Study: Photon-Counting CT for Pulmonary Angiography Allows Significant ICM Reduction

Can photon-counting computed tomography (PCCT) enable reduced iodinated contrast media (ICM) dosing without compromising imaging assessments for pulmonary angiography?

For a new retrospective study, recently published in Academic Radiology, researchers assessed the use of high-pitch dual-source PCCT and bolus tracking to reduce ICM dosing for computed tomography pulmonary angiography (CTPA) in 105 patients (mean age of 69.1). The study authors examined 35 ml of ICM in 29 patients, 45 ml in 62 patients and 60 ml in 14 patients. Employing a Likert scale, four radiologists also assessed image quality ranging from 1 for inadequate to 5 for excellent, according to the study.

The researchers found a mean of 18.5 adequately contrasted segmental pulmonary arteries with group one (35 ml ICM) in comparison to 18.7 for group two (45 ml ICM) and 18.4 for group three (60 ml ICM). The mean overall image quality ratings were 4.6 for group one, 4.5 for group two and 4.1 for group three, according to the study. For the mean attenuation in the pulmonary trunk, the study authors said group one had 321 Hounsfield units (HUs), group two had 345 Hus and group three had 347 HUs.

For the mean contrast-to-noise (CNR) ratio in the pulmonary trunk, the study authors also noted a 7.4 CNR in group one in comparison to 8.0 in group two and 7.9 in group three.

“Utilizing high-pitch scanning, especially with dual-source CT, allows for a short (ICM) bolus. … Further advantages of the high pitch-PCCT method are a lower risk for respiratory artifacts and lower image noise for patients. The disadvantages are the dependency on the exact CM timing, and the limitation of the time-current product in the flash scan mode, which may be insufficient in larger patients. The fact that attenuation in the main pulmonary artery remained stable, despite the reduction of (ICM) dose in our study, is likely an effect of the high-pitch protocol,” wrote Jan Robert Kroeger, M.D., who is affiliated with the Department of Radiology, Neuroradiology and Nuclear Medicine at Johannes Wesling University Hospital at Ruhr University Bochum in Bochum, Germany, and colleagues.

Here one can see similar computed tomography angiography (CTA) axial and coronal maximum intensity projection (MIP) views of the pulmonary trunk done with 35 ml ICM (a), 45 ml ICM (b) and 60 ml ICM (c). (Images courtesy of Academic Radiology.)

(Editor’s note: For related content, see “Could Photon Counting Reduce Iodinated Contrast Media for CT Angiography?,” “Study Examines Photon-Counting CT for CAD Detection in Patients Having TAVR Procedures” and “Study Shows Merits of Photon-Counting CT in Detecting Subtle Post-COVID Lung Abnormalities.”)

While the researchers did not utilize virtual monoenergetic images in the study, they said this is a viable alternative to tube voltage reduction for dual-energy CT views of the pulmonary artery with lower ICM dosing.

“One way to provide favorable image quality with reduced (ICM) dose protocols while maintaining contrast attenuation in the pulmonary trunk is to lower the tube voltage of the scan.… However, lowering the tube voltage is not always possible in dual-energy CT as spectral imaging results are often limited to specific kVp levels (usually 120 kVp),” pointed out Kroeger and colleagues. “Nonetheless, in dual-energy CT, a similar effect can be achieved by employing virtual monoenergetic images, that can be generated from the main dataset and allow for reconstruction at different energy levels, thus facilitating optimal attenuation in the pulmonary artery.”

In addition to a relatively small cohort, the authors acknowledged the lack of comparison to a CTPA scan with standard ICM but attributed this to the overarching goal of the study for assessing objective and subjective CTPA imaging with low ICM protocols.