Abstract:
An image recording carrier includes: an image recording plate including a plate-shaped supporter, and a recording layer which is superposed on the top of the supporter, and which accumulates and recodes a radiograph when irradiated with radioactive rays carrying an image; and a cassette in which the image recording plate is housed. Multiple steps are formed in the direction along the thickness of the image recording plate on at least one side surface of the image recording plate, and a front portion which is one of the multiple steps including the recording layer, protrudes from the rest of the multiple steps. A facing surface of the cassette facing the side surface of the image recording plate while the image recording plate is housed in the cassette has an opposed portion which is opposed to the front portion, and which dents from the rest of the multiple steps.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an image recording carrier which accumulates and records a radiograph when irradiated with radioactive rays carrying an image to be radiographed.  
         [0003]     2. Description of the Prior Art  
         [0004]     Heretofore, there have been known radioactive-energy-accumulating fluorescent substances which accumulate part of radioactive energy when irradiated with radioactive rays, and which emit photostimulated luminescent light depending on the accumulated radioactive energy when irradiated with a beam of visible light or the like. Recent years, CR (computed radiography) has been in increasingly wide use in the medical field and the like. CR is a technique as follows. A radiograph is accumulated and recorded in a radioactive-energy-accumulating fluorescent substance by irradiating the radioactive-energy-accumulating fluorescent substance with radioactive rays having passed through an object. Subsequently, the radioactive-energy-accumulating fluorescent substance is irradiated with excitation light, and thus photostimulated luminescent light is emitted from the radioactive-energy-accumulating fluorescent substance. By reading the photostimulated luminescent light thus emitted, the radiograph is visualized.  
         [0005]     There are two types of image reading apparatuses which are widely used for medical CR: a built-in type and a cassette type. In the case of image reading apparatuses of the built-in type, an IP (imaging plate) and a reading section are altogether housed in a single apparatus body, and thus the IP housed in the single apparatus is irradiated with radioactive rays. The IP is obtained by adhering a radioactive-energy-accumulating fluorescent substance to a surface of a substrate. The reading section irradiates the IP with a laser beam or the like, and thus reads the resultant photostimulated luminescent light. Image reading apparatuses of the built-in type will be hereinafter referred to as “built-in apparatuses.” In the case of image reading apparatuses of the cassette type, an IP is housed in a portable cassette. A radiograph is accumulated on the IP through radiographing. This IP is housed in the cassette. This cassette is attached to an image reading apparatus. The image reading apparatus takes the IP out of the cassette, and thus reads the radiograph. Image reading apparatuses of the cassette type will be hereinafter referred to as “cassette apparatuses.” 
         [0006]     Built-in apparatuses make it possible to read a radiograph made on the spot, and thus to check on the radiograph immediately. This makes it possible for a user to find a failure in radiographing immediately, and to take another shot. For this reason, built-in apparatuses are widely used for a group physical checkup, which requires radiographs to be taken of multiple objects securely.  
         [0007]     On the other hand, in the case of cassette apparatuses, a cassette can be easily moved closer to a part of an object which is intended to be radiographed during radiographing. In a case where, for example, a patient has his/her bone fractured, a cassette apparatus is capable of radiographing an injured part which is intended to be radiographed without forcing the patient to get into uncomfortable poses. In addition, in a case where, for example, an IP is damaged in a cassette, the damaged IP housed in the cassette can be easily replaced with a spare IP. This brings about an advantage that time and costs needed to resume radiographing can be saved to a large extent.  
         [0008]     As described above, since the built-in apparatuses and the cassette apparatuses have different advantages, many hospitals are furnished with both a built-in apparatus and a cassette apparatus in many cases. Usually, they use one of the two types of apparatuses depending on an intended use.  
         [0009]     Moreover, in recent years, mammography apparatuses have become in use. The mammography apparatuses radiograph a mamma while flattening the mamma with the mamma placed and pressed between an IP and a transmission plate having a radioactive transmittivity. The mammography apparatuses are known for their effectiveness for early detection of breast cancer. In many cases, whether or not hospitals are furnished with a mammography apparatus is an important criterion for patients to choose their hospitals.  
         [0010]     There are also two types of mammography apparatuses: a built-in type and a cassette type. In the case of mammography apparatuses of the built-in type, an IP and a reading section in addition to a pressing mechanism and an irradiation unit are altogether housed in a single mammography apparatus body. The reading section reads a radiograph. The pressing mechanism presses a transmission plate toward the IP. The irradiation unit irradiates the IP with radioactive rays. In the case of mammography apparatuses of the cassette type, only elements such as a pressing mechanism and an irradiation unit are installed in a single mammography apparatus body. A cassette in which an IP is housed is attached to the mammography apparatus, and is irradiated with radioactive rays. When using a mammography apparatus of this cassette type, a mamma is radiographed by placing the mamma between the attached cassette and a transmission plate. The cassette which has been used for the radiographing is attached to an image reading apparatus which is equipped separately from the mammography apparatus. Thus, a radiograph which has been accumulated and recorded on the IP is read by the image reading apparatus. In the case of mammography apparatuses of this cassette type, it is easy to replace a damaged IP with a new one. In addition, the conventional cassette apparatuses which have been used in hospitals can be used as image reading apparatuses for reading a radiograph. For these reasons, the mammography apparatuses of the cassette type are more cost-effective and more easy to be introduced than mammography apparatuses of the built-in type.  
