Patent Number: 045132046
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention generally relates to the field of nuclear medicine. In particular, it relates to the field of radiation diagnosis and to examinations of a patient by means of a scintillation camera. Still more particularly, this invention relates to a housing or container for carrying a radioactive isotope which housing is to be attached to the patient's body, the isotope thereby serving as a motion detector or as an anatomical marker for nuclear images. 2. Description of the Prior Art In nuclear medicine, a radioactive tracer such as technicium is administered to a patient undergoing examination, and the distribution of the tracer in the patient's body is viewed by aid of a scintillation camera. A problem associated with this kind of nuclear examination is the movement of the patient. When the patient moves during examination, a blurred image may result. In order to overcome this disadvantage, a diagnostic motion correction scheme has been developed, see U.S. patent application Ser. No. 324,090, filed by Mark W. Groch and James T. Rhodes, under the title "Motion Correction Circuitry and Method for a Radiation Imaging Device", on Dec. 1, 1981. The disclosure of this application is incorporated herein by reference. According to this motion correction scheme, a blurring of e.g. .sup.99m Tc gated blood pool images due to patient motion is corrected. This is accomplished by introducing a special radioactive point source, in particular a gamma ray emitting radioisotope, whose energy window lies outside that of .sup.99m Tc, into the field-of-view of the scintillation camera. The point source remains outside of the patient's body; thus, no gamma rays emitted from the source are scatter events. Then the centroid of the point source is monitored. When a change in the centroid of the point source is detected due to patient motion, the .sup.99m Tc events are corrected and repositioned to take into account the motion artifact. In cardiac studies, for instance, the movement of a special radioactive source which is fixed to the chest of the patient is detected. This movement is subtracted from the detected radiation coming from the tracer isotope of different energy signature flowing in the blood through the heart. Thus the "dual isotope motion correction scheme" eliminates the motion blur in the images as they are acquired. There are two problems that one must keep in mind when using such a centroid (point) source external to the patient's body during image acquisition. First, the special radioactive point source must be within the field-of-view and the events emitted must be detected through the collimator of the camera. Second, since the point source should be encased in a shielding medium which will attenuate .sup.99m Tc events emanating from the patient's body, the point source must not obstruct any important anatomical structures in the field-of-view. SUMMARY OF THE INVENTION 1. Objects An object of this invention is to provide a housing for a radioactive point source which is to be attached to a patient in nuclear medical examinations. Another object of this invention is to provide such a housing which reliably retains and shields the point source, but leaves an opening free for emission of radiation towards a radiation detection system such as a scintillation camera. Still another object of this invention is to provide a housing for a radioactive point source which can be used in routine nuclear examinations either as a motion detector or as an anatomical marker for nuclear images. 2. Summary According to this invention, a housing for a radioactive source comprises a first shielding body, a second shielding body, and connecting means for connecting the two bodies. The first shielding body has a protrusion which contains a first recess for inserting the radioactive source. The second shielding body has a second recess in its surface. The second recess is shaped so that the protrusion fits therein. When the radioactive source is inserted into the first recess and the protrusion is located in the second recess, the radioactive source will emit radiation into the environment primarily through the conical aperture. According to a preferred embodiment, a .sup.241 Am centroid source is encased in a disk shaped tungsten alloy holder. The bottom part of the disk is to be laid on the patient so that the top part which contains the gamma ray escape aperture, faces away from the patient's body. The escape aperture is cone-shaped at an angle of e.g. approximately 120.degree. with an exit hole of approximately 2 mm. The first of the two aforementioned problems is solved by insuring that the source is in the field-of-view and that the disk holder not be tilted by more than 60.degree. from a plane perpendicular to the collimator holes. The second of the aforementioned two problems has a different solution depending on the view and collimator used in imaging. 1. RAO with slant hole collimator: The point source should be placed anatomically below the heart and just to the left side of the chest wall center. 2. ANT with parallel hole collimator: The point source should be placed anatomically anywhere below the heart, as long as the source faces anteriorly. 3. LAO with parallel hole collimator: The point source should be placed anatomically below the heart and on the central left to far left side of the chest wall. Adhesion of the centroid point source to the patient is preferably accomplished by placement of surgical tape in an X-pattern over the top side of the source, adhering the source firmly to the patient, thus insuring that patient and source motion is unified. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.