Image quality and artifacts in coronary CT angiography with dual-source CT: initial clinical experience

Standards for quantitative assessments by coronary computed tomography angiography (CCTA): An expert consensus document of the society of cardiovascular computed tomography (SCCT)

In current clinical practice, qualitative or semi-quantitative measures are primarily used to report coronary artery disease on cardiac CT. With advancements in cardiac CT technology and automated post-processing tools, quantitative measures of coronary disease severity have become more broadly available. Quantitative coronary CT angiography has great potential value for clinical management of patients, but also for research. This document aims to provide definitions and standards for the performance and reporting of quantitative measures of coronary artery disease by cardiac CT.

Diagnostic accuracy of noninvasive fractional flow reserve derived from computed tomography angiography in ischemia-specific coronary artery stenosis and indeterminate lesions: results from a multicenter study in China

Background

To determine the diagnostic performance of a novel computational fluid dynamics (CFD)-based algorithm for in situ CT-FFR in patients with ischemia-induced coronary artery stenosis. Additionally, we investigated whether the diagnostic accuracy of CT-FFR differs significantly across the spectrum of disease and analyzed the influencing factors that contribute to misdiagnosis.

Methods

Coronary computed tomography angiography (CCTA), invasive coronary angiography (ICA), and FFR were performed on 324 vessels from 301 patients from six clinical medical centers. Local investigators used CCTA and ICA to conduct assessments of stenosis, and CT-FFR calculations were performed in the core laboratory. For CCTA and ICA, CT-FFR ≤ 0.8 and a stenosis diameter ≥ 50% were identified as lesion-specific ischemia. Univariate logistic regression models were used to assess the effect of features on discordant lesions (false negative and false positive) in different CT-FFR categories. The diagnostic performance of CT-FFR was analyzed using an invasive FFR ≤ 0.8 as the gold standard.

Results

The Youden index indicated an optimal threshold of 0.80 for CT-FFR to identify functionally ischemic lesions. On a per-patient basis, the diagnostic sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) for CT-FFR were 96% (91%-98%), 92% (87%-96%), 94% (90%-96%), 91% (85%-95%), and 96% (92%-99%), respectively. The diagnostic efficacy of CT-FFR was higher than that of CCTA without the influence of calcification. Closer to the cut point, there was less certainty, with the agreement between the invasive FFR and the CT-FFR being at its lowest in the CT-FFR range of 0.7-0.8. In all lesions, luminal stenosis ≥ 50% significantly affected the risk of reduced false negatives (FN) and false positives (FP) results by CT-FFR, irrespective of the association with calcified plaque.

Conclusions

In summary, CT-FFR based on the new parameter-optimized CFD model has a better diagnostic performance than CTA for lesion-specific ischemia. The presence of calcified plaque has no significant effect on the diagnostic performance of CT-FFR and is independent of the degree of calcification. Given the range of applicability of our software, its use at a CT-FFR of 0.7-0.8 requires caution and must be considered in the context of multiple factors.

Mechanism Analysis of Vascular Calcification Based on Fluid Dynamics

Vascular calcification is the abnormal deposition of calcium phosphate complexes in blood vessels, which is regarded as the pathological basis of multiple cardiovascular diseases. The flowing blood exerts a frictional force called shear stress on the vascular wall. Blood vessels have different hydrodynamic properties due to discrepancies in geometric and mechanical properties. The disturbance of the blood flow in the bending area and the branch point of the arterial tree produces a shear stress lower than the physiological magnitude of the laminar shear stress, which can induce the occurrence of vascular calcification. Endothelial cells sense the fluid dynamics of blood and transmit electrical and chemical signals to the full-thickness of blood vessels. Through crosstalk with endothelial cells, smooth muscle cells trigger osteogenic transformation, involved in mediating vascular intima and media calcification. In addition, based on the detection of fluid dynamics parameters, emerging imaging technologies such as 4D Flow MRI and computational fluid dynamics have greatly improved the early diagnosis ability of cardiovascular diseases, showing extremely high clinical application prospects.

Contrast media timing optimization for coronary CT angiography: a retrospective validation study in swine

OBJECTIVES

The objective was to retrospectively develop a protocol in swine for optimal contrast media timing in coronary CT angiography (CCTA).

METHODS

Several dynamic acquisitions were performed in 28 swine (55 ± 24 kg) with cardiac outputs between 1.5 and 5.5 L/min, for 80 total acquisitions. The contrast was injected (1mL/kg, 5mL/s, Isovue 370), followed by dynamic scanning of the entire aortic enhancement curve, from which the true peak time and aortic and coronary enhancements were recorded as the reference standard. Each dataset was then used to simulate two different CCTA protocols-a new optimal protocol and a standard clinical protocol. For the optimal protocol, the CCTA was acquired after bolus tracking-based trigging using a variable time delay of one-half the contrast injection time interval plus 1.5 s. For the standard protocol, the CCTA was acquired after bolus tracking-based triggering using a fixed time delay of 5 s. For both protocols, the CCTA time, aortic enhancement, coronary enhancement, and coronary contrast-to-noise ratio (CNR) were quantitatively compared to the reference standard measurements.

RESULTS

For the optimal protocol, the angiogram was acquired within -0.15 ± 0.75 s of the true peak time, for a mean coronary CNR within 7% of the peak coronary CNR. Conversely, for the standard CCTA protocol, the angiogram was acquired within -1.82 ± 1.71 s of the true peak time, for a mean coronary CNR that was 23% lower than the peak coronary CNR.

CONCLUSIONS

The optimal CCTA protocol improves contrast media timing and coronary CNR by acquiring the angiogram at the true aortic root peak time.

