Patent Number: 053496256
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS The x-ray diagnostics installation shown in FIG. 1 includes a pick-up unit composed of an x-ray radiator 1 having a gating stage 2, and a radiation receiver 3, which are held opposite one another by a holder 4. The holder 4 is constructed such that the pick-up unit is adjustable along a support 5 for an examination subject 6. Of course, such an x-ray diagnostics installation can also be executed such that the pick-up unit is stationary and the support 5 is adjustable. It is only necessary that the pick-up unit and the support 5 are adjustable relative to one another, so that a sequence of exposures of an examination region can be produced. The drive of the x-ray radiator I for 1 emission of a ray beam, the gating stage 2 for gating the ray beam, the adjustment of the pick-up unit or of the support 5 relative to one another, as well as the production of an image from the examination region of the examination subject 6 from the signals of the radiation receiver 3 on a display 7, ensue under the control of a control unit 8, the details of which shall be set forth in greater detail below with reference to FIG. 2. As shown in FIG. 2, the control unit 8 includes an operating unit 9 by means of which subject-related data, for example the size, the weight and the physique (thin, average, fat; short, average, tail) of an examination subject 6 can be supplied to an arithmetic unit 10. When, for example, the leg of the patient is to be examined, the arithmetic unit 10 calculates the average length of the leg on the basis of this data, and also calculates the number of exposures to be produced resulting therefrom, the step length of the relative adjustment of pick-up unit and support 5 relative to one another, the electrical parameters required for every exposure, and the diaphragm setting of the gating stage 2 arranged in the beam path of the x-ray beam that is required for every exposure. A pre-setting of the means for the relative adjustment of pick-up unit or support 5, the gating stage 2, and a voltage supply 11 which feeds the x-ray radiator 1, ensues by the arithmetic unit 10 on the basis of the calculated data for each of the successive exposures. Further apparatus-related parameters, for example the radiation receiver format as well as the apparatus geometry (focus-to-subject spacing and focus-to-image receiver spacing) and the desired section width and overlap, can be introduced into this calculation. These apparatus-related parameters can be input entered via the operating unit 9, insofar as they cannot be called as data of a memory of the control unit 8. If the x-ray diagnostics installation includes a digital image processing system, the subject-related data and the apparatus-related parameters can be supplied from the image processing system to the arithmetic unit 10 within the framework of the invention. The display 7 can be in the form of a monitor 12, a printer 13 or a display field of the operating unit 9, so that, as shown in FIG. 3, the subject contour 14, the individual exposure positions 15 through 21, the diaphragm settings in the exposure positions 15 through 21 (shown shaded) the image size in the subject plane, as well as the pick-up regions of the subject relative to the radiation field of the radiation beam calculated from the subject-related data and from the apparatus-related parameters are displayed. In addition, the entire presentation region 22 in the subject plane, the usable presentation region 23 in the subject plane, the section width 24 in the subject plane, the overlap 25 in the subject plane, the step length 26, the number of steps and the image format or formats related to the subject plane can also be indicated or displayed. The starting point for the calculation is a patient-related, anatomically typical, reproducible basic setting of the exposure unit, for example to the navel, that can be easily set under optical sighting supervision as the origin for the coordinates of the patient relative to the pick-up system. Of course, these presentations and data can also be displayed on an x-ray monitor on which an image of the examination region can also be portrayed. The data calculated by the arithmetic unit 10 can be supplied in subject-related fashion to a data memory 27, so that these can in turn be called in as needed. It is thus possible to produce repeatable, subsequent examinations under identical system conditions for a patient. Within the framework of the invention, the parameters of a contrast agent injector 28 required for the examination can likewise be calculated by the arithmetic unit 10 and can be pre-set via the control unit 8. The arithmetic operations implemented in the arithmetic unit 10 for the pre-setting of the x-ray diagnostics installation for the exposure sequence are set forth below, with reference to FIGS. 4 and 5. OF=(EF/FBA)FOA, or OF=EF/V; X=SW-r, with r=OF/2; since also