United States Patent
`Berndt
`[45] Date of Patent: Jan. 21, 1997
`
`[19]
`
`[11] Patent Number:
`
`5,595,708
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`lllllllllllllllllllllllllllllllllllll||ll|llllllllllllllllllllllll||||||||l
`US005595708A
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`[54]
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`[751
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`[73]
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`[21]
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`[22]
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`[62]
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`[51]
`[521
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`[58]
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`[56]
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`SYSTEM FOR DETECTING BACTERIAL
`GROWTH IN A PLURALITY OF CULTURE
`VIALS
`
`5,304,492
`5,340,747
`5,396,054
`5,401,465
`
`.. 436/52
`4/1994 Klinkhammer ...........
`436/172
`8/1994 Eden ................
`
`
`3/1995 Krichever ct a1.
`235/462
`3/1995 Smethers et a1.
`......................... 422/52
`
`Inventor: Klaus W. Berndt, Stewartstown, Pa.
`
`FOREIGN PATENT DOCUMENTS
`
`Assignee: Becton Dickinson and Company,
`Franklin Lakes, NJ.
`
`Appl. No.: 341,825
`
`Filed:
`
`Nov. 18, 1994
`
`Related US. Application Data
`
`Division of Ser. No. 113,444, Aug. 27, 1993, Pat. No.
`5,397,709.
`
`Int. Cl.6 ..................................................... G01N 21/01
`US. Cl.
`..................................... 422182.06; 422/82.05;
`436/164; 435/288.7; 356/337
`Field of Search ............................... 422/63, 67, 68.1,
`422/82.057, 82.09; 436/47, 163, 164, 172;
`356/337, 432, 436; 435/291, 240.2, 4
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,773,426 11/1973 Mudd ...................................... 356/205
`4,665,036
`5/1987 Dedden et a].
`435/301
`
`4,772,453
`9/1988 Lisenbee ............ 422/52
`
`4,861,727
`8/1989 Hauenstein et
`.
`.
`436/136
`
`5,096,807
`3/1992 Leaback ...............
`435/6
`
`5,096,835
`3/1992 Yokomori et a1.
`.. 436/165
`
`5,164,796
`11/1992 Di Guiseppi et al.
`356/445
`
`. 73/864.81
`..............
`5,168,766 12/1992 Stoffel
`
`..... 422/73
`5,234,665
`8/1993 Ohta et a1.
`.
`5,268,304 12/1993 Inrnan et al.
`436/172
`
`5,290,701
`3/1994 Wilkins ........
`435/312
`4/1994 Goren ...................................... 235/462
`5,302,813
`
`0025350
`0151855
`0523521
`
`European Pat. Off. .
`3/1981
`8/1985 European Pat. Off. .
`1/1993 European Pat. Off. .
`
`Primary Examiner—James C. House]
`Assistant Examiner—Rachel Heather Freed
`Attorney, Agent, or Firm—Alan W. Fiedler
`[57]
`ABSTRACT
`
`A system for detecting the presence of bacterial growth in a
`plurality of sample vials incorporates a single test station
`moveable along each of the plurality of sample vials. In one
`embodiment, the sensor station is movably mounted on a
`rod, and that rod is movably mounted on a pair of spaced
`rods. The rod which carries the test station may move along
`the spaced rods to change the location of the test station in
`a first dimension and the test station is moveable along its
`rod to change location in a second dimension. In this way,
`the test station may be moved through two dimensions to
`move serially to the location of each of the plurality of
`sample vials. In another aspect of this invention, a bar code
`is associated with each of the sample vials, and the test
`station makes a reading of that bar code concurrent with a
`determination being made as to whether there is any bacte-
`rial growth in the sample vial. In this way, it is ensured that
`the results of the evaluation of whether bacterial growth is
`ongoing will be associated with the proper sample vial. In a
`third aspect of this invention, the sample vial incorporates a
`plurality of distinct types of bacterial sensors. Thus,
`the
`advantages of each of several types of bacterial sensors may
`be incorporated into a single sample vial.
