Low-dose CT coronary angiography using iterative reconstruction with a 256-slice CT scanner

Image reconstruction in cardiovascular CT: Part 2 - Iterative reconstruction; potential and pitfalls

The use of IR in CT previously has been prohibitively complicated and time consuming, however improvements in computer processing power now make it possible on almost all CT scanners. Due to its potential to allow scanning at lower doses, IR has received a lot of attention in the medical literature and has become a successful commercial product. Its use in cardiovascular CT has been driven in part due to concerns about radiation dose and image quality. This manuscript discusses the various vendor permutations of iterative reconstruction (IR) in detail and critically appraises the current clinical research available on the various IR techniques used in cardiovascular CT.

Development of an organ-specific insert phantom generated using a 3D printer for investigations of cardiac computed tomography protocols

INTRODUCTION

An ideal organ-specific insert phantom should be able to simulate the anatomical features with appropriate appearances in the resultant computed tomography (CT) images. This study investigated a 3D printing technology to develop a novel and cost-effective cardiac insert phantom derived from volumetric CT image datasets of anthropomorphic chest phantom.

METHODS

Cardiac insert volumes were segmented from CT image datasets, derived from an anthropomorphic chest phantom of Lungman N-01 (Kyoto Kagaku, Japan). These segmented datasets were converted to a virtual 3D-isosurface of heart-shaped shell, while two other removable inserts were included using computer-aided design (CAD) software program. This newly designed cardiac insert phantom was later printed by using a fused deposition modelling (FDM) process via a Creatbot DM Plus 3D printer. Then, several selected filling materials, such as contrast media, oil, water and jelly, were loaded into designated spaces in the 3D-printed phantom. The 3D-printed cardiac insert phantom was positioned within the anthropomorphic chest phantom and 30 repeated CT acquisitions performed using a multi-detector scanner at 120-kVp tube potential. Attenuation (Hounsfield Unit, HU) values were measured and compared to the image datasets of real-patient and Catphan® 500 phantom.

RESULTS

The output of the 3D-printed cardiac insert phantom was a solid acrylic plastic material, which was strong, light in weight and cost-effective. HU values of the filling materials were comparable to the image datasets of real-patient and Catphan® 500 phantom.

CONCLUSIONS

A novel and cost-effective cardiac insert phantom for anthropomorphic chest phantom was developed using volumetric CT image datasets with a 3D printer. Hence, this suggested the printing methodology could be applied to generate other phantoms for CT imaging studies.

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.

Myocardial CT perfusion imaging for ischemia detection

Coronary computed tomography angiography (CCTA) plays an important role in many specific scenarios such as in symptomatic patients with intermediate pretest of coronary artery disease (CAD), as well as in the triage of patients with acute chest pain with TIMI risk ≤2. However, it cannot detect the presence of associated ischemia, which is critical for clinical decision making among patients with moderate to severe stenosis. Although functional information can be obtained with different non-invasive tools, cardiac CT is the unique modality that can perform a comprehensive evaluation of coronary anatomy plus the functional significance of lesions. Myocardial CT perfusion (CTP) can be performed with different approaches such as static and dynamic CTP. In addition, static CTP can be performed using single energy CT (SECT) or dual energy CT (DECT). In this review, we will discuss the technical parameters and the available clinical evidence of static CTP using both SECT and DECT.

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.

Is there a role for a local inpatient CT coronary angiography service in selected patients with acute coronary syndrome? A cohort analysis of inpatient tertiary centre referrals for invasive coronary angiography

OBJECTIVE

To conduct a retrospective analysis of inpatients referred for invasive coronary angiography (ICA) at a tertiary centre, with suspected or confirmed acute coronary syndrome (ACS).

METHODS

A retrospective cohort study was conducted at Jersey General Hospital. We evaluated 198 inpatients referred for ICA with suspected or confirmed ACS over a 3-year period. Patients presenting with ST elevation myocardial infarction were excluded. The primary outcome was to identify the number of patients who did not require subsequent coronary intervention following ICA. Patient variables were measured to establish those who met European Society of Cardiology (ESC) criteria for consideration of CT coronary angiography (CTCA) as an alternative to ICA. Cost of care for those referred for ICA was calculated.

RESULTS

ICA demonstrated evidence of coronary heart disease requiring coronary intervention in 119 (60%) of the referred patients. 28 (35%) of the patients not requiring coronary intervention at ICA met ESC criteria for preassessment with CTCA. The cost of care for this subgroup was £9089 per patient. Inpatient CTCA was calculated at £376 per patient.

CONCLUSIONS

Low-intermediate risk patients presenting with suspected or confirmed ACS to hospitals without onsite coronary revascularisation should be considered for in-hospital CTCA before consideration of ICA. Using CTCA as a gatekeeper for targeted ICA appears cost-effective, particularly for hospitals without the required onsite facilities.

Low-dose CT coronary angiography for assessment of coronary artery disease in patients with type 2 diabetes--a cross-sectional study

Background

Silent coronary artery disease (CAD) is prevalent in type 2 diabetes mellitus (T2DM). Although coronary computed tomography angiography (CCTA) over recent years has emerged a useful tool for assessing and diagnosing CAD it’s role and applicability for patients with T2DM is still unclarified, in particular in asymptomatic patients. We aimed to assess the role of CCTA in detecting and characterizing CAD in patients with T2DM without cardiac symptoms when compared to gold standard invasive coronary angiography (ICA).

Methods

This was a cross-sectional analysis of patients with T2DM without symptomatic CAD enrolled in the Asker and Baerum Cardiovascular Diabetes Study who, following clinical examination and laboratory assessment, underwent subsequently CCTA and ICA.

