Radionuclidic purity

Radionuclidic impurities in the eluate are directly related to the production mode of parent Mo. In any case, Mo is the most important impurity. The limit of contamination with stated in the Ph. Eur. is 0.1% of the total eluate activity. With irradiation-produced molybdenum-99, other radionuclidic impurities are limited to 0.01% of the total radioactivity. Identified impurities include Sn-113, Au-198, Au-199, Cs-134, and Nb-92. 

On the other hand, fission-produced molybdenum-99 may contain a number of radionuclidic impurities (Briner and Harris 1974 Hammermaier et al. 1986). Limits of contamination are listed in Table 5.5 with reference to the radionuclide and type of radiation. 

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Figure 6. Elution pattern of 70 mCi generator. Key A, mCi Au-195in per eluate and RN, radionuclidic purity of eluates ( /1 Ci Hg-195m/mCi Au-195m).

Production of Sr-82. An important consideration in the development of radioisotope generators is the availability, cost, and radionuclidic purity of the long-lived parent. In the case of Sr-82, the 25 day radionuclide is needed in 100-200 mCi amounts in order to provide adequate elution yields of Rb-82 from one loading of Sr-82 every three months. Initially the Sr-82 for the generator was produced at the Lawrence Berkeley Laboratory (LBL) 88-inch cyclotron by the Rb-85 (p,4n) Sr-82 nuclear reaction (12). However, because of the long irradiation time required to produce... 

Breakthrough. Eluate radionuclidic purity is determined by Nal scintillation spectrometry on 50 ml of eluate. Samples must be held at least one hour before measurement to allow full decay of Rb-82. To improve sensitivity of measurement, the most prominent 511+514 keV peak is counted. Computations are based upon comparison with an aliquot of Sr-82+Sr-85 solution used to prepare the generator.. Data are expressed in units of yCi Sr-82/ml of eluate/ mCi Rb-82 at end of elution. 

Studies of short-lived radionuclide generators (4-6) do not adequately treat the quantitative problems of the daughter nuclide elution or those specific to their optimal clinical use. Two essential physical characteristics of a generator are the yield of the daughter nuclide and its radiochemical and radionuclidic purity. To realize the full potential of a short-lived radionuclide generator for medical studies requires that these two characteristics are optimized and are compatible with parameters important to clinical use such as total perfused volume and duration of the scintigraphic examination. 

Radionuclidic Purity Radionuclidic purity is defined as the fraction of the total radioactivity in the form of the desired radionuclide present in a radiopharmaceutical. Radionuclide impurities may arise from impurities in the target material or from fission of heavy elements in the reactor [2], In radionuclide generator systems, the appearance of the parent nuclide in the daughter nuclide product is a radionuclidic impurity. In a "Mo/"mTc generator, "Mo may be found in the "mTc eluate due to breakthrough of "Mo on the aluminum column. The presence of these extraneous radionuclides increases the radiation dose to the patient and may also obscure the scintigraphic image. 

Radionuclidic purity is determined by measuring the characteristic radiations emitted by individual radionuclides. Gamma emitters are distinguished from another by identification of their y energies on the spectra obtained from a Nal crystal or a Ge (germanium) detector. This method is called y spectroscopy. 

If the number of radionuclides present in the sample is low, the decay curve can be separated by subtraction into the individual decay curves of the radionuclides, either graphically or arithmetically, as shown in Fig. 7.2. The analysis of decay curves is of practical importance for the investigation of radionuclide purity. As examples, contamination of a sample by a short-lived impurity is shown in Fig. 7.3, and contamination by a long-lived impurity in Fig. 7.4. 

The task of quantitative and effective separation of small amounts of radionuclides has appreciably enhanced the development of modem separation techniques. High radionuclide purity is of great importance for application in nuclear medicine as well as for sensitive measurements. In this context, impurities of long-lived radionuclides arc of particular importance, because their relative activity increases with time. For example, if the activity of Sr is only 0.1% of that of Ba after fre.sh separation, it will increase to 11.5% in three months. 

Indirect formation of I via the production of - Xe leads to higher radionuclide purity. Several reactions are feasible ... 

The radionuclidic purity of Lu produced from either a natural or an enriched target was approximately 99.99%, as was ascertained by analysing the... 

Physicochemical Tests Physicochemical tests include the tests for the physical and chemical parameters of a PET radiopharmaceutical, namely physical appearance, isotonicity, pH, radionuclidic purity, chemical purity, and radiochemical purity. 

Radionuclidic purity Not less than 99.5% should correspond to 511 keV, 1.022 MeV, or Compton scatter peaks of 18F... 

Define (a) radionuclide purity, (b) radiochemical purity, (c) chemical purity of a radiopharmaceutical. 

Radionuclidic purity. The fraction of the total radioactivity in the form of the stated radionuclide. Any extraneous radioactivity such as "Mo in "mTc-radiopharmaceuticals is an impurity. 

Hammermaier A, Reich E, Bogl W (1986) Chemical, radiochemical, and radionuclidic purity of el-uates from different commercial fission Mo/ Tc generators. Eur J Nucl Med 12 41-46 Lin MS, McGregor RD, Yano Y (1971) Ionic aluminium (III) in generator eluate as an erythrocyte-agglutinating agent. J Nucl Med 12 297-299... 

Radionuclidic Purity. The European Pharmacopeia and national regulatory agencies recommend determination of Mo in the primary eluate to assure high quality of generator eluates (DIN 6854). 

RADIOPHARMACEUTICALS A radiopharmaceutical is a preparation of adequately constant composition, radiochemical and radionuclidic purity and uniformity of physiological (pharmacological) action for use in medicine as a diagnostic aid or therapeutic agent... 

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