Noninvasive evaluation of the prevalence of noncalcified atherosclerotic plaques by multi-slice detector computed tomography: results of a pilot study

What is the optimal cut-off point for low coronary artery calcium score assessed by computed tomography? Multi-Detector Computed Tomography ANIN Registry

AIM

This prospective study was conducted to evaluate the incidence and predictors of coronary artery disease (CAD) in relation to the low coronary artery calcium (CAC) score among patients with intermediate probability of CAD.

MATERIAL AND METHODS

A total of 1132 consecutive patients were included in the analysis (58.7 ±10.9 years, 46.7% males). Coronary computed tomography (CCT) angiography was performed in a multi-detector computed tomography scanner. Coronary artery calcium score was calculated by the Agatston method. Obstructive CAD was defined as the presence of coronary artery stenosis ≥ 50% on CCT angiography.

RESULTS

Coronary artery disease was diagnosed in nearly one-fourth of patients (n = 272, 24%). In the receiver operating characteristics (ROC) curve analysis a CAC score of 10 was used as an optimal cut-off point for discriminating obstructive CAD (sensitivity: 0.79, specificity: 0.75, p < 0.0001) whereas for a CAC score of 100 the sensitivity and specificity were 0.48 and 0.92, respectively. On multivariate analysis after adjustment for age, gender, hypertension, hyperlipidemia, creatinine levels, only in patients with CAC score ≤ 10 age (OR = 1.05, 95% CI: 1.02-1.08, p = 0.0005, OR = 1.05, 95% CI: 1.03-1.08, p < 0.0001) and male gender (OR = 3.45, 95% CI: 1.92-6.22, p < 0.0001), likewise in group with CAC score ≤ 100 age (OR = 1.05, 95% CI: 1.03-1.08, p < 0.0001) and male gender (OR = 3.31, 95% CI: 1.88-5.81, p < 0.0001) were independent predictors of obstructive CAD.

CONCLUSIONS

The cut-off point of 10 for CAC score determined patients with CAD with the best sensitivity and specificity. Therefore, a total CAC score < 10 should be classified as "low". In patients with a low CAC score obstructive high risk plaques prone to rupture are presented and are associated with increasing age and male gender.

Multidetector-row computed tomography for noninvasive coronary imaging

Computed tomography (CT) permits cross-sectional imaging of the heart. Temporal and spatial resolutions of the technique have been insufficient to cover the heart without motion artefacts until the recent advent of multidetector systems with more than 16 detector rows. The modality is now suited for noninvasive imaging of the coronary arteries, producing detailed morphologic images of the entire coronary tree with upto 0.4 mm of spatial resolution, within a single short breath-hold duration. CT imaging goes beyond the delineation of the coronary lumen as provided by selective invasive angiography; the plaque burden of the coronary artery wall can be visualized directly, utilizing soft-tissue contrast and a high sensitivity even for the small calcifications that are present in hard plaque formations. Therefore, CT combines elements of catheterization angiography for lumen imaging and of intravascular ultrasound imaging for coronary wall imaging. However current CT technology is not yet able to compete with the temporal or spatial resolution of catheterization angiography nor does it provide the detailed spatial or contrast resolution of intravascular ultrasound imaging. At present, its use is therefore restricted to complementing the invasive modalities in appropriate indications. Although CT entails significantly less risk than the invasive procedures, the risks of radiation dose exposure and contrast agent application are not negligible. In the foreseeable future, if the current rate of technological advancement continues, CT may replace the invasive modalities in routine care for diagnostic purposes.

Coronary artery disease detected by multislice computed tomography in patients after long-term cure of Cushing's syndrome

OBJECTIVE

Increased cardiovascular risk persists in Cushing's syndrome (CS), despite remission of hypercortisolism. The aim of this study was to evaluate the prevalence of coronary artery disease in patients after long-term cure of CS.

METHODS

Cardiac multidetector computed tomography was performed in 29 cured CS patients (5 men, 21 of pituitary origin, 50 ± 13 y, mean time of "cure" 11 ± 6 y), using 64-slice Toshiba Aquilion systems (Toshiba Medical Systems, Otawara, Japan). Noncontrast acquisitions were performed to detect coronary calcifications and, after injection of an iodinated contrast agent, for coronary angiography. Calcium was quantified by the Agatston score. Cured patients were compared with 48 gender-matched and age-matched healthy controls.