KEY POINTS

• This study in swine retrospectively developed the mathematical basis of an improved approach for optimal contrast media timing in CCTA. • By combining dynamic bolus tracking with a simple contrast injection timing relation, CCTA can be acquired at the peak of the aortic root enhancement. • CCTA acquisition at the peak of the aortic root enhancement should maximize the coronary enhancement and CNR, potentially improving the accuracy of CT-based assessment of coronary artery disease.

Cardiac CT blooming artifacts: clinical significance, root causes and potential solutions

This review paper aims to summarize cardiac CT blooming artifacts, how they present clinically and what their root causes and potential solutions are. A literature survey was performed covering any publications with a specific interest in calcium blooming and stent blooming in cardiac CT. The claims from literature are compared and interpreted, aiming at narrowing down the root causes and most promising solutions for blooming artifacts. More than 30 journal publications were identified with specific relevance to blooming artifacts. The main reported causes of blooming artifacts are the partial volume effect, motion artifacts and beam hardening. The proposed solutions are classified as high-resolution CT hardware, high-resolution CT reconstruction, subtraction techniques and post-processing techniques, with a special emphasis on deep learning (DL) techniques. The partial volume effect is the leading cause of blooming artifacts. The partial volume effect can be minimized by increasing the CT spatial resolution through higher-resolution CT hardware or advanced high-resolution CT reconstruction. In addition, DL techniques have shown great promise to correct for blooming artifacts. A combination of these techniques could avoid repeat scans for subtraction techniques.

High Temporal Resolution Dual-Source Photon-Counting CT for Coronary Artery Disease: Initial Multicenter Clinical Experience

The aim of this paper is to evaluate the diagnostic image quality of spectral dual-source photon-counting detector coronary computed tomography angiography (PCD-CCTA) for coronary artery disease in a multicenter study. The image quality (IQ), assessability, contrast-to-noise ratio (CNR), Agatston score, and radiation exposure were measured. Stenoses were quantified and compared with invasive coronary angiography, if available. A total of 92 subjects (65% male, age 58 ± 14 years) were analyzed. The prevalence of significant coronary artery disease (CAD) (stenosis ≥ 50%) was 17% of all patients, the range of the Agatston score was 0−2965 (interquartile range (IQR) 0−135). The IQ was very good (one, IQR one−two), the CNR was very high (20 ± 10), and 5% of the segments were rated non-diagnostic. The IQ and assessability were higher in proximal coronary segments (p < 0.001). Agatston scores up to 600 did not significantly affect the assessability of the coronary segments (p = 0.3). Heart rate influenced assessability only at a high-pitch mode (p = 0.009). For the invasive coronary angiography (ICA) subgroup (n = nine), the diagnostic performance for CAD per segment was high (sensitivity 92%, specificity 96%), although the limited number of patients who underwent both diagnostic modalities limits the generalization of this finding at this stage. PCD-CCTA provides good image quality for low and moderate levels of coronary calcifications.

Fat volume measurements as a predictor of image noise in coronary computed tomography angiography

Introduction

Image noise can negatively affect the overall quality of coronary computed tomography angiography (CCTA).

Objectives

The purpose of this study was to evaluate the relationship between image noise and fat volumes in the chest wall. We also aimed to compare these with other patient-specific predictors of image noise, such as body weight (BW) and body mass index (BMI).

Methods

We undertook a cross-sectional, single-center study. A tube voltage of 100 kV was used for patients with BW <85 kg and 120 kV for BW ≥85 kg. The image noise in the aortic root, single-slice fat volume (SFV) at the level of the left main coronary artery and the total fat volume of the chest (TFV) were analyzed.

Results

A total of 132 consecutive patients were enrolled (mean age ± standard deviation, 51 ± 11 years; 64% male). The mean image noise was 30.5 ± 11 Hounsfield units (HU). We found that patients with image noise >30 HU had significantly higher SFV (75 ± 33 vs. 51 ± 24, p < 0.0001) and TFV (2206 ± 927 vs. 1815 ± 737, p < 0.01) compared with patients having noise ≤30 HU, whereas BW and BMI showed no significant difference (78 ± 13 vs. 81 ± 14, p < 0.34) and (28.7 ± 4.7 vs. 26.8 ± 3.8, p < 0.19), respectively. Linear regression analysis showed that image noise has better correlation with SFV (R = 0.399; p < 0.0001); and TFV (R = 0, p < 0.009) than BMI (R = 0.154, p < 0.039) and BW (R = -0.102, p = 0.12).

Conclusions

Fat volume measurements of the chest wall can predict CCTA image noise better than other patient-specific predictors, such as BW and BMI.

Clinical Implications of Moderate Coronary Stenosis on Coronary Computed Tomography Angiography in Patients with Stable Angina

PURPOSE

The present study investigated the diagnostic accuracy and clinical implications of moderate stenosis (50-69%, Coronary Artery Disease Reporting and Data System, grade 3) on coronary computed tomography angiography (CCTA), compared with invasive coronary angiography (ICA).

MATERIALS AND METHODS

Two hundred and seventy-six patients who underwent ICA due to moderate stenosis alone on CCTA were selected from our prospective registry cohort.

RESULTS

Diagnostic concordance between CCTA and ICA was found in only 50 (18%) patients. Among the 396 vessels and 508 segments with moderate stenosis, diagnostic concordance was found in 132 vessels (33%) and 127 segments (25%). Segments with calcified plaque had lower diagnostic concordance than those with mixed or non-calcified plaque (22% vs. 28% vs. 27%, respectively, p=0.001). While calcified plaque burden did not have an influence on severe stenosis (≥70%) on ICA, higher burden of non-calcified plaque was correlated with a greater incidence of ICA-based severe stenosis, which was more frequent in patients with ≥3 segments of non-calcified plaque (75%) than those without non-calcified plaque (22%, p<0.001). Typical angina and mixed or non-calcified plaque were correlated with a higher incidence of under-diagnosis, while the use of next-generation computed tomography scanners reduced the incidence of under-diagnosis. Increased body weight, left circumflex artery involvement, and calcified plaque were independent factors that increased the risk of over-diagnosis of CCTA.