`
`8 Claims, 13 Drawing Sheets
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`1
`SYSTEM FOR DETECTING BACTERIAL
`GROWTH IN A PLURALITY OF CULTURE
`VLALS
`
`This is a division of application Ser No. 08/113,444,
`filed Aug. 27, 1993, now US. Pat. No. 5,397,709.
`
`BACKGROUND OF THE INVENTION
`
`This application in general relates to an improved system
`for monitoring a plurality of sample vials, and making a
`determination of whether the sample vials are experiencing
`bacterial growth.
`
`Sample vials are prepared by injecting a body fluid
`sample into a culture medium in a sample vial. The sample
`vial
`is then incubated, and tested for bacterial growth.
`Systems for detecting bacterial growth in sample vials are
`known, wherein a large number of sample vials are repeat—
`edly and periodically tested for the presence of bacterial
`growth. Several types of sensors are known which have
`changing responses to a light input based on conditions
`within the sample vial. By monitoring the sensor response
`one can determine whether there is bacterial growth.
`Generally,
`in known sensors light is directed into the
`sample vial or sensor. Light reemerging from the sample
`vial, or from the sensor, is monitored to determine whether
`bacterial growth is occurring in the sample vial. Such
`sensors and associated methods of determination are known
`in the art, and the types of changes which indicate bacterial
`growth are known.
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`Known test systems typically hold a large number of such
`sample vials. In one example, they hold 240 sample vials.
`With the known systems an individual
`light source, an
`individual photodeteetor and the required wiring are asso-
`ciated with each sample vial. Thus, such systems are com-
`plicated and expensive. Due to the large number of light
`sources and detectors which are required, such systems have
`sometimes utilized less expensive light sources or detectors
`than those which may be most desirable. Also, since several
`hundred light sources and photodeteetors are utilized within
`each system, station to station variations are inevitable. That
`is, a light source associated with a first station may emit light
`at a different intensity than the other stations. Variation could
`also occur between the photodeteetors associated with the
`hundreds of stations. This could result in potential variations
`in readings between vials within the system. Such variations
`are undesirable.
`‘
`
`Another problem with the prior art systems is that the only
`identification of a vial located at a particular station within
`the system is by a manual bar code reading before the vial
`is placed into the station. Thus, if an operator misplaces the
`vial within the station, there may be misidentification of the
`location of the vial within the station.
`
`types of
`Finally, as discussed above, there are several
`sensors which may be utilized to determine the presence of
`bacterial growth. Each type of sensor has beneficial char-
`acteristics, and other characteristics that are undesirable.
`Further, certain types of bacteria are better detected by
`certain types of sensors. Thus, no one single type of sensor
`provides all desirable characteristics. Even so, the prior art
`has typically utilized vials with only a single type sensor
`incorporated into the vial.
`
`SUMMARY OF THE INVENTION
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`periodically and serially tests each of the sample vials. In a
`preferred embodiment of this invention, the sample vials are
`arranged in a two dimensional array. The test station is
`mounted on a frame which moves along both of the dimen-
`sions to test each vial.
`'
`
`Since a single test station tests each of the hundreds of
`vials, more expensive light sources and detectors may be
`incorporated while still reducing the cost of the overall
`system. More importantly, since only a single source and
`detector are utilized, station to station variations such as
`experienced with the prior art systems are eliminated.
`Several embodiments of this basic concept are disclosed
`in this application. The several embodiments incorporate the
`necessary apparatus for many of the several types of sensors
`which may be utilized to test sample vials.
`In one preferred embodiment of this invention, the test
`station carries only an optical fiber. The optical fiber is
`operably connected to a source of light, and to a photode-
`tector. Thus, the moving test station frame need not carry
`any heavy equipment, or any cables to supply power to
`equipment mounted on the frame. Rather, the frame need
`only move the optical fiber.
`In a second aspect of this invention, a bar code is formed
`on the sample vial, and the test station includes structure for
`reading the bar code from the sample vial. The bar code
`information is then positively associated with the test results
`from the vial. In this way, the results of the test are tied to
`the particular sample vial, and a rnisidentification of test
`results will not occur.
