Ultra-low-dose CT for left atrium and pulmonary veins imaging using new model-based iterative reconstruction algorithm

Reduced Radiation Exposure Protocol during Computer Tomography of the Left Atrium Prior to Catheter Ablation in Patients with Atrial Fibrillation

(1) Background: Computer tomography (CT) is an imaging modality used in the pre-planning of radiofrequency catheter ablation (RFA) procedure in patients with cardiac arrhythmias. However, it is associated with a considerable ionizing radiation dose for patients. This study aims to develop and validate low-dose CT scanning protocols of the left atrium (LA) for RFA guidance. (2) Methods: 68 patients scheduled for RFA of atrial fibrillation were sequentially assigned to four groups of ECG-gated scanning protocols, based on the set tube current (TC): Group A (n = 20, TC = 33 mAs), Group B (n = 18, TC = 67 mAs), Group C (n = 10, TC = 135 mAs), and control Group D (n = 20, TC = 600 mAs). We used a 256-row multidetector CT with body weight-dependent tube voltage of 80 kVp (<70 kg), 100 kVp (70−90 kg), and 120 kVp (>90 kg). We evaluated scanning parameters including radiation dose, total scanning procedure time and signal-to-noise ratio (SNR). (3) Results: The average effective radiation dose (ED) was lower in Group A in comparison to Group B, C and D (0.83 (0.76−1.10), 1.55 (1.36−1.67), 2.91 (2.32−2.96) and 9.35 (8.00−10.04) mSv, p < 0.05). The total amount of contrast media was not significantly different between groups. The mean SNR was 6.5 (5.8−7.3), 7.1 (5.7−8.2), 10.8 (10.1−11.3), and 12.2 (9.9−15.7) for Group A, B, C and D, respectively. The comparisons of SNR in group A vs. B and C vs. D were without significant differences. (4) Conclusions: Optimized pre-ablation CT scanning protocols of the LA can reduce an average ED by 88.7%. Three dimensional (3D) models created with the lowest radiation protocol are useful for the integration of electro-anatomic-guided RFA procedures.

Combination of Deep Learning-Based Denoising and Iterative Reconstruction for Ultra-Low-Dose CT of the Chest: Image Quality and Lung-RADS Evaluation

OBJECTIVE. The objective of our study was to assess the effect of the combination of deep learning-based denoising (DLD) and iterative reconstruction (IR) on image quality and Lung Imaging Reporting and Data System (Lung-RADS) evaluation on chest ultra-low-dose CT (ULDCT). MATERIALS AND METHODS. Forty-one patients with 252 nodules were evaluated retrospectively. All patients underwent ULDCT (mean ± SD, 0.19 ± 0.01 mSv) and standard-dose CT (SDCT) (6.46 ± 2.28 mSv). ULDCT images were reconstructed using hybrid iterative reconstruction (HIR) and model-based iterative reconstruction (MBIR), and they were postprocessed using DLD (i.e., HIR-DLD and MBIR-DLD). SDCT images were reconstructed using filtered back projection. Three independent radiologists subjectively evaluated HIR, HIR-DLD, MBIR, and MBIR-DLD images on a 5-point scale in terms of noise, streak artifact, nodule edge, clarity of small vessels, homogeneity of the normal lung parenchyma, and overall image quality. Two radiologists independently evaluated the nodules according to Lung-RADS using HIR, MBIR, HIR-DLD, and MBIR-DLD ULDCT images and SDCT images. The median scores for subjective analysis were analyzed using Wilcoxon signed rank test with Bonferroni correction. Intraobserver agreement for Lung-RADS category between ULDCT and SDCT was evaluated using the weighted kappa coefficient. RESULTS. In the subjective analysis, ULDCT with DLD showed significantly better scores than did ULDCT without DLD (p < 0.001), and MBIR-DLD showed the best scores among the ULDCT images (p < 0.001) for all items. In the Lung-RADS evaluation, HIR showed fair or moderate agreement (reader 1 and reader 2: κw = 0.46 and 0.32, respectively); MBIR, moderate or good agreement (κw = 0.68 and 0.57); HIR-DLD, moderate agreement (κw = 0.53 and 0.48); and MBIR-DLD, good agreement (κw = 0.70 and 0.72). CONCLUSION. DLD improved the image quality of both HIR and MBIR on ULDCT. MBIR-DLD was superior to HIR_DLD for image quality and for Lung-RADS evaluation.

