AJR Get Involved! Great Benefits! Join ARRS
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Horiguchi, J.
Right arrow Articles by Ito, K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Horiguchi, J.
Right arrow Articles by Ito, K.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati  
What's this?
DOI:10.2214/AJR.05.0052
AJR 2006; 187:W1-W6
© American Roentgen Ray Society

Original Research

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

Jun Horiguchi1, Hideya Yamamoto2, Nobuhiko Hirai1, Yuji Akiyama1, Chikako Fujioka1, Kazushi Marukawa3, Hiroshi Fukuda1 and Katsuhide Ito3

1 Department of Clinical Radiology, Hiroshima University Hospital, 1-2-3, Kasumi-cho, Minami-ku, Hiroshima 734-8551, Japan.
2 Department of Molecular and Internal Medicine, Division of Clinical Medical Science, Programs for Applied Biomedicine, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
3 Department of Radiology, Division of Medical Intelligence and Informatics, Programs for Applied Biomedicine, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.

Received January 10, 2005; accepted after revision May 3, 2005.

 
Address correspondence to J. Horiguchi (horiguch{at}hiroshima-u.ac.jp).

WEB

This is a Web exclusive article.


Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
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 log10 (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.

Keywords: atherosclerosis • cardiac imaging • coronary artery disease • MDCT


Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
Electron beam CT is an accepted standard for the detection and quantification of coronary artery calcium (CAC) [1]. The amount of CAC is related to the risk of myocardial infarction and sudden cardiac death [2]. Monitoring CAC is suggested to assess the progression and regression of coronary atherosclerosis, thereby documenting risk factors and response to lipid-lowering pharmacologic therapy [3]. For this purpose, low interscan variability in CAC measurements is mandatory. The normal progression of a patient's CAC score per year is reported to be 14-27% (average, 24%) [4], whereas it is accelerated up to 33-48% in patients with significant coronary disease [5, 6]. However, in previous studies, the variability of Agatston scores [1] using electron beam CT has ranged from 20% to 37% [7-10], which jeopardizes the detection of any changes in this range. Therefore, serial use of electron beam CT to monitor the response of coronary artery lesions to medical interventions designed to cause regression of disease has not been recommended by the American College of Cardiology-American Heart Association expert committee [2].

Interscan variability of CAC measurements using helical CT has also been examined. By using the conventional Agatston method on nonoverlapping reconstructions, however, high levels of interscan variability between two consecutive scans have been reported: 23% [11], 27% [12], 43.1% [13], 45.5% [14] on 4-MDCT, and 22% [15] on 16-MDCT. In contrast to this, with the use of overlapping reconstructions, a considerable reduction in interscan variability can be achieved: from 23% to 12% [11] and from 22% to 13% [15].

An obvious trade-off of the retrospective ECG-gated helical CT technique enabling overlapping reconstructions is the considerably increased radiation exposure compared with ECG-triggering scan protocols with helical CT or electron beam CT [11]. The purpose of this study was to compare low and standard doses and to compare first and second low doses in helical CT, thus assessing the feasibility of low-dose ECG-gated helical CT for measuring CAC.


Figure 1
View larger version (88K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 1A —Placement of region of interest (ROI, circles) in 64-year-old man complaining of chest pain (heart rate, 68 beats per minute; body weight, 62 kg). Transaxial helical CT images of heart obtained using 100-mA (A), first 60-mA (B), and second 60-mA (C) protocols. Mean and SD CT attenuation values (Hounsfield units) in ROIs set in aorta at level of left coronary artery were 49 ± 14, 47 ± 19, and 45 ± 19 H, respectively. Value means + 2 x SD were 76, 85, and 83 H, respectively. Calcium in left main coronary and anterior descending arteries is well shown on all helical CT scans.

 


Figure 2
View larger version (84K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 1B —Placement of region of interest (ROI, circles) in 64-year-old man complaining of chest pain (heart rate, 68 beats per minute; body weight, 62 kg). Transaxial helical CT images of heart obtained using 100-mA (A), first 60-mA (B), and second 60-mA (C) protocols. Mean and SD CT attenuation values (Hounsfield units) in ROIs set in aorta at level of left coronary artery were 49 ± 14, 47 ± 19, and 45 ± 19 H, respectively. Value means + 2 x SD were 76, 85, and 83 H, respectively. Calcium in left main coronary and anterior descending arteries is well shown on all helical CT scans.

