Synopsis

Greater Trochanteric Pain Syndrome is a debilitating and highly prevalent disorder in women. Quantitative short-TE MRI sequences might overcome conventional MRI limitations in characterizing and staging gluteus tendinopathy. Ten patients and 10 asymptomatic volunteers were evaluated with hip MRI. Manual segmentations of the hip tendons were done to map T1 and T2* relaxation times. Statistically significant results were found for the T1 values of the lateral gluteus medius tendon, and for the T2* values of both parts of the gluteus medius, and the gluteus minimus tendons, indicating very promising results.

Background:

Greater Trochanteric Pain Syndrome (GTPS) is a highly prevalent disorder in women of more than 50 years of age^1,2. GTPS refers to lateral hip pain caused by gluteus tendinopathy³. Conventional MRI, so far, has played a minor role in the staging-process of gluteus tendinopathy.

We hypothesized that T1 and T2* parameters of gluteus minimus (Gmin) and gluteus medius (Gmed) tendons, estimated from short-TE gradient echo (GE) sequences, would be significantly different between patients with GTPS and asymptomatic volunteers.

Materials and method:

Ten patients with GTPS, and 10 asymptomatic volunteers were evaluated with hip MRI using quantitative T1 and T2* mapping sequences based on short-TE GE sequences^4,5,6. MRI was performed on a clinical 3T system (Achieva X-series, Philips Healthcare), using a 16-channel surface coil.

Quantitative T2* mapping was performed using a multi-echo, variable TE, slab-selective 3D GE sequence. Two multi-echo sequences with 6 TEs each were acquired, for a total of 12 TEs: TE=1.1, 2.8, 4.5, 6.2, 7.9, 9.6, 11.3, 13.0, 14.7, 16.4, 18.1 and 19.8 ms. Other acquisition parameters were: TR= 46 ms, FOV= 154 mm x 154 mm x 72 mm, spatial resolution= 0.6 mm x 0.8 mm x 3 mm, flip angle= 18 degrees, bandwidth= 785.7 Hz/pixel, acquisition time= 11min 24sec. Quantitative T1 mapping was performed using a variable flip angle GE sequence⁴ with identical coverage and spatial resolution. Other parameters were: TR= 29 ms, TE= 1.15 ms, flip angles = 5, 15 and 25 degrees, acquisition time= 9min 39sec.

Segmentations of the Gmin, the posterosuperior Gmed, and the lateral Gmed tendons were performed independently by a radiologist and a radiology resident, using ITK-SNAP (http://www.itksnap.org) on the T2* map. The segmentations were then mapped to the co-registered quantitative T1 map (Figure 1). T2* values were estimated on a voxel-by-voxel basis by performing a nonlinear mono-exponential regression, using Matlab (The Mathworks, Natick, MA, USA). T1 values were estimated on a voxel-by-voxel basis using the methodology developed by Grosse et al.⁴ implemented in Matlab. Information from a B1 mapping sequence was included in order to correct for spatial B1 inhomogeneity.

The Mann-Whitney U test was used to compare the mean T2* and mean T1 relaxation times of the various tendons; a p-value < 0.05 was considered statistically significant.

Results

Demographic data of both groups are presented in Table 1.

Table 2 presents the mean T1 and T2* values, for each tendon and for both readers, in the two groups. For both readers and all three tendons, the mean T1 values were lower in the patients compared with the volunteers. The difference in mean T1 values between the both groups was statistically significant in the lateral Gmed tendon for both readers. For both readers and all three tendons, the mean T2* values were generally higher in the patients compared with the volunteers. The difference in mean T2* values between the two groups was statistically significant in all three tendons for reader 2, and for the posterosuperior Gmed and lateral Gmed tendons for reader 1.

Figures 2 and 3 respectively present the scatterplots and the boxplots of the T1 and T2* values of each tendon, for the two groups, as reported by readers 1 and 2.

Discussion

Both readers found significantly lower mean T1 values in the lateral Gmed tendons of the patients compared to the volunteers. This decrease in mean T1 values is potentially linked to structural or cellular tendon changes. Significantly higher mean T2* values were found in all tendons of the patients compared to the volunteers, which suggest a higher water content in pathological tendons and is in accordance with conventional MRI findings.

Our results also suggest that structural changes between pathological and normal tendons may not influence T1 values as much as T2* values. As depicted in Figure 2, T2* values appear to discriminate pathological tendons better as compared to the T1 values.

As shown in Figure 3, we found greater variability between readers for the assessment of the lateral Gmed tendon. This could be explained by technical factors as the lateral Gmed tendon is a relatively thin structure and was found to be more difficult to segment.

Conclusion

Acknowledgements

References

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4. Grosse U, Springer F, Hein T, et al. Influence of physical activity on T1 and T2* relaxation times of healthy Achilles tendons at 3T. Journal of magnetic resonance imaging : JMRI 2015;41:193-201.

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