Imatron, Inc.

Ge Medical Systems Global Technology Company, LLC

Imatron Associates

Siemens Aktiengesellschaft

Telesecurity Sciences, Inc.

Roy E Rand

Douglas P Boyd

Khem Garewal

John L Couch

Kristian R Peschmann

Thomas Clarke Sanders

Jonathan Harman

Patrick B Halahan

Mark C Nicely

Geordie Zapalac

Susan E Plomgren

Eugene Y Tsiang

Glenn R James

John W Mitchell

James F Heilman

Dan Y Wang

An electron beam production and control assembly includes a vacuum chamber, a beam source, and a target. The target has an active section and an inactive section. The active section is adapted to generate x-rays when the beam impinges on the x-ray producing section. The electron beam production and control assembly also includes a focusing unit positioned along the chamber at a location intermediate the rearward end and the forward end. The focusing unit directs the beam towards the target in a converging manner to impinge on the target. The focusing unit sweeps the beam along a scanning path over the active section of the target. The focusing unit moves the beam to a retrace path on the inactive section of the target between sweeps of the scanning path to maintain ion accumulation in the beam between sweeps over the active section.

Method and apparatus for production and maintenance of electron beam space-charge neutralization

A scanning electron beam computed tomographic system eliminates axial offset between target and detector by disposing the target, collimator, and detector such that active portions of the target and detector are always diametrically opposite each other. This result is achieved by providing a helical target, collimator, and detector, or by providing planar target, collimator, and detector components that are inclined relative to the vertical axis such that active portions of the target and detector are always diametrically opposite each other. Either configuration eliminates cone beam error and the necessity to correct for same. Further, the system can provide multi-slice scanning of an object that is in constant motion at a critical velocity, without having to interpolate data. Conventional helical scanning may still be undertaken. Detector elements can be disposed axially to improve signal/noise ratio and to produce a cone beam cancellation effect.

Electron beam computed tomographic scanner system with helical or tilted target, collimator and detector components to eliminate cone beam error and to scan continuously moving objects

An oil-free electron source including a vacuum chamber within which a vacuum is maintained. A rigid insulated receptacle and an anode extend into the vacuum chamber and are mounted to opposite ends of the housing. A cathode-focus electrode assembly is mounted to an outer end of the receptacle and is suspended within the vacuum chamber by the receptacle. A high voltage connector is inserted into the receptacle and conveys voltage in an oil-free environment. The cathode and anode surfaces face each other and are aligned with respect to each other along an electron beam axis. The electron source may be provided within an electron beam scanner including a patient table, an x-ray source and detector obtaining x-ray scans of a patient, and a focus member directing an electron beam onto the x-ray source.

Oil-free electron source for an EBT scanner

An electron source includes a vacuum chamber within which a vacuum is maintained by a vacuum pump. An insulated receptacle is mounted within the vacuum chamber and has a receptacle mounting flange. The receptacle mounting flange is used to establish a coordinate system having an electron beam axis and a lateral plane, wherein the lateral plane is transverse to the electron beam axis. An adapter is mounted to the receptacle and is adjustable in five degrees of freedom with respect to the coordinate system. A cathode and focus electrode are adjustable in at least four degrees of freedom and are pre-aligned with respect to one another prior to being installed on the adapter. An anode is mounted in the vacuum chamber and is aligned at a predetermined distance from the cathode with respect to the coordinate system.

Oil-free electron source having cathode and anode members adjustable with five degrees of freedom

An electron beam tomography (EBT) scanning system comprising an electron source generating an electron beam, a target ring that receives the electron beam and emits an x-ray fan beam upon impingement of the electron beam on the target ring, a pair of detector arrays arranged opposite the target ring, and a collimator arranged concentrically between the target ring and the pair of detector arrays. The collimator has interior and exterior walls concentrically arranged with one another and surrounding a patient examination area. The interior and exterior walls have a first set of apertures aligned to collimate the x-ray fan beam into a first collimated beam having a first width and a second collimated beam having a second width. Each collimated beam may form a single or double tomographic slice. The collimated beams are detected by the pair of detector arrays.