 


Figure 3
View larger version (83K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 1C —Placement of region of interest (ROI, circles) in 64-year-old man complaining of chest pain (heart rate, 68 beats per minute; body weight, 62 kg). Transaxial helical CT images of heart obtained using 100-mA (A), first 60-mA (B), and second 60-mA (C) protocols. Mean and SD CT attenuation values (Hounsfield units) in ROIs set in aorta at level of left coronary artery were 49 ± 14, 47 ± 19, and 45 ± 19 H, respectively. Value means + 2 x SD were 76, 85, and 83 H, respectively. Calcium in left main coronary and anterior descending arteries is well shown on all helical CT scans.

 

Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
The study was approved by our institutional review committee. Informed consent was received from all patients involved after the nature of the procedure had been fully explained. For 10 months, 105 consecutive subjects (72 men and 33 women; mean age ± SD, 68 ± 9 years; range, 37-85 years) who were asymptomatic with at least one cardiac risk factor (n = 74) or complaints of chest pain (n = 31) were included. Three sequential CT scans were obtained using a 16-MDCT scanner (LightSpeed Ultrafast 16, GE Healthcare) with no change in subject positioning. The table was advanced 1 mm each time during the three sequential scans.

Volumetric data of the heart were obtained by helical mode with a 1.25-mm collimation width x 16 detectors. The gantry rotation speed was 0.5 s/rotation, and the tube voltage was 120 kV. The tube current was 100 mA for the first scan; for the second and third scans, the tube current was set to almost equivalent to the patient body weight—for example, 60 mA for a patient weighing 62 kg, 65 mA for a patient weighing 63 kg because the tube current could be set in 5-mA steps. We did not use any other dose modulation methods, such as topogram-based z-axis modulation or modulation within a slice.

CT pitch factors were variable by the heart rate and were set according to the manufacturer's recommendations for coronary CT angiography protocols—that is, 0.275 for patients with a heart rate of less than 45 beats per minute (bpm), 0.3 for 45-49 bpm, 0.325 for 50-59 bpm, 0.3 for 60-75 bpm, and 0.275 for more than 76 bpm (where pitch is defined as table feed per gantry rotation divided by the total X-ray beam width [N x T], where N is the number of active data-acquisition system [DAS] channels and T is the single DAS channel width).

Images of 2.5-mm thickness with the center of the temporal window corresponding to 70% of the R-R interval were retrospectively reconstructed with 1.25-mm spacing. In image reconstruction, single-sector reconstruction, which is derived from approximately 240° of one 360° gantry rotation data, was used when the heart rate was less than 60 bpm. Multisector reconstruction was applied when the heart rate was 60 bpm or more. With this algorithm, by combining some (n = 2-4, depending on the heart rate) adjacent cardiac cycles (segments), temporal resolution is improved while maintaining image quality [16]. Image reconstruction was performed with a 512 x 512 pixel matrix using a standard kernel. A display field of view of 26 cm was sufficient and yielded a pixel size of approximately 0.5 mm.

Calcium Scoring
Agatston and volume scores were determined on a commercially available external workstation (Advantage Windows [version 4.1], GE Healthcare) using CAC-scoring software (SmartScore [version 3.5], GE Healthcare). In accordance with the Agatston method [1], we defined the regions of interest (ROIs) by vessel and slice with the threshold option for pixels greater than 130 H to measure the area and peak density of plaques. Depending on the peak density of the plaque, an area of at least 0.52 mm2 (2 pixels) was multiplied by one of the following cofactors: a cofactor of 1 for ROIs that were 130-199 H; a cofactor of 2, 200-299 H; a cofactor of 3, 300-399 H; and a cofactor of 4, for densities 400 H or greater. The total calcium score was calculated as the sum of the individual lesion scores in all coronary arteries.

The Agatston score was calculated using the following formula:

Formula
The calcium volume [7] was calculated using the following formula:

Formula
The calcium mass was not calculated because no calibration phantom was available. To avoid interobserver variability, all CT scans were scored by a radiologist with 5 years' experience measuring CAC.