`
`In a preferred embodiment of this invention, the bar code
`is printed on a label associated with the sample vial, and a
`reference indicia is placed adjacent to the bar code. The bar
`code and reference indicia are preferably printed on a single
`label. Thus the reference indicia and bar code are always at
`known locations relative to each other. The test station may
`read the position of the reference indicia to ensure that the
`sensor station is properly positioned relative to the bar code
`prior to reading the bar code. Further, the reference indicia
`insures the test station is properly positioned relative to the
`sample vial. In this way, the test station properly reads the
`bar code, and eliminates misidentification due to misposi-
`tioning between the test station and the bar code.
`In a most preferred embodiment of this invention, the bar
`code is printed in a circular pattern, and the reference indicia
`is a circle concentric to the bar code. A circular bar code
`pattern provides the greatest length for bar code information
`per unit space on the vial. Further, the circular bar code and
`reference indicia do not require any particular orientation of
`the sample vial about an axis of the sample vial relative to
`the test station.
`
`In a third aspect of this invention, a sensor patch is placed
`on the bottom of the sample vial. The sensor patch includes
`a plurality of distinct types of sensors. As an example,
`sensors which respond to carbon dioxide concentration, pH
`level, oxygen level or other types of changes in the sample
`vial may all be associated with each vial. In this way, a test
`station can test each of these various types of sensors, and
`make a more informed determination of whether the par-
`tieular sample vial is experiencing bacterial growth.
`These and other features of the present invention can be
`best understood from the following specification and draw—
`ings, of which the following is a brief description.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In a disclosed embodiment of this invention, a single test
`station includes a light source and a light detector, and
`
`FIG. 1A shows a first embodiment of a system according
`to the present invention;
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`FIG. 1B is a partial end View, shown somewhat schemati—
`cally, of a system according to the present invention;
`FIG. 2 shows a Vial bottom with a central bacterial sensor
`and a bar code pattern;
`FIG. 3 is a schematic of a control system associated with
`the system of FIG. 1;
`FIG. 4 shows a second embodiment of a system according
`to the present invention;
`FIG. 5 shows a third embodiment of a system according
`to the present invention;
`FIG. 6 is a schematic of a control system associated with
`the system of FIG. 5;
`FIG. 7 shows a fourth embodiment of a system according
`to the present invention;
`FIG. 8 shows a vial bottom with a plurality of distinct
`sensors, and a bar code pattern;
`FIG. 9 shows a vial bottom with a plurality of sensors, and
`a bar code pattern;
`FIG. 10 shows a fifth embodiment of a system according
`to the present invention;
`FIG. 11 depicts details of the rack area close to a vial
`bottom for the embodiment of FIG. 10;
`FIG. 12 is a cross—sectional view taken along line 12—12
`of FIG. 11;
`FIG. 13 is a schematic illustrating the main optical and
`electronic components of the embodiment of FIG. 10;
`FIG. 14 shows a sixth embodiment of a system according
`to the present invention;
`FIG. 15 is a planar view of a portion of the embodiment
`of FIG. 14;
`FIG. 16 is a cross-section of a light guide stub of the
`embodiment of FIG. 14; and
`
`FIG. 17 shows a vial bottom with a bar code pattern.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`A first system 30 for intensity-based detection of micro-
`organisms is shown in FIG. 1A. System 30 holds a plurality
`of vials 32, each sealed with a septum 34 and containing a
`medium/bodily fluid mixture 36. Typically, the body fluid is
`blood and the medium is prepared by known techniques.
`Each vial 32 contains an intensity-based chemical sensor 38
`disposed on an inner bottom surface 40. While an intensity
`sensor is used with this embodiment, other sensors which
`generate a selective emission or change their reflectivity,
`opacity, or color in the presence of biological activity are
`known and may also be used. In other systems, the sample
`may be scanned without the use of a separate sensor asso—
`ciated with the vial, e.g., scattered photon migration
`(“SPM”), as discussed further below.
