Potential clinical impact of variability in the measurement of coronary artery calcification with sequential MDCT

OBJECTIVE: The potential clinical impact of variability in the measurement of coronary artery calcification with sequential MDCT was evaluated using Agatston, volume, and mass scoring algorithms. SUBJECTS AND METHODS: Fifty-six patients were imaged twice using an identical prospectively ECG-triggered sequential scanning protocol. The Agatston, volume, and mass scores were computed by two observers independently. In addition, a patient's total Agatston score was referenced to an age- and sex-stratified database to determine a percentile ranking. Interscan, interobserver, and intraobserver variability and the resultant impact on patients' risk stratifications were assessed. RESULTS: Significant interscan differences were found for all mean coronary calcium scores (Wilcoxson's signed rank test, p <0.0001). Although the median percentage of interscan variability was low for all scoring methods, the interquartile range was wide, indicating significant variability in the data. Median scores (lower quartile-upper quartile) for observers 1 and 2, respectively, were as follows: Agatston, 5% (0-79%) and 6% (0-83%); volume, 12% (0-51%) and 12% (0-57%); and mass, 14% (0-57%) and 14% (0-58%). Interobserver and intraobserver differences between mean calcium scores were not significant, and consequently, lower interobserver and intraobserver variabilities (narrow interquartile ranges of 0-5%) were observed for all scores. Despite significant interscan differences in calcium scores, the percentile ranking assigned to the two scans differed in only 13% of patients. Interobserver differences resulted in a change in the percentile ranking in 7-9% of patients, whereas intraobserver differences caused a change in only 5% of patients. CONCLUSION: The accuracy of sequential MDCT for coronary calcium quantification is sufficient in most cases for stratification of patient risk.     

Variability of repeated coronary artery calcium measurements by 16-MDCT with retrospective reconstruction

OBJECTIVE: High reproducibility on coronary calcium scoring is an important factor in monitoring the progression of coronary atherosclerosis. The purposes of this study were, using a 16-MDCT scanner with retrospective reconstruction, to compare the effects of thin-slice images and overlapping image reconstruction on the reproducibility of coronary calcium scoring and to compare 16-MDCT with electron beam CT (EBCT). MATERIALS AND METHODS: Fifty patients underwent two sequential examinations using both EBCT and MDCT. For MDCT, images were reconstructed from the same raw data using the following thicknesses and increments (thickness/increment): 1.25 mm/1.25 mm, 2.5 mm/2.5 mm, and 2.5 mm/1.25 mm. The Agatston, volume, and mass scores were calculated on four pairs of image sets. Statistical analysis was performed to determine significant differences in interscan variability among image acquisition protocols and among measurement algorithms. RESULTS: Overlapping reconstructed images (thickness/increment, 2.5 mm/1.25 mm) obtained on a 16-MDCT scanner showed the lowest variability (mean, 13%; median, 10%) when compared with the Agatston score. CONCLUSION: The use of 16-MDCT with overlapping reconstruction by retrospective reconstruction, yielding low variability of coronary artery calcium measurement on two sequential scans, has an advantage over EBCT in monitoring the progression of atherosclerosis.     

Variability of aortic valve calcification measurement with multislice spiral computed tomography

OBJECTIVES: We sought to assess the variability of aortic valve calcifications (AVCs) regarding the reconstruction window at different heart phases using multislice-spiral computed tomography. MATERIALS AND METHODS: A total of 46 patients (26 men; mean age. 65 years) underwent AVC scoring with multislice-spiral computed tomography (12 x 0.75 mm, 120 kV, 133 mAseff). Image reconstruction was performed every 10% of the RR-interval (0-90%). AVC was quantified using Agatston score, calcium volume, and calcium mass. Images were assessed for least motion artifacts. Coefficients of variation and Wilcoxon test were calculated. RESULTS: AVC scores are lowest at 60% and highest at 0% of the RR-interval (P < 0.001). Mean coefficients of variation were 36.2% (Agatston score), 38.7% (calcium volume), and 32.9% (calcium mass). At 60% (50-70%). minimal motion artifacts and the lowest variability of the scores were found. CONCLUSIONS: AVC scores show large variability depending on the point of image reconstruction. Diastolic image reconstruction at 60% of the RR-interval is recommended.     