CONCLUSION

The diagnosis of moderate stenosis by CCTA may be limited in estimating the exact degree of ICA-based anatomical stenosis. Unlike calcific burden, non-calcific burden was positively correlated with the presence of severe stenosis on ICA.

Using coronary CT angiography for guiding invasive coronary angiography: potential role to reduce intraprocedural radiation exposure

OBJECTIVES

We investigated the potential reduction of patient exposure during invasive coronary angiography (ICA) if the procedure had only been directed to the vessel with at least one ≥ 50% stenosis as described in the CT report.

METHODS

Dose reports of 61 patients referred to ICA because of at least one ≥ 50% stenosis on coronary CT angiography (CCTA) were included. Dose-area product (DAP) was documented separately for left (LCA) and right coronary arteries (RCA) by summing up the single DAP for each angiographic projection. The study population was subdivided as follows: coronary intervention of LCA (group 1) or RCA (group 2) only, or of both vessels (group 3), or further bypass grafting (group 4), or no further intervention (group 5).

RESULTS

57.4% of the study population could have benefitted from reduced exposure if catheterization had been directly guided to the vessel of interest as described on CCTA. Mean relative DAP reductions were as follows: group 1 (n = 18), 11.2%; group 2 (n = 2), 40.3%; group 3 (n = 10), 0%; group 4 (n = 3), 0%; group 5 (n = 28), 28.8%.

CONCLUSIONS

Directing ICA to the vessel with stenosis as described on CCTA would reduce intraprocedural patient exposure substantially, especially for patients with single-vessel stenosis.

KEY POINTS

• Patients with CAD can benefit from decreased radiation exposure during coronary angiography. • ICA should be directed solely to significant stenoses as described on CCTA. • Severely calcified plaques remain a limitation of CCTA leading to unnecessary ICA referrals.

Patient-related factors that influence coronary artery density in CCTA: a retrospective clinical study

OBJECTIVES

The aim of this study was to investigate the relationship between various patient-related factors (physical and cardiac hemodynamic parameters) and the coronary artery density on coronary CT angiography (CCTA).

METHODS

A total of 64 patients (female: male ratio, 24:40; age, 58.2 years±9.3, age range, 31-81 years; mean body weight, 65.3 kg±11.6, range 40-88 kg) were effectively enrolled in this approved retrospective study. Patient-related physical factors including height, body weight (BW), body mass index (BMI), systolic blood pressure (BPsys), diastolic blood pressure (BPdis) and blood pulse pressure (Bp) were recorded, measured and calculated prior to the administration of contrast media during the CCTA. Patient-related cardiac hemodynamic parameters, including heart rate (HR), myocardial mass (MM), cardiac output (CO), ejection fraction (EF), end-diastolic dimension (EDV), end-systolic volume (ESV) and stroke volume (SV), were analysed and recorded on the multimodality workplace (MMWP). The mean attenuation values of the left main artery (LMA) were measured and calculated. The correlation of the mean attenuation in the coronary arteries with the physical and hemodynamic parameters was evaluated. The correlations between the physical factors and hemodynamic parameters were also calculated.

RESULTS

A significant negative linear correlation was found between the attenuation of the left main artery (LMA) and BW (P=.001), BMI (P=.006), CO (P=.008), EDV (P=.001) and MM (P<.001). Significant linear correlations were obtained between CO and HR (P<.001), EDV and BW (P=.001) and MM and BW (P<.001).

CONCLUSION

Coronary artery attenuation depends on the patient's specific physical and cardiac function status.

Coronary Computed Tomography Angiography: Patient-related factors determining image quality using a second-generation 320-slice CT scanner

PURPOSE

To investigate the diagnostic confidence of Coronary Computed Tomography Angiography (CCTA) and the effect of patient-related factors on CCTA image quality using a second-generation 320-slice scanner.

METHODS AND RESULTS

200 consecutive patients (mean age 60±12years; 109 men) prospectively underwent CCTA. The mean body mass index (BMI) was 27.1±4.9kg/m(2); the median heart rate (HR) was 60.0 (interquartile range (IQR), 53.9-66.1) beats per minute (bpm). The median segment's diameter was 2.8 (IQR, 2.2-3.4) mm. For each coronary segment ≥1.5mm in diameter, two readers scored: diameter narrowing as < or ≥50%, overall diagnostic confidence and motion-related image quality, with interobserver agreement kappa-values of 0.89, 0.91 and 0.61 respectively. Seventy-nine of the 2505 evaluated segments (3.2%) had non-diagnostic image quality because of coronary calcifications (66/79; 83.5%), stent- (6/79; 7.5%), pacemaker- (2/79; 2.5%) or motion-related artifacts (5/79; 6.5%). The effect of patient-related factors on motion-related image quality was investigated by multinomial logistic regression in 181 patients with calcium score (IQR, 0-446.5). Increasing coronary diameter was the most improving image quality factor (odds ratio (OR), 1.8637; p<0.001), marginally followed by lower HR (OR, 0.9547; p<0.001) and calcium score (OR, 0.9997; p=0.04). Gender (p=0.70), age (p=0.24) and BMI (p=0.45) did not affect image quality.

CONCLUSION

Using a second-generation 320-slice scanner, CCTA diagnostic confidence is predominantly affected by coronary calcifications, whereas motion-related image quality is non-diagnostic only in exceptional cases and mainly influenced by the coronary diameter. For future developments, our study findings therefore suggest greater requirements concerning spatial resolution and calcium-related artifact removal than concerning temporal resolution, especially to improve diagnostic confidence in patient groups with smaller coronary diameters.