Statistical Analysis
The Agatston and volume scores were compared among protocols: 100-mA versus first low-dose, 100-mA versus second low-dose, and first versus second low-dose protocols. Correlation was performed in a form of log10 transformation (Agatston score + 1) to reduce skewness.

The percentage of variability in Agatston and volume scores was calculated as follows:

Formula
This variability was compared between 100-mA and first low-dose, 100-mA and second low-dose, and first and second low-dose protocols. Whether volume quantification algorithms reduce the variability more than the Agatston approach was also tested. Furthermore, the variability was compared between the single-sector (heart rate ≤ 60 bpm) and multisector (heart rate > 61 bpm) reconstruction groups.

The mean and SD of CT attenuation values in ROIs set in the aorta at the level of the left coronary artery were measured and then the value mean + 2 x SD and signal-to-noise ratio (defined as the value mean divided by SD) were calculated (Figs. 1A, 1B, and 1C). These values were compared between the 100-mA and low-dose protocols.

For statistical analysis, repeated-measures analysis of variance, Mann-Whitney U test, and Student's t tests were used to determine differences; p values of < 0.05 were considered to identify significant differences.


Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
All patients were able to hold their breath on the three sequential CT scans. The median heart rate during the 100-mA CT scan was 61 ± 11 (SD) bpm. The mean change in heart rate during the scan was 6 ± 8 bpm. Almost all helical CT images had a temporal resolution of 100-250 msec, although the temporal resolution achieved by multisector reconstructions differed according to the heart rate and the number of cardiac cycles used for image reconstruction. The mean body weight of the patients was 60 ± 10 kg (range, 37-105 kg); therefore, the tube current used as the "low-dose" setting was 60 ± 11 mA (range, 35-105 mA).

Eighty-six of the 105 patients had CAC deposits detected on the three sequential CT scans, and the remaining 19 patients had no CAC deposit seen on any of the scans. There were no patients showing both positive and negative CAC measurements on the three scans.

The Agatston and volume scores on the three scans are summarized in Table 1. There was no statistical significance between the three scans (repeated-measures analysis of variance: Agatston score, p = 0.993; volume score, p > 0.999). The log10 transformed scores (Agatston score + 1) of the 100-mA scans versus the first low-dose scans, 100-mA versus second low-dose, and first versus second low-dose were highly correlated (r = 0.998) (Figs. 2, 3, and 4).


View this table:
[in this window]
[in a new window]

  		TABLE 1: Agatston and Volume Scores on 100-mA and Low-Dose Protocols

 

Figure 4
View larger version (12K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 2 —Graph shows that log10 transformed scores (Agatston scores + 1) of 100-mA scans versus first low-dose scans are highly correlated (r = 0.998). In this logarithm calcium scale, 0, ≤ 1, ≤ 2, ≤ 2.6, and > 2.6 ranges almost correspond to normal, minimal, mild, moderate, and high-risk categories, respectively.

 

Figure 5
View larger version (12K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 3 —Graph shows that log10 transformed scores (Agatston scores + 1) of 100-mA scans and second low-dose scans are highly correlated (r = 0.998). In this logarithm calcium scale, 0, ≤ 1, ≤ 2, ≤ 2.6, and > 2.6 ranges almost correspond to normal, minimal, mild, moderate, and high-risk categories, respectively.

 

Figure 6
View larger version (13K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Fig. 4 —Graph shows that log10 transformed scores (Agatston scores + 1) of first low-dose scans and second low-dose scans are highly correlated (r = 0.998). In this logarithm calcium scale, 0, ≤ 1, ≤ 2, ≤ 2.6, and > 2.6 ranges almost correspond to normal, minimal, mild, moderate, and high-risk categories, respectively.

 

The percentage variability in the CAC scores is summarized in Table 2. Low variability was obtained even using low-dose protocols without significant differences (repeated-measures analysis of variance: Agatston score, p = 0.994; volume score, p = 0.923). The variability was not significantly different between the Agatston and volume algorithms (repeated-measures analysis of variance, p = 0.667, 0.949, and 0.760). The variability in both Agatston and volume scores was not significantly different between the single-sector (heart rate ≤ 60 bpm) and multisector (heart rate > 61 bpm) groups (Mann-Whitney U test, p = 0.218-0.958) (Table 3).


