3D left ventricular extracellular volume fraction by low-radiation dose cardiac CT: assessment of interstitial myocardial fibrosis

Abstract

Background: Myocardial fibrosis leads to impaired cardiac function and events. Extracellular volume fraction (ECV) assessed with an iodinated contrast agent and measured by cardiac CT may be a useful noninvasive marker of fibrosis.

Objective: The purpose of this study was to develop and evaluate a 3-dimensional (3D) ECV calculation toolkit (ECVTK) for ECV determination by cardiac CT.

Methods: Twenty-four subjects (10 systolic heart failure, age, 60 ± 17 years; 5 diastolic failure, age 56 ± 20 years; 9 matched healthy subjects, age 59 ± 7 years) were evaluated. Cardiac CT examinations were done on a 320-multidetector CT scanner before and after 130 mL of iopamidol (Isovue-370; Bracco Diagnostics, Plainsboro, NJ, USA) was administered. A calcium score type sequence was performed before and 7 minutes after contrast with single gantry rotation during 1 breath hold and single cardiac phase acquisition. ECV was calculated as (ΔHUmyocardium/ΔHUblood) × (1 - Hct) where Hct is the hematocrit, and ΔHU is the change in Hounsfield unit attenuation = HUafter iodine - HUbefore iodine. Cardiac magnetic resonance imaging was performed to assess myocardial structure and function.

Results: Mean 3D ECV values were significantly higher in the subjects with systolic heart failure than in healthy subjects and subjects with diastolic heart failure (mean, 41% ± 6%, 33% ± 2%, and 35% ± 5%, respectively; P = 0.02). Interobserver and intraobserver agreements were excellent for myocardial, blood pool, and ECV (intraclass correlation coefficient, >0.90 for all). Higher 3D ECV by cardiac CT was associated with reduced systolic circumferential strain, greater end-diastolic and -systolic volumes, and lower ejection fraction (r = 0.70, r = 0.60, r = 0.73, and r = -0.68, respectively; all P < 0.001).

Conclusion: 3D ECV by cardiac CT can be performed with ECVTK. We demonstrated increased ECV in subjects with systolic heart failure compared with healthy subjects. Cardiac CT results also showed good correlation with important functional heart biomarkers, suggesting the potential for myocardial tissue characterization with the use of 3D ECV by cardiac CT. This trial is registered at www.ClinicalTrials.gov as NCT01160471.

Conflict of interest statement

Conflict of interest: The authors report no conflicts of interest.

Copyright © 2013. Published by Elsevier Inc.

Figures

Figure 1

A screen shot of the extracellular volume (ECV) calculation toolkit (ECVTK). The segmented left ventricle (top, middle) is shown in green. The volume is derived from segmentation and axial orientation in the short-axis and long-axis views.

Figure 2

Calculation of the 3-dimensional (3D) extracellular volume (ECV) map. (A) 3D modeling after iodine for mean measurements of myocardium (green mesh) and blood pool (red balls) densities (in HU). (B) Same mesh is used to extract myocardium and blood pool densities (in HU) from the data set before -iodine, after image registration. (C) The software automatically calculates mean ECV for each segment and then maps the mean ECV onto the 3D model. Hct, hematocrit.

Figure 3

Discrimination between the healthy and heart failure groups with the use of 3-dimensional (3D) extracellular volume (ECV) by cardiac CT. The healthy and heart failure groups had significantly different mean ECV values (P = 0.02). The small vertical lines represent SD of the mean values for ECV.