RESULTS

Cured CS patients had more hypertension and smoked less than controls (P < .05). The prevalence of coronary calcifications (31% vs 21%) and noncalcified plaques (20% vs 7.8%) tended to be higher in cured CS patients than controls. When only women were analyzed (24 CS and 34 controls), more abnormal multidetector computed tomography results were found (42% vs 18%; P < .05). When patients and controls in the youngest tertile (<45 y) were compared, cured CS patients had significantly more noncalcified plaques than controls (30% vs 0%, P = .01); this difference persisted when hypopituitary or dyslipidemic CS patients were excluded.

CONCLUSION

Despite long-term biochemical "cure" of CS, patients exhibit more coronary artery disease, especially in women and in those aged <45 years, in comparison to healthy matched controls.

Prevalence of non-calcified coronary plaque on 64-slice computed tomography in asymptomatic patients with zero and low coronary artery calcium

OBJECTIVES

To study the prevalence of noncalcified plaque in asymptomatic low-risk patients with no or mild coronary artery calcium (CAC).

METHODS

From 502 patients with coronary risk factors who underwent 64-slice computed tomography, 224 asymptomatic patients were identified with no CAC (n=117) or mild CAC (n=107; defined as patients with Agatston scores from 1 to 100).

RESULTS

Patients with no CAC were younger and had diabetes less often. Medications and laboratory data were not significantly different between the two groups. The prevalence of noncalcified plaque was 11.1% in patients with no CAC and 23.4% in the mild CAC group (P=0.0142). Multiple plaques were detected in 2.6% of the group with no CAC and 3.7% of the group with mild CAC (P=0.5934). Significant coronary artery stenosis was found in one patient in the group with no CAC (0.9%) and three patients in the group with mild CAC (2.8%, P=0.3506).

CONCLUSIONS

Significant percentages of noncalcified plaque were found in asymptomatic low-risk patients with no or mild coronary calcium.

Prevalence and clinical characteristics of symptomatic patients with obstructive coronary artery disease in the absence of coronary calcifications

RATIONALE AND OBJECTIVES

The quantification of coronary calcification has established itself as a valid risk marker to predict cardiovascular events. However, data derived from cardiac multi-detector row computed tomography could demonstrate that the exclusion of coronary calcification is not synonymous with the exclusion of coronary artery disease (CAD). The aims of this retrospective analysis were to determine the prevalence of significant CAD in a symptomatic cohort with indications for invasive angiography but without coronary calcification (Agatston score 0) as assessed by multislice computed tomography and to investigate whether there were any differences in terms of risk factors between patients with and without significant CAD.

MATERIALS AND METHODS

Five hundred multislice computed tomographic scans (in 371 men and 129 women) were included in the analysis. Agatston scores were determined on native scans. All patients underwent coronary angiography to detect or rule out obstructive CAD. Patients with negative calcium scoring were selected and divided into two subgroups: those without obstructive CAD and those with obstructive CAD (luminal stenoses > 50%). These subgroups were characterized in terms of clinical characteristics (age and sex) and cardiovascular risk factors (diabetes mellitus, hypertension, hyperlipoproteinemia, familial predisposition, smoking, and overweight).

RESULTS

Sixty-one of 500 patients (12.2%) had negative calcium scores (Agatston score 0). Sixteen of these patients (26.3%, or 3.2% of the total population) had obstructive CAD according to invasive angiography. Patients with obstructive CAD were significantly older (mean age, 64 ± 9 vs 55 ± 10 years; P = .003) and were more frequently diabetic (25% vs 4%, P = .0389) than patients without obstructive CAD. There were no significant differences with regard to the other risk factors.

CONCLUSIONS

In this high-risk population, the absence of coronary calcification was not sufficient to rule out CAD. Among patients without coronary calcification, the presence of significant CAD was associated with increased age and the presence of diabetes mellitus.

Influence of symptomatic status on the prevalence of obstructive coronary artery disease in patients with zero calcium score

BACKGROUND

CAC has been used to predict obstructive CAD on invasive coronary angiography. However, it is unknown how the prevalence of obstructive CAD in patients with zero CAC is influenced by the presence or absence of chest pain.

METHODS

210 consecutive patients referred for CAC and CorCTA were included in this analysis. Chest pain was defined based on the Diamond-Forrester classification.

