Patent Number: 042008034
Section: summary

This invention concerns a multiple collimator apparatus for determining the distribution of radiation from a radioactive source. Such devices generally include a shield block or plate having spaced bores through it in which measuring probes may be inserted for measuring the radiation collimated by the respective bores. Such multiple collimator apparatus are used in nuclear medical diagnosis when radioactive marking substances have been incorporated in the organs or other body parts to be explored and the radiation for this purpose is generally gamma-ray radiation. It is intended that the radioactive radiation registered in each of the detectors or probes should be related to the respective locations at which the detectors are aimed by the respective bores through the shield plate or block through which they "look." Collimators of various kinds of construction are known. Thus there are collimators for individual probes or detectors (cf. G. J. Hine "Instrumentation in Nuclear Medicine," Academic Press, New York/London, 1967, vol. I, pages 429 to 460) providing a generally cylindrical or sometimes conical bore through a lead shield. The lead shield prevents radioactive rays from regions outside the scope of view of the bore from reaching the measuring detector and thereby affecting the measurement. This function is also served when two or more bores each with a different field of view and each serving a separate detector are provided through the same lead shield. Multiple collimators are known in which a multiplicity of similar bores are arranged at regular spacing in a lead plate. Such collimators, which are called multiple collimators, make possible the coverage of a large region of an object to be investigated by a search raster and thereby to provide an image of the entire object field with gamma-ray cameras (cf. H. O. Anger, "Scintillation camera with multi-channel collimators," J. Nucl. Med., 1964, page 515). Combined collimators are also known in which several individual collimators are combined into a collimator block (cf. H. W. Pabst, G. Hor, H.A.E. Schmidt; Nuclear Medicine "Fortschritte der Nuclear-Medizin in klinischer and technologischer Sicht," S. K. Schattauer-Verlag, Stuttgart/New York, 1975, pages 74 to 77). In a particular case it may be sought to reduce the extent of space occupied by such a combination of collimators. In such a way it has been successful to measure object fields and also functional studies of individual organs, for example of the heart, where separate time-activity measurements can be made for different regions of the organ. Such combined collimators, however, just as the other kinds of collimators mentioned above, do not in all cases meet the requirements of medical diagnosis, for a fixed combination of several collimators in one block has the disadvantage that it is not possible to fit the various individual characteristics of organs under investigation. This is already evident because the organs, as for example the heart, are different for each patient with regard to size, shape, position and configuration to an extent that cannot be neglected. Multiple collimators available up to now have the disadvantage that they are not usable for masking out all but a discrete measuring field from a larger field or are usable in that way only with additional provisions which must be depended on in order to assure a shielding effect with respect to everything outside the selected field of view. Furthermore, the cost of the required precautions does not stand in any acceptable ratio to the experimental results desired. If individual collimators are used that are movable with respect to each other in order to cover a discrete object field, the disadvantage arises that the necessary shielding for each individual device tends to interfere with the other devices, as a result of which the detectors cannot be collected together so closely as would be desirable for the measurement. It is an object of the present invention, therefore, to provide a collimator device for the simultaneous use of several detector probes that permit the setting of the detector probes, appropriately for the organ to be investigated, to conditions closely fitting the requirements of diagnosis work in nuclear medicine, while at the same time providing adequate shielding against disturbing rays. SUMMARY OF THE INVENTION Briefly, detectors and collimator tubes through which they "look" are mounted so as to pivot either about an axis or a point in their mounting within a shield plate or block, generally referred to as a shield plate. One of the probes can "look" in a fixed direction without loss of flexibility of the arrangement, since if all the others can be swung, the relation, among the probes, of their various directions of sensitivity is fully adjustable. The pivoted mounting in the shield plate is so organized that a particular region of a body organ under examination can be brought within the optical scope of all of the measuring probes or detectors under a wide range of variable conditions (for example, spacing from the shield plate) and nevertheless in each position of the measuring probes there is sufficient shielding against disturbing radiation from directions not relevant to the measurement. On the basis of the foregoing principle, bores are made in the shield plate having a bearing shell-shaped widened portion for providing an articulated joint with a collimator tube and the remaining portion of the bore as it leads away from the widened portion is divergent in at least one transverse direction. A collimator tube into which a detector probe can be fitted is provided in each bore of the kind just