Image analysis – Applications – Biomedical applications
Reexamination Certificate
2001-03-09
2004-12-28
Mehta, Bhavesh M. (Department: 2621)
Image analysis
Applications
Biomedical applications
C382S321000, C382S294000, C377S010000, C600S156000
Reexamination Certificate
active
06836559
ABSTRACT:
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to automated imaging and data acquisition systems, and more particularly to a table-top system that automatically quantifies the deposition and aggregation kinetics of sub-micrometer- to sub-millimeter-sized particles at an arbitrary surface by simultaneously determining their spatial and temporal distributions at the surface and their diffusion coefficient, velocity, and concentration distributions in the bulk suspension.
2. Description of the Background Art
Colloids are minute particles that are dispersed in different continuous phases. They range from airborne dust and smoke, to foams and emulsions, to proteins and biological cells. Understanding the behavior of these tiny particles is important to research ranging from drug development to environmental remediation. The deposition kinetics of colloids onto different interfaces (e.g., solid/liquid or gas/liquid interfaces) is key to a variety of their applications. For example, in medical drugs, it affects how colloids disperse corrective proteins in body tissue. On the assembly line, it affects how well the paint sprayed onto car bodies will adhere. In the mining industry, it affects how efficiently valuable minerals (like gold) can be separated from waste rock by froth flotation techniques.
Quantifying the deposition kinetics of colloids requires determining their spatial and temporal distribution at a surface (a liquid/solid or gas/liquid interface); determining the position of each colloid when it arrives at, attaches to, and detaches from that surface; and determining the average concentration (or flux) of colliding, attaching, and detaching particles. The large number of particles (typically thousands) that must be tracked and the time-dependence and randomness of their movements rule out quantifying them by manual means.
Experimental methods used to study colloid deposition in different geometries can be classified into either direct or indirect methods. Indirect methods measure quantities that are unequivocally related to the number of deposited colloids. Examples include: (a) the depletion method, in which the change in the number of colloids in the bulk suspension is measured over time and correlated to the average number of deposited colloids, (b) the packed-bed column method, in which the capture of colloids by the packed-bed of a well-defined granular material is determined, by measuring the difference between the inlet and outlet colloid bulk concentrations, and related to the number of deposited colloids onto the surfaces of the granular material, (c) the light scattering method, in which the intensity of light scattering by deposited colloids, in the direction normal to the incident light beam, is measured and related to the number of deposited colloids, and (d) the radioactive tracer method, in which the radiation emitted by deposited colloids tagged with a suitable &ggr;-ray-emitting material is measured and related to their surface concentration.
An inherent limitation to all indirect methods is the inability to quantify the attachment and detachment events of the colloids during the deposition process or their spatial and temporal distribution on the surface. The first two methods (a and b) are also labor intensive and subject to human errors in measuring the changes in the bulk concentration of the colloids. Those changes are typically measured by manually sampling and measuring using, for example, the Coulter principle or light obscuration methods. Moreover, these two methods implicitly assume that the colloid deposition onto the surface is uniform and that the number of deposited colloids equals those lost from the bulk suspension. Thus colloids removed from the bulk suspension by processes other than deposition (e.g., mechanical filtration, coagulation) or by deposition in the sampling tubes are not accounted for, which can potentially skew the experimental results. The last two methods (b and c) are also subject to counting errors due to the background light scattering or radioactivity. Neither method can distinguish between mobile colloids close to the surface and colloids deposited onto the surface.
These limitations of indirect methods have precluded their use in studies aiming at gaining a quantitative understanding of the underlying processes or validating colloid deposition theories or models. Detailed information on the deposition of colloids, larger than ~0.3-0.5 &mgr;m, can be obtained in situ using direct visualization and appropriate image processing methods. These methods can track the time when and the position where each particle attaches to and detaches from the surface, thus the temporal and spatial distributions of the particles at the surface. Direct in situ video microscopic techniques have been successfully employed to investigate colloid deposition at the stagnation point, and in parallel-plate channels. These investigations have demonstrated that direct methods are capable of providing important information beyond the capabilities of indirect methods.
Almost all experiments reported on colloid deposition in parallel-plate geometry have employed in situ direct video microscopic techniques. For example, phase-contrast light microscopy has been used in conjunction with an image processing and data extraction routine to investigate the deposition of 736 nm and 830 nm polystyrene colloids from a flowing suspension through a 0.06 cm aperture parallel-plate channel onto glass and plastic substrates. However, because that system has a relatively low spatial optical resolution, an ultralong working distance objective lens with a relatively high magnification is used, reducing the field of view to only ~1.7×10
−4
cm
2
, and hence decreasing the statistical accuracy of the measurements. Further, the image processing and data extraction routine used could not establish full connectivity between deposited colloids in successive images. Also, the number of attached and detached colloids at the surface was determined by labeling the colloids with different gray-scale values. The 8-bit gray-scale used therewith indicates that the number of labeled colloids is limited to a total of 256, thus the data extraction ceased once the total number of attachment or detachment events reaches 256.
The evanescent field technique has also been utilized in conjunction with an elaborate data extraction routine to quantify the deposition of 310-nm diameter fluorescent polystyrene colloids onto the base surface of a rectangular optical glass prism in contact with a flowing colloid suspension in parallel-plate geometry. However, an optical glass prism is necessary to generate the evanescent field at its base surface, which is used as the deposition surface. The underlying parallel-plate channel has an aperture of 0.1 cm. Although it has an optical resolution of ~1 &mgr;m, that system possesses some inherent disadvantages, including: (a) because of the discontinuous illumination of the surface, continuous visualization is hard to achieve, limiting the time resolution between measurements, (b) colloid deposition can only be studied at the base surface of the optical glass prism and the colloids need to be fluorescence-tagged to enhance visualization and image contrast, and (c) the laser beam used to illuminate the deposition surface may induce unfavorable heat and radiation pressure, thus affecting the accuracy of the results.
In summary, the direct in situ methods can separate and accurately quantify the attachment and detachment processes of colloids mingled with their deposition onto a surface. They allow experimentalists to verify measured quantities and immediately detect and correct setup errors during the course of an experiment, avoiding costly reruns. These methods, however, have several limitations such as low spatial resolutions (>1 &mgr;m), limited time resolutions (~2 to 20 minutes), and small fields of view (>0.035 mm
2
), in addition to being ap
Abdel-Fattah Amr I.
Reimus Paul W.
Choobin Barry
Mehta Bhavesh M.
O'Banion John P.
The Regents of the University of California
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