Emi, LLC

Richard G Gillard

Godfrey N Hounsfield

Colin C Oliver

The output of the circuit is connected to the grid of an X-ray tube (X) by a long cable having a large capacitance (C.sub.c). A 25 kHz variable amplitude drive circuit (1) applies a continuous DC regulating voltage to a first rail (RL2) via a first transformer (T1), rectifier (D1, D2) and a filter (F1). A 25 kHz fixed amplitude drive circuit (2) periodically generates a blanking voltage which is applied to a second rail (RL3) via a second transformer (2), rectifier (D3, D4) and a Zener diode (Z1). The first rail (RL2) is coupled to the second rail (RL3) via a clamping diode (D.sub.c) which is reversed biased by the blanking voltage, so that the regulating voltage is overriden. In order to quickly discharge the large capacitance (C.sub.c) to achieve a rapid transition from blanking voltage to regulating voltage, a discharge path is connected across the output, the path including a transistor (T1). A control circuit (3) comprises a capacitor (C2) which stores an actuating voltage (V.sub.T) produced when the blanking voltage is produced. The circuit (3) also comprises an RC network (R1, C1), in parallel with the control circuit capacitor (C2), the RC junction being connected to the base of the transistor (T1) and to the second rail (RL3). When the blanking voltage is produced the RC junction is maintained at a high voltage and the transistor (T1) is non conductive. During the transition from blanking to regulating, the RC network defines a desired transition voltage which is applied by the transistor (T1) ro the second rail (RL3) and this controls the discharge of the cable capacitance.

Circuit for controlling the grid potential of a pulsed X-ray tube

A technique for ensuring the rapid correction of both amplitude and offset errors in the deflectional movement of an electron beam along an X-ray emissive target is disclosed. The movement is monitored at at least two positions during a sweep and differences, between the two movements and a desired movement, at these positions are combined in unequal proportions to produce a corrective servo signal.

X-ray tube arrangements

Computerized tomographic apparatus is described in which a radiation source and an associated detector array execute, concomitantly, reciprocating lateral scanning movements and rotational scanning movements relative to a patient's body, the scanning movements being effected in the plane of a cross-sectional slice of the body which intersects the patient's heart. The patient is located so that the heart is substantially at the center of the scanning movements. The lateral movements are substantially sinusoidal, arranged so that a substantially linear portion of the movement occurs when the source irradiates the heart, and the rotational movement is continuous or substantially continuous and any pauses are only brief, and during alternate lateral scans when the aforementioned substantially linear portions of movement occur. The scanning movements are synchronized to the patient's heart beats so that the heart is irradiated during a quiescent phase of its movement.

Radiography

A multiple rate discharge circuit is disclosed for application, for example, to an integrator connected to a radiation detector as used in computerized axial tomography. The integrator is charged for a given time and then allowed to discharge at a first, relatively slow, rate for a predetermined time. If, at the expiry of the predetermined time, charge remains in the integrator, the discharge rate is considerably increased. The second-mentioned discharge rate is preferably about eleven times faster than the just-mentioned rate, and the two rates are achieved by the selective connection of resistive discharge paths to the integrator.

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Uxbridge, United Kingdom

Richard G Gillard