US 5,512,755 AGranted

Gamma camera device

AssigneeSummit World Trade Corporation

InventorsDavid S. Vickers, John C. Gibbons, Geoffrey G. Cochrane

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Abstract

An electronic gain control for the photomultipliers of a gamma camera assures that all photomultipliers in the camera have uniform gain for any given gamma event. A specific dynode in the photomultiplier is isolated from the line resistive voltage divider string in the photomultiplier which places each dynode under incremental voltages. A voltage is then applied to the isolated dynode which can vary anywhere from the voltage the isolated dynode would have had if inserted in the voltage divider string to the voltage that the immediately preceding or immediately succeeding dynode in the string has whereby the photomultiplier's gain is controlled. The voltage applied to the isolated dynode is established for each photomultiplier in the camera by individual gain signals developed and stored during calibration of the camera for each radio active isotope whereby all photomultipliers have uniform gain for each isotope.

Claims10

Dependent claims

A scintillation camera comprising:

a) scintillation means receiving radiation and transmitting light in response thereto;
b) a plurality of photomultipliers adjacent said scintillation means and generating electrical output signals indicative of the position and intensity of said light emanating from said scintillation means;
c) each photomultiplier having within a vacuum enclosed space a photocathode connected to ground, an anode and a plurality of dynodes spaced incrementally between said photocathode and said anode and numbered sequentially as d.sub.1, d.sub.2, d.sub.3, etc. from said photocathode with any one specific dynode designated d.sub.n ;
high voltage potential means including a resistor voltage divider string and a power supply for applying a D.C. high voltage to each dynode at incremental potentials corresponding to said numbering of said dynodes whereby the voltage potential at one dynode is less than said voltage potential at the next numbered dynode which in turn is less than the voltage potential at the next numbered dynode, said power supply supplying said D.C. line voltage adjacent said anode;
d) means for converting said electrical signals generated by said photomultiplier tubes into a scintillation image;
e) gain means for electronically establishing the gain of all photomultipliers to be equal to another in accordance with the radiation of a predetermined test beam by establishing the voltage potential for said specific dynode, d.sub.n, at a voltage value which is set between the value of the high voltage potential applied to an immediately preceding dynode d.sub.n-1 and the value of the voltage potential applied by said resistor string to an immediately succeeding dynode d.sub.n-1 for each photomultiplier so that the gain of all photomultipliers are equal;
and,
f) means to regulate said power supply to set said constant D.C. high voltage to different constant voltage levels in accordance with the energy level of the radiation being detected.

5 more elements

In a nuclear camera having a plurality of photomultipliers generating analog output signals in response to a gamma event from radiation emitted by one of a plurality of radioactive isotopes, said analog signals being subsequently refined to produce scintigrams, each photomultiplier having an anode, a photocathode connected to ground and a plurality of dynodes numbered sequentially from said photocathode, the improvement for each photomultiplier comprising:

a) a voltage divider resistor string including a plurality of resistors in series with one another extending from said anode to said photocathode and ground;
b) means to input a constant DC high voltage to said string which is set at a voltage correlated to the specific radioactive isotope sensed by said camera;
c) means to generate a gain signal voltage for each radioactive isotope;
d) means to isolate any one specific dynode d.sub.n from said string;
and
e) means to electronically apply a gain voltage potential on said isolated dynode which can be set at voltage level correlated to said gain voltage signal anywhere between the voltage said d.sub.n dynode would have had if positioned in said string and the string voltage applied to the dynode immediately adjacent and closer to said photocathode whereby the gain of all photomultipliers are automatically adjusted to be equal to another for each isotope sensed by said camera.

3 more elements

Dependencies are inferred from the claim text.