Inter-study reproducibility of left ventricular torsion and torsion rate quantification using MR myocardial feature tracking

Abstract

Background: To determine the inter-study reproducibility of MR feature tracking (MR-FT) derived left ventricular (LV) torsion and torsion rates for a combined assessment of systolic and diastolic myocardial function.

Methods: Steady-state free precession (SSFP) cine LV short-axis stacks were acquired at 9:00 (Exam A), 9:30 (Exam B), and 14:00 (Exam C) in 16 healthy volunteers at 3 Tesla. SSFP images were analyzed offline using MR-FT to assess rotational displacement in apical and basal slices. Global peak torsion, peak systolic and peak diastolic torsion rates were calculated using different definitions ("twist", "normalized twist" and "circumferential-longitudinal (CL) shear angle"). Exam A and B were compared to assess the inter-study reproducibility. Morning and afternoon scans were compared to address possible diurnal variation.

Results: The different methods showed good inter-study reproducibility for global peak torsion (intraclass correlation coefficient [ICC]: 0.90-0.92; coefficient of variation [CoV]: 19.0-20.3%) and global peak systolic torsion rate (ICC: 0.82-0.84; CoV: 25.9-29.0%). Conversely, global peak diastolic torsion rate showed little inter-study reproducibility (ICC: 0.34-0.47; CoV: 40.8-45.5%). Global peak torsion as determined by the CL shear angle showed the best inter-study reproducibility (ICC: 0.90;CoV: 19.0%). MR-FT results were not measurably affected by diurnal variation between morning and afternoon scans (CL shear angle: 4.8 ± 1.4°, 4.8 ± 1.5°, and 4.1 ± 1.6° for Exam A, B, and C, respectively; P = 0.21).

Conclusion: MR-FT based derivation of myocardial peak torsion and peak systolic torsion rate has high inter-study reproducibility as opposed to peak diastolic torsion rate. The CL shear angle was the most reproducible parameter independently of cardiac anatomy and may develop into a robust tool to quantify cardiac rotational mechanics in longitudinal MR-FT patient studies.

Keywords: cardiovascular magnetic resonance; circumferential longitudinal shear angle; feature tracking; inter-study reproducibility; torsion; twist.

Figure 1

Cardiovascular Magnetic Feature Tracking (CMR-FT). Rotational dynamics were assessed in basal (left panel) and apical (right panel) short-axis positions. Rotation resulted in an overall apical counter-clockwise and basal clockwise rotation when viewed from the apex. The lower panel shows the tracking of 48 (sub)endocardial features.

Figure 2

Torsion and torsion rate quantification. Quantification included peak torsion (upper panel) and peak systolic and diastolic torsion rates (lower panel). In this example torsion has been calculating according to the Circumferential-Longitudinal Shear Angle definition.

Figure 3

Global torsion (left panel) and torsion rate (right panel) profiles averaged across the study group. There was good agreement between all three Exams (A-C). Torsion was slightly lower during Exam C, however this difference was not statistically significant.

Figure 4

Bland-Altman Plots for inter-study reproducibility (comparison of Exam A and Exam B) obtained for global peak torsion, global peak systolic torsion rate and global peak diastolic torsion rate, as calculated according to the three different definitions: twist, normalized twist and circumferential-longitudinal shear angle. Dashed red line: zero mean difference. Dashed black line: limits of agreement (1.96 standard deviations).