View this table:
[in this window]
[in a new window]

  		TABLE 2: Percentage of Variability in the Coronary Artery Calcium Scores

 

View this table:
[in this window]
[in a new window]

  		TABLE 3: Single-Sector vs Multisector Reconstruction in the Percentage of Variability in the Coronary Artery Calcium Scores

 

The mean, SD, mean + 2 x SD, and signal-to-noise ratio of the CT attenuation values in the ROIs are summarized in Table 4. On repeated-measures analysis of variance, there was no significant difference in the mean value (p = 0.981); however, there was a significant difference in both the SD (p < 0.01) and signal-to-noise ratio (p < 0.01). On pair-wise comparison using the Student's t test, the SD on the 100-mA scans was lower than those on the first low-dose (p < 0.01) and second low-dose (p < 0.01) scans. The signal-to-noise ratio on the 100-mA scans was higher than those on the first low-dose (p < 0.01) and second low-dose (p < 0.01) scans. In contrast, the SD (p = 0.110) and signal-to-noise ratio (p = 0.559) were not statistically different between the first low-dose and second low-dose scans. With the tube current setting equivalent to the patient's body weight, the value (mean + 2 x SD) did not exceed a CT attenuation of 130 H, whereas the value was 135 H for a patient weighing 105 kg on a scan obtained using a tube current of 100 mA.


View this table:
[in this window]
[in a new window]

  		TABLE 4: Mean and SD of CT Attenuation Values in Regions of Interest Set in the Aorta at the Level of the Left Coronary Artery

 


Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
Factors influencing interscan variability are partial volume effect [17], the use of the step function in the Agatston method to quantitate calcium [8], coronary artery motion [18], image noise [10, 19], field inhomogeneity [20], lack of calibration [21], total amount of CAC [10], and so on. Among these, a major contributor is partial volume effect. To reduce this, the use of thin-slice images [5, 22, 23] or overlapping image reconstructions [11, 14, 24, 25] has been suggested. In a recent study [15] using thin-collimation volume data on helical CT, both thin-slice images and overlapping reconstruction images were shown to be superior to electron beam CT in terms of the variability of CAC measurements. The tube current used in the study was 100 mA; therefore, image quality was satisfactory even in thin-slice images. To reduce radiation exposure, however, overlapping reconstructions seem preferable to thin-slice images because image noise is also an important factor in variability.

The German Cardiac Society recommends a tube current of 100 mA for CAC measurement on MDCT [26]. For most MDCT scanners, a 100-mA tube current is used to achieve sufficient signal-to-noise levels for detection of small calcified lesions. The tube current may be increased for obese patients (e.g., to 150 mA) to maintain a diagnostic signal-to-noise level at the expense of increased radiation exposure [27]. In comparison with prospectively ECG-triggered acquisition using electron beam CT (effective dose, 0.7 mSv) and helical CT (effective dose, 1 mSv), however, CT acquisition using retrospective ECG gating is associated with a higher effective radiation dose (range, 2.6-4.1 mSv) [28]. A retrospective ECG-gated protocol, using standard 100 mA in the current study, yields an effective dose of 3.2-3.7 mSv (varies according to pitch chosen).

Takahashi and Bae [29], with prospectively ECG-gated 4-MDCT, showed that variability in CAC scores was not significantly different between the 40-mA versus 150-mA (23.7%) groups and the 80-mA versus 150-mA (41.8%) groups. The two-group all-over variability of 31.9% in Agatston score was reduced to 22.4% by using the volume score. The variability level, however, does not seem to be satisfactory for monitoring normal or accelerated CAC progression. This is probably due to the use of the prospective ECG-triggering approach. Mahnken et al. [30] proposed individual body weight-adapted tube current settings (body weight in kilograms + 33 mAseff) and showed that no significant changes in CAC score were seen and that there was a relevant increase of noise in comparison with the standard dose (133 mAseff). The variability of CAC scores between the two protocols was not tested in this study.

