GB2170380A - Continuously variable collimator - Google Patents

Abstract

An infinitely variable radiographic collimator (10) includes a pair of rotatably mounted cylinders (14, 16) with grooves (46, 48) about their peripheries, perpendicular to the cylinders' axis of rotation. The grooves are of varying cross section so that the cylinders cooperate to define an aperture of infinitely variable cross section to limit and define a radiative field. The cylinders are mechanically coupled to each other for mechanical simplicity and for precise control of the radiative field. <IMAGE>

Description

SPECIFICATION Continuously variable collimator TECHNICAL FIELD This invention relates to radiographic and fluoroscopic apparatus for use in diagnostic and other analytical procedures. The inventive collimator is particularly advantageous for such use, where a precise and continuously variable radiative field is desired. It will be appreciated that the invention has broader aspects. For example, the continuously variable collimator constructed in accordance with the instant invention could be advantageously applied to electron beam or optical systems, all of which use radiation of one form or another.

BACKGROUND OF THE INVENTION Radiographic and fluoroscopic procedures for purposes of medical diagnosis typically involve exposing a part of the specimen to an x-ray field in an apparatus sensitive to the x-rays. By examining the x-rays after they pass through the specimen, either by reference to the original field or directly, information about the specimen is readily available.

For safety reasons, and to meet applicable safety regulations, the radiation source must be shielded in a housing or enclosure which confines all of the radiation, except that necessary for scanning purposes. Indeed, x-rays are known to be harmful and there is no reason for exposing a patient or the equipment operator to any more radiation than is absolutely required for effective medical treatment.

In other x-ray applications, for instance, x-ray analysis of the weldments of a given mechanical structure, the need for precise control of the radiation field is just as important because there are invariably personnel in proximity to the equipment.

Separate and apart from safety considerations, precise control of a radiation field is highly desirable so that the resulting images are of good quality. If the radiative field extends beyond the area to be viewed, the receptor will tend to adjust itself to the highest intensity, producing a silhouette rather than a true image. A silhouette of the specimen is often useless inasmuch as it is very difficult to glean detailed information therefrom.

In order to control the dimensions of a radiation field, a variety of methods have been used. In particular, aperture systems are disclosed in the following: U.S. Patent No.4,277,685 to Covic et al.; U.S. Patent No. 4,048,498 to Gerlach et al.; U.S.

Patent No. 3,487,218 to Kregs et al.; and U.S. Patent No. 3,060,316 to Peyser.

Covic et al. show a variable collimator which consists of a cylinder with a number of longitudinal slots of differing sizes therein. Slots on opposite sides of the cylinder are of matching size. The cylinder is disposed in the path of the beam of the radiation source, then rotated to change the size and shape of the beam which passes therethrough. It should be noted that only stepwise or discretely variable control of the radiative field is achieved.

Gerlach et al. disclose an aperture system which is made up of plates defining various shapes. The plates are slidingly mounted in a facing relationship so that when they are moved the aperture size changes. Problems with this type of system (see also the '218 Patent to Krebs et a'. and the '316 Patent to Peyser) are at least twofold. Typically, they are complex mechanically, making precise control of the radiation field difficult to achieve. Further, the plates are thin and often don't provide a long enough channel along the beam's path to properly collimate the radiation.

It is accordingly an object of the present invention to provide a method of collimating radiation which is mechanically efficient and limits the field of radiation.

Another object of the invention is to provide for continuous variation of the size and shape of a radiation field, preferably in a linear manner.

Yet another object of the invention is to provide precise and automated control of the size and shape of an aperture.

Still another object of the present invention is to provide a compact and effective beam-limiting device which is automated and reproduces a given set of conditions.

Other objects and advantages of the present invention will become apparent from the discussion which follows.

SUMMARYOFTHE INVENTION The inventive collimator overcomes the deficiencies of the prior art. It solves the problem of how to advantageously provide an aperture of continuously variable dimensions in the path of a radiation source to achieve an infinitely variable radiative field.

