Iterative model reconstruction: Improved image quality of low-tube-voltage prospective ECG-gated coronary CT angiography images at 256-slice CT

Feasibility of Ultra-low Radiation and Contrast Medium Dosage in Aortic CTA Using Deep Learning Reconstruction at 60 kVp: An Image Quality Assessment

OBJECTIVE

To assess the viability of using ultra-low radiation and contrast medium (CM) dosage in aortic computed tomography angiography (CTA) through the application of low tube voltage (60kVp) and a novel deep learning image reconstruction algorithm (ClearInfinity, DLIR-CI).

METHODS

Iodine attenuation curves obtained from a phantom study informed the administration of CM protocols. Non-obese participants undergoing aortic CTA were prospectively allocated into two groups and then obtained three reconstruction groups. The conventional group (100kVp-CV group) underwent imaging at 100kVp and received 210 mg iodine/kg in combination with a hybrid iterative reconstruction algorithm (ClearView, HIR-CV). The experimental group was imaged at 60kVp with 105 mg iodine/kg, while images were reconstructed with HIR-CV (60kVp-CV group) and with DLIR-CI (60kVp-CI group). Student's t-test was used to compare differences in CM protocol and radiation dose. One-way ANOVA compared CT attenuation, image noise, SNR, and CNR among the three reconstruction groups, while the Kruskal-Wallis H test assessed subjective image quality scores. Post hoc analysis was performed with Bonferroni correction for multiple comparisons, and consistency analysis conducted in subjective image quality assessment was measured using Cohen's kappa.

RESULTS

The radiation dose (1.12 ± 0.23mSv vs. 2.03 ± 0.82mSv) and CM dosage (19.04 ± 3.03mL vs. 38.11 ± 6.47mL) provided the reduction of 45% and 50% in the experimental group compared to the conventional group. The CT attenuation, SNR, and CNR of 60kVp-CI were superior to or equal to those of 100kVp-CV. Compared to the 60kVp-CV group, images in 60kVp-CI showed higher SNR and CNR (all P < 0.001). There was no difference between the 60kVp-CI and 100kVp-CV group in terms of the subjective image quality of the aorta in various locations (all P > 0.05), with 60kVp-CI images were deemed diagnostically sufficient across all vascular segments.

CONCLUSION

For non-obese patients, the combined use of 60kVp and DLIR-CI algorithm can be preserving image quality while enabling radiation dose and contrast medium savings for aortic CTA compared to 100kVp using HIR-CV.

Reduction of metal artefacts from bilateral hip prostheses during lower extremity computed tomography angiography: an experimental phantom study

INTRODUCTION

Image quality reduction due to metallic artefacts is a significant challenge during vascular computed tomography (CT) imaging of the lower extremities in patients with hip prostheses. This study aims to analyse various reconstruction algorithms' ability to reduce metal artefacts due to two types of hip prostheses during lower extremity CT angiography examinations.

METHODS

A pelvis phantom was fabricated with the insertion of a tube filled with contrast media to simulate the femoral artery, and the phantom was then CT scanned with and without hip prostheses. Multimodal images were acquired using different kilovoltage peak (kVp) settings and reconstructed with different algorithms, such as filtered back projection (FBP), iterative reconstruction (iDose4), iterative model-based reconstruction (IMR) and orthopaedic metal artefact reduction (O-MAR). Image quality was assessed based on image noise, signal-to-noise ratio (SNR) and Hounsfield unit (HU) deviation.

RESULTS

The IMR approach significantly improved image quality compared to iDose4 and FBP. For the vascular region, O-MAR improves SNR by 5 ± 1, 23 ± 5 and 42 ± 9 for FBP, iDose4 and IMR respectively, and improves HU precision towards the baseline values by 49% and 83% for FBP and IMR, respectively. The noise reduction was 71% and 89% for FBP and IMR, and 57% for iDose4. O-MAR greatly enhances SNR corrections among the most severe artefacts, with 29 ± 1 and 43 ± 4 for FBP and IMR, compared to iDose4 by 37 ± 7.

CONCLUSION

IMR combined with O-MAR could improve the CT angiography of the lower extremities of patients with a hip prosthesis.

The influence of motion-compensated reconstruction on coronary artery analysis for a dual-layer detector CT system: a dynamic phantom study

OBJECTIVES

Cardiac motion artifacts hinder the assessment of coronary arteries in coronary computed tomography angiography (CCTA). We investigated the impact of motion compensation reconstruction (MCR) on motion artifacts in CCTA at various heart rates (HR) using a dynamic phantom.

MATERIALS AND METHODS

An artificial hollow coronary artery (5-mm diameter lumen) filled with iodinated contrast agent (400 HU at 120 kVp), positioned centrally in an anthropomorphic chest phantom, was scanned using a dual-layer spectral detector CT. The artery was translated at constant horizontal velocities (0-80 mm/s, increment of 10 mm/s). For each velocity, five CCTA scans were repeated using a clinical protocol. Motion artifacts were quantified using the in-plane motion area. Regression analysis was performed to calculate the reduction in motion artifacts provided by MCR, by division of the slopes of non-MCR and MCR fitted lines.

RESULTS

Reference mean (95% confidence interval) motion artifact area was 24.9 mm2 (23.8, 26.0). Without MCR, motion artifact areas for velocities exceeding 20 mm/s were significantly larger (up to 57.2 mm2 (40.1, 74.2)) than the reference. With MCR, no significant differences compared to the reference were shown for all velocities, except for 70 mm/s (29.0 mm2 (27.0, 31.0)). The slopes of the fitted data were 0.44 and 0.04 for standard and MCR reconstructions, respectively, resulting in an 11-time motion artifact reduction.

CONCLUSION

MCR may improve CCTA assessment in patients by reducing coronary artery motion artifacts, especially in those with elevated HR who cannot receive beta blockers or do not attain the targeted HR.

CLINICAL RELEVANCE STATEMENT

This vendor-specific motion compensation reconstruction may improve coronary computed tomography angiography assessment in patients by reduction of coronary artery motion artifacts, especially in those with elevated various heart rates (HR) who cannot receive beta blockers or do not attain the targeted HR.

KEY POINTS

• Motion artifacts are known to hinder the assessment of coronary arteries on coronary CT angiography (CCTA), leading to more non-diagnostic scans. • This dynamic phantom study shows that motion compensation reconstruction (MCR) reduces motion artifacts at various velocities, which may help to decrease the number of non-diagnostic scans. • MCR in this study showed to reduce motion artifacts 11-fold.

