Variability of Repeated Coronary Artery Calcium Measurements by 16-MDCT with Retrospective Reconstruction

Impact of combined assessment of coronary artery calcium score, carotid artery plaque score, and brachial-ankle pulse wave velocity for early coronary revascularization in patients with suspected coronary artery disease

Coronary artery calcium score (CACS) measured by multi-detector computed tomography, carotid plaque score (CPS) measured by carotid artery ultrasound, and brachial-ankle pulse wave velocity (baPWV) are noninvasive screening tools for coronary artery disease. The aim of this study was to determine whether the combination of CACS, CPS, and baPWV improves the prognostic value for future cardiac events. CACS, CPS, and baPWV were assessed in 77 patients (mean age, 65 years, 49 males) undergoing invasive coronary angiography. ECG-triggered MSCT was used to assess CACS. CPS was defined as the sum of all plaque heights in bilateral carotid arteries. The highest baPWV was used for analysis. Cardiac events were defined as cardiac death, nonfatal myocardial infarction, or coronary revascularization. Thirty-two cardiac events (41.6%) occurred during follow-up (23.6 ± 20.8 months), consisting of 28 PCIs and 4 CABGs. The best cutoff values of positive CACS, CPS, and baPWV for predicting cardiac events were ≥ 50, ≥ 5, and ≥1.6 m/second, respectively. For the combination of the 3 modalities, the positive test was defined as having at least 1 positive result by each method. The negative predictive value of all 3 modalities combined was better than that of CACS alone. The event-free rate was higher in patients with negative results for all 3 parameters compared with those that were positive (100% versus 44.8%, P < 0.0001). The prognostic value of using combined assessment of CACS, CPS, and baPWV is more effective for predicting cardiac events than CACS alone.

Coronary artery calcification and coronary ischaemia in renal transplant recipients

BACKGROUND

Cardiovascular disease is the leading cause of mortality among renal transplant recipients. Data on the relationship between coronary artery calcification (CAC) and coronary ischaemia in renal transplantation patients are scant. We conducted a study to determine the prevalence and determinants of CAC in these patients; we also examined the frequency of coronary ischaemia in patients with moderate and severe CAC.

METHODS

We used multi-detector spiral computed tomography to examine CAC in 178 consecutive renal transplant recipients. Angina pectoris was sought with the Rose questionnaire. The extent of calcification was measured by Agatston score. Myocardial perfusion scintigraphy was performed in patients with moderate and severe CAC. Multivariate logistic and linear regression analysis was used to evaluate the determinants of CAC presence and CAC score, respectively.

RESULTS

CAC was present in 72 patients (40.4%), mean CAC score was 113.7±275.5 (median: 0 and range: 0-1712). Age, time on transplantation and Rose angina pectoris were the independent determinants of both CAC presence and high CAC scores in all multivariate models. Coronary ischaemia was detected in 17.1% of the patients with moderate-to-severe CAC.

CONCLUSIONS

CAC is highly prevalent in renal transplant recipients; it is associated with symptoms of coronary ischaemia. Time on transplantation is an independent determinant of CAC. Future studies to evaluate the prognostic significance of CAC in these patients are necessary.

Evaluation of attenuation-based tube current control in coronary artery calcium scoring on prospective ECG-triggered 64-detector CT

RATIONALE AND OBJECTIVES

The aims of this study were to investigate image noise (standard deviation of computed tomographic value) and to assess variability in repeated coronary artery calcium (CAC) scoring on prospective electrocardiographically triggered 64-detctor computed tomography.

MATERIALS AND METHODS

Patients (n = 428) suspected of having coronary artery disease were scanned twice using three protocols: with tube current modified by body mass index (BMI; group A), by BMI and body height (group B), and by attenuation at the maximal heart diameter (group C). Image noise was plotted against BMI. Interscan variability of CAC scores was determined. The effective dose was estimated by computed tomographic dose index.

