Dual-energy computed tomography imaging to determine atherosclerotic plaque composition: a prospective study with tissue validation

Abstract

Background: Identifying vulnerable coronary plaque with coronary CT angiography is limited by overlap between attenuation of necrotic core and fibrous plaque. Using x-rays with differing energies alters attenuation values of these components, depending on their material composition.

Objectives: We sought to determine whether dual-energy CT (DECT) improves plaque component discrimination compared with single-energy CT (SECT).

Methods: Twenty patients underwent DECT and virtual histology intravascular ultrasound (VH-IVUS). Attenuation changes at 100 and 140 kV for each plaque component were defined, using 1088 plaque areas co-registered with VH-IVUS. Hounsfield unit thresholds that best detected necrotic core were derived for SECT (conventional attenuation values) and for DECT (using dual-energy indices, defined as difference in Hounsfield unit values at the 2 voltages/their sum). Sensitivity of SECT and DECT to detect plaque components was determined in 77 segments from 7 postmortem coronary arteries. Finally, we examined 60 plaques in vivo to determine feasibility and sensitivity of clinical DECT to detect VH-IVUS-defined necrotic core.

Results: In contrast to conventional SECT, mean dual-energy indices of necrotic core and fibrous tissue were significantly different with minimal overlap of ranges (necrotic core, 0.007 [95% CI, -0.001 to 0.016]; fibrous tissue, 0.028 [95% CI, 0.016-0.050]; P < .0001). DECT increased diagnostic accuracy to detect necrotic core in postmortem arteries (sensitivity, 64%; specificity, 98%) compared with SECT (sensitivity, 50%; specificity, 94%). DECT sensitivity to detect necrotic core was lower when analyzed in vivo, although still better than SECT (45% vs 39%).

Conclusions: DECT improves the differentiation of necrotic core and fibrous plaque in ex vivo postmortem arteries. However, much of this improvement is lost when translated to in vivo imaging because of a reduction in image quality.

Keywords: Atherosclerosis; Dual-energy computed tomography; Necrotic core; Virtual histology intravascular ultrasound.

Fig. 1

Co-registration between VH-IVUS and 140 kV/100 kV DECT. Longitudinal (left) and cross-sectional (right) images for VH-IVUS and co-registered DECT at 100 kV and 140 kV. Calcified plaque is identified 5 mm from a side branch adjacent to characteristic calcification (yellow line). A cross section is taken through this plaque (blue arrow), and, after orientation with the VH-IVUS cross-section region of interest, sampling to obtain Hounsfield unit was performed in the calcified plaque (asterisk). Green indicates fibrous plaque; red, necrotic core; white, calcified plaque. DECT, dual-energy CT; HU, Hounsfield unit; VH-IVUS, virtual histology intravascular ultrasound.

Fig. 2

Attenuation sampling of VH-IVUS–defined necrotic core. (A) Cross section of coronary CTA with attenuation sampling in hypoattenuated area of noncalcified plaque (B). (C) Co-registered VH-IVUS slice shows that sampled area contains significant necrotic core (red). Green indicates fibrous plaque; white, calcified plaque. CTA, CT angiography; VH-IVUS, virtual histology intravascular ultrasound.

Fig. 3

SECT attenuation at 100 kV and 140 kV and DEIs of VH-IVUS–defined plaque. Box and whisker plots of CT attenuation (HU) at 100 kV and 140 kV and DEIs (right) of the VH-IVUS–defined plaque components. DEI, dual-energy index; HU, Hounsfield unit; SECT, sle-energy CT; VH-IVUS, virtual histology intravascular ultrasound.

Fig. 4

DECT imaging compared with postmortem histology. Volume-rendered DECT reconstruction (middle) of postmortem coronary artery with attenuation sampling of noncalcified plaque at 100 kV (158 HU) and 140 kV (153 HU) (left). These attenuation values are above the threshold required to classify necrotic core; however, the DEI (0.002) correctly identifies the NC confirmed by histology (right). DECT, dual-energy CT; DEI, dual-energy index; HU, Hounsfield unit; LU, lumen; NC, necrotic core.