RESULTS

134 patients (64%) were symptomatic and 76 (36%) were asymptomatic. Seventy patients had negative (33%); 140 had positive CAC (67%). In the symptomatic group with zero CAC, 8.2% (4/49) had an obstructive, non-calcified plaque; of these, 3 were <45 years. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of CAC in the symptomatic population for detection of obstructive CAD were 0.86 (0.66-0.95), 0.42 (0.33-0.52), 0.28 (0.19-0.39) and 0.92 (0.8-0.97), respectively (p=0.007). No asymptomatic subject with zero CAC had obstructive CAD. Sensitivity, specificity, PPV and NPV of CAC in the asymptomatic population for detection of obstructive CAD were 1.00 (0.66-1.00), 0.32 (0.21-0.45), 0.18 (0.10-0.31) and 1.00 (0.80-1.00), respectively (p=0.05). Optimal cut-points to predict obstructive CAD and AUC were significantly different in symptomatic versus asymptomatic subjects (91 and 0.78 vs. 296 and 0.89, respectively) (p=0.005). CAC performed much better in symptomatic patients >45 years compared to younger patients to exclude obstructive CAD (AUC: 0.83 vs. 0.5, p<0.001; NPV=0.98).

CONCLUSIONS

CAC is better in asymptomatic compared to symptomatic subjects, especially in patients <age 45, to exclude obstructive CAD. Symptoms and age should be considered when interpreting CAC.

Identification and quantification of coronary atherosclerotic plaques: a comparison of 64-MDCT and intravascular ultrasound

OBJECTIVE

The purpose of this study was to compare the accuracy of 64-MDCT with that of intravascular ultrasound (IVUS) for the identification and quantitative analysis of coronary atherosclerotic plaques.

MATERIALS AND METHODS

Twenty-six patients (17 men, nine women; mean age, 56 years) with suspected coronary atherosclerotic disease were studied using contrast-enhanced 64-MDCT and IVUS. The coronary arteries were divided into 10-mm segments and vascular cross-sectional area (CSA), luminal CSA, and plaque burden were measured in each segment. Plaque analysis software was used to automatically detect both plaques and vessel walls on CT images. Two investigators who were blinded to IVUS results independently determined the presence, classification, and quantitative measurement of atherosclerotic plaques on the CT images, which were then compared with the IVUS images.

RESULTS

Of 40 coronary arteries, 247 of 263 segments were imaged and analyzed by both contrast-enhanced 64-MDCT and IVUS. Sixteen segments were ruled out because of poor CT image quality. Compared with IVUS, 64-MDCT enabled correct detection in 86 of 89 (96.6%) segments containing noncalcified plaques, 25 of 27 (92.6%) segments containing calcified plaques, and 118 of 131 (90.1%) segments without atherosclerotic plaques. Sensitivity, specificity, positive predictive value, and negative predictive value for the detection of plaques by 64-MDCT were 97.4%, 90.1%, 89.7%, and 97.5%, respectively. Plaque analysis software using predetermined Hounsfield unit ranges for different components of plaque was able to distinguish between fibrous, fibrous-soft, and calcified plaques to a significant degree, but was less able to distinguish between soft and fibrous, and between soft and fibrous-soft plaque. Cohen's kappa coefficient for the sole detection of atherosclerotic segments by observers was 0.91. The correlation coefficients to determine vascular CSA, luminal CSA, and plaque burden were r = 0.85, 0.82, and 0.77, respectively (p < 0.01).

CONCLUSION

Compared with IVUS, contrast-enhanced 64-MDCT has a good ability to identify and quantify coronary atherosclerotic plaques. However, the reliable differentiation of the composition of noncalcified plaques is still limited.

Dual-source computed tomography: advances of improved temporal resolution in coronary plaque imaging

OBJECTIVES

The aim of this study was to quantify image quality gains of a moving coronary plaque phantom using dual-source computed tomography (DSCT) providing 83 milliseconds temporal resolution in direct comparison to 64 slice single-source multidetector CT (MDCT) with a temporal resolution of 165 milliseconds.

MATERIALS AND METHODS

Three cardiac vessel phantoms with fixed 50% stenosis and changing plaque configurations were mounted on a moving device simulating cardiac motion. Scans were performed at a simulated heart frequency of 60 to 120 bpm. Image quality assessment was performed in different anatomic orientations inside a thoracic phantom.

RESULTS

A significant improvement of image quality using the DSCT could be found (P=0.0002). Relevant factors influencing image quality aside from frequency (P=0.0002) are plaque composition (P<0.0001), as well as orientation (P<0.0001).

CONCLUSION

Scanning with 83 milliseconds temporal resolution improved image quality of coronary plaque at higher heart frequencies.

