Application of new model-based iterative reconstruction in low-dose upper abdominal CT / 中国医学影像技术

ABSTRACT

Objective To compare the effect on image quality of low-dose upper abdominal CT reconstructed with the new version of model-based iterative reconstruction (MBIRn) focused on low-contrast resolution (MBIRNR40),conventional model-based iterative reconstruction (MBIRc),adaptive statistical iterative reconstruction (ASIR) and routine-dose CT reconstructed with filtered back projection (FBP).Methods Water plantom at rest was scanned with CT,and spatial resolution and density resolution were compared among FBP,ASIR,MBIRc,and MBIRNR40.Sixty patients with 2 times CT in the upper abdomen within a year were enrolled.The initial examination was acquired at a standard radiation dose (noise index [NI] of 10 HU) and reconstructed with the conventional FBP algorithm.The follow-up scan was acquired at a lowdose (NI=20 HU) and reconstructed with the standard ASIR,MBIRc and MBIRNR40.All images were obtained with 0.625 mm slice thickness.CT values and noise of fat,muscle as well as the liver and kidney parenchyma were measured and CNR of liver and kidney parenchyma using the fat SD as background image noise were calculated.Two radiologists independently graded images for noise,sharpness of details of structures and lesion.The quantitative image quality scores of different reconstructions were analyzed with one-way ANOVA using FBP reconstruction as reference of standard.The degree of interobserver consistency was evaluated using Kappa test.Results The phantom study revealed the highest spatial resolution with MBIRc and highest density resolution with MBIRNR40 among all reconstructions.The dose-length product and radiation dose for the first inspection was (93.18 ± 41.21) mGy · cm,(1.40 ± 0.62) mSv,respectively,and were (368.03 ± 146.25)mGy · cm,(5.52 ± 2.19)mSv for the second inspection,representing an approximate overall dose reduction of 74.68％ and 74.64％.The mean image noise of muscle and fat for MBIRNR40 was significantly lower than that of MBIR,ASIR and FBP(P＜0.05).The mean CNR values of liver and spleen for MBIRNR40 were significantly higher than that of ASIR,MBIRc and FBP (P＜0.05).Two radiologists had a good subjective score consistency.Low-dose MBIRNR40 subjective image noise was the lowest,showing the most detailed on the upper abdominal detail structure and lesion edge,better than MBIRc,MBIRc was superior to routine-dose FBP,low dose ASIR was worst,the difference was statistically significant (P＜0.05).Conclusion With 75％ dose reduction in upper abdominal CT,the MBIRNR40 can provide well objective and subjective image quality than MBIRc and ASIR40,and the routine-dose FBP.