X-ray diagnostic apparatus for the preparation of x-ray exposures including a timer switch for determining the exposure time

Abstract

An x-ray diagnostic apparatus for the preparation of x-ray exposures, having a time switch for determining exposure time, and a control circuit for the X-ray dosage output or power with reference to a patient, which includes a dosage output measuring arrangement, a comparator element connected to the latter for comparing the actual value of the dosage output with a reference value, which effects an optimum film darkening for a particular exposure time and setting means for at least one of the operating parameters of the X-ray tube controlled by an output signal of the comparator element for correlating the actual value with the reference value.

Description

FIELD OF THE INVENTION

The present invention relates to an X-ray diagnostic apparatus for the preparation of X-ray exposures, having a time switch for determining the exposure time, and a control circuit for the X-ray dosage output or power with reference to a patient, which includes a dosage output measuring arrangement, a comparator element connected to the latter for comparing the actual value of the dosage output with a reference value, which effects an optimum film darkening for a particular exposure time and setting means for at least one of the operating parameters of the X-ray tube controlled by an output signal of the comparator element for correlating the actual value with the reference value.

DISCUSSION OF THE PRIOR ART

The earlier German Pat. application NO. P2207860.6 describes an X-ray diagnostic apparatus of this type, in which there are provided means for the individual setting of the exposure time for each exposure. In this prior X-ray diagnostic apparatus there is no need for extensive considerations concerning the setting of the X-ray tube voltage, since the latter is automatically derived from the set exposure time. The exposure time may be preprogrammed in conformance with the to-be-imaged body portions and organs.

However, in this X-ray diagnostic apparatus there is nevertheless required a setting sequence prior to the preparation of the exposure, namely, the setting of the exposure time. It is, however, desirable that the examining personnel be relieved as much as possible from technical operations, so as to be able to better devote his time to medical tasks.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an X-ray diagnostic apparatus of the above-mentioned type which, with respect to its setting, is in comparison with the earlier X-ray diagnostic apparatuses much more simplified and improved.

The foregoing object is inventively achieved in that an X-ray tube voltage and a plurality of varied patient constitution-coordinated exposure times are automatically programmed by means of a selector switch. The switch selects the shortest exposure time at the commencement of an exposure and transmits a signal to the comparator element forming a reference value in conformance with the required dosage power or output for this exposure time whereby, through the intermediary of the comparator element, the switch end setting means for the X-ray tube voltage are so controllable in the sense of correlating the actual value of the dosage output with a reference value, so as to effect a reduction in the X-ray tube voltage when the actual value is larger than the reference value, and wherein the switching-over to the next higher exposure time and the input of a new reference value signal corresponding to this exposure time toward the comparator element takes place when the actual value is smaller than the reference value. In the inventive X-ray diagnostic apparatus, prior to the preparation of an exposure, no setting steps are required for the setting of the exposure data. The X-ray tube voltage and the exposure time thereby are so adjusted, wherein a good contrast is achieved at a relatively small degree of unclarity due to movements. The X-ray tube current may be automatically so set on the basis of the X-ray tube nomograph, so that the X-ray tube is always at optimal power.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and details of the invention may be ascertained from the following description of an exemplary embodiment, taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a diagrammatic illustration of an inventive X-ray diagnostic apparatus in accordance with the present invention; and

FIG. 2 a power-time graph representative of the installation of FIG. 1.

DETAILED DESCRIPTION

Referring now in detail to the drawing, a three-phase, high-voltage transformer 1 is schematically illustrated, having a primary winding which is connectable to a power supply circuit through the intermediary of an electronic switch 2, whose operative relationship determines the high voltage of an X-ray tube 3. The X-ray tube 3 is powered from two series-connected high-voltage rectifiers 4 and 5, which are connected with two groups of secondary windings of the high-voltage transformer 1.

In order to carry out the measurement of the X-ray dosage power or output with reference to a patient in front of a film cassette 6, there is employed an X-ray measuring chamber 7 which is connected to a dosage output comparator element 8. The dosage output comparator element 8 includes three reference value inputs 9 through 11 which are connected to a switching element 12, and the latter of which is associated with a timer 13. The timer 13, after completion of the exposure time, actuates three switches 14 for terminating an exposure.