RESULTS

The mean effective dose and image noise, respectively, were 0.9 +/- 0.2 mSv (range, 0.6-1.5 mSv) and 19 +/- 4 Hounsfield units (HU) (range, 10-32 HU) for group A; 0.8 +/- 0.2 mSv (range, 0.5-1.4 mSv) and 18 +/- 4 HU (range, 10-31 HU) for group B; and 0.8 +/- 0.4 mSv (range, 0.3-2.2 mSv) and 20 +/- 2 HU (range, 16-26 HU) for group C. Group C used a wide dose range and controlled noise within a small range. The positive slopes of image noise versus BMI, 0.81 HU/(kg/m(2)) in group A and 0.62 HU/(kg/m(2)) in group B, suggested insufficient control of the tube current. In contrast, the nearly flat slope in group C, 0.091 HU/(kg/m(2)), indicated optimal control. The interscan variability for Agatston score, volume, and mass in patients with CAC (n = 300) was 13% (median, 8%), 12% (median, 7%), and 11% (median, 6%), respectively.

CONCLUSIONS

CAC scoring on prospective electrocardiographically triggered 64-detector computed tomography using attenuation-based tube current control has the potential to favorably control image noise with low dose and low interscan variability.

Coronary artery calcium scoring on low-dose prospective electrocardiographically-triggered 64-slice CT

RATIONALE AND OBJECTIVES

The purpose of this prospective study was to assess image noise and variability in repeated coronary artery calcium (CAC) scoring on low-dose prospective electrocardiographically-triggered 64-slice multidetector computed tomography.

MATERIALS AND METHODS

Patients (n = 115) suspected of having coronary artery disease were scanned twice, using a tube current of 10 x body mass index mA. The standard deviation (SD) of the computed tomographic value in the ascending aorta and (mean + 2 x SD) were obtained. Repeated CAC scores (Agatston, volume, and mass) were measured by two observers, and the interscan and interobserver variability were determined.

RESULTS

The mean tube current used was 246 +/- 36 mA. The mean tube current-time product and mean estimated effective dose were 57 +/- 8 mA and 0.9 +/- 0.2 mSv, respectively. The SD and (mean + 2 x SD) computed tomographic values in the ascending aorta were 16 +/- 3 and 75 +/- 10 Hounsfield units, respectively. Repeated CAC scores were correlated (r(2) = 0.995-0.998). The interscan variability for observer 1 and observer 2, respectively, were 13% and 13% for Agatston score, 12% and 11% for volume, and 11% and 11% for mass. The interobserver variability for scan 1 and scan 2, respectively, were 3% and 3% for Agatston score, 5% and 3% for volume, and 3% and 3% for mass.

CONCLUSION

Low-dose prospective electrocardiographically-triggered 64-slice multidetector computed tomography shows low interscan and interobserver variability on CAC scoring while maintaining low image noise.

Variability of repeated coronary artery calcium scoring and radiation Dose on 64- and 16-slice computed tomography by prospective electrocardiographically-triggered axial and retrospective electrocardiographically-gated spiral computed tomography: a phantom study

RATIONALE AND OBJECTIVES

We sought to compare coronary artery calcium (CAC) scores, the variability and radiation doses on 64- and 16-slice computed tomography (CT) scanners by both prospective electrocardiographically (ECG)-triggered and retrospective ECG-gated scans.

MATERIALS AND METHODS

Coronary artery models (n = 3) with different plaque CT densities (approximately 240 Hounsfield units [HU], approximately 600 HU, and approximately 1000 HU) of four sizes (1, 3, 5, and 10 mm in length) on a cardiac phantom were scanned three times in five heart rate sequences. The tube current-time products were set to almost the same on all four protocols (32.7 mAs for 64-slice prospective and retrospective scans, 33.3 mAs for 16-slice prospective and retrospective scans). Slice thickness was set to 2.5 mm to keep the radiation dose low. Overlapping reconstruction with a 1.25-mm increment was applied on the retrospective ECG-gated scan.

