Clinical utility, dose determination, and safety of ocular contrast-enhanced ultrasonography in horses: A pilot study

Abstract

Objective: To determine efficacy of contrast-enhanced ultrasonography (CEUS) using different sulfur hexafluoride (SF6) doses to assess blood flow and perfusion in equine eyes and to evaluate safety of SF6 in horses.

Procedures: Ocular B-mode and contrast-enhanced ultrasonography were performed bilaterally in nine sedated university-owned horses. Intravenous SonoVue® bolus injections of 5, 10, 15, 20, 25, and 30 mL were administered for 2/18, 5/18, 6/18, 3/18, 1/18, and 1/18 eyes, respectively. Doses were increased based on ascending bodyweight. Each eye within one horse was examined utilizing a different dose. Qualitative blood flow and quantitative perfusion were analyzed. Heart and respiratory rates were monitored nonsedated, sedated, and during first and second minutes of CEUS.

Results: Qualitative contrast enhancement (CE) was visible in 7/9 animals. Quantitative CE was measurable bilaterally in four horses, unilaterally in three individuals, and not detected in two animals. In all horses with unilateral CE, the positive eye received the higher dose. Fifteen mL dose resulted in significantly shorter time to peak than 10 mL (P < .05). Peak intensity, maximum signal increase, and corresponding area under the curve were significantly higher for 15 and 20 mL doses compared with 10 mL (P < .05). Uveal and retinal tissues were enhanced frequently. Twenty-five and 30 mL doses revealed no CE. Only sedation reduced heart rates significantly (P < .05). Clinically relevant changes in respiratory rates or adverse reactions following SF6 application were not observed.

Conclusions: Contrast enhancement was in most instances dose-dependent. Fifteen mL appeared appropriate to assess equine ocular perfusion. The reliability in horses remains questionable; however, CEUS was well-tolerated.

Keywords: contrast-enhanced ultrasonography; dose comparison; eye; horse; safety; sulfur hexafluoride.