Using high-frequency ultrasound to characterize intraocular foreign bodies

We scanned uniformly-sized particles of brass, aluminum, glass, and plastic at ultrasonic frequencies of 10 and 50 MHz to determine the effects of material type and transducer frequency on the ultrasonographic appearance of these particles. The particles were scanned in vitro against both anechoic and echoic backgrounds and in vivo, implanted in the angle of rabbit eyes. Both the metals and glass produced reverberations against an anechoic background; the plastic particles appeared as discrete objects, with no reverberations. Against an echoic background, the plastic particles created prominent shadows, while the metal ones did not. When placed in the angle of a rabbit eye, with the exception of the plastic at 10 MHz, all the materials could be differentiated from surrounding tissues at both frequencies. However, the appearance of the foreign body and the surrounding tissues, as well as their exact location and size, were most obvious with the 50-MHz system. In general, the particles produced more reverberations at 10 than at 50 MHz, and more prominent shadowing at 50 than at 10 MHz. In summary, high-frequency imaging enabled superior characterization of all the particles.