Thoracic CT Angiographies in Children Using Automated Power Injection with Bolus Tracking Versus Manual Contrast Injection: Analysis of Contrast Enhancement, Image Quality and Radiation Exposure

Abstract

Objectives: The purpose of this study was to analyze image quality and radiation exposure of thoracic computed tomography angiography (CTA) in children with congenital heart diseases (CHDs) using either manual contrast medium (CM) injection or automated power injectors with bolus tracking. Methods: A total of 137 thoracic CTAs of 120 consecutive pediatric patients were included in this retrospective study. We analyzed the method of CM administration (power injection with bolus tracking (PI) or manual injection (MI)), injection routes, volumes and flow rates of CM. For the evaluation of objective image quality, attenuation values in the heart chambers and great thoracic vessels were determined by region-of-interest (ROI) analysis and signal-to-noise (SNR) and contrast-to-noise (CNR) ratios calculated thereof. Visual image quality was assessed by two blinded readers (four-point Likert-scale) analyzing the presence of artifacts and the depiction of relevant anatomical structures. Effective radiation doses were calculated with dose length products and specific conversion factors. Results: CM administration was performed using PI in 119/137 CTAs, whereas MI was conducted in 18/137. The smallest size of peripheral venous cannulas was 24 gauge in 36/137 (26.3%) cases. Overall mean CM volume was 17 mL ± 16 mL (mean ± SD). In PI, the mean flow rate of CM was 1.52 ± 0.90 mL/s with a range between 0.5 and 5.0 mL/s. When comparing the overall PI population and an age-, size- and weight-matched PI subpopulation (18 cases) with the MI population, attenuation values in Hounsfield units (HU) and CNR values were significantly higher in the PI groups than in the MI group for each relevant cardiac structure (left ventricle, right ventricle, ascending aorta and pulmonary trunk, p = 0.02-0.001). Overall image quality and depiction of cardiac structures were rated significantly better in CTAs with PI (interquartile ranges: "good" to "excellent" (Likert 3-4)) in PI compared with CTAs acquired with MI (interquartile ranges: "fair" to "good" (2-3)) in MI by both readers (p < 0.001). The inter-observer reliability was strong, with a Kendall's Tau-b correlation coefficient of τ = 0.802 (p < 0.001). The mean effective radiation dose (E) did not differ significantly when comparing the stratified samples (i.e., the matched PI subgroup and the MI group; 0.5 (±0.3) mSv in both, p = 0.76). There were no complications associated with the CM injections for both application approaches. Conclusions: Automated contrast agent applications with power injectors and bolus tracking ensure better image quality in pediatric CTA, even when low volumes and flow rates need to be applied. There is a slight increase in radiation associated with bolus tracking. This approach represents a suitable imaging technique for the work-up of congenital heart disease.

Keywords: automated power injector; bolus tracking; computed tomography angiography; congenital heart disease; contrast medium; image quality; manual injection.

Figure 1

Measurement of CT attenuation values with regions-of-interest (A) at level 1 (IVS: interventricular septum; LV: left ventricle; LVPW: LV posterior wall; RV: right ventricle) and (B) at level 2 (AAO: ascending aorta; PA: main pulmonary artery). Standard deviation of the attenuation values obtained from the ROI placed in the air outside of the body served as background noise.

Figure 2

Frequency distribution of the scores of both readers based on a 4-point Likert-scale. All patients with automated power injection (PI) (A), the subgroup of 18 matched patients with PI (B) and all patients with manual injection (MI) of contrast agent (C). CM: contrast medium; n: number. The rated items (y-axis) are (1) overall image noise, (2) motion artifacts, (3) contrast medium artifacts, (4) depiction of aorta, (5) depiction of pulmonary arteries, (6) depiction of cardiac cavities, (7) depiction of septa, (8) depiction of venous-atrial connections and (9) overall quality of the scan. For each item, the upper bar shows the scoring of reader 1 and the lower bar the scoring of reader 2, respectively. Note that the majority of CTA studies were rated “good” or “excellent” (Likert 3 or 4, light and dark green), in particular with PI (A,B). The vast majority of inferior ratings (Likert 1 or 2, red and yellow) were addressed to CTA studies performed after MI (C).

Figure 3

The quality ratings by reader 1 and reader 2 shown as medians and interquartile range: comparison of the total power injection group (PI) vs. the manual injection group (MI) (A) and comparison of the matched PI subgroup vs. the manual injection group (B). All items were rated significantly better for the PI group and the matched PI group compared to the MI group with the exception of “CM artifacts”. The rated items (y-axis) are Ven conn:depiction of the venous–atrial connections; Septa: depiction of the septa; Cardiac chamb: depiction of the cardia cavities; PA: depiction of the pulmonary arteries; Aorta: depiction of the aorta; CM: contrast medium. The different symbols mark the median of the respective rated item.

Figure 4

Case of a one-month-old male patient with d-transposition of the great arteries ((A) axial and (B) oblique sagittal MPR views). A total of 7 mL of contrast agent was administered by hand injection followed by 10 mL of saline. While the anatomy of the cardiac chambers and the great arteries can clearly be depicted, contrast enhancement within these structures is suboptimal. Effective radiation dose was 0.33 mSv.

Figure 5

Case of a one-month-old male presenting with a truncus arteriosus communis ((A) axial and (B) parasagittal MPR views). A total of 6 mL of contrast agent was administered by hand injection followed by 10 mL of saline. Again, the anatomy of the cardiac chambers and the great arteries can be identified and delineated. Yet, contrast enhancement within the target volume might not be sufficient to identify smaller vascular structures. Effective radiation dose was 0.16 mSv.

Figure 6

Case of a four-day-old male with aneurysm of a patent Ductus arteriosus ((A) axial and (B) parasagittal MPR views). A total of 4 mL of contrast agent was injected with a flow rate of 0.7 mL/s followed by 10 mL of saline using a power injector with bolus tracking. Note the markedly better enhancement of the cardiac chambers and great vessels as compared with Cases 1 and 2. Total effective radiation dose was 0.40 mSv (including 0.04 mSv for the bolus tracking).

Figure 7

Case of six-week-old female after clipping of a patent Ductus arteriosus ((A) axial and (B) coronal MPR views). A total of 4 mL of contrast agent was injected with power injection and bolus tracking at a flow rate of 0.7 mL/s followed by 10 mL of saline, resulting in an excellent enhancement of the heart and great vessels. Total effective radiation dose was 0.42 mSv (including 0.04 mSv for the bolus tracking).