Standardization of 99mTc

60 years of absolute standardization of radionuclides by coincidence counting methods in the Romanian metrology laboratory

This review paper presents the contribution of the Radionuclide Metrology Laboratory (RML) to the development and practical application of the coincidence counting methods. It is also intended to pay tribute to Dr. Enric Leon Grigorescu, the founder of our school of radionuclide metrology. A synthetic treatment of the method, applied to some classes of radionuclides with their common and particular aspects in standardization, is presented: pioneering calculation of instrumental corrections, specific method corrections applied for various types of decay schemes in the variant of efficiency extrapolation, results obtained in international comparisons.

Primary standardisation of technetium-99m by liquid scintillation coincidence counting

Technetium-99m was standardised by the 4π(LS)ce-γ coincidence extrapolation method. Sensitivity of the 4π(LS) channel to two types of radiation, namely conversion electrons and γ-rays, resulted in incorrect activity values being obtained when this was not adequately accounted for. Measurements were more robust when the LS detection efficiency was optimised, and when a γ-window setting was used that monitored the combined LS efficiency for conversion electrons and γ-rays. The primary standard was internationally compared through participation in the BIPM.RI(II)-K4.Tc99m key comparison.

Absolute standardizations of 99mTc and 57Co by 4π electron-gamma liquid scintillation coincidence counting for SIRTI and SIR comparisons

The radionuclides ^99mTc and ⁵⁷Co were standardized via absolute liquid scintillation counting techniques. We provide the first technical report on the absolute standardization of ^99mTc using 4π(LS)e-γ coincidence counting. The low detection efficiency of low-energy conversion electrons translates into a large efficiency extrapolation range. A simulation indicated that the γ-ray interacting with the liquid scintillator introduces curvature to the count rate vs. efficiency relationship, the approximation of the functional form used for extrapolation providing the main measurement uncertainty for ^99mTc. A detection efficiency analysis for both radionuclides is presented. Results from the standardizations, and SIRTI and SIR comparison exercises are reported.

Standardization of (99m)Tc by means of a software coincidence system

The procedure followed by the Nuclear Metrology Laboratory, at IPEN, for the primary standardization of (99m)Tc is described. The primary standardization has been accomplished by the coincidence method. The beta channel efficiency was varied by electronic discrimination using a software coincidence counting system. Two windows were selected for the gamma channel: one at 140 keV gamma-ray and the other at 20 keV X-ray total absorption peaks. The experimental extrapolation curves were compared with Monte Carlo simulations by means of code ESQUEMA.

Comparison for quality assurance of 99mTc activity measurements with radionuclide calibrators

In 2005, the Physikalisch-Technische Bundesanstalt (PTB) and the QSA Global GmbH (QSA) organised a national comparison of (99m)Tc solution measurements. The purpose of this comparison was to gain information on the quality of routine activity measurements carried out in the field of nuclear medicine in Germany. In addition to this, an ampoule containing a calibrated (99m)Tc solution was sent from PTB to the Bureau International des Poids et Mesures (BIPM) to have the activity result entered into the database of the International Reference System (SIR), and thus demonstrating traceability of the measurements to the SI. In the following, we will report on the activity standardisation carried out at the PTB, and on the way in which the national comparison had been organised, and we will provide information on the analysis as well as on its results.