Picker International, Inc.

Picker Corporation

Walter A Dupuis

Theodore A Resnick

William E Szabo

Anthony M Palermo, Jr

Donald A Hescht

Richard J Elliott

An x-ray tube (10) of a CT scanner has a rotating anode and rotor combination which is propelled by AC currents applied to run and phase windings (42, 46) by a starter (22). A monitor (24) includes Hall effect current detectors (40, 44) which detect the actual current flowing through the run and phase windings. The detected analog current values, voltage values, and the like are multiplexed (132) and digitized in a preselected order by an analog to digital converter (60) and stored in that order in a FIFO memory (62). A microprocessor (64) performs a Fourier transform (94, 96) to convert the digital run and phase signals into frequency spectra. The run and phase frequency spectra are compared (100, 102, 104, 106) with frequency spectra indicative of rotor speed, bearing wear, anode vibration, failure of the anode to rotate, and other conditions, analyzed for symmetry or other characteristics, or the like (FIG. 5 ) to generate digital run and phase reference signals. An error amplifier (54) controls a pulse width modulator ( 56) or other power amplifier controls in accordance with a deviation between analog reference signals converted from the digital signals by a reference digital to analog converter (66) and the actually sensed run and phase signals (40, 44) to adjust the starter. A direct coupled driver (122) adjusts DC offsets in the drive currents to maintain balance and drive efficiency.

High speed starter operations monitor

A plurality of medical electronic apparatae (A) including a CT scanner (B) or other medical imaging equipment are disposed at each of a plurality of remote locations. A diagnostic service system (C) monitors each CT scanner to create a malfunction history therefor. A central polling station (D) polls the diagnostic service system of each scanner to retrieve the diagnostic history thereof. The diagnostic service system includes a plurality of monitors (80, 82, 84, 86, 88) which monitor operating conditions and parameters of the scanner. The monitored operating conditions include the operating mode within the sequence of operating modes, operating parameters of an X-ray tube (12), and the operation of other scanner components. When a fault detection circuit (92) detects a malfunction, a latch array (90) immediately stores an indication of the condition monitored by the monitors. A read/write circuit (94) transfers the latched condition data to a malfunction history memory (96). Data from the malfunction history memory may be displayed on diagnostic service display (104) or transmitted by a modem (112) to the central polling station.

Diagonostic service system for CT scanners

An x-ray tube (10) imaging system, such as a computed tomography scanner, includes a cathode (40) for generating a stream of electrons. A rotating anode (42) is placed in a path of the electron stream and generates x-rays as a result of collisions therewith. An induction rotor (44) causes rotation of the anode as a result of electromagnetic interaction with a stator (48) comprised of two windings: a run winding (50) and a phase winding (52). The run winding and the phase winding are connected to three nodes (54, 58, 60), one of which is common to both. The three nodes are actively driven with run, common, and phase signals, respectively. Actively driving the three nodes increases bus drive voltage over 40% over that achieved by half-bridge drives.

Biphase quadrature drive for an x-ray tube rotor

Between scans, a stand-by control (40) causes a filament current power supply (44) to supply a low level of power to a tube filament (46). When x-rays are to be generated, a non-linear digital to analog converter (50) supplies a filament current control signal which is estimated to provide a selected tube current. A space charge compensation circuit adds an offset to the selected filament signal to compensate for the selected voltage at which the tube is to be operated. A current boost circuit (70) adds an incremental current boost (26) of a magnitude in accordance with a function of the difference between the actual filament temperature and the normal operating temperature in order to bring the filament up to operating temperature more quickly. A feedback loop (90 to 98) adjusts the selected filament current signal in accordance with any difference between the selected tube current and the actual tube current. A damping circuit (110) reduces the rate of change of the error signal such that the filament current changes at a rate commensurate with the heating rate of the filament.

Closed loop x-ray tube current control

An x-ray tube voltage generator with automatic stabilization circuitry is disclosed. The generator includes a source of pulsating direct current voltage such as from a rectified 3 phase transformer. This pulsating voltage is supplied to the cathode and anode of an x-ray tube and forms an accelerating potential for electrons within that tube. The accelerating potential is stabilized with a feedback signal which is provided by a feedback network. The network includes an error signal generator which compares an instantaneous accelerating potential with a preferred reference accelerating potential and generates an error function. This error function is transmitted to a control tube grid which in turn causes the voltage difference between x-ray tube cathode and anode to stabilize and thereby reduce the error function. In this way stabilized accelerating potentials are realized and uniform x-ray energy distributions produced.

Constant potential H-V generator

A closed loop feedback system for controlling the current output of an x-ray tube. The system has circuitry for improving the transient response and stability of the x-ray tube current over a substantial nonlinear portion of the tube current production characteristic. The system includes a reference generator for applying adjustable step function reference signals representing desired tube currents. The system also includes means for instantaneous sensing of actual tube current. An error detector compares the value of actual and reference tube current and produces an error signal as a function of their difference. The system feedback loop includes amplification circuitry for controlling x-ray tube filament DC voltage to regulate tube current as a function of the error signal value. The system also includes compensation circuitry, between the reference generator and the amplification circuitry, to vary the loop gain of the feedback control system as a function of the reference magnitude.

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Cleveland Heights, OH, United States of America

Walter A Dupuis