Patent Publication Number: US-2021165202-A1

Title: Examination method and examination device

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to an examination method and an examination device. 
     Description of the Background Art 
     Japanese Patent Laying-Open No. 2019-088339 discloses an examination device that performs a bacteria identification examination or a drug susceptibility examination by observing, with a microscope, the shape and the number of bacteria in each well of a culture plate for bacteria identification culture or drug susceptibility examination, and monitoring how the bacteria divide. 
     SUMMARY OF THE INVENTION 
     Due to, for example, the accuracy of molding, there are slight differences among individual plates on which objects to be observed, such as bacteria or drugs, are arranged. Since a depth of field of a microscope is narrow, it is necessary to set a focal point of a microscope camera for each plate. 
     In monitoring dynamics of a biological factor such as bacteria, images of one observation area are captured a plurality of times. In this case, if a focal point is set every time an image is captured, the time required for one image capturing becomes longer. In addition, when there are a plurality of observation areas and a state of objects to be observed changes over time, it is desirable to capture images of the observation areas included in one plate at the same timing whenever possible. However, when a microscope camera is used, it is necessary to set a focal point for each observation area, and thus, an image capturing timing lag occurs and the lag increases in proportion to an increase in the observation areas. Therefore, the time required to complete image capturing for one plate becomes longer. 
     The present disclosure has been made to solve the above-described problem, and an object of the present disclosure is to provide an examination method and an examination device that can examine dynamics of a biological factor in a short time. 
     An examination method of the present disclosure is an examination method for examining dynamics of a biological factor by capturing, with a microscope camera, an image of at least one observation area on a plate with the biological factor arranged therein. The examination method includes: obtaining a focus position by focusing the microscope camera on the observation area during a first image capturing process for the observation area; storing the obtained focus position in a storage device; and performing a second image capturing process for the observation area after the first image capturing process. The performing includes: reading out the focus position from the storage device; setting a focal point of the microscope camera at the read-out focus position; and capturing an image of the observation area. 
     An examination device of the present disclosure is an examination device that examines dynamics of a biological factor by capturing an image of at least one observation area on a plate with the biological factor arranged therein. The examination device includes: a microscope camera that captures an image of the observation area; a focal point changing unit that changes a focal point of the microscope camera; an obtainment unit that obtains a focus position by focusing the microscope camera on the observation area during a first image capturing process for the observation area; a storage unit that stores the obtained focus position in a storage device; and an image capturing control unit that causes the microscope camera to capture the image of the observation area by controlling the microscope camera and the focal point changing unit. The image capturing control unit performs a second image capturing process for the observation area after the first image capturing process. The second image capturing process includes: reading out the focus position from the storage device; setting the focal point of the microscope camera at the read-out focus position; and capturing an image of the observation area. 
     The foregoing and other objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of the present disclosure when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic configuration of an examination device according to the present embodiment. 
         FIG. 2  is a plan view of a culture plate. 
         FIG. 3  is a schematic view showing an example hardware configuration of a controller. 
         FIG. 4  is a block diagram showing an example functional configuration of the controller. 
         FIG. 5  is a flowchart of an image capturing process performed by the controller. 
         FIG. 6  is a flowchart of an image capturing process performed by a controller according to a first modification. 
         FIG. 7  is a flowchart of an image capturing process performed by a controller according to a second modification. 
         FIG. 8  is a flowchart of a correction process performed by the controller according to the second modification. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present disclosure will be described in detail hereinafter with reference to the drawings, in which the same or corresponding portions are denoted by the same reference characters and description thereof will not be repeated. 
     [Configuration of Examination Device] 
       FIG. 1  shows a schematic configuration of an examination device according to the present embodiment. As one example, the examination device according to the present embodiment is used for a drug susceptibility test. 
     An examination device  100  captures an image of each of a plurality of observation areas provided on a culture plate  10 . An object to be observed obtained by bringing a drug into contact with a test solution including bacteria (biological factor) is arranged at each of the plurality of observation areas. 
     Examination device  100  includes a controller  120 , microscope camera  140 , a stage  160 , and a reading unit  180 . Controller  120  is electrically connected to microscope camera  140 , stage  160  and reading unit  180 . The electrically connected devices may be partly or entirely formed of one piece. 
     In order to capture an image of each observation area  16  (see  FIG. 2 ) on culture plate  10 , controller  120  controls each of microscope camera  140  and stage  160  based on information read by reading unit  180 . 
     Microscope camera  140  includes an objective lens  142 , a focal point changing mechanism  144  and an image sensor  146 . 
     Objective lens  142  magnifies a part of culture plate  10  placed on stage  160 . Objective lens  142  is arbitrarily selected in accordance with the object to be observed. 
     Focal point changing mechanism  144  changes a focal point of microscope camera  140 . As one example, focal point changing mechanism  144  changes the focal point of microscope camera  140  by changing a position of objective lens  142  in an optical axis direction of objective lens  142 . 
     Image sensor  146  is a detector for capturing an image of the object to be observed magnified by objective lens  142 , and is, for example, a charge coupled device (CCD) image sensor, a complementary metal oxide semiconductor (CMOS) image sensor or the like. 
     Stage  160  includes an image-capturing field-of-view changing mechanism  162  and a lighting device  164 . Culture plate  10  is placed on stage  160 . Lighting device  164  is transparent lighting and irradiates stage  160  with light for observation. 
     Image-capturing field-of-view changing mechanism  162  changes an image-capturing field of view of microscope camera  140 . Image-capturing field-of-view changing mechanism  162  includes an X axis moving mechanism  162 X and a Y axis moving mechanism  162 Y. X axis moving mechanism  162 X moves culture plate  10  placed on stage  160  in an X axis direction in  FIG. 1 . Y axis moving mechanism  162 Y moves culture plate  10  placed on stage  160  in a Y axis direction in  FIG. 1 . In  FIG. 1 , a plane of stage  160  on which culture plate  10  is placed is defined as an X-Y plane, and an axis vertical to the X-Y plane is defined as a Z axis. 