`Two rows of vials 32 are arranged on each of several
`tipping racks. Tipping racks 42 are agitated to promote the
`growth of microorganisms within vials 32. Tipping racks 42
`may be biased or held in a known hold position, such as that
`shown in FIG. 1, while a determination of biological activity
`may be made. In some applications it is desirable to hold the
`vials at an angle relative to the vertical to maximize the level
`of fluid. Any structure for moving the tipping rack, or
`holding it at the known position may be used. A plurality of
`tipping racks 42 are used since a tipping rack for as many as
`240 vials would have considerable mass. Racks 42 contain
`only vials 32 and no electronic components and, conse-
`quently, no electrical wires. Vials 32 and tipping racks 42 are
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`arranged inside a known type incubator 44 used to promote
`microorganism growth.
`A single test station or carriage 43 is moved to test all of
`the vials. Light output is generated from a single high energy
`light source, such as laser 46, and is serially directed at
`sensors 38 on a large number of vials 32. Laser 46 and a
`detector module 64 are mounted on test station 43, which is
`movable as part of an XY translation stage 45. XY transla-
`tion stage 45 allows for movement of test station 43 along
`a rod 47 that is fixed to two guide blocks 49. The blocks 49
`move along perpendiculme arranged rods 51. If tipping
`racks 42, containing a total of 240 vials (12 rows and 20
`columns) are used, a single XY translation stage 45 must be
`able to address a maximum of 20 vials in one direction. As
`an alternative, two (or more) test stations can be used with
`each testing plural vials.
`In operation, a system controller described below, directs
`test station 43 from a home position to a first vial station.
`Each of the vials 32 are then serially tested. As shown in
`FIG. 1B, the XY translation stage 45 moves test station 43,
`which carries laser 46. A plurality of sample vials 32 are
`arranged in a two dimensional array. Rods 51 are positioned
`at the top and bottom of the vial array, and guide blocks 49
`carry rod 47 along rods 51. In one embodiment, rods 51
`could include a linear motor for driving guide blocks 49.
`Such linear motors are known, and may operate by passing
`current to move guide blocks 49 axially along bars 51.
`Similarly, test station 43 may move along bar 47 by use of
`a linear motor. In such a motor, test station 43 and guide
`blocks 49 would include magnets. By moving guide blocks
`49 along rods 51, the location of test station 43 can be varied
`to the right and left as shown in FIG. 1B, and the up and
`down position of test station 43 as shown in FIG. 1B can also
`be varied by moving test station 43 along rod 47.
`As stated above, rods 47 and 51 may incorporate linear
`motors which drive the guide blocks 49, and test station 43
`and guide blocks 49 could incorporate magnets to be driven
`along the rods 47 and 51. Alternatively, any other known
`means of guiding the test station 43 through two dimen—
`sional movement may be utilized. Known x—y translators are
`used for navigation, plotting and printing. It is not the
`structure of the translator which is inventive, but rather the
`use of an x-y translator in this environment.
`As shown in FIG. 1A, a beam splitter 48 is mounted on
`test station 43 and splits an output beam 50 from laser 46
`into components 52 and 54. Reference beam component 52
`is directed toward a reference photodeteetor 55. Reference
`photodeteetor 55 measures the intensity of reference beam
`component 52 and generates a reference photocurrent value
`corresponding to the measured intensity. Output beam com—
`ponent 54 passes through mirror 56 having central aperture
`58, and is deflected off of a curved mirror 60 to contact and
`excite a sensor 38 of a selected vial 32. When excited by
`output beam component 54, sensor 38 generates an emission
`which varies with the presence of biological activity in the
`illustrated embodiment, a fluorescence emission generated
`by the sensor increases in proportion to increased biological
`activity. Fluorescence intensity chemical sensors 38 are
`known which react to pH, oxygen concentration, carbon
`dioxide concentration, or in response to other biological
`activities.
