Biomedical Engineering Reference
In-Depth Information
Lens
0.61
λ
Δ
x,y =
πλ
NA
FOV =
2NA
2
2
λ
Δ
z
≈ 0.44
Δλ
Figure 13.1
Transverse and axial resolutions and the FOV in OCM.
An illustration of the transverse and axial resolutions and the FOV is shown in
Figure 13.1
.
For example, using a setup with a light source with a central wavelength
λ
5
840 nm,
abandwidthof
Δλ
5
50 nm, and an objective lens with NA
5
0.6, one can achieve a
transverse resolution
m. The latter
value means that in order to resolve two reflecting layers in the axial axis using an OCM
system, the reflecting layers must be separated by a distance of at least 6
Δx
,
y
1
μ
m, FOV
.
2
μ
m and an axial resolution
Δz
5
6
μ
μ
m.
Other factors governing the system performance include the light source penetration depth
and the sample properties such as scattering and absorption, as well as the detector
characteristics such as data acquisition rate, resolution, and sensitivity. Because OCM is
often used for live cells and tissues and even in vivo, there are further limitations on the
maximum irradiance levels allowed in order to avoid damage to the sample.
The signal to noise ratio (SNR) performance of the system can be derived from the optical
communication field and is given by:
ξP
E
p
NEP
SNR
5
(13.4)
where
P
is the power that reaches the detector after being reflected back from the sample
multiplied by the detector efficiency
,
E
p
is the photon energy, and NEP is the noise
equivalent power. The top expression is the total power that is detected divided by the
electronic bandwidth or data acquisition rate.
ξ
In OCM imaging, two approaches are used to obtain the image: time-domain OCM (TD-
OCM) and Fourier-domain OCM (FD-OCM). Both systems can be implemented using a
Michelson interferometer setup. In TD-OCM, the reference arm path length is scanned
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