Concordance of coronary artery calcium estimates between MDCT and electron beam tomography

OBJECTIVE: The objective of our study was to compare MDCT with electron beam tomography (EBT) for the quantification of coronary artery calcification (CAC). MATERIALS AND METHODS: Sixty-eight patients underwent both MDCT and EBT within 2 months for the quantification of CAC. The images were scored in a blinded fashion and independently by two observers with a minimum of 7 days between the interpretations of images obtained from one scanner type to the other. RESULTS: Presence versus absence of CAC was discordant by EBT versus MDCT in 6% (n = 4) of the cases by observer 1, with one of these cases also discordant by observer 2. All cases except one (aortic calcium misidentified as CAC) were among those with a mean Agatston score of less than 5 present on EBT but absent on MDCT. EBT and MDCT scores correlated well (r = 0.98-0.99). The relative median variability between EBT and MDCT for the Agatston score was 24% for observer 1 and 27% for observer 2 and was 18% and 14%, respectively, for volume score (average for both observers: 27% for Agatston score and 16% for volume score). Scores were higher for EBT than MDCT in approximately half of the cases, with little systematic difference between the two (median EBT-MDCT difference: Agatston score, -0.55; volume score, 3.4 mm3). The absolute median difference averaged for the two observers was 28.75 for the Agatston score and 15.4 mm3 for the volume score. CONCLUSION: Differences in CAC measurements using EBT and MDCT are similar to interscan differences in CAC measurements previously reported for EBT or for other MDCT scanners individually.     

Influence of scoring parameter settings on Agatston and volume scores for coronary calcification

Current multi-detector CT and electron beam tomography (EBT) technology enables the evaluation of coronary calcification. Multiple software packages are available to quantify calcification using several scoring algorithms implementing user-definable scoring parameters. We investigated the effect of scoring parameters on the calcium score outcome. Three parameters (four-connected or eight-connected, lesion size threshold and interpolation) are evaluated. Their theoretical influence on the scoring outcome is shown using simplified examples. To evaluate the effect in real data, we performed calcium scoring on randomly chosen EBT scans from 50 participants in an epidemiological study. Both the Agatston and volume scores were calculated. Changing from eight-connected to four-connected connectivity decreased both Agatston and volume scores (mean variability Agatston 3.15% and volume score –3.52%). Decreasing the threshold from 4 to 2 pixels increased the calcium scores because smaller lesions were also selected as calcified plaques (mean variability Agatston 16.23% and volume score 18.66%). Finally, the use of interpolation had a large negative effect on the volume score (mean variability –29.67%) and almost no effect on the Agatston score. Parameter settings in software for quantification for coronary calcification affect the calcium score outcome. Therefore, parameter settings for calcium scoring should be standardized.     

Coronary calcium quantification using various calibration phantoms and scoring thresholds

RATIONALE AND OBJECTIVES: To compare scoring threshold and calibration method-dependent accuracy and variability of coronary calcium measurements by multidetector computed tomography (MDCT). METHODS: Ninety-five subjects were scanned with MDCT. We calculated Agatston score and volume score. Mineral mass (MM) was calculated using patient-based and scanner-based calibration methods. Accuracy of calibration was validated using artificial calcium cylinders. RESULTS: Patient-based and scanner-based calibration permitted accurate quantification of artificial calcium cylinders (bias: 0 mg and -2 mg). In the subjects, the mean relative difference of MM measurements performed at 90 and 130 Hounsfield units threshold (59%) was lower than for Agatston score (94%) and volume score (109%; P < 0.05). Patient-based and scanner-based calibration yielded systematically different MM measurements (bias: 22%). CONCLUSIONS: MM lowers threshold-dependent variability of coronary calcium measurements. Patient-based and scanner-based calibration allows accurate calcium quantification ex vivo but reveal systematic differences in subjects. Patient-based calibration may better account for subject size and composition.     