Acute coronary syndromes: an emphasis shift from treatment to prevention; and the enduring challenge of vulnerable plaque detection in the cardiac catheterization laboratory

Rupture of vulnerable plaques is the main cause of acute coronary syndromes and myocardial infarctions. Identification of these vulnerable plaques is therefore essential to enable the development of treatment modalities to stabilize them. Several intravascular technologies, investigating coronary areas that will be responsible for future events, are highlighted in this review. The ideal technique would provide morphological, mechanical and biochemical information. Although several imaging techniques are currently under development, none of them alone provides such an all-embracing assessment. Optical coherence tomography has the advantage of high resolution, thermography has the potential to measure metabolism, and Raman spectroscopy obtains information on chemical components. Intravascular coronary ultrasound (IVUS) and IVUS-palpography are easy to perform and assess morphology and mechanical instability. Shear stress is an important mechanical parameter deeply influencing vascular biology. Nevertheless, all these techniques are still under investigation and, at present, none of them can unequivocally and comprehensively identify a vulnerable plaque and, most importantly, predict its further development. From a clinical point of view, most techniques currently assess only one feature of the vulnerable plaque. Thus, a combination of several modalities will be important in the future to ensure a high sensitivity and specificity in detecting vulnerable plaques.

Influence of a Lipid-Lowering Therapy on Calcified and Noncalcified Coronary Plaques Monitored by Multislice Detector Computed Tomography

PURPOSE

Multislice detector computed tomography (MSCT) is an accurate noninvasive modality to detect and classify different stages of atherosclerosis. The aim of the New Age II Study was to detect coronary lesions in men without established coronary artery disease (CAD) but with a distinct cardiovascular risk profile. We also sought to assess the effect after 1 year of a lipid-lowering therapy (LLT) using 20 mg of atorvastatin.

METHODS

Forty-sixe male patients (mean, 61 +/- 10 years) with an elevated risk for CAD (PROCAM score >3 quintile) without LLT were included. Native and contrast-enhanced scans were performed in all patients. A total of 27 of 46 patients received a follow-up scan (after 488 +/- 138 days). Coronary plaque burden (CPB) was assessed volumetrically.

RESULTS

The prevalence of CAD was 83% (38/46 patients), and 11% (5/46) without coronary calcifications still had noncalcified plaques. Total cholesterol and low-density lipoprotein cholesterol levels decreased significantly under LLT (225 +/- 41 mg/dL vs. 162 +/- 37 mg/dL, P < 0.0001 and 148 +/- 7 mg/dL vs. 88 +/- 5 mg/dL, P < 0.001, respectively). On follow-up, calcium score and CPB remained unchanged (Agatston score: 261 +/- 301 vs. 282 +/- 360; CPB: 0.149 +/- 0.108 vs. 0.128 +/- 0.075 mL, P > 0.05), whereas mean plaque volume of noncalcified plaques decreased significantly from 0.042 +/- 0.029 mL versus 0.030 +/- 0.014 mL (P < 0.05, mean reduction 0.012 +/- 0.017 mL or 24 +/- 13%).

CONCLUSIONS

Statin therapy led to a significant reduction of noncalcified plaque burden that was not reflected in calcium scoring or total plaque burden. This finding might explain the risk reduction after the initiation of statin therapy. Using multislice detector computed tomography, physicians have the potential to monitor medical treatment in patients with coronary atherosclerosis.

Diagnostic accuracy of multislice computed tomography for the detection of coronary artery disease in diabetic patients

BACKGROUND

Diabetes mellitus is an important risk factor for coronary artery disease. Cardiac multislice computed tomography (MSCT) permits visualization of the coronary arteries with good sensitivity and specificity. However, at present, there are no data whether MSCT allows an accurate assessment of coronary arteries of diabetic patients, in comparison to nondiabetic patients. Thus, we compared the catheter-controlled MSCT results from diabetic and nondiabetic patients in a cohort of 116 patients with regard to sensitivity, specificity, positive predictive value, and negative predictive value, as well as image quality.

METHODS AND MATERIALS

Twenty-two diabetic patients (age, 64.6+/-8.5 years; number of risk factors, 3.4+/-1.1) and 94 nondiabetic patients (age, 64.2+/-9.2 years; number of risk factors, 2.4+/-1.0) were examined by MSCT (Sensation 16 Speed 4 D, Siemens, Forchheim, Germany; gantry rotation time, 375 ms) and invasive coronary angiography. MSCT results were compared, blinded to the results of the coronary angiography with regard to the presence or absence of a significant stenosis (>50%) in a modified American Heart Association 13-segment model. Image quality was assessed on a qualitative scale between 1 (very good) and 5 (invisible) for each segment.

