Improved Calcium Scoring at Dual-Energy Computed Tomography Angiography Using a High-Z Contrast Element and Novel Material Separation Technique

Abstract

Objectives: The aim of this study was to compare the accuracy of existing dual-energy computed tomography (CT) angiography coronary artery calcium scoring methods to those obtained using an experimental tungsten-based contrast material and a recently described contrast material extraction process (CMEP).

Methods: Phantom coronary arteries of varied diameters, with different densities and arcs of simulated calcified plaque, were sequentially filled with water, iodine, and tungsten contrast materials and scanned within a thorax phantom at rapid-kVp-switching dual-energy CT. Calcium and contrast density images were obtained by material decomposition (MD) and CMEP. Relative calcium scoring errors among the 4 reconstructed datasets were compared with a ground truth, 120-kVp dataset.

Results: Compared with the 120-kVp dataset, tungsten CMEP showed a significantly lower mean absolute error in calcium score (6.2%, P < 0.001) than iodine CMEP, tungsten MD, and iodine MD (9.9%, 15.7%, and 40.8%, respectively).

Conclusions: Novel contrast elements and material separation techniques offer improved coronary artery calcium scoring accuracy and show potential to improve the use of dual-energy CT angiography in a clinical setting.

Figure 1

Axial single energy CT images of the thorax phantom. Calcified walls of the simulated vessels were composed of 60, 40, and 20% hydroxyapatite by weight (radial arrangements of circumferential calcified walls labeled 1, 2, and 3, respectively, and arcs of calcified walls labeled 4, 5, and 6, respectively). Simulated vessel lumen diameters were 3, 6, and 9 mm for the innermost, mid, and outermost vessels, respectively. A) The simulated vessels were filled with water which, because of its similar x-ray attenuation as blood, enables straightforward scoring of the vessel wall calcifications. B) The simulated vessels were filled iodinated contrast material, severely limiting the ability to distinguish the calcifications from intravascular contrast. This demonstrates the requirement for the traditional two-phase coronary CT examination to obtain both calcium scores and a CT angiogram.

Figure 2

Axial material-specific images. A) Iodine-calcium map generated by material decomposition (MD). B) Calcium-iodine MD. C) Iodine-calcium map generated by CMEP. D) Calcium-iodine CMEP. E) Tungsten-calcium MD. F) Calcium-tungsten MD. G) Tungsten-calcium CMEP. H) Calcium-tungsten CMEP. In all images the window width is scaled to the minimum and maximum pixel values observed within in the mediastinal insert for each dataset.

Figure 3

Bar chart showing the mean absolute percentage errors for the four material separation datasets compared to the ground truth 120 kVp dataset. The same accuracy ranking is observed for the four datasets in each of the three calcium scoring methods. Error bars represent the standard error of the mean.