RESULTS

The CAC scores were not different between the four protocols (one-factor analysis of variance: Agatston, P = .32; volume, P = .19; and mass, P = .09). Two-factor factorial analysis of variance test revealed that the interscan variability was different between protocols (P < .01) and scoring algorithms (P < .01). The average variability of Agatston/volume/mass scoring and effective doses were as follows: 64-slice prospective scan: 16%/15%/11% and 0.5 mSv; 64-slice retrospective scan: 11%/11%/8% and 3.7 mSv; 16-slice prospective scan: 20%/18%/13% and 0.6 mSv; and 16-slice retrospective scan: 16%/15%/11% and 2.9 to 3.5 mSv (depending on the pitch).

CONCLUSION

Retrospective ECG-gated 64-slice CT showed the lowest variability. Prospective ECG-triggered 64-slice CT, with low radiation dose, shows low variability on CAC scoring comparable to retrospective ECG-gated 16-slice CT.

Optimal cardiac phase for coronary artery calcium scoring on single-source 64-MDCT scanner: least interscan variability and least motion artifacts

OBJECTIVE

The purpose of our study was to investigate the cardiac phase with the least interscan variability and motion artifacts on coronary artery calcium studies using a 64-MDCT scanner.

SUBJECTS AND METHODS

Ninety-one patients with suspected coronary artery disease were scanned twice on retrospective ECG-gated helical scans. Images with 2.5-mm thickness and 1.25-mm interval at nine cardiac phases (center of cardiac phase: 40-80% in 5% increments) were reconstructed. The interscan variability of coronary artery scores (Agatston, volume, and mass) per patient and motion artifact scores per branch, subjectively assigned by motion artifact grading (1, none; 2, minor; and 3, major), were compared between cardiac phases for all patients, low (< 65 beats per minute [bpm]) and high (>or= 65 bpm) heart rate patient groups.

RESULTS

For all patients, two-factor factorial analysis of variance revealed that the interscan variability was different between cardiac cycles (p < 0.01); however, this was not statistically significant between scoring algorithms (p = 0.46). The least variability was obtained at 70% on Agatston (8%) and volume (7%) and at 75% on mass (7%). Adjacent categories logit model analysis revealed that the motion artifact score was the least at 75% (left anterior descending coronary artery, 1.3; left circumflex coronary artery, 1.4; and right coronary artery, 1.9 in all patients) and that a smaller difference in calcium scores between the scans led to a smaller motion artifact score (p < 0.05).

CONCLUSION

Middiastole reconstruction (center of cardiac phase: 70-75%), with the least interscan variability and the least motion artifacts, is recommended on 64-MDCT.

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.

Coronary arterial calcification on low-dose ungated MDCT for lung cancer screening: concordance study with dedicated cardiac CT

OBJECTIVE

Coronary artery calcification (CAC) is frequently detected on low-dose ungated MDCT performed for lung cancer screening. We aimed to determine the concordance of CAC scores on low-dose ungated and regular-dose ECG-gated MDCT.

SUBJECTS AND METHODS

The subjects were 513 patients consecutively registered for health screening and undergoing both low-dose ungated (120 kVp, 20 mAs) and regular-dose ECG-gated MDCT (120 kVp, 150 mAs, retrospective ECG gating). The first 30 cases were used for protocol optimization and a training session. Agatston score on regular-dose ECG-gated and low-dose ungated MDCT in the other 483 cases (320 men; mean age, 62.2 +/- 13.2 [SD] years) was calculated by two observers in a blinded manner. Interobserver and intertechnique scoring variability and concordance were calculated.

