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Published online before print September 30, 2004, 10.1148/radiol.2332031470
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(Radiology 2004;233:586-589.)
© RSNA, 2004

Technical Developments

Coronary Artery Calcium Score: Influence of Reconstruction Interval at 16–Detector Row CT with Retrospective Electrocardiographic Gating1

Thomas Schlosser, MD, Peter Hunold, MD, Axel Schmermund, MD, Hilmar Kühl, MD, Kai-Uwe Waltering, MD, Jörg F. Debatin, MD and Jörg Barkhausen, MD

1 From the Departments of Diagnostic and Interventional Radiology (T.S., P.H., H.K., K.U.W., J.F.D., J.B.) and Cardiology (A.S.), University Hospital, Hufelandstr 55, 45122 Essen, Germany. Received September 11, 2003; revision requested November 24; final revision received March 12, 2004; accepted April 19. Address correspondence to J.B. (e-mail: joerg.barkhausen@uni-essen.de).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Materials and Methods
Results
 Discussion
 REFERENCES
 
In 30 patients, Agatston and volumetric scores were assessed by using retrospectively gated multi–detector row computed tomography (CT). For each patient, 10 data sets were created at different times and were evenly spaced throughout the cardiac cycle. For each reconstruction, patients were assigned a percentile that described the level of cardiovascular risk. Nineteen (63%) of 30 patients could be assigned to more than one risk group depending on the reconstruction interval used. Agatston and volumetric scores both proved highly dependent on the reconstruction interval used (coefficient of variation, ≤63.1%) even with the most advanced CT scanners. Accurate and reproducible quantification of coronary calcium seems to require analysis of multiple reconstructions.

© RSNA, 2004

Index terms: Computed tomography (CT), multi–detector row • Coronary vessels, calcification, 54.812 • Coronary vessels, CT, 54.12115 • Coronary vessels, diseases, 54.812


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Materials and Methods
Results
 Discussion
 REFERENCES
 
Coronary artery calcium has emerged as a predictive marker of coronary artery disease, and the extent of coronary calcification correlates with the overall coronary plaque burden (1–3). Agatston et al (4) introduced a method for quantifying coronary artery calcium by multiplying the calcified plaque area by a coefficient based on plaque attenuation values. An alternative volumetric scoring method was developed to reduce the high interscan variability inherent to Agatston scoring; with this alternative method, scoring is determined by using electron-beam computed tomography (CT) (5–7).

Results of several studies have demonstrated a close correlation between the progression of coronary artery disease and increasing calcium scores (8,9). Moreover, lipid-lowering treatment with statins has been shown to reduce coronary calcium progression (10,11). In principle, this provides the opportunity to monitor patients treated with statins and to adjust the dose by quantifying the coronary calcium. This type of follow-up requires accurate and reproducible assessment of coronary calcium.

Electron-beam CT had initially been used for the quantification of coronary artery calcification. Recently, multi–detector row CT with fast gantry rotation has been introduced for cardiac CT. For calcium quantification, a good correlation was found between electron-beam and multi–detector row CT (12). However, different reconstruction and scoring algorithms, as well as different image reconstruction intervals, affect the calculated scores and result in poor reproducibility of measurements (13,14).

Reproducibility may be improved with the recently introduced 16–detector row CT systems with decreased rotation time of 420 msec. Thinner sections decrease partial volume effects, and faster gantry rotations reduce cardiac motion artifacts (15). Thus, the aim of our study was to evaluate the effect of the reconstruction interval on coronary artery calcium scores obtained with use of a 16–detector row CT scanner.


   Materials and Methods
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
 REFERENCES
 
Patients
This study was performed in accordance with all regulations of the local institutional review board, and all patients gave written informed consent. A total of 32 patients (age range, 39–78 years; mean age [±standard deviation], 58.3 years ± 9.3) known to have or suspected of having coronary artery disease were included in the study. There were 28 men (age range, 39–78 years; mean age, 57.9 years ± 9.1) and four women (age range, 59–67 years; mean age, 62.1 years ± 5.6). The age between these groups was not significantly different (Mann-Whitney U test, P > .05) (16). Patients who were unable to hold their breath during the scanning or who had arrhythmias, heart rates of more than 65 beats per minute after application of ß-blockers, coronary stents, or coronary bypass grafts had been excluded.

