Biomedical Engineering Reference
In-Depth Information
a
b
100%
100%
80%
80%
60%
60%
40%
40%
20%
20%
0%
0%
350.0
400.0
450.0 500.0
Wavelength(nm)
550.0
600.0
650.0
350.0
550.0
750.0
950.0
1150.0
1350.0
1550.0
Wavelength(nm)
c
d
100%
0.01
80%
0.008
60%
0.006
40%
0.004
20%
0.002
0%
0
350.0
400.0
450.0 500.0
Wavelength(nm)
550.0
600.0
650.0
350.0
400.0
450.0 500.0
Wavelength(nm)
550.0
600.0
650.0
Fig. 9.14
Transmission plots of (
a
) bandpass filter, (
b
) dichroic mirror, and (
c
) longpass filter. (
d
)
The transmission of the light from the UV LED after passing through the bandpass filter, dichroic
mirror twice, and longpass filter (assuming the reflectivity of the sample is 1)
illumination light and signal for OCT and transmits the illumination light and signal
for reflectance and fluorescence imaging.
9.4.5
Detection Path
Fluorescence imaging and polarized reflectance imaging share the same detection
path, including imaging lens and detector, without any moving element. For
polarization imaging, a polarizer with orthogonal axis relative to the polarizer in
front of the white LEDs is placed as the first element in the imaging path. To block
the excitation light, a longpass filter, instead of a bandpass filter, is placed after
the polarizer in the detection path in order to capture visible light for polarized
reflectance imaging. Ideally, the cut-on wavelength of this emission filter should be
low enough so that enough blue light can be transmitted, but not too low, to pass the
excitation light. Figure
9.14
c is the transmission plot of the longpass filter.
Assuming the reflectivity of the sample is 1, Fig.
9.14
d plots the transmission
of light from the UV LED after passing through the bandpass filter, dichroic
mirror twice, and longpass filter. There are some very weak leakages after 460 nm.
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