RESULTS

The mean of interobserver scoring variability for regular-dose ECG-gated MDCT was 3.6% and for low-dose ungated MDCT was 9.6%. Regular-dose ECG-gated MDCT depicted CAC in 221 (46%) of the subjects. With low-dose ungated MDCT, observers 1 and 2, respectively, had five and seven false-positive and five and four false-negative predictions. All the miscategorized scores were 12 or less. The negative predictive values of CAC on low-dose ungated MDCT were 98% and 99% for observers 1 and 2, respectively. For patients with CAC, the mean intertechnique scoring variability was 40-43%. For all 483 subjects, the intertechnique concordance of the four major score ranks (0, 1-100, 101-400, > 400) was high (kappa = 0.89 for the two observers).

CONCLUSION

Low-dose ungated MDCT with an optimized protocol is reliable for prediction of the presence of CAC and categorization of the four major Agatston score ranks. This technique may be useful for coronary artery disease risk stratification of persons undergoing low-dose ungated MDCT for lung cancer screening.

Coronary artery calcification scores in patients with chronic kidney disease prior to dialysis: reliability as a trial outcome measure

BACKGROUND

Coronary artery calcification (CAC) is prevalent in patients with chronic kidney disease (CKD). Data on the reliability and validity of high-resolution computerized tomography (HRCT) in patients with CKD is lacking. The purpose of this study was to evaluate the inter- and intra-reviewer agreement and inter-scan reproducibility of CACS measurement with HRCT in a cohort of patients with CKD prior to dialysis, and to compare the change in CACS at 30 minutes to the change in CACS over 1 year.

METHODS

Thirty-three patients with CKD not yet on dialysis underwent an HRCT scan at baseline and 1 year to assess for CAC and CAC progression. Two radiologists independently reviewed films and each radiologist re-reviewed a randomly selected subset of films they had previously viewed, to assess for inter-reviewer and intra-reviewer reliability, respectively. Patients underwent a repeat scan within 30 min of the first baseline scan to assess for inter-scan reproducibility.

RESULTS

At baseline, eight patients (24%) had no CAC. Of the 25 patients (76%) with CAC, 10 (40%) had severe calcification. Intra-reviewer agreement was 83%. Inter-reviewer agreement ranged between 77 and 94%. Six (27%) of the patients with >30 baseline CACS had >15% change in CACS following repositioning. Four of these patients had an increase in CACS with position change [18% (95% CI: 5-40%)]. Of the 21 patients who underwent a follow-up scan at 1 year, 7 (33%) demonstrated CACS progression.

CONCLUSIONS

There is significant imprecision in HRCT-derived CACS in CKD patients. This suggests a need for standardization of methods of CACS measurement with HRCT.

Calcium scoring using 64-slice MDCT, dual source CT and EBT: a comparative phantom study

Purpose Assessment of calcium scoring (Ca-scoring) on a 64-slice multi-detector computed tomography (MDCT) scanner, a dual-source computed tomography (DSCT) scanner and an electron beam tomography (EBT) scanner with a moving cardiac phantom as a function of heart rate, slice thickness and calcium density. Methods and materials Three artificial arteries with inserted calcifications of different sizes and densities were scanned at rest (0 beats per minute) and at 50–110 beats per minute (bpm) with an interval of 10 bpm using 64-slice MDCT, DSCT and EBT. Images were reconstructed with a slice thickness of 0.6 and 3.0 mm. Agatston score, volume score and equivalent mass score were determined for each artery. A cardiac motion susceptibility (CMS) index was introduced to assess the susceptibility of Ca-scoring to heart rate. In addition, a difference (Δ) index was introduced to assess the difference of absolute Ca-scoring on MDCT and DSCT with EBT. Results Ca-score is relatively constant up to 60 bpm and starts to decrease or increase above 70 bpm, depending on scoring method, calcification density and slice thickness. EBT showed the least susceptibility to cardiac motion with the smallest average CMS-index (2.5). The average CMS-index of 64-slice MDCT (9.0) is approximately 2.5 times the average CMS-index of DSCT (3.6). The use of a smaller slice thickness decreases the CMS-index for both CT-modalities. The Δ-index for DSCT at 0.6 mm (53.2) is approximately 30% lower than the Δ-index for 64-slice MDCT at 0.6 mm (72.0). The Δ-indexes at 3.0 mm are approximately equal for both modalities (96.9 and 102.0 for 64-slice MDCT and DSCT respectively). Conclusion Ca-scoring is influenced by heart rate, slice thickness and modality used. Ca-scoring on DSCT is approximately 50% less susceptible to cardiac motion as 64-slice MDCT. DSCT offers a better approximation of absolute calcium score on EBT than 64-slice MDCT when using a smaller slice thickness. A smaller slice thickness reduces the susceptibility to cardiac motion and reduces the difference between CT-data and EBT-data. The best approximation of EBT on CT is found for DSCT with a slice thickness of 0.6 mm.

