Bio-Rad Personal Molecular Imager™ (PMI™) System - Manual (Page 11)

2.3 Theory of Operation
2.3.1 Storage Phosphor Detection Mechanism
When a radioactive emission strikes the BaFBr:Eu screen, phosphor oxidation occurs and
a high energy site is formed (Figure 2.4, stage 1). When such an activated site is
subsequently illuminated with certain wavelengths of visible light (stage 2), the reduction
reaction occurs. Trapped energy is released as photons that are in turn captured by a
photomultiplier tube (stage 3).
Fig. 2.4. The storage phosphor detection mechanism.
Note: Storage phosphor screens are reusable after erasure.
2.3.2 Data Processing and Analysis
Phosphorescence and fluorescence signals are captured as a 16-bit digital file. This file can
then be analyzed and manipulated by the appropriate image analysis software for visual-
ization and quantitation.
Traditionally the image is displayed in a two-dimensional format, where the darkness of
each pixel is proportional to the signal intensity at that sample location (Figure 2.5, left). For
the purpose of image analysis however, it is helpful and more accurate to think of the data
as a three-dimensional structure, where the signal intensity at each pixel becomes the
height or z-axis dimension (Figure 2.5, right).
Sample spots or bands can also be visualized as peaks in a profile analysis along the
length of a gel lane, or perceived as topographic volumes when quantitating the total signal
from a specific band or spot
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