Imaging and Evaluation
CT examinations were performed by using a commercially available 16–detector row scanner (Somatom Sensation 16; Siemens, Forchheim, Germany) with a gantry rotation time of 420 msec and a routinely used scanning protocol for coronary artery calcium quantification (section thickness, 3 mm; collimation, 1.5 mm; table feed, 5.7 mm per rotation; reconstruction increment, 1.5 mm). For cardiac protocols, the 12 inner detector rings were applied. Image acquisition was performed by using inspiratory breath holding. Ten separate data sets were reconstructed at different times, which were evenly spaced throughout the cardiac cycle (0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% of the R-R interval). All reconstructions were transferred to a PC-based workstation (Syngo CaScoring, Wizard; Siemens Medical Solutions, Erlangen, Germany) for quantification of coronary calcifications.

Coronary calcifications were defined on CT images as the presence of more than two contiguous pixels with greater than 130 HU. These lesions were automatically identified and marked in terms of color at the workstation. In a second step, a radiologist (T.S., 2 years of experience in coronary artery CT) and a cardiologist (A.S., 8 years of experience in coronary artery CT) differentiated between calcium and noise by placing regions of interest around the coronary calcifications. All values for the left main, left anterior descending, circumflex, and right coronary arteries were added to calculate the total Agatston (4) and volumetric (7) scores. Both scores were determined for all reconstructions in all patients. The calcium mass was not calculated because no calibration phantom was available.

Data and Statistical Analysis
The patients were assigned to three groups, depending on the mean Agatston score for all reconstructions. The groups were as follows: group 1, score of less than 100; group 2, score of 100–400; group 3, score of greater than 400. The total range of Agatston and volumetric scores and the mean scores, standard deviations, and variation coefficients were calculated for all patients. The mean Agatston score and standard deviation of three diastolic reconstructions (50%, 60%, and 70% of the R-R interval) were assessed by using a descriptive statistics tool (version 10.0.7; SPSS, Chicago, Ill) and were compared with the mean Agatston score and standard deviation of three systolic reconstructions (10%, 20%, and 30% of the R-R interval; sign test, P ≤ .05 needed to indicate a significant difference).

The distribution of the minimum and maximum total Agatston scores, as well as the Agatston scores in the left main, left anterior descending, circumflex, and right coronary arteries within the cardiac cycle, was assessed for all patients. Moreover, depending on total Agatston score, age, and sex, patients were assigned to a cardiovascular risk group (percentile 0–25, low risk group; 26–50, moderate risk; 51–75, increased risk; 76–90, high risk; >90, very high risk) on the basis of the different reconstructions. The percentile values were derived from an American population described by Hoff et al (17).


   Results
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
Discussion
 REFERENCES
 
The mean heart rate was 57 beats per minute ± 6 (range, 43–65 beats per minute). Two patients had to be excluded from the study because none of the 10 reconstructions in these patients showed any coronary artery calcium.

The mean Agatston score among all patients was 324 ± 458. The mean Agatston score was 25 ± 22 for group 1 (n = 10), 218 ± 99 for group 2 (n = 10), and 948 ± 432 for group 3 (n = 10). The mean coefficient of variation for different reconstruction intervals was 63.1% (range, 25.3%–174.0%) for group 1, 21.5% (range, 11.8%–37.1%) for group 2, and 7.1% (range, 4.3%–9.2%) for group 3.

The mean volumetric score among all patients was 298 ± 404. The mean volumetric score for group 1 was 29 ± 22; for group 2, it was 258 ± 124; and for group 3, it amounted to 953 ± 335. The mean coefficient of variation for different reconstruction intervals was 60.2% (range, 12.1%–169.4%) for group 1, 19.7% (range, 6.5%–33.1%) for group 2, and 9.6% (range, 9.3%–10.1%) for group 3. Table 1 lists the variation of the Agatston score and the volumetric score for one patient in each group as a representative example.