         [0011]     In a case where a mamma is going to be radiographed by use of a mammography apparatus of the cassette type, a side surface of a cassette is pressed against the base of the mamma (the base of the mamma will be referred to as a “chest wall”), and the mamma is irradiated with radioactive rays while the mamma being flattened on the top surface of the cassette by use of a transmission plate. At this time, the mammography apparatus is incapable of accumulating or recording the radiograph corresponding to a part of the IP housed in the cassette even though the IP is irradiated with the radioactive rays. The part in question extends from a place corresponding to the side surface of the cassette to a place beyond which a radioactive-energy-accumulating fluorescent substance is adhered to the IP. This part in question will be hereinafter referred to as an “unrecorded part.” Because of an unrecorded part of this kind, mammography apparatuses of the cassette type have a problem that a part of a mamma which is closer to the chest wall is missing from a radiograph of the mamma.  
         [0012]     With regard to this problem, Japanese Patent Application Laid-open Publication No. 2003-248093 (hereinafter referred to as “JPA-2003-248093”) has disclosed a technique with which an IP is produced by expanding a recording area for accumulating and recording a radiograph in an IP up to the end of a substrate. More specifically, a layer of a radioactive-energy-accumulating fluorescent substance is formed in a place between 0.0 mm and 0.4 mm from the end of the substrate. The technique disclosed by JPA-2003-248093 makes it possible to reduce the unrecorded part in the area, and to accordingly decrease a missing portion of a radiograph.  
         [0013]     It is usual, however, that a cassette is configured of a plastic or the like with a thickness of approximately several millimeters. Even though a recording area of an IP is intended to be expanded by use of the technique disclosed by JPA-2003-248093, in reality, a portion of a mamma in a range of the chest wall to approximately 5 mm therefrom is incapable of being radiographed because of the thickness of a plastic of which the cassette is configured. This means that mammography apparatuses of the cassette type are incapable of radiographing a tumor closer to the chest wall until the tumor develops beyond a range of the chest wall to approximately 5 mm therefrom. This incapability places an obstruction to breast cancer checks which aim at earlier detection of breast cancers. On the other hand, if an unrecorded part is intended to be reduced in area by forming a cassette of a thinner plastic, this decreases the strength of the cassette. This brings about a problem that a hard but fragile IP can not be protected by the cassette securely.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention has been made in view of the above circumstances, and provides an image recording carrier which is capable of reducing a missing portion from a radiograph made by a radiography apparatus such as a mammography apparatus without decreasing the strength of the cassette.  
         [0015]     An image recording carrier according to the present invention includes:  
         [0016]     an image recording plate including a plate shaped supporter and a recording layer which is superposed on a top surface of the supporter, and which accumulates and records a radiograph when irradiated with radioactive rays carrying an image; and  
         [0017]     a cassette in which the image recording plate is housed,  
         [0018]     wherein the image recording plate has multiple steps formed in a direction along a thickness of the image recording plate on at least one side surface of the image recording plate, and has a front portion which is one of the multiple steps including the recording layer and which protrudes from the rest of the multiple steps,  
         [0019]     the cassette has a facing surface facing the side surface of the image recording plate while the image recording plate is housed in the cassette, and  
         [0020]     an opposed portion of the facing surface being opposed to the front portion of the image recording plate dents from the rest of the multiple steps.  
         [0021]     In the image recording carrier according to the present invention, the front portion including the recording layer in which the radiograph is accumulated and recorded protrudes above the rest of the side surface of the image recording plate. The opposed portion in the facing surface of the cassette, which id opposed to the front portion, dents under the rest of the facing surface. Once the image recording plate is housed in the cassette, the front portion of the image recording plate is fitted into the opposed portion of the cassette, and thus comes closer to the side surface of the cassette. This makes it possible to reduce a missing portion of a radiograph which is made of the mamma when pressing the side surface of the cassette against the chest wall of an object. In addition, the protruding of the facing surface of the cassette except for the opposed portion makes it possible to increase the strength of the cassette while causing the recording layer of the image recording plate to remain closer to the side surface of the cassette without increasing the missing portion of the radiograph.  
         [0022]     In the image recording carrier according to the present invention, it is desirable that the front portion of the image recording plate should be beveled.  
         [0023]     The beveling, such as the chamfering, of the front portion of the image recording plate makes it possible to suppress a disadvantage that the recording layer is damaged due to a shock which may occur while the image recording plate is being housed in the cassette.  
         [0024]     In the image recording carrier according to the present invention, it is desirable that the opposed portion of the cassette should be beveled.  
         [0025]     The processing of the opposed portion of the cassette with an angle R makes it possible to avoid a disadvantage that the front portion of the image recording plate hits the opposed portion of the cassette so that the front portion is chipped off.  
         [0026]     In the image recording carrier according to the present invention, it is desirable that the cassette should include a press member which presses the image recording plate housed in the cassette toward the facing surface.  
         [0027]     Pressing the image recording plate toward the facing surface makes it possible to decrease a space between the front portion of the image recording plate and the opposed portion of the cassette, and to thus reduce the missing portion of the radiograph securely.  
         [0028]     In the image recording carrier according to the present invention, it is desirable that the opposed portion of the cassette should be configured of a material which changes in shape when a force is applied to the material so that the opposed portion dents when the press member presses the front portion against the opposed portion.  
         [0029]     Because the opposed portion of the cassette dents when the front portion of the image recording plate is pressed against the opposed portion, this dent makes it possible to securely avoid the image recording plate being damaged even when there occurs a dimensional error such as a too large amount of protrusion of the front portion of the image recording plate.  
         [0030]     In the image recording carrier according to the present invention, it is desirable that an amount of dent of the opposed portion of the cassette should be larger than an amount of protrusion of the front portion.  