Dynamic evaluation of unruptured intracranial aneurysms by 4D-CT angiography: comparison with digital subtraction angiography (DSA) and surgical findings

BACKGROUND

This study was to prospectively investigate the feasibility of four-dimensional computed tomography angiography (4D-CTA) with electrocardiogram-gated (ECG) reconstruction for preoperative evaluation of morphological parameters, and compared with digital subtraction angiography (DSA). We also aimed to detect pulsation in unruptured intracranial aneurysms (UIAs) by using 4D-CTA, as a potential predicting factor of growth or rupture.

MATERIALS

64 patients with 64 UIAs underwent ECG-gated dynamic 4D-CTA imaging before treatment, of which 46 patients additionally underwent DSA. Original scanning data were reconstructed to produce 20 data sets of cardiac cycles with 5%-time intervals. The extent of agreement on UIAs morphological features assessed with 4D-CTA and DSA was estimated using the k coefficient of the Kappa test. The radiation doses were also calculated and compared between 4D-CTA and DSA. In the aneurysmal surgically treated in our institution, we were able to compare the surgical findings of the aneurysm wall with 4D-CTA images. We performed long-term follow-up on untreated patients.

RESULTS

The morphological characteristics detected by 4D-CTA and DSA were consistent in aneurysm location (k = 1.0), shape (k = 0.76), maximum diameter (k = 0.94), aneurysm neck (k = 0.79) and proximity to parent and branch vessels (k = 0.85). 4D-CTA required lower radiation doses (0.32 ± 0.11 mSv) than DSA (0.84 ± 0.37 mSv, P < 0.001). Pulsation was detected in 26 of the 64 unruptured aneurysms, and all underwent neurosurgical clipping or interventional embolization. In aneurysms surgically treated in our hospital, we observed a significant correlation between 4D-CTA findings and surgical evaluation of the aneurysmal wall, in particular the irregular pulsations detected on 4D-CTA have demonstrated to correspond to dark-reddish thinner wall at surgery.

CONCLUSIONS

In this proof-of-concept study, 4D-CTA provided real-time, non-invasive preoperative assessments of UIAs comparable to DSA. Moreover, optimal correlation between the irregular pulsation detected by 4D-CTA and the surgical findings support a possible role of this technique to identify aneurysms with a higher risk of rupture.

Intraindividual evaluation of effects of image filter function on image quality in coronary computed tomography angiography

Objectives

To evaluate whether applying image filters (smooth 3D+ and edge-2) improves image quality in coronary CT angiography (CCTA).

Methods

Ninety patients (routine group) with suspected coronary artery diseases based on 16-cm wide coverage detector CT findings were retrospectively enrolled at a chest pain center from December 2019 to September 2021. Two image filters, smooth 3D+ and edge-2 available on the Advantage Workstation (AW) were subsequently applied to the images to generate the research group (SE group). Quantitative parameters, including CT value, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), image sharpness and image quality score, and diagnostic accuracy were compared between the two groups.

Results

A total of 900 segments from 270 coronary arteries in 90 patients were analyzed. SNR, CNR, and image sharpness for vessels and image quality scores in the SE group were significantly better than those in the routine group (all p < 0.001). The SE group showed a slightly higher negative predictive value (NPV) on the left anterior descending artery and right coronary artery (RCA) stenosis evaluations, as well as total NPV. The SE group also showed slightly higher sensitivity and accuracy than the routine group on RCA stenosis evaluation.

Conclusion

The use of an image filter combining smooth 3D+ and edge-2 on an AW could improve the image quality of CCTA and increase radiologists' diagnostic confidence.

Model-based adaptive filter for a dedicated cardiovascular CT scanner: Assessment of image noise, sharpness and quality

BACKGROUND

Filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR) are ubiquitously applied in the reconstruction of coronary CT angiography (CCTA) datasets. However, currently no data is available on the impact of a model-based adaptive filter (MBAF2), recently developed for a dedicated cardiac scanner.

PURPOSE

Our aim was to determine the effect of MBAF2 on subjective and objective image quality parameters of coronary arteries on CCTA.

METHODS

Images of 102 consecutive patients referred for CCTA were evaluated. Four reconstructions of coronary images (FBP, ASIR, MBAF2, ASIR + MBAF2) were co-registered and cross-section were assessed for qualitative (graininess, sharpness, overall image quality) and quantitative [image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR)] image quality parameters. Image noise and signal were measured in the aortic root and the left main coronary artery, respectively. Graininess, sharpness, and overall image quality was assessed on a 4-point Likert scale.

RESULTS

As compared to FBP, ASIR, and MBAF2, ASIR + MBAF2 resulted in reduced image noise [53.1 ± 12.3, 30.6 ± 8.5, 36.3 ± 4.2, 26.3 ± 4.0 Hounsfield units (HU), respectively; p < 0.001], improved SNR (8.4 ± 2.6, 14.1 ± 3.6, 11.8 ± 2.3, 16.3 ± 3.3 HU, respectively; p < 0.001) and CNR (9.4 ± 2.7, 15.9 ± 4.0, 13.3 ± 2.5, 18.3 ± 3.5 HU, respectively; p < 0.001). No difference in sharpness was observed amongst the reconstructions (p = 0.08). Although ASIR + MBAF2 was non-superior to ASIR regarding overall image quality (p = 0.99), it performed better than FBP (p < 0.001) and MBAF2 (p < 0.001) alone.

CONCLUSION

The combination of ASIR and MBAF2 resulted in reduced image noise and improved SNR and CNR. The implementation of MBAF2 in clinical practice may result in improved noise reduction performance and could potentiate radiation dose reduction.

Study on Model Iterative Reconstruction Algorithm vs. Filter Back Projection Algorithm for Diagnosis of Acute Cerebral Infarction Using CT Images

The aim was to explore the application value of computed tomography (CT) perfusion (CTP) imaging based on the iterative model reconstruction (IMR) in the diagnosis of acute cerebral infarction (ACI). 80 patients with ACI, admitted to hospital, were selected as the research objects and divided randomly into a routine treatment group (group A) and a low-dose group (group B) (each group with 40 patients). Patients in group A were scanned at 80 kV–150 mAs, and the traditional filtered back projection (FBP) algorithm was employed to reconstruct the images; besides, 80 kV–30 mAs was adopted to scan the patients in group B, and the images were reconstructed by IMR1, IMR2, IMR3, iDose4 (a kind of hybrid iterative reconstruction technology), and FBP, respectively. The application values of different algorithms were evaluated by CTP based on the collected CTP images of patients and detecting indicators. The results showed that the gray and white matter CT value, SD value, SNR, CNR, and subjective image scores of patients in group B were basically consistent with those of group A (p > 0.05) after the IMR1 reconstruction, and the CT and SD of gray and white matter in patients from group B reduced steeply (p < 0.05), while SNR and CNR increased dramatically after IMR2 and IMR3 reconstruction in contrast to group A (p < 0.05). Furthermore, the cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT) of contrast agent, and time to peak (TTP) of contrast agent in patients from group B after iDose4 and IMR reconstruction were basically the same as those of group A (p > 0.05). Therefore, IMR combined with low-dose CTP could obtain high-quality CTP images of the brain with stable perfusion indicators and low radiation dose, which could be clinically applied in the diagnosis of ACI.