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  		TABLE 1. Variation of Agatston and Volumetric Scores for One Patient in Each Group

 
The mean Agatston scores of the diastolic reconstructions (331 ± 462) were not significantly different from the mean scores of the systolic reconstructions (329 ± 464, P > .05) for each patient.

Table 2 illustrates the distribution of the minimum and maximum total Agatston scores within the cardiac cycle. Most frequently, the minimum scores were found at 90% (n = 5) and 0% (n = 6) reconstruction intervals, whereas the maximum scores were determined mostly at the 80% (n = 5) and 20% (n = 5) reconstruction intervals. A systematic distribution of maximum and minimum scores to certain reconstruction intervals was not observed; this was also true for distribution of the Agatston scores in the left main, left anterior descending, circumflex, and right coronary arteries. However, in 12 (57%) of 21 patients with calcifications in the left anterior descending coronary artery, maximum scores were found with the 70% or 80% reconstruction interval (Table 3).


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  		TABLE 2. Distribution of Minimum and Maximum Total Agatston Scores in the Cardiac Cycle

 

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  		TABLE 3. Distribution of Maximum and Minimum Agatston Scores in Each Section of the Coronary Arteries

 
In five patients, Agatston and volumetric scores were zero for at least one reconstruction, but further reconstructions resulted in the detection of calcium (Figure). Only 11 patients could be assigned to one risk group regardless of the reconstruction interval used. For the rest of the patients, depending on the reconstruction interval used, 15 patients were assigned to two risk groups, three patients were assigned to three risk groups, and one patient was assigned to four risk groups. Table 4 shows an example of the difference in estimation of coronary risk according to the reconstruction interval.



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  		Transverse CT scans in a 44-year-old man. Left: A 70% reconstruction interval resulted in depiction of calcified plaque in the left anterior descending coronary artery (arrow; total Agatston score, 3.2). Right: With a 60% reconstruction interval, calcification is not detectable (total Agatston score, 0).

 

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  		TABLE 4. Estimation of Coronary Risk Based on the Reconstruction Interval: Example in a 44-year-old Man

 

   Discussion
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
REFERENCES
 
This study was performed to investigate the influence of the reconstruction interval on coronary artery calcium scoring by using retrospectively gated 16–detector row CT scanning. The data indicate that both the Agatston score and the volumetric score greatly depend on the reconstruction time within the cardiac cycle. A substantial proportion of the patients could be assigned to different risk groups on the basis of different reconstructions.

CT has been shown to be highly sensitive in the depiction of coronary artery calcium. Hence, the technique allows for the early identification of coronary artery disease. For the detection and quantification of coronary calcium, two different CT techniques exist: electron beam CT (4,18) and multi–detector row spiral CT (9). Electrocardiographic triggering is a prerequisite for all calcium measurements. For electron-beam CT, it has been demonstrated that optimal electrocardiographic triggering reduces the interscan variation of coronary artery calcium score (19). In contrast to the prospective electrocardiographic triggering used with electron-beam CT, retrospective electrocardiographic gating is used with multi–detector row CT. This provides the opportunity to perform multiple reconstructions at different time points throughout the cardiac cycle. Horiguchi et al (20) demonstrated that this technique produces cardiac images with less motion artifacts than does prospective triggering and showed a high correlation with coronary calcium scores determined by using electron-beam CT.

Mahnken et al (13) have recently shown that the total calcium score depends on the image reconstruction interval. They compared the total mean score acquired at different reconstruction intervals by using a four–detector row CT scanner. The introduction of the latest generation multi–detector row CT scanner, with 16 detector rows, shows promise to improve reproducibility by combining retrospective gating with isotropic volumetric imaging. However, our study results demonstrate a high dependence of both the Agatston and volumetric scores on the reconstruction interval, particularly in patients with mild or moderate amounts of coronary calcium. Furthermore, in five patients in whom coronary calcium was detected in one reconstruction interval, one or more reconstructions failed to demonstrate any calcium at all. Table 4 illustrates the effect of the relatively high variation in patients with mild coronary calcifications. The variable Agatston scores of three diastolic reconstructions result in completely different estimations of coronary risk, which range between low risk and increased risk. Overall, 19 (63%) of 30 patients could be assigned to more than one risk group; of these, three patients could be assigned to three risk groups, and one patient could even be assigned to four risk groups.

