Unlike layers of cultured cells, biological tissues do not consist of only one cell type, but of a mixture of different cell types, extracellular matrix and large structures embedded in the cell layers.

The specialized cells that give the tissue its function have to be maintained by various other cell types which are present in a wide variety of different tissues:
Macrophages remove dying cells and unwanted excellular matrix. Lymphocites and other white blood cells destroy infectious organisms.
Extracellular matrix (mainly consisting of  proteins assembled to various structures) is needed to provide mechanical stability in all kinds of tissues.
Supercellular structures like blood vessels are embedded in tissue and function as support systems for the tissue, wheras other structures 'only' use the tissue as 'embedding medium' (e.g. hair and sweat glands) .

Therefore, biological tissues can be described as highly heterogenous systems.

With our new SCATTERING MICROSCOPE, we present a way to measure the static or dynamic scattering of  tissue samples and are able to gain the visual information about the structures we scatter from by simultanous microscopy.

Therefore, local heterogeneities of biological tissues can be probed and by a statistical analysis of many measurements, we are also able to calculate averages to compare our technique with others.
 

On the LEFT side, the scattering patterns are shown, on the RIGHT the microscope images.
The real space images have a width of 60 micrometer.
 
 

1
Here, smooth muscle from the border of the lung is shown on the left together with pig skin on the right.
Though both tissues seem to have isotropic scattering patterns,  the skin tissue pattern contains small anisotropic
features like little streaks

2
These two tissue samples seem to be completely different, according to their their scattering patterns.
In fact, they are the same tissue type, striated muscles.
The one on the left is oriented perpendicular to the cover slip, the right one parallel.
 

How can one analyze this strange light scattering data??

The scattering patterns are 2- dimensional intensity distributions, they are functions of two variables: the scattering angle and the azimuthal angle, the latter is sensitive to directional motion.Thus, one can show the intensity as function of any of these angles.

The conventional method, however, is an analysis only according to the scattering angle ('formfactor analysis'). We have done this also - and found no differences between the muscles, but a striking difference between muscle and skin (first image below). We explain these difference with arguments borrowed from fractal geometry. According to this argumentation, the scattering from skin is coming mainly from the surface, whereas the scattering from muscle is a volume effect.
 
 

... and what the new kind of analysis might tell you

Analyzed with respect to the azimuthal angle, the tissue data looks much more different, as the azimuthal scattering is a signature of tissue micro-structure. We have analyzed this data further with statistical methods and found out that it can even be used for tissue type classification. Applications of these findings might even lead to an automized method for the detection of deseases in biopsy slices!!!!!
 

 Using the Scattering Scope for biological samples, we are......

• Alois Popp, send email to alpopp@deas.harvard.edu
• Peter Kaplan, send email to kaplan@student.physics.upenn.edu

... and have to thank
 

     for setting it up.

Alois Popp
Department of Physics
Harvard University
40 Oxford Street, ESL
Cambridge, MA 02138
617-496-8049