Prototype 3D OCT imager performs well in initial testing

New York-Evaluation of a prototype three-dimensional (3D) Fourier domain optical coherence tomographer (Topcon 3D-OCT) indicates it provides useful imaging of retinal diseases in both the cross-sectional (B scan) and 3D volumetric modes, according to researchers from the Digital Angiography Reading Center (DARC), New York.

The 3D-OCT instrument records the interferometric information using a spectrometer approach that allows for a very rapid scanning speed of 25,000 A-scans/second. Via integration with a non-mydriatic retinal camera and using a near-infrared, low-coherence Superluminescent 830-nm diode light source, it provides high-resolution cross-sectional images (axial resolution 6 μm, lateral resolution 10 μm) and generates 3D volumetric images of the posterior fundus.

"With its faster scanning, the Fourier domain technology allows more information to be captured in a short time compared with time domain technology," said Dennis Orlock, CRA, technical supervisor, DARC. "It acquires a higher number and density of axial scans, provides more comprehensive coverage of the retina, and reduces the likelihood that focal areas of pathology may be missed. In addition, Fourier domain technology provides the benefits of 3D imaging and allows the physician to make a point-to-point correlation between the OCT findings and pathology seen on a fundus image."

To evaluate its performance, the DARC staff obtained cross-sectional scans with a premarketing version of the 3D-OCT machine in 40 eyes of 20 patients. The patients studied had a variety of retinal diseases, including age-related macular degeneration, diabetic macular edema, central retinal vein occlusion, and papilledema, among others.

The investigators were very satisfied with the scanning experience itself and the quality of the images provided. In addition, when compared with scans obtained using the currently marketed 2D posterior segment OCT system (Stratus OCT, Carl Zeiss Meditec), the B-scan images were considered to be of similar diagnostic value.

"However, we found it was generally less challenging to obtain a good set of scan data with this new technology in our population including patients with low vision," said Novalis. "Motion artifact is more of a problem with the current 2D system because of its slower acquisition speed, and it can particularly limit the ability to get a good scan in eyes where poor fixation is an issue. The Fourier domain technology scans a larger area of the retina much faster, so the patient doesn't have to be still for quite as long or fixate extremely well."

With the 3D-OCT instrument, obtaining a single line scan that consists of 4,096 A-scans takes about 0.30 seconds compared with just less than 1 second using the current 2-D technology (Stratus OCT).

Measurement of retinal thickness with the 3D imaging mode was evaluated in 10 eyes of 10 patients. In that technique, a 20° × 20° area of the retina is scanned and the 3D data rendering software creates a 3D volumetric reconstruction. When obtaining a stack of images for a 3D reconstruction, the device performs 65,336 A-scans encompassing the entire posterior pole in less than 3 seconds.

The investigators considered the 3D approach very useful for visualizing and measuring retinal thickness.

"This instrument offers us the ability to track a patient's response to treatment easily and accurately at a level beyond what is currently available," said Jason Slakter, MD, DARC medical director.

"In the future, additional applications may include volumetric assessment of macular pathology and quantification of sub-retinal pigment epithelium lesions," he added.

Orlock observed that the instrument investigated in the present study is one of several Fourier domain OCT devices that have been recently introduced or will soon be on the market.

"This new technology is really an exciting breakthrough in retinal imaging," he said.