It appears reasonable that the "real" calcium score in a blood vessel is represented by the highest score, since motion may result in smearing artifacts and an underestimation of the score. However, Horiguchi et al (21) demonstrated in a cardiac phantom study that calcium is deformed and blurred in the systolic phase, which results in increased calcium scores. Our data support these findings. The 60% reconstruction interval, which is commonly used in clinical routine because of minimal cardiac motion, did not show the maximum Agatston scores for the left anterior descending coronary artery in any of the patients. Instead, the minimum and maximum scores were evenly distributed within the cardiac cycle. This indicates that a fixed reconstruction interval is inadequate for the assessment of maximum or minimum calcium scores, even with the newest generation of CT scanners.

To estimate the progression of coronary calcification as a marker of atherosclerosis in an individual patient, accurate and reproducible calcium quantification is an indispensable tool. To assess the accurate score for the follow-up examinations, it seems mandatory to perform reconstructions that cover the entire cardiac cycle. However, it is doubtful whether this time-consuming postprocessing is practicable in a routine clinical setting. Therefore, the mean of a limited number of reconstructions acquired at defined time points within the cardiac cycle may minimize random errors and improve the reproducibility of the Agatston and volumetric scores in clinical routine. Further studies will be needed to show whether the mean values of diastolic or systolic measurements are better suited for follow-up examinations than are reconstructions performed at a fixed time point within the cardiac cycle.

With the use of a 16–detector row CT scanner, the Agatston and volumetric scores both proved to be highly dependent on the reconstruction interval used. Minimum and maximum values of the Agatston and volumetric scores were evenly distributed over the entire cardiac cycle. Accurate and reproducible quantification of coronary calcium seems to require the analysis of multiple reconstructions, even with the most advanced CT scanners.


   FOOTNOTES
 
Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, T.S., J.B.; study concepts, T.S., P.H., J.B., A.S.; study design, T.S., H.K., K.U.W., J.F.D.; literature research, T.S., A.S., J.B.; clinical studies, T.S., H.K., P.H.; data acquisition, T.S., H.K., K.U.W.; data analysis/interpretation, T.S., P.H., J.B., A.S., J.F.D.; statistical analysis, T.S., J.B.; manuscript preparation and editing, T.S., P.H., A.S., H.K.; manuscript definition of intellectual content, T.S., K.U.W., J.F.D., J.B.; manuscript revision/review and final version approval, all authors


