Reproducibility of electron-beam CT measures of aortic valve calcification

RATIONALE AND OBJECTIVES

The authors performed this study to establish the interscan, interobserver, and intraobserver reproducibility of aortic valve calcification (AVC) measurements obtained with electron-beam computed tomography (CT).

MATERIALS AND METHODS

The authors evaluated electron-beam CT scans from all patients who had undergone two serial examinations on the same day as part of a study of coronary artery calcification reproducibility. In patients in whom aortic valve calcium was identified at electron-beam CT, AVC scores were measured with both the Agatston and the volumetric methods, which were developed previously to quantify coronary calcium.

RESULTS

Forty-four asymptomatic patients (mean age, 66 years +/- 9) with AVC at electron-beam CT were included in the analyses. AVC score reproducibility was excellent with both the Agatston and the volumetric methods (R2 = 0.99, P = .0001 for both), with median interscan variabilities of 7% and 6.2%, respectively. Interscan reproducibility was similar, whether the analysis included all scans or was restricted to those with scores greater than 10 or greater than 30. For the volumetric method, the median interobserver variability was 5% and the median intraobserver variability was 1%.

CONCLUSION

The low interscan, interobserver, and intraobserver variabilities at electron-beam CT suggest that this method should be useful for the noninvasive monitoring of AVC changes over time and for assessing the efficacy of therapies aimed at slowing AVC accumulation.

Reproducibility of three different scoring systems for measurement of coronary calcium

BACKGROUND

There is great interest in measuring and tracking atherosclerosis using electron beam tomography (EBT). We sought to assess the reproducibility of two new software systems, InSight and AccuImage, and the console workstation of an EBT scanner for measuring coronary calcification.

METHODS

Two sets of non-contrast EBT scans were obtained in 85 subjects. The calcium volume (CV) score and the Agatston score (AS) were analyzed and the relative differences were compared on three workstations.

RESULTS

The intra- and inter-observer variabilities by InSight and AccuImage were both significantly better than variabilities on the console workstation. Both intra- and inter-observer differences for the AS were significantly smaller than those for the CV on each workstation. However, inter-scan variability was lower for the volume method (13.3%) as compared to the AS (17%). Scores were divided into tertiles (T), and the relative inter-scan differences for the AS in T-I (scores < 66) were higher than those in others (T-I 21.0%, T-II 11.9%, T-III 6.8%, p < 0.01). However, there were no significant differences for the CV method (T-I 19.9%, T-II 9.4%, and T-III 5.3%). Thus, while intra- and inter-observer differences with the AS method was lower than volume scoring, the CV inter-scan variability was significantly better.

CONCLUSIONS

Both workstations using volumetric and Agatston methods have higher reliability than the console workstation. Inter- and intra-observer reproducibility was excellent (> 98%). There is minimal inter-scan variability for subjects with higher scores (> 65) for both scoring methods.

EKG-triggered CT data acquisition to reduce variability in coronary arterial calcium score

PURPOSE

To test the hypothesis that computed tomographic (CT) scanning during optimal electrocardiographic (EKG) triggering can minimize image motion artifact and reduce interexamination variation of coronary arterial calcification (CAC) score at electron-beam CT.

MATERIALS AND METHODS

Two hundred patients underwent electron-beam CT once and again 5 minutes later to evaluate interexamination variability of CAC score. Group 1 (104 patients) underwent scanning with use of an optimal EKG-triggering protocol (EKG triggering performed individually at the time of least coronary arterial motion during the cardiac cycle); group 2 (96 patients) underwent scanning with use of conventional 80% R-R interval triggering (the most common protocol with the electron-beam CT scanner). Interexamination, intraobserver, and interobserver variations of CAC measurements were compared between groups by using unpaired t tests for both Agatston and volumetric scores (in square millimeters).

