DENSITOMETER

This measures the optical density of items placed between a light source and a light detector. Optical density is expressed as follows:

D = log10 I1/Ir

where D is the optical density, I1 is the light detected through the test material and Ir is the light detected directly.

Densitometers are common in the pathology laboratory for reading acetate electrophoretic strips. In this case the strip is moved through the light beam and a profile of the optical density along the strip is produced on a chart. The peaks of density recorded in this way represent particular materials in the original test samples.

Densitometers are also used on photographic and X-ray film. For instance, an X-ray film badge contains a small photographic film, and after development the optical density of each part of it is measured to determine radiation exposure. A densitometer may also be found in the X-ray department or used by the X-ray service engineer for checking X-ray set and film processor performance. Typical values for the density of exposed X-ray film might be 0.1 (fog level) up to 3.0 (darkest area).

Content and Design Copyright 2000 Dr. Malcolm C Brown.  See Title Page for more details