Patent Publication Number: US-2023144028-A1

Title: Radiographic imaging apparatus and method for manufacturing the same

Description:
BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to a radiographic imaging apparatus that images a subject using radiation, and a method for manufacturing the radiographic imaging apparatus. 
     Description of the Related Art 
     Radiographic imaging apparatuses, which acquire a radiographic image by detecting an intensity distribution of radiation transmitted through a subject to be imaged, are widely and commonly used in medical diagnostic scenes and industrial non-destructive inspection scenes. Practical examples of the radiographic imaging apparatuses that acquire the radiographic image include imaging apparatuses using a flat panel detector (FPD) having a grid-like arrangement of pixels each including a minute photoelectric conversion element to which a semiconductor process technique is applied and a switching element. 
     The above-described radiographic imaging apparatuses are used in various scenes at medical sites, and are used not only in general imaging rooms but also during ward rounds and emergency care. The radiographic imaging apparatuses may be used in direct contact with patients in various conditions at medical sites, and thus are often cleaned and disinfected with a disinfectant such as alcohol after being used. However, in some situations, the radiographic imaging apparatuses may be unable to be cleaned or disinfected sufficiently. Application of antibacterial treatment to the radiographic imaging apparatuses in consideration of such situations can be an effective method for reducing an infection risk. 
     Meanwhile, portable radiographic imaging apparatuses are frequently used while being inserted under the subject such as a patient, and frequently stored in and taken from a box mounted on a ward round trolley, a storeroom, or the like. Thus, the surface of a casing (also called an “exterior”) thereof is required to have rub-fastness. Applying the antibacterial treatment to the casing of such a radiographic imaging apparatus can create a risk that an antibacterial agent that has peeled from the casing may attach to the patient or enter a wound of the patient, for example. Thus, the coating film strength of an antibacterial layer in applying the antibacterial agent to the casing is important. 
     The size of the radiographic imaging apparatus reaches as large as approximately 460 mm×460 mm in the case of a large one, while the thickness thereof is as extremely thin as approximately 15 mm. Further, a large number of components, such as a radiation detector corresponding to the above-described flat panel detector, a support base supporting the radiation detector, and electric boards, are accommodated within the thickness of approximately 15 mm. Thus, a member large in area but extremely thin in thickness is used to form the casing of the radiographic imaging apparatus. 
     Further, the radiographic imaging apparatus may be used while being laid under the subject such as a patient or be impacted by being accidentally dropped by a user, and thus is also required to be robust enough to withstand such situations. Further, the radiographic imaging apparatus is desired to be as lightweight as possible in consideration of being carried by the user. For example, carbon fiber reinforced plastic (CFRP) is often employed as a material for the casing satisfying these various characteristics. 
     Generally, possible methods for obtaining sufficient coating film strength in the antibacterial treatment include a method that fuses particles of the antibacterial agent or the antibacterial agent and a base material using heating treatment, and a method that thermally cures the antibacterial agent by adding a curing agent. However, applying heat to the thin large-area casing (e.g., the casing made of CFRP) may cause a deformation or contraction, leading to a visual defect or damage on the casing of the radiographic imaging apparatus. Thus, it is desirable to apply the antibacterial treatment at room temperatures, but it may be difficult to achieve high coating film strength at room temperatures. 
     SUMMARY 
     Aspects of the present disclosure are directed to providing a radiographic imaging apparatus with antibacterial treatment applied to the surface of a casing thereof with sufficient coating film strength, without impairing the external appearance of the radiographic imaging apparatus. 
     According to an aspect of the present disclosure, a radiographic imaging apparatus includes a radiation detector configured to convert incident radiation into an electric signal related to a radiographic image, a casing containing the radiation detector, and an antibacterial layer formed on at least part of a surface of the casing. An average thickness of the antibacterial layer is thicker than 0.05 μm and thinner than 0.5 μm. 
     Further, aspects of the present disclosure include a method for manufacturing the above-described radiographic imaging apparatus. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A and  1 B  illustrate an example of an external appearance of a radiographic imaging apparatus according to an exemplary embodiment of the present disclosure. 
         FIG.  2    illustrates an example of an internal configuration of the radiographic imaging apparatus according to the exemplary embodiment of the present disclosure, in A-A′ cross section in  FIG.  1 B . 
         FIGS.  3 A to  3 E  illustrate examples of a configuration at and near a front cover, which is indicated by a broken line box B in  FIG.  2   , in the radiographic imaging apparatus according to the exemplary embodiment of the present disclosure. 
         FIG.  4    illustrates an example of a configuration at and near a frame, which is indicated by a broken line box C in  FIG.  2   , in the radiographic imaging apparatus according to the exemplary embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An exemplary embodiment of the present disclosure will be described below with reference to the attached drawings. Details of configurations that will be described in the exemplary embodiment of the present disclosure are not limited to those in the specification and the drawings. Further, X rays are desirably used as radiation in the exemplary embodiment of the present disclosure, but the radiation is not limited to X rays and includes, for example, α rays, β rays, and γrays in the exemplary embodiment of the present disclosure. 
