| 摘要 |
<p>A toroidal x-ray tube assembly (I) includes a toroidal housing (A) in which a rotor (20) is rotatably mounted. One or more cathodes (C) are mounted on the rotor for generating an electron beam which strikes an anode (B) to generate a beam of x-rays which pass through a patient aperture (62) to strike a detector (60). The assembly includes precollimators (70, 74) having slots (72, 76) for passage of the x-ray subsequent to generation thereof and prior to being collimated by a ring collimator (90). The ring collimator, which collimates the x-rays into a fan shaped beam, includes a first ring (92) and a second ring (94) which are concentric but of different diameters. The distance between the first and second rings (92, 94) is adjustable to adjust the slice thickness of the final image and cause the beam to cut-off when the smaller ring is received within the larger. <MATH></p> |
