Real-time ophthalmic imaging with a handheld, 20-MHz annular array

Ophthalmic ultrasound is almost exclusively performed using single-element, handheld transducers. Linear-array systems are not feasible for ophthalmology for the foreseeable future. Annular arrays permit linear-array image quality but without the system complexity and cost. Here, an annular-array transducer previously demonstrated using a cumbersome immersion-scan technique (i.e., water bath coupled to eye) was integrated into a handheld probe that permitted contact scanning of the human eye. A custom, 5-element, 20-MHz annular array based on a 25-μm, P(VDF-TrFE) membrane was packaged in a stainless steel shell and mounted in a commercial, handheld, mechanical probe specifically designed for clinical ophthalmic imaging. The array had a focal length of 25.8 mm and an aperture of 9 mm. The array was characterized using a 25-μm wire and a calibrated hydrophone. After establishing the acoustic parameters were within safety limits, human subjects were imaged. Human-subject scanning was performed by placing the tip of the fluid-filled probe in contact with the sclera.