RESULTS

Coronary arterial motion artifacts were found in 26% (27 of 104) versus 80% (77 of 96) of patients in groups 1 and 2, respectively (P <.0001). Intraobserver, interobserver, and interexamination variabilities in volumetric score were derived, with values of 1.2%, 9.2%, and 15.9% in group 1 and 2.1%, 11.3%, and 25.9% in group 2, respectively. Interexamination variabilities in both Agatston and volumetric score were significantly reduced with individualized EKG triggering, as compared with conventional triggering (P <.05), but intra- and interobserver variabilities were not (P >.05).

CONCLUSION

Optimal EKG triggering improves the reproducibility of CAC measurement by reducing coronary arterial motion artifacts.

Causes of interscan variability of coronary artery calcium measurements at electron-beam CT

RATIONALE AND OBJECTIVES

The authors performed this study to investigate the causes of interscan variability of coronary artery calcium measurements at electron-beam computed tomography (CT).

MATERIALS AND METHODS

Two sets of electron-beam CT scans were obtained in 298 consecutive patients who underwent electron-beam CT to screen for coronary artery calcium. Interscan variations of coronary artery calcium characteristics and the effects of heart rate, electrocardiographic (ECG) triggering method, image noise, and coronary motion on interscan variability were analyzed.

RESULTS

The interscan mean variabilities were 21.6% (median, 11.7%) and 17.8% (median, 10.8%) with the Agatston and volumetric score, respectively (P < .01). Variability decreased with increasing calcification score (34.6% for a score of 11-50 and 9.4% for a score of 400-1,000, P < .0001). The absolute difference in Agatston score between scans was 44.1 +/- 95.6. The correlation coefficient between the first and second sets of scans was 0.99 (P < .0001). Lower interscan variability was found in younger patients (<60 years), patients with stable heart rates (heart rate changing less than 10 beats per minute during scanning), patients with no visible coronary motion, and those with an optimal ECG triggering method (P < .05 for all). Results of multivariate logistic analysis showed that changes in calcium volume, mean attenuation, and peak attenuation were significant predictors of interscan variability and caused the interscan variations of the coronary artery calcium measurements (r2 = 0.83, P < .0001).

CONCLUSION

Coronary calcification at electron-beam CT varies from scan to scan. Volumetric scoring and optimal ECG triggering should be used to reduce interscan variability. Baseline calcium score and interscan variability must be considered in the evaluation of calcium progression.

Electron beam tomography and angiography: sex differences

BACKGROUND

We sought to study a large cohort of symptomatic women to determine the clinical use of electron beam tomography (EBT), with evaluation of the sensitivity and specificity of obstructive coronary disease and the differences between premenopausal and postmenopausal cohorts.

METHODS

Patients who underwent angiography for evaluation of coronary artery disease (CAD) and EBT within 3 months were enrolled. Receiver operating characteristic curves were used to establish relationships between EBT calcium scores and angiographic disease.

RESULTS

We studied 1120 symptomatic patients, 387 women and 733 men. We found no significant differences with respect to sensitivity for obstructive disease (96% in men and women). However, women had a significantly higher specificity (46% in men versus 57% in women; P =.01). The area under the curves for coronary calcium score predicting angiographic disease was 0.85 for all patients and 0.84 in women. Evaluation of scores on the basis of age revealed a 14.4-year lag between men and women. One hundred thirty-five women had negative EBT study results (score, zero; no calcium present), with 6 with single-vessel disease and 129 with normal coronaries or nonobstructive disease only (negative predictive value, 96%).

CONCLUSION

EBT may have a great value in evaluation of women with possible CAD. The high sensitivity and high negative predictive value may serve as the basis for a new diagnostic approach to filter symptomatic women with suspected CAD before coronary angiography.

Coronary calcium scanning adds incremental value to patients with positive stress tests

BACKGROUND

The sensitivity of coronary calcification by electron beam tomography (EBT) for the detection of coronary atherosclerosis is well-established. Combining the anatomic information of EBT with the functional information of stress testing might reduce the high false-positive result rate seen with treadmill stress test (TMST) alone. No studies have reported the additive value of a negative EBT result (no coronary calcium) for excluding obstructive coronary artery disease (OCAD) in patients with a positive TMST result. This study evaluated the negative predictive value and potential clinical utility of EBT to identify patients with a falsely abnormal TMST.

