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A multipurpose digital imaging device has been developed for applications in quantitative densitometry,
light scatter detection and fluorescence emission measurement. The Scanning Laser Imaging (SLI)
device consists of a three-dimensional laser beam controller, a fiber optic faceplate coupler, a specially
designed photodetector assembly and a support computer that has interactive control over the beam
positioner. Image information is collected as measurement of either total forward light loss, forward
direction scattering or fluorescent emission, depending on the nature of the biological target and the
configuration of the detection assembly. Signal output from the bulk photodetector is digitized and
assigned to the corresponding pixel location illuminated by the laser spot. The target and detector
assembly are stationary while the laser spot is scanned in a programmed pattern. Areas up to 16 cm2
are scanned at a rate of 5.1 x iO pixels/s with 12 bits gray level detection range per pixel. Typically,
1024 x 1024 pixels are captured in less than 30 seconds and stored for display, processing or archiving.
Spatial resolution for image reconstruction is a function of laser spot size and has been demonstrated to
3 pm. Rescan and arbitrary laser spot positioning is accomplished to within Biological, biophysical,
clinical instrumentation and optical and computer engineering applications of this technology are
broad. SLI methods have been developed for quantitative densitometric analysis of electrophoretic gels,
thin-layer chromatography plates and autoradiographic materials generally used in molecular biology
research. These applications are not well suited for conventional scanning densitometry, particularly
when translucent materials such as nylon or nitrocellulose transfer membranes are used because of loss
in resolution due to scattering. The SLI spatial resolution is not affected significantly by such scatter.
Other quantitative analysis such as measurement of immunofluorescent and immunochemical staining of
cells from blood samples and tissue sections can be performed with the SLI device. These applications
are poorly suited for traditional flow cytometry, which requires dispersal of individual cells from the
tissue. In addition to imaging, the SLI device is capable of detecting and analyzing the occurrence of
very rare events. It is routinely capable of scanning a large transparent or translucent target, detecting
submicron particles and recording the position of the particles to within approximately 1 pm. The
system will detect and locate a single submicron particle placed anywhere on a 800 mm2 surface, a task
analogous to locating a standard typewritten character placed on a football field, within 30 seconds.
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