Randomized comparison of 64-slice single- and dual-source computed tomography coronary angiography for the detection of coronary artery disease

Low-dose coronary-CT angiography using step and shoot at any heart rate: comparison of image quality at systole for high heart rate and diastole for low heart rate with a 128-slice dual-source machine

To compare image quality of coronary CT angiography in step-and-shoot mode at the diastolic phase at low heart rates (<70 bpm) and systolic phase at high heart rates (≥70 bpm). We prospectively included 96 consecutive patients then excluded 5 patients with arrhythmia. Coronary CT-angiography was performed using a dual-source 128-slice CT machine, at the diastolic phase in the 55 patients with heart rates <70 bpm (group D) and at the systolic phase in the 36 patients with heart rates ≥70 (group S). Image quality was scored on a 5 point-scale (1, not interpretable; 2, insufficient for diagnosis; 3, fair, sufficient for diagnosis; 4, good; 5, excellent). In addition, we compared the number of stair-step artifacts in the two groups. Mean image quality score was 4 (0.78) in group D and 4.1 (0.34) in group S (NS), with an unequal distribution (p = 0.01). Step artifacts were seen in 44 % of group D and 18 % of group S patients (p = 0.02). In 3 group D patients and no group S patients, the image score was <3 due to artifacts, requiring repeat CT-angiography. When performing dual-source 128-slice CT-angiography, step-and-shoot acquisition provides comparable mean image quality in systole, with less variability and fewer stair-step artifacts, compared to diastole. This method may be feasible at any heart rate in most patients in sinus rhythm, allowing low-dose prospective acquisition without beta-blocker premedication.

Value of coronary computed tomography as a prognostic tool

Coronary computed tomography angiography (CCTA) has become an important part of our armamentarium for noninvasive diagnosis of coronary artery disease (CAD). Emerging technologies have produced lower radiation dose, improved spatial and temporal resolution, as well as information about coronary physiology. Although the prognostic role of coronary artery calcium scoring is known, similar evidence for CCTA has only recently emerged. Initial, small studies in various patient populations have indicated that CCTA-identified CAD may have a prognostic value. These findings were confirmed in a recent analysis of the international, prospective Coronary CT Angiography Evaluation For Clinical Outcomes: An International Multicenter (CONFIRM) registry. An incremental increase in mortality was found with a worse severity of CAD on a per-patient, per-vessel, and per-segment basis. In addition, age-, sex-, and ethnicity-based differences in mortality were also found. Whether changing our management algorithms based on these findings will affect outcomes is unclear. Large prospective studies utilizing targeted management strategies for obstructive and nonobstructive CAD are required to incorporate these recent findings into our daily practice.

Patient radiation doses in cardiac computed tomography: comparison of published results with prospective and retrospective acquisition

Prospective ECG triggering has the potential of reducing radiation exposure while maintaining diagnostic accuracy of cardiac computed tomography (CT). The aim of this study is to review patient radiation doses associated with coronary artery calcium scoring (CACS) and CT coronary angiography (CTCA) and to compare results between prospective and retrospective acquisition schemes. Patient radiation doses from CACS and CTCA were extracted from 67 relevant studies. Mean effective dose for CACS and CTCA with prospective ECG triggering is significantly lower than retrospective acquisition, 0.9±0.4 vs. 3.1±1.4 mSv, p < 0.001, and 3.4±1.4 vs. 11.1±5.4 mSv, p < 0.001, respectively. In both cardiac CT examinations, application of dose modulation techniques result in significantly lower doses in retrospective schemes, however, even with dose modulation, retrospective acquisition is associated with significantly higher doses than prospective acquisition. The number of slices acquired per rotation and the number of X-ray sources of the CT scanner (single or dual source) do not have a significant effect on patient dose.

Dual-source computed tomography angiography for diagnosis and assessment of coronary artery disease: systematic review and meta-analysis

BACKGROUND

Development of an accurate test for noninvasive assessment of coronary arteries has been highly desirable.

OBJECTIVES

We performed a systematic review of diagnostic accuracy of the dual-source computed tomography (DSCT) in the diagnosis of coronary artery disease (CAD).

METHODS

Eight medical databases were searched for articles published from January 2005 through March 2011. Studies compared DSCT coronary angiography (DSCT-CA) and invasive coronary angiography, as the reference standard, in consecutive patients with suspected or known CAD, and relevant data were extracted by 2 independent reviewers. Summary diagnostic accuracies were calculated, and the effect of covariates on the diagnostic performance was evaluated by meta-regression.