         [0031]     Because an amount of dent of the opposed portion of the cassette is larger than an amount of protrusion of the front portion of the image recording plate, this enlargement makes it possible to prevent the front portion of the image recording plate from hitting the opposed portion of the cassette, and to thus suppress damage on the recording layer, while the image recording plate is being housed in the cassette.  
         [0032]     In the image recording carrier according to the present invention, it is desirable that the opposed portion of the cassette should include a shock absorbing member which absorbs a shock which occurs when the front portion hits the opposed portion.  
         [0033]     The image recording carrier according to the present invention makes it possible to efficiently reduce damage on the recording layer of the image recording plate.  
         [0034]     In the image recording carrier according to the present invention, it is desirable that an edge of the recording layer of the image recording plate should be provided with a protection member which protects the edge.  
         [0035]     Presence of the protection member on the edge of the recording layer makes it possible to reduce damage on the recording layer, and to concurrently protect the recording layer from deterioration which occurs due to higher humidity.  
         [0036]     It is desirable that the image recording carrier according to the present invention should be attached to a mammography apparatus.  
         [0037]     Because the mammography apparatus has a problem that there is a missing portion of a radiograph which is closer to the chest wall, it is desirable that the image recording carrier according to the present invention should be capable of being applied to the mammography apparatus.  
         [0038]     The present invention makes it possible to reduce a missing portion from a radiograph made by a radiography apparatus such as a mammography apparatus without decreasing the strength of the cassette. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]      FIG. 1  is a diagram of a schematic configuration of an IP and a cassette according to a first embodiment of the present invention.  
         [0040]      FIG. 2  is a diagram showing a schematic configuration of a radiography system.  
         [0041]      FIG. 3  is a diagram showing an inner configuration of an image reading apparatus.  
         [0042]      FIG. 4  is a cross-sectional view of the cassette which houses the IP, taken along A-A′ line of  FIG. 1 .  
         [0043]      FIG. 5  is a conceptual diagram illustrating an image of a radiograph to be accumulated and recorded on the IP.  
         [0044]      FIG. 6  is a cross-sectional view of an IP and a cassette according to a second embodiment of the present invention, taken along the A-A′ line of  FIG. 1 .  
         [0045]      FIG. 7  is a cross-sectional view of an IP and a cassette according to a third embodiment of the present invention, taken along the A-A′ line of  FIG. 1 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0046]     Descriptions will be provided hereinafter for embodiments of the present invention by referring to the drawings.  
         [0047]     In the embodiments, a radiograph is accumulated and recorded in an IP. This IP is housed in a portable cassette. The cassette is attached to a mammography apparatus, and thus the radiograph is made. After radiographing, the cassette is attached to an image reading apparatus, and thereby the image reading apparatus reads the radiograph. First of all, descriptions will be provided below for a schematic configuration of the IP and the cassette.  
         [0048]      FIG. 1  is a diagram of a schematic configuration of an IP and a cassette according to a first embodiment of the present invention.  
         [0049]     As shown in  FIG. 1 , an IP  10  is housed in a cassette  20  in the present embodiment. The IP  10  is irradiated with radioactive rays, and thus a radiograph is accumulated and recorded on the IP  10 . The cassette  20  is formed of a plastic allowing the radioactive rays to pass therethrough. The IP  10  is an example of the image recording plate as recited in the present invention. The cassette  20  is an example of the cassette as recited in the present invention. In addition, a combination of the IP  10  and the cassette  20  represents the image recording carrier as recited in the first embodiment of the present invention.  
         [0050]     The IP  10  is formed by adhering a sheet  10 B of a radioactive-energy-accumulating fluorescent substance to a substrate  10 A. The edges of the sheet  10 B of the radioactive-energy-accumulating fluorescent substance are provided with a resin-made protection material  10 C so as to prevent the sheet  10 B of the radioactive-energy-accumulating fluorescent substance from being chipped off or damaged in the like manner. The substrate  10 A is an example of the supporter as recited in the present invention. The sheet  10 B of the radioactive-energy-accumulating fluorescent substance is an example of the recording layer as recited in the present invention. The protection material  10 C is an example of the protection material as recited in the present invention.  
         [0051]     In addition, a side surface of the cassette  20  is provided with a lid  21 . A side surface  22  of the cassette  20  on a side opposite to the side surface provided with the lid  21  is provided with push holes  20   a  and  20   b  which are configured to push the IP out of the cassette  20  when a pin is inserted in each of the push holes  20   a  and  20   b.  When the IP  10  is taken out of the cassette  20 , the lid  21  is opened. Subsequently, a pin is inserted in each of the push holes  20   a  and  20   b,  and thereby the IP  10  is discharged out of the cassette  20 . It should be noted that, in a case where this cassette  20  is attached to a mammography apparatus (described later) configured to radiograph a mamma of an object, the cassette  20  is attached thereto in such a way that the side surface  22  of the cassette  20  on the side opposite to the side surface provided with the lid  21  faces the object. Subsequently, the side surface  22  is brought into contact with the chest wall of the object. The side surface  22  will be hereinafter referred to as a “contact side surface  22 .  
         [0052]     Thereafter, descriptions will be provided below for a radiograph, which is accumulated and recorded on the IP  10  housed in the cassette  20  as shown in  FIG. 1 .  
         [0053]      FIG. 2  is a diagram showing a schematic configuration of a radiography system.  
         [0054]     A radiography system  1  as shown in  FIG. 2  comprises a mammography apparatus  100 , an image reading apparatus  200  and a controller  300 . The mammography apparatus  100  radiographs a mamma of an object. The image reading apparatus  200  reads the radiograph which is accumulated and recorded on the IP  10 . The controller  300  displays the radiograph which has been read by the image reading apparatus  200 , and controls the entire radiography system  1 .  