METHODS

A coronary calcium score was determined by EBT for 153 symptomatic patients who underwent coronary angiography because of a positive TMST. The sensitivity, specificity, and predictive values of EBT were determined. A multiple logistic regression analysis compared conventional cardiac risk factors with coronary calcification by EBT for predicting OCAD. A receiver operating characteristic curve was generated plotting sensitivity versus false-positive rate.

RESULTS

The false-positive rate of the TMST compared with angiography was 27% (41 of 153). The sensitivity of a nonzero coronary calcium score for OCAD was 98% (110 of 112), with a negative predictive value of 93%. According to multiple logistic regression, coronary calcification by EBT was a stronger predictor of OCAD than any conventional cardiac risk factor. EBT calcium added incremental value to the results of the TMST. Receiver operating characteristic curve analysis found an area under the curve of 0.91 (P <.001).

CONCLUSIONS

The absence of coronary calcification by EBT reliably identified patients with a false-positive TMST result. The combination of EBT with TMST is a potentially useful diagnostic strategy to reduce the number of false-positive test results.

Continuous probabilistic prediction of angiographically significant coronary artery disease using electron beam tomography

BACKGROUND

We sought to incorporate electron beam tomography-derived calcium scores in a model for prediction of angiographically significant coronary artery disease (CAD). Such a model could greatly facilitate clinical triage in symptomatic patients with no known CAD.

METHODS AND RESULTS

We examined 1851 patients with suspected CAD who underwent coronary angiography for clinical indications. An electron beam tomographic scan was performed in all patients. Total per-patient calcium scores and separate scores for the major coronary arteries were added to logistic regression models to calculate a posterior probability of the severity and extent of angiographic disease. These models were designed to be continuous, adjusted for age and sex, corrected for verification bias, and independently validated in terms of their incremental diagnostic accuracy. The overall sensitivity was 95%, and specificity was 66% for coronary calcium to predict obstructive disease on angiography. With calcium scores >20, >80, and >100, the sensitivity to predict stenosis decreased to 90%, 79%, and 76%, whereas the specificity increased to 58%, 72%, and 75%, respectively. The logistic regression model exhibited excellent discrimination (receiver operating characteristic curve area, 0.842+/-0.023) and calibration (chi2 goodness of fit, 8.95; P=0.442).

CONCLUSIONS

Electron beam tomographic calcium scanning provides incremental and independent power in predicting the severity and extent of angiographically significant CAD in symptomatic patients, in conjunction with pretest probability of disease. This algorithm is most useful when applied to an intermediate-risk population.

HMG CoA reductase inhibitor (statin) and aortic valve calcium

There is no known pharmacological therapy for calcific aortic valvular sclerosis or stenosis. Because leaflet calcification occurs in areas of lipoprotein deposition, we hypothesised that 3-hydroxy-3-methylglutaryl-coenzyme A (HMG COA) reductase inhibitors (statins) might slow aortic valve calcium (AVC) accumulation. We retrospectively identified 65 patients who had undergone two electron-beam computed tomography scans at a mean (SD) interval of 2.5 (1.6) years. 28 (43%) patients were receiving statins. Patients who were treated with statins had a 62-63% lower median rate of AVC accumulation (p=0.006) and 44-49% fewer statin patients had definite AVC progression (p=0.043). These findings suggest that statins may decrease AVC accumulation.

Image quality of three-dimensional electron beam coronary angiography

PURPOSE

This study identifies reasons for poor image quality and nonassessability of coronary artery segments and compares results between early and late diastolic triggering on coronary electron beam angiography (EBA).

METHOD

One hundred patients referred for EBA were studied. Contrast-enhanced transaxial coronary images were acquired using electrocardiographic (ECG) triggering and reconstructed three dimensionally using volume-rendering techniques. The image quality of coronary segments and image artifacts were analyzed statistically.