The mean tube current used as a low-dose protocol in the current study was 60 mA. Although the dose was reduced to 1.9-2.2 mA (by 40%), it was still higher than prospectively ECG-triggered acquisitions with electron beam CT and helical CT. Combined with ECG-controlled modulation, which would enable a 45-48% reduction of radiation [31], an almost 70% reduction in radiation exposure would theoretically be possible using the low-dose protocol. This would result in an effective dose of almost 1 mSv. This dose is comparable to that associated with the prospectively ECG-triggered technique.

Although the optimum definition of a threshold for the detection of CAC is not known, a CT attenuation value of 130 H was selected because that level is more than 2 x SDs above the average attenuation of blood [19]. On the low-dose scan in the current study, this calculation value does not exceed 130 H. Therefore, the images were considered sufficient to maintain the signal-to-noise ratio needed. It remains unresolved as to what level we can reduce the milliampere setting. Takahashi and Bae [29] stated that, in most subjects, a dose of 30 mA (140 kVp) would give a mean noise level of 24 ± 8 H, which is of practical use. This may be true; however, individual dose setting is considered more rational.

The volumetric approach proposed by Callister et al. [7] has been shown to improve the reproducibility of CAC measurement on both electron beam CT [8, 10] and helical CT [11, 25]. Interestingly, reduction of the variability by using the volume scoring algorithm was not effective in our current study. Similar results were experienced through clinical research using retrospective ECG-gated helical CT with overlapping reconstructions [15]. The trend is moving toward obtaining a mass or volume score because of its high reproducibility in CAC measurement. Patient management at this time, however, is difficult because of the paucity of representative data about CAC distribution [32]. In this respect, the high reproducibility of CAC measurements using the Agatston score in a wide range of heart rates is considered advantageous.

In conclusion, low-dose retrospective ECG-gated helical CT, yielding low variability and achieving image quality needed for CAC measurement, can be used to monitor patients with coronary atherosclerosis.