Application of prospective ECG-gated multiphase scanning for coronary CT in children with different heart rates

BACKGROUND

To investigate the application of prospective ECG-gated multiphase scanning in coronary CT imaging in children with different heart rates.

METHODS

In the control group, 160 children aged 2-4 years who underwent a coronary CT examination in our hospital from May 2016 to December 2017 were retrospectively selected. They were divided into five subgroups according to their heart rate frequency: 75-85 beats/min, 86-95 beats/min, 96-105 beats/min, and 106-120 beats/min. There were 40 children in each subgroup. Each child was treated with retrospective ECG-gated scanning technology. Six groups of phase images were reconstructed: 40%, 45%, 50%, 70%, 75% and 80%. The optimal phase was selected for coronary artery reconstruction. In the study group, 240 children aged 2-4 years who underwent coronary artery CT examination in our hospital from January 2018 to May 2019 were prospectively selected and divided into five subgroups according to the heart rate frequency: 75-85 beats/min, 86-95 beats/min, 96-105 beats/min, and 106-120 beats/min. There were 60 children in each subgroup. A prospective ECG-gated multiphase scanning technique was used to reconstruct 70%, 75% and 80% phase images in the subgroups with heart rates < 85/min. In the remaining subgroups, 40%, 45% and 50% phase images were reconstructed, and the optimal phase was selected for coronary artery reconstruction. The scanning parameters, dosage of contrast medium and injection mode of contrast medium were the same in both groups. The radiation dose and image quality of the coronary artery were compared between the two groups at the same heart rate.

RESULTS

When comparing the two groups at the same heart rate, the radiation dose in the study group was 72% lower than that in the control group (P < 0.05). There was no significant difference in coronary artery image quality between the two groups at the optimal phase (P > 0.05).

CONCLUSIONS

Applying prospective ECG-gated multiphase scanning technology to children's coronary CT imaging can significantly reduce the scanning radiation dose without affecting the quality of the coronary artery image.

Coronary CT Angiography with Knowledge-Based Iterative Model Reconstruction for Assessing Coronary Arteries and Non-Calcified Predominant Plaques

Objective

To assess the effects of iterative model reconstruction (IMR) on image quality for demonstrating non-calcific high-risk plaque characteristics of coronary arteries.

Materials and Methods

This study included 66 patients (53 men and 13 women; aged 39–76 years; mean age, 55 ± 13 years) having single-vessel disease with predominantly non-calcified plaques evaluated using prospective electrocardiogram-gated 256-slice CT angiography. Paired image sets were created using two types of reconstruction: hybrid iterative reconstruction (HIR) and IMR. Plaque characteristics were compared using the two algorithms. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the images and the CNR between the plaque and adjacent adipose tissue were also compared between the two reformatted methods.

Results

Seventy-seven predominantly non-calcified plaques were detected. Forty plaques showed napkin-ring sign with the IMR reformatted method, while nineteen plaques demonstrated napkin-ring sign with HIR. There was no statistically significant difference in the presentation of positive remodeling, low attenuation plaque, and spotty calcification between the HIR and IMR reconstructed methods (all p > 0.5); however, there was a statistically significant difference in the ability to discern the napkin-ring sign between the two algorithms (χ² = 12.12, p < 0.001). The image noise of IMR was lower than that of HIR (10 ± 2 HU versus 12 ± 2 HU; p < 0.01), and the SNR and CNR of the images and the CNR between plaques and surrounding adipose tissues on IMR were better than those on HIR (p < 0.01).

Conclusion

IMR can significantly improve image quality compared with HIR for the demonstration of coronary artery and atherosclerotic plaques using a 256-slice CT.

Diagnostic performance and image quality of iterative model-based reconstruction of coronary CT angiography using 100 kVp for heavily calcified coronary vessels

OBJECTIVES

To evaluate the diagnostic performance and image quality of an iterative model-based reconstruction (IMR) using a 100-kVp protocol for the assessment of heavily calcified coronary vessels, compared to those of filtered back projection (FBP) and hybrid iterative technique (iDose4), and also compared to those of IMR with standard 120 kVp protocol.

METHODS

Among patients with Agatston scores ≥ 400 who had undergone both coronary CT angiography (CCTA) and invasive coronary angiography (ICA), age- and sex-matched patients with body mass index < 30 were retrospectively enrolled from CCTA with low-kVp protocol (100 kVp, n = 30) and with standard-kVp protocol (120 kVp, n = 30). Image data were all reconstructed with FBP, iDose4, and IMR. In each dataset, the objective and subjective image quality, and diagnostic accuracy (> 50% in luminal reduction as compared with ICA) were assessed.

RESULTS

IMR showed better objective and subjective image quality than FBP and iDose4 in both 100 kVp and 120 kVp groups (all p < 0.05). IMR showed a significantly improved all diagnostic performance compared with FBP (p < 0.05). Compared with iDose4, IMR significantly improved positive predictive value (85.0% vs. 80.5%; p < 0.05). There was no significant difference in image quality and diagnostic performance using IMR between the 100 kVp and 120 kVp groups.

CONCLUSIONS

100 kVp IMR may be useful for the assessment of heavily calcified coronary vessels, providing better diagnostic performance than FBP or iDose4 at the same dose, while maintaining similar diagnostic accuracy to 120 kVp IMR.

The usefulness of full-iterative reconstruction algorithm for the visualization of cystic artery on CT angiography

PURPOSE

To evaluate the potential of full-iterative reconstruction (IR) for improving image quality of the cystic artery on CT angiography and to assess observer performance.

METHODS

Thirty patients who underwent both liver dynamic CT and conventional angiography were included in this retrospective study. All CT data were reconstructed through filtered back projection (FBP), adaptive iterative dose reduction 3D (AIDR3D), and forward-projected, model-based, iterative reconstruction solution (FIRST), respectively. In objective study, we analyzed mean ΔCT numbers (the difference between the HU peak of the vessel and the background) and full-width at tenth-maximum (FWTM) of three parts of the cystic artery by profile curve method comparing the three reconstructions. Subjectively, visualization was evaluated using a four-point scale performed by two blinded observers. ANOVA was used for statistical analysis.

RESULTS

In all parts of the cystic artery, the mean ΔCT number of FIRST was shown to be significantly better than that of FBP and AIDR3D (p < 0.05). FWTM in FIRST was the smallest in all of the vessels. The mean visualization score was significantly better with FIRST than with other CT reconstructions (p < 0.05).