RESULTS

Twenty-five studies were included. In per-patient analysis (n = 2303), pooled sensitivity was 99% [95% confidence interval (CI), 97%-99%] with specificity of 89% (95% CI, 84%-92%). The summary positive (+LR) and negative (-LR) likelihood ratios were 8.6 (95% CI, 6.4-11.6) and 0.02 (95% CI, 0.01-0.03), respectively. In per-segment analysis (n = 32,615), pooled sensitivity was 94% (95% CI, 92%-96%) with specificity of 97% (95% CI, 96%--98%). Summary +LR and -LR were 30.2 (95% CI, 22.1-43.5) and 0.06 (95% CI, 0.04-0.08), respectively.

CONCLUSIONS

DSCT-CA seems to be robust to elevate heart rates while maintaining a high level of diagnostic performance.

Infarct detection with a comprehensive cardiac CT protocol

BACKGROUND

Cardiac CT has the potential to offer comprehensive infarct detection by assessing regional wall motion abnormalities (RWMAs), rest perfusion defects (RPDs), and delayed contrast enhancement (DCE). However, the diagnostic accuracy of these techniques for the detection of myocardial infarction (MI) is unknown.

METHODS

Forty-eight patients with intermediate-to-high probability for coronary artery disease after single-photon emitting CT myocardial perfusion imaging were prospectively enrolled for a research comprehensive 64-detector row dual-source cardiac CT protocol that included cine images for RWMA, first-pass images for RPD, and delayed images for DCE. Blinded readers independently assessed each technique. Subsequently, a final combined analysis (cine + rest + DCE) was performed. The universal definition for MI by the 2007 American Heart Association task force was used as the "gold standard."

RESULTS

Twenty-four of 48 patients (50%) had infarct by the universal definition. The combined CT analysis was most accurate (90%) with the highest per-patient sensitivity (88%) and specificity (92%) versus individual assessments (RWMA, 79% and 88%; RPD, 67% and 92%; DCE, 79% and 88%). Similar findings were observed on a per-vessel basis analysis. A combination of DCE and cine showed a good accuracy (85%) and high sensitivity (92%).

CONCLUSIONS

Infarct detection with CT is feasible with overall good diagnostic accuracy compared with the universal definition. A combined evaluation that included all techniques (cine, RPD, and DCE) had the highest diagnostic accuracy. These findings may have implications when designing future clinical and research CT protocols for optimal infarct detection.

The role of multi-slice computed tomography in stable angina management: a current perspective

Contrast-enhanced CT coronary angiography (CTCA) has evolved as a reliable alternative imaging modality technique and may be the preferred initial diagnostic test in patients with stable angina with intermediate pre-test probability of CAD. However, because CTCA is moderately predictive for indicating the functional significance of a lesion, the combination of anatomic and functional imaging will become increasingly important. The technology will continue to improve with better spatial and temporal resolution at low radiation exposure, and CTCA may eventually replace invasive coronary angiography. The establishment of the precise role of CTCA in the diagnosis and management of patients with stable angina requires high-quality randomised study designs with clinical outcomes as a primary outcome.

Cardiac computed tomography--evidence, limitations and clinical application

Coronary CT angiography and coronary calcium scoring offer a new approach to the diagnosis of coronary artery disease (CAD). They hold significant promise in improving patient outcomes, through identification of atherosclerosis and improved risk assessment. Coronary calcium scoring has proven predictive value concerning the occurrence of future cardiovascular events and outperforms current risk evaluation methods such as the Framingham Risk Score. Coronary CT angiography allows visualisation of the coronary artery lumen, detection of stenoses as well as visualisation of both calcified and non-calcified plaque. The accuracy of coronary CT angiography to detect obstructive coronary artery disease has been established by numerous trials. In particular the negative predictive value of the test approaches 100% in low and intermediate risk groups. Outcomes data demonstrate significant prognostic ability of coronary CT angiography. Modern techniques allow substantial reduction of dose values and radiation exposure of coronary CT angiography has significantly fallen. Coronary CT angiography can be reliably performed with doses similar to the level of annual background radiation, and less than one-third of a Tc Sestamibi scan. Coronary CT angiography has been approved for Medicare reimbursement for specific indications when performed by accredited providers. High quality examinations, experience and careful patient selection and preparation are required to ensure optimal results of coronary CT angiography, and to guide clinical decisions.

Comparison of dual-source and electron-beam CT for the assessment of coronary artery calcium scoring

OBJECTIVE

Cardiac CT allows the detection and quantification of coronary artery calcification (CAC). Electron-beam CT (EBCT) has been widely replaced by high-end CT generations in the assessment of CAC. The aim of this study was to compare the CAC scores derived from an EBCT with those from a dual-source CT (DSCT).

METHODS

We retrospectively selected 92 patients (61 males; mean age, 60.7 ± 12 years) from our database, who underwent both EBCT and DSCT. CAC was assessed using the Agatston score by two independent readers (replicates: 1, 2; 3=mean of reading 1 and 2).

