Patent Number: 052241459
Section: description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Basic Idea Referring now to FIG. 3, a basic idea of an X-ray beam limiting apparatus according to the present invention will now be described. As shown in FIG. 3, two sets of pivotable blades 6 and 7 are newly employed instead of the conventional horizontally movable blades 16 and 17 within a narrow triangle space V.sub.2 defined by two X-ray focal points "R.sub.2 " and "L.sub.2 " separated with each other by a predetermined distance, e.g., 35 mm, and also inner edges of pyramid-shaped X-ray beams XR.sub.10 and XR.sub.20. The pivotable blades 6 and 7 have a function to beam-limit the inner edges XR.sub.10a and XR.sub.20a of the pyramid-shaped X-ray beams "XR.sub.10 " and "XR.sub.20 " in order that a desirable common projection field "S.sub.2 " at the X-ray detecting plane "I.sub.2 " apart from the two focal points "R.sub.2 " and "L.sub.2 " by the distance of "SID", may be established by these pyramid-X-ray beams "XR.sub.10 " and XR.sub.20 ". Also, the movable blades 22 and 23 outside the above-described pivotable blades 6 and 7 have the function to beam-limit the outer edges "XR.sub.10b " and "XR.sub.20b " of these pyramid-shaped X-ray beams "XR.sub.10 " and "XR.sub.20 ". As previously described, when an X-ray tube with a shorter distance between two focal points R.sub.2 and L.sub.2 is employed, for instance, approximately 35 mm, the triangle space V.sub.2 defined by a line "RL.sub.2 " connecting these focal points "R.sub.2 ", "L.sub.2 " and also the inner edges "XR.sub.10a " and "XR.sub.20a " becomes narrower, as compared with that of the normal distance of 63 mm. Since, according to the basic idea of the present invention, the pivotable blades "6" and "7" are newly employed within the triangle space "V.sub.2 "; and are pivotable around either a common center line of first and second pivot shafts 39 and 39' (see FIG. 4), or two positionally-shafted center lines of pivot shafts 39R and 39L (see FIG. 6), the entire pivotable blade construction may be made compact and therefore may be readily arranged within such a narrower triangle space V.sub.2. Apparently, these pivotable blades 6 and 7 may be pivotable under other different pivoting conditions such that the center line of the first pivot shaft 39 intersects with the center line of the second pivot shaft 39'. CONSTRUCTION OF FIRST X-RAY BEAM LIMITING APPARATUS In FIGS. 4 and 5, there are shown a construction of an X-ray beam limiting apparatus 30 according to a first preferred embodiment of the present invention. Roughly speaking, a major feature of this first X-ray beam limiting apparatus 30 is to substitute the above-described first rectangular blades 16 and 17 which are horizontally moved, by the pivotable blades 6 and 7. As previously described, since other components (i.e., the circular limiting blade 18, compensating filter blade 19, second rectangular blades 20, 21 and third rectangular blades 22 and 23) of the conventional X-ray beam limiting apparatus 10 are similarly employed in this first X-ray beam limiting apparatus 30, no further explanation thereof is made in the following description. Accordingly, both the pivotable blades 6, 7 and a pivoting mechanism 50 will now be described more in detail. A stereoscopic X-ray tube 35 to which the first X-ray beam limiting apparatus 30 has been applied, has two sets of X-ray focal points "R.sub.2 " and "L.sub.2 " mutually separated with each other by a distance of approximately 35 mm. The pivotable blades 6 and 7 are arranged in such a manner that these blades 6 and 7 are pivotable within the triangle space "V.sub.2 " defined by the inner edges "XR.sub.10a ", "XR.sub.20a " of the pyramid X-ray beams XR.sub.10, XR.sub.20 irradiated via the X-ray focal point from this steroscopic X-ray tube 35 and the line "RL.sub.2 " connecting the two focal points "R.sub.2 " and "L.sub.2 ". It should be noted that although the pivoting mechanism 50 are symmetrically positioned for the respective pivotable blades 6 and 7, only one pivoting mechanism 50 for one pivotable blade 6 is illustrated in FIGS. 4 and 5, for the sake of simplicity. As clearly shown in FIG. 4, this pivoting mechanism 50 is constructed of a stepping motor "32L" which is fixed on a base "31L" and functions as a driving source to cause the pivotable blade 6 to be pivotable; a lead screw shaft 35La pivotably journaled to the base 31L by an L-shaped member "33L" and also mechanically coupled by a coupling member "34L" to an output shaft "32La" of this stepping motor 32L; a nut "37L" having a pin "36L" and screwed to a lead screw part "35La" of this shaft "35L"; and also a guide plate "38L" which is pivotable with respect to a center line of a first pivot shaft "39" as a pivotable center by inserting the pin 36L of the nut 37L into a slot "38La". The pivotable blade 6 is fixed at a tip portion of the guide plate 38L so that this blade 6 is pivotable around the center line of this first pivot shaft 39 in cooperation with the pivotable operation of this guide plate 38L. As represented in FIG. 5, the pivotable blade 6 has an X-ray shielding part "6La" made of, for instance, lead, and also the above-described first