Image Quality and Radiation Dose in CT Venography Using Model-Based Iterative Reconstruction at 80 kVp versus Adaptive Statistical Iterative Reconstruction-V at 70 kVp

Objective

To compare the objective and subjective image quality indicators and radiation doses of computed tomography (CT) venography performed using model-based iterative reconstruction (MBIR) at 80 kVp and adaptive statistical iterative reconstruction (ASIR)-V at 70 kVp.

Materials and Methods

Eighty-three patients who had undergone CT venography of the lower extremities with MBIR at 80 kVp (Group A; 21 men and 20 women; mean age, 55.5 years) or ASIR-V at 70 kVp (Group B; 18 men and 24 women; mean age, 57.3 years) were enrolled. Two radiologists retrospectively evaluated the objective (vascular enhancement, image noise, signal-to-noise ratio [SNR], contrast-to-noise ratio [CNR]) and subjective (quantum mottle, delineation of contour, venous enhancement) image quality indicators at the inferior vena cava and femoral and popliteal veins. Clinical information, radiation dose, reconstruction time, and objective and subjective image quality indicators were compared between groups A and B.

Results

Vascular enhancement, SNR, and CNR were significantly greater in Group B than in Group A (p ≤ 0.015). Image noise was significantly lower in Group B (p ≤ 0.021), and all subjective image quality indicators, except for delineation of vein contours, were significantly better in Group B (p ≤ 0.021). Mean reconstruction time was significantly shorter in Group B than in Group A (1 min 43 s vs. 131 min 1 s; p < 0.001). Clinical information and radiation dose were not significantly different between the two groups.

Conclusion

CT venography using ASIR-V at 70 kVp was better than MBIR at 80 kVp in terms of image quality and reconstruction time at similar radiation doses.

Ultra-low-dose chest computed tomography for interstitial lung disease using model-based iterative reconstruction with or without the lung setting

The aim of this study was to assess the effects of reconstruction on the image quality and quantitative analysis for interstitial lung disease (ILD) using filtered back projection (FBP) and model-based iterative reconstruction (MBIR) with the lung setting and the conventional setting on ultra-low-dose computed tomography (CT).Fifty-two patients with known ILD were prospectively enrolled and underwent CT at an ultra-low dose (0.18 ± 0.02 mSv) and a standard dose (7.01 ± 2.66 mSv). Ultra-low-dose CT was reconstructed using FBP (uFBP) and MBIR with the lung setting (uMBIR-Lung) and the conventional setting (uMBIR-Stnd). Standard-dose CT was reconstructed using FBP (sFBP). Three radiologists subjectively evaluated the images on a 3-point scale (1 = worst, 3 = best). For objective image quality analysis, regions of interest were placed in the lung parenchyma and the axillary fat, and standard deviation (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were evaluated. For 32 patients with clinically diagnosed idiopathic interstitial pneumonia, quantitative measurements including total lung volume (TLV) and the percentage of ILD volume (%ILDV) were obtained. The medians of 3 radiologists' scores were analyzed using the Wilcoxon signed-rank test and the objective noise was analyzed using the paired t test. The Bonferroni correction was used for multiple comparisons. The quantitative measurements were analyzed using the Bland-Altman method.uMBIR-Lung scored better than uMBIR-Stnd and worse than sFBP (P < .001), except for noise and streak artifact in subjective analysis. The SD decreased significantly in the order of uMBIR-Stnd, uMBIR-Lung, sFBP, and uFBP (P < .001). The SNR and CNR increased significantly in the order of uMBIR-Stnd, uMBIR-Lung, sFBP, and uFBP (P < .001). For TLV, there was no significant bias between ultra-low-dose MBIRs and sFBP (P > .3). For %ILDV, there was no significant bias between uMBIR-Lung and sFBP (p = 0.8), but uMBIR-Stnd showed significantly lower %ILDV than sFBP (P = .013).uMBIR-Lung provided more appropriate image quality than uMBIR-Stnd. Although inferior to standard-dose CT for image quality, uMBIR-Lung showed equivalent CT quantitative measurements to standard-dose CT.

