Biomedical Engineering Reference
In-Depth Information
Figure 11.2
Coherence-gated xy sections of a multicellular tumor spheroid that is 850
μ
m in diameter. The
m intervals, with one frame in eight being displayed. The reflectance
color scale is logarithmic (dB) showing the bright reflections from the necrotic core and the
dimmer reflections from the proliferating shell.
data are acquired at 10
μ
11.3 Motility Contrast Imaging
The OCI data in
Figures 11.2 and 11.3
are strongly speckled, which is a consequence of the
broad-field illumination of the sample with spatially coherent light. However, at a fixed
depth, the speckle is highly dynamic with large intensity fluctuations in time. These
fluctuations are a direct consequence of the intracellular motions of live tissue. There are
different types of motion for different constituents of the cells and tissues. Membranes
undulate and move, driven by active forces induced by the changing cytoskeleton;
organelles are transported by molecular motors along microtubules; thermal motions and
Brownian diffusion occur for small vesicles; and very large-scale motions take place when
a cell divides. The statistical properties of the different motions lead to fluctuations on
many different time scales. By capturing the degree of fluctuations within the dynamic
speckle, motility maps of tissue can be constructed. In this sense, internal motion of a live
tissue provides the imaging contrast.
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