CONCLUSIONS

The FIRST algorithm led to improved CTA visualization of the cystic artery.

Diagnostic accuracy of low-radiation coronary computed tomography angiography with low tube voltage and knowledge-based model reconstruction

We aimed to evaluate the accuracy of coronary computed tomography angiography (CCTA) with a low-radiation protocol and iterative model reconstruction (IMR), in comparison with invasive coronary angiography (ICA). Sixty-one patients (45 males; mean age, 61.9 ± 9.2 years) with suspected coronary artery disease who underwent CCTA and ICA were retrospectively enrolled. CCTA was performed with low tube voltage (80 or 100 kVp), low tube current (100–200 mAs), prospective ECG triggering, and IMR using a 64-slice computed tomography scanner. Coronary artery disease was defined as luminal narrowing of >50%, as assessed using CCTA and ICA. The sensitivity, specificity, positive (PPV) and negative (NPV) predictive value, and accuracy of CCTA were examined. The mean radiation dose of CCTA was 1.05 ± 0.36 mSv. No non-diagnostic segment was noted. The sensitivity, specificity, PPV, NPV, and accuracy of CCTA were 86.4%, 96.1%, 80.3%, 97.5%, and 94.6% on a per segment basis, 93.1%, 94.7%, 88.3%, 97.0%, and 94.2% on a per vessel basis, and 100%, 83.3%, 93.5%, 100%, and 95.1% on a per patient basis, respectively. In conclusion, a low-radiation CCTA protocol with IMR may be useful for diagnosing coronary artery disease, as it reduces the radiation dose while maintaining diagnostic accuracy.

Basic Concepts of Contrast Injection Protocols for Coronary Computed Tomography Angiography

BACKGROUND

Coronary Computed Tomography Angiography (CTA) has become one of the most important diagnostic imaging modalities for the evaluation of coronary artery diseases. During coronary computed CTA, sufficient vascular enhancement is essential for the accurate detection and evaluation of lesions in the coronary arteries. To obtain optimal contrast enhancement and perform appropriate clinical coronary CTA, physicians, radiologists, and radiology technologists should acquire a basic knowledge of contrast injection protocols.

CONCLUSION

This review article summarizes the basic concepts of contrast injection protocols for coronary CTA.

Non-inferior low-dose coronary computed tomography angiography image quality with knowledge-based iterative model reconstruction for overweight patients

We investigated the feasibility of low-dose coronary computed tomography angiography (CCTA), using a prospective electrocardiogram (ECG)-triggered axial scan protocol, knowledge-based iterative model reconstruction (IMR), and fixed tube current, in overweight subjects. Forty non-overweight (group A; body-mass index [BMI] < 25 kg/m²) and 40 overweight individuals (group B; BMI = 25–30 kg/m²), who underwent CCTA for coronary artery disease screening, were retrospectively and consecutively enrolled. A 64-slice CT scanner was used at 100-kVp tube voltage and 150-mA tube current, and images were reconstructed using IMR techniques. Image noise, attenuation at the aorta, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) at the proximal right and left main coronary arteries (pRCA and LMCA) were calculated. CCTA images were qualitatively evaluated using a four-point scale (1, poor; 4, excellent) and analyzed using a non-inferiority test with a pre-defined non-inferiority margin of -0.2. The mean CCTA radiation dose (Group A: 1.33 ± 0.02 mSv; Group B: 1.35 ± 0.10 mSv; p = 0.151) and mean aortic root CT attenuation values (Group A: 447.9 ± 81.6 HU; Group B: 439.5 ± 63.6 HU; p = 0.571) did not differ significantly between the two groups. The mean noise in groups A and B was 26.0 ± 4.8 HU and 29.2 ± 4.4 HU, respectively (p = 0.005). The noise reduction ratio in the groups, compared to filtered back projection, was 65.0% and 68.1%, respectively. The mean grade of image quality did not differ significantly (3.75 ± 0.04 vs. 3.71 ± 0.04, p = 0.478). Group B CCTA image quality was non-inferior (mean difference = -0.043, 95% CI = -0.162–0.077) to that of Group A. We concluded that low-dose CCTA with prospective ECG-triggering and IMR might be applied to overweight subjects, as well as to normal-weight subjects, by using a fixed tube current without an increase in tube current based on the patient’s body size.

Tailoring protocols for chest CT applications: when and how?

In the medical era of early detection of diseases and tailored therapies, an accurate characterization and staging of the disease is pivotal for treatment planning. The widespread use of computed tomography (CT)-often with the use of contrast material (CM)-probably represents the most important advance in diagnostic radiology. The result is a marked increase in radiation exposure of the population for medical purposes, with its intrinsic carcinogenic potential, and CM affecting kidney function. The radiologists should aim to minimize patient's risk by reducing radiation exposure and CM amount, while maintaining the highest image quality. To achieve this goal, it is necessary to perform "patient-centric imaging". The purpose of this review is to provide radiologists with "tips and tricks" to control radiation dose at CT, summarizing technical artifices in order to reduce image noise and increase image contrast. Also chest CT tailored protocols are supplied, with particular attention to three most common thoracic CT protocols: aortic/cardiac CT angiography (CTA), pulmonary CTA, and routine chest CT.

Thin-slice brain CT with iterative model reconstruction algorithm for small lacunar lesions detection: Image quality and diagnostic accuracy evaluation

This study was aimed to evaluate the image quality and lacunar lesion detection of thin-slice brain computed tomography (CT) images with different reconstruction algorithms, including filtered back projection (FBP), hybrid iterative reconstruction (HIR), and iterative model reconstruction (IMR) by comparison of routine slice images with FBP reconstruction. Sixty-one patients underwent noncontrast brain CT and images were reconstructed with a routine slice of 5.0 mm by FBP and thin slice of 1.0 mm by IMR, HIR, and FBP algorithms, respectively. Objective analyses included CT attenuation, noise, artifacts index of posterior cranial fossa, and contrast-to-noise ratio (CNR). Subjective analyses were performed according to overall image quality using a 5-point scale [1 (unacceptable) to 5 (excellent)]. In addition, lacunar lesion detection was compared in images with different reconstruction settings among 26 patients with lacunar lesions, with magnetic resonance imaging (MRI) as reference.Thin-slice IMR images enabled the lowest noise, artifacts index, and the best CNR. Both IMR and HIR thin-slice images enabled better scores in subjective image quality than routine slice FBP images. Moreover, both thin-slice IMR and HIR images enabled higher sensitivity and positive predictive value (PPV) in lesion detection of 35-mm lacunar lesions compared with routine slice FBP images.Thin-slice IMR images improve image quality, meanwhile yield better detection of small lacunar lesions in brain CT compared with routine slice FBP images.