Multimodality imaging of left atrium in patients with atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia worldwide associated with significant morbidity and mortality and represents a significant health care burden. Goals of AF treatment include prevention of cardioembolic stroke using anticoagulation and device therapy and restoration of sinus rhythm using antiarrhythmic drugs or catheter ablation techniques. A comprehensive assessment of cardiac chamber size and function is often started with echocardiography as a first line diagnostic imaging strategy. Recently, innovations in advanced imaging using cardiac magnetic resonance (CMR) and cardiac computed tomography (CCT) provide a detailed characterization of atrial anatomy and have been shown to accurately exclude thrombus and guide left atrial appendage (LAA) closure or catheter ablation (CA) of atrial fibrillation. Compared to echocardiography, CCT offers an uncompromised spatial resolution and a fast dataset acquisition, with the disadvantages of the need of iodine contrast agent and radiation exposure. CMR, conversely, can rely on very high temporal resolution, the unique feature of tissue characterization and the absence of radiation exposure. However, the main drawbacks of this diagnostic tool are long scan times and low availability. This review will illustrate the vital role of multimodality cardiac imaging in the accurate identification of left atrial, pulmonary vein and LAA size and function, discuss advanced imaging techniques to rule out thrombus and highlight novel CMR and CCT techniques to guide catheter ablation of AF and LAA occlusion.

Submillisievert CT angiography for carotid arteries using wide array CT scanner and latest iterative reconstruction algorithm in comparison with previous generations technologies: Feasibility and diagnostic accuracy

OBJECTIVES

To assess evaluability and diagnostic accuracy of a low dose CT angiography (CTA) protocol for carotid arteries using latest Iterative Reconstruction (IR) algorithm in comparison with standard 100 kVp protocol using previous generation CT and IR.

MATERIALS AND METHODS

105 patients, referred for CTA of the carotid arteries were prospectively enrolled in our study and underwent CTA with 80 kVp and latest IR algorithm (group 1). Data were retrospectively compared with 100 consecutive patients with similar examination indications that had previously undergone CTA of carotid arteries with a standard 100 kVp protocol and a first generation IR algorithm (group 2). Image quality was evaluated with a 4-point Likert-scale. For each exam CT number, image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) at level of common carotid artery (CCA), internal carotid artery (ICA) and at level of Circle of Willis and Effective Dose (ED) were evaluated. 62 Group 1 patients underwent a clinically indicated DSA and results were compared with CTA.

RESULTS

No exams reported as not diagnostic. The overall mean CT number value of all arterial segments was above 450 HU in both groups. Significant lower noise, and higher SNR and CNR values were found in group 1 in comparison with group 2 despite the use of 80 kVp. In 62-group 1 patients studied by DSA, CTA showed in a segment-based analysis a sensitivity, negative predictive value and accuracy of 100%, 100% and 99% respectively. Mean ED in group 1 was 0.54 ± 0.1 mSv with a dose reduction up to 86%.

CONCLUSIONS

CTA for carotid arteries using latest IR algorithm allows to perform exams with submillisievert radiation exposure maintaining good image quality, overall evaluability and diagnostic accuracy.

Head-to-head comparison of adaptive statistical and model-based iterative reconstruction algorithms for submillisievert coronary CT angiography

Aims

Iterative reconstruction (IR) algorithms allow for a significant reduction in radiation dose of coronary computed tomography angiography (CCTA). We performed a head-to-head comparison of adaptive statistical IR (ASiR) and model-based IR (MBIR) algorithms to assess their impact on quantitative image parameters and diagnostic accuracy for submillisievert CCTA.

Methods and results

CCTA datasets of 91 patients were reconstructed using filtered back projection (FBP), increasing contributions of ASiR (20, 40, 60, 80, and 100%), and MBIR. Signal and noise were measured in the aortic root to calculate signal-to-noise ratio (SNR). In a subgroup of 36 patients, diagnostic accuracy of ASiR 40%, ASiR 100%, and MBIR for diagnosis of coronary artery disease (CAD) was compared with invasive coronary angiography. Median radiation dose was 0.21 mSv for CCTA. While increasing levels of ASiR gradually reduced image noise compared with FBP (up to - 48%, P < 0.001), MBIR provided largest noise reduction (-79% compared with FBP) outperforming ASiR (-59% compared with ASiR 100%; P < 0.001). Increased noise and lower SNR with ASiR 40% and ASiR 100% resulted in substantially lower diagnostic accuracy to detect CAD as diagnosed by invasive coronary angiography compared with MBIR: sensitivity and specificity were 100 and 37%, 100 and 57%, and 100 and 74% for ASiR 40%, ASiR 100%, and MBIR, respectively.

Conclusion

MBIR offers substantial noise reduction with increased SNR, paving the way for implementation of submillisievert CCTA protocols in clinical routine. In contrast, inferior noise reduction by ASiR negatively affects diagnostic accuracy of submillisievert CCTA for CAD detection.