       FIGS.  1 A and  1 B  illustrate an example of an external appearance of a radiographic imaging apparatus  100  according to an exemplary embodiment of the present disclosure. 
     More specifically,  FIG.  1 A  illustrates a radiographic imaging apparatus  100  according to the present exemplary embodiment as viewed from a side where a radiation incident surface  101  on which radiation R is incident is located.  FIG.  1 A  also illustrates an XYZ coordinate system in which a Z direction is a direction in which the radiation R is incident, and an X direction and a Y direction are two directions perpendicular to the Z direction and orthogonal to each other.  FIG.  1 B  illustrates the radiographic imaging apparatus  100  according to the present exemplary embodiment as viewed from a side on which a rear surface  102  is located, which is opposite to the side on which the radiation incident surface  101  illustrated in  FIG.  1 A  is located.  FIG.  1 B  also illustrates an XYZ coordinate system corresponding to the XYZ coordinate system illustrated in  FIG.  1 A . 
     As illustrated in  FIG.  1 A , a front cover  111  is disposed as a member forming the radiation incident surface  101  of the casing  110  of the radiographic imaging apparatus  100 . As illustrated in  FIG.  1 B , a rear cover  112  is disposed as a member forming the rear surface  102  of the casing  110  of the radiographic imaging apparatus  100 . Grip portions  1121  are provided in the rear cover  112  so as to enable a user to easily hold the radiographic imaging apparatus  100  with the user&#39;s hand, as illustrated in  FIG.  1 B . 
     Further, as illustrated in  FIG.  1 A , a frame  113  is disposed as a member forming a side surface  103 , with respect to the radiation incident surface  101 , of the casing  110  of the radiographic imaging apparatus  100 . The frame  113  is disposed to be interposed between the front cover  111  and the rear cover  112  at the side surface  103  of the casing  110  of the radiographic imaging apparatus  100 , and is joined with the front cover  111  and the rear cover  112 . Further, as illustrated in  FIG.  1 A , a user interface  120 , including a power switch, a light-emitting diode (LED) indicating a battery remaining amount, a ready switch indicating an imaging preparation state, and a connector for a power cable, is provided on the frame  113 . 
     Further, markings indicating the positions of the center of an imaging region, the user interface  120 , and the like are printed on the radiation incident surface  101  side of the front cover  111  of the casing  110  of the radiographic imaging apparatus  100 . The markings described here may be provided, for example, by directly painting the markings on the front cover  111  made of carbon fiber reinforced plastic (CFRP) or by sticking an illustrative sheet printed on a sheet material to the front cover  111 . 
     Further, an antibacterial layer  301  (refer to  FIG.  3 A ) is formed on the surface of the casing  110  of the radiographic imaging apparatus  100  by applying an antibacterial agent thereto. In this case, in the present exemplary embodiment, the antibacterial layer  301  may be formed on a part of the surface of the casing  110  of the radiographic imaging apparatus  100  instead of the entire surface of the casing  110  of the radiographic imaging apparatus  100 . In other words, the present exemplary embodiment includes a configuration in which the antibacterial layer  301  is formed on at least a part of the surface of the casing  110  of the radiographic imaging apparatus  100 . In the present exemplary embodiment, forming the antibacterial layer  301  by applying the antibacterial agent especially to the radiation incident surface  101 , which is a contact portion with a patient serving as a subject, the grip portions  1121  to be touched by the user, and/or the like is effective to reduce an infection risk. 
       FIG.  2    illustrates an example of an internal configuration of the radiographic imaging apparatus  100  according to the present exemplary embodiment, in A-A′ cross section in  FIG.  1 B . In  FIG.  2   , similar components to those illustrated in  FIGS.  1 A and  1 B  are denoted by the same reference numerals, and the detailed description thereof will be omitted.  FIG.  2    also illustrates an XYZ coordinate system corresponding to the XYZ coordinate system illustrated in  FIG.  1 B . 
     As illustrated in  FIG.  2   , the casing  110  of the radiographic imaging apparatus  100  includes the front cover  111  serving as the member forming the radiation incident surface  101 , the rear cover  112  serving as the member forming the rear surface  102 , and the frame  113  serving as the member forming the side surface  103 . The casing  110  of the radiographic imaging apparatus  100  is formed by these three members (the front cover  111 , the rear cover  112 , and the frame  113 ) in the present exemplary embodiment, but may be formed by a member into which these members are integrated. 
     A radiation detector  130 , a radiation shielding sheet  140 , a support base  150 , a substrate  160 , a shock absorption sheet  170 , a battery (not illustrated), and the like are contained in the casing  110  of the radiographic imaging apparatus  100  while being arranged at predetermined positions. 