RESULTS

Volume rendering failed in seven patients (7%) owing to cardiac and breathing motions. Image quality was the best with the left main (LM) and worst with the left circumflex (LCX) coronary arteries (p < 0.001). The image quality decreased systematically from proximal to distal within each coronary artery (p < 0.001). Forty percent R-R interval triggering on ECG was better than 80% for image quality. The nonassessable segments occurred in 3% of LM, 2, 8, and 5% of proximal, 24, 22, and 12% of mid, and 64, 45, and 20% of distal segments of the left anterior descending, LCX, and right coronary arteries, respectively (p < 0.05).

CONCLUSION

The major limitations of coronary EBA were suboptimal spatial resolution and image artifacts. The image quality could be improved by using optimal ECG triggering.

Coronary calcium and cardiovascular event risk: evaluation by age- and sex-specific quartiles

BACKGROUND

Wide differences in risks for cardiovascular disease (CVD) events associated with coronary artery calcium (CAC) have been reported. We evaluated the relationship of the coronary calcium quartile, on the basis of age-sex cut points from a large sample of asymptomatic patients, to CVD events as a possible standardized means for reporting event risks associated with CAC, in comparison with quartiles of absolute CAC scores.

METHODS

We applied age/sex-stratified cut points to 928 asymptomatic men and women (mean age 54 years) followed up for an average of 3.3 years, during which 28 CVD events were confirmed. Cox regression was used to evaluate the relation of the 2nd, 3rd, and 4th quartiles (compared with the 1st), with and without age/sex stratification, to the risk of future CVD events.

RESULTS

The number of events (and percent incidence) that occurred in the 1st, 2nd, 3rd, and 4th quartiles of coronary calcium was 4 (0.9%), 2 (2.0%), 9 (4.5%), and 13 (6.4%) events (P =.001) for the age/sex-stratified quartiles and 4 (1.0%), 0 (0%), 7 (3.0%), and 17 (7.3%) for the absolute score quartiles (P =.001). In multivariable analysis adjusted for other risk factors, there was a modest increase in CVD events seen among those in the 3rd quartile (relative risk [RR] 4.3, P =.02), with a greater risk seen among those in the 4th quartile (RR 6.0, P <.01) (compared with the 1st quartile). This did not differ from use of absolute CAC scores, where RR = 2.6 (P =.14) for the 3rd quartile and RR = 6.4 (P <.01) for the 4th quartile.

CONCLUSIONS

Our results suggest that age-sex stratification by percentile rank of CAC is as accurate as absolute CAC scores for predicting CVD events in asymptomatic persons. Ongoing longitudinal population-based studies will provide more definitive data.

Ethnic differences in coronary atherosclerosis

OBJECTIVES

The study was done to evaluate whether ethnic differences exist in the prevalence of coronary artery calcification (CAC), and to determine whether differences in calcification correlate with the degree of coronary obstruction.

BACKGROUND

Electron beam tomography (EBT) can be used to quantitate the amount of CAC and assist in prognostication of future cardiac events. It is unclear whether ethnic differences in coronary mortality are related to differences in the prevalence of coronary obstruction and CAC.

METHODS

A total of 782 symptomatic subjects underwent both EBT and angiography. A 50% luminal narrowing defined an angiographic obstruction.

RESULTS

We observed substantial ethnic differences in prevalence of both CAC and angiographic stenosis. In whites (n = 453), prevalence of CAC (score >0) was 84%, and significant obstruction on angiogram was 71%. Compared with whites, blacks (n = 108) had a significantly lower prevalence of CAC (62%, p < 0.001) and angiographic disease (49%, p < 0.01). Hispanics (n = 177) also had a lower prevalence of CAC (71%, p < 0.001) and angiographic obstruction (58%, p < 0.01). Asians (n = 44) were not significantly different in regard to CAC (73%, p = 0.06) or angiographic stenosis (64%, p = 0.30). These ethnic differences remained after simultaneously controlling (by use of multiple logistic regression) for age, gender and cardiac risk factors.