Collimation system for dual slice EBT scanner

Electron beam computed tomographic scanner system with helical or tilted target, collimator, and detector components to eliminate cone beam error and to scan continuously moving objects

A method and apparatus are disclosed for reducing variation in a spot size of an electron beam at a target due to multipole aberrations in an electron beam tomography (EBT) scanner. A magnitude of a DC voltage applied to a positive ion electrode (PIE) within the EBT scanner is adjusted and an orientation of a non-circular aperture of the PIE is aligned with respect to the electron beam. A profile of the spot size is monitored while adjusting the magnitude of the DC voltage and while aligning the orientation of the non-circular aperture of the PIE until the variation in the spot size is sufficiently reduced.

Method and apparatus for correcting multipole aberrations of an electron beam in an EBT scanner

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 &minus;800 V to about &minus;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.

Method and apparatus for clearing ions in a scanning electron beam computed tomographic system using a single potential power source

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. Chicane electrical current directions and magnet positions are such that the electron beam enters and exists the chicane on the axis of the scanning electron beam CT system. A new type of deflecting magnet is provided that has no end windings, and may be used in other beam optical systems.

Chicane magnet focusing system and deflection magnet for a scanning

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.

Method for correcting spherical aberration of the electron beam in a

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. A detector array, concentric with and defining a plane normal to the system axis of symmetry, is located opposite the scan target within the gantry and provides output signals that are computer processed to reconstruct a CT image of a subject placed within the gantry. The scanner axis is preferably above the beam source axis, and preferably the drift tube is straight, defining a drift tube axis that is inclined relative to the scanner axis, or is parallel to the scanner axis but not co-axial therewith. Alternatively, the drift tube may be kinked.

Off-axis scanning electron beam computed tomography system

An x-ray collimator is described which is useful in an electron beam (EB) computed tomography (CT) scanner of the type in which a rotating electron beam is directed to impinge upon a ring-shaped target and the x-rays generated in response thereto are directed to a ring shaped detector array spaced therefrom. The collimator consists of an x-ray blocking septum having an aperture therein, the septum being located in a fixed position substantially co-planer with the planes of the target and the detector, so as to block all x-rays directed from said target to said detector except those which pass through said aperture. Tomographic slice width is determined by the 'view' from the spot where the electron beam impinges upon the target, through the aperture, to the detector, and is variable by adjusting the position where the electron beam impinges upon the width of the x-ray target, and in a preferred embodiment, the position of a movable ring. In the preferred embodiment, a movable ring is provide which has a longitudinal axis positioned coaxial with the axis of the aperture and an end face opposed to and parallel with the septum. As well as forming part of the collimator, this ring acts as a pre-collimation radiation shield. This ring is moved concurrently when moving the position where the electron beam impinges upon the width of the x-ray target when the tomographic slice width is varied, by adjusting the spacing between the end face of the moveable ring and the septum.

Fixed septum collimator for electron beam tomography

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. Varying the PIE potential varies the inter-region boundary position, and thus the relative magnitudes of the beam de-focusing and self-focusing effects. A PIE focus potential is determined by varying the potential while examining the output of electron beam monitors with an oscilloscope. Further, by dynamically varying the PIE potential, the present invention adjusts electron beam focusing, even during a scan. Positive ions are removed from the upstream region by a periodic ion clearing electrode ('PICE') whose high rate of change of axial potential creates alternating axial fields that rapidly sweep away ions.

Method and apparatus for electron beam focusing adjustment by

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. Varying the bias potentials rotates the RICE electric 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. The ICE units sweep away positive ions in regions within the overall assembly not otherwise acted upon by fields. A single power source provides multiple potentials via a voltage divider, which potentials are switchably coupled to the RICE and ICE units to provide the required element potentials that may be controllably switched to rotate the resultant electric field in a predictable manner. The complete electrode assembly neither displaces nor deflects the emergent electron beam from the Z-axis.

Rotatable ion controlling electrode assembly with no offset or

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.

Growing community of inventors

Palo Alto, CA, United States of America

Roy E Rand