1. Field of the Invention
The present invention relates to a radiation imaging apparatus that radiates a radiation onto an object to detect the radiation that transmits the object, and particularly, to a radiation imaging apparatus that uses an optical element that parallelizes the radiation which travels in a divergence manner.
2. Related Background Art
In an X-ray imaging apparatus including a single X-ray source, a distance between the X-ray source and the object is set based on a size of the object and a divergence angle of the X-ray source. If the distance between the X-ray source and the object is increased in order to obtain a required resolution, the size of the apparatus is increased and brightness is lowered. In order to remove such troubles, a technology is known, where an X-ray optical element such as a capillary is used to efficiently collect X-rays to create a high intensity X-ray and capture an image in a short time. Japanese Patent Application Publication (Translation of PCT Application) No. H10-508947 discloses an optical system including an optical element obtained by bundling minute glass tubes (referred to as capillaries). The X-ray is parallelized by the capillary so that the lowering of brightness caused by the increase in the distance where the X-ray reaches the object is restricted. Further, Japanese Patent Application Laid-Open No. 2004-89445 discloses an X-ray image capturing system in which X-ray sources are two-dimensionally disposed and combined with a capillary that restricts the divergence of a generated X-ray to form an image.
An optical element in which the capillaries are bundled is formed by an assembly of minute glass tubes manufactured by a hot drawing. Therefore, it is difficult to manufacture an assembly of capillaries having a large outer diameter (several tens centimeters) which may project a human body with a high precision.
Further, in a configuration in which a plurality of small capillaries is two-dimensionally disposed, X-ray generating sources also need to be two-dimensionally disposed. Therefore, the X-ray generating sources that use high power are two-dimensionally controlled, which causes the complexity of a control system.
The invention provides a radiation imaging apparatus that has a simple structure that efficiently parallelizes a generated radiation, restricts the lowering of the brightness without depending on the size of the object, and reduces the size of the apparatus.