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Method and apparatus for the measurement of X-ray sources
| Details |
Inventors: Zarnstorff, William C.; Ranallo, Frank N.;
Assignee: Wisconsin Alumni Research Foundation (Madison, WI)
Primary Examiner: Church; Craig E.
Assistant Examiner: Porta; David P.
Attorney, Agent or Firm: Isaksen, Lathrop, Esch, Hart, & Clark
An X-ray measurement device (20) is disclosed which utilizes a pair of detector units (29, 30) which receive X-rays through filters (40, 41) of differing attenuation of X-rays. The detector units preferably include two pairs of photodiode detectors arranged symmetrically in four quadrants with the diodes in each detector unit in diagonally opposite quadrants, thereby minimizing the effects of changes in orientation of the device with respect to the axis of the X-ray beam. The outputs of the detector units are passed to variable gain amplifiers (42, 43) the gains of which are automatically adjusted to bring the output voltages within a desired range, and the outputs of the amplifiers are integrated by integrators (49, 50). After a selected period of time, the integration is stopped and the output voltages of the integrators (49, 50) are held and passed to an analog-to-digital converter (57) which determines the ratio of the output signals from the integrators and provides a multi-bit output signal on a bus (58) to the address lines (59) of a preprogrammed memory (60). The data location addressed by the output signal from the conventer may contain data which corresponds to the kVp value of an X-ray machine at the calculated ratio, and the output data from the memory is provided to a display unit (63) to provide a visual display in decimal form of the measured kVp value. |
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DETAILED DESCRIPTION The X-ray measurement apparatus in accordance with the present invention utilizes a pair of detector units each responsive to the intensity of X-rays incident upon it to produce an output signal related to the incident X-ray intensity.
The X-rays reaching the detectors are passed through filters of differing attenuation characteristics; for example, the thickness of the filter over one of the detectors may be greater than the thickness of the filter over the other.
The detector units are preferably arranged in a plane with the centers of the areas of each unit which are responsive to the radiation being coincident so that variations in the outputs of the detectors with changes in the orientation of the device are minimized.
A preferred detector arrangment consists of two pairs of square-surfaced photodiodes arranged in the four quadrants of a square with each pair of detectors, constituting a single detector unit, disposed in diagonally opposite quadrants.
The output signals of the detector units--for example, the diode currents from photodiode detectors--are preferably passed to adjustable gain current-to-voltage amplifiers.
Means are provided to adjust automatically and simultaneously the gain of each of the amplifiers so that the output signals from the amplifiers will be in a desired voltage range.
The switching and adjustment of the gain of the amplifiers is preferably accomplished during an initial delay period after initiation of an X-ray exposure, e.
g.
, during the first 30 milliseconds, and before any measurements of the outputs of the amplifiers are made.
After the selected delay period, which allows for stabilization of the X-ray output signal and selection of the proper gain from the amplifiers, the output of each amplifier is provided to an integrator which is allowed to integrate the signal from the amplifiers until a selected voltage level at one of the integrators is reached or a selected delay time after the X-ray exposure has terminated has elapsed.
At such point, integration of the amplifier output signals is halted and the output of each integrator is held at its then existing level and supplied to an analog-to-digital converter which preferably provides a parallel line, multi-bit digital output signal which corresponds to the ratio between the integrator outputs
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