described having a bearing portion fitting the shape of the bearing shell-shaped widened portion of the bore, so that the remainder of the collimator tube can swing through an angle limited by the divergent portion of the bore. If the articulation is a ball joint, the collimator tube can swing through a solid angle and the divergent portion of the bore is essentially conical, but it is also practical to provide a roller joint articulation, in which case the divergence of the diverging part of the bore need diverge only in one plane and the collimator tubes swing through a plane angle. In any case the shielding, provided by the part of the shield plate not hollowed out for the purposes described and by the bearing-forming portions of the collimator tubes, is made sufficiently great so that no disturbance rays can get into the collimator tubes. The pivoted arrangement of the collimator tubes in the shield plate make it possible to aim the respective detectors at the same target portion of the object to be examined. If desired, the direction of observation of each of the individual detectors in the object field can be made visible by sighting lights. In spite of the movability of the collimator tubes about their pivots, a fully effective shielding is provided against disturbing rays in every position of the collimator tubes. In cases in which it is important to locate the detectors of a multiple collimator according to the invention as close to each other as possible, the diameter of the articulated joints of the shield plate and collimator tubes must be kept as small as possible. In such cases it is practical to put the articulated joints on the side of the multiple collimator apparatus that faces the object to be observed and thereby to assure that the shield plate together with the bearings provides sufficient mass for screening off disturbing rays. In particular cases it can also be practical to constitute the collimator tubes in such a way that they project beyond the shield plate towards the object. The multiple collimator of the present invention is provided by fitting a body rotatably mounted for rotation about its axis of symmetry into a bore of corresponding shape with the rotatable body having a cavity for a collimator tube mounted so as to be pivoted or rotatable therein, the collimator tube and the cavity for it fitting each other in shape. The cavity and the collimator tube fitted into it can be made in different ways according to the particular application in which it is desired to use the apparatus. One of the possible variations of the last-mentioned kind of construction of the multiple collimator according to the invention is the provision of a prismatically shaped cavity in the rotatable body, into which a collimator tube having a rectangular stem is pivoted so that it can swing about an axis running perpendicular to the axis of rotation of the rotatable body. Another variation consists in providing, in the rotatable body, a conical cavity with an axis of symmetry running eccentrically in the rotatable body, while the bore through the collimator tube rotatably mounted in the cavity is arranged eccentrically to the axis of rotation of the collimator tube. In both cases essentially four degrees of freedom of rotation are provided for the adjustment of the movable collimator tube through two simple bearings, so that the setting of the movable collimators can be read by use of two scales. It is therefore appropriate to provide scale graduations on the shield plate and/or on the body rotatable in the bore for determining the angular position of the rotatable body and also scale graduations on the body rotatable in the bore and/or on the collimator tube for determining the position of the collimator tube. The various embodiments of the multiple collimator with collimators adjustable in their respective positions have the advantage that--apart from the reproducibility of the adjustment--statistical data can readily be obtained from which a normal setting, the typical deviations and an optimization of the adjustment procedure can be derived. Thus, for example, the two breast nipples of the patient can for example serve as reference points. With approximately point-shaped radiation regions, the space coordinates of the latter can also be determined. The multiple collimator according to the invention has the great advantage that the detectors can be fitted in an optimum fashion taking account of the object to be measured. A further advantage is that the fields of view of the collimator tubes can be compressed substantially closer together and in the case of combinations of individual collimators, without impairing the effectiveness of shielding. The apparatus, moreover, is particularly well suited for functional analysis of individual organs or segments of organs in using a procedure making use of radioactive marker materials. The invention is further described by way of example with reference to the annexed drawings, in which: FIG. 1 is a top view of a first embodiment of the multiple collimator by which basic principles are explained; FIG. 2 is a section through the multiple collimator apparatus of FIG. 1 along the line A-B; FIG. 3 is a section through the multiple collimator apparatus of FIG. 1 along the line C-D; FIG. 4 is a top view of an embodiment of the multiple collimator according to the invention; FIG. 5 is a section through the multiple collimator apparatus of FIG. 4 along the line A-B; FIG. 6 is a partial top view of a second embodiment of the multiple collimator apparatus according to the invention; and FIG. 7 is a section through the portion of the multiple collimator apparatus shown in FIG. 6, through the line A-B of FIG. 6.