Iterative Model Reconstruction (IMR) in MDCT Below 2 mSv for the Detection of Urinary Calculi: Diagnostic Accuracy and Image Quality in Comparison to Filtered Back-Projection and 4th Generation Iterative Reconstruction (iDose4).

PURPOSE: The purpose of the study was to assess the impact of iterative model reconstruction (IMR) on reader confidence with respect to stone detection and image quality in comparison to filtered back-projection (FBP) and iDose level 4 (iDose4) in abdominal MDCT with radiation doses below 2 mSv. MATERIALS AND METHODS: For 32 consecutive patients with suspected ureteral stone disease, the raw data of unenhanced 256 slice MDCT (120 kV, 40 reference mAs, mean CTDIvol: 2.7 ±â€Š0.8 mGy, mean DLP: 126 ±â€Š38 mGy × cm) were reconstructed using a prototype version of IMR (levels 1 - 3), iDose4 (level 4) and FBP at a 3 mm slice thickness. Image analysis was independently performed by two radiologists in a blinded fashion. The reader confidence level with respect to stone detection was recorded based on a 5-point scale (1 - certain exclusion; 5 - concrement definitely present) as well as for the evaluation of image quality regarding the depiction of anatomical details (1 - poor; 5 - excellent). A clinical reference standard for stone detection was not established. Statistical evaluation included weighted kappa analysis and Wilcoxon test. RESULTS: 17 pelvic and ureteral stones were found. 11 further concrements were located within the ostium of the urinary bladder or the bladder itself. Applying IMR, a distinct improvement in image quality was observed at every level (mean value for FBP, 2.0; iDose4, 2.9; IMR L1, 4.2; IMR L2, 4.0; IMR L3, 3.9; all p < 0.001). Applying the higher IMR levels L2 and L3, a certain level of so-called "blotchiness" of anatomical contours was observed. Reader confidence was significantly improved and was independent of IMR level (certain stone detection FBP, 69 %; iDose4, 81 %; IMR L1 to L3, 95 %; all p > 0.001). With increasing IMR levels, the reduction in streak artifacts was quantified by a decrease in image noise. A loss of anatomical information was not observed. The sensitivity rates for stone detection were equivalent for all MDCTs reconstructed with FBP, iDose4 and IMR. A mean effective dose of 1.9 ±â€Š0.6 mSv was calculated. CONCLUSION: In comparison to FBP and iDose4, a significant increase in mean image quality, reduction in image noise and improvement in subjective reader confidence can be achieved by applying IMR even at significantly reduced dose settings below 2 mSv. Results indicate that a further dose reduction might be possible with IMR. KEY POINTS: · Urinary tract. · urolithiasis. · iterative reconstruction. CITATION FORMAT: · Schmidt-Holtz J, Laqmani A, Butscheidt S et al. Iterative Model Reconstruction (IMR) in MDCT Below 2mSv for the Detection of Urinary Calculi: Diagnostic Accuracy and Image Quality in Comparison to Filtered Back-Projection and 4th Generation Iterative Reconstruction (iDose4). Fortschr Röntgenstr 2018; 190: 630 - 636.

Comparison of image quality and visibility of normal and abnormal findings at submillisievert chest CT using filtered back projection, iterative model reconstruction (IMR) and iDose4™.

