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Visualization of Uveal Perfusion by Contrast-Enhanced Harmonic Ultrasonography at a Low Mechanical Index

A Pilot Animal Study

Department of Ophthalmology, The University of Tokushima, Tokushima, Japan (T.H., M.K., M.H., T.Na., S.Y., H.S.); and Acuson Nippon, KK, Tokyo, Japan (T.Ni., T.M.)

Tomihiko Hirokawa, MD, Department of Ophthalmology, School of Medicine, The University of Tokushima, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan.

Objective. To evaluate contrast-enhanced harmonic ultrasonography at a low mechanical index for its usefulness in visualizing uveal perfusion. Methods. The study was performed with 9 rabbits, 6 intact and 3 with focal impaired blood flow in the uvea. Ultrasonography was performed by harmonic imaging (transmit, 5 MHz; receive, 10 MHz) with a contrast agent. The agent was administered at a dose of 50 µL/kg. Transmission power was at a mechanical index of 0.2, which is below the US Food and Drug Administration guideline. The images were compared between the impaired and intact eyes. For uveal measurements, video signal intensity–versus–time plots were generated in all cases. The plots were analyzed to obtain the rate of signal intensity increase and peak signal intensity. Results. A clear increase of signal intensity was observed after contrast agent administration. The signal intensity of the uvea was lower in the impaired eye than in the intact eye. In the impaired eye, the intensity was lower on the side with impaired flow than on the other side. The differences were significant. Conclusions. Our findings suggest that uveal perfusion can be visualized by contrast-enhanced harmonic ultrasonography in the harmonic imaging mode at a low mechanical index.

Key Words: contrast-enhanced ultrasonography • orbital blood perfusion, low mechanical index • harmonic imaging

Abbreviations: FDA, Food and Drug Administration • ICG, indocyanine green • MI, mechanical index

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