RESULTS

EBCT scores were on average slightly higher than DSCT scores (281 ± 569 vs 241 ± 502; p<0.05). In regression analysis R(2)-values vary from 0.956 (1) to 0.966 (3). We calculated a correction factor as EBCT=(DSCT+1)(1.026)-1. When stratifying into CAC categories (0, 1-99, 100-399, 400-999 and ≥1000), 79 (86%) were correctly classified. From those with positive CAC scores, 7 out of 61 cases (11%, κ=0.81) were classified in different categories. Using the corrected DSCT CAC score, linear regression analysis for the comparison to the EBCT results were r=0.971 (p<0.001), with a mean difference of 6.4 ± 147.8. Five subjects (5.4%) were still classified in different categories (κ=0.84).

CONCLUSION

CAC obtained from DSCT is highly correlated with the EBCT measures. Using the calculated correction factor, agreement only marginally improved the clinical interpretation of results. Overall, for clinical purposes, face value use of DSCT-derived values appears as useful as EBCT for CAC scoring.

Radiation dose and diagnostic accuracy of multidetector computed tomography for the detection of significant coronary artery stenoses: a meta-analysis

We conducted a meta-analysis evaluating the critical ratio between effective radiation dose (ED), feasibility (Fe) and diagnostic accuracy (Ac) of multidetector computed tomography (MDCT) for the detection of significant coronary artery disease. By using our predetermined criteria, we selected human studies published in English in which the ED and raw data of Ac vs. invasive coronary angiography in a segment based model were specified. Data from 31 studies including 3661 patients (mean age 61.9 ± 4.5 years, heart rate 62.5 ± 6.7 bpm) and 50,236 coronary artery segments were analysed and are reported. Overall, Fe, sensitivity, specificity, negative predictive value, positive predictive value, Ac and ED were 95%, 90%, 96%, 99%, 69%, 95% and 10.4 ± 5.4 mSv, respectively. Multivariate analysis showed that prospective ECG-gating (-8.8 mSv CI95% -13.4 to -4.3 mSv, p=0.001), dual-source (-3.7 mSv CI95% -7.9 to 0 mSv, p=0.05) and BMI-adapted scanning protocols (-4.5 mSv CI95% -8.7 to -2.7 mSv, p=0.03) were independent predictors of ED reduction. In patients with low heart rate, the best compromise between ED, Fe and Ac (2.5 mSv, 97% and 98%, respectively) was obtained combining prospective ECG-gating and BMI-adapted scanning protocols, while in patients with high heart rate the strategy associated with the best results (10 mSv, 98% and 97%, respectively) was the use of dual-source MDCT with retrospective ECG gating and modulation dose. In conclusion, careful selection of CT scanning protocols according to the patient's characteristics is critical for keeping the radiation exposure "as low as reasonably achievable" (ALARA) without impairing Fe and Ac.

Detection of coronary artery stenoses by low-dose, prospectively ECG-triggered, high-pitch spiral coronary CT angiography

OBJECTIVES

We sought to evaluate the diagnostic accuracy of a new prospectively electrocardiogram (ECG)-triggered high-pitch scan mode for coronary computed tomography angiography (CTA), which allows an effective dose of less than 1 mSv.

BACKGROUND

Coronary CTA provides increasingly reliable image quality, but the associated radiation exposure can be high.

METHODS

Seventy-five patients with suspected coronary artery disease and in sinus rhythm were screened for participation. After exclusion of 25 patients for body weight >100 kg or failure to lower heart rate to ≤ 60 beats/min, 50 patients were studied by prospectively ECG-triggered high-pitch spiral computed tomography (CT). Coronary CTA was performed using a dual-source CT system with 2 × 128 × 0.6-mm collimation, 0.28-s rotation time, a pitch of 3.4, 100-kVp tube voltage, and current of 320 mA. Data acquisition was prospectively triggered at 60% of the R-R interval and completed within 1 cardiac cycle. Diagnostic accuracy for detection of coronary artery stenoses ≥ 50% diameter stenosis was determined by comparison to invasive coronary angiography. Per-patient diagnostic performance was the primary form of analysis.

RESULTS

In all 50 patients (34 males, 59 ± 12 years of age), imaging was successful. For the detection of 16 patients with at least 1 coronary artery stenosis, CT demonstrated a sensitivity of 100% (95% confidence interval [CI]: 79% to 100%) and specificity of 82% (95% CI: 65% to 93%). The positive predictive value was 72% (95% CI: 49% to 89%) and the negative predictive value was 100% (95% CI: 87% to 100%). Sensitivity was 100% (95% CI: 88% to 100%) and specificity was 94% (95% CI: 89% to 97%) on a per-vessel basis. Per-segment sensitivity was 92% (95% CI: 80% to 97%), and specificity was 98% (95% CI: 96% to 98%). Mean dose-length product for coronary CTA was 54 ± 6 mGy · cm, the effective dose was 0.76 ± 0.08 mSv (0.64 to 0.95 mSv).