Cardiac computed tomography previous to atrial fibrillation ablation - effects of technological improvements and protocol optimization

BACKGROUND

Cardiac computed tomography (CT) can provide a precise tridimentional anatomic map and exclude intra-cardiac thrombus. We aimed to access the impact of CT protocol optimization and technological evolution on the contrast and radiation dose as well as on image quality previous to atrial fibrillation (AF) ablation.

METHODS

From a prospective registry of consecutive patients who underwent cardiac CT in a single center, we selected 270 patients in whom the CT was done for evaluation prior to AF ablation and they were distributed in 3 groups: Group1: the first 150 patients included; Group2: the last 60 patients performed with the same CT scanner; Group3: the first 60 exams performed with the new CT scanner. Quality of the protocol was access based on radiation dose, contrast volume used, the use of a second (delayed) acquisition, and on quantitative image quality analisis (signal to noise and contrast to noise ratios; density homogeneity racio between LA and LAA).

RESULTS

We found a significant radiation dose as well as contrast dose reduction between the first and last subgroups (G1: 5,6mSv and 100ml; G2: 1,3mSv and 90ml; G3: 0,6mSv and 65ml). Even though group 3 had less radiation and contrast used it still had better quantitative image quality (signal/noise of 13,5; contrast/noise 14,8; density homogeneity racio of 0,92).

CONCLUSION

Protocol optimization and technology both contributed to significant lower radiation dose and contrast volume used on cardiac CTs prior to AF ablation, without compromising image quality.

Pulmonary Emphysema Quantification on Ultra-Low-Dose Computed Tomography Using Model-Based Iterative Reconstruction With or Without Lung Setting

OBJECTIVES

To evaluate the influence of model-based iterative reconstruction (MBIR) with lung setting and conventional setting on pulmonary emphysema quantification by ultra-low-dose computed tomography (ULDCT) compared with standard-dose CT (SDCT).

METHODS

Forty-five patients who underwent ULDCT (0.18 ± 0.02 mSv) and SDCT (6.66 ± 2.69 mSv) were analyzed in this retrospective study. Images were reconstructed using filtered back projection (FBP) with smooth and sharp kernels and MBIR with conventional and lung settings. Extent of emphysema was evaluated using fully automated software. Correlation between ULDCT and SDCT was assessed by interclass correlation coefficiency (ICC) and Bland-Altman analysis.

RESULTS

Excellent correlation was seen between MBIR with conventional setting on ULDCT and FBP with smooth kernel on SDCT (ICC, 0.97; bias, -0.31%) and between MBIR with lung setting on ULDCT and FBP with sharp kernel on SDCT (ICC, 0.82; bias, -2.10%).

CONCLUSION

Model-based iterative reconstruction improved the agreement between ULDCT and SDCT on emphysema quantification.

ECG non-gated multi-detector computed tomography protocol prior to catheter ablation of atrial fibrillation provides sufficient data quality with lower radiation exposure compared to ECG-gated protocol - results of a prospective, randomized and blinded study

BACKGROUND

The role of ECG-gating in left atrium (LA) computed tomography (MDCT) imaging is not precisely defined.

METHODS AND RESULTS

62 patients were randomized according to ECG gating with prospective evaluation of image quality, Volume CT Dose Index, Dose Length Product, Effective Dose and registration error between anatomical map and MDCT. We found significant difference in all radiation variables, but not in visual quality, registration error, CA duration, CA fluoroscopy time and CA fluoroscopy dose.

CONCLUSION

Helical non-gated MDCT achieved a radiation dose more than four times lower with comparable image quality and course of ablation compared to ECG-gated protocol.

Exclusion of left atrial thrombus by dual-source cardiac computed tomography prior to catheter ablation for atrial fibrillation

OBJECTIVES

Thromboembolic complications during atrial fibrillation (AF) ablation due to mobilisation of a pre-existing thrombus formation (TF) in the left atrium (LA) are devastating. The gold standard to exclude LA TF is transesophageal echocardiography (TEE). The present study compares sensitivity and specificity of a dual-source cardiac-computed tomography (DS-CT) with TEE for TF exclusion prior to AF ablation. In addition, CT protocols with and without ECG synchronized were evaluated.