Quantitative parameters of image quality in 64-slice computed tomography angiography of the coronary arteries

We explored quantitative parameters of image quality in consecutive patients undergoing 64-slice multi-detector computed tomography (MDCT) coronary angiography for clinical reasons. Forty-two patients (36 men, mean age 61 +/- 11 years, mean heart rate 63 +/- 10 bpm) underwent contrast-enhanced MDCT coronary angiography with a 64-slice scanner (Siemens Sensation 64, 64 mm x 0.6 mm collimation, 330 ms tube rotation, 850 mAs, 120 kV). Two independent observers measured the overall visualized vessel length and the length of the coronary arteries visualized without motion artifacts in curved multiplanar reformatted images. Contrast-to-noise ratio was measured in the proximal and distal segments of the coronary arteries. The mean length of visualized coronary arteries was: left main 12 +/- 6 mm, left anterior descending 149 +/- 25 mm, left circumflex 89 +/- 30 mm, and right coronary artery 161 +/- 38 mm. On average, 97 +/- 5% of the total visualized vessel length was depicted without motion artifacts (left main 100 +/- 0%, left anterior descending 97 +/- 6%, left circumflex 98 +/- 5%, and right coronary artery 95 +/- 6%). In 27 patients with a heart rate < or = 65 bpm, 98 +/- 4% of the overall visualized vessel length was imaged without motion artifacts, whereas 96+/-6% of the overall visualized vessel length was imaged without motion artifacts in 15 patients with a heart rate > 65 bpm (p < 0.001). The mean contrast-to-noise ratio in all measured coronary arteries was 14.6 +/- 4.7 (proximal coronary segments: range 15.1 +/- 4.4 to 16.1 +/- 5.0, distal coronary segments: range 11.4 +/- 4.2 to 15.9 +/- 4.9). In conclusion, 64-slice MDCT permits reliable visualization of the coronary arteries with minimal motion artifacts and high CNR in consecutive patients referred for non-invasive MDCT coronary angiography. Low heart rate is an important prerequisite for excellent image quality.     

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.     

The influence of heart rate, slice thickness, and calcification density on calcium scores using 64-slice multidetector computed tomography: a systematic phantom study

OBJECTIVE: The purpose of this study was to investigate the influence of heart rate, slice thickness, and calcification density on absolute value and variability of calcium score using 64-slice multidetector computed tomography (MDCT). METHODS AND MATERIALS: Three artificial arteries containing each 3 lesions with varying density were scanned using a moving cardiac phantom at rest and at 50 to 110 beats per minute (bpm) at 10-bpm intervals on a 64-slice MDCT. Images were reconstructed at slice thicknesses (increment) of 0.6 (0.4), 0.75 (0.5), 1.5 (1.5), and 3.0 (3.0) mm. The amount of calcium was expressed as an Agatston score, volume score, and equivalent mass. RESULTS: Absolute coronary artery calcium (CAC) scores decreased [average -37% for low density calcification (LDC)] or increased [average +32% for high density calcification (HDC)] at heart rates over 60 bpm depending on slice thickness and scoring method. Thinner slice thicknesses yielded higher CAC scores. Variability of the CAC scores increased with increasing heart rates especially for low density calcifications (8% at rest vs. 50% at 110 bpm). Variability also increased for thicker slices (average 6% for 0.6 mm vs. 18% for 3.0 mm). Variability was lower for HDC compared with LDC (approximately 5% for HDC vs. 27% for LDC at 70 bpm, averaged over all methods and slice thicknesses). CONCLUSION: CAC-scoring is strongly influenced by cardiac motion, calcification density, and slice thickness. CAC scores increase for high density calcifications and decrease for low density calcifications at increasing heart rates. Heart rate should be reduced on 64-slice MDCT to obtain a lower degree of variability of CAC-scoring, preferably below 70 bpm. A thinner slice thickness further enhances the reproducibility.     