Coronary calcification: effect of small variation of scan starting position on Agatston, volume, and mass scores

PURPOSE

To retrospectively evaluate the effect of a small variation of scan starting position on coronary artery calcium scores based on nonoverlapping 3-mm multidetector computed tomographic (CT) data sets.

MATERIALS AND METHODS

Informed consent and institutional review board approval were obtained. A retrospective study was performed by using prospective unenhanced electrocardiographically triggered cardiac multidetector CT scans in 228 women (mean age, 67 years +/- 5 [standard deviation]). From the original 1.5-mm data set, two sets of adjacent images with a section thickness of 3 mm and a variation in starting point of 1.5 mm were obtained. Calcium scoring was performed to acquire Agatston, volume, and mass scores. Subjects were assigned to one of five risk categories (I-V) according to the Agatston score of each 3-mm data set and the average score. Kappa value was calculated to assess agreement in risk category assignment. Differences and relative differences between scores obtained for both 3-mm data sets were calculated overall and according to risk category. The effect of scoring algorithm on the relative differences between scores was analyzed with the Wilcoxon signed rank test.

RESULTS

Categories I-V contained 102, 35, 48, 31, and 12 subjects, respectively. For all scoring algorithms, median relative differences decreased from more than 130% in category II to less than 10% in category V. In the three highest categories, relative differences were significantly smaller for volume and mass scores than for Agatston scores (P < .05). Twenty-one subjects were assigned to different risk categories between the two data sets (kappa = 0.87). Eleven patients were assigned a nonzero score in one and a zero score in the other data set.

CONCLUSION

A small variation in scan starting position can substantially influence calcium measurements and poses an inherent limit to calcium scoring with contiguous 3-mm sections. Mass and volume scores are slightly less affected than are Agatston scores.

Variability of repeated coronary artery calcium measurements by 1.25-mm- and 2.5-mm-thickness images on prospective electrocardiograph-triggered 64-slice CT

High reproducibility on coronary artery calcium scoring is a key requirement in monitoring the progression of coronary atherosclerosis. The purpose of this prospective study is to assess the reproducibility of 1.25-mm- and 2.5-mm-thickness images on prospective electrocardiograph-triggered 64-slice CT with respect to 2.5-mm-thickness images on spiral overlapping reconstruction. One hundred patients suspected of coronary artery disease were scanned twice repeatedly, both on prospective electrocardiograph-triggered step-and-shoot and retrospective electrocardiograph-gated spiral scans. Using 1.25-mm-thickness collimation, 1.25-mm- and 2.5-mm-thickness image sets on prospective scans and 2.5-mm-thickness image sets with 1.25-mm increment (overlapping) on retrospective scans were obtained. Coronary artery calcium scores, interscan variability and interobserver variability were evaluated. The mean interscan variability in coronary artery calcium measurement on 1.25-mm prospective/2.5-mm prospective/2.5-mm overlapping retrospective scans were Agatston: 10%/18%/12%, volume: 10%/12%/10% and mass: 8%/13%/11% for observer 1 and Agatston: 8%/14%/10%, volume: 7%/9%/10% and mass: 7%/10%/9% for observer 2, respectively. The mean interobserver variability was 5% to 14%. In conclusion, prospective electrocardiograph-triggered 64-slice CT using the 1.25-mm prospective scan shows the lowest variability. The 2.5-mm prospective scan on volume or mass scoring shows variability of around 10%, comparable to 2.5-mm-thickness spiral overlapping reconstruction images.

