Radiology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

DOI: 10.1148/radiol.2253011871
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
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 HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Hong, C.
Right arrow Articles by Bradley, D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Hong, C.
Right arrow Articles by Bradley, D.
(Radiology 2002;225:901-906.)
© RSNA, 2002

Technical Developments

Coronary Artery Calcium Measurement with Multi–Detector Row CT: In Vitro Assessment of Effect of Radiation Dose1

Cheng Hong, MD, PhD, Kyongtae T. Bae, MD, PhD, Thomas K. Pilgram, PhD, Jongdae Suh, MD and David Bradley, BS, RT

1 From the Mallinckrodt Institute of Radiology, Washington University School of Medicine, Campus Box 8131, 510 S Kingshighway Blvd, St Louis, MO 63110 (C.H., K.T.B., T.K.P., J.S.); and Siemens Medical Systems, Iselin, NJ (D.B.). Received November 25, 2001; revision requested February 4, 2002; final revision received May 3; accepted May 29. Address correspondence to K.T.B. (e-mail: baet@mir.wustl.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Materials and Methods
Results
 Discussion
 REFERENCES
 
The authors assessed in vitro the effect of radiation dose on coronary artery calcium quantification with multi–detector row computed tomography. A cardiac phantom with calcified cylinders was scanned at various milliampere second settings (20–160 mAs). A clear tendency was found for image noise to decrease as tube current increased (P < .001). No tendency was found for the Agatson score or calcium volume and mass errors to vary with tube current. Calcium measurements were not significantly affected by the choice of tube current. Calcium mass error was strongly correlated with calcium volume error (P < .001). The calcium mass measurement was more accurate and less variable than the calcium volume measurement.

© RSNA, 2002

Index terms: Computed tomography (CT), radiation exposure, 54.12111, 54.12115 • Coronary vessels, calcification, 54.812 • Coronary vessels, CT, 54.12111, 54.12116


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Materials and Methods
Results
 Discussion
 REFERENCES
 
Coronary artery disease is one of the major causes of morbidity and mortality in developed countries. Findings in previous studies have indicated that the presence of coronary calcium is invariably associated with atherosclerosis (1–3) and can be used to predict future cardiac events in asymptomatic patients with cardiovascular risk factors (4–6).

Over the past decade, a number of technologies have been developed to help detect and measure calcification of the coronary artery tree. Electron-beam computed tomography (CT) is one such noninvasive and promising technology (7–9). Based on a section-by-section analysis of electron-beam CT images, a scoring method to semiquantitatively assess the amount of coronary calcium has been introduced by Agatston et al (1). This scoring system, however, has a limited reproducibility (10,11). Alternative methods such as measurement of calcium volume and calcium mass have been proposed and are gradually gaining clinical acceptance (12–14) as a means of more precisely and reproducibly measuring calcified plaques.

Detection and quantification of coronary calcium may be used mainly as a screening tool in potentially healthy subjects; therefore, radiation exposure should be as low as possible. A lower radiation dose will, however, increase image noise (15) and possibly influence the detection of coronary artery calcium (8). Efforts must be made to ensure that CT will be performed with the least radiation dose possible while maintaining accepted calcium measurement results. Performance of comprehensive in vitro studies seems important when considering the effect of a variety of possible tube currents on calcification measurements obtained with different methods. To our knowledge, there are no published data that correlate applied CT tube currents with coronary calcium measurements.

Since the introduction of multi–detector row CT, there has been much interest in its applications in the field of cardiac imaging. Multi–detector row CT is regarded currently as an imaging procedure of choice in both the detection of coronary artery stenosis (16) and the measurement of coronary calcification (17). However, initial data reveal that a relatively high radiation exposure results from cardiac multi–detector row CT (18). The purposes of this study were (a) to assess quantitatively the effect of varying tube current on coronary calcium measurements and (b) to compare results with the calcium mass and volume methods on the basis of findings at multi–detector row CT of a cardiac phantom.


