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Background: When using an anti‐scatter grid, a decrease in receptor dose caused by its X‐ray absorption seems to lead to the misperception that radiation dose needs to be increased even in digital radiography (DR). Objective: To demonstrate that there is no need to increase radiation dose in DR with a grid, based on a visual evaluation using an adult and a pediatric abdomen phantom (PAD and PPD, respectively). Materials and methods: Phantom images with and without a grid were obtained with exposure parameters determined based on a preliminarily measured signal‐to‐noise ratio improvement factor (SIF), an index for potential dose reduction when using a grid. In visual evaluation, four radiologists compared phantom images with a grid applied at different dose reduction rates (0% [no reduction], 18%, 36%, and 59% for PAD and 0% and 11% for PPD) against an image without a grid at the baseline dose (as the reference). They graded the overall image quality of the former relative to that of the latter (reference) on a 3‐point scale (3 = better, 2 = almost equal, 1 = worse). Results: The mean scores for dose reduction rates of 0%, 18%, 36%, and 59% were 3.00, 3.00, 2.75, and 1.00, respectively, for PAD; those for 0% and 11% were 2.13 and 1.63, respectively, for PPD. These results support the validity of our view that no dose increase is necessary when using an anti‐scatter grid. Actually, there is even a potential for improvement in image quality with dose reduction rates of ≤36% for PAD. Conclusion: It is worth reconsidering the necessity of increasing radiation dose in the DR imaging of the adult and pediatric abdomens with an anti‐scatter grid. [ABSTRACT FROM AUTHOR]

Background: Two deep learning image reconstruction (DLIR) techniques from two different computed tomography (CT) vendors have recently been introduced into clinical practice. Purpose: To characterize the noise properties of two DLIR techniques with different training methods, using a phantom containing a simple uniform and a complex non‐uniform region. Methods: A water‐bath phantom with a diameter of 300 mm was used as a base phantom. A textured phantom with a diameter of 128 mm, which was made of two materials, one equivalent to water and the other being 12 mg/ml diluted iodine, irregularly mixed to create a complex texture (non‐uniform region), was placed in the base phantom. Thirty repeated phantom scans were performed using two CT scanners (Revolution CT with Apex Edition, GE Healthcare; Aquilion One PRISM Edition, Canon Medical Systems) at two dose levels (CT dose index: 5 and 15 mGy). Images were reconstructed with each CT system's filtered back projection (FBP) and DLIR [TrueFidelity (TF), GE Healthcare; Advanced intelligent Clear‐IQ Engine Body Sharp (AC), Canon Medical Systems] for three process strengths. For basic characteristics of noise, the standard deviation (SD) and noise power spectrum (NPS) were measured for the uniform (water) region. A noise magnitude map was generated by calculating the inter‐image SD at each pixel position across the 30 images. Then, a noise reduction map (NRM), which visualizes the relative differences in noise magnitude between FBP and DLIR, was calculated. The NRM values ranged from 0.0 to 1.0. A low NRM value represents a less aggressive noise reduction. The histograms of the NRM value were analyzed for the uniform and non‐uniform regions. Results: The reduction in noise magnitude compared with FBP tended to be greater with AC (45%–85%) than with TF (32%–65%). The average NPS frequencies of TF and AC were almost comparable to those of FBP, except for the low‐dose condition and the high noise reduction strength for AC. The NRM values of TF and AC were higher in the uniform region than in the non‐uniform region. In the non‐uniform region, TF's average NRM values (0.21–0.48) tended to be lower than AC's (0.39–0.78). The histograms for TF showed a small overlap between the uniform and the non‐uniform regions; in contrast, those for AC showed a greater overlap. This difference seems to indicate that TF processes the uniform and non‐uniform regions more differently than AC does. Conclusion: This study has revealed a distinct difference in characteristics between the two DLIR techniques: TF tends to offer less aggressive noise reduction in non‐uniform regions and preserve the original signals, whereas AC tends to prioritize noise filtering over edge‐preservation, especially at the low‐dose condition and with the high noise reduction strength. [ABSTRACT FROM AUTHOR]