         [0055]     The controller  300  includes a display monitor  310  and operation buttons  320  when viewed from the outside. The display monitor  310  displays the radiograph read by the image reading apparatus  200 . The operation buttons  320  are used by a user for input instructions.  
         [0056]     The mammography apparatus  100  includes an attachment base  110  to which the cassette  20  housing the IP  10  is to be attached, a transmission plate  120  through which radioactive rays are to pass, a plate driving section  130  which moves the transmission plate  120  in the upward and downward directions, a radioactive ray irradiating section  140 , a supporter  150  and a supporter driving section  160  when viewed from the outside. The radioactive ray irradiating section  140  is provided with a tube  141  configured to emit radioactive rays. The supporter  150  supports the attachment base  110  and the radioactive ray irradiating section  140 . The supporter driving section  160  moves the supporter  150  in the upward and downward directions. A controlling section (not illustrated) is installed in the mammography apparatus  100 . The controlling section controls the entire mammography apparatus  100  in accordance with instructions transmitted from the controller  300 .  
         [0057]     When taking a radiograph, first of all, the contact side surface  22  of the cassette  20  is aligned with a predetermined radiographing position P, and thus attached to the top of the attachment base  110 .  
         [0058]     Once the cassette  20  is attached to the attachment base  110 , an object is moved to the front of the mammography apparatus  100 . A user adjusts the position of the attachment base  110  to the position of a mamma  2  of the object by use of operation buttons  320 . Thereby, a chest wall  2   a  of the object is pressed to the contact side surface  22  of the cassette  20  located at the radiographing position P.  
         [0059]     Subsequently, the user inputs an instruction for radiography preparation by use of the operation buttons  320  of the controller  300 . The instruction for the radiography preparation is transmitted to the mammography apparatus  100 . Thereby, the plate driving section  130  moves the transmission plate  120  in the downward direction. Thus, the mamma  2  of the object is placed between the transmission plate  120  and the cassette  20 , and the mamma  2  is flattened. Thereafter, the radioactive ray irradiating section  140  irradiates radioactive rays on the mamma  2 .  
         [0060]     The radioactive rays emitted from the radioactive ray irradiating section  140  passes through the mamma  2 , and further passes into the cassette  20 . Thus, the IP  10  housed in the cassette  20  is irradiated with the radioactive rays. As a result, a radiograph of the mamma  2  is accumulated and recorded on the IP  10 .  
         [0061]     Once the radiographing is completed, the IP  10  as housed in the cassette  20  is removed from the cassette  20  to be attached to the image reading apparatus  200 .  
         [0062]     Both ends of the image reading apparatus  200  are each provided with a loading port  201 A in which the cassette  20  is to be loaded and a discharging port  201 B from which the cassette  20  is configured to be discharged once the image reading apparatus  200  completes reading the radiograph. The center of the image reading apparatus  200  is provided with a display panel  201 C on which an operational status and the like of the image reading apparatus  200  is to be displayed. The cassette  20  which has been used for the radiographing is to be inserted in the loading port  201 A.  
         [0063]      FIG. 3  showing a diagram showing an inner configuration of the image reading apparatus  200 .  
         [0064]     As shown in  FIG. 3 , the bottom of the loading port  201 A declines such that a portion thereof becomes lower as it is located farther away from the center of the image reading apparatus  200 . The lowermost portion of the decline is provided with a lid member  210 A through which the cassette  20  is to be taken into the interior of the image reading apparatus  200 . In addition, the loading port  201 A is provided with a sensor (not illustrated) configured to detect whether or not the cassette is attached thereto.  
         [0065]     The interior of the image reading apparatus  200  comprises a transfer section  220 , a reading section  230 , an erasing section  240 , a control section  250 . The transfer section  220  transfers the cassette  20  between the loading port  201 A and the discharging port  201 B. The reading section  230  reads the radiograph accumulated and recorded on the IP  10 . The erasing section  240  erases the radiograph remaining on the IP  10 . The control section  250  controls operations of the entire image reading apparatus  200 , and transmits the radiograph read by the reading section  230  to the controller  300 .  
         [0066]     Once the sensor detects that the cassette  20  is attached to the image reading apparatus, a motor mounted on the lid member  210 A of the loading port  201 A is driven in accordance with the instruction from the control section  250 . Thereby, the lid member  210 A is opened. The cassette  20  loaded in the loading port  201 A is transferred to the transfer section  220  by transfer rolls  2211 .  
         [0067]     The transfer section  220  is provided with two guide rails  222  and  223  as well as a transfer member  224 . One of the two guide rails  222 , 223  is arranged above the other. Each of the two guide rails joins a loading position S 1  under the loading port  201 A, a reading position S 2  under the reading section  230 , an erasing position S 3  under the erasing section  240 , and a discharging position S 4  under the discharging port  201 B. The transfer member  224  is configured to move along the guide rails  222  and  223 , and to thereby transfer the cassette  20  between the loading position S 1  and the discharging position S 4 .  