   Materials and Methods
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
 REFERENCES
 
Phantom
A cardiac CT phantom (QRM, Moehrendorf, Germany) was designed as a calibration standard for quantification of coronary calcium. The phantom consists of two parts: an anthropomorphic phantom body and a calibration insert. The phantom body with artificial lungs and a spine insert is surrounded by soft-tissue–equivalent material. The overall dimensions of the phantom are 300 mm wide, 200 mm high, and 150 mm deep. At the position of the heart is a 100-mm-diameter cylindric hole in which the calibration insert can be placed. The calibration insert contains three series of calcified cylinders with diameters and heights in equal dimensions of 1, 3, and 5 mm. The calcium hydroxyapatite (CaHA) densities of each series of cylinders equal 200, 400, and 800 mg/cm3, respectively (Fig 1). In addition, the calibration insert contains two large homogeneous inserts made of water (0 HU ± 3; mean ± SD) and spongy bone (CaHA density of 200 mg/cm3)–equivalent materials.



View larger version (97K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1. Anthropomorphic cardiac phantom with the calibration inserts. HA = hydroxyapatite.

 
CT Imaging
All CT scans were obtained with a multi–detector row CT scanner (Somatom Plus 4 VolumeZoom; Siemens Medical Systems, Forchheim, Germany). The cardiac phantom was positioned on the patient table, and its rear edge was aligned with the laser beam of the gantry. Spiral CT scans were obtained through the two large calibration inserts and the nine calcified cylinders in the phantom with eight effective tube current levels (in milliampere seconds) ranging from 20 to 160 mAs with an interval of 20 mAs. The fixed scanning parameters were 4.0 x 2.5-mm collimation, 120 kVp, and 500 msec per rotation. Eight sets of images were obtained in each acquisition and were then reconstructed with a 3-mm section thickness, 512 x 512-pixel matrix, 100-mm field of view, and medium smooth kernel. The choice of the section thickness was determined to match that used in electron-beam CT and in the scoring method of Agatston et al (1). The window settings were those used for the large calibration inserts (width, 1,000 HU; center, 50 HU) and for the three series of calcified cylinders (width, 2 HU; center, 130 HU), as recommended by the phantom manufacturer.

Image Evaluation
After data acquisition, all reconstructed images were transferred to a dedicated workstation (NetraMD; ScImage, Los Altos, Calif). With the workstation, one experienced radiologist (C.H.) determined the Agatston score, the volume and mass of the calcifications, and the noise on images obtained with each current level. The Agatson score was determined by setting a threshold of 130 HU and ignoring structures smaller than 1 mm2 to exclude noise from the calculation (1). Depending on the peak attenuation of the calcified cylinder, the calcified area was multiplied by one of the following factors: a factor of 1 for 130–199-HU peak attenuation of the calcified cylinder; factor of 2, 200–299 HU; factor of 3, 300–399 HU; and factor of 4, more than 400 HU.

The volume of calcified cylinders was determined as the sum of all the voxels with an attenuation above 130 HU by means of the algorithm of isotropic interpolation (12). To obtain values for the CaHA mass, a calibration measurement of a calcified cylinder with known CaHA density ({rho}CaHA) was performed, and a calibration factor c was determined for each current level according to the following equation: c = {rho}CaHA/(CTcylinder - CTwater) (19). The calibration factor c is therefore given by the CaHA density ({rho}CaHA) of the known calcified cylinder divided by the mean difference in CT numbers of the calcified cylinder and one of the two large inserts made of water-equivalent material (CTcylinder - CTwater) in the calibration measurement. The measured CaHA mass multiplied by the respective calibration factor corresponds to the value of the CaHA mass.

Measurement of image noise, the SD of the CT number of the homogeneous large insert (CaHA density of 200 mg/cm3), was assessed by placing a circular region of interest (102 mm2 ± 2) on images obtained at each current level. The values of the CT number were obtained from the average of findings in the three regions of interest. The CT number and SD in the water insert were measured similarly to calculate the calibration factor.

