X-ray or gamma ray systems or devices – Accessory – Testing or calibration
Patent
1996-03-04
1998-06-02
Hannaher, Constantine
X-ray or gamma ray systems or devices
Accessory
Testing or calibration
378 98, H05G 146
Patent
active
057612706
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to measurement of X-ray radiation as regards certain values and characteristics that are important to recognize in conjunction with exposure from an X-ray instrument. The invention thereby pertains to a method for such measurement as well as an instrument for carrying out the method.
2. Prior Art
The energy in the radiation from an X-ray tube is usually expressed as a kiloVolt-level of radiation peaks representing the radiation of the highest energy. Said energy varies, namely, with time when an exposure of an X-ray film takes place, whereby the peak-levels decide the light and contrast of the picture registered electronically or on a film. This value is usually denoted kVp (kilo Volt peak) and this denotation will also be used in the following. The energy of the radiation is namely dependent on the instantaneous voltage: kVp, which is introduced over the X-ray tube during the exposure. A desired radiation energy and thereby characteristics of exposure may thus be set by choosing the voltage of the X-ray instrument.
It has however been shown that other factors than the voltage also decide the energy of the radiation, so that full correspondence between the set voltage level and the radiation energy is not always obtained. To a large extent, therefore, direct measurement of the peak values of the radiation energy by a particular measurement is used instead whereby the X-ray instrument may be adjusted for correct exposure regardless of the correlation between set voltage and true radiation energy.
Methods and instruments for such measurements are previously known from U.S. Pat. No. 4,355,230 and 4,697,280 (Wilson et al and Zarnstorff et al) respectively. The X-ray radiation from the tube is thereby allowed to pass through two absorbing filters having different absorption levels, normally accomplished by having the filters made with different thicknesses. The radiation after the filters is absorbed by photo-diodes and the current generated in these diodes is led to an instrument which, based on the ratio between the registered levels, indicates the radiation energy expressed as a kVp-value. The generation of this indication requires an amplification of the output current of the photo-diodes in order to carry out the computation of said ratio and its correlation to a corresponding kVp-value as well as an indication of the same. Due to the wide limits within which the radiation energy may exist, this amplification must be given such an adaptation in degree of amplification, that the range within which the computation is to be carried out is limited to the capacity of the computation instrument. Such an adaptation of the instrument is achieved according to U.S. Pat. No. 4,355,230 by having the first exposure of the instrument carried out in such a way that it may be adapted to a correctly limited measurement range before a second exposure is carried out for generating the measurement value. In U.S. Pat. No. 4,697,280, the adaptation is carried out during the measuring sequence by firstly determining the main level of the diode voltages, whereafter each of these is led to an amplifier whose degree of amplification is commonly adjusted, so that the level of the output signal falls within the working range of the instrument.
The first mentioned method suffers from the drawback that a particular exposure must be carried out before the actual measurement is made, which results in a certain time-loss and a longer operation of the X-ray instrument, something which should be avoided for several reasons. In the second-mentioned method, a time period of such duration, that a peak value for the radiation or the entire exposure may have been passed before the actual measurement is made, is required for determining and setting the amplification level. This may render usage of the method impossible when using very short exposure times, such as down to 5-10 milliseconds. Furthermore, the common adjustment of the amplifiers may result in a lack of accuracy fo
REFERENCES:
patent: 4097736 (1978-06-01), Jacobson et al.
patent: 4355230 (1982-10-01), Wilson et al.
patent: 4361900 (1982-11-01), Siedband
patent: 4400821 (1983-08-01), Aichinger et al.
patent: 4697280 (1987-09-01), Zarnstorff et al.
patent: 4843619 (1989-06-01), Sheridan
patent: 4935950 (1990-06-01), Ranallo et al.
patent: 5267295 (1993-11-01), Strommer
Hannaher Constantine
Unfors Instruments AB
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