Electric heating – Microwave heating – Fluid heater
Patent
1992-12-11
1994-05-03
Leung, Philip H.
Electric heating
Microwave heating
Fluid heater
219750, 219696, 219693, 422 21, H05B 670
Patent
active
053089448
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microwave device intended for the treatment of process liquids, preferably the labelling of precursors to radiopharmaceuticals. The invention also relates to a method for treating process liquids, preferably when labelling precursors to radiopharmaceuticals with the aid of microwave radiation.
2. Description of the Prior Art
In certain cases, treatment with microwaves is able to increase drastically the rates of organic reactions. See in this respect R. Gedye et al, Tetrahedron Letters, 27 279 (1986). Microwaves have also been earlier used for the preparation of positron-emitting precursors that are intended for labelling purposes; see R.a. Ferrieri et al, Int. J. Appl. Radiat. Isot. 34 897 (1983). Microwaves have also been used in the preparation of radiopharmaceuticals labelled with .sup.11 C and .sup.18 F. Such microwave treatment processes result in short reaction times and higher yields of the radio-labelled product. The microwave device used in the aforesaid liquid reactions is a conventional domestic microwave oven. An oven of this kind normally has a microwave frequency of 2450 MHz.
In the preparation of radiopharmaceuticals, there is used an accelerator for the preparation of radioactive isotopes which are formed into larger molecules in a subsequent radiochemical process and later administered to the patient, who is subsequently examined with a positron camera. The normal half-life of the isotopes is from 2 minutes to about 110 minutes. It will be realized that the radiochemical process must be capable of being carried out quickly, in view of the short half-life of the isotopes.
The microwave field can be described as a periodically reversed electromagnetic field. The electrons in the polar molecules follow the field direction and are placed in periodic motion, which in turn results in the generation of heat, among other things.
The drawbacks with the use of the aforesaid microwave oven when treating precursors to radiopharmaceuticals are that the microwave field cannot be adapted either to the type or to the quantity of the process liquid to be treated. The geometry of the oven is determined once and for all, and the microwave field can neither be concentrated nor varied with respect to strength and frequency.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and a microwave device of the kind defined in the introduction which will enable a microwave cavity to be adapted geometrically to the amount and to the type of process liquid used, with the intention of shortening the process-liquid treatment time and of increasing the yield in which labelling substances are incorporated in a larger molecule.
This is achieved in accordance with the invention with the aid of a microwave device of the kind defined in the following claim 1 and with the aid of a method of the kind defined in the following claim 5.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference to the accompanying drawings, in which
FIG. 1 illustrates schematically a microwave device constructed in accordance with the invention;
FIG. 2 is a cross-sectional view of an alternative embodiment of the microwave cavity of the microwave device;
FIG. 3 is a diagramme which illustrates the effect of the microwave cavity geometry on solvent boiling times;
FIG. 4 is a diagramme which illustrates the effect of using salt in the process liquid to reduce the boiling time of different solvents;
FIG. 5 is a diagramme which illustrates the relationship between the intensity of the microwave field and the boiling time of given, different solvents with a given microwave cavity geometry;
FIG. 6 illustrates diagrammatically the reaction of .sup.18 F with 4-nitro-4'-fluorobenzophenone;
FIG. 7 is a diagramme which illustrates the yield obtained when incorporating .sup.18 F with the aid of conventional heating processes in the absence of microwave treatment;
FIG. 8 is a diagramme correspo
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Elander Nils
Stone-Elander Sharon A.
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