     Reading unit  180  reads identification information of culture plate  10 . Reading unit  180  is, for example, a barcode reader, a QR code (registered trademark) reader or a reader adapted to a radio frequency (RF) tag, and is selected in accordance with the type of an identification code assigned to culture plate  10 . Reading unit  180  transmits the read identification information to controller  120 . 
     Controller  120  reads out an image capturing condition corresponding to the identification information based on the identification information from reading unit  180 , and controls microscope camera  140  and stage  160  based on the read out image capturing condition, to capture an image of each observation area. 
     Specifically, controller  120  outputs, to image-capturing field-of-view changing mechanism  162 , observation area information indicating a position of the observation area whose image is to be captured. In accordance with the output observation area information, image-capturing field-of-view changing mechanism  162  moves culture plate  10 , such that the observation area whose image is to be captured is located within the image-capturing field of view of microscope camera  140 . 
     In addition, controller  120  provides a focal point changing instruction to focal point changing mechanism  144  in accordance with the image capturing condition. At this time, controller  120  outputs, to focal point changing mechanism  144 , a focus position where microscope camera  140  is in focus on the observation area whose image is to be captured. Focal point changing mechanism  144  sets the focal point of microscope camera  140  at the output focus position. 
     Controller  120  provides an image capturing instruction to image sensor  146  when the image-capturing field of view and the focal point of microscope camera  140  are set, and obtains image data. Controller  120  obtains the number of the bacteria, the shape of the bacteria and the like as an observation result from the image data. 
     [Configuration of Culture Plate] 
       FIG. 2  is a plan view of the culture plate. Culture plate  10  includes a plate-shaped member  12  and a flow path structure. The flow path structure includes an opening portion  13 , an opening  14 , a micro flow path  15 , observation area  16 , and an opening  17 . 
     Opening  14  is a portion provided in opening portion  13  and allowing opening portion  13  and micro flow path  15  to communicate with each other. Namely, opening  14  is connected to one end of micro flow path  15 . Using a fluid pressure, the test solution including the bacteria is injected from opening  14  into micro flow path  15 . On culture plate  10  shown in  FIG. 2 , four micro flow paths  15  are arranged radially around opening  14 . 
     Micro flow path  15  is configured such that the test solution can flow therethrough. Micro flow path  15  extending from opening  14  branches off to a plurality of micro flow paths  15 . The test solution introduced from opening  14  flows through branched micro flow paths  15 . In the present embodiment, one micro flow path  15  branches off to fourteen micro flow paths  15 . 
     Observation area  16  is provided partway through branched micro flow path  15 . Micro flow path  15  allows the test solution introduced from opening  14  to flow to observation area  16 . 
     Observation area  16  has the drug arranged thereat, and is connected to micro flow path  15  to store the test solution introduced from micro flow path  15 . At observation area  16 , the test solution reacts with the drug. The drug is, for example, an antibacterial drug. The drug may be solid, or may be liquid. The drug is preliminarily placed at observation area  16 . That is, the drug is placed at observation area  16  before the test solution flows into observation area  16 . Observation area  16  is formed to have a rectangular parallelepiped shape. One side of observation area  16  has a length of, for example, 10 μm to 10 mm. 
     In  FIG. 2 , fifty-six (=14×4) observation areas  16  are formed on plate-shaped member  12 . That is, in the present embodiment, when one culture plate  10  is observed, fifty-six observation areas  16  are observed using an examination device  100 . The volumes of the test solutions stored in fifty-six observation areas  16  are the same as each other. In contrast, the types and the amounts of the drugs placed at fifty-six observation areas  16  may be the same as each other, or may be different from each other. 
     Plate-shaped member  12  is made of an acrylic resin such as a polymethyl methacrylate resin. A thickness of plate-shaped member  12  is not particularly limited, and is set at, for example, 1 mm to 6 mm. In addition, an identification code  18  for individually identifying culture plate  10  is assigned to plate-shaped member  12 . 
     Identification code  18  is not limited to an optically readable code such as a one-dimensional barcode or a two-dimensional QR code (registered trademark), and may be a code that can be read by wireless communication, such as an RF tag. Identification information indicated by identification code  18  is not limited to the serial number individually assigned to culture plate  10 , and may be the lot number assigned to culture plate  10 . 
     Culture plate  10  is made mainly of an acrylic resin. Therefore, culture plate  10  has a slight individual difference due to a difference in manufacturing condition, storage condition, use condition, or the like. When a camera having a wide depth of field is used, an image that is in focus to some extent is obtained, regardless of the slight individual difference, by focusing on the same position as a position of a focal point that is focused on when capturing an image of one culture plate  10 , and capturing an image of another culture plate  10 . However, in the examination according to the present embodiment, microscope camera  140  having a narrow depth of field is used. Therefore, an in-focus image is not obtained by focusing on the same position as a position of a focal point that is focused on when capturing an image of one culture plate  10 , and capturing an image of another culture plate  10 . 
     Accordingly, in the examination according to the present embodiment using the microscope camera having a narrow depth of field, information for focusing on each observation area  16  is managed, as an image capturing condition, by the identification information indicated by individual identification code  18  assigned to each culture plate  10 . 
     [Overview of Examination] 
     An overview of the examination will be described with reference to  FIG. 1 . In the present embodiment, examination device  100  is used to observe a state of the bacteria after the drug is brought into contact with the bacteria. Culture plate  10  into which the test solution is injected is housed in an incubator  20  set at a temperature (e.g., 37° C.) suitable for culture of the bacteria, and is taken out of incubator  20  at the timing of observation. 