The diagnostic evaluation of dual-source CT (DSCT) in the diagnosis of coronary artery stenoses

Objective: To evaluate the diagnostic accuracy of dual-source computed tomography (DSCT) in the diagnosis of coronary artery stenoses by comparing with conventional coronary angiography (CCA).

Methodology: CCA and DSCT were performed in 64 patients with suspected coronary artery disease (CAD) respectively (46 male, 18 female, age from 48 to 82 years old, mean 68.18 years). Various post-processing reconstructions of coronary artery and its branches, such as volumetric imaging, multi-planar reconstruction, curved planar reconstruction, maximum intensity projection were used. The coronary segments, with statistical evaluations combined with its diameter ≥1.5mm were collected to analyze the diagnosis accuracy of DSCT on coronary artery stenoses, with CCA as the gold standard.

Results: About 4.14% of coronary artery segments could not be evaluated, while 95.86% were evaluable arteries, the sensitivity, specificity, positive and negative predictive value of DSCT for detecting coronary artery stenoses were, 93.58%, 99.61%, 95.31% and 99.48% respectively. There were no significant differences in the diagnostic accuracy of coronary artery stenoses between DSCT and CCA.

Conclusion: DSCT is a reliable tool that is accurately appropriate for patients with CAD, as it has a higher accuracy and specificity, which is valuable in the screening of CAD.

Coronary calcium: new insights, recent data, and clinical role

Calcium artery calcium (CAC) scoring has become an integral part in the era of preventive cardiology, it has been extensively studied and been validated as a powerful tool for cardiovascular risk assessment in conjunction with other traditional well established scoring systems such as Framingham risk score. In addition, CAC testing has found its way into emergency department algorithms assessing low to intermediate risk patients presenting with chest pain, this strategy was recently adopted by the UK NICE guidelines, confidently ruling out cardiac origin of chest pain. Several studies have demonstrated that risk assessment using CAC was motivational to patients leading to better adherence to their preventive practices as well as to medications. Accordingly, this test has several recommendations for use by national and international guidelines.

Relationship of epicardial fat volume to coronary plaque, severe coronary stenosis, and high-risk coronary plaque features assessed by coronary CT angiography

BACKGROUND

Associations of epicardial fat volume (EFV) measured on noncontrast cardiac CT (NCT) include coronary plaque, myocardial ischemia, and adverse cardiac events.

OBJECTIVES

This study aimed to define the relationship of EFV to coronary plaque type, severe coronary stenosis, and the presence of high-risk plaque features (HRPFs).

METHODS

We retrospectively evaluated 402 consecutive patients, with no prior history of coronary artery disease, who underwent same day NCT and coronary CT angiography (CTA). EFV was measured on NCT with the use of validated, semiautomated software. The coronary arteries were evaluated for coronary plaque type (calcified [CP], noncalcified [NCP], or partially calcified [PCP]) and coronary stenosis severity ≥70% with the use of coronary CTA. For patients with NCP and PCP, 2 high-risk plaque features were evaluated: low-attenuation plaque and positive remodeling.

RESULTS

There were 402 patients with a median age of 66 years (range, 23-92 years) of whom 226 (56%) were men. The EFV was greater in patients with CP (112 ± 55 cm(3) vs 89 ± 39 cm(3)), PCP (110 ± 57 cm(3) vs 98 ± 45 cm(3)), and NCP (115 ± 44 cm(3) vs EFV 100 ± 52 cm(3)). In the 192 patients with PCP or NCP, on multivariable analysis, after adjusting for conventional cardiovascular risk factors, EFV was an independent predictor of ≥70% coronary artery stenosis (odds ratio [OR], 3.0; 95% CI, 1.3-6.6; P = 0.008), any high-risk plaque features (OR, 1.7; 95% CI, 0.9-3.4; P = 0.04), and low attention plaque (OR, 2.4; 95% CI, 1.1-5.1; P = 0.02) but not of positive remodeling.

CONCLUSIONS

EFV is greater in patients with CP, PCP, and NCP. In patients with NCP and PCP, EFV is significantly associated with severe coronary stenosis, high-risk plaque features, and low attenuation plaque.

Accuracy of 128-slice dual-source CT using high-pitch spiral mode for the assessment of coronary stents: first in vivo experience

OBJECTIVE

To investigate the accuracy of 128-slice dual-source CT using high-pitch spiral mode (HPS) for the assessment of coronary stents.

METHODS

We conducted a prospective study on patients with previous stent implantation due to recurred suspicious symptoms of angina with positive findings at stress testing scheduled for coronary angiography (CA), while dual source computed tomography (DSCT) examinations were randomly done by one of the three different scan modes [HPS, sequential mode (SEQ), low-pitch spiral mode (LPS)] one week before CA examinations. The image quality, radiation dose and stent patency of DSCT were evaluated blinded to the results of CA.

RESULTS

180 patients with total 256 stents were enrolled in this study. There was no significant difference on the image quality of DSCT by HPS (1.4±0.5), SEQ (1.5±0.5) and LPS (1.3±0.6) (P>0.05). The noise of images reconstructed with B26f kernel in HPS is significantly increased than in SEQ/LPS (P<0.05), while no significant difference with images reconstructed with B46f kernel (P>0.05). Heart rate (HR) variability had a slight impact on the image quality for HPS (P<0.05), not for LPS/SEQ (P>0.05). In the assessment of stent restenosis compared with CA on per-stent basis, there was no significant difference on sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of DSCT using HPS (100%, 97.1%, 83.3%, 100%), LPS (92.3%, 95.9%, 80%, 98.6%) and SEQ (93.3%, 97.3%, 87.5%, 98.6%) (P>0.05). The effective dose of DSCT by HPS (1.0±0.5mSv) is significant less than that by SEQ (3.0±1.4mSv) or LPS (13.0±5.4mSv) (P<0.01).

