Introduction

the aim of this pilot study was to implement ultrashort echo time (UTE) MRI with bi-component analysis on grossly normal Achilles tendons with histologic correlation.

Materials and methods

six tendon samples which were grossly normal on visual inspection and palpation were harvested. A 2D UTE pulse sequence was implemented on a 3T MR scanner and bi-component and single-component T2* analysis was performed. Tendon samples were histologically processed and evaluated.

Results

mean short T2* fraction was 79.2% (95% confidence interval [CI], 70.1 - 88.3%), mean short T2* was 1.8 ms (95% CI, 1.3 - 2.3 ms), mean long T2* fraction was 20.8% (95% CI, 11.7 - 29.9%), mean long T2* was 9.2 ms (95% CI, 5.1 - 13.3 ms), and mean single-component T2* was 2.5 ms (95% CI, 1.8 - 3.1 ms).

Discussion

2D UTE MRI with bi-component and single-component T2* analysis was successfully implemented. Inter-individual variation can be demonstrated in grossly and histologically normal Achilles tendons.

Background

To determine if off-saturation ratio (OSR) measured with the ultrashort echo time magnetization transfer (UTE-MT) sequence could differentiate between tendons under different states of tensile load and to compare these changes between normal versus degenerated tendons.

Methods

Fourteen tendons were imaged at 3 Tesla before and during the application of 0.5-1 kg tension. A two-dimensional (2D) -UTE-MT sequence with 1.5, 3, and 5 kHz frequency offsets was used on nine tendons and a 3D-UTE-MT sequence with 1.5 kHz frequency offset was used on five tendons. OSR was calculated and compared for each condition. Histologic correlation was performed using light microscopy.

Results

In general, OSR increased after the application of tension. Mean increase of 2D OSR was 0.035 (95% confidence interval [CI], 0.013-0.056) at 1.5 kHz offset (P < 0.01), 0.031 (95% CI, 0.023-0.040) at 3 kHz offset (P < 0.01), and 0.013 (95% CI, -0.013-0.027) at 5 kHz offset (P = 0.07) from pre- to posttension states. Mean increase of 3D OSR was 0.026 (95% CI, 0.008-0.044) at a 1.5 kHz offset (P = 0.02) from pre- to posttension states. Mean decrease of 2D OSR at 1.5 kHz offset was 0.074-0.087 when comparing normal versus degenerated tendons (P < 0.01).

Conclusion

OSR as measured with 2D or 3D UTE-MT sequences can detect the changes in hydration seen when tendons are placed under two different states of tensile load, but these changes are smaller than those encountered when comparing between normal versus pathologic tendons. Lower off-resonance saturation frequencies (3 kHz or less) are more sensitive to these changes than higher off-resonance saturation frequencies.

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