Background: As cross-sectional images expanded in clinical practice, the number of renal lesions discovered incidentally has been increasing. CT protocols for renal mass evaluation may include pre-and post-contrast phase. However, a major concern with respect to those multiphase techniques is often the radiation dose. One further critical issue is how to minimize the radiation dose while image quality is optimized in routine daily clinical practice. Objectives: To evaluate the image quality and radiation dose of renal artery CT angiography (CTA) with optimal sinogram affirmed iterative reconstruction (SAFIRE) strength level at 80 kVp for optimizing the scan and reconstruction parameters of renal artery CTA, in comparison to 120 kVp acquisition with filtered back projection (FBP). Patients and Methods: Sixty consecutive patients were classified into three groups prospectively in this study: 1) 80 kVp group (n = 30) with FBP and 2) 80 kVp group with SAFIRE (S4) and 3) 120 kV group (n = 30) with FBP. CT values and noise were measured, contrastto-noise ratio (CNR) and signal-to-noise ratio (SNR) of the renal artery CTA were calculated for quantitative assessment. Subjective image quality was evaluated by two experienced abdominal radiologists with a five-point scale in a blinded and randomized setting for qualitative assessment. Volume CT dose index (CTDIvol) and size-specific dose estimate (SSDE) were calculated and estimated for each subject presented in this study. Results: As for quantitative assessment, CNR, SNR and CT values of renal artery in 80kVp group with SAFIRE strength levels or FBP were higher than those of 120 kVp group with FBP (all Ps < 0. 05), the mean noise gradually decreased in 80kVp group when increasing the SAFIRE strength levels (S1-S5). As for qualitative assessment, the overall image quality, vessel sharpness, segmental renal artery displayed in maximum intensity projection (MIP) or multiplanar reformation (MPR), and diagnostic confidence of the two groups were all accepted by two radiologists (inter-observer agreement ranged from 0. 600 to 0. 940) (score 3). The overall image quality of 80 kVp with SAFIRE 4 was similar to that of 120 kVp group with FBP (P = 0. 412), as well as segmental renal artery displayed in MIP and diagnostic confidence (P = 0. 095 and P = 0. 061, respectively). As for radiation dose reduction, 80kVp group could reduce 32. 7% CTDIvol and 31. 2% SSDE compared to the 120 kVp group. Conclusion: In patients with BMI lower than 28 kg/m2, renal artery CTA at 80 kVp with SAFIRE is feasible and can provide satisfactory images for clinical applications. This method also provides reduction in radiation dose. SAFIRE strength level 4 is recommended for reconstructing renal artery CTA.

Background: The aim of this study was to evaluate the influences of iterative model reconstruction (IMR) and hybrid-iterative reconstruction (HIR) techniques on quantitative and qualitative image analysis of 256-slice coronary computed tomography angiography (CCTA). Methods: Sixty-one patients (30 men and 31 women with mean age of 60. 68 ± 9. 13 years) who had undergone CCTA by the 256-slice CT scanner were evaluated. The raw data were reconstructed using HIR and IMR algorithms. For objective assessment of image quality, parameters of noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were obtained for both reconstruction algorithms. For subjective assessment, two physician specialists evaluated image quality using a 5-point scale. Findings: The mean image noise on HIR and IMR images was 32. 74 ± 6. 04 and 25. 15 ± 3. 59, respectively. In IMR, the CNR method (28. 81 ± 5. 13) was significantly better than HIR method (23. 06 ± 5. 03) (P < 0. 001). However, the HIR method (4. 62 ± 0. 39) was higher than the IMR method (4. 48 ± 0. 45) in terms of qualitative or subjective criteria (P < 0. 001). Conclusion: The IMR method can improve quantitative criteria of image, reduce noise, and increase SNR and CNR of images better than HIR method. However, the images which reconstructed by HIR were superior to IMR in terms of qualitative criteria.

Background: Relative to classical methods in computed tomography, iterative reconstruction techniques enable significantly improved image qualities and/or lowered patient doses. However, the computational speed is a major concern for these iterative techniques. In the present study, we present a method for fast system matrix calculation based on the line integral model (LIM) to speed up the computations without compromising the image quality. In addition, we develop a hybrid line– area integral model (AIM) that highlights the advantages of both LIM and AIMs. Methods: The contributing detectors for a given pixel and a given projection view, and the length of corresponding intersection lines with pixels, are calculated using our proposed algorithm. For the hybrid method, the respective narrow‑ angle fan beam was modeled by multiple equally spaced lines. The computed system matrix was evaluated in the context of reconstruction using the simultaneous algebraic reconstruction technique (SART) as well as maximum likelihood expectation maximization (MLEM). Results: The proposed LIM offers a considerable reduction in calculation times compared to the standard Siddon algorithm: 2. 9 times faster. Differences in root mean square error and peak signal‑ to‑ noise ratio were not significant between the proposed LIM and the Siddon algorithm for both SART and MLEM reconstruction methods (P > 0. 05). Meanwhile, the proposed hybrid method resulted in significantly improved image qualities relative to LIM and the Siddon algorithm (P < 0. 05), though computations were 4. 9 times more intensive than the proposed LIM. Conclusion: We have proposed two fast algorithms to calculate the system matrix. The first is based on LIM and was faster than the Siddon algorithm, with matched image quality, whereas the second method is a hybrid LIM– AIM that achieves significantly improved images though with its computational requirements.

Background: Coronary computed tomography angiography (cCTA) technology as a kind of non-traumatic examination has been widely used in clinical practice. There are major issues that need to be considered. One is how to obtain high quality images and at the same time effectively reduce the radiation dose. The second is coronary artery calcified plaque artifacts that seriously affect the depiction of plaque morphology and luminal stenosis. In case of dose reduction, these artifacts are more outstanding. Objectives: This study determined the value of sinogram-affirmed iterative reconstruction (SAFIRE) technology to assess coronarycalcified plaques. This value was compared with filtered back-projection (FBP) reconstruction. Patients and Methods: Sixty-three cases with calcified plaques diagnosed via coronary CT examination were selected. The mean CT-number, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), number of calcium plaques, edges, lumen situation, and the subjective image quality ratings of the cases using FBP and SAFIRE1– SAFIRE5 (six groups) were analyzed and compared. Results: The subjective ratings of image quality using SAFIRE1– SAFIRE5 reconstructions were significantly higher than those using FBP, with SAFIRE3 achieving the highest rating. Compared with FBP reconstruction, the differences in noise, SNR, and CNR using SAFIRE1-SAFIRE5 were statistically significant (P < 0. 05), with SAFIRE5 reconstruction achieving the highest SNR and CNR, and FBP reconstruction achieving the lowest. The revealed numbers of calcium plaques in the SAFIRE1-SAFIRE5 reconstruction groups were higher than that in the FBP reconstruction without significant differences in the number of calcium plaques among the SAFIRE1– SAFIRE5 groups (P > 0. 05). Conclusion: SAFIRE reconstruction provided better coronary image quality and displayed the number, morphology, and surrounding lumen of calcium plaques more accurately than traditional FBP reconstruction, with SAFIRE3 achieving the best results.