CONCLUSIONS

As compared with whites, blacks and Hispanics had significantly lower prevalence of CAC and obstructive coronary disease. Ethnic differences in risk-factor profiles do not explain these differences. This study demonstrated that whites have a higher atherosclerotic burden than blacks and Hispanics, independent of risk-factor differences among symptomatic patients referred for angiography.

Noninvasive assessment of coronary artery bypass graft patency and flow characteristics by electron-beam tomography

OBJECTIVE

To evaluate the flow characteristics and accuracy for the detection of patent or occluded coronary artery bypass grafts (CABG) with multi-slice flow study of electron-beam tomography (EBT).

METHODS

One hundred and twenty-three patients who had undergone CABG surgery were enrolled in this study. Flow datasets were assessed with time-density curves by EBT. The EBT results were blindly compared with post-operative cardiac catheterizations in 26 patients.

RESULTS

Image quality was adequate to evaluate in 111 patients (90.2%). Flow curves of bypass grafts were technically adequate in 265 of 309 (85.8%) saphenous-vein grafts (SVG) and 35 of 56 (62.5%) internal mammary artery (IMA) grafts (p < 0.05). In comparison to conventional angiographic results, EBT correctly identified 14 of 16 occluded grafts (sensitivity, 87.5%) and 68 of 75 patent grafts (specificity, 90.7%), yielding an accuracy of 90.1%. The intra-graft flows of the IMA and SVG were 4.9 +/- 2.2 ml/min/g and 6.9 +/- 2.8 ml/min/g, respectively (p < 0.001), which was 31.6 +/- 20.4% and 39.4 +/- 21.9% of the ascending aorta's flow (16.7 +/- 5.0 ml/min/g) (p < 0.001).

CONCLUSION

EBT flow study can be used in the assessment of CABG patency and quantification of intra-graft flow of patent CABG vessels.

Optimal ECG trigger point in electron-beam CT studies: three methods for minimizing motion artifacts

RATIONALE AND OBJECTIVES

The authors hypothesized that electrocardiographic triggering near end systole could minimize motion artifacts in electron-beam computed tomography (CT) of the coronary artery.

MATERIALS AND METHODS

The study included 2,660 patients who underwent coronary artery calcium scanning with electron-beam CT. Trigger times were as follows: end of T wave, 120 to 25 msec before end of T wave, 25-50 msec after end of T wave, 40%, 45%, 50%, 55%, 60%, 70%, 75%, 80%, 90%, and 100% of R-R interval. The authors divided each group into seven subgroups according to heart rate. The percentages of cases with motion artifact in the right coronary artery were computed. Optimal trigger times were defined for each group, as well as for scan acquisitions of 250 and 200 msec.

RESULTS

The optimal trigger times were as follows for heart rates of less than 50, 51-60, 61-70, 71-80, 81-90, 91-100, and more than 100 beats per minute, respectively: for 100-msec scans, 359 (27% of the R-R interval), 228 (31%), 314 (34%), 304 (38%), 289 (41%), 283 (45%), and 274 msec (48%) after the R wave; for 250-msec scans, 840 (63%), 654 (60%), 240 (26%), 224 (28%), 219 (31%), 208 (33%), and 200 msec (35%) after the R wave; and for 200-msec scans, 722 (65%), 687 (63%), 249 (27%), 248 (31%), 244 (35%), 233 (37%), and 223 msec (39%) after the R wave.

CONCLUSION

The use of these new electrocardiographic triggers before end systole yielded the lowest percentage of motion artifacts (<3% across all heart rates), much lower than for conventional triggers (51% of cases with motion artifact for 80% trigger, P < .001).

Effect of electrocardiogram triggering on reproducibility of coronary artery calcium scoring

PURPOSE

To test the hypothesis that computed tomographic (CT) scanning during early rather than middle diastole can significantly reduce the interscan variability of coronary artery calcium (CAC) scores.

