Korean Circ J.  2020 Mar;50(3):185-202. 10.4070/kcj.2019.0315.

Future Directions in Coronary CT Angiography: CT-Fractional Flow Reserve, Plaque Vulnerability, and Quantitative Plaque Assessment

• Kay FU
• Canan A
• Abbara S

• KMID: 2470904
• DOI: http://doi.org/10.4070/kcj.2019.0315

Abstract

Coronary computed tomography angiography (CCTA) is a well-validated and noninvasive imaging modality for the assessment of coronary artery disease (CAD) in patients with stable ischemic heart disease and acute coronary syndromes (ACSs). CCTA not only delineates the anatomy of the heart and coronary arteries in detail, but also allows for intra- and extraluminal imaging of coronary arteries. Emerging technologies have promoted new CCTA applications, resulting in a comprehensive assessment of coronary plaques and their clinical significance. The application of computational fluid dynamics to CCTA resulted in a robust tool for noninvasive assessment of coronary blood flow hemodynamics and determination of hemodynamically significant stenosis. Detailed evaluation of plaque morphology and identification of high-risk plaque features by CCTA have been confirmed as predictors of future outcomes, identifying patients at risk for ACSs. With quantitative coronary plaque assessment, the progression of the CAD or the response to therapy could be monitored by CCTA. The aim of this article is to review the future directions of emerging applications in CCTA, such as computed tomography (CT)-fractional flow reserve, imaging of vulnerable plaque features, and quantitative plaque imaging. We will also briefly discuss novel methods appearing in the coronary imaging scenario, such as machine learning, radiomics, and spectral CT.

Keyword

Coronary computed tomography angiography; Coronary plaque; Fractional flow reserve; Plaque characterization; Plaque volume

MeSH Terms

Acute Coronary Syndrome
Angiography*
Constriction, Pathologic
Coronary Artery Disease
Coronary Vessels
Heart
Hemodynamics
Humans
Hydrodynamics
Machine Learning
Myocardial Ischemia

Figure

• 

  Figure 1 Stenosis without ischemia. (A) Coronary computed tomography angiography with stenosis graded >50% (arrow) in the obtuse marginal branch of the left circumflex artery. Multiple calcified plaques with stenosis between 40% and 69% are noted proximally and distally to the lesion. (B) Severe stenosis is confirmed on ICA (arrow). (C) FFRCT shows a value of 0.85. (D) A reference value of 0.84 was confirmed on ICA-fractional flow reserve. Reused with permission from J Am Coll Cardiol 2011;58:1989-97.10) FFR = fractional flow reserve; FFRCT = fractional flow reserve derived from coronary computed tomographic angiography data; ICA = invasive coronary angiography.

• 

  Figure 2 Stenosis with ischemia. (A) Lesion graded with >50% stenosis in the proximal LAD on multiplanar reformat of coronary computed tomography angiography (arrow). (B) Invasive coronary angiography showing the stenosis (arrow) with the corresponding reductions in coronary FFR in the first diagonal branch (FFR=0.78) and distal LAD (FFR=0.58). (C) FFRCT of the first diagonal branch (0.79) and distal LAD (0.57) were determined to be 0.78 and 0.58 by computational fluid dynamics. Reused with permission from J Am Coll Cardiol 2011;58:1989-97.10) FFR = fractional flow reserve; FFRCT = fractional flow reserve derived from coronary computed tomographic angiography data; LAD = left anterior descending artery.

• 

  Figure 3 Direct plaque assessment. (A) Invasive coronary angiography, catheterization of the RCA. Severe stenosis of the mid RCA (arrow). (B) Coronary CT angiography, curved multiplanar reconstruction of the RCA. CT reveals a predominantly noncalcified component (arrowhead) in the obstructive mid RCA plaque. The additional calcified plaques do not cause significantly stenosis. CT = computed tomography; RCA = right coronary artery.

• 

  Figure 4 Positive remodeling. Coronary computed tomography angiography, curved multiplanar reconstruction of the left anterior descending artery showing a predominantly noncalcified plaque in the proximal segment causing stenosis between 50% and 69%. Note the increased diameter of the vessel at the level of the stenosis (arrowheads) when compared to the segments immediately before and after the stenosis (i.e., remodeling index >1.1).

• 

  Figure 5 Napkin ring sign and spotty calcifications. Cross-sectional imaging of coronary atherosclerotic plaque showing higher computed tomography attenuation numbers within the circumferential outer rim (red dashed line) in both the noncontrast (A) and contrast-enhanced (B) images as compared to the attenuation within the central plaque (stars). Correlation with histopathology showed a thin cap fibroatheroma (C, D) with spotty calcification (E), and a necrotic core representing the low attenuation plaque core (stars in C). Fibrous plaque tissue corresponded to the hyperattenuating component within the outer rim (red dashed line). Reused with permission from JACC Cardiovasc Imaging 2010;3:440-4.44)

• 

  Figure 6 Low-attenuation plaque core. (A) Curved multiplanar reconstruction showing extensive atherosclerosis in the RCA, with plaques showing low-attenuation core (arrowheads). (B) Region of interest drawn in the core of the proximal RCA plaque shows a mean attenuation value of 8 HU. HU = Hounsfield units; RCA = right coronary artery.

• 

  Figure 7 Quantitative plaque analysis. Left anterior descending artery. A region of interest was placed in the ascending aorta at the level of the left main coronary artery, and scan-specific thresholds for calcified plaque (yellow) and noncalcified plaque (in red) were automatically generated. Reused with permission from J Cardiovasc Comput Tomogr 2018;12:344-9.66) FFR = fractional flow reserve; LAD = left anterior descending artery.

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