References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

  1. Agatston AS, Janowitz WR, Hildner FJ, Zusmer NR, Viamonte M, Detrano R. Quantification of coronary calcium using ultrafast computed tomography. J Am Coll Cardiol 1990;15 : 827-832[Abstract]
  2. O'Rourke RA, Brundage BH, Froelicher VF, et al. American College of Cardiology/American Heart Association Expert Consensus document on electron-beam computed tomography for the diagnosis and prognosis of coronary artery disease. Circulation 2000;102 : 126-140[Free Full Text]
  3. 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 Med1998; 339:1972 -1978[Abstract/Free Full Text]
  4. Maher JE, Bielak LF, Raz JA, Sheedy PF II, Schwartz RS, Peyser PA. Progression of coronary artery calcification: a pilot study. Mayo Clin Proc 1999; 74:347 -355[Medline]
  5. 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]
  6. Fischbach R, Heindel W. Detection and quantification of coronary calcification: an update [in German]. Rofo2000; 172:407 -414[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. Yoon HC, Greaser LE III, Mather R, et al. Coronary artery calcium: alternate methods for accurate and reproducible quantification. Acta Radiol 1997;4 : 666-673
  9. Wang SJ, 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]
  10. Achenbach S, Ropers D, Mohlenkamp S, et al. Variability of repeated coronary artery calcium measurements by electron beam tomography. Am J Cardiol 2001;87 : 210-213[CrossRef][Medline]
  11. Ohnesorge B, Flohr T, Fischbach R, et al. Reproducibility of coronary calcium quantification in repeat examinations with retrospectively ECG-gated multisection spiral CT. Eur Radiol2002; 12:1532 -1540[CrossRef][Medline]
  12. Van Hoe LR, De Meerleer KG, Leyman PP, Vanhoenacker PK. Coronary artery calcium scoring using ECG-gated multidetector CT: effect of individually optimized image-reconstruction windows on image quality and measurement reproducibility. AJR 2003;181 : 1093-1100[Abstract/Free Full Text]
  13. Daniell AL, Wong ND, Friedman JD, et al. Reproducibility of coronary calcium measurements from multidetector computed tomography. (abstr) J Am Coll Cardiol 2003;41 : 456A
  14. 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]
  15. Horiguchi J, Yamamoto H, Akiyama Y, et al. Variability of repeated coronary artery calcium measurements by 16-MDCT with retrospective reconstruction. AJR 2005;184 : 1917-1923[Abstract/Free Full Text]
  16. Horiguchi J, Nakanishi T, Ito K. Quantification of coronary artery calcium using multidetector CT and a retrospective ECG-gating reconstruction algorithm. AJR 2001;177 : 1429-1435[Abstract/Free Full Text]
  17. Kajinami K, Seki H, Takekoshi N, Mabuchi H. Quantification of coronary artery calcification using ultrafast computed tomography: reproducibility of measurements. Coron Artery Dis1993; 4:1103 -1108[Medline]
  18. Mao S, Bakhsheshi H, Lu B, Liu SCK, Oudiz RJ, Budoff MJ. Effect of electrocardiogram triggering on reproducibility of coronary artery calcium scoring. Radiology 2001;220 : 707-711[Abstract/Free Full Text]
  19. Bielak LF, Kaufmann RB, Moll PP, MacCollough CH, Schwartz RS, Sheedy PF II. Small lesions in the heart identified at electron beam CT: calcification or noise? Radiology 1994;192 : 631-636[Abstract/Free Full Text]
  20. Detrano R, Kang X, Mahaisavariya P, et al. Accuracy of quantifying coronary hydroxyapatite with electron beam tomography. Invest Radiol 1994; 29:733 -738[CrossRef][Medline]
  21. McCollough CH, Kaufmann RB, Cameron BM, Katz DJ, Sheedy PF II, Peyser PA. Electron-beam CT: use of a calibration phantom to reduce variability in calcium quantification. Radiology1995; 196:159 -165[Abstract/Free Full Text]
  22. Callister T, Janowitz W, Raggi P. Sensitivity of two electron beam tomography protocols for the detection and quantification of coronary artery calcium. AJR 2000;175 : 1743-1746[Abstract/Free Full Text]
  23. Vliegenthart R, Song B, Hofman A, Witteman JCM, Oudkerk M. Coronary calcification at electron-beam CT: effect of section thickness on calcium scoring in vitro and in vivo. Radiology2003; 229:520 -525[Abstract/Free Full Text]
  24. Achenbach S, Meissner F, Ropers D, et al. Overlapping cross-sections significantly improve the reproducibility of coronary calcium measurements by electron beam tomography: a phantom study. J Comput Assist Tomogr 2001; 25:569 -573[CrossRef][Medline]
  25. Kopp AF, Ohnesorge B, Becker C, et al. Reproducibility and accuracy of coronary calcium measurements with multi-detector row versus electron-beam CT. Radiology 2002;225 : 113-119[Abstract/Free Full Text]
  26. Hunold P, Vogt FM, Schmermund A, et al. Radiation exposure during cardiac CT: effective doses at multi-detector row CT and electron-beam CT. Radiology 2003;226 : 145-152[Abstract/Free Full Text]
  27. Schoepf UJ, Becker CR, Ohnesorge BM, Yucel EK. CT of coronary artery disease. Radiology 2004;232 : 18-37[Abstract/Free Full Text]
  28. Morin RL, Gerber TC, McCollough CH. Radiation dose in computed tomography of the heart. Circulation2003; 107:917 -922[Free Full Text]
  29. Takahashi N, Bae KT. Quantification of coronary artery calcium with multi-detector row CT: assessing interscan variability with different tube currents—pilot study. Radiology2003; 228:101 -106[Abstract/Free Full Text]
  30. Mahnken AH, Wildberger JE, Simon J, et al. Detection of coronary calcifications: feasibility of dose reduction with a body weight-adapted examination protocol. AJR 2003;181 : 533-538[Abstract/Free Full Text]
  31. Jakobs TF, Becker CR, Ohnesorge B, et al. Multislice helical CT of the heart with retrospective ECG gating: reduction of radiation exposure by ECG-controlled tube current modulation. Eur Radiol2002; 12:1081 -1086[CrossRef][Medline]
  32. Knez A, Becker A, Leber A, et al. Relation of coronary calcium scores by electron beam tomography to obstructive disease in 2,115 symptomatic patients. Am J Cardiol 2004;93 : 1150-1152[CrossRef][Medline]

Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati    What's this?



This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Horiguchi, J.
Right arrow Articles by Ito, K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Horiguchi, J.
Right arrow Articles by Ito, K.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati  
What's this?

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS