Abstract: In a scanning electron beam CT system, a positive ion clearing electrode system is disposed within the CT system solenoid coil, and is operated from a single power source. Mounted coaxially about the electron beam, preferably the electrode system includes three sections, each having two electrode elements, one element being coupled to about −800 V to about −2 kV and the other element being grounded. Within the electrode system, the ratio between element diameter and electron beam diameter is substantially constant. Preferably elements are helically twisted about the beam axis. The electrode configuration cancels net quadrupole (focusing) and octopole (aberration-producing) fields. In the presence of electric discharge, essentially zero electron beam displacement and deflections occurs, and changes in focusing strength remain zero.

Abstract: Tuning, integrating, and operating an electron beam CT scanning system is simplified by using the fringe field from dipole magnets arranged as a chicane to focus the electron beam, thus replacing conventional quadrupole and solenoid coils. Preferably four "chicane" dipole magnets are series-coupled with the windings in the downstream deflection magnet, such that the chicane magnet X and Y coils are energized 90.degree. out of phase with the deflection magnet coils. The alternating current polarity in the chicane magnets creates an "S"-shaped electron beam trajectory that adequately uniformly focuses over the full cross-section of the electron beam. Winding the coils with a cosine distribution permits rotating the magnetic fields to change the azimuthal and deflecting planes of the electron beam, without disturbing the deflection angle and focusing properties.

Abstract: Computed tomographic ("CT") x-ray scanning yields a discrete set of measurement values that are line integrals of attenuation coefficients .mu.(r), which attenuation coefficients may be obtained using suitable reconstruction techniques. Electronic beam computed tomograph ("EBCT") systems add error to the reconstructed attenuation coefficients owing to their unique cone geometry. A method is provided that reduces such errors. At least two scans, "tilted" by the system cone angle, collect data in the neighborhood of a reference plane normal to the system z-axis. These scans are rebinned into parallel projections, and a series expansion is considered for variation of .mu.(r) in the vicinity of the reference plane. If a first order series is considered sufficient, then two scans are required to estimate the slope A of the variation in data. The data can then be corrected for the "tilt" and line integrals on the reference plane normal to the z-axis obtained.

Abstract: In a scanning electron beam CT system, spherical aberration of the electron self-forces produces a deleterious halo around the final electron beam spot, causing loss of definition in the image rendered by the system. The spherical aberration is caused by non-uniform electron beam current density, and by non-uniform distribution of positive ions in the transition region of the beam-optical systems. The non-uniform electron beam current density depends upon the axial position of the electron gun cathode, while the transition region ion distribution depends upon the potential coupled to the washer-shaped positive ion electrode ("PIE") used to segregate the upstream and downstream portions of the electron beam. In the present invention, the beam spot halo is minimized (if not eliminated), and image definition is maximized by selecting the electron gun cathode axial position and the PIE potential such that their contributions to spherical aberrations at the final beam spot cancel.

Abstract: A scanning electron beam CT system generates an electron beam along a beam source axis offset from the scanner axis, or axis of symmetry, thereby permitting the X-ray subject to pass completely through the stationary gantry. The electron beam is produced with the first drift tube region of an evacuated housing chamber, and is directed downstream toward a second region that includes a gantry. A scan target and a tuning target, each concentric with and defining a plane normal to the system axis of symmetry, are located in the gantry. A beam optics system, through which the electron beam passes, is located within the housing intermediate the electron gun and gantry. A control system focusses and scans the electron beam upon the scan target, maintaining a beam spot of desired quality. Upon impingement by the scanning beam spot, the scan target emits a fan beam of X-rays.

Abstract: In a computed tomography X-ray system, the number of A/D converters required to digitize detector output signals is reduced without degrading the resultant tomographic image. This hardware reduction results from combining certain detector output signals into a pseudo detector having a single output. The detector output signals thus combined represent data corresponding to X-ray beams having substantially the same Radon radius. Preferably such X-ray beams also traverse substantially the same region of the CT system's reconstruction circle. Where the pseudo detector includes the output signals read from N sequentially scanned detectors D.sub.i, where i=1 denotes the first read detector and i=N the last read detector, the output of each detector D.sub.i is delayed a time (N-i).tau., and the thus delayed outputs are summed together to provide the pseudo detector output. In the above relationship, .tau. is the interval between reading adjacent detectors D.sub.i and D.sub.i+1.