     Culture plate  10  is housed in incubator  20  for, for example, three hours after the drugs are brought into contact with the bacteria. Then, assuming that the time of bringing the drugs into contact with the bacteria is 0 minute, a state of the bacteria is observed at each of 0 minute, 60 minutes, 90 minutes, 120 minutes, 150 minutes, and 180 minutes. Thus, a change over time in the bacteria when the drugs are brought into contact with the bacteria is observed and a result of examination of dynamics of the bacteria is obtained. 
     Fifty-six observation areas  16  are provided on culture plate  10 . In the examination according to the present embodiment, the process of taking culture plate  10  out of incubator  20 , capturing an image of each of fifty-six observation areas  16  on culture plate  10  using examination device  100 , and returning culture plate  10  back to incubator  20  is repeated. 
     A plurality of culture plates  10  may be observed concurrently. In this case, for each culture plate  10 , the above-described process of taking culture plate  10  out of incubator  20 , capturing an image of each of fifty-six observation areas  16 , and returning culture plate  10  back to incubator  20  is repeated. 
     [Hardware Configuration of Controller] 
       FIG. 3  is a schematic view showing an example hardware configuration of the controller. As one example, controller  120  is formed in accordance with a general-purpose computer architecture. 
     As main components, controller  120  includes a processor  122 , a memory  124 , and an input and output interface (I/F)  126 . These components are communicably connected to each other through a bus  128 . 
     Processor  122  is typically a processing unit such as a central processing unit (CPU) or a multi processing unit (MPU). Processor  122  reads out and executes a program stored in memory  124 , to thereby control the operation of each portion of examination device  100 . Specifically, processor  122  executes the program, to thereby implement each process of examination device  100  described below. In the example of  FIG. 3 , controller  120  includes a single processor. However, controller  120  may include a plurality of processors. 
     Memory  124  is implemented by a nonvolatile memory such as a random access memory (RAM), a read only memory (ROM) and a flash memory, or a storage device such as a magnetic disk. Memory  124  stores a program executed by processor  122 , data used by processor  122 , or the like. Specifically, memory  124  stores the image capturing condition for capturing an image of each observation area  16  on each culture plate  10 . 
     Input and output I/F  126  is an interface for exchanging various types of data with focal point changing mechanism  144 , image sensor  146 , image-capturing field-of-view changing mechanism  162 , and reading unit  180 . 
     [Functional Configuration of Controller] 
       FIG. 4  is a block diagram showing an example functional configuration of the controller. Controller  120  includes an obtainment unit  222 , a storage unit  224 , a readout unit  226 , an image capturing control unit  228 , and an analysis unit  230 . Each of these functions is implemented by processor  122  executing a program stored in memory  124 . 
     Obtainment unit  222  obtains a focus position  424  where microscope camera  140  is in focus on observation area  16 . Using the existing autofocus technique, obtainment unit  222  obtains focus position  424  by focusing microscope camera  140  on observation area  16 , in cooperation with focal point changing mechanism  144 . 
     Focus position  424  refers to, for example, a position of objective lens  142  when microscope camera  140  is in focus on observation area  16 , and a distance in a Z axis direction from a surface of stage  160  to objective lens  142 . 
     A method for obtaining focus position  424  is not limited to a method using the existing autofocus technique. For example, the focus position may be obtained by measuring a distance from a predetermined position to observation area  16  with a laser-type displacement sensor, calculating a distance from the X-Y plane of stage  160  to observation area  16 , and adding a focal length of microscope camera  140  to the calculated distance. 
     Storage unit  224  stores, as an image capturing condition  240 , identification information  44  and camera information  42  in memory  124  in association with each other. Camera information  42  includes observation area information  422  and focus position  424 . Storage unit  224  stores, as camera information  42 , observation area information  422  and focus position  424  in memory  124  in association with each other, focus position  424  being for focusing microscope camera  140  on observation area  16  indicated by observation area information  422 . 
     Observation area information  422  is information indicating a position of one observation area  16  on culture plate  10 . In the present embodiment, observation area information  422  is a number of observation area  16  indicating each of fifty-six observation areas  16  provided on culture plate  10 . 
     Readout unit  226  reads out image capturing condition  240  from memory  124 , based on identification information  44  read by reading unit  180 . Readout unit  226  transmits the read out result to image capturing control unit  228 . When image capturing condition  240  corresponding to identification information  44  is not stored, readout unit  226  outputs, to image capturing control unit  228 , a notification that image capturing condition  240  is not stored. When image capturing condition  240  corresponding to identification information  44  is stored, readout unit  226  outputs image capturing condition  240  to image capturing control unit  228 . 
     Image capturing control unit  228  controls microscope camera  140  and image-capturing field-of-view changing mechanism  162 , to thereby obtain image data of each observation area  16 . 
     When image capturing control unit  228  receives, from readout unit  226 , the notification that image capturing condition  240  is not stored, image capturing control unit  228  obtains the image data while generating image capturing condition  240 . Specifically, image capturing control unit  228  outputs, to image-capturing field-of-view changing mechanism  162 , the number of observation area  16  that is observation area information  422 . Observation area information  422  indicating the position of observation area  16  on culture plate  10  is prestored in memory  124 . 
     In accordance with observation area information  422  output from image capturing control unit  228 , image-capturing field-of-view changing mechanism  162  moves culture plate  10 , such that observation area  16  having the designated number (position) is located within the image-capturing field of view of microscope camera  140 . 
     In addition, image capturing control unit  228  instructs obtainment unit  222  to obtain focus position  424 . In cooperation with focal point changing mechanism  144 , obtainment unit  222  obtains focus position  424  by focusing microscope camera  140  on observation area  16  located within the image-capturing field of view of microscope camera  140 . At this time, focal point changing mechanism  144  focuses microscope camera  140  on observation area  16  located within the image-capturing field of view of microscope camera  140 . 
     In response to completion of the focus adjustment, image capturing control unit  228  provides an image capturing instruction to image sensor  146  and obtains image data of observation area  16 . 
