The race of three different contrast agent application protocols for the optimal and safe thoracic CT angiography in neonates, infants and toddlers

Objectives:

Imaging of congenital thoracic and cardiovascular malformations is a challenging task considering that younger children are most vulnerable to contrast agent (CA) -induced osmotic changes and kidney injury. In order to minimize the amount of applied CA without compromising the clinical purpose of the examination, the “Microbolus Technique” (MBT) was developed in our center for chest CTA. During MBT a 2 : 1 mixture of 300 mg% Iodine CA and saline is applied at 80 kV, the bolus threshold is set to 450HU. Current work aimed to evaluate the clinical usability of MBT compared to other CA application protocols.

Methods:

70 patients (age < 24 months), who underwent CTA were divided into three groups based on the applied CA protocol. In group I MBT was used, in group II dual phase protocol was applied for CTA with bolustracking injecting CA at a constant rate followed by a saline flush. In Group III CA was administered with fixed bolus delay. Iodine concentration (300 mg%) was identical in all patients and the amount of CA was individually adapted to age and weight. Objective image quality was assessed by measuring peak enhancement, signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) in different thoracic regions. Results were adjusted after patient age and weight. Subjective image quality and image artefacts were analyzed by two observers as a consensus decision.

Results:

The mean patient age and weight in Group I was 5.81 ± 5.18 months and 5.73 ± 2.47 kg, in Group II 7.74 ± 6.44 months and 6.77 ± 2.63 kg while in Group III 7.4 ± 0.14 months and 7.03 ± 2.03 kg, respectively. Significantly lower amount of contrast agent (mean ± SD) was used in the MBT Group compared to Group II and Group III (9.03 ± 3.72 mL, 12.91 ± 4.5 mL and 12.13 ± 5.15 mL respectively). Despite less CA volume, peak enhancement measured over most thoracic regions did not differ from each other within the three groups. Additionally, the most homogenous enhancement was reached in group I and III. The best subjective image quality with the fewest artefacts was found in Group I.

Discussion:

MBT offers a nearly 25% cutback of applied CA by maintaining peak enhancement and artefact reduction-thus being the ideal technique for CTA in patients younger than 24 months.