MATERIALS AND METHODS

Five hundred thirty-eight patients were initially enrolled; 282 of them were found to have CAC at electron-beam CT and underwent repeat scanning to measure interscan variability with different electrocardiogram (ECG) triggers. Eight patients were excluded owing to respiratory motion; thus, 274 asymptomatic patients were examined. Patients were randomly assigned to different ECG trigger interval groups: 40% (group 1), 50% (group 2), 60% (group 3), and 80% (group 4). Patients in whom more than one-third of sections had greater than 10% ECG trigger variability were classified in the untriggered group (group 5). Interscan variation was compared among all five groups.

RESULTS

Interscan variabilities in CAC groups 1-5 were 11.5%, 15.3%, 20.3%, 17.4%, and 33.1%, respectively, for total calcium area, and 15.0%, 23.3%, 25.6%, 24.0%, and 42.4%, respectively, for total calcium score. CAC score variability was reduced by 34%; and calcium area variability, by 38% in group 1, as compared with the reduced variabilities in group 4 (P <.01 for both measures). Breath holding was adequate in 812 cases, and ECG triggering was correct in 790 of cases.

CONCLUSION

Study results strongly support the use of an ECG trigger of 40% rather than 80% of the R-R interval in electron-beam CT calcium studies.

Effects of window and threshold levels on the accuracy of three-dimensional rendering techniques in coronary artery electron-beam CT angiography

RATIONALE AND OBJECTIVES

The authors performed this study to evaluate the effect of window level and gray-scale threshold on the demonstration of coronary artery lumina at three-dimensional electron-beam computed tomographic (CT) angiography.

MATERIALS AND METHODS

Forty-four coronary artery branches in postmortem pigs were evaluated with electron-beam CT angiography, and the findings were compared with those from conventional angiography. Images from electron-beam CT angiography were reconstructed with maximal intensity projection (MIP), multiplanar reformation (MPR), and shaded-surface display (SSD). Four categories of window level and gray-scale threshold were evaluated.

RESULTS

Three-dimensional electron-beam CT angiography accurately depicted the luminal diameters of the coronary arteries compared with conventional angiography (r = 0.83-0.90, P < .0001). The length of lumina visualized at electron-beam CT angiography was significantly shorter than that visualized with conventional angiography (P < .001). The use of MPR enabled visualization of longer segments of coronary arteries than did the use of MIP or SSD (P < .05). The higher the window level and gray-scale threshold used, the smaller the coronary luminal diameters measured (P < .05). The most accurate window level and gray-scale threshold (82.6 HU +/- 29.8 and 89.5 HU +/- 29.7, respectively) were found to correspond to the attenuation of the lumina (275.8 HU +/- 58.8). Results of simple linear regression showed a strong correlation between luminal attenuation and window level (r = 0.89, P < .0001) or gray-scale threshold (r = 0.95, P < .0001).

CONCLUSION

Electron-beam CT angiography shows promise in the visualization of coronary artery lumina. For accurate display of lumina, a proper window level and gray-scale threshold for three-dimensional rendering techniques should be determined and used on the basis of the attenuation of the target vessel.

Coronary artery disease progression assessed by electron-beam computed tomography

The ability to observe changes in atherosclerotic plaque burden over time should provide an accurate measure of efficacy for different cardiovascular therapies. Electron-beam computed tomography (EBCT), by quantification of coronary artery calcification, is a noninvasive measure of atherosclerosis burden. This article summarizes data from abstracts and publications related to coronary artery calcium measurement and its use in progression studies. The issues related to interscan variability and reproducibility of this measure are detailed. The limitations of multidetector spiral computed tomography (high radiation dose and poor reproducibility) are also addressed. Several studies of progression using 2 scans, administered > or =1 year apart, demonstrate significant annual progression (22% to 52% per year). All studies demonstrate that therapy with cholesterol-lowering agents slows the atherosclerotic process, and that it may lead to regression of coronary calcium over time. There are 2 small prognostic studies that demonstrate that coronary events predominantly occur in those patients who exhibit significant progression of coronary artery calcium. Large multicenter trials are underway to evaluate the prognostic significance of coronary artery calcium progression. The progression of coronary artery atherosclerosis can be observed noninvasively by monitoring the progression of coronary calcification with EBCT. With annual progression rates of 22% to 52% and a median interscan variability of only 5% to 8%, this technology provides an opportunity to noninvasively monitor patients to assess the clinical efficacy of medical therapies in studies as short as 1 year.

