Recent technologic developments on high-resolution beta imaging systems for quantitative autoradiography and double labeling applications

Abstract

Two novel beta imaging systems, particularly interesting in the field of radiopharmacology and molecular biology research, were developed these last years. (1) a beta imager was derived from research conducted by Pr Charpak at CERN. This parallel plate avalanche chamber is a direct detection system of β radioactivity, which is particularly adapted for qualitative and quantitative autoradiography. With this detector, autoradiographic techniques can be performed with emitters such as 99mTc because this radionuclide emits many low-energy electrons and the detector has a very low sensitivity to low-range γ-rays. Its sensitivity (smallest activity detected: 0.007cpm/mm2 for 3H and 0.01 for 14C), linearity (over a dynamic range of 104) and spatial resolution (50μm for 3H or 99mTc to 150μm for 32P or 18F (β+)) gives a real interest to this system as a new imaging device. Its principle of detection is based on the analysis of light emitted during the interaction with an intensified CCD camera. This property may suggest new potential applications, particularly in the field of β-rays selection according to their energy. This detector provides a new fast way to detect all β-emitting isotopes in biological samples up to 20cm×25cm (electrophoresis gels, hybridization membranes, tissue sections on glass slides, TLC plates and any other planar two-dimension samples). It is ideal for tritium detection, 500 times faster than classical film, thus maximizing the research productivity. (2) A micro imager is based on contact imaging through a solid scintillator sheet. Light emitted is amplified through an image intensifier tube and is analyzed with a CCD camera. The full field of view is smaller than the first one (24mm×32mm) but a better spatial resolution is obtained (typically 15μm for 3H, 20μm for 14C and 35S). The specifications of this detector are: efficiency 50–100% depending on isotope, linear response over a dynamic range of 104, smallest activity detected: 0.4cpm/mm2 for 3H and 0.04cpm/mm2 for 14C. Using these detectors, quantification is much easier and more precise than that of the radiological film because of direct counting of radioactivity. However, this quantification imposes a few limitations among which are the necessity of fabrication and simultaneous measurement of standards. With new developments of these devices it is possible to detect in the same sample two different isotopes: 3H and 14C for example, which is very attractive to many researchers today.