     The radiation detector  130  is a radiation detection panel that detects the radiation R emitted from a radiation generation apparatus (not illustrated) and transmitted through the subject. More specifically, the radiation detector  130  is a radiation detection panel that detects the radiation R by converting the incident radiation R into an electric signal related to a radiographic image. The electric signal related to the radiographic image that is acquired by the radiation detector  130  is transferred to the outside of the radiographic imaging apparatus  100 , and is displayed on a monitor or the like as the radiographic image and used for a diagnosis or the like. The radiation detector  130  is generally formed using a glass substrate, and thus may be broken if receiving a strong impact or load, or a displacement. Thus, the radiation detector  130  is stuck to the support base  150  having high strength and flatness. 
     The radiation shielding sheet  140  has a function of protecting the substrate  160  such as an electric board from the radiation R transmitted through the subject and the radiation detector  130 , and a function of preventing the transmitted radiation R from being incident on the radiation detector  130  again due to reflection or the like. 
     The support base  150  supports the radiation detector  130  via the radiation shielding sheet  140 . 
     The substrate  160  such as an electric board is arranged closer to the rear surface  102  than the support base  150 . 
     The shock absorption sheet  170  is interposed between the front cover  111  and the radiation detector  130 , and used to protect the radiation detector  130  by absorbing an impact received by the casing  110 . 
     Further, the Japanese Industrial Standards (JIS) stipulates that the thickness of the radiographic imaging apparatus  100  is no thicker than approximately 15 mm, depending on the product, and the above-described inner components  130  to  170  are to be contained in the casing  110  having the thin thickness. 
     If the components arranged between the radiation incident surface  101  and the radiation detector  130  are formed of a substance having a high atomic weight, the transmitted amount of the radiation R reduces, resulting in a failure to acquire a radiographic image with a high-definition image quality or resulting in the need to increase the dose of the radiation R. Thus, basically, the front cover  111  serving as the member forming the radiation incident surface  101  is often made of a resin material instead of a metal material. In this case, CFRP is desirable as the resin material for forming the front cover  111  from the viewpoints of robustness and weight. In the present exemplary embodiment, the thickness of the front cover  111  made of CFRP is 1.5 mm or thinner, more desirably, 1.0 mm or thinner. 
     The radiation incident surface  101  is a contact surface with the subject such as a patient and is also a surface through which the radiation R is transmitted, and thus basically has no large uneven shape and is formed by a flat surface. On the other hand, the recess-shaped grip portions  1121  for enabling the user to easily hold the radiographic imaging apparatus  100 , a battery storage portion (not illustrated), and the like are provided on the rear surface  102  as illustrated in  FIG.  1 B . 
     Further, the user interface  120 , including the power button and the connector for the power cable, is provided on the side surface  103  as illustrated in  FIG.  1 A . This means that an uneven shape, a step, a groove, and the like are formed on the rear surface  102  and the side surface  103 . 
     The rear cover  112  forming the rear surface  102  and the frame  113  forming the side surface  103  have less influence on the transmittance of the radiation R, and thus may not necessarily be made of a resin material unlike the front cover  111  forming the radiation incident surface  101 , except in cases of considering the weight. On the contrary, it is advantageous to make the rear cover  112  forming the rear surface  102  and the frame  113  forming the side surface  103  by using a metal material because this can prevent the emitted radiation R from entering the inside of the radiographic imaging apparatus  100  again by being reflected within an imaging room. In a case where a metal material is employed for the rear cover  112  forming the rear surface  102  and the frame  113  forming the side surface  103 , the material is desirably as lightweight as possible and, for example, magnesium (Mg) or aluminum (Al) is suitable as the material. The present exemplary embodiment includes a configuration in which the rear cover  112  and the frame  113  serving as the members forming the rear surface  102  and the side surface  103  of the casing  110 , respectively, are at least partially made of a metal material. 
     Next, the antibacterial agent to be applied when the antibacterial layer  301  is formed on at least a part of the surface of the casing  110  of the radiographic imaging apparatus  100  according to the present exemplary embodiment will be described. 
     The antibacterial agent in the present exemplary embodiment refers to a substance having at least an effect of suppressing multiplication of bacteria and viruses, and includes an agent exhibiting a sterilization effect. Various antibacterial agents, such as organic and inorganic types, are proposed as the antibacterial agent, but the inorganic type is desirable in consideration of chemical resistance and effect on human bodies. In this case, examples of the inorganic antibacterial agent include a titanium-based type, a silver-based type, a copper-based type, a zinc-based type, and a mercury-based type, but the titanium-based type, the silver-based type, and the copper-based type are particularly desirable in consideration of the viewpoints of the antibacterial effect and the use on the contact portion with the subject such as a patient. 
     Further, in recent years, a photocatalyst has been often used as the antibacterial agent. Especially, the development of titanium oxide-based antibacterial agents has been advanced, and an antibacterial agent exhibiting an antibacterial effect with not only ultraviolet light but also slight visible light has been developed (refer to Japanese Patent Application Laid-Open No. 2012-139690). Further, titanium oxide has less influence on human bodies. Moreover, even when used on the contact surface with the subject such as a patient, titanium oxide provides a less sticky texture and thus is suitable for use in the radiographic imaging apparatus  100 . The types of titanium oxide include an anatase type, a rutile type, a brookite type, and an amorphous type, and the anatase type and the rutile type are desirable from the viewpoint of the antibacterial effect. In the present exemplary embodiment, in a case where titanium oxide is used as the antibacterial agent, the antibacterial agent includes not only titanium oxide itself but also a titanium oxide-based antibacterial agent. Further, in the present exemplary embodiment, titanium oxide supported by a porous member, such as hydroxyapatite, activated carbon, zeolite, and silica gel, may also be used as titanium oxide. Further, titanium oxide coated with resin such as silicone, or titanium oxide doped with sulfur may be used. 