RESULTS

Sensitivity, specificity, positive predictive value, and negative predictive value were statistically not different in diabetic and nondiabetic patients (0.85/0.98/0.92/0.96 vs. 0.84/0.97/0.91/0.95). One diabetic and three nondiabetic patients had to be excluded from analysis. Diabetic patients had relevantly more risk factors (P < .05), but calcium scoring was not different in both groups (Agatston score 1090+/-1278 vs. 798+/-1033). The image quality in both cohorts was comparable.

CONCLUSIONS

MSCT allows the assessment of the coronary arteries noninvasively in diabetic patients with a good sensitivity and specificity, and diabetes does not have an impact on the number of evaluable segments. Thus, MSCT is a noninvasive tool in the care of these patients.

New acquisition method to exclusively enhance the left side of the heart by a small amount of contrast material achieved by multislice computed tomography with 64 data acquisition system

PURPOSE

To exclusively enhance the left side of the heart by a small amount of contrast material (CM) using rapid acquisition of multislice computed tomography (MSCT) with a 64-data acquisition system (DAS).

MATERIALS AND METHODS

Forty consecutive subjects underwent MSCT (Light Speed VCT, GE) with 0.625mm slice thickness to evaluate coronary arteries. We first measured transit time, using 8ml of CM followed by 20ml saline. Dependent upon transit time, total volume of CM was determined, ranging from 45 to 63ml. After injection of CM at a rate of 4ml/s, followed by 47ml saline at 3.5ml/s, ECG-gated MSCT scanning was performed. The mean and standard deviation (S.D.) of CT values of the right atrium (RA), right ventricle (RV), left atrium (LA), left ventricle (LV), ascending aorta (Ao) and each coronary artery were measured.

RESULTS

The mean of the CT values of the RA, RV, LA, LV, Ao, right coronary artery, left main, left anterior descending branch, and left circumflex branch were 225+/-76, 251+/-72, 353+/-55, 355+/-51, 352+/-34, 312+/-65, 296+/-57, 285+/-55, and 267+/-60HU, respectively. The corresponding S.D.s of the CT values were 39+/-22, 37+/-16, 32+/-7, 31+/-8HU, 25+/-5, 36+/-15, 31+/-13, 36+/-23, and 40+/-18HU, respectively. The mean of CT values of the RA and RV were significantly lower than those of the LA, LV, Ao, and each coronary artery (P<0.01), with excellent S.D.s. We could easily obtain three-dimensional coronary arterial and LV images without artifact of the RA and RV.

CONCLUSIONS

Using 64-DAS MSCT, we successfully obtained exclusive enhancement of the left side of the heart using a small amount of CM.

Influence of heart rate on the detectability and reproducibility of multislice computed tomography for measuring coronary calcium score using a pulsating calcified mock-vessel in comparison with electron beam tomography

BACKGROUND

The influence of heart rate on detectability and reproducibility of multislice computed tomography (MSCT) for measuring coronary calcium score was evaluated using pulsating calcified mock-vessels and compared with electron beam tomography (EBT).

MATERIALS AND METHODS

Four calcified mock-vessels with 200-350 HU were made to pulsate at a rate of 40-80 beat/min. Retrospective ECG-gating MSCT (Light Speed Ultra 16) scanning with 0.625 mm slice-thickness was performed twice at each pulsation rate. For comparison, EBT (Imatron C150 XP) was performed with 3 and 1.5 mm beam collimation with prospective ECG-gating and calcium scores were measured.

RESULTS

The comparison revealed that MSCT did not have better reproducibility than EBT, but the calcium scores with MSCT were less influenced by pulsation rates than those with EBT. Especially in mild calcification, the calcium scores decreased with EBT with 3 mm beam collimation with increasing pulsation rate, but the scores were stable in any rate with MSCT.

CONCLUSION

MSCT effectively detects coronary calcification, especially mild calcification, without being influenced by heart rate. This is accomplished by reducing the partial volume effect in the through plane using sub millimeter slice thickness, and using appropriate reconstruction methods, which improve temporal resolution.

Synergy of MDCT and Cine MRI for the Evaluation of Cardiac Motility

OBJECTIVE

The objective of our study was to validate the feasibility of the synergistic use of cardiac MR and CT data sets for ventricular motility analysis and to correlate measurement variability with underlying heart rate.