Screening patients with chest pain in the emergency department using electron beam tomography: a follow-up study

OBJECTIVES

The high sensitivity of electron beam tomography (EBT) in the detection of coronary artery calcium (CAC) and obstructive coronary artery disease prompted us to investigate the association between CAC detection and future cardiac events in patients with acute chest pain syndromes requiring hospitalization.

BACKGROUND

Three studies have documented that EBT is a rapid and efficient screening tool for patients admitted to the emergency department (ED) with chest pain, but there is a paucity of long-term follow-up data on these chest pain patients.

METHODS

We conducted a prospective observational study of 192 patients admitted to the ED of a large tertiary care hospital for chest pain syndromes. Upon admission, patients underwent EBT scanning in addition to the usual care for chest pain syndromes. During the 17-month enrollment period, 221 patients were scanned (54% men with a mean age of 53 +/- 9 years). Average follow-up was 50 +/- 10 months using chart review.

RESULTS

Fifty-eight patients had coronary events confirmed by a blinded medical record review. The presence of CAC (a total calcium score >0) and increasing score quartiles were strongly related to the occurrence of hard cardiac events including myocardial infarction and death (p < 0.001) and all cardiovascular events (p < 0.001). Stratification by age- and gender-matching further increased the prognostic ability of EBT (for scores above vs. below the age- and gender-matched CAC scores; odds ratio: 13.1, 95% confidence intervals: 5.62, 35.9).

CONCLUSIONS

These data support previous reports demonstrating that the presence of CAC in a symptomatic cohort is a strong predictor of future cardiac events. This study supports the use of EBT in a symptomatic cohort with prompt discharge of those patients with negative scans. Furthermore, the absence of CAC is associated with a very low risk of future cardiac risk events in this population over the subsequent seven years (annual event rate <1%).

Improved reproducibility of coronary artery calcium scoring by electron beam tomography with a new electrocardiographic trigger method

RATIONALE AND OBJECTIVES

To improve the interscan reproducibility with electron beam tomography (EBT) by choosing an optimal electrocardiographic (ECG) trigger time.

METHODS

Two hundred fourteen asymptomatic subjects found to have coronary artery calcium (CAC) on EBT were rescanned immediately to measure the interscan variability. Subjects were randomized to one of two different ECG trigger interval groups: the new trigger method (group 1) and the 80% R-R interval trigger method (group 2). The new trigger method was derived from a previous study of motion in the coronary arteries. In group 1 (new trigger method), the ECG trigger was programmed for a certain time (in ms) after the R wave, based on the resting heart rate. The triggers for group 1 were 360 (heart rate <50 beats per minute [bpm]), 340 (51--60 bpm), 314 (61--70 bpm), 300 (71--80 bpm), 290 (81--90 bpm), 280 (91--100 bpm), and 270 ms (>100 bpm). The interscan variation (CAC area and Agatston score) was compared between the two groups.

RESULTS

The interscan variability was significantly reduced using the new trigger method for both CAC area and score compared with the 80% trigger method. The individual lesion variation was also significantly reduced by the new trigger method compared with the 80% trigger method. Area measure had a significantly lower variability compared with the Agatston score.

CONCLUSIONS

These results strongly support the use of this new ECG trigger that relies on a rate-adjusted millisecond delay after the R wave instead of the more commonly used 80% R-R interval in EBT calcium studies.

Coronary artery motion during the cardiac cycle and optimal ECG triggering for coronary artery imaging

RATIONALE AND OBJECTIVES

Our purpose was to investigate the motion characteristics of the coronary arteries and determine optimal electrocardiographic (ECG) trigger time during the cardiac cycle to minimize motion artifacts.

METHODS

Contrast-enhanced multislice movie studies of electron beam tomography (EBT) images were performed on 70 subjects. The EBT datasets, which covered an entire cardiac cycle at 58-ms intervals, were acquired for a short-axis view of the heart with ECG triggering. The pixel values along x and y axes were measured at multiple intervals during the cardiac cycle to establish the motion distance and velocity of three major coronary arteries.

