Ergonomic handheld OCT angiography probe optimized for pediatric and supine imaging

Abstract

OCT angiography is a functional extension of OCT that allows for non-invasive imaging of retinal microvasculature. However, most current OCT angiography systems are tabletop systems that are typically used for imaging compliant, seated subjects. These systems cannot be readily applied for imaging important patient populations such as bedridden patients, patients undergoing surgery in the operating room, young children in the clinic, and infants in the intensive care nursery. In this manuscript, we describe the design and development of a non-contact, handheld probe optimized for OCT angiography that features a novel diverging light on the scanner optical design that provides improved optical performance over traditional OCT scanner designs. Unlike most handheld OCT probes, which are designed to be held by the side of the case or by a handle, the new probe was optimized for ergonomics of supine imaging where imagers prefer to hold the probe by the lens tube. The probe's design also includes an adjustable brace that gives the operator a point of contact closer to the center of mass of the probe, reducing the moment of inertia around the operator's fingers, facilitating stabilization, and reducing operator fatigue. The probe supports high-speed imaging using a 200 kHz swept source OCT engine, has a motorized stage that provides + 10 to -10 D refractive error correction and weighs 700g. We present initial handheld OCT angiography images from healthy adult volunteers, young children during exams under anesthesia, and non-sedated infants in the intensive care nursery. To the best of our knowledge, this represents the first reported use of handheld OCT angiography in non-sedated infants, and the first handheld OCT angiography images which show the clear delineation of key features of the retinal capillary complex including the foveal avascular zone, peripapillary vasculature, the superficial vascular complex, and the deep vascular complex.

Conflict of interest statement

J.A.I. and Duke University have licensed technology to and have a financial interest (R,P) in Bioptigen/Leica Microsystems Inc., which manufactures hand-held and intrasurgical OCT systems. C.V, C.A.T, J.A.I., and Duke University have a patent application pending on the novel hand-held probe described in this manuscript.

Figures

Fig. 1

Schematics for a 4F (top) and our novel 5F (bottom) retinal OCT scanner design. The solid red lines denote the location of the intermediate image plane of the respective scanner. Red arrows denote the collimating lenses. The distance between the fiber tip and the collimating lens is increased in the 5F design to produce diverting light on the scanner.

Fig. 2

Curvature of the intermediate and retinal image planes for the 4F scanner (blue) and novel 5F scanner (red) designs. The slight negative curvature of the 4F scanner in the intermediate image plane resulted primarily from the use of an offset galvonometer pair and lens aberrations.

Fig. 3

Zemax spot diagrams for the 4F scanner (top) and the novel 5F scanner (bottom) as a function of angle (measured as the angle between the chief ray and the optic axis in the eye). The circle denotes the airy radius (12.0 µm for both systems at 0°). The background grid is 30µm x 30µm. For the 5F system the 15° spot shows performance being limited by clipping on a lens aperture.

Fig. 4

Demonstration of the grip used for a conventional gun-style OCT probe design for supine imaging of infants in the Duke ICN. The pictured system is the Leica (Bioptigen) Envisu C2300.

Fig. 5

Left: Rendering of the HH-OCTA optomechanics from the side. Center: Rendering of the HH-OCTA optopmechanics stabilization brace, and enclosure from the side. Right: Rendering of the HH-OCTA optopmechanics, adjustable stabilization brace, and enclosure from the front.

Fig. 6

Left: The novel HH-OCTA probe being used to image an infant in the ICN. Right: Picture of the operator grip employed with the HH-OCTA probe.

Fig. 7

Selected B-scans and volume renders of the retina from research HH-SSOCT imaging of non-sedated infants. a) In a premature-born infant imaged in the outpatient clinic one week after estimated date for term birth, CME elevates the central macula (red star). b) In a premature infant imaged in the intensive care nursery weeks before estimated date for term birth, the fovea has a normal depression without edema (yellow star), but there are large superficial vessels on the surface of the retina (yellow arrow). c) Peripheral images from the same infant as b) reveal preretinal neovascular elevations (purple star) and a ridge at the vascular/avascular junction (purple arrow). All images were acquired at 950 A-scans/B-scan and 128 averaged B-scans/volume. Each B-scan was averaged twice.

Fig. 8

Representative OCTA images from a healthy adult volunteer. Left: ~1.5x1.5mm angiogram of the fovea showing the FAZ with well-demarcated capillaries at the margin. Center: ~3x3mm angiogram of the optic nerve head showing multiple levels of large to small vessels of the optic nerve head (upper right corner) and retina. Right: ~1.5x1.5mm angiogram of nasal retina. The red arrows denote the location of artifacts caused by saccades while the yellow arrows denote the location of artifacts caused by operator hand motion.

Fig. 9

Comparison of FA to HH-OCTA during EUA from an infant with a history of ROP. HH-OCTA from a) the optic nerve (red), b) peripapillary region (blue), c) perifoveal region (purple), d) and the margin of the fovea (green). The red arrows denote examples of tortuous blood vessels. OCTA images were taken with 300 A-scans/B-scan, 4 repeated B-scans, and 300 lateral locations sampled per volume e) FA from the same infant. Colored boxes denote the location of the corresponding HH-OCTA scans. f,g) image from b) separated into superficial f) and deep g) layers. Representative B-scans with the manually corrected segmentations superimposed on the image are shown below the respective angiograms

Fig. 10

Imaging of vascular plexuses with HH-OCTA in a child undergoing EUA due to a family history of familial exudative vitreoretinopathy. Left: Projection of all vascular layers in the outer retina. Center: Projection of the SVC. Right: projection of the DVC. Images show relatively normal vascular patterns in each projection and were taken with 500 A-scans/B-scan, 4 repeated B-scans, and 500 lateral locations sampled per volume.

Fig. 11

HH-OCTA images from a 41 week PMA infant with a history of ROP, imaged without sedation during a follow up clinic visit. Top: Overlaid angiograms of all vascular layers showing the optic nerve head, peripapillary vasculature, and the edge of the fovea. The red star denotes the edge of the fovea near which are several bulb-like vascular terminations. The inset image is a magnified view of these bulbs with the corresponding regions marked by the red boxes. Bottom: the peripapillary/foveal angiogram of SVC (left) and DVC (right). Selected B-scans with and without OCTA flow superimposed are shown below the angiograms. The horizontal dashed yellow line denotes the location of the selected B-scan. The vertical dashed blue lines denote the same lateral location on the angiograms and selected B-scans. The green line on the B-scans denotes the manually corrected IPL. Images were taken with 500 A-scans/B-scan, 4 repeated B-scans, and 500 lateral locations sampled per volume.

Fig. 12

Vascular structure of a preretinal neovascular elevation in a 41 week PMA infant who was treated for ROP. Infant was imaged without sedation in the ICN. a) OCTA image of all retinal vasculature. Yellow line denotes the location of the B-scan shown in (b). b) Selected B-scan with manually corrected segmentations. White – surface of the retina including the neo-vascular plaque. Purple – surface of the retina excluding the neo-vascular plaque. Teal – IPL. Yellow – RPE c) OCTA of the vasculature excluding the neo-vascular plaque (purple to yellow). d) OCTA of the neo-vascular plaque (white to purple). e) The neo-vascular plaque divided into slices that are 25% of the total thickness of the plaque. The red arrow denotes the location of the “trunk” within the neovascular plaque.