Feasibility study of iterative model reconstruction combined with low tube voltage, low iodine load, and low iodine delivery rate in craniocervical CT angiography

AIM

To investigate the feasibility of iterative model reconstruction (IMR) combined with low tube voltage, low iodine load, and low iodine deliver rate in craniocervical computed tomography angiography (CTA).

MATERIALS AND METHODS

Sixty patients were randomly divided into two groups (n=30 for each): group A: 120 kVp, 50 ml of iopromide at a flow rate of 5 ml/s; filtered back projection (FBP) reconstruction; group B: 80 kVp, 30 ml of iohexol at 4.5 ml/s; hybrid iterative reconstruction (HIR) for group B1 and IMR for group B2. CT attenuation values, image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), subjective image quality, effective dose (ED), iodine load, and iodine delivery rate (IDR) were compared.

RESULTS

CT attenuation values of the arteries were higher in groups B1 and B2 than group A. The SNR and CNR were higher, while image noise was lower, for group B2 compared with groups B1 and A. The best subjective image quality was obtained with group B2. ED, iodine load, and IDR reduction of 69.6%, 51.4%, 27%, respectively, was obtained in group B compared with group A.

CONCLUSION

IMR combined with 80 kVp and 30 ml of iohexol at a flow rate of 4.5 ml/s for craniocervical CTA can reduce ED, iodine load, and IDR, while improving image quality.

Low kV and Low Concentration Contrast Agent with Iterative Reconstruction of Computed Tomography (CT) Coronary Angiography: A Preliminary Study

Background

The aim of this study was to evaluate the image quality and radiation dose of CT coronary angiography (CTCA) with low kV, low concentration contrast agent, and iterative reconstruction.

Material/Methods

Ninety cases were randomly divided into 3 groups according to contrast agent concentration: group A 270 mg/ml (100 kV), group B 350 mg/ml (120 kV), and group C 370 mg/ml (120 kV), with 30 cases per group. Tube current was 200–250 mAs. Collimator width was 128×0.6 mm. Rotation speed was 0.27 s. The CT value of the left and right coronary arteries and the ascending aortic root was measured. The SNR and CNR of the images were calculated to evaluate the image quality objectively. The CTDI, DLP, and contrast injection were recorded.

Results

There were no significant differences in sex, age, weight, height, and BMI among the 3 groups. There was no statistically significant difference between left and right coronary artery and ascending aortic root CT value, background noise, SNR, and CNR. Compared to B and C, the ED in group A decreased by about 27.58% and 28.21%, respectively. The total amount of iodine in group A was decreased by about 21.27% and 24.83%, respectively compared with groups B and C.

Conclusions

Low kV and low concentration contrast agent combined with iterative reconstruction for CTCA imaging produced image quality consistent with that of conventional CTCA and significantly reduced the dosage of the radiation and injected iodine.

Coronary Artery Stent Evaluation with Model-based Iterative Reconstruction at Coronary CT Angiography

RATIONALE AND OBJECTIVES

This study aims to compare the image quality of coronary artery stent scans on computed tomography images reconstructed with forward projected model-based iterative reconstruction solution (FIRST) and adaptive iterative dose reduction 3D (AIDR 3D).

MATERIALS AND METHODS

Coronary computed tomography angiography scans of 23 patients with 32 coronary stents were used. The images were reconstructed with AIDR 3D and FIRST. We generated computed tomography attenuation profiles across the stents and measured the width of the edge rise distance and the edge rise slope (ERS). We also calculated the stent lumen attenuation increase ratio (SAIR) and measured visible stent lumen diameters. Two radiologists visually evaluated the image quality of the stents using a 4-point scale (1 = poor, 4 = excellent).

RESULTS

There was no significant difference in the edge rise distance between the two reconstruction methods (P = 0.36). The ERS on FIRST images was greater than the ERS on AIDR 3D images (325.2 HU/mm vs 224.4 HU/mm; P <0.01). The rate of the visible stent lumen diameter compared to the true diameter on FIRST images was higher than that on AIDR 3D images (51.4% vs 47.3%, P <0.01). The SAIR on FIRST images was lower than the SAIR on AIDR 3D images (0.19 vs 0.30, P <0.01). The mean image quality scores for AIDR 3D and FIRST images were 3.18 and 3.63, respectively; the difference was also significant (P <0.01).

CONCLUSION

The image quality of coronary artery stent scans is better on FIRST than on AIDR 3D images.

Low-dose CT imaging of a total hip arthroplasty phantom using model-based iterative reconstruction and orthopedic metal artifact reduction

OBJECTIVE

To compare quantitative measures of image quality, in terms of CT number accuracy, noise, signal-to-noise-ratios (SNRs), and contrast-to-noise ratios (CNRs), at different dose levels with filtered-back-projection (FBP), iterative reconstruction (IR), and model-based iterative reconstruction (MBIR) alone and in combination with orthopedic metal artifact reduction (O-MAR) in a total hip arthroplasty (THA) phantom.

MATERIALS AND METHODS

Scans were acquired from high- to low-dose (CTDI_vol: 40.0, 32.0, 24.0, 16.0, 8.0, and 4.0 mGy) at 120- and 140- kVp. Images were reconstructed using FBP, IR (iDose⁴ level 2, 4, and 6) and MBIR (IMR, level 1, 2, and 3) with and without O-MAR. CT number accuracy in Hounsfield Units (HU), noise or standard deviation, SNRs, and CNRs were analyzed.

RESULTS

The IMR technique showed lower noise levels (p < 0.01), higher SNRs (p < 0.001) and CNRs (p < 0.001) compared with FBP and iDose⁴ in all acquisitions from high- to low-dose with constant CT numbers. O-MAR reduced noise (p < 0.01) and improved SNRs (p < 0.01) and CNRs (p < 0.001) while improving CT number accuracy only at a low dose. At the low dose of 4.0 mGy, IMR level 1, 2, and 3 showed 83%, 89%, and 95% lower noise values, a factor 6.0, 9.2, and 17.9 higher SNRs, and 5.7, 8.8, and 18.2 higher CNRs compared with FBP respectively.

CONCLUSIONS

Based on quantitative analysis of CT number accuracy, noise values, SNRs, and CNRs, we conclude that the combined use of IMR and O-MAR enables a reduction in radiation dose of 83% compared with FBP and iDose⁴ in the CT imaging of a THA phantom.

The Influence of Iterative Reconstruction on Coronary Artery Calcium Scoring-Phantom and Clinical Studies

RATIONALE AND OBJECTIVES

We compared the effect of iterative model reconstruction (IMR), filtered back projection (FBP), and hybrid iterative reconstruction (HIR) on coronary artery calcium (CAC) scoring.

