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.

Purpose: The main goal of this study was to determine the optimal collimator in the absence of medium energy collimators along with the impact of Attenuation Correction (AC) and different ITERATIVE RECONSTRUCTION protocols on the quantitative evaluation of Gallium-67 (67Ga) SPECT/CT imaging. Materials and Methods: A GE Discovery 670 dual-head SPECT/CT scanner and a NEMA phantom filled with 67Ga solution were used to scan the patients. The projections were acquired with both Low Energy High Resolution (LEHR) and High Energy General Purpose (HEGP) collimators, and CT images were acquired to evaluate the effect of attenuation correction. SPECT data were reconstructed using the ordered subset expectation maximization (OSEM) method with various combinations of iterations and subsets. The performance was quantified, and a clinical study validated the phantom study. Results: Acquired images by the HEGP collimator yielded higher Contrast Recovery (CR) and Contrast to Noise Ratio (CNR) in images with AC than those without non-AC (41.6% and 74.2%, respectively). The CNR in all spheres after AC was increased by 80.4% (82.1%) for the HEGP collimator against the LEHR collimator. Also, an increase in iterations × subsets from 16 to 48 led to the Coefficient of Variation (COV) increasing by 17.2%, 16.67%, 15.50%, 14.4%, 14.2%, and 14.1% for 10 mm to 37 mm sphere diameter, respectively. Conclusion: CT-based AC and HEGP collimators can yield improved 67Ga SPECT quantification compared to Non-AC and LEHR collimators. The choice of the optimal collimator with the RECONSTRUCTION protocol led to changes in the image quality and quantitative accuracy, emphasizing the need to carefully select the appropriate combination of data acquisition factors.

Introduction: Recent studies of Computed Tomography (CT) conducted on patient dose reduction have recommended using an ITERATIVE RECONSTRUCTION algorithm and mA (mili-Ampere) dose modulation. The current study aimed to evaluate ITERATIVE Dose Reduction Algorithm (IDREAM) as an ITERATIVE RECONSTRUCTION algorithm. Material and Methods: Two CT protocols (i. e., A: 120 KV /150 mA, FBP; B: 120KV/ (20-150) mAs, IDREAM) to scan water and acrylic phantoms. A number of 40 patients were assigned to two CT protocols (C: n=20, 120KV/160 ± 10 mAs, FBP and D: n=20, 120 KV/ (30-150 mAs, IDREAM), the two groups (C and D) were then referred to abdomen and pelvis CT scan (Sinovision, insitum 16) with contrast. Image quality parameters, dose calculations were measured for all groups (i. e., A, B, C, and D). Results: Group B had a highly significant SNR with less significant noise (P<0. 05), in comparison with group A. In addition, uniformity was markedly higher for group B (P<0. 05) in water phantom and insignificantly different (P>0. 05) in acrylic phantom, as compared to group A. CTDIvol (A: 13. 94 mGy; B: 6. 91 mGy, P<0. 05 ) and DLP (A: 501. 76 mGy. cm; B: 248. 88 mGy. cm). Noise and SNR were significantly different (P<0. 05) in group D against C. CTDIvol (C: 30. 3± 5. 2 mGy; D: 15. 4 ± 2. 7 mGy, P<0. 05 ), DLP (C: 544± 100 mGy. cm; D: 272. 3± 50. 3 mGy. cm, P<0. 05) and the effective dose (C: 8. 1± 1. 5 mSv; D: 4. 08± 0. 75 mSv, P<0. 05) Conclusion: The results of the present study were indicative of the feasibility of IDREAMas an ITERATIVE RECONSTRUCTION algorithm.