DE3001131A1 - Low-noise X=ray radiation detector circuit for computer tomography - switches integrator capacitor voltage at end of integration period - Google Patents

Abstract

A circuit for a radiation detector converting radiation into corresp. electrical signals is applicable to X-ray detecting for computer tomography of X-rays passing through the body of a patient. An integrator circuit contg. a capacitance is connected to the detector output. The amplifier's internal noise does not have a negative effect. This permits the use of a low beam intensity or low output detectors. The capacitor (2) is connected directly in parallel with the detector (1). A switching transistor (4) enables the voltage on the capacitor (2) to be connected to an amplifier (5) for further processing at the end of the integrating period. The detector (1) may be a photodiode subjected to light produced from X-rays via a scintillating crystal.

Description

Circuit arrangement for a radiation detector

The invention relates to a circuit arrangement for a radiation detector for converting radiation into corresponding electrical signals, in the case of the radiation detector an integrator circuit for the detector output signal with a capacitance connected downstream is.

A circuit arrangement of this type is described in DE-OS 26 27 433. The known circuit arrangement is used for a computer tomograph, in which several detectors are provided for measuring the X-rays, the have penetrated a patient. The integrator circuit has an amplifier arrangement on. So that the signal-to-noise ratio is sufficiently large, i.e. the inherent noise of the amplifier in the integrator does not have an unfavorable effect on the measurement signal a sufficiently high radiation intensity is required.

The invention is based on the object of a circuit arrangement to create of the type mentioned, in which the inherent noise in the circuit arrangement provided amplifier does not have a negative effect, so that the radiation intensity kept low and, if necessary, used detectors with a small output signal can be.

According to the invention, this object is achieved in that the capacitance the integrator circuit is directly parallel to the radiation detector and switching means to connect the voltage on the capacitance to an amplifier for further processing are present at the end of the integration interval. In the circuit arrangement according to the invention the output signal of the detector is directly integrated in a capacitance.

Repeater between the integrating member and the detector are not available. At the end of an integration interval, the charge of the Capacity can be reduced by a parallel switch, so that the capacity is discharged at the beginning of the next integration interval.

The invention is illustrated below with reference to one in the drawing Embodiment explained in more detail.

In the drawing, a photodiode 1 is shown as a radiation detector, which is struck by light radiation, for example in a computer tomograph by converting X-rays into light radiation in a scintillation crystal can be formed. Immediately parallel to the photodiode 1 is a capacitance 2, which can be discharged by a switch 3. The voltage on the capacitance 2 becomes above an impedance stage 4 is fed to the input of an amplifier 5. In the example it is assumed that a plurality of channels of the shown Kind is present, which are connected to a multiplexer 6, which successively feeds the output signals of the channels to an analog-to-digital converter 7.

A computer can be connected to the output of the analog-digital converter 7 be derived from the output signals of the individual channels in the case in which this Channels are the signal channels of a computer tomograph, an image produced by radiation investigated object layer calculated.

Since the capacitance 2 is connected directly in parallel to the photodiode 1 is, the voltage tapped at capacitor 2 is free of amplifier noise. At the end of an integration interval, i.e. after querying the voltage at the Capacity 2 through the impedance stage 4, the amplifier 5 and after processing these Voltage through the analog-digital converter 7, the switch 3 is closed and the capacity 2 discharged.

It is then available for the next integration. The desk 3 is expediently an electronic switch.

Summary circuit arrangement for a radiation detector Die The invention relates to a circuit arrangement for a radiation detector (1) for converting radiation into corresponding electrical signals, in the case of the radiation detector (1) a detector output integrator circuit having a capacitance (2) is connected downstream. The capacitance (2) is directly parallel to the radiation detector (1) and there are switching means (4) for switching on the voltage at the capacitance (2) to an amplifier (5) for further processing at the end of the integration interval available.

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Claims (1)

Circuit arrangement for a radiation detector for Conversion of radiation into corresponding electrical signals in the case of the radiation detector an integrator circuit for the detector output signal with a capacitance connected downstream is, that the capacitance (2) is immediate parallel to the radiation detector (1) and switching means (4) for switching on the Voltage on the capacitance (2) to an amplifier (5) for further processing on Are present at the end of the integration interval.