[Detection of coronary calcifications by electron beam tomography and multislice spiral CT: clinical relevance]

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.

Vascular preventive measures: the progression from asymptomatic to symptomatic atherosclerosis management. Evidence on usefulness of early diagnosis in women and children

This review reports our experience in evaluating the progression from asymptomatic to symptomatic atherosclerosis in an evidence-based context. In particular, studies published in the last 5 years were analyzed in more detail and their relevance to cardiovascular prevention in women and children is discussed. The evaluation of carotid artery intima-media thickness by ultrasonography and the measurement of coronary artery calcification using computed tomography scanning can provide evidence for the presence and extent of atherosclerosis in adults. Intima-media thickness was demonstrated to predict prognosis and help in clinical decision making. Computed tomography estimates of advanced coronary atherosclerosis are markers of advanced atherosclerosis and are of value for screening adult men, but their value in women and children is doubtful owing to radiation risk. Intima-media thickness measurement, even when acknowledging its limitations, is a preferred approach, with the promising perspective of the availability of portable devices of lower cost in the near future. Further evaluation of the potential role for the emerging biomarkers and imaging techniques could clarify the clinical relevance of emerging risk profiles such as the metabolic syndrome. Ultrasound methods provide information regarding the extent and progression of early atherosclerotic abnormalities in women and in children and predict cardiovascular prognosis.

Radiation dose exposure in multislice computed tomography of the coronaries in comparison with conventional coronary angiography

BACKGROUND

Radiation dose exposure is increased in multislice spiral computed tomography (MSCT) compared to conventional coronary angiography (CXA).

METHODS

Retrospective data analysis of 56 patients (66+/-8 years, 49 males, body surface area 1.98+/-0.18 m(2), heart rate 64+/-11 bpm) who underwent MSCT and CXA was performed (MSCT: 16-slice scanner, rotation time 0.375 s, 120 kV, ECG-pulsing; CXA: current technique system build in 2003). Ten patients with bypass grafts underwent bypass angiography in CXA and MSCT. To compare the radiation doses of both investigations, the effective dose (ED) was chosen as the analysis variable.

RESULTS

The mean ED for MSCT was 9.76+/-1.84 mSv (n=46) for patients without bypass grafts; with calcium scoring the mean ED was 12.46+/-2.23 mSv (n=46). In comparison, the mean ED of CXA was 2.60+/-1.27 mSv (n=46) for patients without bypass grafts; with bypass grafts (n=10) the mean ED for MSCT was 12.95+/-1.75 mSv, for CXA of 6.27+/-4.04 mSv, respectively. In MSCT heart rates of <or=60 bpm resulted in lower mean ED than heart rates of >60 bpm (8.86+/-1.24 mSv versus 10.53+/-1.86 mSv).

CONCLUSIONS

MSCT is still associated with a higher radiation dose exposure than CXA. The radiation dose relation is more favorable for MSCT than for CXA in patients with bypass grafts in comparison to patients without bypass grafts. This study emphasizes the importance of dose reduction techniques.

Cardiovascular risk factors and signs of subclinical atherosclerosis in the Heinz Nixdorf Recall Study

INTRODUCTION

Modern investigation modalities allow markers of atherosclerosis to be detected at a subclinical stage. The aim of the study was to analyze the prevalence of these markers in relation to traditional risk factors.

METHODS

The population based study included 4814 participants, aged 45 to 75 years, with a response rate of 55.8% of those contacted. The patients' history, psychosocial and environmental risk factors were assessed.

RESULTS

The prevalence of obesity was 26.2% in men and 28.1% in women, 26% of men and 21% of women were smokers. Hypertension was found in 46% of men and 31% of women, diabetes in 9.3% of men and 6.3% of women. Markers of subclinical peripheral arterial disease were found in 6.4% of men and 5.1% of women, of subclinical carotid artery disease in 43.2% and 30.7%, and of subclinical coronary artery calcification in 82.3% and 55.2%, respectively. The prevalence of coronary calcification measured using an Agatston Score >100 was in 40% in men and 15% in women, using a score >400, 16.8% and 4.5%, respectively.

DISCUSSION

A high prevalence of subclinical atherosclerosis was found in the older population. The follow-up period will demonstrate whether the detection of markers of subclinical atherosclerosis will improve risk stratification beyond that offered by traditional risk factors.

Use of automatic exposure control in multislice computed tomography of the coronaries: comparison of 16-slice and 64-slice scanner data with conventional coronary angiography

OBJECTIVE

To evaluate the radiation-dose-reduction potential of automatic exposure control (AEC) in 16-slice and 64-slice multislice computed tomography (MSCT) of the coronary arteries (computed tomography angiography, CTA) in patients. The rapid growth in MSCT CTA emphasises the necessity of adjusting technique factors to reduce radiation dose exposure.

