Medical Design Briefs - June 2022 - 14

Designing Lenses
Current NIR Fluorescence
Imaging Applications
Compared to visible light fl uorescence
imaging, NIR fl uorescence
imaging exhibits superior tissue
penetration and causes less
autofl uorescence in adjacent tissue.
For these reasons, the technique is
becoming increasingly important in
many medical applications:
* Cancer detection. Both
nonspecifi c and specifi c cancertargeted
fl uorescent agents are
currently being used for in vivo
cancer detection.
* Lymphatic imaging. ICG, a
blood fl ow tracer, can visualize
lymphatic fl ow from cancer
lesions. Separate visualizations of
different lymphatic drainages are
also possible using fl uorescent
agents with multiple colors.
* Surgical guidance. NIR
fl uorescence imaging systems
are playing a growing role in
applications requiring surgical
or endoscopic guidance.
tial refl ection, this coating also reduces
undesired fl are and ghosting to deliver
sharp, clear images even in very poor
lighting conditions.
Compared with other antirefl ective
coatings, eBAND is suitable for wavelengths
from 400 to 1,700 nm, which includes
the visible to near-infrared range.
This capability enables users of eBAND to
conduct in-depth examinations with indocyanine
green (ICG), a medical dye
frequently used in tests that involve the
heart and liver, as well as certain parts of
the eye.
High Optical Density
In addition to antirefl ective coatings,
fl uorescence endoscopy relies on lenses
with highly precise optical fi lters, as well
as lenses with a high optical density (OD).
The purpose of these fi lters is to selectively
transmit only certain wavelengths on
the optical spectrum and reject others,
while OD describes the amount of energy
blocked by the fi lter.
A high OD indicates low energy transmission,
while a low OD indicates high
14
Cov
MDB Tamron Feature 0622-CC_1.indd 14
FWHM
X
X2
Fig. 1 - The full width at half maximum (FWHM).
No Focus shift from Visible to Near Infrared -corresponding NIRX
Center
Corner
Fig.
2 - The focus shift with a Tamron lens across the visible and NIR light range.
transmission. Optical densities of six or
greater are typically used in applications
that require extreme blocking like fl uorescence
endoscopy.
Fluorescence endoscopy requires optical
fi lters that enable precise control of
both the laser beam incident angle and
full-width-at-half-maximum (FWHM)
value. The laser beam incident angle indicates
the degree at which a laser beam
hits the fi lter, whereas FWHM measures
the optical bandwidth of a light source.
FWHM is the distance between the
points on a curve at which the function
reaches half its maximum value - in
other words, the width of the curve's
bump. When applied to optics, it refers
to the width of an optical signal at half its
maximum intensity and provides the
bandwidth of a light source operating at
50 percent capacity.
The ability to manage both the laser
beam incident angle and FWHM results
in highly accurate control of a
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ToC
5/25/22 2:47 PM
Fig. 3 - OD6-level fi lters with low-fi lm thickness.
light source, enabling affected areas in
fluorescence endoscopy procedures to
be seen more clearly (see Figure 1).
Minimal Focus Shift
Lenses for fl uorescence endoscopy
need to feature an optimized optical design
that maintains image quality across
Medical Design Briefs, June 2022
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Medical Design Briefs - June 2022

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