Rationale and Objectives
The purpose of our study was to compare test bolus techniques using undiluted or diluted contrast material for their ability to predict aortic enhancement on coronary computed tomographic angiography (c-CTA) images.
Materials and Methods
We divided 200 consecutive patients who underwent c-CTA on a 64-MDCT scanner into two groups. In group A ( n = 100), we used a test bolus of undiluted contrast material and in group B ( n = 100), the contrast material was diluted. The injection volume was body weight × 0.2 (contrast material 100%) in group A and body weight × 0.7 (contrast material 30%, saline 70%) in group B. We then compared the CT number in the ascending aorta on c-CTA images obtained with undiluted and diluted contrast media to the CT number on c-CTA images.
Results
The mean CT number in the ascending aorta was significantly higher in group B than group A (217.1 vs. 157.4 HU, P < .001). There was a significant difference in the correlation between the CT number of the ascending aorta on c-CTA images and on images acquired with the test bolus using undiluted or diluted test bolus ( P < .001). In group B, the correlation had a strong positive linear relationship ( r = 0.72, P < .001), whereas in group A the positive linear relationship was weak ( r = 0.36).
Conclusions
The test bolus with diluted contrast material was useful for predicting aortic enhancement before c-CTA scanning.
Introduction
Coronary computed tomographic angiography (c-CTA) is an accurate noninvasive modality to assess coronary artery disease. To be diagnostically useful the c-CTA images must be of the highest quality. One index of their quality is the contrast-to-noise ratio (CNR) of the coronary artery determined by the contrast enhancement of the coronary artery and the background noise. Although the image noise can be regulated with the tube current at CT scanning, patient variability renders the regulation of coronary artery enhancement difficult. However, with the aid of the time-density curve of the test bolus, arterial enhancement in individual patients can be predicted before c-CTA , and this may make it possible to obtain the optimal CNR for c-CTA by selecting the appropriate tube current second setting. With the test bolus technique, not only the aortic time-density curve, but also aortic peak enhancement can be obtained before c-CTA. The bolus-tracking technique, on the other hand, is a real-time method and it cannot be used to predict enhancement before c-CTA. In general, the total contrast material volume used for the test bolus is low (approximately 10 mL), and large interpatient variability in arterial enhancement renders its prediction for CTA difficult . We hypothesized that the injection of a larger volume of diluted contrast material would yield a better correlation between arterial enhancement obtained with the test bolus and c-CTA than the injection of the conventional volume of undiluted contrast material.
The purpose of our study was to compare the value of test bolus techniques that delivered diluted or undiluted contrast material for predicting aortic enhancement on c-CTA images.
Materials and methods
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Patient Selection
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Table 1
Patient Characteristics for Test Bolus Technique with Undiluted and Diluted Contrast Materials
Undiluted Contrast Material Diluted Contrast Material_P_ Value Number of patients ( n ) 100 100 Sex (male/female) 48/52 44/56 .57 Age (y) 67.5 ± 10.9 (38–92) 70.0 ± 11.3 (40–89) .31 Body height (cm) 158.5 ± 8.6 (137–178) 156.5 ± 8.5 (140–182) .1 Body weight (kg) 57.0 ± 7.7 (39–69) 55.0 ± 7.1 (39–69) .16 Body surface area (m 2 ) 1.6 ± 0.1 1.58 ± 0.1 .19 Body mass index (kg/m 2 ) 22.3 ± 2.4 22.5 ± 2.6 .81 Heart rate (bpm) 59.0 ± 7.2 (44–85) 60.5 ± 7.2 (44–80) .51 Ejection fraction (%) 66.0 ± 8.9 (35–85) 68.0 ± 6.2 (51–88) .39
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CT and Contrast Injection Protocols
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Table 2
Contrast Injection Protocol for Test Bolus and Coronary Computed Tomographic Angiography with Undiluted and Diluted Contrast Materials
Parameter Undiluted Contrast Material Diluted Contrast Material Test bolus Iodine dose (mgI/kg) 70.0 70.0 Injection volume (mL) Body weight (BW) (kg) × 0.2 (contrast material: 100%) BW (kg) × 0.7 (contrast material: 30%, saline: 70%) Injection rate (mL/s) BW (kg) × 0.07 BW (kg) × 0.07 Injection duration (s) 3.0 10.0 Saline chaser (mL) 20.0 20.0 Coronary computed tomographic angiography Iodine dose (mgI/kg) 245.0 Injection volume (mL) BW (kg) × 0.7 (contrast material: 100%) Injection rate (mL/s) BW (kg) × 0.07 Injection duration (s) 10.0 Saline chaser (mL) 20.0
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c-CTA Scanning
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Data Analysis
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Statistical Analysis
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Results
Test Bolus Technique
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Table 3
Contrast Administration Parameters
Parameter Undiluted Contrast Material Diluted Contrast Material_P_ Value Arrival time (sec) 19.0 ± 2.9 20.0 ± 2.5 .27 Injection rate (mL/sec) 3.9 ± 0.5 3.9 ± 3.1 .63 Injection volume (mL) (Test-bolus) Contrast material 11.0 ± 1.6 11.0 ± 1.7 .77 Saline solution – 27.0 ± 6.8 Total volume 11.0 ± 1.5 39.0 ± 5.1 Injection volume (mL) (Coronary CTA) Contrast material 40.0 ± 5.2 39.0 ± 5.1 .29
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Coronary CT Angiography
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Discussion
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Conclusions
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