Low-dose Study Of Atlantoaxial Spine Imaging With Cone-beam Computerized Tomography

Objective:To investigate the implementation of cone beam computed tomography(CBCT)for atlantoaxial imaging at low doses;to compare the differences in dose and quality between CBCT and multilayer spiral CT(MSCT)for atlantoaxial imaging.Methods:1.The head and neck body models were scanned using a Planmeca CBCT scanner,and the dentate scan program was selected for 3D dental imaging,and the scan volume size was set toΦ70×50mm.The body models were scanned with 30 exposure conditions in 5 body types,3 resolution modes,and 2 dose modes,and the dose-area product(DAP,in m Gy·cm~2)values of 30 sets of CBCT images were recorded.The DAP values of the 30CBCT images were recorded and evaluated for examination dose;objective image quality evaluation was performed at the level of CBCT coronal reconstruction by measuring the CT values(mean±standard deviation)of the atlantoaxial region of interest and the background,using the mean as the signal and the standard deviation as the noise,and calculating the contrast-to-noise ratio(CNR);subjective image quality was evaluated on a 5-point Likert scale and consensus was reached,which included overall image quality,contrast,sharpness,noise and artifacts.2.Head and neck body models were scanned using 30 exposure conditions of CBCT and 15 exposure conditions of Toshiba 320-row MSCT.The effective dose(ED)of CBCT was calculated based on Monte Carlo algorithm dose evaluation software PCXMC.The ED value of MSCT was obtained by multiplying the dose-length product(DLP)by the adult neck specific conversion factor.The T-test for two independent samples or the Wilcoxon rank sum test were used to compare the examination dose and subjective and objective image quality between the two imaging methods.Results:1.Dose examined:The DAP values of different dose modes and resolutions were statistically different(P<0.05),and the DAP valuesof conventional dose mode were higher than those of ultra-low dosemode.The DAP values of the 150μm resolution group were higher than those of the200μm resolution group than those of the 400μm resolution group.There was no significant difference in DAP value among different body types(P>0.05).The volume dose index and median ED value of CBCT were 2.9m Gy and 27.61μSv,respectively,lower than 8.8m Gy and 433.16μSv of MSCT,and the difference was statistically significant(P<0.05);2.Objective evaluation of image quality:CNR value and noise were statistically different among different dose modes(P<0.05).CNR value of conventional dose mode was higher than that of ultra-low dose mode,and noise of ultra-low dose mode was higher than that of conventional dose mode.There were no significant differences in noise and CNR values among different body shapes and resolutions(P>0.05).The noise and CNR values of the CBCT group and the MSCT group were statistically different(P<0.05).The median noise of the CBCT group was 27.74Hu higher than that of the MSCT group(7.84Hu),and the median CNR of the CBCT group was3.69,lower than that of the MSCT group(27.1);3.Subjective evaluation of image quality:there were statistical differences in subjective image quality scores among different body types(P<0.05).There were statistical differences in the overall image quality,contrast,sharpness and noise score among different dose modes and resolutions(P<0.05),while there were no statistical differences in the pseudo-film score among different dose modes and resolutions(P>0.05).There were statistical differences in overall image quality,contrast and pseudo-film review score between CBCT group and MSCT group(P<0.05).Overall image quality,contrast and pseudo-film review score of CBCT group were 3.5,3.0 and 5,respectively,which were higher than those of MSCT group 2.0,2.0 and 4.0.There was no significant difference between the articulation score of CBCT group and MSCT group(P>0.05).Conclusions:1.Based on the subjective and objective image quality evaluation and the principle of as low as reasonably achievable(ALARA),the optimal balance between image quality and inspection dose can be achieved with the S-shape under the 200μm resolution group in the ultra-low dose mode.2.Both atlantoaxial CBCT and MSCT scans provide image quality that meets diagnostic requirements.Compared to MSCT,CBCT atlantoaxial scans effectively reduce radiation dose,in line with the principle of optimal radiation protection.