Atherosclerosis and its consequences are the main cause of mortality in the United States and the western world. Detection of metabolically active regions of atherosclerotic plaque can provide insights on those plaques that are prone to rupture, leading to a tissue infarction. The metabolic activity of these plaques can be identified using positron emission tomography (PET). However, such detection has been elusive in the coronary arteries due to motion and detection sensitivity. One of the techniques capable of improving precision as an affordable alternative is the use of an optical scintillating fiber for the detection of 18-Fluorine Fluorodeoxyglucose (18F-FDG), a compound that is accumulated in metabolically active areas of the atherosclerotic plaque. Here we report on a prototype scintillating fiber detection system designed to characterize the beta emission, particularly positron emission, by 18F-FDG. We demonstrate the ability to effectively measure the presence of 18F-FDG contained in-vivo along with the ability discriminate against ambient light based on energy. This paper presents a catheter-based hardware and software platform based on the use of a scintillating fiber optic catheter. The system measures a short (2-3 ns) burst of photons that are generated by the stimulation of the plastic scintillating fiber by a positron (633 kEv) emitted by the radioactive compound. It can be used to determine the presence of 18F-FDG in-vivo and accurately detect the active decay as the 18F-FDG retained in the metabolically active plaque. The proposed instrument was tested in-vitro and its sensitivity was also measured in-vivo. The developed system may be used in the detection of 18F-FDG, as surrogate of inflammation, providing critical in-vivo information of the metabolism in areas of inflammation.