         [0068]     First of all, the cassette  20  which has been transferred by the transfer rolls  2211  is held by the transfer member  224  at the loading position S 1 . Thereafter, the cassette  20  is transferred along the guide rails  222  and  223  to the reading position S 2 . A lid opening section  225  configured to open the lid  21  of the cassette  20  is arranged in a vicinity of the upper guide rail  222  at the reading position S 2 . A discharging section  226  is arranged in the lower guide rail  223 . The discharging section  226  has two pins and a solenoid for inserting and pulling out the two pins. Once the cassette  20  is transferred to the reading position S 2 , the lid opening section  225  opens the lid  21  of the cassette  20 , and thus the pins provided at the discharging section  226  are inserted in the push holes  20   a  and  20   b.  Hence, the IP  10  is pushed out of the cassette  20 . The IP  10  which has been pushed out of the cassette  20  is transferred to the reading section  230  by transfer rolls  2212 . The cassette  20  which is empty after the IP  10  is discharged from the cassette  20  is transferred along the guide rails  222  and  223  to the erasing position S 3 .  
         [0069]     The reading section  230  is provided with a transfer route R which extends upward in the vertical direction. The reading section  230  includes shutters  231 A and  231 B, an excitation light irradiating section  233 , an image reading section  235 , two guide rails  236  and  237 , and a pair of nip rolls  238  and  239 . The shutters  231 A and  231 B are provided at two parts through which the IP  10  enters and exits. The excitation light irradiating section  233  irradiates an excitation light L in a main scanning direction (equal to a direction from the front to the back of the paper on which  FIG. 3  is drawn). The image reading section  235  collects photostimulated luminescent light by use of a collective guide  234  extending in the main scanning direction, and to thus read the radiograph which has been accumulated and recorded on the IP  10 . The guide rails  236  and  237  extend in the horizontal direction. One of the two guide rails is arranged above the other. The pair of nip rolls  238  and  239  are configured to transfer the IP  10  in the horizontal direction. One of the pair of nip rolls is arranged above the other of the pair of nip rolls. The upper nip roll  238  moves along the guide rail  236 , and the lower nip roll  239  moves along the guide rail  237 .  
         [0070]     The IP  10  which has been discharged from the cassette  20  is transferred in the upward direction along the transfer route R toward the guide rails  236  and  237  by transfer rolls  2321  and  2322 . Once the forward edge of the IP reaches the elevation at which the excitation light irradiating section  233  is arranged, the shutters  231 A and  231 B are closed. Thus, the interior of the reading section  230  is blocked from light. The IP  10  is transferred further upward by transfer roll  2322  and  2323 . Subsequently, the excitation light irradiating section  233  irradiates excitation light L on the IP  10  which is being transferred. Thus, the image reading section  235  reads photostimulated luminescent light emitted from the IP  10 . A radiograph which has been read by the image reading section  235  is transmitted to the control section  250 , and thereafter is transmitted to the controller  300  as shown in  FIG. 2 .  
         [0071]     In addition, the IP  10  from which the radiograph has been read is transferred to the nip rolls  238  and  239  by the transfer rolls  2322  and  2323 . Thus, the IP  10  is nipped by the nip rolls  238  and  239 . The nip rolls  238  and  239  move along the guide rails  236  and  237  in the horizontal direction while holding the IP  10 . Once the nip rolls  238  and  239  reach the ends of the respective guide rails  236  and  237 , the IP  10  is transferred downward. The IP is moved further downward by transfer rolls  2324  and  2231 , and is transferred to the erasing section  240 .  
         [0072]     The erasing section  240  is provided with multiple fluorescent lamps  241  which are arranged both in the main scanning direction (equal to a direction from the front to the back of the paper on which  FIG. 3  is drawn) and in a sub-scanning direction (equal to a direction from the top to the bottom of the paper on which  FIG. 3  is drawn). Once erasing light Q is emitted from the multiple fluorescent lamps  241 , the erasing light Q is irradiated on the IP  10  which is being transferred. As a result, the radioactive energy which has been accumulated on the IP  10  is discharged from the IP  10 , and thus the radiograph is erased.  
         [0073]     The IP  10  from which the radiograph has been erased is transferred further downward by the transfer rolls  2214 . Thus, the IP  10  is housed in the cassette  20  which has been empty, and which has been transferred to the erasing position S 3 . A lid closing section  227  for closing the lid  21  of the cassette  20  is arranged at the erasing position S 3 . Once the IP  10  is housed in the cassette  20 , the lid  21  of the cassette  20  is closed.  
         [0074]     The cassette  20  housing the IP  10  from which the radiograph has been read, and from which the radioactive energy has been discharged, is transferred along the guide rails  222  and  223  to the discharging position S 4 .  
         [0075]     A lid member  210 B is arranged in the discharging port  201 B as in the case of the loading port  201 A. Once the cassette  20  is transferred to the discharging position S 4 , the lid member  210 B of the discharging port  201 B is opened. The cassette  20  which has been transferred to the discharging position S 4  is transferred toward the discharging port  201 B by transfer rolls  2215 , and is discharged from the discharging port  201 B.  
         [0076]     In the foregoing manner, a radiograph is made, and the radiograph which is accumulated and recorded on the IP  10  is read.  
         [0077]     In the the mammography apparatus  100  as shown in  FIG. 2 , the contact side surface  22  of the cassette  20  is pressed against the chest wall  2   a  of an object, and thus the mamma  2  is radiographed. If the cassette  20  is formed of a thicker plastic, the distance from the chest wall  2   a  to the IP  10  housed in the cassette  20  is accordingly longer. This makes it impossible to radiograph part of the mamma  2  closer to the chest wall  2   a.  On the other hand, if the cassette  20  is formed of a thinner plastic, a missing portion corresponding to the part of the mamma  2  which could not be otherwise radiographed is eliminated from the radiograph. However, this configuration brings about a problem that the strength of the cassette  20  decreases so that the cassette  20  is incapable of protecting the IP  10 . The problem of this kind is solved in the IP  10  and the cassette  20  according to the present embodiment. Descriptions will be provided below for the configurations of each of the IP  10  and the cassette  20 .  