MATERIALS AND METHODS

CAC scans of 30 consecutive patients (18 men and 12 women, age 70.1 ± 12.2 years) were reconstructed with FBP, HIR, and IMR, and the image noise was measured on all images. Two radiologists independently measured the CAC scores using semiautomated software, and interobserver agreement was evaluated. Statistical analysis included the Spearman correlation coefficient and Bland-Altman analysis.

RESULTS

The mean image noise on FBP, HIR, and IMR images was 48.0 ± 7.9, 29.6 ± 4.8, and 9.3 ± 1.3 Hounsfield units, respectively. The difference among all reconstruction combinations was significant (P < .01). The CAC score on HIR and IMR scans was 4.2% and 8.9% lower, respectively, than the CAC score on FBP images. There was no significant difference in the mean CAC score among the three reconstructions. The interobserver correlation was excellent for all three reconstructions (r² = 0.96 FBP, 0.99 HIR, 0.99 IMR); the best Bland-Altman measure of agreement was with IMR, followed by HIR and FBP.

CONCLUSION

For CAC scoring, IMR can reduce the image noise and blooming artifacts, and consequently lowers the measured CAC score. IMR can lessen measurement variability and yield stable, reproducible measurements.

Computed Tomography Imaging of a Hip Prosthesis Using Iterative Model-Based Reconstruction and Orthopaedic Metal Artefact Reduction: A Quantitative Analysis

OBJECTIVES

To quantify the combined use of iterative model-based reconstruction (IMR) and orthopaedic metal artefact reduction (O-MAR) in reducing metal artefacts and improving image quality in a total hip arthroplasty phantom.

METHODS

Scans acquired at several dose levels and kVps were reconstructed with filtered back-projection (FBP), iterative reconstruction (iDose) and IMR, with and without O-MAR. Computed tomography (CT) numbers, noise levels, signal-to-noise-ratios and contrast-to-noise-ratios were analysed.

RESULTS

Iterative model-based reconstruction results in overall improved image quality compared to iDose and FBP (P < 0.001). Orthopaedic metal artefact reduction is most effective in reducing severe metal artefacts improving CT number accuracy by 50%, 60%, and 63% (P < 0.05) and reducing noise by 1%, 62%, and 85% (P < 0.001) whereas improving signal-to-noise-ratios by 27%, 47%, and 46% (P < 0.001) and contrast-to-noise-ratios by 16%, 25%, and 19% (P < 0.001) with FBP, iDose, and IMR, respectively.

CONCLUSIONS

The combined use of IMR and O-MAR strongly improves overall image quality and strongly reduces metal artefacts in the CT imaging of a total hip arthroplasty phantom.

Iterative model reconstruction reduces calcified plaque volume in coronary CT angiography

OBJECTIVE

To assess the impact of iterative model reconstruction (IMR) on calcified plaque quantification as compared to filtered back projection reconstruction (FBP) and hybrid iterative reconstruction (HIR) in coronary computed tomography angiography (CTA).

METHODS

Raw image data of 52 patients who underwent 256-slice CTA were reconstructed with IMR, HIR and FBP. We evaluated qualitative, quantitative image quality parameters and quantified calcified and partially calcified plaque volumes using automated software.

RESULTS

Overall qualitative image quality significantly improved with HIR as compared to FBP, and further improved with IMR (p<0.01 all). Contrast-to-noise ratios were improved with IMR, compared to HIR and FBP (51.0 [43.5-59.9], 20.3 [16.2-25.9] and 14.0 [11.2-17.7], respectively, all p<0.01) Overall plaque volumes were lowest with IMR and highest with FBP (121.7 [79.3-168.4], 138.7 [90.6-191.7], 147.0 [100.7-183.6]). Similarly, calcified volumes (>130 HU) were decreased with IMR as compared to HIR and FBP (105.9 [62.1-144.6], 110.2 [63.8-166.6], 115.9 [81.7-164.2], respectively, p<0.05 all). High-attenuation non-calcified volumes (90-129 HU) yielded similar values with FBP and HIR (p=0.81), however it was lower with IMR (p < 0.05 both). Intermediate- (30-89 HU) and low-attenuation (<30 HU) non-calcified volumes showed no significant difference (p=0.22 and p=0.67, respectively).

CONCLUSIONS

IMR improves image quality of coronary CTA and decreases calcified plaque volumes.

CT Angiography in Patients with Peripheral Arterial Disease: Effect of Small Focal Spot Imaging and Iterative Model Reconstruction on the Image Quality

RATIONALE AND OBJECTIVES

We investigated the effects of small focal spot (SFS) imaging and iterative model reconstruction (IMR) on the image quality of computed tomography angiographs (CTA) in patients with peripheral arterial disease.

MATERIALS AND METHODS

We divided 60 consecutive patients with suspected or confirmed peripheral artery disease into two equal groups. One group underwent large focal spot scanning under our standard CTA protocol with hybrid iterative reconstruction (iDose(4)) (protocol 1), and the other underwent scanning with the SFS protocol and IMR (protocol 2). Quantitative image quality parameters, ie, arterial computed tomography attenuation, image noise, and the contrast-to-noise ratio, were compared and the visual image quality (depiction of each vessel) was scored on a 5-point scale.

RESULTS

There was no significant difference in the arterial attenuation among all evaluated slice levels. The mean image noise was significantly lower under protocol 2 and the contrast-to-noise ratio was significantly higher at all slice levels. The visual scores assigned to the two protocols for the depiction of large vessels, such as the abdominal aorta and iliac artery, were comparable. However, the mean visual scores for small vessels in the lower extremities were significantly higher under protocol 2.

CONCLUSION

CTA with SFS and IMR yielded significantly better qualitative and quantitative image quality especially for small vessels.

Diagnostic accuracy of coronary CT angiography using 3rd-generation dual-source CT and automated tube voltage selection: Clinical application in a non-obese and obese patient population

PURPOSE

To investigate diagnostic accuracy of 3^rd-generation dual-source CT (DSCT) coronary angiography in obese and non-obese patients.

METHODS

We retrospectively analyzed 76 patients who underwent coronary CT angiography (CCTA) and invasive coronary angiography. Prospectively ECG-triggered acquisition was performed with automated tube voltage selection (ATVS). Patients were dichotomized based on body mass index in groups A (<30 kg/m², n = 37) and B (≥30 kg/m², n = 39) and based on tube voltage in groups C (<120 kV, n = 46) and D (120 kV, n = 30). Coronary arteries were assessed for significant stenoses (≥50 % luminal narrowing) and diagnostic accuracy was calculated.