CONCLUSIONS

DSCT using HPS provides good diagnostic accuracy on coronary stent patency compared with CA, similar to that by SEQ/LPS, whereas with lower effective dose in patients with HR lower than 65bpm.

Computed tomography coronary angiography and invasive coronary angiography demonstrate high correlation for area stenosis quantification in noncalcified and mixed plaques

We compared the variance of area and diameter significant stenosis measurement between quantitative computed tomography coronary angiography (QCTA) and quantitative invasive coronary angiography (QCA). Fifty patients presenting 65 significant coronary artery stenoses (≥70% area stenosis) in QCTA and QCA were included. Spearman's rank correlation revealed that area stenosis measurement by QCTA and QCA yields higher correlation than diameter stenosis and is highest for noncalcified and mixed lesions.

CT coronary angiography: 256-slice and 320-detector row scanners

Multidetector computed tomography (MDCT) has rapidly evolved from 4-detector row systems in 1998 to 256-slice and 320-detector row CT systems. With smaller detector element size and faster gantry rotation speed, spatial and temporal resolution of the 64-detector MDCT scanners have made coronary artery imaging a reliable clinical test. Wide-area coverage MDCT, such as the 256-slice and 320-detector row MDCT scanners, has enabled volumetric imaging of the entire heart free of stair-step artifacts at a single time point within one cardiac cycle. It is hoped that these improvements will be realized with greater diagnostic accuracy of CT coronary angiography. Such scanners hold promise in performing a rapid high quality "triple rule-out" test without high contrast load, improved myocardial perfusion imaging, and even four-dimensional CT subtraction angiography. These emerging technical advances and novel applications will continue to change the way we study coronary artery disease beyond detecting luminal stenosis.

Comparison of the extent and severity of myocardial perfusion defects measured by CT coronary angiography and SPECT myocardial perfusion imaging

OBJECTIVES

We compared electrocardiogram-gated computed tomography (CT) myocardial perfusion imaging (MPI) based on quantification of the extent and severity of perfusion abnormalities to that measured with single-photon emission computed tomography (SPECT) MPI.

BACKGROUND

Contrast-enhanced CT-MPI has been used for the identification of myocardial ischemia.

METHODS

We performed CT-MPI during intravenous adenosine infusion in 30 patients with perfusion abnormalities on rest/adenosine stress SPECT-MPI acquired within 60 days (18 stress-rest CT-MPI and 12 stress CT-MPI only). The extent and severity of perfusion defects on SPECT-MPI were assessed on a 5-point scale in a standard 17-segment model, and total perfusion deficit (TPD) was quantified by automated software. The extent and severity of perfusion defects on CT-MPI was visually assessed by 2 observers using the same grading scale and expressed as summed stress score and summed rest score; visually quantified TPD was given by summed stress score/(maximal score of 68) and summed rest score/68. The magnitude of perfusion abnormality on CT-MPI in regions of the myocardium was defined.

RESULTS

On a per-segment basis, there was good agreement between CT-MPI and SPECT-MPI with a kappa of 0.71 (p < 0.0001) for detection of stress perfusion abnormalities. Automated TPD on SPECT-MPI was similar to visual TPD from CT-MPI (p = 0.65 stress TPD, and p = 0.12 ischemic TPD stress-rest) with excellent agreement (bias = -0.3 for stress TPD, and bias = 1.2 for ischemic TPD) on Bland-Altman analysis. Software-based quantification of the magnitude of stress perfusion deficit and ischemia on CT-MPI were similar to that for automated TPD measured by SPECT (p = 0.88 stress, and p = 0.48 ischemia), with minimal bias (bias = 0.6, and bias = 1.2).

CONCLUSIONS

Stress and reversible myocardial perfusion deficit measured by CT-MPI using a visual semiquantitative approach and a visually guided software-based approach show strong similarity with SPECT-MPI, suggesting that CT-MPI-based assessment of myocardial perfusion defects may be of clinical and prognostic value.

In vivo CT detection of lipid-rich coronary artery atherosclerotic plaques using quantitative histogram analysis: a head to head comparison with IVUS

BACKGROUND

Coronary atherosclerotic plaque characterisation may contribute to risk stratification for future cardiovascular events. The ability of computed tomography to classify plaques as 'fibrous' or 'lipid-rich' based on their average CT attenuation has been investigated but is fraught with substantial limitations. In this study, we evaluated the potential of analysing the distribution of CT attenuation values measured in Hounsfield Units (HU) within coronary atherosclerotic plaques to classify non-calcified plaques into fibrous and lipid-rich subtypes. Intravascular ultrasound (IVUS) served as the gold standard.

PATIENTS AND METHODS

We evaluated the data sets of 40 patients (30 males, 59±10 years) who had been referred for invasive coronary angiography for clinical reasons and in whom IVUS was performed in at least one coronary vessel. Using dual source CT, coronary CT angiography was performed as a part of a research protocol within 24 h previous to invasive coronary angiography. A contrast-enhanced volume dataset was acquired with retrospective ECG gating (120 kV, 400 mAs/rot, collimation 2 mm×64 mm×0.6 mm, 60-80 ml contrast agent i.v). IVUS was performed using a 40-MHz IVUS catheter (Atlantis, Boston Scientific Corporation, Natick, MA) and motorized pullback at 0.5 mm/s. Fifty five corresponding non-calcified plaques within the coronary artery system were identified in both DSCT and IVUS using bifurcation points as fiducial markers. In DSCT data sets, serial parallel cross-sections (1mm slice thickness) were rendered orthogonally to the centre line of the coronary artery for each of the 55 plaques. For each cross section and each plaque, a histogram of CT attenuation values (increments of 10HU) was determined. The percentage of pixels with a density ≤30 HU was calculated. Using IVUS as the gold standard, plaques were classified as predominantly fibrous (hyperechoic) or predominantly lipid-rich (hypoechoic).