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
 REFERENCES
 

  1. Mautner GC, Mautner SL, Froehlich J, et al. Coronary artery calcification: assessment with electron beam CT and histomorphometric correlation. Radiology 1994; 192:619-623.[Abstract/Free Full Text]
  2. Rumberger JA, Simons DB, Fitzpatrick LA, Sheedy PF, Schwartz RS. Coronary artery calcium area by electron-beam computed tomography and coronary atherosclerotic plaque area: a histopathologic correlative study. Circulation 1995; 92:2157-2162.[Abstract/Free Full Text]
  3. Sangiorgi G, Rumberger JA, Severson A, et al. Arterial calcification and not lumen stenosis is highly correlated with atherosclerotic plaque burden in humans: a histologic study of 723 coronary artery segments using nondecalcifying methodology. J Am Coll Cardiol 1998; 31:126-133.[Abstract/Free Full Text]
  4. Agatston AS, Janowitz WR, Hildner FJ, Zusmer NR, Viamonte M, Jr, Detrano R. Quantification of coronary artery calcium using ultrafast computed tomography. J Am Coll Cardiol 1990; 15:827-832.[Abstract]
  5. Bielak LF, Sheedy PF, Peyser PA. Coronary artery calcification measured at electron-beam CT: agreement in dual scan runs and change over time. Radiology 2001; 218:224-229.[Abstract/Free Full Text]
  6. Wang S, Detrano RC, Secci A, et al. Detection of coronary calcification with electron-beam computed tomography: evaluation of interexamination reproducibility and comparison of three image-acquisition protocols. Am Heart J 1996; 132:550-558.[CrossRef][Medline]
  7. Callister TQ, Cooil B, Raya SP, et al. Coronary artery disease: improved reproducibility of calcium scoring with an electron-beam CT volumetric method. Radiology 1998; 208:807-814.[Abstract/Free Full Text]
  8. Schmermund A, Baumgart D, Mohlenkamp S, et al. Natural history and topographic pattern of progression of coronary calcification in symptomatic patients: an electron-beam CT study. Arterioscler Thromb Vasc Biol 2001; 21:421-426.[Abstract/Free Full Text]
  9. Shemesh J, Apter S, Stroh CI, Itzchak Y, Motro M. Tracking coronary calcification by using dual-section spiral CT: a 3-year follow-up. Radiology 2000; 217:461-465.[Abstract/Free Full Text]
  10. Achenbach S, Ropers D, Pohle K, et al. Influence of lipid-lowering therapy on the progression of coronary artery calcification: a prospective evaluation. Circulation 2002; 106:1077-1082.[Abstract/Free Full Text]
  11. Callister TQ, Raggi P, Cooil B, Lippolis NJ, Russo DJ. Effect of HMG-CoA reductase inhibitors on coronary artery disease as assessed by electron-beam computed tomography. N Engl J Med 1998; 339:1972-1978.[Abstract/Free Full Text]
  12. Becker CR, Kleffel T, Crispin A, et al. Coronary artery calcium measurement: agreement of multirow detector and electron beam CT. AJR Am J Roentgenol 2001; 176:1295-1298.[Abstract/Free Full Text]
  13. Mahnken AH, Wildberger JE, Sinha AM, et al. Variation of the coronary calcium score depending on image reconstruction interval and scoring algorithm. Invest Radiol 2002; 37:496-502.[CrossRef][Medline]
  14. Mao S, Bakhsheshi H, Lu B, Liu SC, Oudiz RJ, Budoff MJ. Effect of electrocardiogram triggering on reproducibility of coronary artery calcium scoring. Radiology 2001; 220:707-711.[Abstract/Free Full Text]
  15. Nieman K, Cademartiri F, Lemos PA, Raaijmakers R, Pattynama PM, de Feyter PJ. Reliable noninvasive coronary angiography with fast submillimeter multidetector-row spiral computed tomography. Circulation 2002; 106:2051-2054.[Abstract/Free Full Text]
  16. Applegate KE, Tello R, Ying J. Hypothesis testing III: counts and medians. Radiology 2003; 228:603-608.[Abstract/Free Full Text]
  17. Hoff JA, Chomka EV, Krainik AJ, Daviglus M, Rich S, Kondos GT. Age and gender distributions of coronary artery calcium detected by electron beam tomography in 35 246 adults. Am J Cardiol 2001; 87:1335-1339.[CrossRef][Medline]
  18. Janowitz WR, Agatston AS, Viamonte M, Jr. Comparison of serial quantitative evaluation of calcified coronary artery plaque by ultrafast computed tomography in persons with and without obstructive coronary artery disease. Am J Cardiol 1991; 68:1-6.[Medline]
  19. Lu B, Zhuang N, Mao SS, et al. EKG-triggered CT data acquisition to reduce variability in coronary arterial calcium score. Radiology 2002; 224:838-844.[Abstract/Free Full Text]
  20. Horiguchi J, Nakanishi T, Ito K. Quantification of coronary artery calcium using multidetector CT and a retrospective ECG-gating reconstruction algorithm. AJR Am J Roentgenol 2001; 177:1429-1435.[Abstract/Free Full Text]
  21. Horiguchi J, Nakanishi T, Tamura A, Ito K. Coronary artery calcium scoring using multicardiac computed tomography. J Comput Assist Tomogr 2002; 26:880-885.[CrossRef][Medline]



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