Intra-individual comparison of liver stiffness measurements by magnetic resonance elastography and two-dimensional shear-wave elastography in 888 patients

Abstract

Purpose: Quantitative elastography methods, such as ultrasound two-dimensional shear-wave elastography (2D-SWE) and magnetic resonance elastography (MRE), are used to diagnose liver fibrosis. The present study compared liver stiffness determined by 2D-SWE and MRE within individuals and analyzed the degree of agreement between the two techniques.

Methods: In total, 888 patients who underwent 2D-SWE and MRE were analyzed. Bland-Altman analysis was performed after both types of measurements were log-transformed to a normal distribution and converted to a common set of units using linear regression analysis for differing scales. The expected limit of agreement (LoA) was defined as the square root of the sum of the squares of 2D-SWE and MRE precision. The percentage difference was expressed as (2D-SWEMRE)/ mean of the two methods×100.

Results: A Bland-Altman plot showed that the bias and upper and lower LoAs (ULoA and LLoA) were 0.0002 (95% confidence interval [CI], -0.0057 to 0.0061), 0.1747 (95% CI, 0.1646 to 0.1847), and -0.1743 (95% CI, -0.1843 to -0.1642), respectively. In terms of percentage difference, the mean, ULoA, and LLoA were -0.5944%, 19.8950%, and -21.0838%, respectively. The calculated expected LoA was 17.1178% (95% CI, 16.6353% to 17.6002%), and 789 of 888 patients (88.9%) had a percentage difference within the expected LoA. The intraclass correlation coefficient of the two methods indicated an almost perfect correlation (0.8231; 95% CI, 0.8006 to 0.8432; P<0.001).

Conclusion: Bland-Altman analysis demonstrated that 2D-SWE and MRE were interchangeable within a clinically acceptable range.

Keywords: Bland-Altman analysis; Intraclass correlation coefficient; Magnetic resonance elastography; Proton density fat fraction; Two-dimensional shear-wave elastography.

Fig. 1.. Flowchart of patient selection.

HCC, hepatocellular carcinoma.

Fig. 2.. Two-dimensional shear-wave elastography (2D-SWE) and magnetic resonance elastography (MRE) in three representative patients.

The degree of liver stiffness determined by 2D-SWE and MRE increased with the degree of fibrosis progression, defined as the staging of liver fibrosis in chronic hepatitis C by MRE [19]. The left figure shows no fibrosis (F0, 58-year-old, female, hepatitis C virus [HCV] infection), the middle shows moderate fibrosis (F2, 82-year-old, female, HCV infection), and right shows advanced fibrosis (F4, 82-year-old, female, HCV infection).

Fig. 3.. Bland-Altman analysis.

A. Bland-Altman plot where differences are presented as units. The Bland-Altman plot demonstrated that the bias, upper limit of agreement (ULoA), and lower limit of agreement (LLoA) were 0.0002 (95% confidence interval [CI], -0.0057 to 0.0061), 0.1747 (95% CI, 0.1646 to 0.1847), and -0.1743 (95% CI, -0.1843 to -0.1642), respectively. B. Bland-Altman plot shows the difference as a percentage (% difference). The figure shows the difference (% difference) between the adjusted log LS_SWE values and the log LS_SWE values, where the mean, ULoA, and LLoA were –0.5944%, 19.8950%, and –21.0838%, respectively. C. Intraclass correlation coefficients are as follows: r=0.8231; 95% CI, 0.8006 to 0.8432. The relationship between the modified log LS_SWE and log LS_SWE values is shown; the intraclass correlation coefficient (ICC) is 0.8231, indicating almost perfect agreement (P<0.001). MRE, magnetic resonance elastography; 2D-SWE, twodimensional shear-wave elastography; LS_MRE, liver stiffness according to MRE; LS_SWE, liver stiffness according to 2D-SWE; modified log LS_SWE=0.4176+0.8193×log LS_MRE; % difference=[modified log LS_SWElog LS_SWE)/(0.5×(modified log LS_SWE+log LS_SWE]×100%.

Fig. 4.. Intraclass correlation coefficients (ICCs) according to body mass index (BMI).

The correlation between different BMI values is shown: BMI <25.0 kg/m² (n=569) (A); 25.0≤BMI<30.0 kg/m² (n=254) (B); BMI ≥30.0 kg/m² (n=65) (C). The ICCs gradually decreased as BMI increased, but indicated almost perfect agreement except for patients with a BMI ≥30 kg/m². LS_MRE, liver stiffness according to magnetic resonance elastography; LS_SWE, liver stiffness according to twodimensional shear-wave elastography; CI, confidence interval.

Fig. 5.. Intraclass correlation coefficients (ICCs) according to steatosis grade.

The correlation between different PDFF is shown: grade 0 (n=512), PDFF <5.2% (A); grade 1 (n=185), 5.2%≤PDFF<11.3% (B); grade 2 (n=91), 11.3%≤PDFF<17.1% (C); grade 3 (n=100), PDFF ≥17.1% (D). LS_MRE, liver stiffness according to magnetic resonance elastography; LS_SWE, liver stiffness according to twodimensional shear-wave elastography; CI, confidence interval.