ECG-gated 16-MDCT of the coronary arteries: assessment of image quality and accuracy in detecting stenoses

OBJECTIVE: The aim of this study was to investigate image quality and diagnostic accuracy in detecting coronary artery lesions using a 16-MDCT scanner. MATERIALS AND METHODS: Thirty-seven patients (28 men, nine women) underwent unenhanced helical CT and MDCT angiography of the coronary arteries. After patients received oral beta-blocker medication, CT scans were obtained during a single breath-hold with a 16-MDCT scanner using ECG-gating (0.75-mm collimation, 2.8-mm table feed/rotation, 0.42-sec rotation time). The image quality was assessed in terms of artifacts and segment visibility by two reviewers. Stenosis severity was compared with the results of conventional invasive coronary angiography. RESULTS: The data evaluation of the image quality was based on a total of 488 segments, of which 380 segments were considered to have diagnostic image quality. One hundred eight segments (22.1%) could not be sufficiently evaluated because of severe calcifications (35 segments) and motion artifacts (73 segments). The mean calcium score (Agatston score equivalent [ASE]) was 524.3 +/- 807.6. Twenty-eight (75.7%) of the 37 patients had an ASE of less than 1,000 (mean ASE, 90.8 +/- 152.3 [SD]), and nine (24.3%) patients had an ASE of 1,000 or greater (mean ASE, 1,761.0 +/- 637.6). For detecting lesions 50% or greater (without any exclusion criteria), the overall sensitivity, specificity, positive predictive value, and negative predictive value were 59%, 87%, 61%, and 87%, respectively. When limiting the number of patients to those with a calcium score of less than 1,000 ASE, the threshold-corrected sensitivity for lesions 50% or greater was 93%; specificity, 94%; positive predictive value, 68%; and negative predictive value, 99%. CONCLUSION: In patients with no or moderate coronary calcification, MDCT of coronary arteries using 16-MDCT technology allows the reliable detection of coronary artery stenoses with high diagnostic accuracy. Obtaining an initial unenhanced scan was found to be mandatory to avoid performing useless examinations in patients with severe calcifications.     

Overlapping cross-sections significantly improve the reproducibility of coronary calcium measurements by electron beam tomography: a phantom study

PURPOSE: We conducted phantom studies to investigate whether overlapping cross-sections and volumetric scoring would significantly improve interscan reproducibility of electron beam tomography (EBT) for coronary artery calcium quantification. METHOD: Fifteen phantoms simulating various amounts of coronary calcification were scanned in five different positions with a slice thickness of 3.0 mm and a table feed of 3.0, 2.5, and 2.0 mm. For the conventional "Agatston score" and a "volume score" (total volume of calcified lesions), interscan variabilities were compared between the three image acquisition protocols. RESULTS: Agatston score variability was significantly lower for the 2.0 mm table feed than for the 3.0 or 2.5 mm table feed (3.0 mm: 22.9 +/- 10.3%; 2.5 mm: 13.6 +/- 8.2%; 2.0 mm: 8.9 +/- 5.5%). Volume score variability was significantly lower for 2.5 and 2.0 mm table feed than for 3.0 mm table feed (3.0 mm: 21.7 +/- 11.0%; 2.5 mm: 10.9 +/- 5.9%; 2.0 mm: 9.8 +/- 5.9%). CONCLUSION: Overlapping cross-sections, especially in combination with volumetric scoring, significantly improved interscan reproducibility of EBT calcium quantification in a phantom study.     

Calcium score of small coronary calcifications on multidetector computed tomography: Results from a static phantom study

Introduction

Multi detector computed tomography (MDCT) underestimates the coronary calcium score as compared to electron beam tomography (EBT). Therefore clinical risk stratification based on MDCT calcium scoring may be inaccurate. The aim of this study was to assess the feasibility of a new phantom which enables establishment of a calcium scoring protocol for MDCT that yields a calcium score comparable to the EBT values and to the physical mass.

Materials and methods

A phantom containing 100 small calcifications ranging from 0.5 to 2.0 mm was scanned on EBT using a standard coronary calcium protocol. In addition, the phantom was scanned on a 320-row MDCT scanner using different scanning, reconstruction and scoring parameters (tube voltage 80–135 kV, slice thickness 0.5–3.0 mm, reconstruction kernel FC11–FC15 and threshold 110–150 HU). The Agatston and mass score of both modalities was compared and the influence of the parameters was assessed.

