Rationale and Objectives
Our aim was to evaluate the correlation of test bolus (TB) curve parameters with main bolus (MB) contrast density for cardiac 16-slice computed tomography, and to correlate observed enhancement with patient body weight.
Materials and Methods
Sixty patients with known or suspected coronary artery disease were included in a prospective double-blind study. Contrast material containing 300 mg iodine/mL (Iomeprol 300; Imeron 300, Bracco Imaging SpA, Milan, Italy) and 400 mg iodine/mL (Iomeprol 400; Imeron 400) was injected at a rate of 1 g of iodine/second. Contrast densities (Hounsfield units) of the MB were determined in the left cardiac system. The peak density (PD) of maximum attenuation and the area under the curve (AUC) of the TB curve were calculated for each patient. The dependency of MB contrast attenuation on these parameters and on patient body weight was evaluated.
Results
Positive correlations ( r = 0.52 and r = 0.56, respectively; P < .0001) were obtained between the PD and AUC of the TB curve with the mean density of the MB. Stronger correlations ( r = 0.63 and r = 0.64, respectively; P < .0001) between PD and AUC of the TB curve and MB attenuation were found when patient body weight was included in the analysis.
Conclusions
Strong correlation of the PD and AUC of the TB curve with the mean density of the MB is observed when patient body weight is considered. Contrast injection protocols may be optimized, and variations of MB contrast density in the left ventricle and main coronary arteries reduced, by taking these TB parameters and the weight of the patient into account.
The introduction of multislice computed tomography (MSCT) coronary angiography has led to markedly reduced overall scan times and thus to a greater need for accurate timing of the contrast bolus injection relative to the start of data acquisition ( ). Overall homogeneous vessel lumen attenuation of approximately 250–300 Hounsfield units (HU) is essential for cardiac CT, requiring injection of contrast material at a rate of about 1 g of iodine/second ( ). Approaches to obtaining this target attenuation include injecting contrast media (CM) containing a standard concentration of iodine (approximately 300 mg iodine/mL) at a moderate flow rate or, alternatively, injecting a smaller volume of a CM with a higher iodine content at a reduced injection rate ( ). The possibility to obtain excellent artifact-free contrast enhancement on MSCT coronary angiography with high-contrast resolution permits not only the improved identification of small coronary vessels, but also, if the vessel lumen is opacified adequately, the differentiation of low-density coronary artery atherosclerotic lesions from intermediate fibrous plaques and calcified lesions ( ).
Typically, precise timing of the contrast bolus in MSCT angiography is achieved by means of an automated bolus tracking technique or by using a test bolus (TB) that permits accurate determination of the arrival time of the main contrast bolus in the vasculature close to the region to be examined ( ). Test bolus approaches use a defined small bolus of contrast material that is injected at the same injection flow rate as the main bolus (MB). Subsequently, a series of stationary low-dose scans is acquired that provides information on TB geometry, allowing calculation of a time-attenuation curve from which the exact circulation time and optimal time point for initiation of the CT scan after injection of the MB can be determined.
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Methods and materials
Legal and Ethical Conduct of the Study
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Subjects
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MSCT Angiography
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Contrast Injection Protocol
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Acquisition of Test Bolus Curve
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Density Measurements
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Correlation Between Test Bolus Curve and Main Bolus
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Statistical Analysis
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Results
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Contrast Attenuation of the Main Bolus and PD and AUC of the Test Bolus
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Correlations Between PD and AUC of the Test Bolus Curve and Mean Density in the Left Ventricle
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Table 1
Correlations of TB Parameters with MB Density Measurement in the Left Ventricle
TB Parameter Not Body Weight–Adapted Body Weight–Adapted PD 133.71 ± 36.7 HU (minimum 76.4; maximum 248.9)r = 0.52; r 2 = 0.27 1.73 ± 0.72 HU/kg (minimum 0.61; maximum 3.77)r = 0.63; r 2 = 0.40P < .0001P < .0001 AUC 1217.3 ± 411 HU*s (minimum 424; maximum 2377)r = 0.56; r 2 = 0.31 15.83 ± 7.51 HU*s/kg (minimum 4.58; maximum 38.34)r = 0.64; r 2 = 0.41P < .0001P < .0001
TB: test bolus; MB: main bolus; PD: peak density; HU: Hounsfield unit.
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Prediction of Main Bolus Densities in the Left Ventricle from Test Bolus Parameters and Patients’ Body Weight
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LV=1.51*BW+0.107*AUC LV
=
1.51
*
BW
+
0.107
*
AUC
LV=1.25*BW+1.13*PD LV
=
1.25
*
BW
+
1.13
*
PD
where LV is the estimated attenuation in the left ventricle (HU) and BW is the patients’ body weight (kg).
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Discussion
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