RESULTS

15 predominantly fibrous plaques vs. 40 predominantly lipid-rich plaques were identified in IVUS. The mean CT attenuation in both plaque types was significantly different (67±31 HU vs. 96±40 HU, p=0.006), yet with a wide overlap. For the 15 fibrous plaques identified in IVUS, the mean percentage of pixels ≤30 HU in CT was 6±10%. For lipid-rich plaques it was 16±10% (p<0.0001). ROC curve analysis revealed that a cut-off of 5.5% pixels with an attenuation ≤30 HU identified lipid rich plaques in CT angiography with a sensitivity of 95% (38/40, 95% CI 83-99) and a specificity of 80% (12/15, 95% CI 52-96) [AUC 0.9, 95% CI 0.7-1.0]. Using this threshold, the negative predictive value was 86% (12/14, 95% CI 57-98) and the positive predictive value was 93% (38/41, 95% CI 80-98).

CONCLUSION

Lipid-rich coronary atherosclerotic plaques contain a significantly higher percentage of pixels with low CT attenuation as compared to fibrous plaques. Histogram analysis may help to differentiate both plaque types. A cut-off of 5.5% of pixels with an attenuation of ≤30 HU allowed identification of lipid-rich plaques with a sensitivity of 95% and a specificity of 80%.

Assessment of the relationship between stenosis severity and distribution of coronary artery stenoses on multislice computed tomographic angiography and myocardial ischemia detected by single photon emission computed tomography

BACKGROUND

The relationship between luminal stenosis measured by coronary CT angiography (CCTA) and severity of stress-induced ischemia seen on single photon emission computed tomographic myocardial perfusion imaging (SPECT-MPI) is not clearly defined. We sought to evaluate the relationship between stenosis severity assessed by CCTA and ischemia on SPECT-MPI.

METHODS AND RESULTS

ECG-gated CCTA (64 slice dual source CT) and SPECT-MPI were performed within 6 months in 292 patients (ages 26-91, 73% male) with no prior history of coronary artery disease. Maximal coronary luminal narrowing, graded as 0, ≥25%, 50%, 70%, or 90% visual diameter reduction, was consensually assessed by two expert readers. Perfusion defect on SPECT-MPI was assessed by computer-assisted visual interpretation by an expert reader using the standard 17 segment, 5 point-scoring model (stress perfusion defect of ≥5% = abnormal). By SPECT-MPI, abnormal perfusion was seen in 46/292 patients. With increasing stenosis severity, positive predictive value (PPV) increased (42%, 51%, and 74%, P = .01) and negative predictive value was relatively unchanged (97%, 95%, and 91%) in detecting perfusion abnormalities on SPECT-MPI. In a receiver operator curve analysis, stenosis of 50% and 70% were equally effective in differentiating between the presence and absence of ischemia. In a multivariate analysis that included stenosis severity, multivessel disease, plaque composition, and presence of serial stenoses in a coronary artery, the strongest predictors of ischemia were stenosis of 50-89%, odds ratio (OR) 7.31, P = .001, stenosis ≥90%, OR 34.05, P = .0001, and serial stenosis ≥50% OR of 3.55, P = .006.

CONCLUSIONS

The PPV of CCTA for ischemia by SPECT-MPI rises as stenosis severity increases. Luminal stenosis ≥90% on CCTA strongly predicts ischemia, while <50% stenosis strongly predicts the absence of ischemia. Serial stenosis of ≥50% in a vessel may offer incremental value in addition to stenosis severity in predicting ischemia.

CT angiography: current technology and clinical use

Since 1958, catheter angiography has assumed the role of gold standard for vascular imaging, despite the invasive nature of the procedure. Less invasive techniques for vascular imaging, such as computed tomographic angiography (CTA), have been developed and have matured in conjunction with developments in catheter arteriography. In a few cases, such as imaging, the aorta and the pulmonary arteries, CTA has supplanted catheter angiography as the gold standard. The expanding role of CTA emphasizes the need for deep, broad-based understanding of physical principles. This review describes CT hardware and associated software for angiography. The fundamentals of CTA physics are complemented with several clinical examples.

Coronary computed tomographic angiography (CCTA) in community hospitals: "current and emerging role"

Coronary computed tomographic angiography (CCTA) is a rapidly evolving test for diagnosis of coronary artery disease. Although invasive coronary angiography is the gold standard for coronary artery disease (CAD), CCTA is an excellent noninvasive tool for evaluation of chest pain. There is ample evidence to support the cost-effective use of CCTA in the early triage process of patients presenting with chest pain in the emergency room. CCTA plays a critical role in the diagnosis of chest pain etiology as one of potentially fatal conditions, aortic dissection, pulmonary embolism, and myocardial infarction. This 'triple rule out' protocol is becoming an increasingly practicable and popular diagnostic tool in ERs across the country. In addition to a quick triage of chest pain patients, it may improve quality of care, decrease cost, and prevent medico-legal risk for missing potentially lethal conditions presenting as chest pain. CCTA is also helpful in the detection of subclinical and vulnerable coronary plaques. The major limitations for wide spread acceptance of this test include radiation exposure, motion artifacts, and its suboptimal imaging with increased body mass index.

