Patent Number: 043485910
Section: description

BEST MODE FOR CARRYING OUT THE INVENTION Now referring to FIG. 1. A multiple aperture collimator adapter 10 according to the invention is mounted to the front face of a gamma camera (not shown) by means of fasteners 12. The adapter 10 is substituted for the normal multi-holed collimator supplied with the camera, such as shown in U.S. Pat. No. 3,814,938, issued June 4, 1974 to R. J. Martone et al. The adapter 10 may conveniently be of the same size and shape as the lower portion of the cone of prior art pinhole collimators. That is, the top opening of the cone at the face of the gamma camera may be 14.7 inches and the adapter 10 may be in the form of a multi-walled structure of aluminum or steel for structural support with one or more layers of lead for shielding attached thereto. Approximately six and one-half inches away from the face of the gamma camera the cone is truncated at 14 and supplied with a locking device generally indicated at 16 for locking the remainder of the cone 18 and an interchangeable pinhole generally indicated at 20. The opening across truncated end 14 is six inches in diameter but may be as small as about three inches in diameter. Now referring to FIG. 2. The pinhole supporting portion of the cone 18 may be removed and a generally cylindrical collimator 22, preferably a right circular cylinder, may be mounted to the adapter 10 by means of the locking device 16. The cylinder 22 may be of lead or a multi-element structure similar to the cones of the prior art and may be provided with additional support means generally indicated at 24. The walls of the cylinder 22 are preferably thicker at the end 26 near the gamma camera than at the outer end 28. This is because the outer end 28 mainly serves to prevent stray radiation from around the patient from getting to the scintillation crystal, whereas the inner walls 26 prevent oblique rays from the radiating organ from reaching the outer portions of the gamma camera. Those skilled in the art will realize that by masking off the larger portion of the gamma camera (preferably for tyroid uptake studies the cylinder 22 has an inner diameter of approximately three inches) nearly all of the gamma rays from the patient reaching the central area of the gamma camera will be counted and the gamma camera will not be overloaded with counts. As previously stated this is because the outer portions of the gamma camera crystal will not be producing scintillations which would have to be processed by the camera. The walls of the cylinder 22 are approximately one-half inch thick, thus the outside diameter of the cylinder 22 is approximately four inches and the opening in the outer end 14 of the adapter 10 must be at least this diameter. The smallest practical dimension for the inner diameter (or largest inner dimension, if collimator 26 is not circularly symmetrical) is approximately two inches due to the size of the organs studied. Thus the smallest practical inner diameter (or largest dimension) of the opening in the outer end of the adapter 10 is three inches and this distinguishes the adapter 10 from the pinhole collimators of the prior art which have much smaller openings for multiple pinholes. Thus the length of the cylinder 22 is substantially greater than its inner diameter as shown in FIG. 2. Referring to FIG. 3. A straight ultrafine collimator generally indicated at 30 is shown mounted to the adapter 10. The collimator comprises a support structure 32 which is held to the adapter by means of the locking ring 16. Inside the support structure 32 is a straight ultrafine collimator 34 formed of lead having a plurality of fine parallel channels therethrough. As previously explained the straight ultrafine collimator 30 may be utilized for small organ studies such as heart studies of increased resolution. Referring to FIG. 4. A converging collimator generally indicated at 36 may be top loaded into adapter 10 as shown. It comprises the lead collimator 38 having a plurality of conically diverging channels therethrough which provide an enlarged image of image plane 40 on the scintillating crystal of the gamma camera. The collimator itself 38 is surrounded by a light filler material 42 forming part of the collimator insert 36. In FIG. 5 there is shown an alternative method of mounting pinhole supporting truncated cone 18 to adapter 10. This means comprises fasteners 44 which conveniently may be spring loaded locking pins which must be pushed or pulled and rotated to lock or unlock the sections 10 and 18. Now referring to FIG. 6. There is shown an alternative form of straight bore flat field, or uptake, collimator generally indicated at 46. This comprises a flat plate portion 48 and an upstanding right cylindrical portion 50 both formed of radiation shielding material mounted to the gamma camera by means of fasteners 12 in the same way that adapter 10 is mounted. The smallest practical dimension for the inner diameter of cylinder 50 is two inches as previously explained. The largest practical inner diameter is about five inches (the wall thickness being one-half inch) as increasing the opening exposes the camera to more and more background radiation and the camera cannot correctly process these counts. It will thus be seen that the objects set forth above among those made apparent from the preceding description are efficiently attained and since certain changes may be made in carrying out the above methods and articles without departing from the scope of the invention it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all of the statements of the scope of the invention which as a matter of language might be said to fall therebetween.