     When the image capturing is completed, image capturing control unit  228  changes the number of observation area  16  and repeats the instruction to image-capturing field-of-view changing mechanism  162 , the instruction to obtainment unit  222 , and the image capturing instruction to image sensor  146 . By repetition of these instructions by image capturing control unit  228 , focus position  424  is obtained, image capturing condition  240  is generated and image data is obtained for each observation area  16 . 
     Analysis unit  230  analyzes the image data obtained by image capturing control unit  228 , to thereby obtain an observation result  242 . Analysis unit  230  stores obtained observation result  242  in memory  124 . Observation result  242  may include, for example, binarized data of the image data, data indicating the number of the bacteria and the shape of the bacteria obtained by analyzing the image data, the image capturing time, observation area information  422  indicating the image capturing position, and the like. 
     When image capturing condition  240  is output from readout unit  226 , image capturing control unit  228  controls microscope camera  140  and image-capturing field-of-view changing mechanism  162  in accordance with output image capturing condition  240  (i.e., read out image capturing condition  240 ), to thereby obtain image data of each observation area  16 . Analysis unit  230  outputs, to memory  124 , observation result  242  obtained by analyzing the obtained image data. 
     Specifically, image capturing control unit  228  outputs the number of the observation area to image-capturing field-of-view changing mechanism  162  and outputs the focus position corresponding to the number of the observation area to focal point changing mechanism  144  of microscope camera  140 , and provides the image capturing instruction to image sensor  146  of microscope camera  140 . 
     As a result, observation area  16  having the designated number is located within the image-capturing field of view of microscope camera  140  and microscope camera  140  is in focus on this observation area  16 , and thus, the in-focus image data is obtained. At this time, focal point changing mechanism  144  may only set the position of objective lens  142  at the designated focus position and adjustment of the position of objective lens  142  for focusing is unnecessary. Therefore, the time required to focus microscope camera  140  on observation area  16  can be reduced. 
     As described above, when image capturing of each observation area  16  on culture plate  10  is performed for the first time (a first image capturing process), examination device  100  according to the present embodiment adjusts the position of objective lens  142  to focus microscope camera  140  on observation area  16 . When image capturing is performed for the second and subsequent times (a second image capturing process), examination device  100  according to the present embodiment uses the adjustment result obtained in the image capturing performed for the first time. Thus, the time required to perform the image capturing for the second and subsequent times can be reduced. As a result, the time required to obtain the result of the bacteria dynamics examination can be reduced. 
     Focus position  424  may be obtained for each observation area  16  on culture plate  10  before the test solution is injected into culture plate  10 , and then, the test solution may be injected into culture plate  10  and the examination may be started. That is, in the image capturing performed for the first time, examination device  100  may obtain only focus position  424  by focusing microscope camera  140  on observation area  16 , without obtaining the observation result. In other words, in the image capturing performed for the first time, examination device  100  may obtain only focus position  424  by focusing microscope camera  140  on observation area  16 , without actually performing the image capturing. 
     As described above, fifty-six observation areas  16  are provided on culture plate  10 . Therefore, if the time to complete image capturing of one observation area  16  becomes longer, a time lag between the time when an image of first observation area  16  is captured and the time when an image of last fifty-sixth observation area  16  is captured becomes larger. 
     In addition, in the case of observing a plurality of culture plates  10  concurrently, if the time to complete image capturing of one observation area  16  becomes longer, the time to complete observation of one culture plate  10  becomes longer. For example, when observation is performed at thirty-minute intervals, it is necessary to finish observation of all culture plates  10  for thirty minutes at the latest. Therefore, if the time to complete observation of one culture plate  10  becomes longer, the number of culture plates  10  that can be processed concurrently becomes smaller. 
     When one observation area  16  is observed a plurality of times, examination device  100  according to the present embodiment reads identification code  18  assigned to culture plate  10  and sets the focal point of microscope camera  140  by using focus position  424  corresponding to identification information  44  indicated by read identification code  18 . Therefore, when one observation area  16  is observed a plurality of times using examination device  100 , the time to complete image capturing of one observation area  16  can be reduced, as compared with the case of making an adjustment to focus microscope camera  140  on observation area  16  whenever observation area  16  on culture plate  10  is observed. As a result, the time lag between the time when an image of first observation area  16  is captured and the time when an image of last observation area  16  is captured can be reduced, and the number of culture plates  10  that can be processed concurrently can also be increased. 
     Although  FIG. 4  shows the configuration example in which the necessary functions are provided by processor  122  executing the program, a part or all of these provided functions may be implemented using a dedicated hardware circuit (such as, for example, an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA)). 
     [Flowchart] 
       FIG. 5  is a flowchart of an image capturing process performed by the controller. The image capturing process is started when culture plate  10  is placed on stage  160 . In the following description, a step will be simply denoted as “S”. 
     In S 102 , controller  120  obtains identification information  44 . In S 104 , controller  120  determines whether or not image capturing condition  240  corresponding to obtained identification information  44  is stored in memory  124 . 
     When controller  120  determines that image capturing condition  240  is not stored in memory  124  (NO in S 104 ), controller  120  performs the processing in S 106  to S 120 , and then, ends the image capturing process. 
     In S 106 , controller  120  sets the number of observation area  16  at  1 . In S 108 , controller  120  positions observation area  16  having the set number within the image-capturing field of view. 
     In S 110 , controller  120  performs an autofocus process. The autofocus process refers to a process of focusing microscope camera  140  on observation area  16  located within the image-capturing field of view of microscope camera  140  using the existing autofocus technique. Focus position  424  is thus obtained. 
     In S 112 , controller  120  causes image sensor  146  of microscope camera  140  to start image capturing. In S 114 , controller  120  obtains an observation result from image data obtained by microscope camera  140 . The obtained observation result is stored in memory  124 . Controller  120  stores, for example, the image capturing time, the number of observation area  16  set when the image is captured, and information obtained by analyzing the image data in memory  124  as the observation result. 
