Intravoxel incoherent motion (IVIM) imaging in human achilles tendon

Background Limited microcirculation has been implicated in Achilles tendinopathy and may affect healing and disease progression. Existing invasive and noninvasive approaches to evaluate tendon microcirculation lack sensitivity and spatial coverage. Purpose To develop a novel Achilles tendon intravoxel incoherent motion (IVIM) MRI protocol to overcome the limitations from low tendon T-2/T-2* value and low intratendinous blood volume and blood velocity to evaluate tendon microcirculation. Study Type Prospective. Subjects Sixteen healthy male participants (age 31.0 +/- 2.1) were recruited. Field Strength/Sequence A stimulated echo readout-segmented echo planar imaging (ste-RS-EPI) IVIM sequence at 3.0T. Assessment The feasibility of the proposed ste-RS-EPI IVIM protocol combined with Achilles tendon magic angle effect was evaluated. The sensitivity of the protocol was assessed by an exercise-induced intratendinous hemodynamic response in healthy participants. The vascular origin of the observed IVIM signal was validated by varying the diffusion mixing time and echo time. Statistical Tests Two-tailed t-tests were used to evaluate differences (P < 0.05 was considered significant). Results Consistent with known tendon hypovascularity, the midportion Achilles tendon at baseline showed significantly lower IVIM-derived perfusion fraction (f(p)) (3.1 +/- 0.9%) compared to the proximal and distal Achilles tendon (6.0 +/- 1.8% and 6.1 +/- 2.0%, respectively; P < 0.01). Similarly, the midportion Achilles tendon exhibited significantly lower baseline blood flow index (D*xf(p)) (40.9 +/- 19.2, 18.3 +/- 5.3, and 32.0 +/- 9.4 in proximal, midportion, and distal Achilles tendon, respectively; P < 0.01). Eccentric heel-raise exercise led to similar to 2 times increase of Achilles tendon blood flow in healthy participants. Consistent with its vascular origin, the estimated f(p) demonstrated a high dependency to IVIM protocol parameters, while the T-1/T-2-corrected absolute intratendinous microvascular blood volume fraction (V-b) did not vary. Data Conclusion Achilles tendon ste-RS-EPI IVIM noninvasively assessed baseline values and exercise-induced changes to tendon microcirculation in healthy tendon.