Patent Number: 044141459
Section: summary

The present invention relates generally to a method for preparing a .sup.195m Au-containing liquid comprising adsorbing .sup.195m Hg on an adsorption agent and then eluting the daughter radioisotope .sup.195m Au from the adsorption agent. The present invention also relates to a method for conducting a radiodiagnostic examination using a .sup.195m Au-containing liquid and to a radioisotope generator capable of producing a .sup.195m Au-containing liquid. Radioisotopes are frequently employed in medicine for diagnostic purposes. One radioisotope frequently used for diagnostic purposes such as diagnostic examinations is .sup.99m Tc, generally in the form of a pertechnetate. .sup.99m Tc is a useful radioisotope for diagnostic examinations because it emits gamma rays of a suitable energy level and in sufficient quantity that commonly used detection systems such as gamma cameras can be used with maximum efficiency. However, for certain applications, the comparatively long half-life of .sup.99m Tc, about six hours, is disadvantageous since the radioactive .sup.99m Tc material remains circulating in the body for a relatively long period of time. Consequently, an immediate repetition of a particular diagnostic examination is not possible. Moreover, the relatively long half-life of .sup.99m Tc has an adverse influence on the radiation load, i.e., the overall quantity of radiation to which a patient undergoing diagnosis is exposed is comparatively large. In particular, .sup.99m Tc is less than suitable for cardiological examinations due to its relatively long half-life. For example, a radioisotope having a relatively short half-life is required to evaluate the movements of the ventricle walls of the heart and to perform quantatative measurements of heart functions such as ejection fraction computations and determination of the size of shunts. Therefore, a radioisotope having a half-life between, for example, about 4 and 45 seconds would consequently be of great importance in radiodiagnostic examinations, particularly in cardiological examinations. Of course, a radioisotope having such a short half-life could not be transported any significant distance and would therefore have to be produced at approximately the same location where it is to be used. It is, therefore, apparent that stringent requirements must be imposed upon the mode of preparation of such a radioisotope, since only a very simple and hence rapid preparation, preferably from an isotope generator, can be conducted in a hospital or clinical laboratory to effectively produce such a radioisotope having a relatively short half-life with a minimum of radiation complications. Of the many possible radioisotopes, the radioisotope .sup.195m Au would apparently be very suitable for the above-mentioned purposes since .sup.195m Au emits only gamma rays, the emitted rays are of a suitable energy (about 261 KeV), and the rays are emitted in a sufficient quantity to enable observation with a suitable detection apparatus such as a gamma camera. Furthermore, the half-life of .sup.195m Au is only about 30.6 sec. The .sup.195m Au radioisotope is formed as a decay product from the parent isotope .sup.195m Hg having a half-life of about 40 hours which is of sufficient duration for practical use. The parent isotope can be produced in a cyclotron by irradiating .sup.197 Au with protons and then isolating the parent isotope from the exposed material. Y. Yano (Radiopharmaceuticals, Ed. Subramanian et al., Soc. Nucl.-Medic. Inc., N.Y. 1975, pp. 236-245) stated that the generation of .sup.195m Au from .sup.195m Hg was under investigation and that a separation of the parent isotope and the daughter radioisotope by means of an ion exchanger was being studied. However, in the meantime, no publication has reported that anyone has succeeded in satisfactorily obtaining this radioisotope which appears well adapted for certain radiodiagnostic examinations. Furthermore, the above-mentioned literature article suggested the use of an ion exchanger in the separation of the .sup.195m Hg parent isotope from the .sup.195m Au radioisotope. An ion exchanger is usually understood to be a resin, for example, a sulphonated phenol-formaldehyde resin or a phenol-formaldehyde resin provided with other functional groups. However, these resins or copolymerisates would be less than suitable to serve as an adsorption agent for the .sup.195m Hg parent isotope because their adsorptivity for mercury ions usually does not differ significantly from that for gold ions and, in addition, their radiation stability is usually rather low. Furthermore, these resins often contain monomers or other low-molecular weight compounds which can contaminate the eluate upon elution of the daughter isotope. Due to the relative short half-life of the daughter isotope, any purification of the eluate is practically impossible. In accordance with one aspect of the present invention, a method is provided for preparing a .sup.195m Au containing liquid in a simple and efficient manner by adsorbing .sup.195m Hg on a suitable adsorption agent and subsequently eluting the daughter isotope .sup.195m Au from the adsorption agent with a suitable eluant, the adsorption agent comprising a mercury-ion binding material having a greater adsorption affinity for mercury ions than for gold ions. In another aspect of the present invention, a radioisotope generator capable of producing a .sup.195m Au-containing liquid is provided, the generator including an adsorption agent comprising a mercury-ion binding material having a stronger adsorption affinity for mercury ions than for gold ions. The method for preparing a .sup.195m Au-containing liquid and the radioisotope generator capable of producing a .sup.195m Au-containing liquid in accordance with the present invention preferably are used in conjunction with processes for conducting radiodiagnostic examinations in warm-blooded animals such as a human, particularly in examinations of the heart of the animal. Other potential uses for the .sup.195m Au-containing liquid are in studies of peripheral arterial blood supply such as renal artery flow studies, cerebral arterial flow studies and the like. Thus, in a further aspect of the present invention, a process for conducting a radiodiagnostic examination using a .sup.195m Au-containing liquid is provided, the process comprising administering to an animal the .sup.195m Au-containing liquid and monitoring the radioactivity emitted from the animal in a desired location such as the heart or portion thereof.