each group were analyzed.Group 1: A total of 90 nodules contained 6 nodules in each diameter and each density.Group 2: A total of 45 nodules contained 9 nodules for each diameter;CT density was-650 HU.The image noise of nodules,SNR and CNR were analyzed by t one-way ANOVA;if there were significant differences,then using the post hoc test(equal variance: LSD;unequal variance: Dunnett T3);the detection of nodules was analyzed by Fisher's Exact Test.Results: There were significant differences in the image noise of nodules,SNR and CNR for-800,-650 and 100 HU nodules at different levels of VMS image(P<0.05).VMS image at 70 ke V yielded the lowest image noise of nodules and the highest SNR and CNR.However,there were no significant differences in the image noise of nodules,SNR and CNR for the same density nodules between the 65 ke V and 70 ke V images(P>0.05)or between the 75 ke V and 70 ke V images There were no significant differences in the image noise of nodules,SNR and CNR for each diameter nodule with CT density of-650 HU at the same level of VMS images(P>0.05).The detection rate of-800,-650 and 100 HU at 60~140 ke V was 100%,>5mm nodules were all detected at different levels of VMS images.The detection rate of-800 HU and 3mm nodules at 40 and 50 ke V were inferior to 60~140ke V(P<0.05).Conclusion: VMS image for chest DECT at 70 ke V yields the lowest image noise of nodules and the highest SNR and CNR.Choosing more than 60 ke V can improve the detection rate of solitary pulmonary nodules.PART 2:Feasibility study of non-linear image blending technique in dual-energy CT on solitary pulmonary nodulesObjective: To investigate the feasibility and to optimize the parameters of non-linear blending technique in dual-energy CT on solitary pulmonary nodules(SPN).Methods: The simulated enhanced SPN were used the mixture of non-ionic iodinated contrast agent(Iopromide 370 mg I/100ml)and normal saline and then randomly placed inside an anthropomorphic chest phantom.The phantom was examined on SOMATOM definition flash with dual mode(80/140 k V)and single energy mode(120 k V)(the same CTDIvol).Non-linear blending images and linear blending images with a weighting factor of 0.3 were generated and the image qualities were analyzed.Results: For different simulated density SPN,when 0 HU was chosen as the Blending Center(BC)and 0 to 30 HU were chosen as the Blending width(BW),the non-linear blending images yielded a higher contrast-to-noise(CNR).There were significant differences in the image noise and signal-to-noise(SNR)of different simulated density SPN at non-linear blending images?linear blending images and 120 k V images(P<0.05);But the differences of CNR between the three groups were not statistically significant(P>0.05).The SNR of different simulated density SPN at non-linear blending images was significantly increased compared with it at linear blending images and 120 k V images(P<0.05);And the image noise at non-linear blending was lower than it at linear blending images(P<0.05).Conclusion: Non-linear blending technique in dual-energy CT can increase the SNR of enhanced SPN,and it is helpful in diagnosis of SPN.