Improved high-resolution ultrasonic imaging of the eye

Abstract

Currently, virtually all clinical diagnostic ultrasound systems used in ophthalmology are based on fixed-focus, single-element transducers. High-frequency (> or = 20-MHz) transducers introduced to ophthalmology during the last decade have led to improved resolution and diagnostic capabilities for assessment of the anterior segment and the retina. However, single-element transducers are restricted to a small depth of field, limiting their capacity to image the eye as a whole. We fabricated a 20-MHz annular array probe prototype consisting of 5 concentric transducer elements and scanned an ex vivo human eye. Synthetically focused images of the bank eye showed improved depth of field and sensitivity, allowing simultaneous display of the anterior and posterior segments and the full lens contour. This capability may be useful in assessment of vitreoretinal pathologies and investigation of the accommodative mechanism.

Figures

Figure 1

A 20-MHz immersion scan image of a healthy eye in vivo. Typical clinical sector-scan systems use single-element, fixed-focus transducers designed to place the focal zone near the retina in a contact scan. While this provides satisfactory images of the posterior segment, the eye as a whole is poorly depicted owing to the limited depth of field of this type of transducer.

Figure 2

Bank eye images were acquired with the 20-MHz annular array for cases of fixed focusing (A) and synthetic focusing with the 31-mm geometric focus (triangles) positioned just beyond the cornea (B) and with the geometric focus placed 1 cm deeper into the eye (C).

Figure 3

A, Manually segmented stack of bank eye images permitted a 3-dimensional visualization of the retina (orange), iris (blue), lens (white), ciliary body (brown), and sclera (gray). B, Anterior segment from a posterior perspective shows the lens and ciliary body.