Statistical Analysis
Differences between the measured value and the true value of the calcium volume and mass were calculated as a percentage of the true value for each tube current. Correlation analysis was performed to evaluate trends in continuous variables and the relationships of the calcium measurements obtained with the different methods (Agatson score and calcium volume and mass) to eight tube currents, image noise, and CaHA densities. Analysis of variance was performed to evaluate the distribution of errors in the measurement of calcium volume and mass. Differences with a P value of .05 were considered statistically significant.

At each tube current, the Agatson score, calcium volume, and CaHA mass were measured for each individual cylinder. Statistical analysis was performed of individual measurements for each cylinder with different size and CaHA density. We believe the results based on the individual measurements are more meaningful than those based on the summed measurements because the summed measurements combine information with considerable differences, such as for cylinders with different size and CaHA density.


   Results
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
Discussion
 REFERENCES
 
CT attenuation averaged for all tube current levels was 259.7 HU ± 11.4 for the CaHA insert and -0.6 HU ± 10.3 for the water insert. All nine calcified cylinders were visually identifiable on CT images obtained at each tube current. However, only six cylinders were definitely measurable at the 130-HU threshold at each tube current. Quantification of three cylinders with 1-mm diameter was inconsistent and unreliable because of their size limitation; therefore, these data were not included in further statistical analysis. Various measurements summed for all calcified cylinders at each tube current level are shown in the Table. The summed data showed a consistency in the Agatson score and calcium volume and mass errors on the scale of tube current levels, while individual measurement revealed the tendencies for calcium volume and mass errors.


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

  		Various Measurements Summed for Calcified Cylinders in Calibration Insert at Different Tube Currents

 
Image noise expressed as the SD of the CT number of the CaHA insert ranged from 19.3 HU at 20 mAs to 8.3 HU at 160 mAs. There was a clear tendency for image noise to decrease as tube current increased (r = 0.90, P = .002) (Fig 2). The images obtained at lower tube currents were noisier and more grainy than those obtained at higher tube currents. Figure 3 shows a series of representative images obtained at 20, 100, and 160 mAs.



View larger version (18K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2. Plot shows relationship between tube current and image noise. As tube current increased, image noise decreased in a consistent fashion (r = 0.90, P = .002).

 


View larger version (45K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 3. Representative multi-detector row CT scans of calcified cylinders in the phantom were obtained at (left) 20, (middle) 100, and (right) 160 mAs. The image obtained at 20 mAs shows the most noise.

 
There was no tendency for the Agatson score (r = 0.02, P = .89), calcium volume error (r = 0.03, P = .82) (Fig 4), or calcium mass error (r = 0.06, P = .70) (Fig 5) to vary with tube current. Neither calcium volume error (r = 0.03, P = .82) nor calcium mass error (r = 0.06, P = .67) varied with image noise. Both calcium volume and mass errors tended to change as CaHA density changed but in opposite directions: calcium volume error increased from a mean of -33% at 200 mg/cm3 CaHA density to a mean of 77% at 400 mg/cm3 and then to a mean of 213% at 800 mg/cm3 (P < .001) (Fig 6), while calcium mass error decreased from a mean of -57% at 200 mg/cm3 CaHA density to a mean of -22% at 400 mg/cm3 and then to a mean of 8% at 800 mg/cm3 (P = .001) (Fig 7).



View larger version (30K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 4. Plot shows relationship between tube current and calcium volume error expressed as a percentage of the true value. There appears to be no relationship between the tube current and calcium volume error (r = 0.03, P = .82). Size of data points indicates size of lesion: small = 3-mm diameter, large = 5-mm diameter. Color of data points indicates calcium density: white = 200 mg/cm3, gray = 400 mg/cm3, and black = 800 mg/cm3.

 


View larger version (63K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 5. Plot shows relationship between tube current and calcium mass error expressed as a percentage of the true value. There appears to be no relationship between the tube current and calcium mass error (r = 0.06, P = .70). Size of data points indicates size of lesion: small = 3-mm diameter, large = 5-mm diameter. Color of data points indicates calcium density: white = 200 mg/cm3, gray = 400 mg/cm3, black = 800 mg/cm3.