The same is accomplished by having an aperture defining member with a groove of continuously varying cross section about its periphery. This member is rotatably mounted in the path of a radiation beam in such a way that the radiation is incident on the groove. The member is rotated by whatever desired amount in order to continuously change the size of the aperture, depending on the particular application. Further refinements of the invention include adding digital controls and aligning a shutter device with the groove of the aperture defining member.

BRIEF DESCRIPTION OF THE DRAWINGS Several ways of carrying out the invention are described in detail below with reference to the drawings, which illustrate only specific embodiments. In the drawings: Figure 1 is an exploded perspective view of an apparatus constructed in accordance with the present invention; Figure 2 is a top plan view of part of the apparatus shown in Figure 1, wherein the collimating cylinders have been partially rotated; Figure 3 is a schematic side elevational view of the invention collimator showing additional apparatus; Figure 4 is a detail of the apparatus of Figure 1; Figure 5 is a schematic representation of a detail of Figure 1; Figure 6 is a detail of the apparatus of Figure 1; Figure 7 is an elevational view of a detail of Figure 1; Figure 8 is a detail of an alternative embodiment of the inventive apparatus;; Figure 9 is a detail of a second alternative embodiment of the present invention; Figure 10 is an exploded perspective view of an inventive shutter arrangement for aligning with the collimating cylinders; and Figure 11 is an elevational view, partially in cross section, ofthe shutter of Figure 10 mounted adjacent the collimating cylinders.

DETAILED DESCRIPTION Referring now specifically to the drawings, Fig. 1 showsthevarious parts of an apparatus 10 constructed in accordance with the present invention. Apparatus 10 comprises generally a housing 12 surrounding a pairofcollimating cylinders 14 and 16 driven by a motor 18. Housing 12 includes a cone aperture 20 mounted atop a top cover22 byway of studs 24. Also included isasub- housing 26. A pair of outer housing plates 28,30 are provided with a plurality of slots 31 to allow for adjusting the height of cylinders 14 and 16.

At one end of sub-housing 26 a pair of mounting blocks 32 and 34 are adapted to mount housing 12 on a C-arm (not shown) or other apparatus adjacent a conventional radiographic source such as an x-ray tube manufactured bythe Eureka X-RayTube Co. of Chicago, Illinois.

Atthe base of housing 12there is a base plate 36 with a rectangular aperture 38. Base plate 36 is adapted to be secured to the housing ofthe radiation source so that aperture 38 is aligned with the focal area thereof. Immediately adjacent plate 388 is another cone aperture 40 with an upper portion 441 adapted to surround a portion ofthe periphery of cylinders 14and 16 respectively. Inthisway, radiation entering apparatus 10 through aperture 38 is confined to the intended path between cylinders 14 and 16.

Cylinders 14 and 16 have a pair of sleeves 50,52 pressed into them for receiving shafts 42 and 44 which are secured to the sleeves by set screws. This mode, or equivalent constructions, are preferable when the cylinders are made of relatively soft material, such as lead. The cylinders have conical grooves 46 and 48 extending about approximately 270 of their periphery (such grooves will be discussed further hereinbelow). The cylinders are also provided with pluralities of gearteeth 54 and 56 for preventing radiation from escaping between the cylinders.

As should be apparentfrom the foregoing and Fig.

1, the various parts ofthe inventive collimator are joined together by shafts 42 and 44 and a plurality of screws and bolts fitted to the various holes, such as slots 31 and holes 57 provided forthis purpose.

While many ofthe parts may be made of any suitable material, parts defining the path of radiation through inventive collimator 10 should be made of a material which is impervious to the radiation. Thus, cone 40, cone aperture 20 and cylinders 14 and 16 are preferably made of lead.

Adjacent sub-housing 26 are a pair of gearing support plates 58 and 60, provided with a pair of holes 62 and 64to hold sleeves 50 and 52. Each shaft 44,42 extends through the plates and has a spur gear 66,68 fixed on one end thereof. As seen more clearly in Fig. 2, these gears are coupled by drive-shaft 42 and bevel gears 82, 84to a motor 18 so thatthey are driven thereby. Shaft42 drives spur gear 68 and rotates cylinder 14. Gear 68, in turn, drives gear 66 on the end of shaft 44 so that cylinder 16 rotates synchronously and in the opposite direction as cylinder 14.

