Improving image quality with model-based iterative reconstruction at quarter of nominal dose in upper abdominal CT.

OBJECTIVE:: To evaluate the ability of a model-based iterative reconstruction (MBIR) for improving image quality in upper abdominal CT with quarter of the normal dose, in comparison with adaptive statistical iterative reconstruction (ASiR) at normal dose.

METHODS:: 40 upper abdominal patients were randomly divided into two groups: normal-dose group (n = 20) with tube current modulation for noise index (NI) of 10 HU and 40% ASiR reconstruction; low-dose group (n = 20) with NI = 20  HU in the delay phase and MBIR and 40%ASiR. Images in the delay phase were compared. The CT values and standard deviation (SD) values of the liver, spleen, pancreas, kidney, erector spine and fat were measured. Contrast-noise-ratio (CNR = (CTtissue -CT fat )/SDfat ) of each measured organ were calculated and compared with one-way ANOVA among the three reconstruction groups. The subjective image scores of the three groups were assessed blindly by two experienced physicians using a 5-point system and the score consistency was compared by the κ test.

RESULTS:: Dose reduction of 75 % was achieved for the low-dose scan. The subjective scores (95 % confidence intervals) of the three groups (NI 10-40 %  ASiR, NI 20-40%  ASiR and NI 20-MBIR) were 4.00 ± 0.79 (3.62-4.37), 3.35 ± 0.58 (3.07-3.62) and 3.90 ± 0.64 (3.60-4.19), respectively with no difference between the NI 10-40%  ASiR and NI20-MBIR groups and good consistency between reviewers (κ = 0.726). MBIR had statistically lower SD values and higher contrast-to-noise ratio values in the liver, spleen, pancreas, kidney and erector spine than NI 10-40%  ASiR and NI 20-40%  ASiR (all p < 0.05).

CONCLUSION:: At 75 % dose reduction, MBIR provides similar image quality compared to 40% ASiR at normal-dose.

ADVANCES IN KNOWLEDGE:: MBIR provides good image quality at 25 % of the normal dose.