Abstract
Conventional optical coherence tomography is based on A-scans, i.e., the fast scan direction is the z-direction. While this technique has been successfully demonstrated for two-dimensional cross sectional imaging of various tissues, it is rather slow if three-dimensional information is to be obtained. We report on a new technique that combines the transverse scanning approach of a confocal scanning laser ophthalmoscope with the depth sectioning capability of OCT. A stable high-frequency carrier is generated by use of an acousto optic modulator, and high frame rate is obtained by using a resonant scanning mirror for the priority scan (x-direction). Our prototype instrument records 64 transverse images consisting of 256x128 pixels in 1.2 seconds, thus providing the fastest retinal 3D OCT scanning system reported so far. We demonstrate the capabilities of our system by measuring and imaging the fovea and the optic nerve head region of healthy human volunteers in vivo.
Highlights
Optical coherence tomography (OCT) is known since more than a decade as a noncontact high resolution technique for obtaining cross sectional images of transparent and translucent structures [1,2,3]
The reference mirror, which is coupled to a stepper motor, acts as a variable path delay unit (PDU) that is used to vary the length of the reference path between successive C-scans, changing the position of the coherence gate within the retinal tissue
The reason for the rather small amount of published work on 3D OCT, at least in case of retinal imaging, is probably the recording time of at least several seconds, up to several minutes, which makes in vivo 3D imaging rather difficult
Summary
Optical coherence tomography (OCT) is known since more than a decade as a noncontact high resolution technique for obtaining cross sectional images of transparent and translucent structures [1,2,3]. The main application field of OCT is imaging of the human retina where several reports have shown the diagnostic power of the technology [4,5,6]. Despite the success of OCT in retinal diagnostic applications, the technology still has, in its present state, a major shortcoming: it is rather slow if three-dimensional data are to be obtained. To record a 3D data set with transversal resolution of at least 100x100 pixels in x and y direction would require 25 – 100 seconds – too slow for imaging of patients. Highspeed OCT with up to 4000 A-scans/s has been demonstrated in human skin and animal tissues [7]. The wavelength used in that report (1300 nm) is not applicable for imaging the human retina because it is absorbed by the water contained in aqueous and vitreous humors of the eye
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