`
`An emission 62 from a particular sensor 38 is collected by
`curved mirror 60, planar mirror 56 and directed toward an
`optical sensing detector module 64 where the emission is
`monitored. Detector module 64 includes a spectral emission
`filter 66, and a high-sensitivity photodeteetor 68. Filter 66 is
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`used to block unwanted short—wavelength or. excitation
`radiation that can affect readings. Photodetector 68 measures
`the intensity of emission 62 and generates a sensor photo-
`current value representative of the measured intensity.
`In one preferred embodiment, laser 46 is a green helium
`neon (HeNe) laser having a wavelength in the range of about
`543.5 nm, with approximately 1.5 mW of output power. The
`diameter of output beam 50 should be no greater than about
`2 mm. The short-wavelength light and output power reacts
`well with a fluorescence sensor 38 in the presence of
`biological activity.
`With this embodiment, and all other embodiments dis-
`closed in this invention, the thrust of the invention is to the
`moving test station and associated structure, to bar code
`reading, and to a plural sensor embodiment as will be
`disclosed below. The parameters used to evaluate the read—
`ings made on the particular sensors are as known in the art.
`The present invention does not disclose any new testing
`logic. Rather, the detected emission, etc. are evaluated as
`known in the art to make a determination of whether a
`particular vial is experiencing bacterial growth.
`The test station 43 canied on XY translation stage 45 also
`includes a monitor photodiode 80 for measuring light back-
`seattered from a bar code label 82 shown in FIG. 2,
`preferably placed on a bottom outer surface 84 of vial 32. In
`the illustrated embodiment, bar code 82 includes a central
`opening 86 so that sensor 38 is exposed. In an alternative
`embodiment, bar code 82 may be printed on a label placed
`on bottom inner surface 40 which also includes sensor 38. A
`circular bar code pattern 88 comprises a plurality of marks
`89 extending radially outwardly from central opening 86.
`The marks 89 carry information with regard to the vial, the
`sample, or the patient associated with the sample. Bar code
`pattern 88 includes a reference indicia, here an outer con-
`centric circle 90. If used with a standard blood culture vial,
`bar code pattern 88 can have a diameter of approximately 25
`mm. With such a diameter, the bar code information char—
`acterizing the vial can be distributed over a circle circum—
`ference length of 78.5 mm. The effective length of a circular
`pattern is at a maximum compared to other patterns for any
`given vial diameter.
`To read out the bar code information 88, small sinusoidal
`deflection signals are sent to XY translation stage 45 via X
`and Y output channels 106 and 108, as shown in FIG. 3. The
`two signals have equal amplitude, but show a phase difier—
`ence of 90 degrees. This results in a movement of output
`beam component 54 along the circumference of a circle. The
`amplitude of laser 46 is adjusted and output beam compo-
`nent 54 scans bar code pattern 88 including concentric circle
`90. This light is backseattered to be read by photodiode 80.
`If XY translation stage 43 is initially incorrectly positioned
`with respect to a vial 32, concentric circle 90 is used as a
`position encoder to more accurately position XY translation
`stage 45 with respect to a vial 32 before reading the bar code.
`The test station 43 moves until concentric circle 90 is read
`as being at an expected position relative to test station 43.
`The concentric circle 90 and bar code pattern 88 are printed
`onto a label at known relative positions.
`In the embodiment of FIG. 1A, output beam component
`54 is focussed onto vial bottom surface 84 using mirror 60.
`As mentioned above, the available geometrical length of the
`bar code pattern 88 is approximately 78.5 mm. Green HeNe
`lasers such as preferred for use in the FIG. 1 embodiment
`typically have beam diameters of 0.5 mm. With such dimen-
`sions, no extreme focussing is required to read out the bar
`code information. However, when necessary, stronger focus—
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`sing is accomplished very easily by a simple lens attached to
`laser 46.
`
`Under some circumstances, a larger diameter for output
`beam component 54 may be desired. A small beam could
`result in sensor bleaching, since only a very small surface
`area of the sensor is exposed to the test light. To avoid such
`a result, output beam component 54 can be moved about a
`small circle. In other words, small sinusoidal deflection
`signals may be sent to KY translation stage 45 via the X and
`Y channels 106 and 108 continuously. To move from the
`above described circular movements for reading the bar
`code, and then to switch from bar code reading to sensor
`reading, only the amplitude of the sinusoidal signals would
`have to be changed.