     In S 116 , controller  120  stores focus position  424  obtained by the autofocus process in S 110  as focus position  424  of observation area  16  having the set number, in association with identification information  44  obtained by the processing in S 102 . At this time, controller  120  stores focus position  424  in association with observation area information  422  indicating the set number. 
     In S 118 , controller  120  increments the number of observation area  16  by 1. In S 120 , controller  120  determines whether or not the number of observation area  16  exceeds fifty six. Controller  120  repeats the processing in S 108  to S 120  until the number of observation area  16  exceeds fifty six, and then, ends the image capturing process. 
     When controller  120  determines that image capturing condition  240  is stored in memory  124  (YES in S 104 ), controller  120  performs the processing in S 122  to S 136 , and then, ends the image capturing process. 
     In S 122 , controller  120  obtains focus position  424  (camera information  42 ) corresponding to identification information  44  obtained from memory  124  in S 102 . 
     In S 124 , controller  120  sets the number of observation area  16  at  1 . In S 126 , controller  120  positions observation area  16  having the set number within the image-capturing field of view. 
     In S 128 , controller  120  changes the focal point of microscope camera  140  such that the focal point of microscope camera  140  is brought to focus position  424  corresponding to the set number (observation area information  422 ). 
     In S 130 , controller  120  causes image sensor  146  of microscope camera  140  to start image capturing. In S 132 , controller  120  obtains an observation result from image data obtained by microscope camera  140 . The obtained observation result is stored in memory  124 . Controller  120  stores, for example, the image capturing time, the number of observation area  16  set when the image is captured, and information obtained by analyzing the image data in memory  124  as the observation result. 
     In S 134 , controller  120  increments the number of observation area  16  by 1. In S 136 , controller  120  determines whether or not the number of observation area  16  exceeds fifty six. Controller  120  repeats the processing in S 126  to S 136  until the number of observation area  16  exceeds fifty six, and then, ends the image capturing process. 
     The processing in S 106  to S 120  is the processing performed when the image capturing process is performed on culture plate  10  for the first time (a first image capturing process), and is the processing of concurrently performing generation of image capturing condition  240  and image capturing of each observation area  16 . In contrast, the processing in S 122  to S 136  is the processing performed when the image capturing process has already been performed on culture plate  10 , and is the processing performed when image capturing of observation area  16  is performed for the second and subsequent times (a second image capturing process). In the processing in S 122  to S 136 , an image of each observation area  16  is captured using image capturing condition  240  generated by performing the processing in S 106  to S 120 . 
     [First Modification] 
     Culture plate  10  is housed in incubator  20 , and is taken out at the predetermined timing and placed on stage  160 . Since culture plate  10  is made of resin, culture plate  10  is expected to become deformed when culture plate  10  is housed in incubator  20 . Accordingly, in image capturing performed for the second and subsequent times, image capturing condition  240  generated in image capturing performed for the first time may be corrected and used. In image capturing performed for the second and subsequent times, controller  120  according to a first modification performs a process of correcting image capturing condition  240  (focus position  424 ). 
       FIG. 6  is a flowchart of an image capturing process performed by a controller according to the first modification. The image capturing process performed by controller  120  according to the first modification is different from the image capturing process performed by controller  120  according to the above-described embodiment in that controller  120  according to the first modification performs the processing in S 123 . 
     In S 123 , controller  120  according to the first modification corrects focus position  424  based on a culture condition. The culture condition is a factor that deforms culture plate  10 , and includes a temperature and a humidity of the environment where culture plate  10  is placed, a time period during which culture plate  10  is housed in incubator  20 , and the like. 
     For example, a degree of deformation of culture plate  10  under the environment equivalent to the environment during examination of culture plate  10  may be measured and focus position  424  may be corrected based on the obtained degree of deformation. Alternatively, focus position  424  may be corrected in accordance with a correction equation including the culture condition as a parameter. 
     The processing in S 123  may be performed separately from the image capturing process. The processing in S 123  may be performed at any timing after generation of image capturing condition  240 . 
     [Second Modification] 
     Although controller  120  according to a second modification is common to controller  120  according to the first modification in that controller  120  according to the second modification corrects image capturing condition  240 , controller  120  according to the second modification is different in a correction method from controller  120  according to the first modification. A process performed by controller  120  according to the second modification will be described below with reference to  FIGS. 7 and 8 . 
       FIG. 7  is a flowchart of an image capturing process performed by the controller according to the second modification. In  FIG. 7 , a part of the process (processing in S 102  to S 120 ) common to the image capturing process performed by the controller according to the above-described embodiment is omitted. 
     The image capturing process performed by controller  120  according to the second modification is different from the image capturing process performed by controller  120  according to the above-described embodiment in that controller  120  according to the second modification performs the processing in S 132 ′ instead of the processing in S 132  and performs the processing in S 131 - 1  to S 131 - 7 . The processing different from that of the above-described embodiment will be mainly described below. 
     Subsequent to S 130 , in S 131 - 1 , controller  120  according to the second modification stores image data together with the focus position. 
     In S 131 - 2 , controller  120  according to the second modification moves the focal point of microscope camera  140  upward in a vertical direction (in the Z axis direction in  FIG. 1 ) by a prescribed distance a. Specifically, the focal point is moved from focus position  424  stored as image capturing condition  240  in a direction away from stage  160  (culture plate  10 ) by predetermined distance a. The distance of movement may be set in accordance with the depth of field of microscope camera  140 , or may be set in accordance with the environment where culture plate  10  is placed. 
     In S 131 - 3 , controller  120  according to the second modification causes image sensor  146  of microscope camera  140  to start image capturing. 
     In S 131 - 4 , controller  120  according to the second modification stores image data together with the focus position. That is, controller  120  according to the second modification stores the image data in association with the position of the focal point of microscope camera  140  when the image data is obtained. 