METHODS

In 622 patients, DS-CT as well as TEE to exclude TF was performed less than 48 h prior to AF ablation. Mean age of patients was 60 ± 10 years (69% males, 61% paroxysmal AF). During DS-CT, 280 patients (45%) were in AF. An ECG-synchronized DS-CT was performed in 332 patients, whereas 290 patients underwent DS-CT without ECG synchronization.

RESULTS

In all patients without suspected TF on DS-CT (n = 552; 88.7%), no thrombus was found on TEE. A TF was suspected on DS-CT in 70 patients, of whom only three patients showed TF on TEE. No TF was detected in the other 67 patients (Fig. 1). Overall, sensitivity for TF detection in DS-CT was 100% and specificity was 89.2% (positive predictive value 4.3%, negative predictive value 100%). The CT protocol (ECG-synchronized versus non-ECG-synchronized) had no significant influence on diagnostic accuracy. Mean dose length product during DS CT was 282 ± 287 mGy cm (synchronized) versus 136 ± 55 mGy cm (non-synchronized) with p < 0.0001.

CONCLUSIONS

DS-CT is a highly sensitive method for LA thrombus detection in patients undergoing AF ablation. It delivers additional anatomic details of pulmonary veins and LA anatomy with an acceptable radiation exposure. Non-ECG-synchronized DS-CT showed a significantly lower radiation exposure, whereas diagnostic accuracy was comparable. Therefore, DS-CT might serve as primary method to exclude LA TF in patients undergoing AF ablation.

X-Ray Exposure in Cardiac Electrophysiology: A Retrospective Analysis in 8150 Patients Over 7 Years of Activity in a Modern, Large-Volume Laboratory

Background

Only a few studies have systematically evaluated fluoroscopy data of electrophysiological and device implantation procedures. Aims of this study were to quantify ionizing radiation exposure for electrophysiological/device implantation procedures in a large series of patients and to analyze the x‐ray exposure trend over years and radiation exposure in patients undergoing atrial fibrillation ablation considering different technical aspects.

Methods and Results

We performed a retrospective analysis of all electrophysiological/device implantation procedures performed during the past 7 years in a modern, large‐volume laboratory. We reported complete fluoroscopy data on 8150 electrophysiological/device implantation procedures (6095 electrophysiological and 2055 device implantation procedures); for each type of procedure, effective dose and lifetime attributable risk of cancer incidence and mortality were calculated. Over the 7‐year period, we observed a significant trend reduction in fluoroscopy time, dose area product, and effective dose for all electrophysiological procedures (P<0.001) and a not statistically significant trend reduction for device implantation procedures. Analyzing 2416 atrial fibrillation ablations, we observed a significant variability of fluoroscopy time, dose area product and effective dose among 7 different experienced operators (P<0.0001) and a significant reduction of fluoroscopy use over time (P<0.0001) for all of them. Considering atrial fibrillation ablation techniques, fluoroscopy time was not different (P = 0.74) for radiofrequency catheter ablation in comparison with cryoablation, though cryoablation was still associated with higher dose area product and effective dose values (P<0.001).

Conclusions

Electrophysiological procedures involve a nonnegligible x‐ray use, leading to an increased risk of malignancy. Awareness of radiation‐related risk, together with technological advances, can successfully optimize fluoroscopy use.

Image quality of low-radiation dose left atrial CT using filtered back projection and an iterative reconstruction algorithm: intra-individual comparison in unselected patients undergoing pulmonary vein isolation

Background Computed tomography (CT) of the left atrium (LA) is performed prior to pulmonary vein isolation (PVI) to improve success of circumferential ablation for atrial fibrillation. The ablation procedure itself exposes patients to substantial radiation doses, therefore radiation dose reduction in pre-ablational imaging is of concern. Purpose To assess and compare diagnostic performance of low-radiation dose preprocedural CT in patients scheduled for PVI using two types of reconstruction algorithms. Material and Methods Forty-six patients (61 ± 10 years) scheduled for PVI were enrolled in this study irrespective of body-mass-index or cardiac rhythm at examination. An electrocardiographically triggered dual-source CT scan was performed. Filtered back projection (FBP) and iterative reconstruction (IR) algorithms were applied. Images were integrated into an electroanatomic mapping (EAM) system. Subjective image quality was scored independently by two readers on a five-point scale for both reconstruction algorithms (1 = excellent to 5 = non-diagnostic). Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and effective radiation dose were calculated. Results Data acquisition and EAM integration were successful in all patients. Median image quality score was 1 for both FBP (quartiles = 1, 1.62; range = 1-3) and IR (quartiles = 1, 1.5; range = 1-3). Mean SNR was 7.61 ± 2.14 for FBP and 9.02 ± 2.69 for IR. Mean CNR was 5.92 ± 1.80 for FBP and 6.95 ± 2.29 for IR. Mean effective radiation dose was 0.3 ± 0.1 mSv. Conclusion At a radiation dose of 0.3 ± 0.1 mSv, high-pitch dual-source CT yields LA images of consistently high quality using both FBP and IR. IR raises SNR and CNR without significantly improving subjective image quality.

