The applications of computer-assisted, or comput(eriz)ed, tomography (CT) are reviewed. The major emphasis is on medical applications, but all relevant technical sciences are covered. A unified descriptive account of the underlying principles is presented (detailed reviews of algorithms and their mathematical backgrounds can be found elsewhere in this special issue). Deficiencies in existing hardware and software are identified and the possible means of remedying the more urgent of these are outlined. Promising approaches for future research and development into CT are suggested.

Overview of computerized tomography with emphasis on future developments

A toroidal x-ray tube (I) is supported (II) for rotation about a horizontal axis (170), translation along a vertical axis (172), and translation along a horizontal axis (174). The x-ray tube includes a toroidal housing (A), an annular anode (B), and a cathode (0) which rotates a beam of electrons around the annular anode. A plurality of parallel connected voltage sources (901, 902, . . . , 90n) provide a sufficiently high bias voltage between the electron source and the anode that x-rays are generated. The x-ray beam passes through a compensator crystal (62), an annular window (20), a collimator (132), through a subject received in a central bore (26) of the x-ray tube, and impacts an arc segment of radiation detectors (130). The x-ray detectors are stationarily mounted outside of the plane of the annular window (FIGS. 2 and 7), nutate into the plane of the windows opposite of the origin of the x-ray beam (FIG. 6 ), rotate in part (FIG. 9 ) or rotate in full (FIG. 8 ) Angular position monitors (58, 154) determine the angular position of the cathode assembly, hence the x-ray beam, and the angular position of the detectors in the rotating detector embodiment.

Computerized tomographic scanner having a toroidal x-ray tube with a stationary annular anode and a rotating cathode assembly

A toroidal x-ray tube housing (A) has an evacuated interior. An annular anode (B) is connected with the housing closely adjacent the window such that a cooling fluid passage (12) is defined in intimate thermal communication with the anode. A cathode assembly (32) is mounted within the evacuated housing or an annular ring (30) that rotates an electron beam (22) around the large diameter annular anode. In the embodiment of FIGS. 1 and 2, the annular ring is magnetically levitated (40) and rotated by a motor (50). A collimator (62) and filter (64) are rotated with the cathode assembly closely adjacent an electron emitter or cathode cup (32) such that the generated x-rays are collimated and filtered within the x-ray tube. Preferably, a plurality of cathode cups (120) are provided, whose operation is selected by a series of magnetically controlled switches (76). The cathode cup is insulated (106) from the annular ring and isolated by a transformer (104, 112) from the filament current control switches. In the embodiment of FIGS. 4-6, the cathode assembly (C) includes a multiplicity of stationarily mounted electron cups (120) which are selectively actuated to rotate the electrode beam by a switch (130). An electron beam scan control (134) may bias the potential applied to grids (124, 126) to scan the electron beam generated by electron emitter over a commensurate arc length of the anode with the arc length of the emitter. In the embodiment of FIG. 7 , multiple anode surface as well as multiple cathode cups are provided.

Ring tube x-ray source

A toroidal x-ray tube housing (A) is composed of multiple sections which are clamped together and sealed by elastomeric gaskets (128). An annular anode (B) is mounted to the housing with coolant passages (12, 14) extending thereadjacent. A rotor (30) is rotated within the toroidal housing by a motor (60). At least one cathode assembly (C) is mounted to the rotor adjacent the anode. The rotor is supported by magnetic bearings (40) whose active coils are separated from the vacuum region by a magnetic window (48). Alternately, a series of vanes (136, 138) are provided to divide the vacuum chamber into a high vacuum region (132) adjacent the cathode and anode and a low vacuum region (134) adjacent the motor (60) and bearings (40, 150, 152) for rotatably supporting the rotor within the housing. An active vacuum pump, preferably a ion pump (112) and a getter (114) are hermetically sealed into the vacuum region for maintaining the vacuum.

Ring tube x-ray source with active vacuum pumping

Cardiac computed tomography imaging: a history and some future possibilities

Computerized tomographic imaging of the heart has great potential diagnostic value. The difficulty is that heart motion limits the data acquisition time to below 0.1 sec., but standard X-ray sources are not of sufficient intensity or mobility. A simple solution is proposed by using a rotating cathode filament with a fixed large stationary circular anode. In this design, X-ray detectors are placed on a concentric circle interior to the anode. To allow true planar X-ray projections, the detectors near the focal spot which would block the X-ray beam are moved synchronously out of the slice plane. An alternative method is also discussed where the detectors remain stationary and the nearer blocking detectors act as a filter for the X-ray beam.

Z. H. Cho

Papers

A New Design for High Speed Computerized Tomography