High-Z Contrast Media for Coronary Photon-counting Detector CT Angiography: Improved Quantification of Calcified...

Blooming artifacts from calcified plaques can obscure the vessel lumen, leading to overestimation of stenosis severity. Spectral coronary angiography with photon-counting detector CT (PCD-CT) provides virtual monoenergetic images (VMIs) for coronary artery disease assessment. While VMIs at high VMI energy levels reduce calcium blooming, iodine contrast is diminished, limiting diagnostic value. This study evaluated whether contrast media with an atomic number higher than iodine (high-Z) preserve vascular contrast using high VMI energy levels, thereby improving the accuracy of stenosis quantification.

A phantom with 4 and 6 mm diameter rods to mimic small diameter vessels containing eccentric calcified plaques causing 25%, 50%, and 75% diameter stenoses was scanned with a dual-source PCD-CT system. Five different contrast media, including iodine, tungsten, holmium, hafnium, and bismuth, were tested. VMIs were reconstructed from 40 to 190 keV in 1-keV steps. Vessel attenuation, contrast-to-noise ratio (CNR), and stenoses were measured. Qualitative assessment of image quality was performed.

Iodine attenuation was high at lower VMI energy levels and dropped below 250 HU at >100 keV. Tungsten, holmium, hafnium, and bismuth maintained >250 HU attenuation throughout the entire energy range. Vessel CNR of iodine was high at lower and decreased at higher VMI energy levels, similar to the CNR of holmium and bismuth, though to a lesser extent. In distinction, CNRs of tungsten and hafnium were lower at lower VMI energy levels and increased to a relatively constant level at higher keV. Tungsten CNR increased with energy, approaching ~40 at high keV. Across all contrast media and stenosis degrees, stenoses were overestimated on low VMI energy levels (24% to 32.5% at 40 keV), while the degree of overestimation decreased at higher VMI energy levels (0% to 13.5% at 190 keV). At 190 keV, tungsten, hafnium, and bismuth showed ≤2.5% stenosis overestimation, compared with iodine (10% to 13.5%). Image quality varied between contrast media and energy levels: new very high-Z contrast media achieved higher scores, while iodine peaked at lower keV (55 to 70 keV) and, due to loss of contrast at higher energies, received the lowest overall scores.

As compared with iodine, very high-Z contrast media enable superior lumen definition and more accurate stenosis assessment, also at high VMI energy levels, which minimize calcium blooming.