[Cardiac SPECT/CT: correlation between atherosclerosis, significant coronary artery stenoses and myocardial perfusion parameters in patients with known coronary artery disease]

Invasive coronary angiography (ICA) and CT angiography (CTA) both enable significant coronary artery stenoses to be detected, but they are not suitable for assessing their hemodynamic relevance. This can be accomplished using myocardial perfusion scintigraphy (MPS) which, however, has limited specificity and spatial resolution. Regarding patients with known coronary artery disease (CAD) it is furthermore important to stratify patient's individual risk for severe cardiac events to guide therapy management.The results of our investigations in 158 patients with CAD indicate that global and regional calcium scores (CAC) do not correlate with the presence of myocardial perfusion defects and significant coronary artery stenoses, respectively. However, published literature has reported CAC as being an independent predictor of long-time survival.For clinical purposes it seems that non-invasive diagnostics with CTA, MPS and CAC screening can be useful even in patients with known CAD. CAC and global scar burden enable long-term risk-stratification, whereas fusion of CTA and MPS is useful to detect the culprit lesion of relevant perfusion defects and to select options for revascularization.

Nonlinear registration of serial coronary CT angiography (CCTA) for assessment of changes in atherosclerotic plaque

PURPOSE

Coronary CT angiography (CCTA) is a high-resolution three-dimensional imaging technique for the evaluation of coronary arteries in suspected or confirmed coronary artery disease (CAD). Coregistration of serial CCTA scans would allow precise superimposition of images obtained at two different points in time, which could aid in recognition of subtle changes and precise monitoring of coronary plaque progression or regression. To this end, the authors aimed at developing a fully automatic nonlinear volume coregistration for longitudinal CCTA scan pairs.

METHODS

The algorithm combines global displacement and local deformation using nonlinear volume coregistration with a volume-preserving constraint. Histogram matching of intensities between two serial scans is performed prior to nonlinear coregistration with dense nonparametric local deformation in which sum of squared differences is used as a similarity measure. The approximate segmentation of coronary arteries obtained from commercially available software provides initial anatomical landmarks for the coregistration algorithm that help localize and emphasize the structure of interest. To avoid possible bias caused by incorrect segmentation, the authors convolve the Gaussian kernel with the segmented binary coronary tree mask and define an extended weighted region of interest. A multiresolution approach is employed to represent coarse-to-fine details of both volumes and the energy function is optimized using a gradient descent method. The authors applied the algorithm in ten paired CCTA datasets (20 scans in total) obtained within 10.7 +/- 5.7 months from each other on a dual source CT scanner to monitor progression of CAD.

RESULTS

Serial CCTA coregistration was successful in 9/10 cases as visually confirmed. The global displacement and local deformation of target registration error obtained from four anatomical landmarks were 2.22 +/- 1.15 and 1.56 +/- 0.74 mm, respectively, and the inverse consistency error of local deformation was 0.14 +/- 0.06 mm. The observer variability between two expert observers was 1.31 +/- 0.91 mm.

CONCLUSIONS

The proposed coregistration algorithm demonstrates potential to accurately register serial CCTA scans, which may allow direct comparison of calcified and noncalcified atherosclerotic plaque changes between the two scans.

Geometric feature-based multimodal image registration of contrast-enhanced cardiac CT with gated myocardial perfusion SPECT

PURPOSE

Cardiac computed tomography (CT) and single photon emission computed tomography (SPECT) provide clinically complementary information in the diagnosis of coronary artery disease (CAD). Fused anatomical and physiological data acquired sequentially on separate scanners can be coregistered to accurately diagnose CAD in specific coronary vessels.

METHODS

A fully automated registration method is presented utilizing geometric features from a reliable segmentation of gated myocardial perfusion SPECT (MPS) volumes, where regions of myocardium and blood pools are extracted and used as an anatomical mask to de-emphasize the inhomogeneities of intensity distribution caused by perfusion defects and physiological variations. A multiresolution approach is employed to represent coarse-to-fine details of both volumes. The extracted voxels from each level are aligned using a similarity measure with a piecewise constant image model and minimized using a gradient descent method. The authors then perform limited nonlinear registration of gated MPS to adjust for phase differences by automatic cardiac phase matching between CT and MPS. For phase matching, they incorporate nonlinear registration using thin-plate-spline-based warping. Rigid registration has been compared with manual alignment (n=45) on 20 stress/rest MPS and coronary CTA data sets acquired from two different sites and five stress CT perfusion data sets. Phase matching was also compared to expert visual assessment.

RESULTS

As compared with manual alignment obtained from two expert observers, the mean and standard deviation of absolute registration errors of the proposed method for MPS were 4.3 +/- 3.5, 3.6 +/- 2.6, and 3.6 +/- 2.1 mm for translation and 2.1 +/- 3.2 degrees, 0.3 +/- 0.8 degree, and 0.7 +/- 1.2 degrees for rotation at site A and 3.8 +/- 2.7, 4.0 +/- 2.9, and 2.2 +/- 1.8mm for translation and 1.1 +/- 2.0 degrees, 1.6 +/- 3.1 degrees, and 1.9 +/- 3.8 degrees for rotation at site B. The results for CT perfusion were 3.0 +/- 2.9, 3.5 +/- 2.4, and 2.8 +/- 1.0 mm for translation and 3.0 +/- 2.4 degrees, 0.6 +/- 0.9 degree, and 1.2 +/- 1.3 degrees for rotation. The registration error shows that the proposed method achieves registration accuracy of less than 1 voxel (6.4 x 6.4 x 6.4 mm) misalignment. The proposed method was robust for different initializations in the range from -80 to 70, -80 to 70, and -50 to 50 mm in the x-, y-, and z-axes, respectively. Validation results of finding best matching phase showed that best matching phases were not different by more than two phases, as visually determined.

CONCLUSIONS

The authors have developed a fast and fully automated method for registration of contrast cardiac CT with gated MPS which includes nonlinear cardiac phase matching and is capable of registering these modalities with accuracy <10 mm in 87% of the cases.