OPTimal IMAging strategy in patients suspected of non-traumatic pulmonary disease at the emergency department: chest X-ray or ultra-low-dose CT (OPTIMACT)-a randomised controlled trial chest X-ray or ultra-low-dose CT at the ED: design and rationale

BACKGROUND

Chest X-ray has been the standard imaging method for patients suspected of non-traumatic pulmonary disease at the emergency department (ED) for years. Recently, ultra-low-dose chest computed tomography (ULD chest CT) has been introduced, which provides substantially more detailed information on pulmonary conditions that may cause pulmonary disease, with a dose in the order of chest X-ray (0.1 vs. 0.05 mSv). The OPTimal IMAging strategy in patients suspected of non-traumatic pulmonary disease at the emergency department: chest X-ray or CT (OPTIMACT) study is a randomized trial designed to evaluate the effectiveness of replacing chest X-ray for ULD chest CT in the diagnostic work-up of patients suspected of non-traumatic pulmonary disease at the ED.

METHODS

Two thousand four hundred patients presenting at the ED with pulmonary complaints and suspected of non-traumatic pulmonary disease will be enrolled in this multicenter, pragmatic, randomized trial. During randomly assigned periods of one calendar month, either conventional chest X-ray or ULD chest CT scan will be used as the imaging strategy. Randomization will rely on computer-generated blocks of 2 months to control for seasonal effects. Chest X-ray and ULD chest CT will be performed in a standardized way, after obtaining the clinical history and performing physical examination and initial laboratory tests. The primary outcome measure is functional health at 28 days. Secondary outcome measures are mental health, length of hospital stay, mortality within 28 days, quality-adjusted life years (QALYs) during the first 28 days, correct diagnoses at ED discharge as compared to the final post hoc diagnosis, and number of patients in follow-up because of incidental findings on chest X-ray or ULD chest CT. In an economic evaluation, we will estimate total health care costs during the first 28 days.

DISCUSSION

This pragmatic trial will clarify the effects of replacing chest X-ray by ULD chest CT in daily practice, in terms of patient-related health outcomes and costs, in the diagnostic work-up of patients suspected of non-traumatic pulmonary disease at the ED.

TRIAL REGISTRATION

The OPTIMACT trial is registered in the Netherlands National Trial Register under number NTR6163. The date of registration is December 6, 2016.

Assessment of noise reduction potential and image quality improvement of a new generation adaptive statistical iterative reconstruction (ASIR-V) in chest CT

OBJECTIVE

To evaluate the image quality improvement and noise reduction in routine dose, non-enhanced chest CT imaging by using a new generation adaptive statistical iterative reconstruction (ASIR-V) in comparison with ASIR algorithm.

METHODS

30 patients who underwent routine dose, non-enhanced chest CT using GE Discovery CT750HU (GE Healthcare, Waukesha, WI) were included. The scan parameters included tube voltage of 120 kVp, automatic tube current modulation to obtain a noise index of 14HU, rotation speed of 0.6 s, pitch of 1.375:1 and slice thickness of 5 mm. After scanning, all scans were reconstructed with the recommended level of 40%ASIR for comparison purpose and different percentages of ASIR-V from 10% to 100% in a 10% increment. The CT attenuation values and SD of the subcutaneous fat, back muscle and descending aorta were measured at the level of tracheal carina of all reconstructed images. The signal-to-noise ratio (SNR) was calculated with SD representing image noise. The subjective image quality was independently evaluated by two experienced radiologists.

RESULTS

For all ASIR-V images, the objective image noise (SD) of fat, muscle and aorta decreased and SNR increased along with increasing ASIR-V percentage. The SD of 30% ASIR-V to 100% ASIR-V was significantly lower than that of 40% ASIR (p < 0.05). In terms of subjective image evaluation, all ASIR-V reconstructions had good diagnostic acceptability. However, the 50% ASIR-V to 70% ASIR-V series showed significantly superior visibility of small structures when compared with the 40% ASIR and ASIR-V of other percentages (p < 0.05), and 60% ASIR-V was the best series of all ASIR-V images, with a highest subjective image quality. The image sharpness was significantly decreased in images reconstructed by 80% ASIR-V and higher.

