Abstract: 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 (90.sub.1, 90.sub.2, . . . , 90.sub.n) 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.

Abstract: During surgery, a physician speaks commands that are received by a microphone (10). A speech processor (12) converts audio signals from the microphone into word signals. A command interpreter (14) compares each word signal with a list of previously authorized command words. When the word signal corresponds to one of the preselected command words, a corresponding command signal is generated and sent to a volume imager (18), a video recorder (20), a hard copy, printer (28), or other system component. The volume imager generates an image representation signal indicative of a portion of image data stored therein which is displayed on a video monitor (B) or recorded on the video recorder.

Abstract: A CT or other radiographic scanner (A) generates data that is arranged into sets (32). Each set is convolved (40) with a convolution function (42) and backprojected (44) into an image memory (46) along a corresponding one of a plurality of rays. A corresponding gradient image (52) in which each pixel value has either a one or a zero value is forward projected (54) and compared (60) with a standard. The comparison indicates along which rays data sets including bad data were projected. To subtract the bad data contribution from the image, the image representation is forward projected (90) along the identified rays, convolved (40) with a negative of the convolution function (84), and backprojected (44) along the identified ray into the image memory (46). Further correction may be obtained by replacing the subtracted data with interpolated data.

Abstract: An x-ray source (20) rotates about a fixed cylinder (16) within which a subject of non-uniform cross-section is received. Radiation from the x-ray source passes through the subject and impinges on an arc of radiation detectors (28). Because the subject is of non-uniform cross-section, the average x-ray energy fluence impinging on the detectors across the arc varies with the relative angular position of the x-ray source and the subject. In one embodiment, a motor (18) which rotates the x-ray tube relative to the subject is controlled by a digital motor control (50). The digital motor control varies the rotational speed to a preselected angular velocity indicated by a look-up table (52) at each of a multiplicity of angular positions around the subject.

Abstract: An apparatus and method is disclosed for facilitating calibration of a dual energy digital radiography system having a focused multi-element detector assembly. The apparatus includes two sets of calibration elements, each set made of a different basis material. Each calibration element defines a segment of an annulus and is positionable between the system source and detector such that the center defined by the annulus is substantially coincident with the focal spot of the source. Within individual sets, the thicknesses of the respective member elements differ one from another in accordance with a binary progression. Each of the calibration elements is positioned and sized such that it intercepts and attenuates all radiation which ultimately falls upon the detector.

Abstract: A plurality of segmented radiation sensitive arrays (30) receive radiation from a radiation source (16) which has transversed an examination region (14) of a CT scanner (10). Each array includes a plurality of rows (A, B, C) of radiation sensitive cells, e.g. photodiodes, which produce an electrical signal indicative of the intensity of radiation received. Within each of the rows, there are larger cells and smaller cells. The electrical signals from each of the plurality of cells within each row are serialized (34) and amplified (36A, 36B, 36C). Selected combinations of the electrical signals from the various rows and larger and smaller elements within each row are combined (46) and reconstructed (50) into an image representation (52) for display on a video monitor or the like.

Abstract: Detectors (20) of a CT scanner (10) have a radiation receiving face (34) which is larger than a photosensitive face (30) of a photodiode (22). Lead wires (28) connect the ends of the diode photosensitive surface to terminals (26). A scintillation crystal (32) has an overhanging portion (38) which overhangs at least the interconnection between the lead wires and the photosensitive face to protect the adjoining areas of the photosensitive face from incident radiation. This enables the radiation receiving surface to be larger than the photosensitive surface. The crystal is either undercut to define the overhanging area or a section of light pipe (60) is provided between the photosensitive surface and the crystal. Increasing the radiation receiving face decreases rotor ripple artifacts. Decreasing the photosensitive face area decreases diode capacitance and increases resistance which improves amplifier performance.

Abstract: A radiographic apparatus (10) includes an x-ray tube (16), an off-focal radiation collimator (20), a shutter (22), and a primary beam defining collimator (24) between the x-ray tube and patient receiving region (14). The off-focal collimator is mounted within a collar (48) which surrounds an x-ray port (36) of the x-ray tube. The tube port is sealed from the atmosphere by an aluminum window (46). A plate (62) of a radiation blocking material is rotatably mounted by a bearing (70) within the collar closely adjacent the aluminum window. By rotating the moveable plate, aperture or radiation passing slots or portions (62, 64) of different sizes are selectively brought into alignment between a focal spot (34) of the x-ray tube and a radiation passing region or slot (52) of a stationary plate (50) at the distal end of the collar. The aligned slots block the passage of off-focal radiation. Moreover, rotating slots of different sizes into alignment changes the size or angle of the x-ray fan beam.

Abstract: An improved computed tomography radiation detector is disclosed. One embodiment includes first and second layers of crystalline scintilation material mutually aligned in a path of x-rays to be detected, to receive the x-rays in sequence. The layer upstream in the x-ray path comprises a scintillation material having a relatively high efficiency for converting x-ray energy to light. The downstream one of the layers comprises a scintillation material having a relatively lower efficiency for x-ray/light conversion. A photodiode is positioned to view both scintillation layers simultaneously and to respond to scintillations in either or both. Scintillation crystal material surfaces can be coated with reflective material to enhance the effects of their scintillations. The photodiode thus combines x-ray indicating scintillations from both crystals while in analog form. The detector exhibits enhanced response to lower energy x-rays.