SUBJECTS AND METHODS

Twenty patients underwent concurrent ECG-gated MDCT and MRI for evaluation of ventricular motility, expressed as ventricular wall thickening and motion. Initially, individual measurement repetition series were analyzed by determining intraobserver variability and detecting intraobserver bias related to heart rates. Subsequently, absolute measurement differences of CT or MR data were statistically evaluated. Finally, absolute measurement differences were correlated with underlying heart rates by curve estimation regression.

RESULTS

Analysis of measurement reproducibility proved that data variability was dependent on only the anatomic localization of the analyzed ventricular segment, not on the imaging technique used or underlying heart rate, in normofrequent patients. Comparing MR and CT image data sets, no statistically significant differences were identified when ventricular motility was evaluated based on data sets of either imaging technique in normofrequent patients. Tachycardic frequencies, above 100 beats per minute, led to exponential error propagation due to insufficient temporal resolution of the current CT technology.

CONCLUSION

This study proved that cardiac motility assessment based on ECG-gated CT and MR data sets resulted in comparable ventricular function results for normofrequent patients; however, the high spatial resolution of cardiac MDCT cannot compensate for the lack of temporal resolution in patients with tachycardia, thus emphasizing the necessity of reporting ventricular motility analysis results in combination with heart rate to allow consideration of this possible cause for measurement variation.

Noninvasive assessment of coronary stents in patients by 16-slice computed tomography

BACKGROUND

The usefulness of thin-slice multi-detector computed tomography (MDCT) has been highly expected to assess the lumens of coronary artery stents. We evaluated the usefulness of 16-slice MDCT to assess the in-stent lumen after coronary artery stenting.

METHODS

In 42 consecutive patients after coronary artery stenting, retrospective ECG-gated CT-angiography using 16-slice MDCT (0.5-s rotation time, 16x0.625-mm detector collimation) was performed. The qualitative assessability of the lumens of 61 coronary stents (14 different types) by MDCT and the reasons for non-assessability were investigated. Furthermore, the evaluation of in-stent restenosis in 21 assessable stents of 16 patients, including quantitative density analysis by MDCT, was performed and the results were compared with those of conventional coronary angiography (CAG).

RESULTS

Of 61 stents, 42 (68.9%) were assessable. The assessability of diameter > or =3.5-mm stents made of stainless steel or cobalt was high (88.6%, 31/35), that of 3.0-mm stents was low (57.9%, 11/19) and all 2.5-mm stents were non-assessable due to partial volume effects and metal artifacts of stents. The lumens of stents made of tantalum were totally obscured and the metal artifacts of Bestent2 (gold markers) and S670 were severer than others. All non-assessable stents due to banding artifact and calcification were implanted in segment #1-3 and #6, respectively. In comparison to CAG, MDCT correctly detected the 5 in-stent restenoses and identified absence of restenoses was influenced strongly by the stent strut.

CONCLUSION

Despite some limitations, 16-slice MSCT is sufficiently useful for assessment of various coronary stents in patients and can detect in-stent restenoses of assessable stents with high accuracy in comparison to CAG.

Computed Tomographic Angiography of the Coronary Arteries: Techniques and Applications

Computed tomographic coronary angiography (CT-CA) is a direct but minimally invasive method of visualizing coronary arteries. Multidetector-row computed tomography (MDCT) is currently the CT modality most commonly used for coronary artery imaging. MDCT has been successfully used to detect stenoses in coronary arteries and coronary artery bypass grafts and to assess congenital coronary anomalies. Patients should not undergo CT-CA with MDCT if they have an irregular heart rhythm, a heart rate greater than 70 beats/min, and contraindications to pharmacologic agents for heart rate control, or if they have severe coronary artery disease or are likely to require revascularization.

Noninvasive detection of coronary artery disease -- challenges for prevention of disease and clinical events

Atherosclerosis is a chronic inflammatory disease that affects essentially all arterial beds including the aorta, coronaries, carotids, and peripheral arteries. It is the main cause of death in the western hemisphere, due to cardiovascular syndromes such as myocardial infarction, heart failure, and cerebrovascular accidents. Very substantial economic and human resources have been used on treatments of its complications, including imaging studies, coronary bypass surgery, catheter interventions, pacemakers, and medical treatments. Treating complications, however, are remedial actions. A better alternative is to prevent the development of atherosclerosis, or at least to identify patients who are at risk of acute events and intervene before they occur. The aims of this review are to discuss the predictive value of traditional and emerging risk factors, as well as the role of noninvasive diagnostic methods for coronary atherosclerosis, including exercise stress test, echo stress test, duplex ultrasound, computed tomography, and magnetic resonance. A combination of serum biomarkers and noninvasive approaches is of practical utility for identifying early disease. It is to be expected that future developments will soon perfect our ability to identify the vulnerable patient and allow a more individualized approach.

