Tech Briefs Magazine - November 2021 - PIT-16

Fiber optic illumination
channels (4X)
that connect to the light box should equal
the exiting NA of the light box. The taper
will convert the low-angle light to highangle
light to achieve the broadest illumination
angle. Figure 2 shows what happens
to a beam of light entering and exiting
the taper.
Visualization
channels
Figure 3. To illuminate the large volumes in laparoscopic surgery, the illumination design should attempt
to use as much available cross section of the device tip. Dividing the fiber bundle into sections allows for
easier integration into the shaft of the device. In the example shown, there are 4 fiber optic illumination
ports (represented by the white dots) and 2 visualization (detection) channels with sapphire windows.
An alternative to using a taper to reach
high output angles is to design a lens to
spread light out exiting the tip of the
laparoscope. A lens-aided illumination system
allows for higher output angles,
enabling higher FOV cameras for use in
the body, but comes at a cost of a less compact
design.
Once light is transmitted to the fiber
optics of the laparoscope, the fibers are
packaged to output light across the tip,
shown in Figure 3. This is more beneficial
than having a single light output face for
two reasons. First, it enables easier integration
of the fibers into the scope, and
second it prevents unwanted shadows
from surgical tools impacting the image.
Calibration and Testing
Considerations
Operator aligning lenses for a 3D stereo endoscope.
16
Cov
ToC
When designing the light source, the
team must also consider the image signal
pipeline (ISP) that will convert the captured
image and display it on a high definition
2D and 3D monitor for the surgical
team. The ISP can have various calibrations
that are applied to the system, including
dark signal non-uniformity on the
image sensor, photo-response non-uniformity,
color calibration, and white-balancing.
These calibrations allow corrections
that create a high-quality image; however,
if the ISP relies too heavily on calibrations,
the image may look highly processed and
is a distraction to the surgical team.
An ISP will have blocks that require calibration
of each unit. The calibration data
is typically saved in memory installed on
the endoscope. Starting the definition of
the calibration process early and coordinating
with ISP development engineers
will reduce risk of late-stage development
issues. By considering the ISP and calibrations
early, multiple revisions of the light
source and firmware are possible prior to
product launch. Calibrations do have limits,
and if the illumination system is
designed closer to the intended surgical
use, less troubleshooting of calibrations in
the development process is required.
Examples of calibrations related to the
illumination source are photo-response
non-uniformity (PRNU), white balance,
and color correction. These calibrations
are all limited in their effectiveness if the
Photonics & Imaging Technology, November 2021

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Tech Briefs Magazine - November 2021

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