Biomedical Engineering Reference
In-Depth Information
25-50 mm/s. Although, only the velocity component along the viewing direction is
measured and this generally varies with position the 3D flow field can be
synthesized from three or more data sets.
The methods of CSI and confocal microscopy have been included in this chapter
because of their close relationship to the other techniques. As described in Section 3
both quasi-monochromatic CSI and confocal microscopy derive 3D information by
illuminating the object with plane waves from different angles within the NA of the
objective. Additionally, broadband CSI exploits spectral information like OCT.
According to linear theory, CSI and confocal microscopy will work with more
densely seeded flows than DHM and offer significantly better resolution than OCT.
Nevertheless OCT remains the method of choice for in vivo flow measurement
for several reasons. Fundamentally, OCT is different from all the other methods.
In DHM, CSI and confocal microscopy lateral and depth resolution are coupled as
they are proportional to NA and the square of the NA, respectively. In OCT the
depth resolution is proportional to the bandwidth of the source and this decoupling
allows the PSF of OCT to be tailored to suit different scales. This is exploited in
many examples of in vivo imaging since propagation through a rough distorting
surface (e.g., the epidermis) generally ruins the fidelity of images with large NA.
It is this flexibility, plus the efficiency of swept-source scanning that makes OCT
such a powerful tool for biomedical applications.
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