     The antibacterial agent comes in various states such as powder and sol, but the antibacterial agent in sol state is suitable for the coating purpose in the present exemplary embodiment because the antibacterial agent is assumed to be applied in a state of being dispersed in a liquid. 
       FIGS.  3 A to  3 E  illustrate examples of a configuration at and near the front cover  111 , which is indicated by a broken line box B in  FIG.  2   , in the radiographic imaging apparatus  100  according to the present exemplary embodiment. In  FIGS.  3 A to  3 E , similar components to those illustrated in  FIGS.  1 A,  1 B, and  2    are denoted by the same reference numerals, and the detailed description thereof will be omitted. Each of  FIGS.  3 A to  3 E  also illustrates an XYZ coordinate system corresponding to the XYZ coordinate system illustrated in  FIG.  2   . 
     As indicated by each of the configuration examples illustrated in  FIGS.  3 A to  3 E , the antibacterial layer  301  is formed on the radiation incident surface  101  side of the front cover  111  in the present exemplary embodiment. Further, the front cover  111  is formed using CFRP in the present exemplary embodiment. More specifically,  FIG.  3 A  illustrates the configuration example in which only the antibacterial layer  301  is formed on the radiation incident surface  101  side of the front cover  111 .  FIG.  3 B  illustrates the configuration example in which a base layer  302  is interposed between the front cover  111  and the antibacterial layer  301  illustrated in  FIG.  3 A .  FIG.  3 C  illustrates the configuration example in which a print layer  303  is interposed between the front cover  111  and the antibacterial layer  301  illustrated in  FIG.  3 A .  FIG.  3 D  illustrates the configuration example in which the base layer  302  illustrated in  FIG.  3 B  is interposed between the print layer  303  and the antibacterial layer  301  illustrated in  FIG.  3 C .  FIG.  3 E  illustrates the configuration example in which an illustrative sheet  304  is interposed between the front cover  111  and the antibacterial layer  301  illustrated in  FIG.  3 A . 
     The present exemplary embodiment is characterized in that the average thickness of the antibacterial layer  301  formed on the radiation incident surface  101  side of the front cover  111  is thinner than 0.5 μm. The antibacterial layer  301  illustrated in  FIGS.  3 A to  3 E  is extremely thin in order to reduce contact between particles of the antibacterial agent applied in forming the antibacterial layer  301 , thereby actively bring the antibacterial agent and the base material into contact with each other. In many cases, general antibacterial agents for use in coating applications are thermally cured to enhance adhesion by blending a curing agent and a reactive group in a solution in which the antibacterial agent is dispersed, or are heated at a high temperature to establish strong adhesion between the antibacterial agent particles without a curing agent. Examples of a method for curing the antibacterial agent include a method using ultraviolet light, but titanium oxide is not suitable for fixation using ultraviolet curing because titanium oxide absorbs ultraviolet light. 
     Applying heat to the members forming the casing  110  of the radiographic imaging apparatus  100 , especially to the front cover  111  made of CFRP may cause contraction or a deformation, and thus heating such a member is not desirable. If the front cover  111  of the casing  110  of the radiographic imaging apparatus  100  is warped on the radiation incident surface  101  side, there may be a case where the edge of the side surface of the front cover  111  is lifted. The lifted edge of the side surface of the front cover  111  may cause an injury to the subject, such as a patient, touching the edge, or cause a gap between the front cover  111  and the frame  113  and result in entry of a disinfectant into the radiographic imaging apparatus  100  and also a leak of light from the gap. Especially, in a case where paint is applied to the front cover  111 , the deformation caused by heating the front cover  111  has a significant influence due to a difference in heat contraction rate, and the paint may crack in some cases. Further, the thermal deformation depends on the thickness of the front cover  111 . If the thickness of the front cover  111  is 1.5 mm or thinner, a thermal deformation is likely to occur even at a temperature of approximately 60° C. If the thickness of the front cover  111  is 1.0 mm or thinner, a deformation may occur even at a temperature of approximately 50° C. or lower. On the other hand, increasing the thickness of the front cover  111  leads to a failure to accommodate the components within the casing  110  and an increase in the weight. In light of this, in the present exemplary embodiment, the thickness of the front cover  111  is 1.5 mm or thinner, more desirably, 1.0 mm or thinner. 