CONCLUSION

In routine dose, non-enhanced chest CT, ASIR-V shows greater potential in reducing image noise and artefacts and maintaining image sharpness when compared to the recommended level of 40%ASIR algorithm. Combining both the objective and subjective evaluation of images, non-enhanced chest CT images reconstructed with 60% ASIR-V have the highest image quality. Advances in knowledge: This is the first clinical study to evaluate the clinical value of ASIR-V in the same patients using the same CT scanner in the non-enhanced chest CT scans. It suggests that ASIR-V provides the better image quality and higher diagnostic confidence in comparison with ASIR algorithm.

The role of advanced reconstruction algorithms in cardiac CT

Non-linear iterative reconstruction (IR) algorithms have been increasingly incorporated into clinical cardiac CT protocols at institutions around the world. Multiple IR algorithms are available commercially from various vendors. IR algorithms decrease image noise and are primarily used to enable lower radiation dose protocols. IR can also be used to improve image quality for imaging of obese patients, coronary atherosclerotic plaques, coronary stents, and myocardial perfusion. In this article, we will review the various applications of IR algorithms in cardiac imaging and evaluate how they have changed practice.

Extremely low-frame-rate digital fluoroscopy in catheter ablation of atrial fibrillation: A comparison of 2 versus 4 frame rate

Despite the technological advance in 3-dimensional (3D) mapping, radiation exposure during catheter ablation of atrial fibrillation (AF) continues to be a major concern in both patients and physicians. Previous studies reported substantial radiation exposure (7369-8690 cGy cm) during AF catheter ablation with fluoroscopic settings of 7.5 frames per second (FPS) under 3D mapping system guidance. We evaluated the efficacy and safety of a low-frame-rate fluoroscopy protocol for catheter ablation for AF.Retrospective analysis of data on 133 patients who underwent AF catheter ablation with 3-D electro-anatomic mapping at our institute from January 2014 to May 2015 was performed. Since January 2014, fluoroscopy frame rate of 4-FPS was implemented at our institute, which was further decreased to 2-FPS in September 2014. We compared the radiation exposure quantified as dose area product (DAP) and effective dose (ED) between the 4-FPS (n = 57) and 2-FPS (n = 76) groups.The 4-FPS group showed higher median DAP (599.9 cGy cm; interquartile range [IR], 371.4-1337.5 cGy cm vs. 392.0 cGy cm; IR, 289.7-591.4 cGy cm; P < .01), longer median fluoroscopic time (24.4 min; IR, 17.5-34.9 min vs. 15.1 min; IR, 10.7-20.1 min; P < .01), and higher median ED (1.1 mSv; IR, 0.7-2.5 mSv vs. 0.7 mSv; IR, 0.6-1.1 mSv; P < .01) compared with the 2-FPS group. No major procedure-related complications such as cardiac tamponade were observed in either group. Over follow-up durations of 331 ± 197 days, atrial tachyarrhythmia recurred in 20 patients (35.1%) in the 4-FPS group and in 27 patients (35.5%) in the 2-FPS group (P = .96). Kaplan-Meier survival analysis revealed no significant different between the 2 groups (log rank, P = .25).In conclusion, both the 4-FPS and 2-FPS settings were feasible and emitted a relatively low level of radiation compared with that historically reported for DAP in a conventional fluoroscopy setting.

Prospective ECG-triggering cardiac CT for infants with complex congenital heart disease using low-dose contrast medium, low tube voltage, and adaptive statistical iterative reconstruction

AIM

To demonstrate the clinical value of prospective electrocardiography (ECG)-triggered cardiac computed tomography (CT) with low concentration contrast medium, low tube voltage, and adaptive statistic iterative reconstruction (ASIR) to reduce both radiation and contrast dose in examining infants with complex congenital heart disease (CHD).

MATERIALS AND METHODS

Forty-four consecutive infants (19 male, 25 female, age: 8.06±4.33 months, weight: 7.31±1.36 kg) with complex CHD underwent prospective ECG-triggered low-dose cardiac CT using 80 kVp and 120 mA. The contrast agent was iodixanol (270 mg iodine/ml, Visipaque, GE Healthcare, Co. Cork, Ireland). Cardiac CT images were reconstructed with 70% ASIR. The quantitative CT image quality was assessed by image noise in adipose tissue and contrast-to-noise ratio (CNR) in the aorta. The qualitative image analysis was performed on a five-point grading scale by two independent reviewers and interobserver variability was calculated. The results of 32 CT examinations were also compared with the available surgical results for diagnostic accuracy evaluation.