         [0078]      FIG. 4  is a cross-sectional view of the cassette housing the IP, which is taken along the A-A′ line of  FIG. 1 .  FIG. 5  is a conceptual diagram illustrating an image of a radiograph to be accumulated and recorded on the IP.  
         [0079]     As shown in  FIG. 4 , the IP  10  is obtained by superposing the sheet  10 B of the radioactive-energy-accumulating fluorescent substance on the substrate  10 A with an adhesive  10 D interposed in-between such that an end portion including an edge  11  of the sheet  10 B of the radioactive-energy-accumulating fluorescent substance is shifted from the corresponding end portion of the substrate  10 A, and by adhering the sheet  10 B to the substrate  10 A with the adhesive  10 D. As a result, a step is formed in a side surface of the IP  10 . The IP  10  is housed in the cassette  10  such that the side surface of the sheet  10 B, in which the end portion of the sheet  10 B of the radioactive-energy-accumulating fluorescent substance protrudes from the corresponding end portion of the substrate  10 A, is opposed to the contact side surface  22  of the cassette  20 . The end portion of the sheet  10 B which protrudes from the corresponding end portion of the substrate  10 A is an example of the front portion as recited in the present invention.  
         [0080]     The both edges  11  of the sheet  10 B of the radioactive-energy-accumulating fluorescent substance are chamfered at an elevation angle θ of approximately 70 degrees to 85 degrees to the horizontal plane. The chamfered edges  11  are each provided with a protection material  10 C.  
         [0081]     The cassette  20  is formed in such a way that the thickness W 1  of a wall of a recording-side portion  22   a  is smaller than the thickness W 3  of a wall of a substrate-side portion  22   b  in the contact side surface  22 . The recording-side portion  22   a  in the contact side surface  22  is opposed to the sheet  10 B of the radioactive-energy-accumulating fluorescent substance of the IP  10 . The substrate-side portion  22   b  in the contact side surface  22  is opposed to the substrate  10 A of the IP  10 . It should be noted that the length L of the end portion of the sheet  10 B of the radioactive-energy-accumulating fluorescent substance which protrudes from the corresponding end portion of the substrate  10 A is smaller than the difference (W 3 −W 1 ) between the thickness W 3  of the wall of the substrate-side portion  22   b  and the thickness W 1  of the wall of the recording-side portion  22   a.  Thereby, a slight space intervenes between the sheet  10 B of the radioactive-energy-accumulating fluorescent substance and the recording-side portion  22   a.  In addition, the recording-side portion  22   a  of the cassette  20  is processed with an angle R. The lid  21  of the cassette  20  is provided with a plate spring  23  configured to bias the IP  10 , which is housed in the cassette  20 , toward the contact side surface  22 . The recording-side portion  22   a  is an example of the opposed portion as recited in the present invention. The plate spring  23  is an example of the press member as recited in the present invention.  
         [0082]     Once the IP  10  is housed in the cassette  20 , the sheet  10 B of the radioactive-energy-accumulating fluorescent substance is fitted into the recording-side portion  22   a  of the cassette  20 . In addition, the substrate  10 A is biased by the plate spring  23 , and thus is pressed against the substrate-side portion of  22   b  of the cassette  20 . Thereby, the sheet  10 B of the radioactive-energy-accumulating fluorescent substance comes closer to the contact side surface  22  of the cassette  20 . It should be noted that the edges  11  of the sheet  10 B of the radioactive-energy-accumulating fluorescent substance are chamfered, and are each provided with the protection material  10 C. In addition, the recording-side portion  22   a  of the cassette  20  is processed with the angle R. Moreover, the slight space intervenes between the sheet  10 B of the radioactive-energy-accumulating fluorescent substance and the recoding-side portion  22   a.  These arrangements make it possible to reduce disadvantages including damage of the IP  10  which might otherwise occur when the sheet  10 B of the radioactive-energy-accumulating fluorescent substance hits the cassette  20  while the IP  10  is being housed in the cassette  20 .  
         [0083]     Subsequently, the cassette  20  housing the IP  10  is attached to the mammography apparatus  100  as shown in  FIG. 2 , and the chest wall of the object is pressed against the contact side surface  22  of the cassette  20 . Thereby, the sheet  10 B of the radioactive-energy-accumulating fluorescent substance of the IP  10  comes closer to the base of the mamma  2  (the chest wall) of the object, as shown in  FIG. 5 . That is because the sheet  10 B of the radioactive-energy-accumulating fluorescent substance of the IP  10  comes forward to the contact side surface  22  of the cassette  20  than the substrate  10 A.  
         [0084]     The conventional type IP and cassette have a disadvantage that, in a case where a radiograph is intended to be made after housing the IP in the cassette, the IP and the cassette are incapable of radiographing part of the mamma in a range of approximately several millimeters from the chest wall of an object. However, in the case of the IP  10  and the cassette  20  according to the present embodiment, the thickness W 1  of the wall of the recording-side portion  22   a  of the cassette  20  is smaller compared with that of the conventional IP and cassette, and thus the sheet  10 B of the radioactive-energy-accumulating fluorescent substance of the IP  10  comes closer to the contact side surface  22  of the cassette  20 . This makes it possible to reduce a missing portion of the radiograph to a width in a range of approximately 0.5 mm from the chest wall. In addition, the thickness W 3  of the wall of the substrate-side portion  22   b  opposed to the substrate  10 , and which has nothing to do with the recording of the radiograph, is larger. This makes it possible to increase the strength of the cassette  20  without increasing the distance W 2  between the sheet  10 B of the radioactive-energy-accumulating fluorescent substance and the contact side surface  22  of the cassette  20 .  
