(2026) Schwartz | Mixed-bolus low-keV PCCT improves CTPA robustness

Daniel Stromer

In 150 patients undergoing PCCT pulmonary angiography, the investigators compared three contrast-injection strategies while reconstructing images at 40, 55, and 67 keV. Pulmonary arterial enhancement increased progressively at lower energies, with 40 keV providing the strongest vascular enhancement and highest reader preference.

The most robust protocols used contrast mixed 1:1 with saline and a fixed scan delay, rather than a small undiluted bolus with bolus tracking. Both the 50/50-mL and 35/35-mL contrast/saline approaches produced no examinations with pulmonary arterial enhancement below 350 HU at 40 keV, whereas the bolus-tracking cohort had three such injections.

The practical message is that PCCT can make CTPA less dependent on precise bolus timing: a longer mixed bolus, fixed timing, high-pitch acquisition, and 40-keV VMI provided a robust protocol while allowing contrast volume to be reduced to 35 mL.

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Protocol

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Detail	Value
Scanner	NAEOTOM Alpha
Scan area	CT pulmonary angiography
Acquisition mode	high-pitch
Tube voltage [kV]	140
IQ level	105
Dose modulation	CareDose4D
Detector slice collimation	2 × 144 × 0.4 mm
VMI reconstructions	40, 55, and 67 keV
Cohort 1 injection	50 mL contrast / 0 mL saline; bolus tracking
Cohort 2 injection	50 mL contrast + 50 mL saline; fixed scan delay
Cohort 3 injection	35 mL contrast + 35 mL saline; fixed scan delay
Optimized contrast strategy	Equal-volume contrast/saline mixture: 50/50 mL or 35/35 mL
Injection rate	4 mL/s for optimized mixed-bolus protocols
Scan timing	Acquisition started at the end of the mixed-bolus injection
Recommended vascular reconstruction	Thin-slice 40-keV VMI
Recommended soft-tissue reconstruction	Thicker 67-keV VMI

Key Results

• Population: 150 patients, 50 per protocol; mean age 60.6 ± 16.6 years.
• Pulmonary arterial attenuation was significantly higher with 40 > 55 > 67 keV (p < 0.001).
• At 40 keV, 3 examinations in cohort 1 had attenuation <350 HU, versus none in cohorts 2 or 3.
• Reader-rated vascular contrast was highest at 40 keV; in cohort 2, scores were 4.7 ± 0.5 at 40 keV, 4.5 ± 0.7 at 55 keV, and 3.6 ± 1.0 at 67 keV (p < 0.001).
• The authors favored 50/50-mL or 35/35-mL contrast/saline mixtures with fixed delay, concluding that this approach minimized suboptimal enhancement and repeat examinations.

Source:
Schwartz FR, Khanungwanitkul K, Czajkowski B, Duraisamy S, Jhala K, Hammer MM, Sodickson AD. Optimizing photon-counting CT pulmonary angiography for robustness, combining mixed bolus, fixed scan delay and low keV. European Journal of Radiology. 2026;195:112540. doi:10.1016/j.ejrad.2025.112540.