Results

On EBT the Agatston and mass scores were between 0 and 20, and 0 and 3 mg, respectively. On MDCT the Agatston and mass scores were between 0 and 20, and 0 and 4 mg, respectively. All parameters showed an influence on the calcium score. The Agatston score on MDCT differed 52% between the 80 and 135 kV, 65% between 0.5 and 3.0 mm and 48% between FC11 and FC15. More calcifications were detected with a lower tube voltage, a smaller slice thickness, a sharper kernel and a lower threshold. Based on these observations an acquisition protocol with a tube voltage of 100 kV and two reconstructions protocols were defined with a FC12 reconstruction kernel; one with a slice thickness of 3.0 mm and a one with a slice thickness of 0.5 mm. This protocol yielded an Agatston score as close to the EBT as possible, but also a mass score as close to the physical phantom value as possible, respectively.

Conclusion

With the new phantom one acquisition protocol and two reconstruction protocols can be defined which produces Agatston scores comparable to EBT values and to the physical mass.     

Effect of varying slice thickness on coronary calcium scoring with multislice computed tomography in vitro and in vivo

OBJECTIVES: To compare coronary calcium scoring results (calcium volume, calcium mass, Agatston score, and number of lesions) of different slice thicknesses using a 16-slice CT (MSCT) scanner. MATERIALS AND METHODS: A nonmoving anthropomorphic thorax phantom with calcium cylinders of different sizes and densities was scanned 30 times with repositioning applying a standardized retrospectively ECG-gated MSCT (SOMATOM Sensation 16; Siemens, Forchheim, Germany) scan protocol: collimation 12 x 0.75 mm, tube voltage 120 kV, effective tube current time-product 133 mAs(eff). Fifty patients (29 male; age 57.2 +/- 8.4 years) underwent a nonenhanced scan applying the same scan protocol. Two image sets (effective slice thicknesses 3 mm and 1 mm) were reconstructed at 60% of the RR interval. Image noise was measured in both studies. Calcium volume, calcium mass and Agatston score were calculated using a commercially available software tool. RESULTS: Due to increased image noise in thinner slices, calcium scoring in all scans was performed applying a scoring threshold of 350 HU. In the phantom study, 1-mm slices showed significantly higher scoring results in respect to calcium volume (+8.2%), calcium mass (+12.5%), and Agatston score (+5.3%) (all P < 0.0001). In the patient study, 27 patients had coronary calcifications in 3-mm slices, and 31 patients had coronary calcifications in 1-mm slices. Thinner slices showed significantly higher scoring results in respect to volume (+47.1%), mass (+47.2%), and Agatston score (+29.7%) (all P < 0.0001). CONCLUSIONS: When comparing 3-mm and 1-mm slices in coronary calcium scoring in MSCT, thinner slices lead to significantly increased scoring results.     

Variability of coronary calcium scores throughout the cardiac cycle: implications for the appropriate use of electrocardiogram-dose modulation with retrospectively gated computed tomography