OBJECTIVE: To compare both image quality and visibility of normal and abnormal findings at submillisievert chest CT (smSv-CT) using filtered back projection (FBP) and the two different iterative reconstruction (IR) techniques iterative model reconstruction (IMR) and iDose4™. MATERIALS AND METHODS: This institutional review board approved study was based on retrospective interpretation of clinically indicated acquired data. The requirement to obtain informed consent was waived. 81 patients with suspected pneumonia underwent smSv-CT (Brilliance iCT, Philips Healthcare; mean effective dose: 0.86±0.2mSv). Data were reconstructed using FBP and two different IR techniques iDose4™ and IMR (Philips Healthcare) at various iteration levels. Objective image noise (OIN) was measured. Two experienced readers independently assessed all images for image noise, image appearance and visibility of normal anatomic and abnormal findings. A random intercept model was used for statistical analysis. RESULTS: Compared to FBP and iDose4™, IMR reduced OIN up to 88% and 72%, respectively (p<0.001). A mild blotchy image appearance was seen in IMR images, affecting diagnostic confidence. iDose4™ images provided satisfactory to good image quality for visibility of normal and abnormal findings and were superior to FBP (p<0.001). IMR images were significantly inferior for visibility of normal structures compared to iDose4™, while being superior for visibility of abnormal findings except for reticular pattern (p<0.001). CONCLUSION: IMR results for visibility of normal and abnormal lung findings are heterogeneous, indicating that IMR may not represent a priority technique for clinical routine. iDose4™ represents a suitable method for evaluation of lung tissue at submillisievert chest CT.

CT Pulmonary Angiography at Reduced Radiation Exposure and Contrast Material Volume Using Iterative Model Reconstruction and iDose4 Technique in Comparison to FBP.

PURPOSE: To assess image quality of CT pulmonary angiography (CTPA) at reduced radiation exposure (RD-CTPA) and contrast medium (CM) volume using two different iterative reconstruction (IR) algorithms (iDose4 and iterative model reconstruction (IMR)) in comparison to filtered back projection (FBP). MATERIALS AND METHODS: 52 patients (body weight < 100 kg, mean BMI: 23.9) with suspected pulmonary embolism (PE) underwent RD-CTPA (tube voltage: 80 kV; mean CTDIvol: 1.9 mGy) using 40 ml CM. Data were reconstructed using FBP and two different IR algorithms (iDose4 and IMR). Subjective and objective image quality and conspicuity of PE were assessed in central, segmental, and subsegmental arteries. RESULTS: Noise reduction of 55% was achieved with iDose4 and of 85% with IMR compared to FBP. Contrast-to-noise ratio significantly increased with iDose4 and IMR compared to FBP (p<0.05). Subjective image quality was rated significantly higher at IMR reconstructions in comparison to iDose4 and FBP. Conspicuity of central and segmental PE significantly improved with the use of IMR. In subsegmental arteries, iDose4 was superior to IMR. CONCLUSIONS: CTPA at reduced radiation exposure and contrast medium volume is feasible with the use of IMR, which provides improved image quality and conspicuity of pulmonary embolism in central and segmental arteries.

Reduced-dose abdominopelvic CT using hybrid iterative reconstruction in suspected left-sided colonic diverticulitis.

OBJECTIVES: To assess the effect of hybrid iterative reconstruction (HIR) and filtered back projection (FBP) on abdominopelvic CT with reduced-dose (RD-APCT) in the evaluation of acute left-sided colonic diverticulitis (ALCD). METHODS: Twenty-five consecutive patients with suspected ALCD who underwent RD-APCT (mean CTDIvol 11.2 ± 4.2 mGy) were enrolled in this study. Raw data were reconstructed using FBP and two increasing HIR levels, L4 & L6. Two radiologists assessed image quality, image noise and reviewer confidence in interpreting findings of ALCD, including wall thickening, pericolic fat inflammation, pericolic abscess, and contained or free extraluminal air. Objective image noise (OIN) was measured. RESULTS: OIN was reduced up to 54 % with HIR compared to FBP. Subjective image quality of HIR images was superior to FBP; subjective image noise was reduced. The detection rate of extraluminal air was higher with HIR L6. Reviewer confidence in interpreting CT findings of ALCD significantly improved with application of HIR. CONCLUSIONS: RD-APCT with HIR offers superior image quality and lower image noise compared to FBP, allowing a high level of reviewer confidence in interpreting CT findings in ALCD. HIR facilitates detection of ALCD findings that may be missed with the FBP algorithm. KEY POINTS: HIR significantly reduces objective image noise in comparison to conventional FBP. HIR offers superior subjective image quality in comparison to conventional FBP. HIR allows reduced-dose abdominopelvic CT with acceptable image quality. Reviewer confidence in interpreting CT findings in ALCD significantly improves with HIR.