Evaluation of Microvascular Flow Imaging and Power Doppler Ultrasonography in an Equine Model of Induced Superficial Digital Flexor Tendonitis.

Superficial digital flexor tendon (SDFT) injuries are common in athletic horses and are associated with prolonged healing and high reinjury rates. Conventional ultrasonography provides structural information but limited physiologic assessment. This study compared microvascular imaging (MVI) and Power Doppler (PD) for evaluating vascular changes in a collagenase-induced equine SDFT injury model and assessed the effect of scanning technique on vascular signal detection. Eight adult Thoroughbred horses underwent bilateral collagenase-induced SDFT injury, with one forelimb randomly assigned to intralesional autologous protein solution treatment and the contralateral limb receiving intralesional saline. Ultrasonographic examinations were performed at baseline and Weeks 0, 2, 4, 8, and 12 post-injury. Longitudinal and transverse MVI and PD images were evaluated using semiquantitative vascularity scores and quantitative vascularity ratios. Mixed-effects Poisson regression accounted for repeated measures and assessed effects of imaging modality, time, scanning plane, weight-bearing (WB) stance, stand-off use, and observer experience. MVI detected higher vascularity than PD at all post-injury time points (2.04 [95% confidence intervals-CI: 1.73-2.34] vs. 0.87 [0.64-1.10]) with peak vascularity at Week 2 followed by gradual decline during healing. Quantitative vascularity ratios mirrored semiquantitative findings. Longitudinal imaging yielded greater vascular detection than transverse imaging for both techniques (1.97 [95% CI: 1.72-2.22] vs. 0.92 [0.69-1.15]), whereas WB status and stand-off pad use had no statistical significant effect. Observer experience influenced vascularity scores but not temporal trends. These findings demonstrate MVI detects more intratendinous vascularity than PD during SDFT injury and healing, and support its use as a complementary tool for monitoring equine tendinopathy.