Abstract: A xenon concentration phantom (A) is mounted in a CT scanner (B). A xenon/oxygen breathing gas mixture from a breathing gas supply system is (C) circulated through an analysis chamber (12) of the phantom before a human scan is commenced. The CT scanner measures the amount of radiation absorption attributable to the gas in the analysis chamber, which absorption varies in proportion to the concentration of xenon gas. The measured radiation absorption is converted into a precise measurement or indication of the xenon concentration of the breathing gas. The precise xenon concentration measurement may be utilized to calibrate xenon gas detectors (80, 100) in the breathing gas supply system or to calibrate xenon concentration dependent diagnostic data generated during a subsequent patient scan while the patient is breathing the breathing gas.

Abstract: In a fourth generation CT scanner, source views or data sets are generated for reconstruction processing. A fan beam (16) of radiation rays is rotated around an image region (12) to irradiate subsets of detectors of a detector ring (10). A data sampler (B) samples the detectors of each irradiated subset a plurality of times, each time with the radiation fan beam displaced incremently from the preceding time to generate a plurality of the source views or data sheets from the same detectors. A plurality of consecutive source views or data sets are interleaved to produce a signal interleaved view or data fan. More specifically, the data sets are stored in data set memories (20-26) and interleaved serially into a data fan memory (30). Each time the fan beam rotates sufficiently to irradiate a different detector subset, an additional plurality of data sets are generated and interleaved into another data fan.

Abstract: Method and apparatus for a computed tomography patient localization scan. A source of radiation that orbits a patient during a normal computed tomography scan is fixed relative an array of radiation detectors. The patient is then moved in a direction generally perpendicular to the plane of the radiating source and array to obtain a first shadowgraph data set. The source is orbited a small amount and the patient is again moved relative the source and detector array to obtain a second shadowgraph set of data. The two sets of data are then interleaved to obtain a shadowgraph image having higher resolution than either the first or second shadowgraph.

Abstract: An off-focal radiation collimator is disclosed which includes a plurality of radiation absorbing elements supported in spaced relationship with respect to one another in a housing such that each element is aligned along radii extending from the focal spot of a radiation source. The off-focal collimator is preferably disposed between the radiation source and a primary beam collimator. The off-focal collimator also acts as a radiation beam compensator. By varying the spatial density of the radiation absorbing elements by a function of location within the housing, the radiation beam can be shaped to any desired profile.

Abstract: A phantom (FIG. 1) has a bone mineral standard (B) surrounded by tissue equivalent material (A) with a plurality of different cross sections. The phantom is disposed in an image region (44) of a tomographic scanner (FIG. 2). Scans are conducted through a plurality of different cross sections of the phantom to reconstruct a plurality of phantom image representations (62). The plurality of phantom image representations are stored by size in a correction memory (70). Thereafter, a patient is disposed on a patient table (50) in the image region and an image is taken through the patient's mid-section between the L2 and L5 vertebrae. A patient image representation is reconstructed and stored in an image memory (64). A slice size calculation circuit (72) determines the size of the patient slice. The correction memory is addressed with the calculated size to retrieve the phantom image representation of the most similar size.

Abstract: An improved method for computed tomographic scanning is disclosed. A beam of electromagnetic radiation subtending an angle .phi. is alternately translated and rotated past a patient. The intensity of the beam is detected by an array after the radiation passes the patient and a reconstructed image created from the detected intensities. Each rotation of the array is through an angle less than the angle .phi. subtended by the array producing redundant intensity readings for similarly oriented beam paths through the patient. This redundant intensity data is modified according to a scheme which tends to reduce motion and misalignment artifacts within the patient.

Abstract: An improved method and apparatus for transaxial tomographic scanning of a patient. A scanning system is provided having a rotatably mounted X-ray radiation source/detector pair which orbits and radially scans the patient in the plane of orbit. The source provides a plurality of beams of radiation having axes in the orbital plane. The beams pass through the patient to an array of detectors each of which is aligned with one of the beams. Radiation intensity data is collected at predetermined orientations of each beam/detector pair as the assembly orbits about the patient. In a preferred embodiment the rotatably mounted source-detector pair is rotated as a unit through a preselected rotation angle .phi. about an axis effectively passing through the source. The axis and the source-detector pair connected to it are then orbited around the patient through an orbit angle .gamma. while maintaining the preselected rotation angle .phi.. The axis is orbited about an origin lying in the orbital plane.

Abstract: A dual axial scanner in a transverse tomography system collects nonredundant data throughout one or more substantially 360.degree. orbital scan paths with uniform motion about a patient. A set of N X-ray beams scans the patient in a manner to allow collection of two sets of non-redundant data corresponding to a pair of 180.degree. scans in each 360.degree. scan. Overall time to conduct the study is decreased, and the number of required accelerations and decelerations of the assemblies is minimized.Adjacent beams of radiation are separated by an angle .alpha., which is one degree in the preferred embodiment to provide a radiation field of ##EQU1## degrees on either side of a center of the radiation field. The source and detector assemblies are positioned prior to the first orbit such that the field center is offset a distance D from a center of orbit lying in the orbital plane. The source and detector assemblies are mounted for rotation through a rotation angle .phi..sub.

Abstract: An improved method and apparatus for transaxial tomographic scanning of a patient. A scanning system is provided having a rotatably mounted X-ray radiation source/detector pair which orbits and radially scans the patient in the plane of orbit. The source provides a plurality of beams of radiation having axes in the orbital plane. The beams pass through the patient to an array of detectors each of which is aligned with one of the beams. Radiation intensity data is collected at predetermined orientations of each beam/detector pair as the assembly orbits about the patient. In a preferred embodiment the rotatably mounted source-detector pair is rotated as a unit through a preselected rotation angle .phi. about an axis effectively passing through the source. The axis and the source-detector pair connected to it are then orbited around the patient through an orbit angle .gamma. while maintaining the preselected rotation angle .phi.. The axis is orbited about an origin lying in the orbital plane.