Atherothrombosis and High-Risk Plaque

This second part of the review on atherothrombosis highlights the diffuse nature of the disease analyzing the feasibility and potential of the noninvasive imaging modalities, including computed tomography (electron-beam computed and multi-detector computed tomography) and magnetic resonance imaging for its detection and monitoring. These imaging modalities are being established as promising tools in high-risk cardiovascular patients for identification and/or management of coronary calcification, stenotic or obstructive disease, high-risk plaques (not necessarily stenotic), and overall burden of the disease. In addition, such technology facilitates the understanding of the processes involved in the development and progression of atherothrombosis responsible for coronary, cerebral, and peripheral ischemic events.

Quantification of Calcification in Atherosclerotic Lesions

Calcification can be deposited throughout the vasculature in several forms of calcium phosphate, including calcium hydroxyapatite (CHA). Calcium accumulation in arteries by mineralization and calcium loss from bone by osteoporosis often coexist, and vascular calcification may share common mechanisms with bone remodeling. Deposition of calcification in valves and arteries diminishes the valvular or arterial wall elasticity, a major cause of aneurysm and stenosis. Obstruction of arteries by calcification and other components can lead to heart attack and stroke. Mineralization in the femoral arteries can cause intermittent claudication in the legs, causing decreased mobility. Accurate measurement of calcification is essential for identifying other factors associated with this process and ultimately for elucidating the mechanism(s) of calcification. A wide range of methods for visualizing and measuring calcification for diagnosis and treatment in vivo and for studying the calcification process ex vivo are available. This review provides a critical comparison of older established methods and newer evolving technologies for quantifying calcification.

Multislice spiral computed tomographic angiography of coronary arteries in patients with suspected coronary artery disease: an effective filter before catheter angiography?

BACKGROUND

Despite impressive image quality, it is unclear if noninvasive coronary angiography with multislice spiral computed tomography (CT) is powerful enough to act as a filter before invasive angiography (INV-A) in symptomatic patients.

METHODS AND RESULTS

We therefore studied 133 consecutive symptomatic patients with suspected coronary artery disease (CAD) and an indication for INV-A (chest pain and signs of ischemia in conventional stress tests). Patients with known CAD, acute coronary syndrome, or a calcium volume score >1000 were excluded. In all patients, both INV-A and multislice CT angiography (MSCT-A) (Philips MX 8000 multislice spiral CT, scan time 250 milliseconds, slice thickness 1.3 mm, 120 mL of contrast agent, 4 mL/s, retrospective gating) were directly compared by 2 independent investigators using the American Heart Association 15-segment model. Altogether, we studied 1596 segments, 74% had diagnostic image quality. Multislice CT angiography correctly identified 68 significant stenoses of the 75 stenoses seen with INV-A (sensitivity 91%). In 945 of 1185 diagnostic segments, stenosis could correctly be ruled out with MSCT-A. There were 3 times more stenoses seen with MSCT-A compared with INV-A (positive predictive value 29%) mainly because of misclassification of nonobstructive plaques as stenosis. The per-patient analysis allowed to exclude significant CAD in 42 (32%) of 133 patients. In only 6 of 53 patients, MSCT-A failed to detect significant stenosis, 4 of those were in small segments not requiring intervention. Calcium scoring alone was less suited as a filter before angiography: 25 patients (18% of study group) had a calcium score = 0, and 8 of these patients turned out to have significant stenoses.

CONCLUSION

Multislice CT angiography, but not calcium scoring alone, offers promise to reduce the number of INV-A in symptomatic patients with suspected CAD by up to one third with minimal risk for the patient.

Visualising noncalcified coronary plaques by CT

Due to a rapid improvement of the new generation submillimetre multislice CT-technology noninvasive tomographic imaging of the coronary vessel wall has become reality. First clinical studies have shown the ability in particular of 16-slice CT to determine plaque burden, plaque composition and compensatory vessel-wall remodelling. These novel findings already constitute an important step forward to assess coronary atherosclerosis noninvasively in a detailed manner which opens promising new opportunities for a better understanding and riskstratification of coronary atherosclerosis. Current limitations, mainly the insufficient accuracy to detect small lesions in distal coronary segments, might be overcome by improved spatial and temporal resolution of the new generation scanners operating with 64 and more detectors.