RESULTS

Per-patient overall sensitivity, specificity, positive predictive value, negative predictive value (NPV) and accuracy were 96.9 %, 95.5 %, 93.9 %, 97.7 % and 96.1 %, respectively. Sensitivity and NPV were lower in groups B and D compared to groups A and C, but no statistically significant differences were observed (group A vs. B: sensitivity, 100.0 % vs. 93.3 %, p = 0.9493; NPV, 100 % vs. 95.5 %, p = 0.9812; group C vs. D: sensitivity, 100.0 % vs. 92.3 %, p = 0.8462; NPV, 100.0 % vs. 94.1 %, p = 0.8285).

CONCLUSION

CCTA using 3^rd-generation DSCT and (ATVS) provides high diagnostic accuracy in both non-obese and obese patients.

KEY POINTS

• Coronary CTA provides high diagnostic accuracy in non-obese and obese patients. • Diagnostic accuracy between obese and non-obese patients showed no significant difference. • <120 kV studies were performed in 44 % of obese patients. • Current radiation dose-saving approaches can be applied independent of body habitus.

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.

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, >400), 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 < 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.

First experiences with model based iterative reconstructions influence on quantitative plaque volume and intensity measurements in coronary computed tomography angiography

PURPOSE

Investigate the influence of adaptive statistical iterative reconstruction (ASIR) and the model-based IR (Veo) reconstruction algorithm in coronary computed tomography angiography (CCTA) images on quantitative measurements in coronary arteries for plaque volumes and intensities.

METHODS

Three patients had three independent dose reduced CCTA performed and reconstructed with 30% ASIR (CTDI_vol at 6.7 mGy), 60% ASIR (CTDI_vol 4.3 mGy) and Veo (CTDI_vol at 1.9 mGy). Coronary plaque analysis was performed for each measured CCTA volumes, plaque burden and intensities.

RESULTS

Plaque volume and plaque burden show a decreasing tendency from ASIR to Veo as median volume for ASIR is 314 mm³ and 337 mm³-252 mm³ for Veo and plaque burden is 42% and 44% for ASIR to 39% for Veo. The lumen and vessel volume decrease slightly from 30% ASIR to 60% ASIR with 498 mm³-391 mm³ for lumen volume and vessel volume from 939 mm³ to 830 mm³. The intensities did not change overall between the different reconstructions for either lumen or plaque.

CONCLUSION

We found a tendency of decreasing plaque volumes and plaque burden but no change in intensities with the use of low dose Veo CCTA (1.9 mGy) compared to dose reduced ASIR CCTA (6.7 mGy & 4.3 mGy), although more studies are warranted.

Recent Update on Radiation Dose Assessment for the State-of-the-Art Coronary Computed Tomography Angiography Protocols

OBJECTIVES

This study aimed to measure the absorbed doses in selected organs for prospectively ECG-triggered coronary computed tomography angiography (CCTA) using five different generations CT scanners in a female adult anthropomorphic phantom and to estimate the effective dose (HE).

MATERIALS AND METHODS

Prospectively ECG-triggered CCTA was performed using five commercially available CT scanners: 64-detector-row single source CT (SSCT), 2 × 32-detector-row-dual source CT (DSCT), 2 × 64-detector-row DSCT and 320-detector-row SSCT scanners. Absorbed doses were measured in 34 organs using pre-calibrated optically stimulated luminescence dosimeters (OSLDs) placed inside a standard female adult anthropomorphic phantom. HE was calculated from the measured organ doses and compared to the HE derived from the air kerma-length product (PKL) using the conversion coefficient of 0.014 mSv∙mGy-1∙cm-1 for the chest region.

RESULTS

Both breasts and lungs received the highest radiation dose during CCTA examination. The highest HE was received from 2 × 32-detector-row DSCT scanner (6.06 ± 0.72 mSv), followed by 64-detector-row SSCT (5.60 ± 0.68 and 5.02 ± 0.73 mSv), 2 × 64-detector-row DSCT (1.88 ± 0.25 mSv) and 320-detector-row SSCT (1.34 ± 0.48 mSv) scanners. HE calculated from the measured organ doses were about 38 to 53% higher than the HE derived from the PKL-to-HE conversion factor.

CONCLUSION

The radiation doses received from a prospectively ECG-triggered CCTA are relatively small and are depending on the scanner technology and imaging protocols. HE as low as 1.34 and 1.88 mSv can be achieved in prospectively ECG-triggered CCTA using 320-detector-row SSCT and 2 × 64-detector-row DSCT scanners.

Radiation dose and diagnostic image quality associated with iterative reconstruction in coronary CT angiography: A systematic review

The aim of this systematic review is to evaluate the radiation dose reduction achieved using iterative reconstruction (IR) compared to filtered back projection (FBP) in coronary CT angiography (CCTA) and assess the impact on diagnostic image quality. A systematic search of seven electronic databases was performed to identify all studies using a developed keywords strategy. A total of 14 studies met the criteria and were included in a review analysis. The results showed that there was a significant reduction in radiation dose when using IR compared to FBP (P < 0.05). The mean and standard deviation (SD) difference of CTDIvol and dose-length-product (DLP) were 14.70 ± 6.87 mGy and 186 ± 120 mGy.cm respectively. The mean ± SD difference of effective dose (ED ) was 2.9 ± 1.7 mSv with the range from 1.0 to 5.0 mSv. The assessment of diagnostic image quality showed no significant difference (P > 0.05). The mean ± SD difference of image noise, signal-noise ratio (SNR) and contrast-noise ratio (CNR) were 1.05 ± 1.29 HU, 0.88 ± 0.56 and 0.63 ± 1.83 respectively. The mean ± SD percentages of overall image quality scores were 71.79 ± 12.29% (FBP) and 67.31 ± 22.96% (IR). The mean ± SD percentages of coronary segment analysis were 95.43 ± 2.57% (FBP) and 97.19 ± 2.62% (IR). In conclusion, this review analysis shows that CCTA with the use of IR leads to a significant reduction in radiation dose as compared to the use of FBP. Diagnostic image quality of IR at reduced dose (30-41%) is comparable to FBP at standard dose in the diagnosis of CAD.

Feasibility study of low tube voltage (80 kVp) coronary CT angiography combined with contrast medium reduction using iterative model reconstruction (IMR) on standard BMI patients

OBJECTIVE

To investigate the feasibility of low-tube-voltage (80 kVp) coronary CT angiography (CCTA) combined with contrast medium (CM) reduction and iterative model reconstruction (IMR) on patients with standard body mass index compared with clinical routine protocol.

