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Feasibility and Reproducibility Study of Diffusion-Tensor Imaging in Rotator Cuff Muscles of Asymptomatic Volunteers.
Cyril Tous, PhD1, Alexandre Jodoin, MD2, Detlev Grabs, MD, PhD3, Elijah Van Houten, PhD4, and Nathalie J Bureau, MD MSc FRCP(C)1,2
1Radiology, Centre de recherche du Centre hospitalier de l’Université de Montréal, Montreal, QC, Canada, 2Radiology, Centre hospitalier de l’Université de Montréal, Montréal, QC, Canada, 3Anatomy, Université du Québec à Trois-Rivières, Trois-Rivières, QC, Canada, 4Mechanical Engineering, Université de Sherbrooke, Sherbrooke, QC, Canada

Synopsis

Surgical planning of rotator cuff tears does not benefit from quantitative measurement of muscles stiffness and microstructure leading to retears in the following years. Since stiffness is dependent on anisotropy, Diffusion Tensor Imaging can simplify the inversion algorithm of Magnetic resonance elastography. Repeatability of DTI metrics from three scans in six shoulders of six asymptomatic volunteers was achieved (coefficient of variance <10%) for the fractional anisotropy, mean diffusivity, mode and eigenvalues. Clear convergence of myocytes to the tendons was observed with tractography in the supraspinatus as known in dissection. This MRI protocol is promising for developing biomarkers for surgical planning.

Introduction

Surgical planning of rotator cuff tears does not benefit from quantitative measurement of muscles stiffness and microstructure leading to retears in the following years. Since stiffness is dependent on anisotropy, Diffusion Tensor Imaging can simplify the inversion algorithm of Magnetic resonance elastography. Repeatability of DTI metrics from three scans in six shoulders of six asymptomatic volunteers was achieved (coefficient of variance <10%) for the fractional anisotropy, mean diffusivity, mode and eigenvalues. Clear convergence of myocytes to the tendons was observed with tractography in the supraspinatus as known in dissection. This MRI protocol is promising for developing biomarkers for surgical planning.

Methods

Six shoulders of six volunteers (median=41, IQR=13 years) were scanned at 3T with DTI at b=0s/mm² (2averages), 12 diffusion-encoding gradients at b=500 s/mm² (2averages), b=800 s/mm² (4averages), TR=5.8s, TE=57ms, slices=46, voxel size=3x3x3 mm3, resolution=106, FOV read=318. The supraspinatus (SSP) and infraspinatus (ISP) segmented from T1 vibe DIXON (TE=2.46ms, TR=5.76ms, voxel=1x1x1mm3 and FOV=320) were rigidly coregistered with MrTrix3[7]. One way analysis of variance (ANOVA), pairwise comparison of distribution, coefficient of variance (CV) and Bland-Altman analysis were used to assess the repeatability within subjects of the three tensors eigenvalues (λ1,λ2,λ3) the fractional anisotropy (FA), the mode and the apparent diffusion coefficient (ADC).

Results

Across 6 volunteers, the ADC was higher in ISP than SSP with a CV inferior to 11% (Table 1). Mean FA was between 0.42 and 0.45 in SSP and ISP, with a CV inferior to 12%. One individual had CVADC and CVFA levels over 18% in 2/3 of tests. Bias and limit of agreement in FA was 0 ± 0.071 and 0.005 ± 0.157 x10-3 mm2/s in ADC (Figure 1 and 2). Pairwise comparison of repeated tests (1-2, 1-3, 2-3) of eigenvalues showed nonsignificant difference (p>0.05) in 3/6 volunteers for the SSP and 5/6 volunteers between test 2 and 3. Pairwise comparison of eigenvalues demonstrates significant difference and between the ISP and SSP. Thus, tractography could be achieved in the ISP and the SSP showing interleaved tracks in the ISP and organized tracks in the SSP (Figure 3 and 4). The mean λ1 is in average 2.80±0.63 times higher in the ISP than in the SSP across volunteers and tests.

Discussion

Our results are consistent with other inter and intra scanner studies performing DTI in muscles[8,9,10]. Single scanner study on myocardial DTI reported CVADC of 19% and 7.2% for CVFA [8,9], while in the upper leg had CVADC reported at 4.5% and CVFA at 15.2% [10]. DTI metrics in the ISP are reproducible according to the bias and level of agreement in the Bland-Altman plot, and from CV values based on the mean and standard deviation, but reproducibility fails for ANOVA of the DTI metric in the ISP. The SSP has a “fishbone” like structure where the insertion angle between the myocytes and the bundle separation is consistent (Figure 4) while the ISP has a more complex microstructure with interleaved myocytes (low FA at 0.45) (Figure 3) and inhomogeneity proximal to the lungs which may explain the lower repeatability of the eigenvalues in this muscle.

Conclusion

The bland-Altman analysis showed good repeatability (CV<10%) of ADC and FA which is promising for establishing DTI biomarkers across volunteers and scanners that will allow the identification of structural characteristics of RC tears.

Acknowledgements

Québec Bio-Imaging Network Pilot Project #35450

References

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8. Grech‐Sollars, M., P. W. Hales, K. Miyazaki, F. Raschke, D. Rodriguez, M. Wilson, S. K. Gill, T. Banks, D. E. Saunders, J. D. Clayden, M. N. Gwilliam, T. R. Barrick, P. S. Morgan, N. P. Davies, J. Rossiter, D. P. Auer, R. Grundy, M. O. Leach, F. A. Howe, A. C. Peet, and C. A. Clark. Multi‐centre reproducibility of diffusion MRI parameters for clinical sequences in the brain. NMR Biomed. 28:468–485, 2015.

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Figures

Figure 1) Bland-Altman plots of ADC across three scans (pairwise comparison of scans 1-2, 1-3, 2-3) for each volunteer (1 to 6) in the supraspinatus (sup) or infraspinatus (inf). Limit of agreement (loa) is 0.157x10-3 mm2/s with a bias at 0.005x10-3 mm2/s

Figure 2) Bland-Altman plots of FA across three scans (pairwise comparison of scans 1-2, 1-3, 2-3) for each volunteer (1 to 6) in the supraspinatus (sup) or infraspinatus (inf). Limit of agreement (loa) is 0.071 with a bias at 0.0.

Figure 3) Coronal (A), axial (B) views of the supraspinatus and infraspinatus from 10,000 tracks generated from MrTrix using multishell multi tissues algorithm and constrained spherical deconvolution. Criss-cross of myocytes tracks are observed longitudinally and transversely corresponding to the low FA measured (0.42±0.07).

Figure 4) The mask delineates the supraspinatus (A-white background on muscle) where tractography is performed (A-colors) overlaid by a T1 VIBE image. The line separation (A-blue line) corresponds to the separation between the posterior and anterior bundle (B-arrows) where myocytes insert posteriorly (red tracks) and anteriorly (green track).

Table1) Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) and their respective coefficient of variance (CV) measured in the supraspinatus and infraspinatus of six volunteers, scanned three times.

Proc. Intl. Soc. Mag. Reson. Med. 29 (2021)
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