`Photodiode 80 is not necessary if bar code pattern 88 is
`printed using a dye which fluoresces within the same wave-
`length range as the emission from sensor 38. In this way, the
`same detector module 64, including photodetector 68, can be
`used for microorganism detection and for bar code reading.
`A major advantage of system 30 is that both laser 46 and
`detector module 64 may be moved closely to individual vials
`32. Therefore, an extremely high spatial resolution for the
`bar code reading and improved light detection sensitivity
`can be realized. Further, greater accuracy is achieved by
`using a single test station for many vials in place of
`individual devices for each vial. More expensive and precise
`instrumentation can be used at a reasonable cost. Further, the
`need for instrument calibration is greatly reduced, if not
`eliminated by the present invention.
`As known, vials 32 are continuously scanned until either
`there is a presence of biological activity, or a predetermined
`period of time, typically five days, has passed. Generally, the
`presence of biological activity in a vial is indicated by a
`pronounced change in the measured sensor emission 62.
`As shown schematically in FIG. 3, laser 46 generates an
`output beam 50. Beam splitter 48 splits output beam 50 into
`reference beam component 52 and output beam component
`54. With XY translation stage 45, shown in FIG. 1, correctly
`positioned, output beam component 54 is directed to a
`preselected sensor 38 associated with a vial 32. The sensor
`then generates an emission 62. Photodetector 68 monitors
`emission 62 and generates a sensor photocurrent 92. Pho—
`tocurrent 92 is routed to a detector DC meter 94. An output
`96 from DC meter 94 is fed to a controller 98, such as a
`computer.
`Reference beam component 52 is directed to reference
`photodetector 55, which monitors reference beam compo-
`nent 52 and generates a reference photocurrent 100. Photo-
`current 100 is routed to a reference DC meter 102. An output
`104 from meter 102 is also fed into controller 98. If the
`reference beam component 52 varies from an expected
`value, then the intensity of output beam 50 is also not as
`expected, or desired. The intensity of output beam 50 is
`adjusted as necessary.
`Controller 98 stores and analyzes outputs such as 96 and
`104 to make a determination concerning microorganism
`growth. As is known, controller 98 compares incoming data
`to earlier collected data. In addition to collecting and ana-
`lyzing information, controller 98 positions XY translation
`stage 45, with signals being sent through X output channel
`line 106 and Y output channel line 108. Known control logic
`is used for moving station 43 as desired. Thus, output beam
`component 54 is directed serially from vial to Vial allowing
`a determination of microorganism growth to be made for
`each vial 32. Backseattered light 99 may be detected by
`photodetector 80, as discussed above, to accurately position
`XY translation stage 45 and read the bar code information.
`
`Agilent Exhibit 1239
`
`Page 17 of 21
`
`Agilent Exhibit 1239
`Page 17 of 21
`
`

`

`~ 5,595,708
`
`7
`
`A typical green HeNe laser head of 0.2 mW output power
`only has a weight of 0.34 kg and a length of 25 cm.
`However, it still needs a high-voltage power cable. Similar
`considerations apply to high-sensitivity photodetectors such
`as photomultipliers. Thus,
`in the FIG. 1A embodiment
`cables must extend from the moving test station to a fixed
`power source and to the controller. These requirements are
`addressed by system 120 as illustrated in FIG. 4. A test
`station 122 is arranged on an XY translation stage 124. As
`in the embodiment of FIG. 1, XY translation stage 124
`allows for movement of test station 122 along a rod 123 that
`is fixed to two guide blocks 125. In turn, the blocks 125 can
`move along perpendicularly arranged rods 127. Test station
`122 holds an output end 126 of an optical fiber 128, and an
`imaging lens 130. In this embodiment, laser 46 and detector
`module 64 are mounted to a pedestal 127 in close proximity
`to one another at a fixed position within system 120. The
`input end 132 of fiber 128 is mounted so that it receives the
`full optical output of output beam component 54. Light
`travels along fiber 128 and reaches output end 126. Beam
`component 54 exiting fiber output end 126 is imaged onto
`bottom inner surface 40 of vial 32. An emission 62 reemerg-
`ing from surface 40 is re-focussed by lens 130 into output
`end 126, back along fiber 128 and out input end 132. The
`emission 62 that emerges from input end 132 is directed by
`mirrors 60 and 56 through filter 66 and to photodetector 68.
