Korean J Radiol.  2009 Aug;10(4):340-346. 10.3348/kjr.2009.10.4.340.

Effect of Heart Rate and Body Mass Index on the Interscan and Interobserver Variability of Coronary Artery Calcium Scoring at Prospective ECG-Triggered 64-Slice CT

• Horiguchi
• Matsuura N
• Yamamoto H
• Kiguchi M
• Fujioka C
• Kitagawa T
• Ito K

• KMID: 1777261
• DOI: http://doi.org/10.3348/kjr.2009.10.4.340

Abstract

OBJECTIVE
To test the effects of heart rate, body mass index (BMI) and noise level on interscan and interobserver variability of coronary artery calcium (CAC) scoring on a prospective electrocardiogram (ECG)-triggered 64-slice CT.
MATERIALS AND METHODS
One hundred and ten patients (76 patients with CAC) were scanned twice on prospective ECG-triggered scans. The scan parameters included 120 kV, 82 mAs, a 2.5 mm thickness, and an acquisition center at 45% of the RR interval. The interscan and interobserver variability on the CAC scores (Agatston, volume, and mass) was calculated. The factors affecting the variability were determined by plotting it against heart rate, BMI, and noise level (defined as the standard deviation: SD).
RESULTS
The estimated effective dose was 1.5 +/- 0.2 mSv. The mean heart rate was 63 +/- 12 bpm (range, 44-101 bpm). The patient BMIs were 24.5 +/- 4.5 kg/m2 (range, 15.5-42.3 kg/m2). The mean and median interscan variabilities were 11% and 6%, respectively by volume, and 11% and 6%, respectively, by mass. Moreover, the mean and median of the algorithms were lower than the Agatston algorithm (16% and 9%, respectively). The mean and median interobserver variability was 10% and 4%, respectively (average of algorithms). The mean noise levels were 15 +/- 4 Hounsfield unit (HU) (range, 8-25 HU). The interscan and interobserver variability was not correlated with heart rate, BMI, or noise level.
CONCLUSION
The interscan and interobserver variability of CAC on a prospective ECG-triggered 64-slice CT with high image quality and 45% of RR acquisition is not significantly affected by heart rate, BMI, or noise level. The volume or mass algorithms show reduced interscan variability compared to the Agatston scoring (p < 0.05).

Keyword

Coronary artery; Calcium; Computed tomography (CT); Heart rate; Body mass index

MeSH Terms

Adult
Aged
Aged, 80 and over
*Body Mass Index
Calcium/*analysis
Coronary Angiography/*methods
Coronary Vessels/*chemistry
*Electrocardiography
Female
*Heart Rate
Humans
Male
Middle Aged
Observer Variation
Prospective Studies
Tomography, X-Ray Computed/*methods

Figure

• 

  Fig. 1 Measurement of image noise. Region of interest (typically about 150 mm2) is set in ascending aorta on slice image at level of left coronary artery. Mean and standard deviation of CT values are 40 HU and 17 HU, respectively. Image noise is defined as standard deviation.

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  Fig. 2 Discrepancy in interpretation of calcium deposit. A-C. Calcium (arrow in A) is interpreted to be located in aorta by one observer and in left main coronary artery by other observer; calcium (arrow in B) interpreted to be in epicardium versus in left anterior descending artery; calcium (arrow in C) interpreted to be in left atrial wall versus in left circumflex artery.

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  Fig. 3 Interscan and interobserver variability of Agatston, volume, and mass scores. Graph shows interscan and interobserver variability (Agatston; black, volume; white, mass; gray). Bars and vertical lines indicate mean and standard deviation, respectively. Interscan variability was different between scoring algorithms (p < 0.05) and observers (p < 0.05). Mean variability values are referenced in text.

• 

  Fig. 4 Scatterplots show ratio (A) between heart rate (bpm) and interscan variability: r2 = 0.016, slope = -0.002 /bpm, intersection = 25%, p = 0.27 ratio (B) between body mass index (kg/m2) and interscan variability: r2 < 0.001, slope = 0.0003 /kg per millimeter squared, intersection = 12%, p = 0.94 and ratio (C) between noise level (HU) and interscan variability: r2 = 0.0007, slope = 0.0013 /HU, intersection = 11%, p = 0.82. Exceptional high variability is observed in case with low coronary artery calcium score.

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  Fig. 5 Scatterplot shows ratio between body mass index (kg/m2) and standard deviation (HU). r2 = 0.260, slope = 0.40 HU/kg per millimeter squared, intersection = 4.72 HU. Some exceptionally high (or low) standard deviations are due to individual body habitus (i.e., spinal spur is responsible for noisy image) or motion artifacts.

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  Fig. 6 Scatterplot shows ratio between body weight (kg) and standard deviation (HU). r2 = 0.301, slope = 0.16 HU/kg per millimeter squared, intersection = 4.67 HU.

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