RESULTS

The effective dose was 0.55±0.10 mSv for the patient population. The iodine load was 3.95±0.73 g iodine. Image noise in adipose tissue was 16.24±1.42 HU and CNR in aorta was 21.90±7.10. All images were acceptable for diagnosis with an average score of 4.52±0.38 and good agreement between reviewers (kappa=0.75). Compared to the surgery results in 32 cases, CT was 97% and 88% accurate diagnosing extracardiac and intracardiac defects, respectively.

CONCLUSION

Prospective ECG-triggered cardiac CT using 80 kVp, low-concentration iodinated contrast agent (270 mg iodine/ml) and 70% ASIR reconstruction provides excellent image quality and accurate diagnosis for complex congenital heart disease in infants with reduced contrast medium dose and low radiation dose.

Influence of model based iterative reconstruction algorithm on image quality of multiplanar reformations in reduced dose chest CT

Background

Model-based iterative reconstruction (MBIR) reduces image noise and improves image quality (IQ) but its influence on post-processing tools including maximal intensity projection (MIP) and minimal intensity projection (mIP) remains unknown.

Purpose

To evaluate the influence on IQ of MBIR on native, mIP, MIP axial and coronal reformats of reduced dose computed tomography (RD-CT) chest acquisition.

Material and Methods

Raw data of 50 patients, who underwent a standard dose CT (SD-CT) and a follow-up RD-CT with a CT dose index (CTDI) of 2–3 mGy, were reconstructed by MBIR and FBP. Native slices, 4-mm-thick MIP, and 3-mm-thick mIP axial and coronal reformats were generated. The relative IQ, subjective IQ, image noise, and number of artifacts were determined in order to compare different reconstructions of RD-CT with reference SD-CT.

Results

The lowest noise was observed with MBIR. RD-CT reconstructed by MBIR exhibited the best relative and subjective IQ on coronal view regardless of the post-processing tool. MBIR generated the lowest rate of artefacts on coronal mIP/MIP reformats and the highest one on axial reformats, mainly represented by distortions and stairsteps artifacts.

Conclusion

The MBIR algorithm reduces image noise but generates more artifacts than FBP on axial mIP and MIP reformats of RD-CT. Conversely, it significantly improves IQ on coronal views, without increasing artifacts, regardless of the post-processing technique.

Submillisievert CT using model-based iterative reconstruction with lung-specific setting: An initial phantom study

OBJECTIVE

To assess image quality of filtered back-projection (FBP) and model-based iterative reconstruction (MBIR) with a conventional setting and a new lung-specific setting on submillisievert CT.

METHODS

A lung phantom with artificial nodules was scanned with 10 mA at 120 kVp and 80 kVp (0.14 mSv and 0.05 mSv, respectively); images were reconstructed using FBP and MBIR with conventional setting (MBIR_Stnd) and lung-specific settings (MBIR_RP20/Tx and MBIR_RP20). Three observers subjectively scored overall image quality and image findings on a 5-point scale (1 = worst, 5 = best) compared with reference standard images (50 mA-FBP at 120, 100, 80 kVp). Image noise was measured objectively.

RESULTS

MBIR_RP20/Tx performed significantly better than MBIR_Stnd for overall image quality in 80-kVp images (p < 0.01), blurring of the border between lung and chest wall in 120p-kVp images (p < 0.05) and the ventral area of 80-kVp images (p < 0.001), and clarity of small vessels in the ventral area of 80-kVp images (p = 0.037). At 120 kVp, 10 mA-MBIR_RP20 and 10 mA-MBIR_RP20/Tx showed similar performance to 50 mA-FBP. MBIR_Stnd was better for noise reduction. Except for blurring in 120 kVp-MBIR_Stnd, MBIRs performed better than FBP.

CONCLUSION

Although a conventional setting was advantageous in noise reduction, a lung-specific setting can provide more appropriate image quality, even on submillisievert CT.

KEY POINTS

• Lung-specific submillisievert 10 mA-MBIR CT setting has similar performance to 50 mA-FBP • The new lung-specific settings improve vessel clarity and blurring of borders • The new settings may provide more appropriate images than conventional settings.