Purpose: We have developed a new stationary grid named a pixel‐aligned grid (PA grid), in which the grid lines are aligned to the pixel lines with submicron‐order precision. Further, we have evaluated its performance relative to that of a conventional grid combined with grid‐line removal (GLR) processing. Methods: A flat‐panel detector system of an indirect type, with a pixel pitch of 150 μm, was employed. Four PA grids having a grid ratio of 6:1 associated with abdominal bedside radiography, with the grid‐line pitch (GP) varied around the target value of 150 μm, were produced. Blank images were obtained with four PA grids for measuring the period and amplitude of the grid artifact. In performance evaluation, acrylic and anthropomorphic abdominal phantom images were used with the PA grid, a conventional grid (40 lines/cm, grid ratio 6:1), and no grids. The grid artifacts were evaluated by power spectrum (PS) analysis. Also, the signal‐to‐noise ratio (SNR) improvement factor (KSNR) was measured. Results: Grid artifacts were hardly recognizable with PA grids with GP errors of 0.3 μm and 0.6 μm because of the prolonged grid artifact periods. The measured artifact amplitudes of these PA grids were less than 0.6%. Furthermore, the PA grids did not produce notable frequency peaks in PS. In contrast, the conventional grid without GLR processing produced two conspicuous peaks. With GLR processing, notable reductions in PS were observed around the two peak frequencies, which caused blurring in bone structures. For the acrylic thickness of 20 cm, the KSNRs for the PA grid were around 1.4, suggesting some SNR improvement in abdominal bedside radiography. Conclusion: The present study has demonstrated that PA grids with their grid‐line pitches close to the pixel‐line pitch within errors of 0.6 μm produce grid artifact‐free images without any signal losses. Thus, the proposed PA grid will prove to be effective and useful in various clinical applications. [ABSTRACT FROM AUTHOR]

Purpose: To propose an optimization method of contrast medium injection for the split-bolus protocol based on the contrast medium pharmacokinetics and investigate the utility of the optimized split-bolus protocol in 3D CT angio-venography for laparoscopic gastrectomy. Materials and methods: A pharmacokinetic relationship between injection duration and time to the peak enhancement was taken into account in the protocol design. The first 20 consecutive patients underwent a multi-phase scan with a single-bolus injection (single-bolus protocol), and the next 20 underwent the proposed split-bolus protocol. CT attenuations of the arteries and veins and dose-length products (DLPs) were compared between the two protocols. Two radiologists visually assessed arterial and venous depictions and the misregistrations. Results: Mean arterial CT attenuations were not significantly different between the two protocols. Though mean venous CT attenuations for the split-bolus protocol were 7–11% lower than those of the single-bolus protocol, they were visually evaluated as similar. The mean DLP of the split-bolus protocol was 46% lower than that of the single-bolus protocol. Misregistration between the arteries and veins occurred 35–80% during the single-bolus protocol, but was not indicated in the split-bolus protocol. Conclusion: The split-bolus protocol with optimized timing was more effective for providing improved image quality with reduced radiation dose compared with the single-bolus protocol in 3D CT angio-venography for laparoscopic gastrectomy. [ABSTRACT FROM AUTHOR]

Purpose: Two ultra‐high‐resolution (UHR) computed tomography (CT) scanners are clinically available. One is achieved by a CT system with a 0.25 mm × 160 row detector (Detector‐UHR), whereas the other is with a 0.6 mm × 32 row detector with in‐plane comb filtering in a dual source CT (Comb‐UHR). We compared radiation dose efficiencies of the two UHR modes to that of a routine scan mode (RS), using physical image quality measures for an assumed condition of abdominal CT angiography (CTA). Methods: A wire phantom, a 300‐mm cylindrical water bath phantom, and a microdisk phantom were used for measuring the modulation transfer function (MTF), noise power spectrum (NPS), and slice sensitivity profiles (SSP), respectively, at CTDIvol of 20 mGy. Images with minimal slice thicknesses were reconstructed by filtered back projection methods. System performance functions (SPF2) based on the prewhitening theorem were calculated by dividing MTF2 by NPS measurements. The ideal observer's detectability index (d'2) was also estimated for a task corresponding to a 1‐mm diameter vessel. Furthermore, a bar‐pattern phantom placed in a water phantom resembling an adult abdomen was scanned, and the visibility of the bars was observed. Results: System performance function (SPF2) results showed that Comb‐UHR has a 70% dose efficiency compared to RS and provides better than twofold SPF2 compared to Detector‐UHR. The d'2 values of Detector‐UHR, Comb‐UHR, and RS were 6.5, 14.7, and 16.0, respectively. Although the bar‐pattern phantom images were consistent with the SPF results, bar widths < 1.0 mm for Detector‐UHR and < 0.75 mm for Comb‐UHR and RS were not resolved. Conclusions: Though both the UHR modes exhibited system performances extending to 2.6 cycles/mm, they appeared not to be advantageous compared to RS in the conditions applicable to abdominal CTA, because of their insufficient dose efficiencies. [ABSTRACT FROM AUTHOR]