Prospectively ECG-triggered high-pitch spiral acquisition for coronary CT angiography using dual source CT: technique and initial experience

OBJECTIVE

We evaluated radiation exposure and image quality of a new coronary CT angiography protocol, high-pitch spiral acquisition, using dual source CT (DSCT).

MATERIAL AND METHODS

Coronary CTAwas performed in 25 consecutive patients with a stable heart rate of 60 bpm or less after premedication, using 2 x 128 0.6-mm sections, 38.4-mm collimation width and 0.28-s rotation time. Tube settings were 100 kV/320 mAs and 120 kV/400 mAs for patients below and above 100-kg weight, respectively. Data acquisition was prospectively ECG-triggered at 60% of the R-R interval using a pitch of 3.2 (3.4 for the last 10 patients). Images were reconstructed with 75-ms temporal resolution, 0.6-mm slice thickness and 0.3-mm increment. Image quality was evaluated using a four-point scale (1 = excellent, 4 = unevaluable).

RESULTS

Mean range of data acquisition was 113 +/- 22 mm, mean duration was 268 +/- 23 ms. Of 363 coronary artery segments, 327 had an image quality score of 1, and only 2 segments were rated as "unevaluable". Mean dose-length product (DLP) was 71 +/- 23 mGy cm, mean effective dose was 1.0 +/- 0.3 mSv (range 0.78-2.1 mSv). For 21 patients with a body weight below 100 kg, mean DLP was 63 +/- 5 mGy cm (0.88 +/- 0.07 mSv; range 0.78-0.97 mSv).

CONCLUSION

Prospectively ECGtriggered high-pitch spiral CT acquisition provides high and stable image quality at very low radiation dose.

Comparison of dual source computed tomography versus intravascular ultrasound for evaluation of coronary arteries at least one year after cardiac transplantation

This study evaluated the ability of dual-source computed tomography (DSCT) to detect coronary allograft vasculopathy (CAV) in heart transplant recipients using intravascular ultrasound (IVUS) as the standard of reference. Thirty patients with heart transplants (81% men, mean age 40 years) underwent DSCT (330-ms gantry rotation, 2 x 64 x 0.6-mm collimation, 60- to 80-ml contrast agent, no additional beta blockers) before invasive coronary angiography including IVUS of 1 vessel. Detection of CAV by DSCT was qualitatively defined as the presence of any coronary plaque. Mean heart rate during dual-source computed tomographic scanning was 80 +/- 14 beats/min. Four hundred fifty-nine segments with a vessel caliber >or=1.5 mm according to quantitative coronary angiography were evaluated in 30 patients. Of these, 96% were considered to have excellent or good image quality. IVUS detected CAV in 17 of 30 patients (57%) and in 41 of 110 coronary segments (37%). Compared to IVUS, sensitivity, specificity, positive and negative predictive values for the detection of CAV by DSCT were 85%, 84%, 76%, and 91%, respectively. In conclusion, DSCT permits the investigation of transplant recipients concerning the presence of CAV with good image quality and high diagnostic accuracy.

Automated 3-dimensional quantification of noncalcified and calcified coronary plaque from coronary CT angiography

INTRODUCTION

We aimed to develop an automated algorithm (APQ) for accurate volumetric quantification of non-calcified (NCP) and calcified plaque (CP) from coronary CT angiography (CCTA).

METHODS

APQ determines scan-specific attenuation thresholds for lumen, NCP, CP and epicardial fat, and applies knowledge-based segmentation and modeling of coronary arteries, to define NCP and CP components in 3D. We tested APQ in 29 plaques for 24 consecutive scans, acquired with dual-source CT scanner. APQ results were compared to volumes obtained by manual slice-by-slice NCP/CP definition and by interactive adjustment of plaque thresholds (ITA) by 2 independent experts.

RESULTS

APQ analysis time was <2 sec per lesion. There was strong correlation between the 2 readers for manual quantification (r = 0.99, p < 0.0001 for NCP; r = 0.85, p < 0.0001 for CP). The mean HU determined by APQ was 419 +/- 78 for luminal contrast at mid-lesion, 227 +/- 40 for NCP upper threshold, and 511 +/- 80 for the CP lower threshold. APQ showed a significantly lower absolute difference (26.7 mm(3) vs. 42.1 mm(3), p = 0.01), lower bias than ITA (32.6 mm(3) vs 64.4 mm(3), p = 0.01) for NCP. There was strong correlation between APQ and readers (R = 0.94, p < 0.0001 for NCP volumes; R = 0.88, p < 0.0001, for CP volumes; R = 0.90, p < 0.0001 for NCP and CP composition).

CONCLUSIONS

We developed a fast automated algorithm for quantification of NCP and CP from CCTA, which is in close agreement with expert manual quantification.

High-pitch spiral acquisition: a new scan mode for coronary CT angiography

Coronary CT angiography allows high-quality imaging of the coronary arteries when state-of-the-art CT systems are used. However, radiation exposure has been a concern. We describe a new scan mode that uses a very high-pitch spiral acquisition, "Flash Spiral," which has been developed specifically for low-dose imaging with dual-source CT. The scan mode uses a pitch of 3.2 to acquire a spiral CT data set, while covering the entire volume of the heart in one cardiac cycle. Data acquisition is prospectively triggered by the electrocardiogram and starts in late systole to be completed within one cardiac cycle. Images are reconstructed with a temporal resolution that corresponds to one-quarter of the gantry rotation time. Throughout the data set, subsequent images are reconstructed at later time instants in the cardiac cycle. In a patient with a heart rate of 49 beats/min, the Flash Spiral scan mode was used with a first-generation dual-source CT system and allowed artifact-free visualization of the coronary arteries with a radiation exposure of 1.7 mSv for a 12-cm scan range at 120 kVp tube voltage.