Strain and torsion quantification in mouse hearts under dobutamine stimulation using 2D multiphase MR DENSE

Abstract

In this study, a 2D multiphase magnetic resonance displacement encoding with stimulated echoes (DENSE) imaging and analysis method was developed for direct quantification of Lagrangian strain in the mouse heart. Using the proposed method, <10 ms temporal resolution and 0.56 mm in-plane resolution were achieved. A validation study that compared strain calculation by displacement encoding with stimulated echoes and by magnetic resonance tagging showed high correlation between the two methods (R(2) > 0.80). Regional ventricular wall strain and twist were characterized in mouse hearts at baseline and under dobutamine stimulation. Dobutamine stimulation induced significant increase in radial and circumferential strains and torsion at peak systole. A rapid untwisting was also observed during early diastole. This work demonstrates the capability of characterizing cardiac functional response to dobutamine stimulation in the mouse heart using 2D multiphase magnetic resonance displacement encoding with stimulated echoes.

Figure 1

Multi-phase MR DENSE pulse sequence (a) and schematic data processing diagram (b). The positive and negative (dotted line) displacement encoding/unencoding gradients are implemented separately to generate two DENSE data sets. The subtraction of these two data sets eliminated systematic phase errors and doubled the sensitivity of displacement encoding.

Figure 2

Representative end-systolic DENSE images and the corresponding displacement and strain maps. a&b. original (a) and unwrapped (b) phase images with displacement encoding in the horizontal direction; c. 2D displacement field; d&e. radial and circumferential strain maps; f. magnitude image of the unfiltered image; g&h. phase gradient maps in the horizontal direction with (g) and without (h) discontinuity; i&j. radial and circumferential strain maps directly quantified from phase gradient maps.

Figure 3

Comparison of strain quantification by MR DENSE and MR tagging. a-c. Correlation between tagging and DENSE quantification of radial (a), circumferential strains (b), and ventricular twist (c); d-f. Bland–Altman plots of radial (d), circumferential strains (e), and ventricular twist (f) measured by tagging and DENSE. Strain calculation from DENSE images used direct strain quantification method.

Figure 4

Comparison of strain calculation by phase unwrapping and direct strain quantification methods. a&b. Correlation between strain quantified by phase unwrapping and direct strain quantification on radial (a) and circumferential strains (b). c&d. Bland–Altman plots of radial (c) and circumferential strains (d), measured by phase unwrapping and direct strain quantification methods.

Figure 5

Radial (a&b) and circumferential (c&d) strains at apex (a&c) and base (b&d). S, septum; P, posterior; L, lateral; A, anterior; Ave, slice average. White and black bars are strains at baseline and under dobutamine stimulation, respectively. *P<0.05 baseline versus dobutamine stimulation. ^#P<0.05 comparing with other segments. ^†P<0.05 comparing with the posterior and lateral segments. ^‡P<0.05 comparing with the posterior. Strain calculation from DENSE images used direct strain quantification method.

Figure 6

Ventricular twist (a), torsion (b) and torsion rate (c) at baseline and under dobutamine stimulation. *P<0.05 baseline versus dobutamine stimulation.