Evaluation of the influence of acquisition and reconstruction parameters for 16-row multidetector CT on coronary calcium scoring using a stationary and dynamic cardiac phantom

A calcium-scoring phantom with hydroxyapatite-filled cylindrical holes (0.5 to 4 mm) was used. High-resolution scans were performed for an accuracy baseline. The phantom was mounted to a moving heart phantom. Non-moving data with the implementation of an ECG-signal were acquired for different pitches (0.2/0.3), heart rates (60/80/95 bpm) and collimations (16 x 0.75/16 x 1.5 mm). Images were reconstructed with a cone-beam multi-cycle algorithm at a standard thickness/increment of 3 mm/1.5 mm and the thinnest possible thickness (0.8/0.4 and 2/1). Subsequently, ECG-gated moving calcium-scoring phantom data were acquired. The calcium volume and Agatston score were measured. The temporal resolution and reconstruction cycles were calculated. High-resolution scans determine the calcium volume with a high accuracy (mean overestimation, 0.8%). In the non-moving measurements, the volume underestimation ranged from about 6% (16 x 0.75 mm; 0.8/0.4 mm) to nearly 25% (16 x 1.5 mm; 3/1.5 mm). Moving scans showed increased measurement errors depending on the reconstructed RR interval, collimation, pitch, heart rate and gantry rotation time. Also, a correlation with the temporal resolution could be found. The reliability of calcium-scoring results can be improved with the use of a narrower collimation, a lower pitch and the reconstruction of thinner images, resulting in higher patient doses. The choice of the correct cardiac phase within the RR interval is essential to minimize measurement errors.

Coronary Artery Calcification and Chronically Decreased GFR in Living Kidney Donors

BACKGROUND

In the presence of decreased glomerular filtration rate (GFR), the risk of morbidity and mortality caused by cardiovascular disease (CVD) is increased markedly. Increased coronary artery calcification (CAC) is proposed as a pathogenetic link between CVD and chronic kidney disease. We examined the frequency and severity of CAC in living kidney donors to test the hypothesis that decreased GFR is associated with increased CAC.

METHODS

We used multidetector spiral computed tomography to examine CAC in 101 living kidney donors and 99 age- and sex-matched healthy control subjects without diabetes and a history of coronary artery disease. The extent of calcification was measured by means of the Agatston score. GFR was calculated by using the abbreviated Modification of Diet in Renal Disease formula. The frequency of risk factors for coronary artery disease was compared in kidney donors and controls, and the relation between kidney donors' clinical characteristics and the presence or absence of CAC was examined.

RESULTS

CAC frequency and mean calcification scores were similar between kidney donors (13.9%; 4.5 +/- 22.6) and controls (17.2%; 13.2 +/- 89.2). CAC was not associated with decreased GFR, and the correlation between CAC and GFR was not statistically significant. Kidney donors with calcification were more likely to be older (P = 0.003) and male (P = 0.001). Age- and sex-adjusted analysis showed an association between greater parathormone levels (odds ratio, 1.023; 95% confidence interval, 1.001 to 1.045; P = 0.037) and CAC in kidney donors.

CONCLUSION

A mild decrease in GFR without the presence of diabetes does not seem to be associated with increased CAC. These findings need to be confirmed in different and larger study populations.

