Comprehensive comparison of in- and ex-vivo whole heart fiber architecture: similar yet different

Martijn Froeling^{1}, Gustav J Strijkers^{2}, Laura W M Vergoossen^{3}, Eibert A ten Hove^{3}, Aart J Nederveen^{4}, Tim Leiner^{1}, and Peter R Luijten^{1}

Nine healthy volunteers (5 Female, mean age 24 [22-34])were imaged
with a 3T scanner (Philips, Achieva, Release 5.1.7) using a 32-channel cardiac
coil. DWI was performed using a cardiac triggered SE-EPI sequence in free
breathing with asymmetric bipolar gradients (5) and additional flow
compensation (2). The b-values were 0, 10, 20,
30 ,50, 100, 200 and 400 s/mm^{2} with 6, 3, 3, 3, 3, 3, 3, and 24 gradient-directions,
respectively. Other imaging parameters were; TR: 14 heart-beats, FOV: 280x150
mm^{2}, slices: 14, voxel size: 7x2.5x2.5 mm^{3}, acquisition
matrix: 112x48, SENSE: 2.5, partial Fourier: 0.85, trigger delay: 220 ms, and
acquisition time: 12 min. Ex-vivo DWI data was acquired using a multi shot
STEAM-EPI sequence using Stejskal-Tanner gradients. In total twelve datasets of
formalin fixed porcine hearts were acquired (6): nine with a “low” resolution
of 6x2x2 mm^{3} and three with a “high” resolution of 2x1x1 mm^{3}
with b-values of 500, 1000, 2000 and 3000 s/mm^{2} and 30 gradient-directions
per b-value.

Data processing was done using *DTITools* (Mathematica 10) and
comprised the following steps: registration to correct for subject motion and
eddy current deformations (in vivo: 2D b-spline, ex-vivo: 3D affine), Rician
noise suppression, IVIM correction (7), tensor calculation using WLLS,
manual segmentation of the ventricles (**Figure
1A**), calculation of the local myocardial coordinate system (LMCS) (**Figure 1**), voxel wise FAM calculation (4) and whole heart fiber
tractography of all three eigenvectors (**ε**_{1}
**ε**_{2} and **ε**_{3}) using the vIST/e toolbox (**Figure 2**). The FAM is defined as the angle between the LMCS and the
projection of the eigenvalues along the axes of the LMCS (see **Figure 3**). Transmural profiles (180 radial
profiles per slice) of the FAM were obtained for 15 points along the myocardial
wall using first order interpolation along the radial axes of the LMCS (green
vectors in **Figure 1C**). To validate
the obtained transmural profiles, they were fitted using three quadratic
transmural functions describing the transmural rotation around the three axes
of the LMCS.

1. Rohmer D, Sitek A, Gullberg G. Reconstruction and visualization of fiber and laminar structure in the normal human heart from ex vivo diffusion tensor magnetic resonance imaging s(DTMRI) Data. Invest. Radiol. 2007;42:777–789.

2. Froeling M, Strijkers GJ, Nederveen AJ, Chamuleau SAJ, Luijten PR. Diffusion Tensor MRI of the Heart – In Vivo Imaging of Myocardial Fiber Architecture. Curr. Cardiovasc. Imaging Rep. 2014;7:9276. doi: 10.1007/s12410-014-9276-y.

3. Froeling M, Strijkers GJ, Nederveen AJ, Chamuleau SAJ, Luijten PR. Feasibility of in vivo whole heart DTI and IVIM with a 15 minute acquisition protocol. J. Cardiovasc. Magn. Reson. 2014;16:O15. doi: 10.1186/1532-429X-16-S1-O15.

4. Mekkaoui C, Nielles-Vallespin S, Jackowski M, Reese TG, Gatehouse P, Firmin D, Sosnovik DE. Dynamics of the Fiber Architecture Matrix in the Human Heart In Vivo. In: Proceedings 21st Scientific Meeting, International Society for Magnetic Resonance in Medicine. Vol. 21. ; 2013. p. 581.

5. Stoeck CT, von Deuster C, Genet M, Atkinson D, Kozerke S. Second-order motion-compensated spin echo diffusion tensor imaging of the human heart. Magn. Reson. Med. 2015;000:n/a–n/a. doi: 10.1002/mrm.25784.

6. Froeling M, Mazzoli V, Nederveen AJ, Luijten PR, Strijkers GJ. Ex vivo cardiac DTI: on the effects of diffusion time and b-value. J. Cardiovasc. Magn. Reson. 2014;16:P77. doi: 10.1186/1532-429X-16-S1-P77.

7. Froeling M, Luijten PR, Leemans A. Correcting for perfusion and isotropic free diffusion in diffusion weighted imaging and DTI and CSD analysis. In: Proceedings 22nd Scientific Meeting, International Society for Magnetic Resonance in Medicine. Toronto; 2015. p. 4469.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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