08 May 2019
University of Washington project improves scanning efficiency and ease of use.
The difficulties involved in using clinical OCT systems on young patients, along with the relatively low scan rates available in existing hand-held alternatives, has certainly hindered the detection and diagnosis of infant eye diseases such as retinopathy of prematurity (ROP), according to Ruikang Wang at the University of Washington.
A project in Wang's Biophotonics and Imaging Laboratory has now demonstrated a new design of miniature hand-held OCT probe, capable of high-speed OCT and OCT angiography (OCTA) of young children and infants in a clinical setting. The work was published in Biomedical Optics Express.
"General improvements to the speed and sensitivity of OCT will always benefit pediatric imaging, because the improvement of those characteristics can mitigate motion artifacts in angiography imaging, delivering higher quality of OCTA images," Wang commented to Optics.org.
"On the other hand, the overall challenges of pediatric imaging can only be fully overcome by using a unique design of imaging probe. This particular application requires an easily accessible and conveniently operable probe, since the time window allowed for imaging is very short and easily interrupted by the movements of the patients."
The team tackled the problem by developing a portable OCT system based around a 200 kHz swept-source laser from Axsun Technologies. Particular features redesigned to support infant imaging included a direct-view iris camera incorporated into the hand-held probe; an on-probe display for the operator when performing imaging; and on-probe controls allowing the operator to operate the motorized optomechanical components.
The probe was designed to feature a scanning angle of ± 36 degrees on the pupil, covering the full perifoveal region of the eye, and to allow 3D OCT and OCTA scan times of 0.8 and 3.2 seconds respectively.
More comfortable and more efficient
"Our core considerations in making the hand-held probe, and in designing the whole OCT system, were to improve the efficiency of data collection and user friendliness," said Wang.
"There have been many attempts in the past to improve the experience of the OCT operator, but our direct-view iris camera is a useful assistance for rapid alignment. Mounting a screen on the probe means that the operator does not need to look away from the patient, while the swept source engine at 200 kHz enables high-speed, wide-field angiography imaging while extending the field-of-view, a particular challenge in a hand-held probe."
In tests on adult volunteers and premature infants, the probe proved capable of providing capillary-level resolution en face OCTA images. Operators reported that the prototype hand-held OCT probe was significantly more comfortable and efficient, thanks to the introduction of the iris viewer and the visual feedback available from the on-probe display when positioning the probe.
The project's next steps will focus on two main topics. One will be more improvements to the field-of-view on the infant retina, since the peripheral retina is important for screening the characteristics of ROP. Another task is to further improve the imaging speed and the capacity for real-time en face viewing of the infant's fundus, reducing the burden on the operator further and enhancing data collection efficiency.
"We recognize that our OCTA imaging quality on infants' retina is still not as good as traditional, bench-top OCT systems, in terms of image resolution and amount of motion-artifacts," commented Wang.
"However, imaging infants and premature babies using traditional ophthalmic OCT systems is simply not feasible, and other existing hand-held OCT probes have shown very limited field-of-view capabilities for angiographic imaging, if any. We have now demonstrated a newly developed probe designed for this purpose, and successfully tested its feasibility for providing retinal structural images and angiograms in both adults and premature infants."
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