DQF-MT MRI of connective tissues: application to tendon and muscle.

Object: The sequence combining DQF (double quantum filtering) with magnetisation transfer (DQF-MT) was tested as an alternative to the DQF sequence for characterising tendon and muscle by MR imaging.
Materials and Methods: DQF-MT images of tendon-muscle phantoms were obtained at 4.7 T using ultra-short time to echo (UTE) methods in order to alleviate the loss of SNR due to the short T2 of the tissues. Two different sampling schemes of the k-space, Cartesian or radial, were employed. In vivo images of the human ankle on a clinical 1.5 T scanner are also presented. Parameters providing optimal tendon signal as well as optimal contrast between this tissue and muscle were determined.
Results: Two sets of parameters resulting in different contrasts between the tissues were found. For the first set (short creation time τ = 10 μs and magnetisation exchange time t LM = 100 ms), DQF-MT signals in muscle and tendon were detected, with that of the tendon being the larger one. For the second set (long creation time τ = 750 μs and magnetisation exchange time 10 μs < t LM < 100 ms), the DQF-MT signal was detected only in the tendon, and the decay of the double quantum coherence was slower than that observed for the first one, which allowed us to acquire DQF-MT MR images on a clinical 1.5 T MR scanner with minimal software interventions. In favourable conditions, the DQF-MT signal in the tendon could represent up to 10 % of the single-quantum signal.
Conclusion: Dipolar interaction within macromolecules such as collagen and myosin is at the origin of the DQF-MT signal observed in the first parameter set. This should enable the detection of muscle fibrosis.