Could Photon Counting Reduce Iodinated Contrast Media for CT Angiography?

In a new study comparing photon-counting detector computed tomography (PCD CT) to energy-integrating detector CT (EID CT) for thoracoabdominal CT angiography, researchers found a 25 percent higher contrast-to-noise ratio (CNR) with PCD CT and subsequently determined that a revised protocol with PCD CT could reduce iodinated contrast media (ICM) by 25 percent in comparison to EID CT.

Noting the potential risk for contrast-induced acute kidney injury (CI-AKI) in patients with multiple computed tomography angiography (CTA) exams, the researchers sought to develop and assess the use of PCD CT with a reduced ICM protocol in this patient population.

For the prospective study, which was recently published in Radiology: Cardiothoracic Imaging, researchers assessed 100 patients (mean age of 75) who had CTA with PCD CT and prior EID CT for imaging of the thoracoabdominal aorta.

In the first group of 40 patients, the study authors noted the use of PCD CT with virtual monoenergetic images (VMI) at 50 keV had a 25 percent higher contrast-to-noise ratio (CNR) than EID CT. In the second group of 60 patients, the researchers found that a 25 percent reduction of ICM with PCD CT at VMI of 50 keV was non-inferior to EID CT for imaging of the thoracoabdominal aorta.

“Compared with EID CT, VMI at 50 keV from PCD CT had noninferior objective and subjective image quality, with mean differences in CNR and subjective image quality between EID CT and PCD CT at 50 keV being above the pre-defined boundaries of noninferiority …, illustrating the potential of PCD CT to reduce contrast media exposure to potentially susceptible patients,” wrote Hatem Alkadhi, M.D., MPH, EBCR, FESER, a professor of radiology at the Institute of Diagnostic and Interventional Radiology of the University Hospital Zurich in Switzerland, and colleagues.

(Editor’s note: For related content, see “Five Takeaways from New Consensus Recommendations for CT Imaging and Reporting in Patients with CAD” and “HeartFlow Garners FDA Clearances for Two AI-Powered Assessment Tools with CCTA.”)

In an accompanying editorial, James Dundas, MBBS, MRCP and Jonathon A. Leipsic, M.D., FRCPC, MSCCT., noted a number of potential benefits with PCD CT, ranging from virtual non-contrast imaging for coronary calcium scoring and reducing metallic artifacts in close proximity to implanted cardiac devices to utility in assessing myocardial fibrosis and complex congenital heart disease. While acknowledging the “framework” of the study’s findings with photon-counting CT, Drs. Dundas and Leipsic said measurable clinical impact demonstrated in future studies will be more of a driver for wider adoption than ICM reduction in aortic imaging.

“Delivering benefit in clinically relevant outcomes would make a stronger case for embracing photon counting in routine clinical practice,” noted Dr. Dundas, an advanced cardiac imaging fellow at the University of British Columbia, and Dr. Leipsic, a professor and head of the Department of Radiology at the University of British Columbia.

In regard to study limitations, the study authors acknowledged a small proportion of women in the study and the overall small cohort size. The researchers also noted the study was not designed to compare the diagnostic accuracy of photon-counting detector CT (PCD CT) versus energy-integrating detector CT (EID CT). Pointing out that their image quality comparison of PCD CT and EID CT was based on single-energy mode imaging, Alkadhi and colleagues maintained that future studies should assess dual-energy CT use as well as the impact of quantum iterative reconstruction (QIR) upon image quality.