     In S 131 - 5 , controller  120  according to the second modification moves the focal point of microscope camera  140  downward in the vertical direction (in the Z axis direction in  FIG. 1 ) by prescribed distance a. Specifically, the focal point is moved from focus position  424  stored as image capturing condition  240  in a direction approaching stage  160  (culture plate  10 ) by predetermined distance a. The distance of movement does not necessarily need to be the same as the distance of movement in S 131 - 2 . 
     In S 131 - 6 , controller  120  according to the second modification causes image sensor  146  of microscope camera  140  to start image capturing. 
     In S 131 - 7 , controller  120  according to the second modification stores image data together with the focus position. 
     In S 132 ′, controller  120  according to the second modification obtains an observation result from the most in-focus image data, of the image data obtained in S 131 - 1 , the image data obtained in S 131 - 4  and the image data obtained in S 131 - 7 . For example, controller  120  according to the second modification extracts a feature quantity related to focus from the image data. The feature quantity related to focus can be calculated using the existing image processing technique. Controller  120  according to the second modification specifies the most in-focus image data based on the extracted feature quantity. At this time, controller  120  according to the second modification stores the obtained observation result in association with the focus position when the most in-focus image data is obtained. 
     By performing the processing in S 128  to S 131 - 7 , the images captured at the positions of the focal point of microscope camera  140  displaced upward and downward in the vertical direction (in the Z axis direction in  FIG. 1 ) with respect to the focus position by the prescribed distance are obtained, in addition to the image captured at the focus position stored as image capturing condition  240 . 
     In addition, by performing the processing in S 132 ′, the most in-focus image is specified, of the image captured at the focus position stored as image capturing condition  240  and the images captured at the positions of the focal point of microscope camera  140  displaced upward and downward in the vertical direction (in the Z axis direction in  FIG. 1 ) with respect to the focus position by the prescribed distance. 
     The information composed of the image data and the focus position stored in S 131 - 1 , S 131 - 4  and S 131 - 7  may be deleted after the most in-focus image data is specified in the processing in S 132 ′. 
       FIG. 8  is a flowchart of a correction process performed by the controller according to the second modification. In the correction process, image capturing condition  240  is corrected based on the image captured at the focus position and the images captured at the positions displaced upward and downward with respect to the focus position by the prescribed distance. 
     Specifically, in S 202 , controller  120  according to the second modification sets the number of observation area  16  at  1 . 
     In S 204 , controller  120  according to the second modification obtains a focus position corresponding to observation result  242  of observation area  16  having the set number. At this time, by performing the processing in S 132 ′ in  FIG. 7  as described above, observation result  242  obtained from the most in-focus image, of the image captured at the focus position stored as image capturing condition  240  and the images captured at the positions of the focal point of microscope camera  140  displaced upward and downward in the vertical direction (in the Z axis direction in  FIG. 1 ) with respect to the focus position by the prescribed distance, is stored in memory  124  in association with the focus position when the most in-focus image is captured. 
     That is, by performing the processing in S 204 , there is obtained the focus position indicating the position of the focal point when the most in-focus image is captured, of the image captured at the focus position stored as image capturing condition  240  and the images captured at the positions of the focal point of microscope camera  140  displaced upward and downward in the vertical direction (in the Z axis direction in  FIG. 1 ) with respect to the focus position by the prescribed distance. 
     In S 206 , controller  120  according to the second modification corrects the focus position stored as image capturing condition  240  to the focus position obtained in S 204 . 
     In S 208 , controller  120  according to the second modification increments the number of observation area  16  by 1. In S 210 , controller  120  according to the second modification determines whether or not the number of observation area  16  exceeds fifty six. Controller  120  according to the second modification repeats the processing in S 204  to S 210  until the number of observation area  16  exceeds fifty six, and then, ends the correction process. 
     When culture plate  10  is deformed under the culture environment, the images captured at the positions of the focal point of microscope camera  140  displaced upward and downward along the vertical direction of microscope camera  140  by the prescribed distance may in some cases be more in-focus than the image captured at the focus position stored as image capturing condition  240 . 
     Accordingly, by performing the correction process shown in  FIG. 8 , the focus position stored as image capturing condition  240  can be corrected to the focus position indicating the position of the focal point of microscope camera  140  when the in-focus image is captured. 
     The correction process may be performed at any timing during a time period from the n-th image capturing to the n+1-th image capturing. Alternatively, the correction process may be performed when a preset condition is satisfied, such as when a time period during which culture plate  10  is housed in incubator  20  becomes equal to or longer than a prescribed time period. The condition for performing the correction process is set based on, for example, a condition that causes deformation of culture plate  10 . 
     The correction process may be performed whenever image capturing is performed the prescribed number of times. Culture plate  10  is gradually deformed with the progress of the culture time. Therefore, the position of the focal point of microscope camera  140  where microscope camera  140  is in focus on observation area  16  changes gradually with the progress of the culture time. By performing the correction process whenever image capturing is performed the prescribed number of times, image capturing condition  240  can be corrected in accordance with the position of the focal point that changes gradually with the progress of the culture time. 
     Although controller  120  according to the second modification performs image capturing at three different focal point positions in the image capturing process, the number of the focal point positions may be two or more and is not limited to three. 
     Controller  120  according to the second modification may perform the processing in S 132 ′ at the timing different from the timing of the image capturing process. For example, the processing in S 132 ′ may be incorporated into a part of the correction process shown in  FIG. 8 . The correction process may be performed during the image capturing process. Specifically, the processing in S 206  may be performed after the processing in S 132 ′. 
     [Other Modifications] 
     Although controller  120  stores image capturing condition  240  in memory  124  of controller  120 , a location to store image capturing condition  240  is not limited thereto. For example, image capturing condition  240  may be stored in the storage device communicably connected to controller  120 . When identification code  18  is a writable RF tag, image capturing condition  240  may be stored in the RF tag. 