RESULTS

Coronary artery motion varied greatly throughout the cardiac cycle in three major coronary arteries and increased with the patient's baseline heart rate. The greatest and lowest velocities of coronary arterial movement during the cardiac cycle were determined. Based on the lowest velocity of right coronary artery movement during the cardiac cycle, the optimal ECG trigger times were located at approximately 35% (31.4%-37.6%) or 70% (68.7%-71.4%) of the R-R interval in patients whose resting heart rate was < or =70 beats per minute (bpm); at 50% (47.2%-61.1%) of the R-R interval in the 71- to 100-bpm group; and at 55% (52.8%-59.1%) of the R-R interval in the >100-bpm group. Our data demonstrated that the motion characteristics of the left circumflex artery were quite similar to those of the right coronary artery and that the left anterior descending coronary artery had no significant differences in motion throughout the cardiac cycle. A minimum scan speed of 35.4 to 75.5 ms per slice is needed to completely diminish cardiac motion artifacts (in-plane coronary artery motion with <1-mm displacement).

CONCLUSIONS

For coronary artery screening, the optimal ECG trigger time should be determined according to the patient's heart rate, thus greatly reducing motion and motion artifacts during 100-ms acquisitions.

Diabetes and the associated incidence of subclinical atherosclerosis and coronary artery disease: Implications for management

BACKGROUND

We sought to examine the prevalence, sensitivity, and specificity of coronary calcium (CC), a marker of atherosclerosis, in a population of symptomatic and asymptomatic diabetic persons.

METHODS

We used electron beam tomography (EBT) to quantitate CC in 168 symptomatic (chest pain or anginal equivalent) persons with diabetes who underwent coronary angiography and then compared this with a cohort of 155 asymptomatic persons with diabetes.

RESULTS

In the 168 symptomatic diabetic persons, 124 (74%) had obstructive coronary artery disease (CAD) by angiography. Receiver-operator characteristic curve analysis was used to maximize sensitivity and specificity for obstructive CAD (>50% stenosis), which established a CC score of 102 as optimal. With use of this cut point, EBT has a sensitivity of 77% and a specificity of 77% for detecting obstructive CAD. Of the 155 asymptomatic diabetic persons, 72% had CC and 48% had a CC score >102. The presumed prevalence of obstructive disease (on the basis of EBT scores and prevalence of CC) among asymptomatic diabetic persons is quite high (as high as symptomatic persons without diabetes). Analyzing the 323 diabetic patients demonstrated no significant age difference in CC scores between women and men.

CONCLUSIONS

This study confirms that higher CC scores should be used in diabetic patients to improve the specificity of CC to determine obstructive disease. EBT can allow a noninvasive diagnosis of CAD before clinical presentation, allowing for more therapy for those in which CC is detected. These results suggest that asymptomatic diabetic persons have the same atherogenic burden of those patients with CAD without diabetes. The high prevalence of CC in asymptomatic persons with diabetes supports the need for aggressive management of diabetes and associated risk factors.

Coronary artery stenoses: a phantom study using contrast enhanced three-dimensional electron beam tomography

This paper evaluated the accuracy of electron beam tomographic angiography (EBA) with conventional coronary arteriography (CCA) using four graded artificial stenoses in a postmortem swine coronary phantom model. The sensitivity, specificity, and accuracy of EBA for diagnosing significant stenosis (> or =50% stenosis) were 94.3%, 96.7%, and 95.8%, respectively. The diagnostic accuracy of EBA had no significant difference with CCA (chi(2)=0.0162; P>.05). EBA three-dimensional (3D) procedures had high interobserver reproducibility (k=.92-.95, P>.05). Maximum intensity projection (MIP) was the most sensitive and curved planar reformation (CPR) was the most accurate 3D procedure for quantitatively identifying coronary stenosis. EBA yields promising results concerning the visualization of coronary artery stenosis with high accuracy for stenoses >50%.