Coronary artery calcifications: a critical assessment of imaging techniques

The presence of coronary artery calcifications is a distinct marker of atherosclerosis and the severity of calcifications is claimed to reflect a patient's individual plaque burden. Calcium deposits can be detected non-invasively by cardiac computed tomography (CT). This enables detection of coronary artery disease in a subclinical stage, description of the extent of the disease and risk estimation of future cardiovascular events. However, calcium quantification may also be used to monitor atherosclerotic disease, for example in the context of an intensified medical treatment. For years, electron-beam CT has been considered the gold-standard for calcium scoring. However, multi-slice spiral CT has recently captured the market and seems to achieve better measuring results with regard to the accuracy and reproducibility of calcium scores because of its superior image quality. For an optimal comparability of different CT techniques the calcium load should now be reported as absolute calcium mass rather than the traditional scoring methods.

Variability of Repeated Coronary Artery Calcium Measurements on Low-Dose ECG-Gated 16-MDCT

OBJECTIVE

High reproducibility on coronary artery calcium (CAC) scoring is a key requirement in monitoring the progression of coronary atherosclerosis. Retrospective ECG-gated helical CT has been shown to be superior to prospective gating helical CT in the reproducibility of CAC measurements. However, it brings with it a high level of radiation exposure. The purpose of this study was to compare low- and standard-dose protocols in the variability of CAC scores and in image quality, thereby assessing the feasibility of low-dose retrospective ECG-gated helical CT in CAC measurements.

SUBJECTS AND METHODS

Eighty-six patients with CAC were scanned using a tube current setting of 100 mA once and then a tube current setting equivalent to the patient's body weight twice. CAC scores (Agatston and volume) and interscan variability were evaluated. The mean and SD of the CT attenuation values in regions of interest in the aorta were measured, and the value (mean + 2 x SD) was obtained.

RESULTS

A high correlation of log(10) (Agatston score + 1) was observed between sequential helical CT scans (r = 0.998). The variability in CAC measurements ranged from 11% to 12% for both the Agatston and volume scores. With the tube current equivalent to body weight, the value (mean + 2 x SD) did not exceed a CT attenuation value of 130 H.

CONCLUSION

Low-dose retrospective ECG-gated helical CT-yielding low variability and achieving the level of image quality needed to measure CAC-can be used to monitor patients with coronary atherosclerosis.

The impact of motion artifacts on the reproducibility of repeated coronary artery calcium measurements

The purpose of this study is, using a 16-section multidetector-row helical computed tomography (MDCT) scanner with retrospective reconstruction, to compare variability in repeated coronary calcium scoring and qualitative scores of the motion artifacts. One hundred forty-four patients underwent two subsequent scans using MDCT. According to Agatston and volume algorithms, the coronary calcium scores during mid-diastole (the center corresponding to 70% of the R-R cycle) were calculated and the inter-scan variability was obtained. Motion artifacts from coronary artery calcium were subjectively evaluated and classified using a 5-point scale: 1, excellent; no motion artifacts; 2, fine, minor motion artifacts; 3, moderate, mild motion artifacts; 4, bad, severe motion artifacts; 5, poor, doubling or discontinuity. Each reading was done by vessels (left main, left descending, left circumflex and right coronary arteries) and the motion artifact score (mean of the scales) was determined per patient. The variability in the low (1.2+/-0.2) and high (2.4+/-0.6) motion artifact score groups was 7+/-6 (median, 6)% and 19+/-15 (16)% on the Agatston score (P<0.01) and 7+/-7 (6)% and 16+/-13 (14)% on the volume score (P<0.01), respectively. In conclusion, motion has a significant impact on the reproducibility of coronary calcium scoring.

Non-Coronary Cardiac CT Imaging

Cardiac multidetector CT (MDCT) has moved from purely anatomic imaging, to assessment of cardiac function. Significant advances since the advent of multidetector CT now make it feasible to assess not only the coronary arteries, but also ejection fraction, ventricular volumes, myocardial mass and the presence of wall-motion abnormalities. Advances include improvements in EKG-gating, including improvements in temporal resolution, as well as the addition of delayed contrast-enhanced methods. Anatomic imaging has improved as well, with thinner collimation and better reconstruction methods. Three-dimensional software programs now permit excellent surface rendered displays and multiplanar reconstructions suitable as surgical and procedural "road maps."