DESIGN

A retrospective data analysis was performed for 154 patients who had undergone MSCT CTA. Group 1 (n = 56) had undergone 16-slice MSCT without AEC, and group 2 (n = 51), with AEC. In group 1, invasive coronary angiography (ICA) had been performed in addition. Group 3 (n = 47) had been examined using a 64-slice scanner (with AEC, without ECG-triggered tube current modulation).

RESULTS

In group 1, the mean (SD) effective dose (ED) for MSCT CTA was 9.76 (1.84) mSv and for ICA it was 2.6 (1.27) mSv. In group 2, the mean ED for MSCT CTA was 5.83 (1.73) mSv, which signifies a 42.8% dose reduction for CTA by the use of AEC. In comparison to ICA, MSCT CTA without AEC shows a 3.8-fold increase in radiation dose, and the radiation dose of CTA with AEC was increased by a factor of 1.9. In group 3, the mean ED for MSCT CTA was 13.58 (2.80) mSV.

CONCLUSIONS

This is the first study to show the significant dose-reduction potential (42.8%) of AEC in MSCT CTA in patients. This relatively new technique can be used to optimise the radiation dose levels in MSCT CTA.

Radiation-reducing planning of cardiac catheterisation

Any radiation exposition for medical purposes should be kept as low as is reasonably achievable. Mean patient radiation exposure of diagnostic cardiac catheterisation is high (16-106 Gy x cm2) and for this reason the International Commission on Radiological Protection (ICRP) recommends credentialing radiation protection training programmes. Twenty cardiologists each documented various dose parameters of 10 cardiac catheterisations, before and after a 90-minute mini-course of the ELICIT study group ("Encourage to Less Irradiating Cardiologic Interventional Techniques"), and could achieve a reduction of the mean dose-area product by 15.9+/-9.0 Gy x cm2, equivalent to 47%. The presented radiation-reducing planning of invasive cardiac catheterisation for this reason is the first one validated in clinical routine and consists of 6 standard runs--one for the left ventricle, 3 and 2 for the left (LCA) and right coronary artery (RCA), respectively--depending on anatomy and findings supplemented by 1...4 special projections. The caudal posteroanterior (PA) view documents the left coronary main stem, proximal and distal left anterior descending artery (LAD), and proximal and mid circumflex segments. The cranial PA view however is suitable for the left coronary orifice, circumflex periphery, LAD, all diagonal bifurcations, and collateral pathways towards the RCA. LCA standard angiography is completed by lateral 90 degrees/0 degrees left anterior oblique (LAO) angulation. The 60 degrees/0 degrees LAO angulation visualises the right posterolateral artery (RPL) and the RCA to its bifurcation. The more proximal one finds the bifurcation, the more the second standard cranial PA view for RCA should vary towards the cranial right anterior oblique (RAO) and finally 30 degrees/0 degrees RAO view. The efficiency of these less-irradiating angulations are improved by radiation-reducing techniques as follows: restriction to essential radiographic frames and runs, consistent collimation to the region of interest--particularly during coronary intubation--, adequate instead of best possible image quality, short skin-to-image-intensifier distance, inspiration during radiography, preference for projections that rotate out the spine, optimisation of fluoroscopy time, well-experienced and well-rested interventionists.

[Value of coronary artery calcium measurements in primary prevention]

Frequently, myocardial infarction or sudden coronary death are the index manifestations of coronary artery disease. In view of the high out-of-hospital mortality of acute myocardial infarction, medical care is unable to provide a benefit for many patients. Against this background, it is an important aim of measuring coronary calcium to identify asymptomatic subjects with an increased coronary risk who are likely to derive a benefit from risk-modifying therapy. Coronary calcium is a largely specific expression of coronary atherosclerosis and is correlated with overall coronary plaque volume. Due to the complex biology of the vessel wall and its ability to undergo compensatory remodelling, coronary calcium does not necessarily indicate significant stenosis. Coronary calcium is found in 70-80% of plaque ruptures but only in a minority of plaque erosions. It neither indicates a "vulnerable" nor a "stable" plaque. Six independent studies including healthy self-referred and physician-referred volunteers consistently describe the predictive value of coronary calcium with regard to coronary and cardiovascular clinical events. After adjusting for coronary risk factors, increased amounts of coronary calcium are associated with a 5- to 10-times elevated relative risk. Only recently have the first results from strictly unselected, population-based cohorts been reported which confirm the predictive ability of coronary calcium measurements. Concordant with actual guidelines issued by US-American and European expert panels, coronary calcium measurements can be used especially in patients with an indeterminate risk on the basis of clinical assessment and risk factor analysis. Substantially elevated coronary calcium scores provide a rationale for intensified risk-modifying therapy. This is also true for elderly patients in whom the established risk factors lose some of their predictive power. The use of coronary calcium measurements in self-referred patients or as a primary means for risk stratification is not encouraged.

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.