Radiology: Cardiac CT shows potential to assess myocardial tissue fibrosis
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| Cardiac MR imaging region of interest measurements obtained, A, before and, B, after gadolinium chelate administration and reformatted cardiac CT region of interest measurements obtained, C, before and, D, after administration of an iodinated contrast agent. Source: Radiology. |
Although cardiac MR serves as the standard to assess myocardial scar, its utility is compromised by several factors, including limited availability and contraindications. Recent innovations in MR enable assessment of diffuse interstitial myocardial fibrosis, which is common among patients with cardiomyopathies and heart failure. However, cardiac CT is more widely available, well-tolerated and has been validated for use in detection of focal myocardial scar.
Thus, Marcelo Souto Nacif, MD, PhD, of the National Institutes of Health in Bethesda, Md., and colleagues sought to establish a cardiac CT method to calculate extracellular volume (ECV) fraction, which is increased in association with diffuse myocardial fibrosis, with cardiac MR as the reference standard.
The study population included 24 participants (mean age, 63.2 years). The cohort was comprised of 13 patients with New York Heart Association grade II or greater heart failure and either left ventricular ejection fraction less than 40 percent or diagnosis of diastolic dysfunction and left ventricular ejection fraction greater than 50 percent, and 11 healthy individuals.
Participants underwent cardiac MR and cardiac CT within a four-hour time window. Two readers blinded to clinical data evaluated the cardiac MR data. CT angiography data were reconstructed and analyzed before review by a pair of readers blinded to clinical data.
The researchers produced 65 of 72 ECV values with cardiac MR imaging and 68 of 72 ECV values with cardiac CT data and reported good correlation between the two methods. They noted a small bias toward higher ECV for cardiac CT.
With both cardiac CT and cardiac MR, ECV was lower in healthy participants than in those with heart failure. “The correlation coefficients for inter- and intraobserver agreement for cardiac CT were 0.95 and 0.98, respectively, for myocardium density measurement and 0.99 and 0.99, respectively, for blood pool density measurement,” wrote Nacif et al. “For cardiac MR imaging, the correlation coefficients for inter- and intraobserver agreement were 0.98 and 0.98, respectively, for myocardium and 0.99 and 0.99, respectively, for blood pool relaxivity measurements.”
Given the good reproducibility of cardiac CT and its correlation with cardiac MR ECV values, the researchers wrote, “[This] is a potential new approach toward the clinical assessment of diffuse myocardial fibrosis.”