CONCLUSIONS

In nonobese patients with a low and stable heart rate, prospectively ECG-triggered high-pitch spiral coronary CTA provides high diagnostic accuracy for the detection of coronary artery stenoses.

CT angiography with cardiac MRI: non-invasive functional and anatomical assessment for the etiology in newly diagnosed heart failure

Exclusion of ischemia is important in patients with newly diagnosed systolic heart failure (HF). We prospectively compared standard-of-care invasive catheter angiography (iCA) and echocardiography to a novel non-invasive strategy of both Coronary Computed Tomographic Angiography (CCTA) and Cardiovascular MRI (CMR) to determine the etiology of myocardial dysfunction Prospective data were collected from consecutive patients referred for iCA to investigate echocardiographically-confirmed new onset HF. CMR (1.5T GE) and dual source CCTA were performed within 2-7 days of iCA. Results were blinded and separately analyzed by expert readers. 426 coronary segments from 28 prospectively enrolled patients were analyzed by CCTA and quantitative iCA. The per-patient sensitivity and specificity of CCTA was 100% and 90%, respectively, negative predictive value (NPV) 100%, positive predictive value (PPV) 78%. Mean ejection fraction by CMR was 24%. Presence of ischemic-type LGE on CMR conferred a 67% sensitivity, 100% specificity, 90% NPV and 100% PPV. Combining CCTA with CMR conferred 100% specificity, 100% sensitivity, 100% PPV and 100% NPV for detection or exclusion of coronary disease. In patients with negative CCTA all invasive angiograms could have been avoided. In addition, two patients with no ischemic LGE by CMR had severe coronary disease on both CCTA and iCA, indicating global hibernation. This is a noteworthy finding in contrast to previous reports which suggested that absence of LGE rules out significant CAD. CCTA with CMR in newly-diagnosed HF enables non-invasive assessment of coronary artery disease, the severity and etiology of myocardial dysfunction and defines suitability for revascularization. Absence of ischemic-type LGE at CMR does not exclude CAD as a cause of LV dysfunction. A first-line strategy of functional and anatomic imaging with CMR and CCTA appears appropriate in newly diagnosed HF.

A systematic review of the clinical effectiveness of 64-slice or higher computed tomography angiography as an alternative to invasive coronary angiography in the investigation of suspected coronary artery disease

Background

This systematic review summarized recent evidence pertaining to the clinical effectiveness of 64-slice or higher computed tomography angiography (CTA) in patients with suspected coronary artery disease (CAD). If CTA proves to be a successful diagnostic performance measure, it could prevent the use of invasive diagnostic procedures in some patients. This would provide multiple health and cost benefits, particularly for under resourced areas where invasive coronary angiography is not always available.

Methods

A systematic method of literature searching and selection was employed with searches limited to December 2006 to March 2009. Included studies were quality assessed using National Health and Medical Research Council (NHMRC) diagnostic levels of evidence and a modified Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool. Individual and pooled diagnostic performance measures were calculated using standard meta-analytic techniques at the patient, vessel and segment level. A positive result was defined as greater than or equal to 50% stenosis.

Results

Twenty-eight studies were included in the systematic review examining 3,674 patients. The primary meta-analysis at the patient-level indicated a sensitivity of 98.2% and specificity of 81.6%. The median (range) positive predictive value (PPV) was 90.5% (76%-100%) and negative predictive value (NPV) 99.0% (83%-100%). In all vessels, the pooled sensitivity was 94.9%, specificity 89.5%, and median (range) PPV 75.0% (53%-95%) and NPV 99.0% (93%-100%). At the individual artery level, overall diagnostic accuracy appeared to be slightly higher in the left main coronary artery and slightly lower in the left anterior descending and circumflex artery. In all segments, the sensitivity was 91.3%, specificity 94.0% and median (range) PPV 69.0% (44%-86%) and NPV 99.0% (98%-100%).

Conclusions

The high sensitivity indicates that CTA can effectively identify the majority of patients with significant coronary artery stenosis. The high NPV at the patient, vessel and segment level establishes CTA as an effective non-invasive alternative to invasive coronary angiography (ICA) for the exclusion of stenosis.

The diagnostic performance of multi-slice coronary computed tomographic angiography: a systematic review

BACKGROUND

The use of coronary computed tomographic angiography (CCTA) for evaluation of patients with suspected coronary artery disease (CAD) is growing rapidly, yet questions remain regarding its diagnostic accuracy and its impact on clinical decision-making and patient outcomes.

