Development of a high-sensitivity radiation detector for chromatography

Radionuclide techniques will be increasingly important for the development of biofuels, since they can both uniquely characterize metabolic pathways and image large model systems. We are investigating the application of nuclear medical imaging tools and techniques to biofuel development, using high-sensitivity chromatographic radiation detectors and compounds radiolabeled with short-lived, cyclotron-produced, positron-emitting isotopes (e.g., ¹¹C). The application of high-sensitivity radiation detectors to standard chromatographic techniques should allow for the measurement of numerous pathway constituents whose levels normally fall below detection limits of conventional instrumentation. In this paper, we describe a proposed parallel-plane PET camera designed for HPLC (high performance liquid chromatography) with over 40 times greater sensitivity than a conventional HPLC radiation detector; this PET camera could be used to image radioactivity in the HPLC exit tube or column. We also present results using a high-sensitivity HPLC radiation detector comprised of 8 HR+ PET detector modules arranged into a parallel plane and read out with HRRT electronics. This high-sensitivity radiation detector was placed in line after a conventional HPLC radiation detector (a small CsI:Tl scintillator crystal coupled to a PIN photodiode). If we inject 9.3 ¿Ci of [¹⁸F]FDG into the HPLC system, we see similarly shaped peaks with an excellent signal-to-noise ratio from both radiation detectors. If we inject only 4.1 nCi of [¹⁸F]FDG, we measure a signal-to-noise ratio of 27:1 with the high-sensitivity radiation detector and about 3:1 for the conventional radiation detector. We have therefore demonstrated that a high-sensitivity radiation detector, using a parallel-plane PET camera, could become an important tool for fundamental biofuel research.