State of the art: iterative CT reconstruction techniques

Owing to recent advances in computing power, iterative reconstruction (IR) algorithms have become a clinically viable option in computed tomographic (CT) imaging. Substantial evidence is accumulating about the advantages of IR algorithms over established analytical methods, such as filtered back projection. IR improves image quality through cyclic image processing. Although all available solutions share the common mechanism of artifact reduction and/or potential for radiation dose savings, chiefly due to image noise suppression, the magnitude of these effects depends on the specific IR algorithm. In the first section of this contribution, the technical bases of IR are briefly reviewed and the currently available algorithms released by the major CT manufacturers are described. In the second part, the current status of their clinical implementation is surveyed. Regardless of the applied IR algorithm, the available evidence attests to the substantial potential of IR algorithms for overcoming traditional limitations in CT imaging

Low radiation dose in computed tomography: the role of iodine

Recent approaches to reducing radiation exposure during CT examinations typically utilize automated dose modulation strategies on the basis of lower tube voltage combined with iterative reconstruction and other dose-saving techniques. Less clearly appreciated is the potentially substantial role that iodinated contrast media (CM) can play in low-radiation-dose CT examinations. Herein we discuss the role of iodinated CM in low-radiation-dose examinations and describe approaches for the optimization of CM administration protocols to further reduce radiation dose and/or CM dose while maintaining image quality for accurate diagnosis. Similar to the higher iodine attenuation obtained at low-tube-voltage settings, high-iodine-signal protocols may permit radiation dose reduction by permitting a lowering of mAs while maintaining the signal-to-noise ratio. This is particularly feasible in first pass examinations where high iodine signal can be achieved by injecting iodine more rapidly. The combination of low kV and IR can also be used to reduce the iodine dose. Here, in optimum contrast injection protocols, the volume of CM administered rather than the iodine concentration should be reduced, since with high-iodine-concentration CM further reductions of iodine dose are achievable for modern first pass examinations. Moreover, higher concentrations of CM more readily allow reductions of both flow rate and volume, thereby improving the tolerability of contrast administration

Coronary Computed Tomographic Angiography at 80 kVp and Knowledge-Based Iterative Model Reconstruction Is Non-Inferior to that at 100 kVp with Iterative Reconstruction

The aims of this study were to compare the image noise and quality of coronary computed tomographic angiography (CCTA) at 80 kVp with knowledge-based iterative model reconstruction (IMR) to those of CCTA at 100 kVp with hybrid iterative reconstruction (IR), and to evaluate the feasibility of a low-dose radiation protocol with IMR. Thirty subjects who underwent prospective electrocardiogram-gating CCTA at 80 kVp, 150 mAs, and IMR (Group A), and 30 subjects with 100 kVp, 150 mAs, and hybrid IR (Group B) were retrospectively enrolled after sample-size calculation. A BMI of less than 25 kg/m2 was required for inclusion. The attenuation value and image noise of CCTA were measured and the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated at the proximal right coronary artery and left main coronary artery. The image noise was analyzed using a non-inferiority test. The CCTA images were qualitatively evaluated using a four-point scale. The radiation dose was significantly lower in Group A than Group B (0.69 ± 0.08 mSv vs. 1.39 ± 0.15 mSv, p < 0.001). The attenuation values were higher in Group A than Group B (p < 0.001). The SNR and CNR in Group A were higher than those of Group B. The image noise of Group A was non-inferior to that of Group B. Qualitative image quality of Group A was better than that of Group B (3.6 vs. 3.4, p = 0.017). CCTA at 80 kVp with IMR could reduce the radiation dose by about 50%, with non-inferior image noise and image quality than those of CCTA at 100 kVp with hybrid IR

Low radiation dose calcium scoring: evidence and techniques

Coronary computed tomography (CT) allows for the acquisition of thin slices of the heart and coronary arteries, which can be used to detect and quantify coronary artery calcium (CAC), a marker of atherosclerotic cardiovascular disease. Despite the proven clinical value in cardiac risk prognostication, there remain concerns regarding radiation exposure from CAC CT scans. There have been several recent technical advancements that allow for significant radiation dose reduction in CAC scoring. This paper reviews the clinical utility and recent literature in low radiation dose CAC scoring

Prospective Evaluation of the Influence of Iterative Reconstruction on the Reproducibility of Coronary Calcium Quantification in Reduced Radiation Dose 320 Detector Row CT.