Grooves 46 and 48 have continuouslyvariable cross sections and are adjacently facing each other so that a beam of radiation (Fig. 3, discussed below) passes through a circular hole 15 of continuously varying area when the cylinders are rotated.

Gearteeth 54 and 56 on the peripheries of cylinders 14 and 16 respectively prevent radiation from escaping through the interface between the cylinders. Since itwould be extremely difficult, as a practical matter, to have two cylinders of perfectly matched dimensions and orientation,the gearteeth provide an effective and cost efficient method of blocking the beam. It should be noted thatwhen using a soft material such as lead to fabricate the cylinders, the gear teeth thereon are soft and subject to wear, therefore teeth 54,56 are not in contact in a preferred construction of the invention.

Collimator 10 is aligned with a radiation source 72 (Fig. 3) such that the beam, generally designated by arrows 76 and 78, is axially aligned with apertures 38 and 40 and grooves 46 and 48, aperture 38 being slightly above the focal point 91 of the x-ray tube. In orderto prevent unwanted radiation from escaping into proximate areas, the lower part of the apparatus is surrounded by a cylindrical enclosure 80.

The specimen to be examined is placed between aperture 20 and a receptor, generally shown at 88.

The receptor mightsimply be a film cassette retained by ridges 89 or a more sophisticated apparatus such as a video camera coupled to an intensifier tube 87.

The receptor may include a radiation level detectorto output a signal to controls 90, which in turn convert the signal to digital form so that it may be displayed to a technician who could make any necessary adjustments by rotating the cylinders.

Alternatively, motor 18 is coupled to a feedback potentiometer 92 by bevel gears 84,82 and 94 (see Fig. 2). The potentiometer acts as a position transducer and is calibrated against the angular position of cylinders 14 and 16. Once a technician chooses the desired aperture size, a counter within another set of controls 96 is activated. Depending on whetherthe size of aperture 15 has to be increased or decreased to change the size and angle ofthe beam, the counter goes up or down accordingly. This signal is then fed to a decoderwhich in turn appears on a LED display and gives the size of the opening, and feeds DAC (Digital to Analog Converter) associated with controls 96. The output of the D/A converter feeds a comparator which receives another input from an amplifier fed by feed-back potentiometer 92.

The comparator, after comparing the two inputs, feeds a power amplifier which, in turn, drives motor 18 to increase or decrease the aperture size. The total accuracy of the system is a function of the individual accuracies of the feed-back potentiometer, counter, and the D/A converter. The otentiometer is linear to better than .25 percent, i.e.

less than 1 part in 400. The D/A converter can be 8, 12, or 16 bits depending on the required accuracy.

An 8 bit DAC offers 256 levels of changes. A 12 bit, 4096 levels and a 16 bit considerably greater number of levels and a correspondingly better level of accuracy. In any event, automated control of the inventive collimator allows for efficient adjustment of the radiation field and reproducible results.

Details of the inventive cylinders 14 and 16 are better understood by reference to Figures 4 and 5.

Only cylinder 16 is shown, it being clear that cylinder 14 is identical to cylinder 16. Cylinder 16 has gear teeth 56 and groove 46 about its periphery.

Groove 46 is a continuously decreasing half conical groove (Fig. 5) extending around an angle 0 of 270 .

It should be noted that the radii from the center 98 of cylinder 16 to the line 100 at the bottom of the grooves are becoming continuously shorter in a linearly decreasing manner as the value of O increases so that the area of aperture 15, and accordingly the image at 88 linearly changes with the angle of rotation of the cylinders. This feature of the inventive collimator facilitates control and adjustment thereof.

Of course, the channel could extend more than 270 about cylinder 16, however this is undesirable since rotation of the cylinders more than 270 will cause interference with aperture 15 by other portions of the cylinders as these portions rotate to the position of the aperture. Channel 46 also has a rectangular portion 102 in its periphery which defines a square fixed field (see Fig. 7) when such is desired, as might be the case when an image on a square x-ray film is to be produced.