METHODS

A systematic literature review was conducted to identify studies examining (a) CCTA's diagnostic accuracy; and (b) the impact of CCTA on clinical decision-making and/or patient outcomes. Diagnostic accuracy estimates were limited to patient-based analyses of occlusion; outcome studies were eligible for inclusion if they involved patients at low-to-intermediate risk of CAD. Pooled accuracy estimates were derived using bivariate random effects models; non-diagnostic CCTA results were conservatively assumed to be false positives.

RESULTS

A total of 42 diagnostic accuracy studies and 11 patient outcome studies were identified. The pooled mean sensitivity for CCTA in primary analyses was 98% (95% CI: 96%, 99%); specificity was 85% (81%, 89%). A small number of outcome studies set primarily in the emergency department found triage of low-risk patients using CCTA produced no serious adverse outcomes and was time-saving relative to standard triage care. Outcome studies in the outpatient setting were limited to four case series that did not directly compare patient care or outcomes with those of contemporaneous patients evaluated without CCTA.

CONCLUSIONS

CCTA appears to have high diagnostic accuracy in patients with suspected CAD, but its potential impact on clinical decision-making and patient outcomes is less well-understood, particularly in non-emergent settings.

Safety, efficacy, and indications of beta-adrenergic receptor blockade to reduce heart rate prior to coronary CT angiography

For selected indications, coronary computed tomographic (CT) angiography is an established clinical technology for evaluation in patients suspected of having or known to have coronary artery disease. In coronary CT angiography, image quality is highly dependent on heart rate, with heart rate reduction to less than 60 beats per minute being important for both image quality and radiation dose reduction, especially when single-source CT scanners are used. β-Blockers are the first-line option for short-term reduction of heart rate prior to coronary CT angiography. In recent years, multiple β-blocker administration protocols with oral and/or intravenous application have been proposed. This review article provides an overview of the indications, efficacy, and safety of β-blockade protocols prior to coronary CT angiography with respect to different scanner techniques. Moreover, implications for radiation exposure and left ventricular function analysis are discussed.

Coming of age: coronary computed tomography angiography

Technical development has substantially improved diagnostic performance of coronary computed tomography angiography (CCTA). A large number of studies have addressed proof of concept, feasibility, and clinical robustness of this noninvasive diagnostic technique, and most have consistently described the ability of CCTA to reliably rule out significant coronary artery stenosis. Clinical evidence supports the significant role of CCTA in an increasing number of scenarios, including the detection of coronary disease in symptomatic patients who are at intermediate risk and evaluation of coronary revascularization procedures. After initial feasibility testing, the scientific evaluation of CCTA now points toward analyzing prognosis, outcome, and cost-effectiveness of this noninvasive diagnostic tool. In this article, appropriate clinical indications, diagnostic performance, current clinical applications, prognostic value, and cost-effectiveness of CCTA are reviewed.

Current techniques for MR imaging of atherosclerosis

Vessel wall imaging of large vessels has the potential to identify culprit atherosclerotic plaques that lead to cardiovascular events. Comprehensive assessment of atherosclerotic plaque size, composition, and biological activity is possible with magnetic resonance imaging (MRI). Magnetic resonance imaging of the atherosclerotic plaque has demonstrated high accuracy and measurement reproducibility for plaque size. The accuracy of in vivo multicontrast MRI for identification of plaque composition has been validated against histological findings. Magnetic resonance imaging markers of plaque biological activity such as neovasculature and inflammation have been demonstrated. In contrast to other plaque imaging modalities, MRI can be used to study multiple vascular beds noninvasively over time. In this review, we compare the status of in vivo plaque imaging by MRI to competing imaging modalities. Recent MR technological improvements allow fast, accurate, and reproducible plaque imaging. An overview of current MRI techniques required for carotid plaque imaging including hardware, specialized pulse sequences, and processing algorithms are presented. In addition, the application of these techniques to coronary, aortic, and peripheral vascular beds is reviewed.

Safety and efficacy of a drug regimen to control heart rate during 64-slice ECG-gated coronary CTA in children

BACKGROUND

The adult practice for ECG-gated single-source 64-slice coronary CTA (CCTA) includes administering beta-blockers to reduce heart rate. There are limited data on this process in children.

OBJECTIVE

To evaluate the safety and efficacy of a drug regimen to decrease heart rate before performing CCTA in children.

MATERIALS & METHODS

IV remifentanil and esmolol infusion were chosen to decrease heart rate in 41 children (mean age 6.5 years) while they were under general anesthesia (GA) for CCTA. Drug doses, changes in heart rate and procedural complications were recorded. CCTA image quality was graded on a scale of 1 to 5. The relationships between image quality and heart rate and image quality and age were evaluated. Patient effective radiation doses were calculated.