Abstract: A method of reconstructing data acquired on a fan beam CT system first rebins the data to parallel beam format using limited angle weighting that fold-over redundant data by adding corner rays of one scan to the center rays of another scan. For each view, now parallel beam data are filtered with a parallel beam kernel, and transformed. The transform is replicated, and multiplied by an interpolation filter. Next, the replicated, multiplied transform is convolved with the gridding function, and added into the Fourier image at an angle corresponding to the view angle. In the case of an n-scan cone beam correction a two-dimensional weighting function is calculated for each view giving the view's contribution to each pixel in the image. Multiplication by this weighting function is accomplished by convolution of the transform of the weighting function with the above transformed view. These steps are repeated for all views, whereafter the two-dimensional inverse Fourier transform is taken to get a preliminary image.

Abstract: In a scanning electron beam CT system, the electron beam is focused by controlling the distribution of beam-generated ions electrostatically. The upstream (self-expanding, de-focusing) beam region and downstream (converging, self-focusing) beam region are distinguished by the absence or presence of beam-generated positive ions. The relative lengths of these two beam regions are electrostatically controlled such that beam de-focusing in the upstream region compensates for beam self-focusing in the downstream region. In this fashion, essentially zero external focusing strength is required, and the magnetic focus coil used in the prior art is eliminated. Located downstream from the electron gun, a positive ion electrode ("PIE") determines the position of the boundary between the two regions, and thus the relative length of each region. The PIE is a disk-like electrode, mounted coaxially to the beam optic axis within the drift tube, and coupled to a large positive potential.

Abstract: An electron beam scanning system producing an electron beam in a relatively short chamber includes an ion controlling electrode assembly located between the electron gun and system beam optics. The assembly includes a somewhat cone-shaped rotating field ion controlling electrode ("RICE") unit disposed between first and second ion controlling electrode units ("ICE"s). The RICE and ICEs each comprise element pairs symmetrically disposed on opposite sides of the chamber Z-axis, preferably forming regular polygons in cross-section. Preferably corresponding elements in each ICE are electrically coupled to each other and to an opposite element in the RICE. Preferably equal and opposite bias potentials, with respect to an average potential, are coupled to the RICE and ICE elements comprising an element pair. Because it is somewhat cone-shaped, the RICE and electron beam create a transverse electric field with no axial component.

Abstract: A scanning electron beam computed tomography scanner is disclosed herein and includes means defining a vacuum chamber, means for producing an electron beam at one location in the chamber and for directing it to a second location therein, a target located at a third position therein of the type which produces X-rays as a result of the impingement thereon by the electron beam, means for focusing the beam onto the target in the form of a beam spot and for scanning the beam spot across the target along a particular scan path in order to produce X-rays, and means for monitoring the profile, position, and orientation of the beam spot at a plurality of locations along the scan path. The specific scanner disclosed also includes an arrangement for determining from the signals produced by the monitoring devices if the beam spot conforms to as desired profile, position, and orientation and automatically adjusting the electron beam such that its profile, position, and orientation conform to desired values.

Abstract: A helical CT scanning system includes a real time averager that rapidly processes data from the system's detector array, to enable substantially real time production of X-ray images. The averager, which may be used with an scanning electron beam CT system operating in conventional or helical mode, or with a rotating mechanical gantry CT scanner operated in conventional or helical mode, includes an adder and first and second memory banks and an input FIFO register. The FIFO register synchronously communicates system detector array data to the adder. The adder combines this input data with data previously stored in one of the memory banks. For example, after a first X-ray scan, detector data are written via the FIFO and adder into the first data bank, and after a subsequent scan, the sum of the original data in the first data bank is added to the new data corresponding to the second scan, and the new summation is written into the second data bank.

