Optimize Non-contrast Head CT Imaging Tasks Using Multiple Sets Virtual Monochromatic Images And Post-ASIR-V

Objective To determine the optimal energy levels in non-contrast head CT using multiple sets virtual monochromatic images(VMI)and Post-ASIR-V.Methods We included patients(age older than 18 years)with routine clinical indications(eg,headache,stroke,trauma,or hemorrhage)who had undergone non-contrast dual-energy CT of the head.21 sets of VMI from 40 to 140 keV at 5 keV intervals and a set of polychromatic image(120k Vp-like)were reconstructed for each of the 98 patients who underwent non-contrast head CT in GSI mode.Objective assessment of image quality including the index as follows: gray and white matter SNR,CNR,subcalvarial artifact index(SAI)and posterior fossa artifact index(PFAI).The signal-to-noise ratio(SNR)for gray matter(GM)and white matter(WM),contrast-to-noise ratio(CNR)between GM and WM,subcalvarial artifact index(SAI)and posterior fossa artifact index(PFAI)were measured by placing regions-of-interest(ROIs)in nine areas of the brain.Subjective image quality in terms of the GM-WM differentiation,beam harden artifacts in the subcalvarial space,and posterior fossa and overall image noise was evaluated using a 5-point Likert scale by two radiologists blindly.Addly,three ROIs were measured on three layers by 40%,60%,80% Post-AISR-V respectively.Objective assessment of image quality including CT attenuation,SD,SNR in centrum semivalte,basal ganglia region and posterior fossa.And overall image noise was evaluated using a 5-point Likert scale by two radiologists blindly.Measurements were statistically analyzed by means of LSD-t test and Wilcoxon test.Statistical analysis of all the data after collation showed that there was statistical significance in defining P < 0.05,whereas there was no statistical significance in defining P > 0.05.Results The optimal energys level for viewing the non-contrast head are 65-75 keV.However,when it comes to 65 kev,it shows higher gray and white matter SNR(12.10±2.51,9.25±2.59),higher CNR(1.26±0.24);when it comes to 75 keV,it shows lower SAI(5.76±0.99)and PFAI(3.13±1.04).All corresponding measurements at optimal energy levels were significantly better than those measured at polychromatic image(all P < 0.05),except for PFAI(P=0.2).With the Post-ASIR-V was higher,SD was less,CNR and SNR was higher.60%Post-ASIR-V was the best on subjective assessment.Conclusion The optimal energy level for viewing the supratentorial brain was 65 keV,and reducing beam hardening artifacts in the subcalvarial space and posterior foss was75 keV,respectively.60%Post-ASIR-V was the best.