Myocardial extracellular volume quantification with computed tomography-current status and future outlook

Abstract

Non-invasive quantification of the extracellular volume (ECV) is a method for the evaluation of focal and diffuse myocardial fibrosis, potentially obviating the need for invasive endomyocardial biopsy. While ECV quantification with cardiac magnetic resonance imaging (ECV_MRI) is already an established method, ECV quantification with CT (ECV_CT) is an attractive alternative to ECV_MRI, similarly using the properties of extracellular contrast media for ECV calculation. In contrast to ECV_MRI, ECV_CT provides a more widely available, cheaper and faster tool for ECV quantification and allows for ECV calculation also in patients with contraindications for MRI. Many studies have already shown a high correlation between ECV_CT and ECV_MRI and accumulating evidence suggests a prognostic value of ECV_CT quantification in various cardiovascular diseases. Adding a late enhancement scan (for dual energy acquisitions) or a non-enhanced and late enhancement scan (for single-energy acquisitions) to a conventional coronary CT angiography scan improves risk stratification, requiring only minor adaptations of the contrast media and data acquisition protocols and adding only little radiation dose to the entire scan.Critical relevance statementThis article summarizes the technical principles of myocardial extracellular volume (ECV) quantification with CT, reviews the literature comparing ECV_CT with ECV_MRI and histopathology, and reviews the prognostic value of myocardial ECV quantification for various cardiovascular disease.Key points• Non-invasive quantification of myocardial fibrosis can be performed with CT.• Myocardial ECV quantification with CT is an alternative in patients non-eligible for MRI.• Myocardial ECV quantification with CT strongly correlates with ECV quantification using MRI.• Myocardial ECV quantification provides incremental prognostic information for various pathologies affecting the heart (e.g., cardiac amyloidosis).

Keywords: Computed tomography; Extracellular volume; Late enhancement; Myocardial fibrosis; Tissue characterization.

Fig. 1

Schematic illustration of myocardial fibrosis. Left: normal myocardium and iodine distribution after contrast media administration. Right: four pathologic conditions related to the expansion of the extracellular matrix: inflammation with edema; replacement fibrosis; interstitial reactive fibrosis and amyloidosis

Fig. 2

Extracellular volume (ECV) calculation using the single-energy attenuation-based and the spectral method in a 77-year-old male patient. ECV was not elevated with a mean ECV of 23.5% and 22.4% using the attenuation-based and spectral method, respectively. No focal scar was seen, which was confirmed by previous CMR. Abbreviations: Ht, hematocrit; ΔHU_myo, change in attenuation of the myocardium; ΔHU_blood, change in attenuation of the blood pool; [Iodine_myo], iodine concentration within the myocardium; [Iodine_blood], iodine concentration within the blood pool

Fig. 3

Extracellular volume (ECV) images and maps calculated using the spectral method from late enhancement CT shows elevated myocardial ECV in a 78-year-old male patient with confirmed transthyretin cardiac amyloidosis (ATTR)

Fig. 4

Late enhancement scan and extracellular volume (ECV) calculation in an 89-year-old male patient. Conventional images and iodine maps from the late enhancement scan show increased transmural contrast enhancement of the inferoseptal, inferior and inferobasal myocardium. Elevated ECV_CT values were observed in these regions suggesting a focal scar. Findings were confirmed by cardiac MRI. Note the identical extent of the scar on both modalities