BACKGROUND: Coronary artery calcium (CAC) predicts coronary heart disease events and is important for individualized cardiac risk assessment. This report assesses the interscan variability of CT for coronary calcium quantification using image acquisition with standard and reduced radiation dose protocols and whether the use of reduced radiation dose acquisition with iterative reconstruction (IR; reduced-dose/IR ) allows for similar image quality and reproducibility when compared to standard radiation dose acquisition with filtered back projection (FBP; standard-dose/FBP ) on 320-detector row computed tomography (320-CT). METHODS: 200 consecutive patients (60 ± 9 years, 59% male) prospectively underwent two standard- and two reduced-dose acquisitions (800 total scans, 1600 reconstructions) using 320 slice CT and 120 kV tube voltage. Automated tube current modulation was used and for reduced-dose scans, prescribed tube current was lowered by 70%. Image noise and Agatston scores were determined and compared. RESULTS: Regarding stratification by Agatston score categories (0, 1-10, 11-100, 101-400, \u3e400), reduced-dose/IR versus standard-dose/FBP had excellent agreement at 89% (95% CI: 86-92%) with kappa 0.86 (95% CI: 0.81-0.90). Standard-dose/FBP rescan agreement was 93% (95% CI: 89-96%) with kappa = 0.91 (95% CI: 0.86-0.95) while reduced-dose/IR rescan agreement was similar at 91% (95% CI: 87-94%) with kappa 0.88 (95% CI: 0.83-0.93). Image noise was significantly higher but clinically acceptable for reduced-dose/IR (18 Hounsfield Unit [HU] mean) compared to standard-dose/FBP (16 HU; p \u3c 0.0001). Median radiation exposure was 74% lower for reduced- (0.37 mSv) versus standard-dose (1.4 mSv) acquisitions. CONCLUSION: Rescan agreement was excellent for reduced-dose image acquisition with iterative reconstruction and standard-dose acquisition with filtered back projection for the quantification of coronary calcium by CT. These methods make it possible to reduce radiation exposure by 74%. CLINICAL TRIAL REGISTRATION: URL: https://clinicaltrials.gov/ct2/show/NCT01621594. UNIQUE IDENTIFIER: NCT01621594

Pure iterative reconstruction improves image quality in computed tomography of the abdomen and pelvis acquired at substantially reduced radiation doses in patients with active Crohn disease

Objective: We assessed diagnostic accuracy and image quality of modified protocol (MP) computed tomography (CT) of the abdomen and pelvis reconstructed using pure iterative reconstruction (IR) in patients with Crohn disease (CD). Methods: Thirty-four consecutive patients with CD were referred with suspected extramural complications. Two contemporaneous CT datasets were acquired in all patients: standard protocol (SP) and MP. The MP and SP protocols were designed to impart radiation exposures of 10% to 20% and 80% to 90% of routine abdominopelvic CT, respectively. The MP images were reconstructed with model-based IR (MBIR) and adaptive statistical IR (ASIR). Results: The MP-CT and SP-CT dose length product were 88 (58) mGy.cm (1.27 [0.87] mSv) and 303 [204] mGy.cm (4.8 [2.99] mSv), respectively (P < 0.001). Median diagnostic acceptability, spatial resolution, and contrast resolution were significantly higher and subjective noise scores were significantly lower on SP-ASIR 40 compared with all MP datasets. There was perfect clinical agreement between MP-MBIR and SP-ASIR 40 images for detection of extramural complications. Conclusions: Modified protocol CT using pure IR is feasible for assessment of active CD

Radiation dose reduction in pediatric great vessel stent computed tomography using iterative reconstruction: A phantom study

Background To study dose reduction using iterative reconstruction (IR) for pediatric great vessel stent computed tomography (CT). Methods Five different great vessel stents were separately placed in a gel-containing plastic holder within an anthropomorphic chest phantom. The stent lumen was filled with diluted contrast gel. CT acquisitions were performed at routine dose, 52% and 81% reduced dose and reconstructed with filtered back projection (FBP) and IR. Objective image quality in terms of noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) as well as subjective image quality were evaluated. Results Noise, SNR and CNR were improved with IR at routine and 52% reduced dose, compared to FBP at routine dose. The lowest dose level resulted in decreased objective image quality with both FBP and IR. Subjective image quality was excellent at all dose levels. Conclusion IR resulted in improved objective image quality at routine dose and 52% reduced dose, while objective image quality deteriorated at 81% reduced dose. Subjective image quality was not affected by dose reduction