 


View larger version (25K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 6. Plot shows relationship between CaHA density and calcium volume error expressed as a percentage of the true value: small circles = individual values, large circles = means, and error bars = 1 SD. There is a clear tendency for the calcium volume error to be larger with larger CaHA densities. Differences between the means of the errors are statistically significant (P < .001).

 


View larger version (20K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 7. Plot shows relationship between CaHA density and calcium mass error expressed as a percentage of the true value: small circles = individual values, large circles = means, and error bars = 1 SD. There is a clear tendency for the calcium mass error to be smaller with larger CaHA densities. Differences between the means of the errors are statistically significant (P < .001).

 
Overall, calcium mass error was both smaller and less variable than calcium volume error (calcium mass error, mean = -24%, SD = 29%; for calcium volume error, mean = 86%, SD = 106%). Although calcium volume error was considerably larger than calcium mass error, and they had different trends in relation to CaHA density, calcium mass and volume errors were strongly correlated (r = 0.90, P < .001) (Fig 8).



View larger version (26K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 8. Plot shows relationship between calcium volume and mass errors expressed as a percentage of the true value. There is a clear relationship between the relative size of the errors, though the calcium volume error has a much larger range than that of the calcium mass error (r = 0.90, P < .001). The data points are clustered in terms of CaHA density, as noted in Figures 6 and 7. Size of data points indicates size of lesion: small = 3-mm diameter, large = 5-mm diameter. Color of data points indicates calcium density: white = 200 mg/cm3, gray = 400 mg/cm3, black = 800 mg/cm3.

 

   Discussion
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
REFERENCES
 
The presence of coronary artery calcification on a screening CT image effectively provides relevant prognostic information for the development of future coronary events (4–6). It is highly desirable to use the smallest radiation dose in CT imaging as a screening tool. For a given subject and a constant x-ray tube potential, the value of the effective dose from a cardiac CT examination is directly proportional to the amperage at a fixed kilovoltage, scanning time, and section thickness and the total number of images acquired (20). While the scanning parameters of electron-beam CT are fixed, those of conventional CT, including multi–detector row CT, allow a reduction in the radiation dose by means of decreasing the x-ray tube current.

Findings in our study show that although a reduction in the tube current from 160 to 20 mAs resulted in a noisier image, no significant differences were found in the calcium measurements obtained with the Agatson score and calcium volume and mass methods. This finding is compatible with findings in previous studies of chest CT examinations performed with low radiation doses (20). An optimal radiation dose is the minimal dose required to distinguish lesions from normal tissue. When materials with high intrinsic tissue contrast are measured—such as coronary calcium deposits, bone minerals, or lung nodules—the use of radiation doses lower than those used in routine CT examinations may be acceptable.

Findings in our study and another (21) demonstrate a clear inverse relation between tube current and image noise. Noise in CT images caused by a low radiation dose might hinder the detection of small calcified plaques (8). No significant difference in calcium measurements was observed with increased image noise in our phantom study, but whether the noise and milliampere second values determined for this anthropomorphic phantom are applicable to clinical cases needs to be evaluated. In the scanning of obese patients or those with very small calcified coronary plaques, an increase in tube current would probably help accurate quantification of coronary calcifications. A balance between diagnostic efficiency and dose consideration should also be made in relation to the clinical requirements of the examination.

In our study, small calcified nodules (diameter, 1 mm; density, <1 mg) could not be measured at a 130-HU threshold on multi–detector row CT images obtained with both lower and higher tube current levels. For these nodules, the attenuation in CT images depends more on the partial volume effect than on the true density of the calcified lesion. However, lesions with diameters of 2–3 pixels do not substantially change the reproducibility of coronary calcium measurement (13), and such tiny calcified nodules are weak predictors of stenotic lesions in a calcified area (22). An alternative threshold of 90 HU may improve the detectability of small calcifications (17). Another way to reduce the partial volume effects is to decrease section thickness, which may result in an increase in patient dose and image noise to maintain a comparable image quality.

