X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
1999-12-17
2001-12-25
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S108000
Reexamination Certificate
active
06333964
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a method for measuring the imaging dose in the framework of the pickup of a radiation image of a subject, particularly an x-ray image, whereby a radiation source is employed for generating radiation, a solid-state radiation detector is employed for image pick up, and a sensor is employed for determining the imaging dose.
2. Description of the Prior Art
In medical x-ray diagnostic installations that serve the purpose of generating radiation images and wherein the determination of the imaging dose is required in order to expose the patient under examination to only the minimally required x-radiation, an ionization chamber is employed for determining the imaging dose. This is arranged in the region of the solid-state radiation detector (with reference to the direction of the incident radiation) and should be as radiation-transparent and shadow-free as possible, so that it is not imaged thereon. The functioning of the ionization chamber is then such that, due to the x-radiation in a charged air capacitor, it generates a current usually lying in the pico-ampere range that is proportional to the dose. Measuring the pico-ampere current is difficult and is particular difficult when the ionization current drops into the femto-ampere range given employment of correspondingly low tube operating voltages. Further problems in the employment of ionization chambers are that the signal of the ionization chamber is determined by the air density in its interior, i.e., the air pressure and the temperature of the measuring chamber must be known and the chamber signal must be corrected by counter-measures in order to be able to determine the correct imaging dose.
The publication. “Bildgebende Systems fur die medizinische Diagnostik”. H. Morneburg, Ed., Publicic MCD, 1995, pp. 282-283, discloses the arrangement of a semiconductor radiation detector for dose measurement behind a film cassette in which an X-ray film is arranged.
SUMMARY OF THE INVENTION
An object of the present invention is thus to provide a method as well as a corresponding apparatus with which the imaging dose can be measured in a simple way without employment of an ionization chamber and, thus, while avoiding the initially cited difficulties, given employment of a solid-state radiation detector for image pickup.
This object is inventively achieved in a method and an apparatus of the type initially described, but inventively having a radiation sensor on a semiconductor base that, with reference to the direction of the radiation incident onto the solid-state radiation detector, lies following the solid-state radiation detector, the radiation penetrating the solid-state radiation detector being measured the radiation sensor and the radiation sensor supplying an output signal that is representative of the measured radiation, and wherein the imaging dose established in front of the solid-state radiation detector is determined based on the output signal, and wherein the output signal of the radiation detector is processed dependent on the transmission behavior of the solid-state radiation detector within the framework of determining the imaging dose in front of the solid-state radiation detector.
The inventive method is based on the recognition that non-radiation-transparent semiconductor radiation detectors have been known for a short time, i.e. solid-state detectors that do not have the initially cited disadvantages in view of temperature and air density problems. The second important perception is that adequate measurable x-radiation is still present following the solid-state radiation detector, and that the absorption behavior of the solid-state radiation detector which is composed of different materials in sandwich structure can be identified exactly enough, so that conclusions can be ultimately drawn about the radiation dose incident in the illumination plane. The inventive method thus enables the creation of a completely new system that employs only solid-state detectors (the aforementioned “radiation sensor” could also be referred to as a “radiation detector,” however, the term “radiation sensor” will be used herein to avoid confusion with the solid-state radiation detector which is used for detecting the radiation image). These perceptions make it possible to correspondingly process the output signal supplied by the radiation detector, for example a Si-semiconductor receiver, this output signal being a criterion for the admittedly very slight x-radiation penetrating the solid-state radiation detector, in order to determine the imaging dose. Within the framework of determining the imaging dose in front of the solid-state radiation detector, the output signal of the radiation detector can be inventively processed dependent on the transmission behavior of the solid-state radiation detector, on the spectrum of the radiation source, particularly of the x-radiator, and on the transparency of the transirradiated subject. This can ensue with an algorithm derivable therefrom, as is similarly the case given known ionization chamber systems. Differing therefrom, however, the determination ensues based on the signal measured following the solid-state radiation detector as well as taking the transmission behavior of the solid-state radiation detector into consideration. It is especially advantageously possible with the inventive method to determine the imaging dose with adequate precision independently of the external parameters to the farthest-reaching extent, whereby, further, all occlusion and transparency difficulties at the detector side are eliminated. The dependable and, above all else, very fast determination of the imaging dose particularly advantageously enables the control of the registration mode dependent on the identified imaging dose.
In conjunction therewith, it is also advantageous when the output signal of the radiation detector is processed dependent on the spectrum of the radiation source and/or on the transparency of the transirradiated subject in the framework of determining the imaging dose preceding the solid-state radiation detector. Thus, all influencing quantities can be dependable taken into consideration, as a result whereof an unnecessary radiation load on the subject is avoided and images of the transirradiated subject that can be easily diagnosed can be produced.
Within the framework of determining the imaging dose preceding the solid-state radiation detector, the output signal of the radiation detector is advantageously processed by a computer; in particular, a memory wherein data dependent on the transmission behavior and/or on the spectrum and/or on the transparency are stored is allocated to the computer for this purpose. The computer can then access these data in the determination of the imaging dose. A memory has proven advantageous wherein the data are stored in the form of a look-up table.
In addition to the above-described method, the invention is directed to an apparatus for the registration of radiation images, particularly a medical x-ray system for the implementation of the inventive method, having a radiation source, a solid-state radiation detector and a sensor for determining the image dose. In the inventive apparatus the sensor is a radiation detector on a semiconductor base for measuring the radiation penetrating the solid-state radiation detector that, with reference to the direction of the radiation incident onto the solid-state radiation detector, is arranged following the solid-state radiation detector, this sensor supplying an output signal that is representative of the measured radiation, and the imaging dose established in front of the solid-state radiation detector is determined based on the output signal.
For determining the imaging dose, a computer can be inventively provided with which the output signal of the radiation detector can be processed dependent on the transmission behavior of the solid-state radiation detector, on the spectrum of the radiation source, particularly of the x-radiator, and
Church Craig E.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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