Interstitial myocardial fibrosis assessed as extracellular volume fraction with low-radiation-dose cardiac CT

Abstract

Purpose: To develop a cardiac computed tomographic (CT) method with which to determine extracellular volume (ECV) fraction, with cardiac magnetic resonance (MR) imaging as the reference standard.

Materials and methods: Study participants provided written informed consent to participate in this institutional review board-approved study. ECV was measured in healthy subjects and patients with heart failure by using cardiac CT and cardiac MR imaging. Paired Student t test, linear regression analysis, and Pearson correlation analysis were used to determine the relationship between cardiac CT and MR imaging ECV values and clinical parameters.

Results: Twenty-four subjects were studied. There was good correlation between myocardial ECV measured at cardiac MR imaging and that measured at cardiac CT (r = 0.82, P < .001). As expected, ECV was higher in patients with heart failure than in healthy control subjects for both cardiac CT and cardiac MR imaging (P = .03, respectively). For both cardiac MR imaging and cardiac CT, ECV was positively associated with end diastolic and end systolic volume and inversely related to ejection fraction (P < .05 for all). Mean radiation dose was 1.98 mSv ± 0.16 (standard deviation) for each cardiac CT acquisition.

Conclusion: ECV at cardiac CT and that at cardiac MR imaging showed good correlation, suggesting the potential for myocardial tissue characterization with cardiac CT.

Figure 1:

Flowchart of image acquisition methods. CTA = CT angiography, MOLLI = modified Look Locker sequence with inversion recovery, LGE = late gadolinium enhancement.

Figure 2:

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. For cardiac CT, the anterolateral myocardium was most reliably identified before administration of an iodinated contrast agent. There, a region of interest from the anterolateral myocardium was used for attenuation measurements. A focal myocardial scar was identified on delayed cardiac MR images and was not included in the region of interest. Orange outline = myocardium, white circle = blood pool.

Figure 3a:

Results obtained for ECV at (a) MR imaging and (b) CT. (a) Correlation and linear regression analysis shows good correlation between the methods (r = 0.82, P < .001). (b) Bland-Altman plot shows a small bias (3.01%) toward higher ECV at cardiac CT (black line), with 95% limits of agreement between the two methods of −2.82% and 8.85% (thick gray lines).

Figure 3b:

Results obtained for ECV at (a) MR imaging and (b) CT. (a) Correlation and linear regression analysis shows good correlation between the methods (r = 0.82, P < .001). (b) Bland-Altman plot shows a small bias (3.01%) toward higher ECV at cardiac CT (black line), with 95% limits of agreement between the two methods of −2.82% and 8.85% (thick gray lines).

Figure 4:

Box plots show median and interquartile range. Minimum and maximum values are represented in each group by the whiskers of the plot. Healthy and heart failure groups had significantly different mean ECV values at both cardiac MR imaging and cardiac CT (P = .03 for both).