pivot shaft 39 fixed at a tip portion of this X-ray shielding part "6La". A size of this X-ray shielding part "6La" is so selected as to sufficiently cover an extending angle ".THETA." between the two pyramid-shaped X-ray beams "XR.sub.10 " and "XR.sub.20 " irradiated from the focal points R.sub.2 and L.sub.2 of the stereoscopic X-ray tube 35. As previously explained, a center of the first pivot shaft 39 of one pivotable blade 6 is so arranged as to be positionaly coincident with a center of a second pivot shaft 39' (shown in FIG. 5) of the other pivotable blade 7 (i.e., a common center line of the first and second pivot shafts), whereby the entire pivoting mechanism for causing both these blades 6 and 7 pivotably may be made compact. An intermediate part of the first pivot shaft 39 passes through a through hole "38Lb" of the guide plate 38L and fixed therein, whereas a ball bearing 40 for rotatably supporting the first pivot shaft 39 is arranged at a rear end part of the second pivot shaft 39'. One pivotable blade 6 limits one inner edge "XR.sub.10a " of the pyramid-shaped X-ray beam "XR.sub.10 ", whereas the other pivotable blade 7 limits the other inner edge XR.sub.20a of the pyramid-shaped X-ray beam "XR.sub.20 ". The stepping motors 32L and 32R (not shown) drive these pivotable blades 6 and 7 to pivot up to a center portion of each of these pyramid-shaped X-ray beams XR.sub.10 and XR.sub.20, as shown in FIG. 4, in such a manner that the angle extending between these pyramid-shaped X-ray beams XR.sub.10 and XR.sub.20 emitted from the stereoscopic X-ray tube 35 via the X-ray focal points R.sub.2 and L.sub.2 corresponds to the common X-ray projection field at the X-ray detecting plane I.sub.2. In other words, upon rotation of the stepping motor 32L, the nut 37L is transported via the lead screw part 35La up to a position 37' indicated by a two-dot/dash line, the guide plate 38L pivots around the first pivot shaft 39 as a center up to a position 38' also indicated by a two-dot/dash line, and thus one blade 6 many pivot up to a position 6' indicated by a two-dot/dash line. Similarly, the other pivotable blade 7 many pivot up to another position 7' represented by a two-dot/dash line by means of the stepping motor 32R (not shown), whereby this pivotable blade 7 may continuously pivot up to the symmetric position with respect to the pivoting position of the remaining pivotable blade 6. In accordance with the first X-ray beam limiting apparatus 30 with the above-described common pivotable center line for both the pivotable blades 6 and 7; these pivotable blades 6 and 7 may be arranged within the triangle space V.sub.2 defined by the inner edges XR.sub.10a and XR.sub.20a of the respective pyramid-shaped X-ray beams XR.sub.10 and XR.sub.20, and also the line RL.sub.2 for connecting the focal points R.sub.2 and L.sub.2, and may perform the X-ray beam limiting function, even if the stereoscopic X-ray tube 35 with the narrower distance between the X-ray focal points R.sub.2 and L.sub.2. As a consequence, it may provide such an X-ray beam limiting apparatus 30 capable of the enlarged type stereoscopic radiography or fluoroscopy without restricting the dimensions of SID and common projection field. CONSTRUCTION OF SECOND X-RAY BEAM LIMITING APPARATUS FIg. 6 schematically represents a construction of an X-ray beam limiting apparatus 80 according to a second preferred embodiment of the present invention. A major feature of the second X-ray beam limiting apparatus 80 is such that one pivot shaft 39L for one pivotable blade 6 is positionally shifted from the other pivot shaft 39R for the other pivot blade 7, namely a center line of the first pivot shaft 39L is not positionally coincident with another center line of the second pivot shaft 39R. As a result, an X-ray shielding part "6La" of the first pivot shaft 39L is positionally shifted with respect to the other X-ray shielding part "6Ra" of the second pivot shaft 39R, as illustrated in FIG. 6. MODIFICATIONS As apparent from the foregoing descriptions, the present invention is not limited to the above-described first and second preferred embodiments, but may be readily modified without departing from the technical scope and spirit of the present invention. For instance, as illustrated in FIG. 7, another X-ray beam limiting apparatus 90 may be realized by employing the combination of the pivotable blades 6 and 7 with the common pivot center, and furthermore only the circular fixing blade 18, the rectangular blades 22, 23 and the rectangular blades 20, 21, which are positioned in this order along the X-ray beam travelling path. As obvious from FIG. 7, a feature of this X-ray beam limiting apparatus 90 is that the compensating filter blade 19 has been omitted and the positional relationship between the rectangular blades 20;21 and 22;23 is different from that of the first and second X-ray beam limiting apparatuses 30 and 80. Moreover, although not shown in the drawings, many other X-ray beam limiting apparatuses with other blade combinations may be realized, for instance, the combination of the circular fixing blade 18, compensating filter blade 19 and rectangular blades 22, 23 with the pivotable blades 6 and 7 shown in FIG. 6.