Figure 6 shows cylinders 14 and 16 as they would be viewed along the path of the radiation beam within collimator 10. As can be seen, the cylinders are matched to define a symmetrical circular aperture of varying size as the cylinders are rotated.

Moreover, gear teeth 54 and 56 are proximate to each other so as to confine the beam to the area between the cylinders.

Further embodiments of the instant invention are illustrated in Figures 8 and 9. Figure 8 is numbered 200 numerals higher than Figure 1, while Figure 9 is numbered 300 numerals higher than Figure 1 for purposes of brevity. Figure 8 shows a cylinder 216 with a rectangular groove 246 having a linearly decreasing cross-sectional area, while Figure 9 shows a cylinder 316 with a triangular groove 346 of linearly decreasing cross-sectional area. Matched sets of these cylinders can be mounted in collimator 10 and operated in the same manner as discussed in connection with Figures 1 through 7 when a radiative field of different shape is desired. The discussion hereinabove of collimator 10 is incorporated here by reference.

The design of a collimator in accordance with the instant invention offers the user a higher degree of flexibility in selecting the size and shape of the radiation field inasmuch as it reduces the radiation field by collimating it to precise and accurate shapes and values. The collimator serves the dual function of collimating a varying-sized field in the fluoroscopic examination mode, and if so desired, a fixed shape in the radiographic mode. This feature is achieved by having a linear variable cut of whatever shape from zero degrees to 270 degrees in the cylinders. The invention is further refined by adding an inventive shutter device 410 adjacent the cylinders as will now be discussed in connection with Figures 10 and 11.

Figure 10 is an exploded view of a compact variable iris device for use in connection with viewing or x-ray devices. The inventive shutter device 410 includes a shutter housing 412 made from one or more plates defining a cavity 414.

Disposed within housing 412 are two gearing plates 416 and 418 supported within the cavity. Plates 416 and 418 have holes or areas 420 and 422 respectively.

Between plates 416 and 418 there is provided two shutters 424 and 426 mounted on pins which engage grooves in plates 416 and 418, the grooves being adapted to track the pins.

Specifically, plate 416 has a pair of parallel slots 428 adapted to receive outer pins 430, which are made of a plurality of parts as shown. Plate 418 has a clover-leaf slot 432 facing plate 416 and adapted to engage inner pins 434. Pins 434 also engage a pair ofcollinear slots 436 in plate 416.

Shutter housing 412 supports an upper drive motor 438 and a lower drive motor 440. The drive motors have gears 442 and 444 on their shafts which engage gear teeth 446 and 448 respectively.

Shutter device 410 is assembled with screws, bolts or by any other method and has a cover plate 450 to secure the gearing plates. Housing 412 also has two end plates 452 which are sized so as to adapt device 410 to be secured to the inventive collimator 10, as shown in Figure 11.

Holes 420, 422 are aligned with aperture 15 such that shutter plates 424 and 426 are in the path of the beam. The radiative field is adjusted as described in connection with Figures 1 through 7 and then further refined with inventive shutter device 410.

In particular, by rotating upper plate 418 by means of motor 438 while maintaining lower plate 416 stationary, the width of the substantially rectangular slit defined by shutters 424 and 426 changes. This is achieved by means of pins 434 which necessarily follow the tracks of grooves 432 and 436.

When plate 418 is held stationary and plate 416 is rotated by means of motor 440 the slit defined by the shutters rotates and changes its width in accordance with the tracking of pins 430,434 in grooves 428, 432, and 436. When both plate 418 and 416 are rotated by motors 438 and 440 running in the same direction at substantially equal speed, the width of the longitudinal slit remains substantially constant, yet the slit will rotate about the circle of the gearing plates.

Thus, the radiative beam is collimated by cylinders 14, 16 to a first shape and then further adjusted by device 410. These features allow very precise control of the radiation field and are particularly advantageous where it is desired to expose a longitudinal specimen, for instance, an arm, to a radiative field. By proper adjustment of the field to the orientation of the specimen, silhouette problems are eliminated.