X=r-U, then U=SW-ZX; Z=OF/2-U/2=r-U/2; SB=2[(OF/2).sup.2 -(OF/2-U/2).sup.2 ].sup.1/2 =2(r.sup.2 -Z.sup.2).sup.1/2 ; L.sub.1 =SZ.multidot.SW+OF; L.sub.2 =SZ.multidot.SW+OF-U+SZ.multidot.SW+2Z; and L.sub.3 =L.sub.2 +U/2; wherein; FOA=focus-to-subject distance FTA=focus-to-table distance FBA=focus-to-image intensifier distance in the plane of the blanking OF=subject field EF=input field of the image intensifier U=overlap SW=step width SZ=number of steps SB=section width L.sub.1 =overall subject length L.sub.2 =subject length between the section widths L.sub.3 =medically usable region V=magnification factor Z=pick-up field in the subject plane X and r are parameters shown in FIG. 5. According to a first exemplary embodiment of the invention, an image intensifier input field of 40 cm, a focus-to-image intensifier distance of 123 cm, a focus-to-subject distance of 100 cm, a step length of 20 cm, and a number of steps of 5, are to be entered into the arithmetic unit 10 via the operating unit 9, as a numerical example. On the basis of these inputs, the arithmetic unit 10 then implements the arithmetic operations 1 through 6 recited below: ______________________________________ 1. OF = (EF/FBA)FOA = (40 cm/123 cm)100 cm = 32.52 cm 2. r = OF/2 = 32.52 cm/2 = 16.26 cm 3. X = SW - r = 20 cm - 16.26 cm = 3.74 cm 4. U = SW - 2X = 20 cm - 2(3.74 cm) = 12.52 cm 5. SB = 2[(OF/2).sup.2 - (OF/2 - U/2).sup.2 ].sup.1/2 = 2[(16.26 cm).sup.2 - (16.26 - 12.52/2).sup.2 ].sup.1/2 = 25.64 cm 6. L.sub.3 = SZ .multidot. SW + OF - U + U/2 = 5 .multidot. 20 cm + 32.52 cm - 12.52 cm + 6.26 cm = 126.26 cm ______________________________________ The table recited below can be displayed on the display 7: ______________________________________ overlap = 12.52 cm section width = 25.64 cm usable examination region = 126.26 cm. ______________________________________ According to another exemplary embodiment of the invention, three keys (short, average, tall) are provided at the operating unit 9, which are to be operated in conformity with the physique of the patient to be examined. Upon actuation of a key, the arithmetic unit 10 interrogates a corresponding memory of a data store and, given examination of the leg of a patient as an example, thus obtains the following data for further calculation: ______________________________________ key "short" = 105 cm, key "average" = 115 cm, key "tall" = 130 cm. ______________________________________ Of course, it is also possible within the framework of the invention to enter the actual length/width of the overall examination region of the subject (leg) via the operating unit 9. Further data corresponding to the apparatus geometry can be stored in the data store as permanent values, these being interrogated by the arithmetic unit 10 and being capable of being utilized for the calculation. Permanent values for the apparatus geometry are the image intensifier input field, the focus-to-image intensifier spacing, the focus-to-subject spacing, the overlap and the section width. The arithmetic unit 10 thus calculates the optimum number of steps. According to a third exemplary embodiment of the invention, it is possible in an expansion of the second exemplary embodiment to prescribe the desired overlap and/or the section width via the operating unit 9, which then enters into the calculation. It is possible within the framework of the invention to define the subject contour via suitable separate means and to supply the subject-related data thus obtained to the arithmetic unit 10 on a disk or in some other stored form for further calculation. The pre-setting of the gating stage 2 likewise ensues on the basis of subject-related data, for example by the arithmetic unit 10--on the basis of subject-related data "short, average, tall; thin, average, fat)--interrogating corresponding data of a data store, so that the gating stage 2 is then correspondingly driven via the control unit 8. Data corresponding to the following table for gatings with reference to the example of exposure positions 15 through 21 can be contained in the data store: ______________________________________ Exposure Position 15 16 17 18 19 20 21 ______________________________________ thin 40 cm 40 cm 38 cm 33 cm 35 cm 30 cm 31 cm aver- 40 cm 40 cm 40 cm 35 cm 37 cm 32 cm 33 cm age fat 40 cm 40 cm 40 cm 38 cm 39 cm 36 cm 37 cm ______________________________________ The pre-setting of the voltage supply 11 likewise ensues on the basis of the entry of subject-related data. The arithmetic unit 10 for this purpose also interrogates a data store that contains data of electrical parameters corresponding to the subject-related data, so that the control unit 8 then correspondingly drives the voltage supply 11. A display or an output in some other form of the calculated data on a monitor or printer in tables and/or graphic presentation is possible in accord with all exemplary embodiments of the invention. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.