Theoretical study of multispectral structured illumination for depth resolved imaging of non-stationary objects: focus on retinal imaging

Abstract

Current implementations of structured illumination microscopy for depth-resolved (three-dimensional) imaging have limitations that restrict its use; specifically, they are not applicable to non-stationary objects imaged with relatively poor condenser optics and in non-fluorescent mode. This includes in-vivo retinal imaging. A novel implementation of structured illumination microscopy is presented that overcomes these issues. A threewavelength illumination technique is used to obtain the three sub-images required for structured illumination simultaneously rather than sequentially, enabling use on non-stationary objects. An illumination method is presented that produces an incoherent pattern through interference, bypassing the limitations imposed by the aberrations of the condenser lens and thus enabling axial sectioning in non-fluorescent imaging. The application to retinal imaging can lead to a device with similar sectioning capabilities to confocal microscopy without the optical complexity (and cost) required for scanning systems.

Structured illumination microscopy for in-vivo human retinal imaging: a theoretical assessment

“…[6]. In summary, the sample to be imaged is illuminated by a sinusoidally-varying intensity pattern given by:…”

“…We have recently proposed the use of this technique applied to imaging the retina in the living human eye using a Structured Illumination Ophthalmoscope (SIO) [6]. The SIO uses a modified, incoherent fringe projection technique to produce the structured illumination, using the interference pattern generated by a Michelson interferometer setup [6,7].…”

“…The SIO uses a modified, incoherent fringe projection technique to produce the structured illumination, using the interference pattern generated by a Michelson interferometer setup [6,7]. The application of structured illumination to ophthalmoscopy has the potential to provide a low-cost, three-dimensional retinal imaging device that offers significant advantages over existing retinal imaging techniques [6].…”

Structured Illumination for In-Vivo Retinal Imaging

“…Defocus increases with each successive plot. The fourth image if for a defocus of u=8 (u = 4knz sin 2 (α/2) as defined in Refs [6,7,10]) and corresponds to the minimum reached in the integrated intensity curve (for constant modulation) shown in Fig. 2.…”

“…There has been considerable work in applying structured illumination to fluorescence micropscopy [1,3] and to a lesser extent to reflectance microscopy [4]. There is some early work on proposing the application of structured illumination to retinal imaging [5][6][7] and fluorescence images of ex-vivo eyes [8].…”