Although several embodiments of the inventive collimator have been discussed hereinabove, it is to be understood that various modifications will be obvious to those of ordinary skill in the art. Such modifications are within the spirit and scope of the present invention, which is limited and defined only by the appended claims.

Claims (16)

1. In or for an apparatus for collimating radiant energy of the general class having an aperture positioned, configured and dimensioned for limiting and directing radiation emanating from a source to an area where receptor means responsive to the radiation are positioned, a collimator for defining said aperture in a continuous range of sizes comprising: (a) an aperture-defining member with a groove of varying cross section about a portion of its periphery acting with another member to define said aperture; (b) support means for rotatably supporting said aperture-defining member about an axis of rotation; and (c) drive means coupled to said support means for imparting a rotational motion to said aperture-defining member so that the dimensions of said aperture are variable.

2. The collimator according to claim 1, wherein the cross section of said groove is substantially half-conical.

3. The collimator according to claim 2, wherein said aperture-defining member is substantially cylindrical.

4. The collimator according to claim 3, wherein a radius from said axis of rotation to the bottom of said groove changes continuously with angular position about the axis of said cylinder.

5. The collimator according to claim 2, wherein the radius of said half-conical groove continuously changes over said portion of said aperture-defining member with increasing angular position about said axis of rotation.

6. The collimator according to claim 5, wherein the radius of said half-conical groove linearly changes over said portion of said aperture-defining member.

7. The collimator according to claim 6, wherein said groove is positioned, configured, and dimensioned so that said groove extends from about two degrees of rotation about said axis of rotation to any degree of rotation up to about two hundred and seventy degrees of rotation about said axis.

8. The collimator according to claim 2, wherein said aperture-defining member has a rectangular portion adjacent said substantially half-conical groove.

9. A continuously variable collimator for collimating radiation comprising: (a) a first aperture-defining member with a first groove of varying cross section about a portion of its periphery; (b) first support means for rotatably supporting said first aperture-defining member about a first axis of rotation; (c) a second aperture-defining member with a second groove of varying cross section about a portion of its periphery; and (d) second support means for rotatably supporting said second aperture-defining member adjacent said first aperture-defining member adjacent so that said first and second grooves cooperate to define a first aperture.

10. The variable collimator according to claim 9, further comprising drive means for rotating said first and said second aperture-defining members.

11. The variable collimator according to claim 10, further comprising control means coupled to said drive means for activating said drive means.

12. The variable collimator according to claim 9, wherein said first and said second aperturedefining members are gearably coupled to each other.

13. The variable collimator according to claim 12, wherein said first and said second aperturedefining members have pluralities of matching gear teeth about their peripheries.

14. An apparatus for collimating and limiting a field of radiation comprising in combination a continuously variable collimator device defining a first aperture and an iris device cooperatively associated with said collimator defining a second aperture axially aligned with said first aperture, said collimator having an aperture-defining member with a groove of varying cross section about a portion of its periphery acting with another member to define said first aperture, support means for rotatably supporting said aperture-defining member about an axis of rotation, drive means coupled to said support means for imparting a rotational motion to said aperture-defining member so that the dimensions of said field of radiant energy incident on an area is variable;; said iris device having first plate means defining a first central area for passage of radiation therethrough and first tracking means, second plate means defining a second central area for passage of radiation therethrough and second tracking means, means for rotatably supporting said first and said second plate means in a facing relationship so that said first central area is axially aligned with said second central area, shutter means disposed between said first and second plate means for defining said second aperture mechanically coupled to said first and second tracking means, said tracking means being positioned, configured and dimensioned to change the width and orientation of said aperture upon rotation of said plate means.

15. A collimator comprising an adjustable member which is formed with an elongate, peripheral groove of variable cross-sectional size such as to present to a beam to be collimated a beam-collimating aperture of a size dependent on the adjustment of said member.

16. A collimator substantially as herein described with reference to any of the accompanying drawings.