     Further, in a case where no heat is applied when the antibacterial layer  301  is formed on the radiation incident surface  101  side of the front cover  111 , the antibacterial agent particles having weak adhesion therebetween and failing to strongly adhere with the aid of, for example, an intermolecular force with the base material, can easily peel off. The radiographic imaging apparatus  100  of a mobile type (a portable type) is used in direct contact with the subject who is a patient, and thus the coating film strength of the antibacterial agent is especially important for the mobile type. 
     In the present exemplary embodiment, the average thickness of the antibacterial layer  301  formed on the radiation incident surface  101  side of the front cover  111  illustrated in  FIGS.  3 A to  3 E  is desirably thicker than 0.05 μm and thinner than 0.5 μm. More desirably, the average thickness of the antibacterial layer  301  formed on the radiation incident surface  101  side of the front cover  111  is 0.1 μm to 0.3 μm (0.1 μm or thicker and 0.3 μm or thinner). For example, if the average thickness of the antibacterial layer  301  formed on the radiation incident surface  101  side of the front cover  111  is thicker than 0.5 μm, the antibacterial layer  301  may fail. In other words, this condition causes damage to the external appearance of the radiographic imaging apparatus  100  and also makes it difficult to perform the antibacterial treatment of the surface of the casing  110  with sufficient coating film strength. On the other hand, if the average thickness of the antibacterial layer  301  formed on the radiation incident surface  101  side of the front cover  111  is thinner than 0.05 μm, the antibacterial agent may peel off in the form of a film, or a sterilization effect of ultraviolet light may be unable to be obtained in a case where titanium oxide is used as the antibacterial agent. 
     In other words, this condition causes damage to the external appearance of the radiographic imaging apparatus  100  and also makes it difficult to perform the antibacterial treatment of the surface of the casing  110  with sufficient coating film strength. Examples of a method for measuring the average thickness of the antibacterial layer  301  include a method that observes the cross section of the antibacterial layer  301  with an electron scanning microscope and calculates an average value of thicknesses at a plurality of points. 
     Further, in the radiographic imaging apparatus  100  according to the present exemplary embodiment, the adhesion strength of the antibacterial layer  301  is assumed to satisfy, for example, classification 2 in the cross-cut test defined in JIS-K5600-5-6. 
     Further, the use of titanium oxide as the antibacterial agent to be applied when the antibacterial layer  301  is formed has such an advantage that the antibacterial effect lasts a long time because titanium oxide is used as a solid, unlike silver ions and the like, and titanium oxide itself is not consumed, unlike silver ions. The radiographic imaging apparatus  100  is used over a plurality of years, and thus it is desirable to use titanium oxide capable of producing the long-lasting antibacterial effect, as the antibacterial agent to be applied when the antibacterial layer  301  is formed. Further, in the present exemplary embodiment, when the antibacterial layer  301  is formed on the surface of the casing  110 , the surface is coated by applying the antibacterial agent thereto, and thus the surface can be coated again at the time of breakage due to unexpected use. CFRP in which an antibacterial agent is kneaded at the pre-impregnated (prepreg) stage (refer to Japanese Patent Application Laid-Open No. 2021-51069) is not desirable because the need to replace the expensive CFRP itself arises when the antibacterial effect vanishes. 
     Further, in the present exemplary embodiment, the average particle diameter of the antibacterial agent to be applied when the antibacterial layer  301  is formed is desirably 10 nm to 100 nm (10 nm or larger and 100 nm or smaller, or 0.01 μm or larger and 0.1 μm or smaller). More specifically, in the present exemplary embodiment, the antibacterial agent to be applied when the antibacterial layer  301  is formed is small in average particle diameter and thus is large in surface area, thereby making it possible to enhance the antibacterial effect even if the antibacterial layer  301  is thin. Pulverized titanium oxide used as a white pigment is not desirable as the antibacterial agent according to the present exemplary embodiment because the average particle diameter thereof is large and visible light is easily scattered thereby. 
     Further, in the present exemplary embodiment, the antibacterial layer  301  contains a metal material such as titanium oxide, but has an extremely small influence on the transmittance of the radiation R because the average thickness of the antibacterial layer  301  illustrated in  FIGS.  3 A to  3 E  is thinner than 0.5 μm. Further, because the average particle diameter is smaller than the wavelength of visible light, the antibacterial layer  301  has less influence on the visibility of the print layer  303 , which is located on a more inner side than the antibacterial layer  301  in the configuration examples illustrated in  FIGS.  3 C and  3 D . 
       FIG.  4    illustrates an example of a configuration at and near the frame  113 , which is indicated by a broken line box C in  FIG.  2   , in the radiographic imaging apparatus  100  according to the present exemplary embodiment. In  FIG.  4   , similar components to those illustrated in  FIGS.  1 A to  3 E  are denoted by the same reference numerals, and the detailed description thereof will be omitted. Further,  FIG.  4    also illustrates an XYZ coordinate system corresponding to the XYZ coordinate system illustrated in  FIG.  2   . 