`A major advantage of system 120 is that a minimum
`amount of mass has to be moved on test station 122 for
`scanning an array of vials 32. In addition, no electrical
`cables or wires are required On moving test station 122.
`Output end 126 may be located closely to the bottoms of
`vials 32. In so doing, an extremely high bar code resolution
`and good light detection sensitivity are achieved. Sensor and
`bar code reading may be performed by moving the test
`station 122 as described above with respect to the embodi-
`ment of FIG. 1A. As an alternative, a pair of fibers may be
`used, with one directing light at the sensor, and one receiv-
`ing emissions from the sensor.
`A third system 140 according to the present invention for
`use with time decay detection of bacteria, is shown in FIG.
`5. System 140 is similar to system 30 illustrated in FIG. 1A.
`However, a different type of optical sensor, a fluorescence
`decay time sensor 142, is disposed on inner bottom surface
`40 of each of vials 32. Fluorescence decay time sensors are
`known which change their decay time in response to chang—
`ing pH, oxygen concentration, carbon dioxide concentration,
`or in response to other biological activities. Using this
`method,
`intensity measurements are replaced with time
`measurements, so intensity changes do not influence the
`results. For sensors 142 to work properly, a modulated light
`source 144 includes a high-frequency intensity modulator
`146 arranged between laser 46 and beam splitter 48. The
`laser may be the same as that disclosed in the embodiment
`of FIG. 1A. Modulator 146 may be of any known type, such
`as acousto-optic, electro—optic or elasto—optic.
`Output 148 from modulated light source 144 is split into
`components 150 and 152. Reference beam component 150
`is directed toward a reference photodetector 56 while output
`beam component 152 passes through planar mirror 56
`having a central aperture 58, and is deflected off of a curved
`mirror 60 to contact and excite a sensor 142 of a selected vial
`32.
`
`A modulated emission 154 generated by a particular
`sensor 142 is time modulated in response to increasing
`biological activity. It is the modulation rather than intensity
`that is primarily monitored by detector module 64. As long
`as the modulation can be measured, a determination of
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`biological activity can be made. Therefore, minor vial mis—
`positioning, light source or detector module aging, and dark
`current changes such as those resulting from outside light
`leakage into incubator 44, are not critical.
`Currently available fluorescence decay time sensors
`require high light modulation frequencies, typically above
`100 MHz. In known systems with individual light sources at
`each vial 32, green light emitting diodes (“LED”s) are used.
`LEDs cannot be modulated at such high frequencies. In
`apparatus 140, however, with laser 46 and modulator 146,
`high-frequency intensity modulation may be easily accom-
`plished. Since only a single laser is necessary, the use of a
`laser which is more expensive then an LED is still practical.
`As shown schematically in FIG. 6, controller 98 controls
`modulator 146 using an amplifier 156. Controller 98 sends
`a signal 158 to amplifier 156, and an output signal 160 from
`amplifier 156 is sent to modulator 146. Beam splitter 48
`splits output beam 148 from modulator 146 into reference
`beam component 150 and output beam component 152.
`With XY translation stage 45 correctly positioned, output
`beam component 152 is directed to a preselected sensor 142
`associated with a vial 32. Sensor 142 selectively generates
`a modulated sensor emission 154. Photodetector 68 moni-
`tors sensor emission 154 and generates a modulated photo—
`current 162 which is routed to a vector voltmeter 164.
`Reference photodetector 56 monitors reference beam com-
`ponent 150 and generates a modulated reference photocur—
`rent 166 which is also routed