RESULTS

Heart rates were lowered utilizing esmolol (4 children), remifentanil (2 children) or both (35 children); 26 children received nitroglycerin for coronary vasodilation. The mean decrease in heart rate was 26%. There were no major complications. The average image-quality score was 4.4. Higher heart rates were associated with worse image quality (r = 0.67, P < 0.0001). Older age was associated with better image quality (r = 0.66, P < 0.0001). Effective radiation doses were 0.7 to 7.0 mSv.

CONCLUSION

Heart rate reduction for pediatric CCTA can be safely and effectively achieved while yielding high-quality images.

320-row CT coronary angiography: effect of 100-kV tube voltages on image quality, contrast volume, and radiation dose

To prospectively evaluate image quality parameters, contrast volume and radiation dose at the 100-kilovolt (kV) setting during coronary computed tomographic angiography (CCTA) on a 320-row computed tomography scanner. We enrolled 107 consecutive patients with a heart rate <65 beats per minute (bpm) undergoing prospective electrocardiogram (ECG)-triggered CCTA. Forty patients with a body mass index (BMI) <25 kg/m(2) were scanned using 100-kV tube voltage settings, while 67 patients were scanned using 120-kV protocols. Image quality was assessed by two readers unaware of patient information and scan parameters. Attenuation in the aorta and perivascular fat tissue and image noise were measured. Contrast-to-noise ratios (CNRs) and contrast material volumes were calculated. The effective radiation doses were estimated using a chest conversion coefficient (0.017). Diagnostic image quality was achieved in 98.2% of coronary segments with 100-kV CCTA and 98.6% of coronary segments with 120-kV CCTA, with no significant differences in image quality scores for each coronary segment. Vessel attenuation, image noise, and CNR were not significantly different between the 100- and 120-kV protocols. Mean contrast injection rate and mean material volume were significantly lower for the 100-kV CCTA (4.35 ± 0.28 ml/s and 53.13 ± 3.77 ml, respectively) than for the 120-kV CCTA (5.16 ± 0.21 ml/s and 62.40 ± 3.66 ml respectively; P < 0.001). The effective radiation dose was 2.12 ± 0.19 mSv for 100-kV CCTA, a reduction of 54% compared to 4.61 ± 0.82 mSv for 120-kV CCTA. A 100-kV CCTA can be implemented in patients with a BMI < 25 kg/m(2). The 100-kV setting allows significant reductions in contrast material volume and effective radiation dose while maintaining adequate diagnostic image quality.

Dual-energy computed tomography for integrative imaging of coronary artery disease: principles and clinical applications

The introduction of coronary CT angiography (cCTA) has reinvigorated the debate whether management of patients with suspected coronary artery disease (CAD) should be primarily based on physiological, functional versus anatomical testing. Anatomical testing (i.e., cCTA or invasive catheterization) enables direct visualization and grading of coronary artery stenoses but has shortcomings for gauging the hemodynamic significance of lesions for myocardial perfusion. Rest/stress myocardial perfusion imaging (MPI) has been extensively validated for assessing the clinical significance of CAD by demonstrating fixed or reversible perfusion defects but has only limited anatomical information. There is growing evidence that contrast medium enhanced dual-energy cCTA (DECT) has potential for the comprehensive analysis of coronary artery morphology as well as changes in myocardial perfusion. DECT exploits the fact that tissues in the human body and iodine-based contrast media have unique absorption characteristics when penetrated with different X-ray energy levels, which enables mapping the iodine (and thus blood) distribution within the myocardium. The purpose of this communication is to describe the practical application of this technology for the comprehensive diagnosis of ischemic heart disease. We examine recent scientific findings in the context of current pivotal transitions in cardiovascular disease management and demonstrate the potential of cardiac DECT for the integrative assessment of patients with known or suspected CAD within a single CT-based protocol.

Contraindications and side effects of commonly used medications in coronary CT angiography

For certain clinical applications, coronary CT angiography (CCTA) has become a useful tool for the noninvasive evaluation of coronary artery atherosclerosis. To optimize image quality in CCTA, medications are often given prior to scanning to slow the heart rate or distend the arteries. These medications have side effects and are contraindicated in certain patient populations. Metoprolol is the ß-blocker of choice in CCTA, and it has been shown to be effective in achieving the goal heart rate of less than 65 beats per minute for CCTA and in minimizing variability of heart rate. It is contraindicated in patients with hypotension or high degree AV block, and it must be used with caution in patients with asthma or obstructive pulmonary disease, patients with decompensated heart failure, and those with vasospastic or vasoocclusive disease. Diltiazem, the calcium channel blocker of choice in CCTA, is a reasonable alternative for heart control, particularly in patients with asthma or bronchospastic disease, and patients with orthotopic heart transplants that have been sympathetically denervated. Sublingual nitroglycerin is especially useful in order to dilate distal arteries to improve stenosis visibility. However, it is contraindicated in patients on erectile dysfunction medications and those with severe anemia. It must be used cautiously in patients with aortic stenosis or other preload-dependant cardiac pathologies.