     As illustrated in  FIG.  4   , in the present exemplary embodiment, the antibacterial layer  301  is formed on the surface of the rear cover  112  forming the rear surface  102  and the surface of the frame  113  forming the side surface  103 , in addition to the surface of the front cover  111  forming the radiation incident surface  101 . In the example of  FIG.  4   , the average thickness of the antibacterial layer  301  on the surface of the rear cover  112  forming the rear surface  102  and the surface of the frame  113  forming the side surface  103  is thicker than the average thickness of the antibacterial layer  301  on the surface of the front cover  111  forming the radiation incident surface  101 . More specifically, in the present exemplary embodiment, the average thickness of the antibacterial layer  301  on the surface of the front cover  111  forming the radiation incident surface  101  is desirably thicker than 0.05 μm and thinner than 0.5 μm as described above. In the present exemplary embodiment, the average thickness of the antibacterial layer  301  on the surface of the rear cover  112  forming the rear surface  102  and the surface of the frame  113  forming the side surface  103  is desirably thicker than 0.5 μm. 
     With the configuration according to the present exemplary embodiment, the antibacterial layer  301  with excellent abrasion resistance can be formed also on the frame  113  serving as the member forming the side surface  103  and the rear cover  112  serving as the member forming the rear surface  102 , without applying heat thereto. As described above, the antibacterial layer  301  on the rear surface  102  and the side surface  103  has less influence on the transmittance of the radiation R even if being thicker than the antibacterial layer  301  on the radiation incident surface  101 . If, for example, a printed marking requiring visibility is not present on the rear surface  102  or the side surface  103 , the antibacterial layer  301  may not necessarily be thinly formed on the rear surface  102  or the side surface  103 . 
     Further, the strength of the rear cover  112  serving as the member forming the rear surface  102  and the frame  113  serving as the member forming the side surface  103  is enhanced by provision of an uneven shape thereto, and this can reduce the deformation due to heating even when CFRP is used as the material. Further, if being made of a metal material, the rear cover  112  and the frame  113  can be heated. It is difficult to make the front cover  111  serving as the member forming the radiation incident surface  101 , using a metal material as described above. On the other hand, it is possible to make the rear cover  112  and the frame  113  using a metal material. Thus, in a case where the rear cover  112  and the frame  113  are made of a metal material, the adhesion of the antibacterial agent can be improved by heating after the application of the antibacterial agent. Further, in this case, the rear cover  112  and the frame  113  can be corrected into an appropriate shape by annealing treatment. 
     The rear cover  112  and the frame  113  may not necessarily be entirely made of a metal material, and may be at least partially made of a metal material. For example, the rear cover  112  and the frame  113  may be partially formed of a metal material within a range capable of suppressing the deformation due to heating, and an area around the metal material may be thickened with a resin material by insert molding. 
     Further, the advantages of using the photocatalyst as the antibacterial agent according to the present exemplary embodiment include an effect of blocking ultraviolet light. Ultraviolet light (UV) is known to be capable of destroying bacteria and viruses but has an issue where a material irradiated with ultraviolet light is deteriorated. The photocatalyst is capable of absorbing ultraviolet light, and the antibacterial agent having extremely small particles is employed in the present exemplary embodiment. Thus, the penetration of ultraviolet light into the inside of the casing  110  can be hindered by reducing gaps between the particles to create a state in which the photocatalyst is densely distributed. 
     Referring now back to  FIGS.  3 A to  3 E , the present exemplary embodiment will be further described. 
     As illustrated in  FIG.  3 C , the print layer  303  may be interposed between the front cover  111  and the antibacterial layer  301  in the present exemplary embodiment. By employing a white pigment containing rutile-type titanium oxide or a black pigment containing carbon black as paint for the print layer  303 , the deterioration of the paint can be suppressed even if ultraviolet light passes through the antibacterial layer  301  and enters the inside of the casing  110 . 
     Further, in the present exemplary embodiment, the casing  110  contains CFRP and the metal member robust against ultraviolet light in the base material, and thus has less deterioration and prevents ultraviolet light from reaching as far as the inside of the casing  110  in which the internal components including the substrate  160  are arranged. 
     The radiographic imaging apparatus  100  includes portions difficult to disinfect with alcohol, such as the electric contact with the battery and the connection portion with the power supply cable. Ultraviolet sterilization is effective for such portions. Disposing the antibacterial layer  301  according to the present exemplary embodiment near the electric contact enables the electric contact to be sterilized without alcohol disinfection. 
     The radiographic imaging apparatus  100  according to the present exemplary embodiment makes it possible to prevent multiplication of and infection with bacteria and viruses by using the antibacterial effect and the ultraviolet sterilization in combination. 
     In the present exemplary embodiment, the surface of the casing  110  is to be thinly coated with the antibacterial agent so that the antibacterial layer  301  illustrated in  FIGS.  3 A to  3 E  has an average thickness thinner than 0.5 μm as described above. 
     One method for achieving the extremely thin film thickness of the antibacterial layer  301  is a vaper deposition-based method conventionally used for semiconductors or the like, but this method leads to a significant cost increase and thus is not appropriate as the coating method for the radiographic imaging apparatus  100 . Coating methods such as spin-coating, spraying, and dipping enable the application of the antibacterial agent at a relatively low cost, but it is difficult to achieve the film thickness of the antibacterial layer  301  thinner than 0.5 μm by simply applying the antibacterial agent. 
