Page 61 - Computational Retinal Image Analysis

3 Ophthalmic instruments 51

FIG. 24
(A) In vivo B-scan image of the human optic nerve showing lamina cribrosa. Size of the
image: 4.2 × 3.7 mm. (B) 36 images of human lamina produced simultaneously and in
real-time using a MS OCT instrument. (C) Confocal en-face image produced at the same
time as the OCT images. The size of each en-face image is 2 × 2 mm. The en-face images
are separated by 15 μm. Here only 36 images are presented, however the technology
allows more images to be displayed in real-time. All distances are measured in air.

resolution than the near-infrared instruments, as well as different spectroscopic
contrast hence unique benefits to both fundamental research and clinical care of
several eye diseases [62].
Optical Coherence Elastography (OCE). Unlike OCT, which uses endogenous
contrast mechanisms within a sample, OCE adds an externally induced mechanical
stimulus alongside OCT to obtain structural information about the biomechanical
properties of the sample. Although not demonstrated yet for real-time in vivo in-
vestigations of the human eye, the technique has a huge clinical potential as OCE
relies on the fact that the elastic properties of tissues depend on whether they are
diseased or not.
Real-time OCT (RT-OCT). Speed on data acquisition and processing is cru-
cial when imaging moving organs and for instruments equipped with hand-held
probes. Although in the last years, in terms of data acquisition, a huge progress
has been made with the development of MHz line-rate swept lasers, the process-
ing of data is still not sufficiently fast to allow for true real-time display of images.
To alleviate the problem of data processing and display, parallel approaches in-
volving graphics processing unit (GPU) cards on CUDA parallel computing plat-
forms or field programmable gate arrays (FPGAs) are used but they add to the cost
of the instrument. Even if the processing time is drastically reduced, such methods
are not genuinely real-time, as the brightness of each pixel in the transversal sec-
tion is not established simultaneously with the beam being incident on that pixel.
To allow for real-time display, methods such as the Master/Slave, which do not
add complexity to the instrument is probably a trend that many researchers in the
field will follow.