Intravoxel incoherent motion (IVIM) imaging in human achilles tendon

Abstract

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 T₂ /T₂ * 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*×f_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 ∼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 T₁ /T₂ -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.

Level of evidence: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1690-1699.

Keywords: Achilles tendon; IVIM; RS-EPI; intravoxel incoherent motion imaging; stimulated echo; tendinopathy.