     In light of this, in a method for manufacturing the radiographic imaging apparatus  100  according to the present exemplary embodiment, a coating solution in which the antibacterial agent is dispersed in a solvent having a saturated vapor pressure of 1 mmHg or higher, more desirably, 10 mmHg or higher at a temperature of 20° C. is applied to the surface of the casing  110  when the antibacterial layer  301  is formed thereon. The saturated vapor pressure of 10 mmHg or higher enables the solvent to be evaporated quickly after the application at room temperature, and there is less concern that the antibacterial agent particles may aggregate when the solvent is evaporated or the solvent may remain without being evaporated. On the other hand, too fast evaporation causes non-uniform application, and thus the saturated vapor pressure at a temperature of 20° C. is desirably 10 mmHg. 
     Further, in the method for manufacturing the radiographic imaging apparatus  100  according to the present exemplary embodiment, a contact angle between the coating solution and a coating surface, which is a surface of the casing  110 , is desirably 60 degrees or smaller when the antibacterial layer  301  is formed thereon. The contact angle within this range provides high wettability and enables the coating solution to quickly wet the surface and spread thereon at the time of the coating, thereby obtaining the thin uniform antibacterial layer  301 . In contrast, if the contact angle is large, the amount of the coating solution is to be increased, thereby resulting in an increase in the film thickness of the antibacterial layer  301 . Also in this case, the molecules of the solvent are likely to gather when the solvent is evaporated, thereby causing unevenness in the distribution of the antibacterial agent. 
     Further, in the method for manufacturing the radiographic imaging apparatus  100  according to the present exemplary embodiment, the coating solution desirably uses a solvent having a surface tension of 70 dyn/cm or lower, more desirably, 50 dyn/cm or lower at a temperature of 20° C. when the antibacterial layer  301  is formed. Reducing the surface tension of the coating solution in this manner can broaden choices of the material for forming the coating surface, thereby enabling the above-described contact angle to be adjusted to 60 degrees or smaller even with hydrophobic CFRP. Examples of the solvent to be used include ethanol, isopropyl alcohol, and ethyl acetate, but are not limited thereto. The solvent to be used may be one type of solvent, or two or more types of solvents mixed together. 
     Further, to apply the antibacterial agent to the surface of the casing  110 , the antibacterial agent is to be dispersed as evenly as possible in the coating solution. In the present exemplary embodiment, water can be mixed in the solvent within a range that satisfies the above-described saturated vapor pressure and surface tension in order to increase the dispersibility of the antibacterial agent in the solution. Adding water in this manner enables the antibacterial agent to be applied to the base material while maintaining an even concentration distribution. The solution containing such an antibacterial agent is less viscous, and thus spin-coating or spray-coating is desirable from the viewpoint of the application of the low viscous solution, and spin-coating is more desirable from the viewpoint of the reduction in the film thickness. 
     Further, a dispersant may be added to the solution as another method for facilitating the dispersion of the antibacterial agent. In this case, examples of the dispersant include polyhydric alcohols such as polyether polyol and polyester polyol, fatty acid salt such as magnesium stearate, aliphatic amine, sulfonate, and polysiloxanes, but are not limited thereto. 
     Further, the temperature at which the surface of the casing  110  is coated with the antibacterial agent is desirably 60° C. or lower, more desirably, 50° C. or lower in order to suppress the deformation of the base material. Under a low-temperature environment, a temperature not causing aggregation or separation of the content is desirable and the antibacterial agent is desirably applied under an environment of, for example, 5° C. or higher, though this depends on the solvent and the blending agent. 
     Further, in the present exemplary embodiment, various materials other than the antibacterial agent can be blended together in the solution containing the antibacterial agent. In this case, examples of the blended materials include a stabilizer, a dispersant, a hydrophilizing agent, a viscosity modifier, and a pH modifier, but are not limited thereto. Further, a small amount of pigment may be blended in the solution so that the peel-off state of the antibacterial agent and the coating state can be checked. 
     Further, increasing the wettability between the coating solution and the coating surface, which is a surface of the casing  110 , is important in order to thinly form the antibacterial layer  301  as described above. Thus, the present exemplary embodiment provides a configuration that improves the coatability by not only defining the properties of the coating solution to be used but also performing hydrophilic treatment of at least part of the surface of the casing  110  (the coating surface) to which the coating solution containing the antibacterial agent is to be applied. For example, the hydrophilicity can be improved by applying the hydrophilic treatment, such as plasma treatment or chemical treatment, to at least part of the surface of the casing  110  (the coating surface) before the coating solution containing the antibacterial agent is applied thereto. In a case where CFRP employed for a member forming the casing  110  is painted, the hydrophilicity can be increased by blending not only a surfactant agent and a hydrophilizing agent but also a hydrophilic compound in the paint. The range of the solvents usable from the viewpoint of the contact angle can be widened by increasing the hydrophilicity on the base material side in this manner. 