For effecting the setting of the X-ray tube voltage, the electronic switch 2 is connected to a kV-regulator 15 which, in turn, is connected with the dosage output comparator element 8. The setting of the X-ray tube current is provided for by means of a current regulator 16, and which has a function generator 17 associated therewith. The function generator 17 includes inputs 18, 19, 20 and 21. Signals are provided at inputs 18 through 20 which correlate with the actual values of the X-ray tube current and the X-ray tube voltage, as well as with the particularly set exposure time. The input 21 has a signal conveyed thereto which correlates with the reference value of the permissible power or output of the X-ray tube at the particular exposure time.

In the illustrated exemplary embodiment, there are provided three exposure times of, respectively, 5 ms, 0.1 second and 1 second. Each exposure is initiated with a fixedly programmed intermediate X-ray tube voltage of 70 kv, the timer 13 thereby assuming the particular setting which corresponds to the exposure time of 5 ms, and with the switching element 12 delivering a signal to the dosage output comparator element 18 in conformance with the reference value of the dosage output for this exposure time, in effect meaning, a signal which results in an optimum degree of film darkening for this exposure time.

When the actual value of the dosage output is larger than this reference value, the dosage output comparator element 8, by means of the kv regulator 15, effects a downward regulation of the X-ray tube voltage until the actual value of the dosage output becomes equal to the reference value. In that case, the exposure is also completed within the time interval of 5 ms. Due to the reduction of the X-ray tube voltage, there is obtained a good image contrast. The described regulating steps naturally must take place within an extremely short time in comparison with the exposure time of 5 ms, so as to achieve optimum film darkening.

If, during the first phase of an exposure, it is determined, at the dosage output comparator element 8, that the actual value of the dosage output is smaller than the required reference value for an optimum film darkening at the exposure time of 5 ms, then the exposure output comparator element 8, through the switching element 12, effects a switching-over of the timer 13 to the 0.1 second exposure time. The switching element 12 concurrently switches in a new reference value at one of the inputs 9 through 11 of the dosage output comparator 8, which correlates with the required dosage output or power at an 0.1 second exposure time for optimum film darkening. If the actual value of the dosage quantity is now greater than the reference value, then the X-ray tube voltage is so far downwardly regulated through the kv regulator 15 until the actual value is equal to the reference value.

If, after the switching-over of the exposure time from 5 ms to 0.1 second, the actual value of the dosage output is still smaller than the reference value, then the timer 13 is switched-over to the 1 second exposure time. Concurrently, a new reference value signal is conveyed to one of the reference value inputs 9 through 11 of the dosage output comparator element 8, so that the reference value of the dosage output conforms to an optimum film darkening at the 1 second exposure time. However, if the actual value of the dosage output becomes larger than the reference value, then again there is effected a downward regulation of the X-ray tube voltage. If, nevertheless, the new reference value is still larger than the actual value then, by means of the dosage output comparator element 8 and the kV-regulator 15, there is effected an increase in the X-ray tube voltage to a second programmed maximum value of 110 kv. At this maximum value, correlation is assuredly achieved, or meaning that at this maximum value during the first exposure phase in all instances the actual value of the dosage output is assuredly higher than the reference value, so that by a downward regulation of the X-ray tube voltage correlation or balancing of values becomes possible.

It may be readily ascertained that in the herein-described X-ray diagnostic apparatus there are rigidly preprogrammed three exposure periods, and that an exposure is always initiated with an intermediate X-ray tube voltage of, for example, 70 kV, as well as a dosage output-reference value which is correlated with the shortest exposure time. Consequently, always when the actual value of the dosage output is smaller then that required for an optimum film darkening within the particular set exposure time, there is effected an automatic switching-over to the next higher exposure time. When the actual value is larger than the reference value, a downward regulation of the X-ray tube voltage is provided until balancing is achieved. If, also during the longest set exposure time of 1 second, correlation or balancing has not been achieved, meaning that also herein the actual value of the dosage output is smaller then the reference value, there is effected an increase in the X-ray tube voltage to the above-mentioned second preprogrammed value.