OBJECTIVE: To study how much the calcium scores at various phases throughout the cardiac cycle deviate from the score in the most motionless phase during retrospectively electrocardiogram (ECG)-gated multidetector row computed tomography (MDCT) of the heart and to evaluate how to optimize ECG-based tube current modulation so that errors in calcium scoring can be minimized while dose savings can be maximized. MATERIALS AND METHODS: In 73 subjects with known or suspected coronary artery disease we performed retrospectively ECG-gated 64-detector row computed tomography for calcium scoring. Four subjects were excluded after scanning because of breathing artifacts or lack of coronary calcification. The scans of 69 subjects (46 men, mean age 62 +/- 6 years) were used for further analysis. Heart rate during the scan was recorded. In each patient, calcium scoring [Agatston score (AS), mass score (MS), and volume score, (VS)] was performed on 10 data sets reconstructed at 10%-intervals throughout the cardiac cycle. The most motionless phase was subjectively determined and used as the reference phase. For the score in each phase, deviation from the score in the reference phase was determined. An ECG-simulator was used to determine the amount of dose saving while scanning with dose modulation and applying diagnostic dose during 1 or several phases. RESULTS: Mean heart rate was 63 (+/-13) beats per minute (bpm). In 51% of patients the reference phase was the 70% phase. Using the calcium score in the 70% phase (mid-diastole) instead of the reference at heart rates below 70 bpm would have induced a median score deviation of 0% [interquartile range: 0%-6% (AS, MS, and VS)] and using the calcium score in the 40% phase (end-systole) at heart rates > or =70 bpm would also have induced a median score deviation of 0% [interquartile range: 0%-7% (AS), 0%-5% (MS), and 0%-3% (VS)]. Errors in calcium scores of more than 10% occur in around 10% of subjects for all 3 scoring algorithms. Dose savings increased with lower heart rates and shorter application of diagnostic dose. CONCLUSIONS: The optimum phases for dose modulation are 70% (mid-diastole) at heart rates below 70 bpm and 40% (end-systole) at heart rates above 70 bpm. Under these conditions dose saving is maximum and a median error of 0% is found for the various calcium scoring techniques with score errors of more than 10% in around 10% of subjects.     

Variation of the coronary calcium score depending on image reconstruction interval and scoring algorithm

RATIONALE AND OBJECTIVES: To evaluate the reconstruction interval dependent bandwidth of the coronary calcium score, considering different methods of image reconstruction and quantification of coronary calcifications. MATERIALS AND METHODS: Seventy-five patients underwent coronary calcium scoring by use of retrospectively ECG-gated multislice spiral CT. In all patients overlapping and nonoverlapping image reconstruction was performed every 10% of the RR-interval. Coronary calcium score was calculated for every reconstructed image series using the Agatston score and a volumetric scoring method. In 25 patients the analysis was performed twice to determine the reconstruction interval dependent intraobserver variability. RESULTS: For nonoverlapping image reconstruction the median of the calcium score determined by the Agatston method ranged from 125.8 to 216.2 and from 166.9 to 211.7 for the volumetric scoring method. For overlapping image reconstruction the corresponding values ranged from 91.6 to 160.5 for the Agatston score and 128.3 to 175.3 for the volumetric calcium score. Reconstruction interval dependent median (mean) variation of the coronary calcium score ranged from 24.1 (45.5)% for nonoverlapping image reconstruction using the Agatston score to 17.5 (25.2)% utilizing a volumetric calcium score with overlapping image reconstruction. There was no statistical significant (P< 0.05) difference between the different methods. Intraobserver variability for the different image reconstruction intervals ranged from 0.78% to 21.51%. The least intraobserver variability was found for overlapping image reconstruction during the diastole using the volumetric scoring method. CONCLUSIONS: Diastolic image reconstruction at 50% or 60% of the RR-interval is recommendable for retrospectively ECG-gated multislice spiral CT. Volumetric calcium scoring and overlapping image reconstruction are beneficial to reduce the variation of the coronary calcium score.     

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.     

Controversies about effects of low-kilovoltage MDCT acquisition on Agatston calcium scoring

Recent articles have advocated the possibility of obtaining Agatston coronary calcium scoring at 100 kVp by using a single adapted elevated calcium threshold. To evaluate the influence of kilovoltage potential protocols on the Agatston score, we acquired successive scans of a calcium scoring phantom at 4 levels of kilovoltage potential (80, 100, 120, and 140 kVp, 55 mAs) and measured semiautomatically the individual and the total Agatston score of 6 inserts (of 5-mm and 3-mm diameter) containing hydroxyapatite at different concentrations (800, 400, 200 mg/cm³). Our results showed that Agatston scores obtained at various low-kilovoltage potential protocols can be highly overestimated in some particular cases. At 80 kVp, for example, mean measured Agatston score was multiplied by a factor from 1.06 (5-mm highest density insert) to 2.67 (3-mm lowest density insert) compared with the Agatston scores performed at 120 kVp. Indeed in the one hand, reducing kilovoltage potential in multidetector CT acquisitions increase the CT density of coronary calcifications that can be measured on the reconstructed images. On the other hand, Agatston score is a multi-threshold measurement (with a step weighting function). Consequently low kilovoltage potential can lead to overweight some calcifications scores. For these reasons, Agatston score with low kilovoltage potential acquisition cannot be reliably adapted by a unique recalibration of the standard calcium attenuation threshold of 130 HU and requires a standardized CT acquisition protocol at 120 kVp. Alternatives to performing low-dose coronary artery calcium scans are either using coronary calcium scans with reduced tube current (low mAs) at 120 kVp with the iterative reconstructions or using mass/volume scoring (not influenced by kilovoltage potential variations). Finally, we emphasized that incorrect Agatston score evaluation may have important clinical, financial, and health care implications.     