Non-invasive evaluation of atherosclerosis with contrast enhanced 16 slice spiral computed tomography: results of ex vivo investigations

OBJECTIVE

To evaluate the diagnostic accuracy of 16 slice computed tomography (CT) in determining plaque morphology and composition in an experimental setting. The results were compared with histopathological analysis as the reference standard.

METHODS

Nine human popliteal arteries derived from amputations because of atherosclerotic disease were investigated with multislice spiral CT (MSCT). Atherosclerotic lesions were morphologically classified (completely or partially occlusive, concentric, eccentric), and tissue densities were determined within these plaques. In addition, vessel dimensions were quantitatively measured.

RESULTS

The results were compared with histological analysis. The concordance index kappa for morphological classification was 0.88. Plaque density (n = 51 lesions) was significantly different (p < 0.0001) between lipid rich, fibrotic, and calcified lesions (Stary stage III: n = 2, 58 (8) Hounsfield units (HU); Stary V: n = 11, 50 (21) HU; Stary VI: n = 14, 96 (42) HU; Stary VII: n = 6, 858 (263) HU; Stary VIII: n = 18, 126 (99) HU). The concordance index kappa for the classification of plaques based on density was 0.51. Vessel dimensions had a good correlation (r = 0.98).

CONCLUSIONS

16 slice CT was found to be a reliable non-invasive imaging technique for assessing atherosclerotic plaque morphology and composition. Although calcified lesions can be differentiated from non-calcified lesions, the diagnostic accuracy in further subclassifying non-calcified plaques as lipid rich and fibrotic is low, even under experimental conditions.

Magnetic resonance imaging and computed tomography in assessment of atherosclerotic plaque

The two most promising noninvasive imaging modalities for the study of atherosclerosis are magnetic resonance imaging (MRI) and computed tomography (CT). Both have been shown to be capable of imaging vessel wall structures and differentiating various stages of atherosclerotic wall changes. MRI has been applied in various in vivo human studies to image atherosclerotic plaques in coronary arteries, carotid arteries, and aorta. The latest generation of multidetector row computed tomography (MDCT) systems allows for the noninvasive characterization of different plaque components in various vascular structures. MDCT allows evaluation of the whole arterial vasculature. In addition, MDCT has the ability to visualize the vessel wall and to give a quantitative measurement of calcified and noncalcified plaque. Using either technique, the repeatable, noninvasive study of atherosclerotic disease during its natural history and after therapeutic intervention will enhance our understanding of disease progression and regression. MDCT and MRI, therefore, may help in selecting appropriate treatments.

MDCT: cardiology indications

In the past 2 years mechanical multidetector-row CT (MDCT) systems with simultaneous acquisition of four slices and half-second scanner rotation have become widely available. Data acquisition with these scanners allows for considerably faster coverage of the heart volume compared with single-slice scanning. This increased scan speed can be used for retrospective gating together with 1-mm collimated slice widths and allows coverage of the entire cardiac volume in one breath hold. Initial results from studies in correlation with intracoronary ultrasound suggest that MDTC technology not only offers the possibility to visualize intracoronary stenoses non-invasively but also to differentiate plaque morphology. This is especially the case with the next generation of 16-row multidetector CT. An increased number of simultaneously acquired slices and sub-millimeter collimation for cardiac applications allows true isotropic scanning with high temporal resolution. Contrast-enhanced MDTC is a promising non-invasive technique for the detection, visualization, and characterization of stenotic artery disease. It could act as a gate keeper prior to cardiac catherization and finally replace conventional diagnostic modalities.

Imaging of coronary atherosclerosis using computed tomography: Current status and future directions

Computed tomography (CT) imaging of the coronary arteries, using either electron beam tomography (EBT) or multidetector row CT (MDCT), offers two possibilities to assess coronary atherosclerosis. Without injection of contrast agent, coronary calcifications can be detected and quantified. Their presence and extent correlates to the presence and amount of coronary atherosclerotic plaque. Prospective studies have demonstrated a high predictive value concerning the occurrence of coronary artery disease events and overall mortality. An emerging consensus seems to indicate that calcium imaging may be clinically useful in patients at intermediate risk for coronary artery disease events as determined based on traditional risk factors. In addition, recent studies have shown that after injection of contrast agent and using high-resolution scan protocols, the visualization of noncalcified plaque is also possible with CT techniques. However, data on the accuracy of plaque detection, quantification of plaque volume, and characterization of plaque (eg, lipid-rich vs fibrous) is currently limited, and the prognostic significance of noncalcifed coronary atherosclerotic plaque detection is unclear.