Our results suggest that absolute quantification of CaHA is a more reliable measurement than the conventional Agatson score. Although the Agatson score has been an accepted method for many years in the clinical evaluation of disease in patients suspected of having coronary artery disease or in the screening of asymptomatic subjects with high cardiovascular risk factors, it shows poor reproducibility of the results from repeated scans, or imaging with different scanners (3,10–13). The main reasons are that calculation of the Agatson score involves multiplication of the area of a calcified plaque by an arbitrary coefficient that is based on peak plaque attenuation and the imaging parameters used. Differences in peak attenuation caused by image noise can have a large effect on the Agatson score. The lack of comparability between instruments with respect to both calibration and evaluation procedures also contributes to low reproducibility (23).

The use of calcium mass as a quantitative index for the amount of calcium is more precise than are other methods because the pixels that compose each calcified lesion are corrected by an appropriate calibration factor to compensate for the decreased mean CT numbers that result from the linear partial volume effects. This yields a significant decrease in error and variation and can be obtained by scanning a calibration phantom, as was done in the present study. Although excellent correlation was obtained between errors of CaHA mass and volume measurements, the error and variability of the volume measurements were greater. The accuracy of a calcium volume measurement can be strongly affected by the partial volume effect in cases of smaller calcifications imaged with relatively thicker sections. The error is due to voxels that contain both high density CaHA and soft tissues. This partial volume effect will be reduced with a decrease in the section thickness.

Results in the current study show that overestimation of CaHA volume and mass measurements was associated with a higher CaHA density, whereas underestimation was associated with a lower CaHA density. The energy shift of the x-ray beam through objects with different densities may cause differences in the mean CT number, which would result in erroneous measurements of coronary artery calcium volume and mass. This potential error can be reduced by using a standard calibration phantom.

Our study has some limitations. First, the cardiac phantom we used cannot simulate cardiac motion, which adds an additional source of artifact that will consequently degrade the reproducibility of the calcium measurement (24). Second, image noise depends not only on inherent technical details of the scanner and the parameter settings but also on the anatomic region being scanned. Information about the noise level relative to the distribution of coronary vessels cannot be given for the present study. In a recent study of coronary screening with electron-beam CT, Raggi et al (25) reported a substantial increase in image noise at the base of the heart compared with that at the apex because of x-ray beam attenuation by the liver and diaphragm. This positional variation should be taken into account when an acceptable range of errors is calculated for low-dose CT for coronary screening. Third, we did not measure the effective doses for each tube current because the effective dose measurements require additional factors, such as the CT scanning range, to be considered in the calculation. A clinical validation study is warranted to address these limitations and to test how well our in vitro method applies in a clinical setting.

In conclusion, the findings in our phantom study indicate that the calcium measurements obtained with the Agatson score and calcium volume and mass methods do not differ significantly with those obtained by changing the tube current level during multi–detector row CT; therefore, use of low-dose multi–detector row CT may be possible for routine coronary screening. The calcium mass measurement was more accurate and less variable than the volume measurement and thus better suits the quantification of coronary artery calcium deposits.


   FOOTNOTES
 
Author contributions: Guarantors of integrity of entire study, C.H., K.T.B.; study concepts, C.H., K.T.B., D.B.; study design, C.H., K.T.B.; literature research, C.H., J.S.; experimental studies, C.H., K.T.B., J.S.; data acquisition, C.H., J.S., T.K.P.; data analysis/interpretation, C.H., T.K.P.; statistical analysis, T.K.P.; manuscript preparation, C.H.; manuscript definition of intellectual content, K.T.B.; manuscript editing, C.H., J.S.; manuscript revision/review, T.K.P., D.B.; manuscript final version approval, K.T.B.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
 REFERENCES
 