         [0085]     As described above, the present invention makes it possible to reduce a missing portion of a radiograph to be made by a mammography apparatus without decreasing the strength of the cassette  20 , and to thus detect a small tumor or the like in a position closer to the chest wall securely.  
         [0086]     The descriptions for the first embodiment of the present invention end with the preceding paragraph. From now, descriptions will be provided for a second embodiment of the present invention. An IP and a cassette according to the second embodiment of the present invention have the substantially same configurations as the IP and the cassette according to the first embodiment of the present invention have. For this reason, in the second embodiment, elements which are the same as those of the first embodiment are denoted by the same reference numerals, and the descriptions for the elements will be omitted. The second embodiment will be described while focusing on what makes the second embodiment different from the first embodiment.  
         [0087]      FIG. 6  is a cross-sectional view of the IP and the cassette according to the second embodiment of the present invention, taken along the A-A′ line of  FIG. 1 .  
         [0088]     An IP  40  according to the present embodiment has the substantially same configuration as the IP  10  according to the first embodiment as shown in  FIG. 4  has. The IP  40  according to the present embodiment is different from the IP  10  according to the first embodiment in that the IP  40  is not provided with the protection material  10 C.  
         [0089]     In addition, a cassette  30  according to the present embodiment has the substantially same configuration as the cassette  20  according to the first embodiment as shown in  FIG. 4  has. The cassette  30  according to the present embodiment is different from the cassette  20  according to the first embodiment in that neither a recording-side portion  32   a  opposed to the sheet  10 B of the radioactive-energy-accumulating fluorescent substance of the IP  40  nor a substrate-side portion  32   b  opposed to the substrate  10 A of the IP  40  is processed with the angle R, and in that the recording-side portion  32   a  is configured of a material (for example, a sponge) which dents when pressed.  
         [0090]     Once the IP  40  is inserted in the cassette  30 , the substrate  10 A is biased by the plate spring  23 , and thus is pressed against the substrate-side portion  32   b  of the cassette  30 . In addition, the sheet  10 B of the radioactive-energy-accumulating fluorescent substance presses, and thus dents, the recording-side portion  32   a.  Thereby, the sheet  10 B of the radioactive-energy-accumulating fluorescent substance comes closer to the contact side surface  22  of the cassette  30 . Because the recording-side portion  32   a  is configured of a pliable material such as a sponge as described above, the IP  40  and the cassette  30  are capable of causing the sheet  10 B of the radioactive-energy-accumulating fluorescent substance to come closer to the contact side surface  22  of the cassette  30  securely, and concurrently capable of preventing the sheet  10 B of the radioactive-energy-accumulating fluorescent substance from being damaged, even if there is a dimensional error such as a too-long protruding portion of the sheet  10 B of the radioactive-energy-accumulating fluorescent substance.  
         [0091]     The descriptions for the second embodiment of the present invention end with the preceding paragraph. From now, descriptions will be provided for a third embodiment of the present invention. An IP and a cassette according to the third embodiment of the present invention have the substantially same configurations as the IP and the cassette according to the first embodiment of the present invention have. For this reason, in the third embodiment, elements which are the same as those of the first embodiment are denoted by the same reference numerals, and the descriptions for the elements will be omitted. The third embodiment will be described while focusing on what makes the third embodiment different from the first embodiment.  
         [0092]      FIG. 7  is a cross-sectional view of the IP and the cassette according to the third embodiment of the present invention, taken along the A-A′ line of  FIG. 1 .  
         [0093]     As described above, the IP  10  according to the first embodiment is obtained by adhering the sheet  10 B of the radioactive-energy-accumulating fluorescent substance to the top of the substrate  10 A in a way that the sheet  10 B of the radioactive-energy-accumulating fluorescent substance is shifted, as shown in  FIG. 4 . Unlike the IP  10  according to the first embodiment, however, an IP  60  according to the present embodiment is obtained by forming a step in a side surface of a substrate  60 A, adhering a sheet  60 B of the radioactive-energy-accumulating fluorescent substance to the top of the substrate  60 A, and thereby forming a protruding portion  60 ′ which is configured of the sheet  60 B of the radioactive-energy-accumulating fluorescent substance and the upper portion of the substrate  60 A. The forming of the protruding portion  60 ′ of the sheet  10 B of the radioactive-energy-accumulating fluorescent substance and the upper portion of the substrate  60 A makes it possible to increase the strength of the protruding portion  60 ′. This protruding portion  60 ′ is also an example of the front portion as recited in the present invention.  
         [0094]     In addition, in the case of a cassette  50  according to the present embodiment, a recording-side portion  52   a  opposed to the protruding portion  60 ′ of the IP  60  dents under a substrate-side portion  52   b  opposed to a lower portion of the substrate  60 A. The recording-side portion  52   a  is provided with a cushioning material  52   c  (for example, leather) configured to absorb a shock which occurs when the protruding portion  60 ′ hits the recording-side portion  52   a.  The cushioning material  52   c  is an example of a shock absorbing member as recited in the present invention.  
         [0095]     The IP  60  and the cassette  50  according to the present embodiment make it possible to efficiently suppress breaking of the sheet  60 B of the radio-energy-accumulating fluorescent substance, because the strength of the protruding portion  60 ′ of the IP  60  is increased, and because a shock on the protruding portion  60 ′ is absorbed by the cushioning material  52   c  of the cassette  50 .  