Abstract: An electron beam scanning system employing a relatively short housing chamber wherein an electron beam is produced includes an ion controlling electrode assembly. Located in the housing between the electron gun and system beam optics, the assembly includes a generally cone-shaped rotating field ion controlling electrode (or "RICE") unit comprising cylindrically symmetrical element pairs disposed on opposite sides of the housing Z-axis. Preferably equal and opposite potential sources coupled to elements comprising an element pair create a transverse electric field therebetween. The vector sum of the fields produced by all element pairs is the transverse field created by the RICE unit. The potentials are varied, rotating the overall RICE field to controllably remove most but not all positive ions. The remaining ions improve the electron beam space-charge density, resulting in a sharply focused scanning electron beam.

Abstract: A rotating x-ray tube includes an electron-beam accelerator assembly having an indirectly heated cathode structure. The cathode structure includes an electron-emitting region mounted at the center of a rotationally symmetric Pierce-cathode configuration. An electron beam travels along a selected path as the tube rotates so that the electron beam strikes selected portions of a target mounted within the tube as it rotates. Two magnetic coils and a ferromagnetic mirror plate are arranged to function as a single quadrupole electromagnet, which has its axis parallel to and offset from the electron beam and which elongates the electron beam in a radial direction.

Abstract: A scanner assembly having a C-shaped gantry rotatably supported by a support head. An x-ray source and a detector assembly are mounted on said gantry for independent movement with respect to one another along said gantry.

Abstract: X-ray tube includes a rotatable envelope in which is mounted an electron gun at one end and a target anode at the other end. A fixed means for deflecting the electron beam from the electron gun is provided to deflect the electron beam on a fixed path as the envelope of the x-ray tube rotates about an axis. The electron beam being confined to a fixed path results in the electron beam striking various positions of the target anode to provide for improved heat dissipation. The electron beam is deflected along the fixed path using magnetic deflection means including magnetic deflection coils positioned external of the envelope to provide a deflection field transverse to the electron beam. The target anode is cooled by directing a cooling fluid on an external side of the target anode.

Abstract: A compact computerized tomographic x-ray scanner having a patient tunnel in which the walls and the ends of the patient tunnel include shielding material to form a shielded enclosure in which the patient body portion is scanned.

Abstract: Disclosed is a composite metal structure of a desired configuration and a method of fabricating the composite metal structure by preshaping at least one metal layer prior to assembly of the metal layers in a die of a second preshape configuration. Following brazing of the metal layers while in the die, the brazed structure is removed from the die and springs to the final desired configuration. The process has proved to be particularly useful in fabricating composite electron beam targets for use in X-ray scanners.

Abstract: A tomogram is obtained by tomosynthesis in a high speed CT scanning system in which fan beams of radiation are generated by sweeping an electron beam along a target, and collimated X-rays emitted by the target are received by an array of detectors after passing through a patient area between the target and array of detectors. The patient is moved through the collimated x-rays as the measurments are obtained, and the measurements are time-correlated to correspond to data measurements for a plurality of projection radiographs. The measurements for the plurality of radiographs are combined to tomosynthesize a tomogram at a selected plane in the patient.

Abstract: A stereoscopic or three dimensional radiograph or a continuously rotating three dimensional radiograph of a patient is obtained using a high speed CT scanning system in which fan beams of radiation are generated by sweeping an electron beam along a target. Collimated X-rays emitted by the target are received by an array of detectors after passing through a patient area between the target and the array of detectors. Two detector positions, comprising one or more detectors, each can be employed to obtain a pair of two dimensional projection radiographs. The radiographs are alternately viewed by a viewer by selectively opening and closing shutter means associated with the eyes of the viewer as the radiographs are alternately assembled for viewing whereby one eye sees one radiograph and the other eye sees the other radiograph. Alternatively, a plurality of pairs of detector positions can be employed in measuring radiation and obtaining a continuously rotating three dimensional projection radiograph.

Abstract: A deflecting magnet assembly for scanning an incident beam of charged particles in a scanning electron beam computed tomography scanner. The configuration (including angular orientation and coil end connection geometry) of the coils which comprise the magnet is selected to approximate the field of a pure dipole. In addition, a magnetic shield is used which equalizes the effective radii of the constituent coils and thereby simplifies construction of the assembly.