  1. 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]
  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 correlation study. Circulation 1995; 92:2157-2162.[Abstract/Free Full Text]
  3. Wexler L, Brundage B, Crouse J, et al. Coronary artery calcification: pathophysiology, epidemiology, imaging methods, and clinical implications: a statement for health professionals from the American Heart Association Writing Group. Circulation 1996; 94:1175-1192.[Free Full Text]
  4. Janowitz WR, Agatston AS, Kaplan G, Viamonte M, Jr. Differences in prevalence and extent of coronary artery calcium detected by ultrafast computed tomography in asymptomatic men and women. Am J Cardiol 1993; 72:247-254.[CrossRef][Medline]
  5. Arad Y, Spadaro LA, Goodman K, et al. Predictive value of electron beam computed tomography of the coronary arteries: 19-month follow-up of 1173 asymptomatic subjects. Circulation 1996; 93:1951-1953.[Abstract/Free Full Text]
  6. Detrano RC, Wong ND, Doherty TM, Shavelle R. Prognostic significance of coronary calcific deposits in asymptomatic high-risk subjects. Am J Med 1997; 102:344-349.[CrossRef][Medline]
  7. Kajinami K, Seki H, Takekoshi N, Mabuchi H. Noninvasive prediction of coronary atherosclerosis by quantification of coronary artery calcification using electron beam computed tomography: comparison with electrocardiographic and thallium exercise stress test results. J Am Coll Cardiol 1995; 26:1209-1221.[Abstract]
  8. Bielak LF, Kaufmann RB, Moll PP, McCollough CH, Schwartz RS, Sheedy PF. Small lesions in the heart identified at electron beam CT: calcification or noise? Radiology 1994; 192:631-636.[Abstract/Free Full Text]
  9. O’Rourke R, Brundage B, Froelicher V, 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]
  10. Devries S, Wolfkiel C, Shah V, Chomka E, Rich S. Reproducibility of the measurement of coronary calcium with ultrafast computed tomography. Am J Cardiol 1995; 75:973-975.[CrossRef][Medline]
  11. 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]
  12. Callister TQ, Cooil B, Raya SP, Lippolis NJ, Russo DJ, Raggi P. Coronary artery disease: improved reproducibility of calcium scoring with an electron-beam CT volumetric method. Radiology 1998; 208:807-814.[Abstract/Free Full Text]
  13. Yoon HC, Greaser LE, Mather R, Sinha S, McNitt-Gray MF, Goldin JG. Coronary artery calcium: alternate methods for accurate and reproducible quantitation. Acad Radiol 1997; 4:666-673.[CrossRef][Medline]
  14. Hong C, Becker CR, Schoepf UJ, Ohnesorge B, Bruening R, Reiser MF. Coronary artery calcium: absolute quantification in nonenhanced and contrast-enhanced multi-detector row CT studies. Radiology 2002; 223:474-480.[Abstract/Free Full Text]
  15. Sprawls P. CT image detail and noise. RadioGraphics 1992; 12:1041-1046.[Abstract]
  16. Achenbach S, Giesler T, Ropers D, et al. Detection of coronary artery stenoses by contrast-enhanced, retrospectively electrocardiographically-gated, multislice spiral computed tomography. Circulation 200; 103:2535-2538.[Abstract/Free Full Text]
  17. 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]
  18. Ohnesorge B, Flohr T, Becker C, Kopp A, Knez A, Reiser M. Dose evaluation and dose reduction strategies for ECG-gated multislice spiral CT of the heart (abstr). Radiology 2000; 217(P):487.[Abstract/Free Full Text]
  19. Ulzheimer S, Kachelriess M, Kalender WA. New phantoms for quality assurance in cardiac CT (abstr). Radiology 1999; 213(P):402.
  20. Mayo JR, Hartman TE, Lee KS, Primack SL, Vedal S, Mueller NL. CT of the chest: minimal tube current required for good image quality with the least radiation dose. AJR Am J Roentgenol 1995; 164:603-607.[Abstract/Free Full Text]
  21. Wang G, Vannier MW. Low-contrast resolution in volumetric x-ray CT analytical comparison between conventional and spiral CT. Med Phys 1997; 24:373-376.[CrossRef][Medline]
  22. Kajinami K, Seki H, Takekoshi N, Mabuchi H. Coronary calcification and coronary atherosclerosis: site by site comparative morphologic study of electron beam computed tomography and coronary angiography. J Am Coll Cardiol 1997; 29:1549-1556.[Abstract]
  23. McCollough CH, Kaufmann RB, Cameron BM, Katz DJ, Sheedy PF, Peyser PA. Electron-beam CT: use of a calibration phantom to reduce variability in calcium quantitation. Radiology 1995; 196:159-165.[Abstract/Free Full Text]
  24. Chanllande P, Plainfosse MC. Reliability of coronary calcium quantification with electron beam CT. Radiology 1994; 193:282-283.[Medline]
  25. Raggi P, Callister TQ, Cooil B. Calcium scoring of the coronary artery by electron beam CT: how to apply an individual attenuation threshold. AJR Am J Roentgenol 2002; 178:497-502.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 Am. J. Roentgenol.Home page
N. Matsuura, J. Horiguchi, H. Yamamoto, N. Hirai, T. Tonda, N. Kohno, and K. Ito
Optimal Cardiac Phase for Coronary Artery Calcium Scoring on Single-Source 64-MDCT Scanner: Least Interscan Variability and Least Motion Artifacts
Am. J. Roentgenol., June 1, 2008; 190(6): 1561 - 1568.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Roentgenol.Home page
S. M. Kim, M. J. Chung, K. S. Lee, Y. H. Choe, C. A. Yi, and B.-K. Choe
Coronary Calcium Screening Using Low-Dose Lung Cancer Screening: Effectiveness of MDCT with Retrospective Reconstruction
Am. J. Roentgenol., April 1, 2008; 190(4): 917 - 922.
[Abstract] [Full Text] [PDF]