METHODS

Retrospectively gated helical CCTA scans were acquired using a 256-slice multi-slice CT (Brilliance iCT; Philips Healthcare, Cleveland, OH) on 94 patients with standard body mass index (20-25 kg m(-2)) who were randomly assigned into 2 groups. The scan protocol for Group 1 was 100 kVp and 600 mAs with 70 ml CM at an injection rate of 4.5-5.5 ml s(-1); images were reconstructed by a hybrid iterative reconstruction technique (iDose(4); Philips Healthcare). Group 2 was scanned at 80 kVp and 600 mAs with 35 ml CM at an injection rate of 3.5-4.5 ml s(-1); images were reconstructed with IMR. Objective measurements such as the mean image noise and contrast-to-noise ratio of the two groups were measured on CT images and compared using the paired t-test. In addition, a subjective image quality evaluation was performed by two radiologists who were blinded to the scan protocol, using a 5-point scale [1 (poor) to 5 (excellent)]. The results of the two groups were compared using Mann-Whitney U test.

RESULTS

The iodine delivery rate of Group 2 was 1.0 ± 0.5 gI s(-1) compared with 2.1 ± 0.5 gI s(-1) in Group 1 resulting in a reduction of 52.4%. In addition, an effective radiation dose reduction of 56.4% was achieved in Group 2 (2.4 ± 1.2 mSv) compared with Group 1 (5.5 ± 1.4 mSv). The mean CT attenuation, contrast-to-noise ratio and image quality of all segments in Group 2 were significantly improved compared with those in Group 1 (all, p < 0.01).

CONCLUSION

The use of IMR along with a low tube voltage (80 kVp) combined with a low CM protocol for CCTA can reduce both radiation and CM dose with improved image quality.

ADVANCES IN KNOWLEDGE

In this study, we used a novel knowledge-based IMR which remarkably reduced the image noise. We compared the quality of the images obtained when the tube voltage was reduced to 80 kVp and that of those obtained according to the clinical routine protocols to determine whether ultra-low-dose imaging plus IMR is feasible in CCTA scans. We found that a low dose protocol combined with 80 kVp and reduced CM for CCTA can reduce both radiation dose and CM dose with improved image quality by the use of IMR in non-obese patients.

Plaque assessment by coronary CT

Coronary CT angiography (CTA) has emerged as a highly reliable and non-invasive modality for the exclusion of coronary artery disease. Recent technological advancements in coronary CTA imaging allow for robust qualitative and quantitative assessment of atherosclerotic plaques. Furthermore, CTA is a promising modality for functional evaluation of coronary lesions. Individual plaque features, the extent and severity of atherosclerotic plaque burden were proposed to improve cardiovascular risk stratification. It has been suggested that total atherosclerotic plaque burden is a stronger predictor of coronary events than total ischemia burden. The quest to noninvasively detect individual vulnerable plaques still remains. In the current review we sought to summarize state-of-the-art coronary artery plaque assessment by CTA.

256-Slice coronary computed tomographic angiography in patients with atrial fibrillation: optimal reconstruction phase and image quality

OBJECTIVES

To assess the optimal reconstruction phase and the image quality of coronary computed tomographic angiography (CCTA) in patients with atrial fibrillation (AF).

METHODS

We performed CCTA in 60 patients with AF and 60 controls with sinus rhythm. The images were reconstructed in multiple phases in all parts of the cardiac cycle, and the optimal reconstruction phase with the fewest motion artefacts was identified. The coronary artery segments were visually evaluated to investigate their assessability.

RESULTS

In 46 (76.7 %) patients, the optimal reconstruction phase was end-diastole, whereas in 6 (10.0 %) patients it was end-systole or mid-diastole, and in 2 (3.3 %) patients it was another cardiac phase. In 53 (88.3 %) of the controls, the optimal reconstruction phase was mid-diastole, whereas it was end-systole in 4 (6.7 %), and in 3 (5.0 %) it was another cardiac phase. There was a significant difference between patients with AF and the controls in the optimal phase (p < 0.01) but not in the visual image quality score (p = 0.06).

CONCLUSIONS

The optimal reconstruction phase in most patients with AF was the end-diastolic phase. The end-systolic phase tended to be optimal in AF patients with higher average heart rates.

KEY POINTS

The optimal reconstruction phase in 76.7 % of patients with atrial fibrillation (AF) was end-diastole. The end-systolic phase was optimal in AF patients with higher heart rates. ECG and heart-rate control are necessary to obtain end-diastolic images with fewer motion artefacts.

Iterative reconstruction in cardiac CT

Iterative reconstruction (IR) has the ability to reduce image noise in CT without compromising diagnostic quality, which permits a significant reduction in effective radiation dose. This been increasingly integrated into clinical CT practice over the past 7 years and has been particularly important in the field of cardiac CT with multiple vendors introducing cardiac CT-compatible IR algorithms. The following review will summarize the principles of IR algorithms, studies validating their noise- and dose-reducing abilities, and the specific applications of IR in cardiac CT.

Low contrast and radiation dose coronary CT angiography using a 320-row system and a refined contrast injection and timing method

BACKGROUND

Among CT scanners, 320-row instruments feature decreased photon energy and yield strong contrast enhancement. Consequently, the contrast medium (CM) dose can be reduced. The results of low-tube-voltage coronary CT angiography (CCTA) performed on 320-row scanners have not been adequately assessed.

OBJECTIVE

We evaluated the effects of a low-contrast-dose protocol on the image quality of CCTA using 80 kVp tube voltage, iterative reconstruction (IR), and a 320-row scanner.

METHODS

We randomly assigned 90 patients (mean body weight, 56.5 ± 11.0 kg) to 1 of 3 CCTA protocols. Under protocol A, 30 were scanned using a conventional 120-kVp protocol and a standard CM dose (280 mg iodine/kg body weight [mgI/kg]). Another 30 underwent scanning at 80 kVp with a 25% CM dose reduction (210 mgI/kg; protocol B). Under protocol C, the remaining 30 patients were scanned at 80 kVp with a 50% CM dose reduction (140 mgI/kg). The 120 and 80 kVp images were processed with IR. Images obtained under the 3 protocols were subjected to quantitative and qualitative analysis.

RESULTS

The amount of CM used in protocol A, B, and C was 43.6 ± 10.1, 30.3 ± 4.4, and 21.0 ± 4.0 mL, respectively. Mean CT attenuation of the coronary arteries tended to be higher under protocol B than the other 2 protocols. The contrast-to-noise ratio was significantly higher under protocol B. The mean visual scores were significantly higher for protocols A and B than protocol C. The mean effective radiation dose was significantly lower under the 80-kVp protocol.

CONCLUSION

With a 320-row scanner and our refined CM injection and timing protocol, it is technically feasible to obtain sufficient vascular enhancement with a reduction in the CM and/or radiation dose at 80-kVp CCTA with IR.