     Although the plurality of observation areas  16  are provided on culture plate  10  in the above-described embodiment, the present disclosure is not limited thereto. The number of observation areas  16  provided on culture plate  10  may be one, or may be two or more, or may be fifty seven or more. When one observation area  16  is provided on culture plate  10 , image capturing condition  240  does not need to include the information indicating the position of observation area  16 , and image-capturing field-of-view changing mechanism  162  does not need to be provided. 
     Although the information indicating the position of observation area  16  is the number of observation area  16  in the above-described embodiment, the present disclosure is not limited thereto. For example, the information indicating the position of observation area  16  may be a coordinate on the plane (X-Y plane) of stage  160  on which culture plate  10  is placed. That is, the information indicating the position of observation area  16  may be any information indicating a relative positional relationship between microscope camera  140  and observation area  16 . 
     Although observation area information  422  is prestored in memory  124 , observation area information  422  may be read when identification code  18  is read. 
     Although image-capturing field-of-view changing mechanism  162  changes the image-capturing field of view of microscope camera  140  by moving stage  160  in the above-described embodiment, the present disclosure is not limited thereto. For example, image-capturing field-of-view changing mechanism  162  may change the image-capturing field of view of microscope camera  140  by moving microscope camera  140 . 
     In the above-described embodiment, description has been given of the example in which the result obtained by analysis of the image data by analysis unit  230  is stored as observation result  242 . However, the present disclosure is not limited thereto. Controller  120  does not need to include analysis unit  230  and may store the image data as observation result  242 . Alternatively, controller  120  may transmit the image data to another information processing device and cause the information processing device to have the function of the analysis unit. Although observation result  242  is stored in memory  124  in the above-described embodiment, observation result  242  may be represented on a display unit such as a monitor and observation result  242  may be deleted in response to an input indicating that a user has checked the representation. 
     Although microscope camera  140  includes focal point changing mechanism  144  in the above-described embodiment, the present disclosure is not limited thereto. For example, focal point changing mechanism  144  may be any mechanism as long as it can change the position of the focal point of microscope camera  140  with respect to culture plate  10 , and may be, for example, a mechanism that moves stage  160  in the Z axis direction. 
     In the above-described embodiment, the image capturing condition for focusing on each observation area  16  is managed by the identification information indicated by individual identification code  18  assigned to each culture plate  10 . However, a method for managing the image capturing condition for each culture plate  10  is not limited to the method using the identification information. For example, the image capturing condition for each culture plate  10  may be managed using information of a position (storage position) where each culture plate  10  is stored. In this case, it is unnecessary to assign identification code  18  to culture plate  10 , and it is also unnecessary to provide reading unit  180  in examination device  100 . 
     For example, readout unit  226  may read out the image capturing condition corresponding to the storage position, based on reception of an input of the storage position. In this case, the image capturing condition may be deleted at the timing of performing a new examination or at the timing of the end of examination. The storage position refers to, for example, a position in the incubator. The storage position may be output by the user operating a prescribed input unit. Alternatively, when the process of taking culture plate  10  in and out of the incubator is performed by a machine, the storage position may be output from a controller that controls the machine. A placement position during observation of culture plate  10 , not the storage position, may be predetermined for each culture plate  10  and the image capturing condition for each culture plate  10  may be managed using the placement position. 
     When one culture plate  10  is examined at a time, it is unnecessary to manage the image capturing condition using the identification information. 
     [Aspects] 
     It is understood by a person skilled in the art that the above-described embodiment and the modifications thereof are provided as specific examples of the following aspects. 
     (Clause 1) 
     An examination method according to one aspect is an examination method for examining dynamics of a biological factor by capturing, with a microscope camera, an image of at least one observation area on a plate with the biological factor arranged therein. The examination method includes: obtaining a focus position by focusing the microscope camera on the observation area during a first image capturing process for the observation area; storing the obtained focus position in a storage device; and performing a second image capturing process for the observation area after the first image capturing process. The performing includes: reading out the focus position from the storage device; setting a focal point of the microscope camera at the read-out focus position; and capturing an image of the observation area. 
     With such a configuration, in the second image capturing process for the observation area after the first image capturing process, the focal point of the microscope camera is set at the focus position obtained in the first image capturing process. That is, it is unnecessary to focus the microscope camera on the observation area in the second image capturing process for the observation area. As a result, the time required for focusing can be reduced and the dynamics examination of the biological factor can be performed in a short time. 
     (Clause 2) 
     The examination method according to clause 1 further includes reading identification information assigned to the plate. In this case, the storing the obtained focus position further includes storing the focus position in association with the identification information. The reading out further includes reading out the focus position corresponding to the read identification information. 
     With such a configuration, each focus position is stored in the storage device in association with the identification information assigned to the plate, and thus, the focus position where the microscope camera is in focus on the observation area can be managed for each plate having an individual difference. Thus, the examination can be simplified when a plurality of plates are observed concurrently. 
     (Clause 3) 
     In the examination method according to clause 1 or 2, the plate may have a plurality of observation areas. In this case, the storing further includes storing observation area information in association with the focus position, the observation area information indicating a relative positional relationship between the microscope camera and the observation area. The performing further includes setting an image-capturing field of view of the microscope camera in accordance with the observation area information corresponding to the read out-focus position. 
     With such a configuration, the time required for focusing for each observation area can be reduced. Therefore, the plurality of observation areas can be observed concurrently and an image capturing timing lag among the observation areas can be reduced. 
     (Clause 4) 
     In the examination method according to any one of clauses 1 to 3, the biological factor is bacteria. In this case, an object to be observed is arranged at the observation area, the object to be observed being obtained by bringing an antibacterial drug into contact with a sample including the bacteria. 
     (Clause 5) 
     The examination method according to clause 4 may further include: housing the plate in an incubator for a predetermined time period; and correcting the focus position stored in the storage device in accordance with a culture condition. 
     With such a configuration, although the plate is expected to become deformed when the plate is housed in the incubator, the focus position is corrected in accordance with the culture condition, and thus, obtainment of the image that is in focus on the observation area can be continued. 