Imaging of coronary atherosclerosis by computed tomography

Modern computed tomography (CT) systems afford sufficient spatial and temporal resolution for imaging of the heart and coronary arteries. The detection of coronary artery calcium (CAC) is relatively straightforward and it is applied to detect and quantify subclinical coronary atherosclerosis even in asymptomatic individuals. A large body of evidence has accumulated that uniformly attests to a high predictive value of CAC for future cardiac events. More complex data acquisition protocols, which require higher spatial and temporal resolution, specific patient preparation, and the intravenous injection of contrast agent, allow to perform coronary CT angiography (CTA). With CTA, the presence of luminal stenoses and, given sufficient image quality, calcified as well as non-calcified atherosclerotic plaque can be visualized. Initial studies have shown that certain plaque characteristics, such as positive remodelling or very low CT attenuation, are associated with plaque vulnerability. So far, the available clinical data are not sufficient to draw specific conclusions as to the risk-benefit ratio of contrast-enhanced coronary CTA for risk prediction, especially for asymptomatic individuals. Hence, CTA is currently not recommended for risk stratification purposes. However, the technology of coronary CTA continues to evolve at a rapid pace and clinical applications for plaque imaging and characterization may become possible in the future.

Evaluation of contraindications and efficacy of oral Beta blockade before computed tomographic coronary angiography

Multidetector computed tomographic coronary angiography (CTA) image quality is inversely related to the heart rate (HR). As a result beta-blocking medication is routinely administered before investigation. In the present study, the use, contraindications, and efficacy of prescan beta blockade with regard to HR reduction and CTA image quality were assessed. In 537 patients referred for CTA, the baseline HR and blood pressure were measured on arrival, and contraindications for beta blockade were noted. Unless contraindicated, a single dose of metoprolol was administered orally 1 hour before data acquisition in patients with a HR of > or =65 beats/min according to a predefined medication protocol. After 1 hour, the HR was remeasured. A total of 283 patients (53%) had a HR of > or =65 beats/min. In this group, beta blockade was contraindicated in 46 patients (16%). Metoprolol was administered to the remaining 237 patients. However, 26 patients (11%) received suboptimal (lower dose than prescribed by protocol) beta blockade because of contraindications. Of the 211 patients receiving optimal beta blockade, 57 (27%) did not achieve the target HR. Of the patients with contraindications to beta blockade, 43 (60%) did not achieve the target HR. Compared to patients with optimal HR control, those receiving no or suboptimal beta blockade because of contraindications had significantly fewer examinations of good image quality (40% vs 74%, p <0.001), and significantly more examinations of poor image quality (20% vs 6%, p <0.001). In conclusion, most patients require HR reduction before CTA. Contraindications to beta blockade are present in a substantial proportion of patients. This results in suboptimal HR control and image quality, indicating the need for alternative approaches for HR reduction.

Incremental value of adenosine-induced stress myocardial perfusion imaging with dual-source CT at cardiac CT angiography

PURPOSE

First, to assess the feasibility of a protocol involving stress-induced perfusion evaluated at computed tomography (CT) combined with cardiac CT angiography in a single examination and second, to assess the incremental value of perfusion imaging over cardiac CT angiography in a dual-source technique for the detection of obstructive coronary artery disease (CAD) in a high-risk population.

MATERIALS AND METHODS

Institutional review board approval and informed patient consent were obtained before patient enrollment in the study. The study was HIPAA compliant. Thirty-five patients at high risk for CAD were prospectively enrolled for evaluation of the feasibility of CT perfusion imaging. All patients underwent retrospectively electrocardiographically gated (helical) adenosine stress CT perfusion imaging followed by prospectively electrocardiographically gated (axial) rest myocardial CT perfusion imaging. Analysis was performed in three steps: (a)Coronary arterial stenoses were scored for severity and reader confidence at cardiac CT angiography, (b)myocardial perfusion defects were identified and scored for severity and reversibility at CT perfusion imaging, and (c)coronary stenosis severity was reclassified according to perfusion findings at combined cardiac CT angiography and CT perfusion imaging. The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of cardiac CT angiography before and after CT perfusion analysis were calculated.

RESULTS

With use of a reference standard of greater than 50% stenosis at invasive angiography, all parameters of diagnostic accuracy increased after CT perfusion analysis: Sensitivity increased from 83% to 91%; specificity, from 71% to 91%; PPV, from 66% to 86%; and NPV, from 87% to 93%. The area under the receiver operating characteristic curve increased significantly, from 0.77 to 0.90 (P < .005).

