Biomedical Engineering Reference
In-Depth Information
Mirror
(Lateral Scan)
Detector
Laser
Source
Beam
Splitter
Pinhole
Objective
Object
(Vertical Scan)
Fig. 8.19
Confocal microscope
From the discussions above it is clear that CSI and confocal microscopy are able
to resolve twice the spatial frequency of OCT or DHM. It is also noted that at low
NA the axial extent of the PSF for both CSI and OCT is inversely proportional to
the source bandwidth. For quasi-monochromatic CSI and confocal microscopy,
however, the axial extent is inversely proportional to the squared NA. For broad-
band CSI systems the axial extent is either bandwidth or NA limited and for typical
systems a crossover is observed when NA
0.3.
8.6
Imaging Performance
In the previous sections we have introduced the methods of coherent microscopy
and optical tomography and have characterized their performance in terms of 3D
linear imaging theory. The response of the system to spatial frequencies within the
object function, or refractive index contrast, is characterized by the TF which,
in turn, depends on the aperture of both the illumination and observation optics.
The PSF describes the appearance of a point-like object and is the inverse Fourier
transform of the TF. The PSF has been calculated for backscatter DHM, OCT, and
CSI configurations of equal NA as it provides a useful way to compare the 3D
imaging performance of the techniques.
In all the calculated cases the PSF has a cyclic variation in phase along
the central axis with a period approximately equal to half the mean wavelength.
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