Bio-Rad Personal Molecular Imager™ (PMI™) System - Manual (Page 12)

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Fig. 2.5. Two and three-dimensional representations of a digitized image.
Note: Storage phosphor screens are reusable after erasure.
2.4 Overview of the Imaging Process
2.4.1 Steps in Storage Phosphorescence Imaging
Storage phosphor imaging is a simple four-part process:
Step 1 involves erasing the reusable phosphor screen to remove any background or residual
image. This normally takes 10 minutes. The screens should be erased to the background
level of 100 counts or less.
Step 2 involves placement of the prepared sample in an exposure cassette for subsequent
close proximity exposure to the imaging screen. The captured signal generates a latent
image of the sample, which is encoded in the number and pattern of charged phosphor
crystals.
Step 3 involves placing the screen in a laser scanner. As each pixel of the screen is
scanned, the electrons in charged areas of the latent image return to the ground state,
releasing energy in the form of emitted photons of visible light. The emitted photons are
collected and precisely counted by a photomultiplier tube, generating an intensity for each
scanned pixel. This intensity is expressed in counts or pixel density units, which are
analogous to the optical density of exposed x-ray film in autoradiography.
Step 4 is analogous to the procedure for imaging fluorescence samples; the resulting
image can then be reviewed and analyzed using an appropriate software package.
Upon completion of the four-step process, the storage phosphor screen can be erased and
the cycle repeated with a new sample.
2-D view
3-D view
Intensity
Single Pixel