Image analysis – Applications – Biomedical applications
Reexamination Certificate
2000-09-22
2003-12-16
Patel, Jayanti K. (Department: 2625)
Image analysis
Applications
Biomedical applications
C435S032000, C435S173800, C435S176000, C435S177000, C435S182000
Reexamination Certificate
active
06665429
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and an associated apparatus for automatically determining positions of antibiotic-containing disks in a microbiological testing procedure.
Agar disk diffusion is a widely recognized microbiological assay for measuring susceptibility—a parameter effectively defined by the assay itself. The susceptibility of a microorganism to a given antibiotic is essentially a description of the size of the inhibitory zone resulting from placement of a permeable disk impregnated with the given antibiotic onto an agar surface inoculated with a sample culture of the microorganism. This parameter provides a measure of the ability of the antibiotic compound to stem growth of the target culture, but it is also a complex function of diffusion constants and other kinetic factors.
Of additional use to the clinician is a related quantitative measure of susceptibility, known as “minimum inhibitory concentration”(MIC). Although still requiring additional information to translate the parameter into a prescription for clinical practice, this quantitative measure eliminates some sources of complexity and uncertainty relative to qualitative susceptibility. A additional useful clinical parameter is the “inhibitory quotient”, which expresses the ratio of the drug concentration in a particular body tissue at a lowest clinical dose to the minimum inhibitory concentration.
The MIC is ideally determined by an assay appropriately called the dilution method, which straightforwardly involves inoculating a series of test tubes with the target culture, the test tubes containing a series of dilutions of the target antibiotic. One series of test tubes therefore tests only one culture and one antibiotic, in contradistinction to an agar diffusion assay petri dish, which may test a plurality of antibiotics simultaneously with less material and expense. The advantage of the dilution method is that it provides less ambiguously interpretable quantitative results relative to the agar diffusion method, while its disadvantage is primarily its expense, both in materials and labor.
It is therefore desirable to have a device which automatically translates a dimension of an inhibition zone on an agar diffusion assay plate into a more clinically useful quantitative measure of drug-bacterium interaction, such as the MIC. Such a device is disclosed by U.S. Pat. No. 4,701,850. It is further desirable to have a device which automates the process of reading the apposite linear dimension of the inhibition zone, such devices being revealed in subsequent United States patents. The relation of the diameter of the inhibition zone to the MIC for an unknown biological agent is approximated by a linear relation, the parameters for which assumed relation for a particular antibiotic being determined by statistical estimation based on the scatter of data points whose coordinates are inhibition zone diameters and actual minimum inhibitory concentrations determined by dilution assay for a particular microorganism, the relation being assumed linear and being assumed to persist for untested organisms.
Current commercial microbiological assay machines have largely automated the detection or measurement of agar-plate drug diffusion zones. One current automated test plate reader system requires the user to determine and record the positions of all drug disks on agar plates or panels. While inserting a test plate in the reader, the user must align a reference disk as prompted on screen with a mark on the reader drawer (reference disk is user-defined during drug panel setup). The software then searches for all disks and assigns a correct drug name to each disk based on identified orientation of the reference disk. Each plate is searched for disks in an area approximately 24 mm around the usually 6 mm diameter disk position assigned during drug panel setup. Because the drug code printed on all disks is small and difficult to read visually, it would be a significant advantage for the system to determine a reference disk position automatically without having users align it specifically to the drawer mark.
Sometimes a drug disk may be dropped on the plate in the wrong position(s), or the user may have selected the wrong drug panel name containing the wrong drug disk names. It would be another significant advantage for the system to detect if drug disk(s) were misplaced; this would improve the quality control and reliability of the result reading.
One known technology which has been proposed for use in automatic identification of microbiological assay disks is optical character recognition (OCR) technology. This technology requires input of the orientation of the target characters on each disk prior to reading and recognizing them. It is inherently difficult to know character orientation without an orientation mark in addition to the drug code on each disk. Conventional OCR technology is difficult without an orientation mark, but it can be done through extensive computer processing to assess multiple possible orientations of each disk. Providing an orientation mark on each disk is a solution limited in its usefulness insofar as it requires the supply of special disks in substitution for conventional commercially available disks.
OBJECTS OF THE INVENTION
An object of the present invention is to provide an improved apparatus and/or associated method for use in microbiological testing.
A more specific object of the present invention is to provide a microbiological testing apparatus and/or method wherein positions of antibiotic-containing disks are automatically determined.
A related object of the present invention is to provide a microbiological testing apparatus and/or method wherein the zone surrounding a given antibiotic disk is associated with the subject antibiotic compound without further operator intervention or opportunity for human error.
Yet another related object of the present invention is to provide a microbiological testing apparatus and/or method which does not require orientation marks on the disks and the extensive computer processing required by conventional OCR to read codes without that mark.
It is a supplemental object of the present invention to provide such a microbiological testing apparatus and/or method which is inexpensive to use.
A further object of the present invention is to provide an essentially automated microbiological testing apparatus and/or method wherein a dimension of an inhibition zone associated with an antibiotic impregnated disk on an agar plate is measured automatically.
A more particular object of the present invention is to provide such a microbiological testing apparatus and/or method which facilitates association of a microorganism susceptibility measurement with a particular antibiotic agent.
These and other objects of the present invention will be apparent from the descriptions and illustrations provided herein.
SUMMARY OF THE INVENTION
A method in accordance with the present invention is adapted for use in a microbiological assay procedure wherein a plurality of diffusion disks are placed on a nutrient medium on a plate, each of the disks carrying a respective antibiotic agent and each having an identification code identifying the respective antibiotic agent, the disks being positioned on the plate in a preselected relative arrangement. The method comprises optically scanning the disks on the plate, consequently generating a digitally encoded image including digitized representations of the identification codes, and electronically processing the digitally encoded image to determine an angle of rotation of the plate relative to a pre-established reference frame (coordinate system), wherein the electronic processing of the digitally encoded image includes detecting a region of the plate occupied by a unique subset of the disks.
The unique subset of the disks may include an absence of a disk in a location within the region, or a pattern or configuration of disks in the region. The unique subset of the disks may alternatively include a reference disk having
Coleman Henry
Giles Scientific, Inc.
Patel Jayanti K.
Sapone William
Sudol R. Neil
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