         [0096]     The foregoing descriptions have been provided for the case where the two steps are formed in the side surface of the IP. In the case of the image recording plate as recited in the present invention, however, three steps or more may be formed in the side surface.  
         [0097]     In addition, the foregoing descriptions have been provided for the case where the plate spring is used as the biasing member configured to bias the IP toward the cassette. In the case of the biasing member as recited in the present invention, however, any elastic member other than the plate spring may be used as the biasing means.  
       EXAMPLE  
       [0098]     Descriptions will be provided below for an example of the present invention.  
         [0000]     (1) Preparation of Various Members Constituting IP  
         [0099]     A plane substrate (with the in-frame dimension of 174 mm×239 mm), a radiograph converting panel (with the dimension of 178 mm×238 mm; its edge is chamfered) and a double-sided adhesive sheet (with a dimension of 172 mm×237 mm, a 3M product, 4597FL) were prepared for use. A POM (polyoxymethylene)-made frame with a 0.7-mm height and a 5-mm width was formed in the two short sides and one long side of the plane substrate. Specifically, the radiograph converting panel was prepared by using the same method as in the example described in US Patent Publication Number 2006/0065852 A1.  
         [0000]     (2) Adhesion of Double-Sided Adhesive Sheet to Substrate  
         [0100]     First of all, a detachment film on the top side of the double-sided adhesive sheet was peeled off to expose the adhesive surface on the top side.  
         [0101]     Subsequently, the substrate with the frames formed thereon was fixed to the top of a base whose surface surrounded by the frames was flat or slightly dented. Thereafter, the top of the resultant substrate was cleaned of dust. Afterward, the double-sided adhesive sheet was brought into intimate contact with the approximate center of the surface of the substrate surrounded by the frames. The double-sided adhesive sheet thus adhered was visually observed, and neither dust nor an air bubble was seen.  
         [0000]     (3) Adhesion of Radiograph Conversion Panel to Substrate  
         [0102]     The radiograph conversion panel was obtained by chamfering the edge portion of the layer of the fluorescent substance, and by thereafter applying resin to the edge. Subsequently, the radiograph conversion panel was adhered to the resultant substrate with the double-sided adhesive sheet interposed in-between such that the two marginal end portions of the radiograph conversion panel protrude from the long side of the substrate without a frame by 2 mm (the short sides of the substrate correspond to the short sides of the radiograph converting panel, respectively). Here, a portion of the radiograph conversion panel which protrudes from the substrate is equal to a protruding portion of the IP which will be described later. Incidentally, the remaining detachment film of the double-sided adhesive sheet on the substrate was peeled off immediately before adhering the radiograph conversion panel to the substrate. The radiograph conversion panel thus adhered was visually observed, and no damage was seen on the radiograph converting panel from the long side of the substrate which was provided with no frame.  
         [0000]     (4) Preparation of Cassette and Insertion of IP in Cassette  
         [0103]     A cassette as follows was prepared for use. The IP was capable of being inserted in the cassette from the long side thereof. The interior of the cassette had a 0.5-mm play in total. The side farthest away from the insertion port of the cassette had a concave portion capable of accommodating the protruding portion (2 mm) of the IP. More specifically, the concave portion is a groove with a 2.3-mm depth, a 1.0-mm width and a 240-mm length. Furthermore, the insertion lid was provided with a spring mechanism configured to bias the IP inward by 500 gf. When the IP was inserted in the cassette, a positional relationship between the side end of the layer of the fluorescent substance on the protruding portion of the IP which was the farthest away from the insertion port of the cassette and the external side end of the cassette which was the farthest away from the insertion port of the cassette represented a 0.5 mm difference in distance between the two.  
         [0000]     (5) Radiographing for Mammography  
         [0104]     The IP loaded in the cassette was radiographed by an X-ray generating apparatus with a Mo (molybdenum) tube (28 KV). In this occasion, a mammography phantom (a sample of an object) was placed on the radiographing surface of the cassette, and was arranged such that the external side of the cassette which was designed to contact the chest wall was brought into contact with one side of the mammography phantom. Subsequently, the mammography phantom was radiographed. Thereafter, the film was observed, and it was found that part of the radiograph of the mammography phantom was missing by 0.5 mm from the chest wall.  
         [0105]     The present example made it possible to reduce a missing portion of the radiograph down to approximately 0.5 mm from the chest wall as described above, although, in the case of the conventional technique, part of a radiograph is missing by approximately 5 mm from the chest wall. By this, the present invention was proved to be effective.  
         [0106]     It should be noted that, although the IP made of the radioactive-energy-accumulating fluorescent substance is used as the image recording plate, it goes without saying that the IP may be of an application type, of a vapor deposition type, or of any other type. The IP of the application type is obtained by dispersing the radioactive-energy-accumulating fluorescent substance in a binding agent, and by thus applying the resultant fluorescent substance. The IP of the vapor deposition type is obtained by forming the radioactive-energy-accumulating fluorescent substance in a column structure by vapor deposition.  
         [0107]     In addition, a radiograph detector of a fixed-detector type may be used as the image recording plate. The radiograph detector of this type generates electric charges when irradiated with radioactive rays, and obtains a radiograph of an object by accumulating or reading the electric charges thus generated. In this case, unlike the IP, the radiograph detector used as the image recording plate need not be taken out of the cassette when the radiograph is going to be read from the image recording plate. However, the radiograph detector used as the image recording plate has the same effect as the IP used as the image recording plate has in a sense that a missing portion of a radiograph to be made can be reduced without decreasing the strength of the cassette.