Home page
 RadiologyHome page
J. Shemesh, R. Evron, N. Koren-Morag, S. Apter, J. Rozenman, D. Shaham, Y. Itzchak, and M. Motro
Coronary Artery Calcium Measurement with Multi-Detector Row CT and Low Radiation Dose: Comparison between 55 and 165 mAs
Radiology, September 1, 2005; 236(3): 810 - 814.
[Abstract] [Full Text] [PDF]

Home page
 CirculationHome page
F. Moselewski, C. J. O'Donnell, S. Achenbach, M. Ferencik, J. Massaro, A. Nguyen, R. C. Cury, S. Abbara, I.-K. Jang, T. J. Brady, et al.
Calcium Concentration of Individual Coronary Calcified Plaques as Measured by Multidetector Row Computed Tomography
Circulation, June 21, 2005; 111(24): 3236 - 3241.
[Abstract] [Full Text] [PDF]

Home page
 RadiologyHome page
U. J. Schoepf, C. R. Becker, B. M. Ohnesorge, and E. K. Yucel
CT of Coronary Artery Disease
Radiology, July 1, 2004; 232(1): 18 - 37.
[Abstract] [Full Text] [PDF]

Home page
 RadiologyHome page
R. Vliegenthart, B. Song, A. Hofman, J. C. M. Witteman, and M. Oudkerk
Coronary Calcification at Electron-Beam CT: Effect of Section Thickness on Calcium Scoring in Vitro and in Vivo
Radiology, November 1, 2003; 229(2): 520 - 525.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Roentgenol.Home page
A. H. Mahnken, J. E. Wildberger, J. Simon, R. Koos, T. G. Flohr, S. Schaller, and R. W. Gunther
Detection of Coronary Calcifications: Feasibility of Dose Reduction with a Body Weight-Adapted Examination Protocol
Am. J. Roentgenol., August 1, 2003; 181(2): 533 - 538.
[Abstract] [Full Text] [PDF]

Home page
 RadiologyHome page
C. Hong, K. T. Bae, and T. K. Pilgram
Coronary Artery Calcium: Accuracy and Reproducibility of Measurements with Multi-Detector Row CT—Assessment of Effects of Different Thresholds and Quantification Methods
Radiology, June 1, 2003; 227(3): 795 - 801.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
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 HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Hong, C.
Right arrow Articles by Bradley, D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Hong, C.
Right arrow Articles by Bradley, D.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
RADIOLOGY RADIOGRAPHICS RSNA JOURNALS ONLINE