CONCLUSION

A combination protocol involving adenosine perfusion CT imaging and cardiac CT angiography in a dual-source technique is feasible, and CT perfusion adds incremental value to cardiac CT angiography in the detection of significant CAD.

Influence of slice thickness and reconstruction kernel on the computed tomographic attenuation of coronary atherosclerotic plaque

BACKGROUND

The computed tomographic (CT) attenuation of coronary atherosclerotic plaque has been proposed as a marker for tissue characterization and may thus potentially contribute to the assessment of plaque instability.

OBJECTIVE

We analyzed the influence of reconstruction parameters on CT attenuation measured within noncalcified coronary atherosclerotic lesions.

METHODS

Seventy-two patients were studied by contrast-enhanced dual-source CT coronary angiography (330 millisecond rotation time, 2 x 64 x 0.6 mm collimation, 120 kV, 400 mAs, 80 mL contrast agent intravenously at 6 mL/s), and a total of 100 distinct noncalcified coronary atherosclerotic plaques were identified. Image data sets were reconstructed with a soft (B20f), medium soft (B26f), and sharp (B46f) reconstruction kernel. With the medium soft kernel, image data sets were reconstructed with a slice thickness/increment of 0.6/0.3 mm, 0.75/0.4 mm, and 1.0/0.5mm. Within each plaque, CT attenuation was measured.

RESULTS

Mean CT attenuation using the medium soft kernel was 109 +/- 58 HU (range, -16 to 168 HU). Using the soft kernel, mean density was 113 +/- 57 HU (range, -13 to 169 HU), and using a sharp kernel, mean density was 97 +/- 49 HU (range, -23 to 131 HU). Similarly, reconstructed slice thickness had a significant influence on the measured CT attenuation (mean values for medium soft kernel: 102 +/- 52 HU versus 109 +/- 58 HU versus 113 +/- 57 HU for 0.6-mm, 0.75-mm, and 1.0-mm slice thickness). The differences between 0.75-mm and 0.6-mm slice thickness (P = 0.05) and between medium sharp and sharp kernels (P = 0.02) were statistically significant.

CONCLUSIONS

Image reconstruction significantly influences CT attenuation of noncalcified coronary atherosclerotic plaque. With decreasing spatial resolution (softer kernel or thicker slices), CT attenuation increases significantly. Using absolute CT attenuation values for plaque characterization may therefore be problematic.

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.

Identification of unexpected nonatherosclerotic cardiovascular disease with coronary CT angiography

OBJECTIVES

The aim of this study was to assess, in a general cardiology cohort screened for obstructive coronary artery disease (CAD), the effectiveness and frequency with which multidetector computed tomography (MDCT) angiography unexpectedly imaged and identified other nonatherosclerotic cardiovascular diseases.

BACKGROUND

MDCT angiography is a novel imaging strategy employed primarily to diagnose CAD that, in the course of these studies, can also potentially identify other important but previously unrecognized cardiovascular abnormalities.

METHODS

Consecutive 64-slice MDCT angiography studies were obtained in 4,543 patients with suspected atherosclerotic CAD at the Minneapolis Heart Institute, over a 29-month period (2005 to 2007).

RESULTS

Nonatherosclerotic-related cardiovascular abnormalities judged to be of potential clinical relevance were identified in 201 patients (4.4%). In 50 of these patients (1.1% of 4,543) the abnormality was previously unrecognized despite other imaging studies performed in 40%. Most common among the 50 patients were: congenital coronary artery anomalies (38%; largely right coronary artery from the left aortic sinus); ascending aortic aneurysms > or = 45 mm (22%); hypertrophic cardiomyopathy with apical left ventricular (LV) wall thickening (14%); valvular heart diseases (8%), congenital heart diseases, including ventricular septal defect (6%); pulmonary embolus (6%); as well as LV noncompaction, left atrial myxoma, and LV apical aneurysm (2% each). As a consequence of MDCT angiography findings, new management strategies were instituted in 15 of 50 patients (30%), including surgical correction of coronary artery anomalies of wrong sinus origin, ascending aneurysm graft repair, thrombolytic therapy for pulmonary embolism, and myxoma resection.

CONCLUSIONS

Approximately 1% of patients undergoing MDCT angiography for suspicion of CAD proved to have otherwise unsuspected, but clinically relevant, cardiovascular abnormalities unrelated to coronary atherosclerosis. Almost one-third of these patients had cardiovascular diseases with major clinical implications for subsequent therapy. These findings underscore the value of MDCT angiography and the importance of careful assessment of scans for the recognition of a variety of cardiovascular abnormalities.