By means of the inventive X-ray diagnostic apparatus there is provided a satisfactory compromise between the requirement for a short exposure time so as to obtain minimum unclarity in the X-ray image due to movements, and a low X-ray tube voltage for obtaining a good image or picture contrast. Within the scope of the invention, there may also be provided for the rigid programming of two, or possibly more than three exposure periods.

The setting of the X-ray tube current is fully automatically effected in the inventive X-ray diagnostic apparatus according to the drawing by means of the function generator 17 and the current regulator 16. At the reference value input 21 of the function generator 17 there is provided a signal which corresponds to the X-ray nomograph, meaning, the duration of the highest permissible X-ray tube output as a function of or in dependence upon the time. Signals are supplied to the inputs 18 through 20 which correspond to the actual values of the X-ray tube current, the X-ray tube voltage, and to the selected exposure time. The function generator 17 operates through a current regulator 16 to always so set the X-ray tube current whereby the X-ray tube 3 is optimally discharged. In this manner, assurance is provided that the exposure time is always maintained as short as possible.

The electronic switch 2 may be constructed as set forth in the disclosure in German Laid-Open Specification No. 1,961,621. A signal may be provided at the input 21 of the function generator 17 as represented, for example, by the graph of FIG. 2. FIG. 2 illustrates the permissible course of the X-ray power in dependence upon or function of the exposure time. The function generator 17 compares the signal at its input 21, which is in accordance with FIG. 2, with the signals at its inputs 18 through 20, so as to influence the X-ray tube current in the above-described manner. The generation of the signal pursuant to FIG. 2 at the input 21 may be the result of capacitors being discharged, and which are switched together to derive the desired voltage sequence pursuant to FIG. 2. The current regulator 16 may be constructed as described in the disclosure of U.S. Pat. No. 2,962,594.

While there has been shown what is considered to be the preferred embodiment of the invention, it will be obvious that modifications may be made which come within the scope of the disclosure of the specification.

Claims

What is claimed is:

1. In an X-ray diagnostic apparatus for the preparation of X-ray exposures, including timing switch means for determining the exposure time; and a control circuit for providing a predetermined X-ray dosage to a patient, said control circuit having a dosage output measuring arrangement, comparator means connected to said measuring arrangement for comparing the actual value of the dosage output with a reference value so as to effect an optimum X-ray image darkening within the respective exposure time, and setting means for at least one of the operating parameters of an X-ray tube in said apparatus, said setting means being controlled by an output signal from said comparator means for correlating said actual value with said reference value, the improvement comprising; selector switch means for programming an X-ray tube voltage and automatically set exposure time periods suitable for a plurality of varied patient constitutions, said selector switch means selecting a first exposure time for initiating an exposure and transmitting a reference value-forming signal to said comparator means representative of the required dosage output for said exposure time, said selector switch means and setting means for the X-ray tube voltage adapted to be controlled by said comparator means upon initiation of an exposure so as to correlate the actual value of the dosage output with a reference value, so as to effect a reduction in the X-ray tube voltage upon said actual value being higher than the reference value, and to effect a switching-over sequence to a successively longer exposure time and conveyance of a new reference value to said comparator means in conformance with said last-mentioned exposure time upon said actual value being lower than the reference value.

2. An apparatus as claimed in claim 1, said selector switch means being programmed for setting an intermediate value and a maximum value for said X-ray tube voltage, said switch means effecting a switching-over sequence of said X-ray tube voltage from said intermediate value to said maximum value upon the signal corresponding to the reference value at the longest exposure time failing to be correlated through a reduction in the X-ray tube voltage.

3. An apparatus as claimed in claim 1, comprising a function generator, said function generator having a plurality of inputs adapted to respectively receive signal representative of the particular set exposure time, actual value-signals of the actual values of the X-ray tube voltage and current, and a reference value signal representative of the power output curve of the X-ray tube, said function generator being adapted to set the X-ray tube current to produce optimum utilization of the X-ray tube output.