Use of Electron Density Maps and Fused Images in Dual-Energy Cardiac Computed Tomography to Facilitate Detection of Late Iodine Enhancement

Abstract

Background: This study aimed to optimize the fusion of quantitative maps and morphological images to improve late iodine enhancement (LIE) imaging using cardiac dual-energy computed tomography (DECT).

Methods and results: We retrospectively analyzed 15 patients with suspected old myocardial infarction who underwent cardiac DECT. Virtual monochromatic images (VMI) ranging from 40 to 200 keV and quantitative maps (e.g., iodine concentration, effective atomic number, and electron density [(%EDW: percentage relative to the electron density of water)] were generated. The contrast-to-noise ratio (CNR) between LIE areas and the left ventricular (LV) blood pool and normal myocardium was calculated to determine the optimal image fusion for LIE delineation. VMI at 40 keV demonstrated superior CNR between LIE areas and normal myocardium. Electron density was significantly higher in LIE areas [105.5%EDW (interquartile range (IQR): 105.15-105.65)] than in the LV blood pool [104.4%EDW (IQR: 104.3-104.6)] and normal myocardium [104.4%EDW (IQR: 104.2-104.65)] (P<0.001). Iodine concentration and effective atomic number differed significantly between LIE areas and normal myocardium, but did not differ significantly between LIE areas and the LV blood pool. Fusion of 40 keV VMI with electron density maps yielded the highest area under the receiver operating characteristic curve (0.917).

Conclusions: Fused images combining 40 keV VMI with electron density maps significantly enhanced the visualization of LIE areas on DECT, offering improved contrast and diagnostic accuracy for the assessment of myocardial territories.

Keywords: Dual-energy computed tomography; Electron density map; Iodine; Late enhancement; Myocardial infarction.

Figure 1.

Flowchart of the patient inclusion criteria. CT, computed tomography; LIE, late iodine enhancement; OMI, old myocardial infarction.

Figure 2.

Quantitative map analysis of CT number, image noise, contrast, and CNR between the normal and LIE areas. The CT numbers (A) of the normal myocardium, LV blood pool, and LIE areas increased with low energy in all regions. The image noise (B) did not vary greatly with energy. The contrast (C) and CNR (D) between the LIE areas and the normal myocardium increased with low energy, while that between the LIE areas and the LV blood pool decreased with low energy. CNR, contrast-to-noise ratio; CT, computed tomography; LIE, late iodine enhancement; LV, left ventricular.

Figure 3.

Quantitative map analysis of iodine concentration, effective atomic number, and electron density. There were no significant differences in the iodine concentration (A) and the effective atomic number (B) between the LV and LIE areas. Alternatively, there was a significant difference in the electron density (C) between the LV and LIE areas. LIE, late iodine enhancement; LV, left ventricle.

Figure 4.

Results of the ROC curve analysis to identify the vessel responsible for LIE, performed by 2 readers. The ROC curves of the electron density (blue line), effective atomic number (yellow line), iodine concentration (green line), 120 kVp images (purple line) and 40-keV images (red line) to detect the vessels responsible for LIE areas, produced by Reader 1 (A) and Reader 2 (B). LIE, late iodine enhancement; ROC, receiver operating characteristic.

Figure 5.

Case 1: 58-year-old patient with acute coronary syndrome 3 years previously. Occluded lesion in right coronary artery #2 (red arrow) (A). Post-PCI image (B). DECT analysis with LIE was performed at the 3-year follow-up cardiac CT. The coronary arterial phase images show myocardial wall thinning in the inferior wall (C). The LIE 40-keV VMI (D) show sufficient iodine contrast but unclear borders between the LV blood pool and the LIE areas. The electron density map clearly depicts the LIE areas (yellow arrowheads) (E), but it is difficult to separate the LIE areas from the LV blood pool in the iodine concentration map (F) and the effective atomic number map (G). In the fused 40-keV VMI and quantitative maps, the electron density map (H) is able to delineate the LV blood pool and LIE areas (yellow arrowheads), but the iodine concentration map (I) and effective atomic number (J) have difficulty identifying the LIE areas. CT, computed tomography; DECT, dual-energy computed tomography; LIE, late iodine enhancement; LV, left ventricular; PCI, percutaneous coronary intervention; VMI, virtual monochromatic images.

Figure 6.

Case 2: 61-year-old man who underwent cardiac CT for stent evaluation. He had a history of acute coronary syndrome in 2014 with emergency PCI in the left anterior descending artery. Occluded lesion in left anterior descending artery #6 (red arrow) (A). Post-PCI image (B). Arterial-phase CT shows thinning of the infarct on the anterior wall. (C). The LIE provided insufficient contrast on 120-kV images (D), but LIE areas were detected in the anterior wall on 40-keV VMI (E). Fusion of the 40-keV VMI with the electron density map clearly delineated the LIE areas (yellow arrow) (F), but it was difficult to separate the LIE areas from the LV blood pool in the fused images with the iodine concentration map (G) and effective atomic number map (H). CT, computed tomography; LIE, late iodine enhancement; LV, left ventricular; PCI, percutaneous coronary intervention; VMI, virtual monochromatic images.