Results

In total 48 Caucasian patients with T2DM (36 men, age 64.0 ± 7.3 years, diabetes duration 14.6 ± 6.4 years, HbA1c 7.4 ± 1.1 %, BMI 29.6 ± 4.3 kg/m²) consented to, and underwent, both procedures (CCTA and ICA). The population was at intermediate cardiovascular risk (mean coronary artery calcium score 269, 75 % treated with antihypertensive therapy). ICA identified a prevalence of silent CAD at 17 % whereas CCTA 35 %. CCTA had a high sensitivity (100 %) and a high negative predictive value (100 %) for detection of patients with CAD when compared to ICA, but the positive predictive value was low (47 %).

Conclusions

Low-dose CCTA is a reliable method for detection and exclusion of significant CAD in T2DM and thus may be a useful tool for the clinicians. However, a low positive predictive value may limit its usefulness as a screening tool for all CAD asymptomatic patients with T2DM. Further studies should assess the applicability for risk assessment beyond the evaluation of the vascular bed.

Dose reduction with iterative reconstruction for coronary CT angiography: a systematic review and meta-analysis

OBJECTIVE

To investigate the achievable radiation dose reduction for coronary CT angiography (CCTA) with iterative reconstruction (IR) in adults and the effects on image quality.

METHODS

PubMed and EMBASE were searched, and original articles concerning IR for CCTA in adults using prospective electrocardiogram triggering were included. Primary outcome was the effective dose using filtered back projection (FBP) and IR. Secondary outcome was the effect of IR on objective and subjective image quality.

RESULTS

The search yielded 1616 unique articles, of which 10 studies (1042 patients) were included. The pooled routine effective dose with FBP was 4.2 mSv [95% confidence interval (CI) 3.5-5.0]. A dose reduction of 48% to a pooled effective dose of 2.2 mSv (95% CI 1.3-3.1) using IR was reported. Noise, contrast-to-noise ratio and subjective image quality were equal or improved in all but one study, whereas signal-to-noise ratio was decreased in two studies with IR at reduced dose.

CONCLUSION

IR allows for CCTA acquisition with an effective dose of 2.2 mSv with preserved objective and subjective image quality.

128-slice CT angiography of the aorta without ECG-gating: efficacy of faster gantry rotation time and iterative reconstruction in terms of image quality and radiation dose

OBJECTIVE

To evaluate image quality and radiation dose of non ECG-gated 128-slice CT angiography of the aorta (CTAA) with fast gantry rotation time and iterative reconstruction.

METHODS

Four hundred and eighty patients underwent non ECG-gated CTAA. Qualitative and quantitative image quality assessments were performed. Radiation dose was assessed and compared with the dose of patients who underwent ECG-gated CTAA (n = 126) and the dose of previous CTAA performed with another CT (n = 339).

RESULTS

Image quality (aortic root-ascending portion) was average-to-excellent in more than 94% of cases, without any non-diagnostic scan. For proximal coronaries, image quality was average-to-excellent in more than 50%, with only 21.5% of non-diagnostic cases. Quantitative analysis results were also good. Mean radiation dose for thoracic CTAA was 5.6 mSv versus 20.6 mSv of ECG-gated protocol and 20.6 mSv of 16-slice CTAA scans, with an average dose reduction of 72.8% (p < 0.001). Mean radiation dose for thoracic-abdominal CTAA was 9.7 mSv, versus 20.9 mSv of 16-slice CTAA scans, with an average dose reduction of 53.6% (p < 0.001).

CONCLUSIONS

Non ECG-gated 128-slice CTAA is feasible and able to provide high quality visualization of the entire aorta without significant motion artefacts, together with a considerable dose and contrast media volume reduction.

KEY POINTS

• CT image quality of aortic root-ascending aorta is challenging. • Non ECG-gated scans are often limited by pulsatility artefacts. • ECG-gated examinations are usually limited by high radiation doses. • Non ECG-gated 128-slice low dose CTAA provides high quality images. • 128-slice CTAA low dose protocol could frequently replace ECG-gated CTAA.

Comparison of myocardial perfusion evaluation with single versus dual-energy CT and effect of beam-hardening artifacts

RATIONALE AND OBJECTIVES

We sought to explore the feasibility and diagnostic performance of dual-energy computed tomography (DECT) versus single-energy computed tomography (SECT) for the evaluation of myocardial perfusion in patients with intermediate to high likelihood of coronary artery disease.

MATERIALS AND METHODS

The present prospective study involved patients with known or suspected coronary artery disease referred for myocardial perfusion imaging by single-photon emission computed tomography. Forty patients were included in the study protocol and scanned using DECT imaging (n = 20) or SECT imaging (n = 20). The same pharmacologic stress was used for DECT, SECT, and single-photon emission computed tomography scans.

RESULTS

A total of 1360 left ventricular segments were evaluated by DECT and SECT. The contrast-to-noise ratio was similar between groups (DECT 8.8 ± 2.9 vs. SECT 7.7 ± 4.2; P = .22). The diagnostic performance of DECT was greater than that of SECT in identifying perfusion defects (area under the receiver operating characteristic curve of DECT 0.90 [0.86-0.94] vs SECT 0.80 [0.76-0.84]; P = .0004) and remained unaffected when including only segments affected by beam-hardening artifacts (area under the receiver operating characteristic curve = DECT 0.90 [0.84-0.96) vs. SECT 0.77 [0.69-0.84]; P = .007).

CONCLUSIONS

Our results suggest that myocardial perfusion by DECT imaging is feasible and might have improved diagnostic performance compared to SECT imaging for the assessment of myocardial CT perfusion. Furthermore, the diagnostic performance of DECT remained unaffected by the presence of beam-hardening artifacts.

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.