Application of half-dose spectral CT based on the automatic spectral imaging mode selection and adaptive statistical iterative reconstruction in the CT examination of upper abdomen in obese patients.

Abstract

Objective: To investigate the value of combined use of half-dose spectral CT based on the automatic spectral imaging mode selection (GSI Assist) and adaptive statistical iterative reconstruction (ASIR) in the CT examination of upper abdomen in obese patients as compared with conventional CT. Methods: Eight-two obese patients (body mass index≥29 kg/m(2)) were prospectively selected from October to December 2016, and contrast-enhanced CT during arterial phase (AP) and portal venous phase (PVP) were carried out in those patients.The patients were randomly assigned to the study group and control group with random number table (41 cases in each group). In the study group, half-dose spectral CT based on GSI Assist was applied and monochromatic images (40 to 70 keV, 10 keV as increment) were reconstructed using 50% ASIR (group A). In the control group, the fixed tube potential of 120 kVp was done with images reconstruction using 30% ASIR (group B). Quantitative parameters of radiation dose, CT value, contrast to noise ratio (CNR) and image noise were compared between the two groups by using two sample t test, while qualitative visual parameters (overall image quality as graded on a 5-point scale) were compared with Mann-Whitney U test. Results: There was significant difference in effective radiation dose between the two groups[(5.2±0.8) vs (10.4±1.7) mSv, t=-17.822, P<0.001], and it was decreased for 50% in group A. During the arterial phase (AP) and portal venous phase (PVP), at the energy level of 40 keV and 50 keV, higher CT values, higher or similar CNRs, higher image noise and lower overall image quality scores were found in group A when compared with group B. At the energy level of 60 keV, group A had higher CT values, higher or similar CNRs, similar overall image quality scores with higher or similar image noise as compared with group B. At the energy level of 70 keV, the two groups had similar CT values, CNRs and image noise, and higher overall image quality scores were found in group A. Conclusions: In obese patients, combined use of half-dose spectral CT based on GSI Assist and ASIR can reduce effective radiation dose up to 50% when compared with conventional upper abdominal CT.Monochromatic images at 70 keV can maintain CNR and improve overall image quality.