     (Clause 6) 
     The examination method according to clause 4 may further include: housing the plate in an incubator for a predetermined time period; capturing an image of the observation area at a position of the focal point of the microscope camera displaced from the focus position in a vertical direction with respect to the plate by a prescribed distance; and obtaining an observation result using an in-focus image, of the image captured at the focus position and the image captured at the position displaced in the vertical direction by the prescribed distance. 
     With such a configuration, although the plate is expected to become deformed when the plate is housed in the incubator, image capturing at the focus position and image capturing at the position displaced in the vertical direction by the prescribed distance are performed, and thus, the observation result using the image that is in focus on the observation area is obtained even when the plate is deformed. 
     (Clause 7) 
     The examination method according to clause 4 may further include: housing the plate in an incubator for a predetermined time period; capturing an image of the observation area at a position of the focal point of the microscope camera displaced from the focus position in a vertical direction with respect to the plate by a prescribed distance; and correcting the focus position stored in the storage device to a position of the focal point of the microscope camera in capturing an in-focus image, of the image captured at the focus position and the image captured at the position displaced in the vertical direction by the prescribed distance. 
     With such a configuration, although the plate is expected to become deformed when the plate is housed in the incubator, the focus position is corrected to the position of the focal point of the microscope camera in capturing the in-focus image, of the image captured at the focus position and the image captured at the position displaced in the vertical direction by the prescribed distance, and thus, obtainment of the in-focus image can be continued. 
     (Clause 8) 
     An examination device according to one aspect is an examination device that examines dynamics of a biological factor by capturing an image of at least one observation area on a plate with the biological factor arranged therein. The examination device includes: a microscope camera that captures an image of the observation area; a focal point changing unit that changes a focal point of the microscope camera; an obtainment unit that obtains a focus position by focusing the microscope camera on the observation area during a first image capturing process for the observation area; a storage unit that stores the obtained focus position in a storage device; and an image capturing control unit that causes the microscope camera to capture the image of the observation area by controlling the microscope camera and the focal point changing unit. The image capturing control unit performs a second image capturing process for the observation area after the first image capturing process. The second image capturing process includes: reading out the focus position from the storage device; setting the focal point of the microscope camera at the read-out focus position; and capturing an image of the observation area. 
     With such a configuration, in the second image capturing process for the observation area after the first image capturing process, the focal point of the microscope camera is set at the focus position obtained in the first image capturing process. That is, it is unnecessary to focus the microscope camera on the observation area in the second image capturing process for the observation area. As a result, the time required for focusing can be reduced and the dynamics examination of the biological factor can be performed in a short time. 
     (Clause 9) 
     The examination device according to clause 8 may further include a reading unit that reads identification information assigned to the plate. In this case, the storage unit stores the focus position in the storage device in association with the identification information. The image capturing control unit reads out the focus position corresponding to the identification information read by the reading unit from the storage device in the second image capturing. 
     With such a configuration, each focus position is stored in the storage device in association with the identification information assigned to the plate, and thus, the focus position where the microscope camera is in focus on the observation area can be managed for each plate having an individual difference. Thus, the examination can be simplified when a plurality of plates are observed concurrently. 
     (Clause 10) 
     The examination device according to clause 8 or 9 may further include an image-capturing field-of-view changing unit that changes an image-capturing field of view of the microscope camera. The plate may have a plurality of observation areas. In this case, the storage unit stores observation area information in association with the focus position, the observation area information indicating a relative positional relationship between the microscope camera and the observation area. The image capturing control unit causes the image-capturing field-of-view changing unit to set an image-capturing field of view of the microscope camera by controlling the image-capturing field-of-view changing unit in accordance with the observation area information corresponding to the read-out focus position. 
     With such a configuration, the time required for focusing for each observation area can be reduced. Therefore, the plurality of observation areas can be observed concurrently and an image capturing timing lag among the observation areas can be reduced. 
     (Clause 11) 
     In the examination device according to any one of clauses 8 to 10, when the image of the observation area on the plate taken out of an incubator is captured, the image capturing control unit may correct the focus position stored in the storage device in accordance with a culture condition of an object to be observed arranged on the observation area. 
     With such a configuration, although the plate is expected to become deformed when the plate is housed in the incubator, the focus position is corrected in accordance with the culture condition, and thus, obtainment of the image that is in focus on the observation area can be continued. 
     (Clause 12) 
     In the examination device according to any one of clauses 8 to 10, the image capturing control unit may obtain a first image and a second image when the image of the observation area on the plate taken out of an incubator is captured, the first image being an image captured at the focus position, the second image being an image captured at a position displaced from the focus position in a vertical direction with respect to the plate by a prescribed distance, and obtain an observation result using an in-focus image, of the first image and the second image. 
     With such a configuration, although the plate is expected to become deformed when the plate is housed in the incubator, image capturing at the focus position and image capturing at the position displaced in the vertical direction by the prescribed distance are performed, and thus, the observation result using the image that is in focus on the observation area is obtained even when the plate is deformed. 
     (Clause 13) 
     In the examination device according to any one of clauses 8 to 10, the image capturing control unit may obtain a first image and a second image when the image of the observation area on the plate taken out of an incubator is captured, the first image being an image captured at the focus position, the second image being an image captured at a position displaced from the focus position in a vertical direction with respect to the plate by a prescribed distance, and correct the focus position stored in the storage device to a position of the focal point of the microscope camera in capturing an in-focus image, of the first image and the second image. 
     With such a configuration, although the plate is expected to become deformed when the plate is housed in the incubator, the focus position is corrected to the position of the focal point of the microscope camera at the time of capturing the in-focus image, of the image captured at the focus position and the image captured at the position displaced in the vertical direction by the prescribed distance, and thus, obtainment of the in-focus image can be continued. 
     Although the embodiment of the present disclosure has been described, it should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.