     Further, in the present exemplary embodiment, the base layer  302  may be additionally formed as illustrated in  FIGS.  3 B and  3 D  in order to reduce the surface tension of the surface (the coating surface) of the casing  110  to which the coating solution containing the antibacterial agent is to be applied. The use of the base layer  302  can improve the wettability of the surface to which the antibacterial agent is to be applied, without making an improvement to the base material or the paint, and thus is optimum as the hydrophilizing method. 
     In  FIG.  3 B , the base layer  302  is disposed between the front cover  111  made of CFRP and the antibacterial layer  301 . In  FIG.  3 D , the base layer  302  is disposed between the print layer  303  and the antibacterial layer  301 . 
     The base layer  302  is made of a hydrophilic material. The hydrophilic material employable for the base layer  302  is not particularly defined, but the material desirably includes polymer or metal having a hydrophilic group, an oxidized inorganic substance, or hydroxide as a structure thereof. Further, examples of the above-described polymer having a hydrophilic group include polymers having a silanol group, a carboxyl group, a hydroxy group, an oxyalkylene group, an amino group, a sulfone group, and the like, but are not limited thereto. Further, the thickness of the base layer  302  is not particularly defined, but the base layer  302  affects the absorption of the radiation R if being too thick, and thus the thickness thereof is desirably 10 μm or thinner. If the base layer  302  is heated when being applied, a deformation occurs in CFRP or the like forming the front cover  111 , and thus it is important to apply the base layer  302  without heating, similarly to the antibacterial agent for use in forming the antibacterial layer  301 . 
     Further, a layer that absorbs less visible light is desirable as the base layer  302  that is used on the radiation incident surface  101  side. In a case where the base layer  302  that can easily absorb or reflect visible light is used on the radiation incident surface  101  side, it is desirable to reduce the thickness of the base layer  302 . Further, the base layer  302  may contain the above-described disperser and curing agent, a silane coupling agent, a surfactant agent, an ultraviolet absorbent, and/or the like. 
     The user interface  120  including the power switch and the connector for the power cable, and the battery (not illustrated) are disposed on the casing  110  of the radiographic imaging apparatus  100  as described above, and a groove or the like may be formed at the joint portion. It is difficult to form the antibacterial layer  301  thinner than 0.5 μm on this groove portion by applying the antibacterial agent using spin-coating, but the groove portion is less likely to come into contact with an object and thus the antibacterial layer  301  may not necessarily have the thickness described in the present exemplary embodiment in such a portion from the viewpoint of abrasion resistance. 
     Further, in  FIG.  3 E , the illustrative sheet  304  is disposed between the front cover  111  and the antibacterial layer  301 . As illustrated in  FIG.  3 E , the illustrative sheet  304  may be used as the coating surface for applying the antibacterial agent that is used to form the antibacterial layer  301 . In the example of  FIG.  3 E , at the time of sticking the illustrative sheet  304  to the front cover  111 , the antibacterial layer  301  on the illustrative sheet  304  may crack or peel off. Thus, it is desirable to apply the antibacterial agent, which is used to form the antibacterial layer  301 , to the illustrative sheet  304  in a state where the illustrative sheet  304  has already been stuck to the front cover  111 . 
     As described above, the method for manufacturing the radiographic imaging apparatus  100  according to the present exemplary embodiment defines the film thickness (the average thickness) of the antibacterial layer  301 , the wettability of the coating surface, and the vapor pressure of the coating solution. This makes it possible to form the antibacterial layer  301  with high coating film strength without heating at the time of application of the antibacterial agent that is used to form the antibacterial layer  301  on at least the radiation incident surface  101  of the radiographic imaging apparatus  100 . Further, the radiographic imaging apparatus  100  can be provided without a defect such as a deformation on the surface of the casing  110  of the radiographic imaging apparatus  100 . 
     As described above, in the radiographic imaging apparatus  100  according to the present exemplary embodiment, the antibacterial layer  301  is formed on at least a part of the surface of the casing  110 , and the average thickness (σ) of the antibacterial layer  301  is thicker than 0.05 μm and thinner than 0.5 μm. 
     The above-described configuration makes it possible to provide the radiographic imaging apparatus  100  with the antibacterial treatment applied to the surface of the casing  110  with sufficient coating film strength, without impairing the external appearance of the radiographic imaging apparatus  100 . 
     The above-described exemplary embodiment of the present disclosure is merely an example of how to embody the present disclosure when implementing the present disclosure, and the technical scope of the present disclosure shall not be construed limitedly by the exemplary embodiment. An exemplary embodiment of the present disclosure can be implemented in various manners without departing from the technical idea thereof or the main features thereof. 
     According to the exemplary embodiment of the present disclosure, it is possible to provide a radiographic imaging apparatus with antibacterial treatment applied to a surface of a casing thereof with sufficient coating film strength, without impairing the external appearance of the radiographic imaging apparatus. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of priority from Japanese Patent Application No. 2021-183885, filed Nov. 11, 2021, which is hereby incorporated by reference herein in its entirety.