Electron beam CT versus 16-MDCT on the variability of repeated coronary artery calcium measurements in a variable heart rate phantom

OBJECTIVE: High reproducibility of coronary artery calcium (CAC) scoring is a key requirement for monitoring the progression of coronary atherosclerosis. The purposes of this study were to compare electron beam CT and 16-MDCT scanners in the variability of repeated CAC measurements and to assess the factors influencing this variability. MATERIALS AND METHODS: CAC models of different sizes attached to a cardiac phantom with a programmable variable heart rate were scanned three times, and interscan variability of the CAC measurement was calculated each time. For helical CT, different slice-thickness images of either retrospective ECG-gated or prospective ECG-triggering reconstruction were obtained. The detection of small amounts of calcium, variability of the Agatston score, and CAC measurement algorithms (Agatston, volume, and mass scores) were compared between CT scanners and protocols. RESULTS: All 1-mm-sized calcium models were detected on 0.625- and 1.25-mm helical CT, whereas some were missed on electron beam CT and 2.5-mm helical CT. Retrospective ECG-gated thin-slice helical CT showed the lowest variability. Reduction of variability by volume and mass scoring algorithms was less effective on 0.625- and 1.25-mm-thickness CT. CONCLUSION: Retrospective ECG-gated thin-slice helical CT has the potential to be a useful tool for monitoring coronary atherosclerosis.     

Evaluation of reconstruction windows for multislice computed tomography in quantification of coronary calcium

RATIONALE AND OBJECTIVES: To search for an optimum reconstruction window in retrospectively gated multislice computed tomography (MSCT) for quantification of coronary calcium. MATERIALS AND METHODS: Coronary calcium quantified was examined as Agatston and volume scores by two experienced observers at 10 time points across the R-R interval of the electrocardiogram in 42 patients. A combination of statistical approaches was used to evaluate the distributions of minimum and maximum scores and of interobserver variability for both scoring methods across the cardiac cycle. RESULTS: Based on the combination of evaluation approaches, 60% to 70% of the R-R interval appeared to be the optimum time point for obtaining maximum calcium scores with minimum interobserver variability. The optimum time point was more clearly defined for the Agatston score than for the volume score. CONCLUSION: A reconstruction window beginning at 60% to 70% of the R-R interval seems to be most advantageous for retrospective gating of MSCT studies performed to quantify coronary calcium.     

A method for calcium quantification by means of CT coronary angiography using 64-multidetector CT: very high correlation with agatston and volume scores

To find out whether calcium scoring of the coronary arteries (CAC scoring) could be carried out with a CT angiography of the coronary arteries (CTCA) in a single CT data acquisition. The Agatston and V130 scores for 113 patients were assessed. A calcium volume score (V600 score) was compiled from the CTCA data sets. Intra- and interobserver correlations were excellent (ρ > 0.97). The intra- and interobserver repeatability coefficients were extremely low, increasing in magnitude from the V600 score to the V130 and Agatston scores. The V600 score underestimates the coronary calcium burden. However, it has a linear relation to the Agatston and V130 scores. Thus, they are predictable from the values of the V600 score. The V600 score shows a linear relation to the classic CAC scores. Due to its extremely high reliability, the score may be a feasible alternative for classic CAC scoring methods in order to reduce radiation dosages.