All settings listed below were calculated for a 256-slice multidetector scanner (Revolution APEX, GE Healthcare, Milwaukee, WI), by using a dual-head injection (CT Exprès™ Bracco, Milan, Italy) and i.v. administration of Omnipaque/Accupaque™ 300—Iohexol iodinated contrast medium (300 mg/ml) (GE HealthCare, Milwaukee, WI).

The aim of this pediatric split-bolus protocol is to perform accurate arterial and venous opacification along with parenchymal impregnation, following two contrast media injections in a single CT acquisition. The first injection will provide venous opacification and parenchymal impregnation whereas the second injection will serve to opacify the arterial bed.

All different settings including acquisition time, contrast media and saline volumes, flow rate injection, injection time, and pause time between the two injections are calculated based exclusively on the patient weight in kilograms, which is the only information to insert in the calculator. Settings can be calculated for a weight range between 4 and 100 kg.

As suggested by Kim et al. [6], the total injected contrast media volume in milliliters is two times the patient weight for small children weighing ≤ 30 kg. The primary reasoning is that lighter patients have faster heart rates, smaller body sizes, and reduced blood volumes, resulting in quicker circulation. However, for patients > 30 kg, who have more adult-like physiology and blood pool, a volume of 30 ml is added to the patient weight, up to a maximum of 80 ml. However, contrary to Kim et al. [6], two-thirds of the so-obtained total contrast volume is injected in the first bolus (venous phase) and the remaining one-third in the second bolus (arterial phase). This adjustment ensures adequate parenchymal impregnation and venous opacification, which are more critical than arterial opacification following intravenous injection.

The timing of image acquisition (venous phase) is set to 50 s after the beginning of the first bolus for patients≤15 kg, 55 s for patients>15 kg and ≤ 30 kg, and 65 s for patients>30 kg of weight.

The timing of the second bolus (arterial phase) is set to 7 s before image acquisition for the patients weighting≤5 kg, 10 s for those>5 kg and ≤ 10 kg, 15 s for those10 kg and ≤ 18 kg, and 20 s for those > 18 kg of weight.

Between the two boluses, a calculated pause is set for the patients ≤ 15 kg and a saline flush for the others, with their duration resulting from the time interval remaining between the two contrast media boluses. The saline volume results from the rate of injection allowed by the patient weight, with a minimum volume set at 10 ml, which is the volume of the tubing of the pump. After the two contrast media injections, a saline flush with 5 ml is set for patients ≤ 15 kg and with 20 ml for those > 15 kg.

The flow rate of each contrast media bolus and saline flush was set based on five weight categories (Table 1). The total fluid load, of contrast media and saline, was limited to 3 ml/kg of patient weight.

As the timings are calculated from the start of the first contrast media injection, the tubing must be purged with contrast media for all patients.

The calculator following the previously described rules was built in a Google Sheet table, to ensure file compatibility and transmission. To facilitate its use, we chose a similar design to the display of the dual-headed injector (CT Exprès™ Bracco, Milan, Italy) used in our department (Fig. 1). The calculator is accessible by a QR code link (Fig. 2).

Calculator display. The only modifiable cell is the light green one where the patient’s weight is inserted in kg (arrow) and automatically all injection settings and acquisition timings are presented

Quick response (QR) code leading to the Google Sheets with the calculator