A Preliminary Analysis of Using the Sinogram-affirmed Iterative Reconstruction Strength Levels based on the Original Data of Low-dose Chest CT to Evaluate Different Types of Small Pulmonary Nodules

Objective: We intend to explore the Corresponding relations between the Sinogram-affirmed iterative reconstruction (SAFIRE) strength levels and the optimized display of different types (solid, partially solid, and pure ground glass) of small pulmonary nodules in low-dose chest CT (LDCT). Materials and methods: We analyzed 105 small pulmonary nodules in 101 patients who underwent LDCT from September 2020 to January 2021 and also met the criteria for small pulmonary nodules. Based on nodule composition, they were divided into the solid nodule Group (n=27), the partially solid nodule group (n=37) and the pure ground glass nodule group (n=41). First we adopted the one-way analysis of variance, Chi-square test or Kruskal-Wallis H test to analyze the general data in groups, then took the filtered back projection algorithm (FBP, B50f) as the reference to compare the difference in objective image quality (including noise value, CT value of small pulmonary nodules, SNR and CNR) and subjective image quality in groups under different SAFIRE modes (I50f and I70f, strength levels 1 to 5 respectively).Results: 1 There was no significant difference in gender, body mass index, and nodule distribution in three groups. The age and length of the nodules in the pure ground-glass nodule group were smaller than those in the solid and partial solid nodule groups; 2 The image noise values in SAFIRE I50f 1-5 and I70f-5 were lower than that in FBP B50f while SAFIRE I50f-5 showed the lowest noise value. There was no significant difference in CT values of small pulmonary nodules in the three groups under different modes, the SNR and CNR of small pulmonary nodules in SAFIRE I50f-5 were higher than those of FBP B50f and other SAFIRE modes; 3 SAFIRE I50f 3~5 of solid and partial solid pulmonary nodule groups obtained higher subjective scores than that of FBP B50f and other SAFIRE modes except I70f-5. SAFIRE I50f-4 of pure ground glass nodule group obtained a higher subjective score than those of FBP B50f and other SAFIRE modes except I50f-3 and I50f-5, and there was no significant difference in the subjective scores in three groups under this mode (P=0.428). Conclusion: SAFIRE I50f-4 performed well and displayed a balanced effect in the objective and subjective evaluation of solid, partial solid and pure ground glass small pulmonary nodules in LDCT. We suggest it can be applied to evaluate different types of small pulmonary nodules in LDCT.