Holographic Motility Contrast Imaging of Live Tissues - Biomedical Optical Phase Microscopy and Nanoscopy - page 210

Tumor spheroid

Petri dish

Full isosurface Eroded isosurface

Figure 11.3
Three-dimensional visualizations of OCI data from a multicellular tumor spheroid resting on a
Petri dish.

The drifting intensities at a fixed depth inside a tumor spheroid are shown in Figure 11.4A .The
horizontal axis is a row of reconstructed pixels, and the vertical axis is time. For a selected
pixel, the intensity varies randomly (but with an average correlation time). The data in
Figure 11.4B are for a punctuated flythrough for which 40 frames are acquired, then the
coherence gate is moved deeper and 40 frames are acquired again, and the process is repeated.

For each fixed-depth stack of images, the statistical properties of the fluctuating intensities
for each pixel are evaluated. One of the simplest statistical measures of temporal fluctuations
is the normalized standard deviation (NSD), also known as temporal speckle contrast. For a
given pixel, the standard deviation in the intensity values is divided by the mean intensity.
Values of the NSD approaching unity represent highly variable pixels. An example of the
NSD at several depths inside a tumor spheroid is shown in Figure 11.5 . The data are color
coded with red denoting highly variable pixels and blue denoting smaller deviations. Around
the midsection, the proliferating shell is clearly observed as strongly variable pixels
surrounding the blue core which has much less motion. The core of a tumor is composed of
dead or dying cells. However, even in regions where there are intact cells in the core, the
tissue is hypoxic because oxygen is consumed by the surrounding proliferating shell. The
hypoxic tissue has low metabolic activity which is reflected by lower intracellular motions.
The stack of motility maps for increasing depth into the tumor spheroid can be combined into
a three-dimensional visualization of the motility in the tumor tissue. The volumetric motility
contrast of a tumor that is 800 μ m in diameter is shown in Figure 11.6 [6] .

The motility contrast is a quantitative measure of intracellular motion and can be used
to monitor changes in internal motions induced by changing environmental conditions or