Μοντελοποιηση Ιατρικων Απεικονιστικων Συστηματων Ρετ Για Την Μελετη Βελτιστοποιησης Της Χορηγουμενης Δοσης

Abstract

The continuous development of clinical applications in Positron Emission Tomography (PET) raises the need for a more effective usage of the injected radiopharmaceuticals. The design of a protocol for the injected dose, which will be adapted according to the special characteristics of both the patient and the imaging system, consists a long-term research objective for many laboratories worldwide.This diploma thesis presents an approach in modeling a medical imaging system which uses Positron Emission Tomography technology. Its aim is to accurately estimate those performance parameters that are related to the system response time, and are affected by the injected dose and the individual characteristics of the scanned object.The modeling process included analytical and static cylindrical phantoms that were placed inside the PET system, with the use of the simulation software package GATE. Two series of simulations were carried out; the first included a point source and the second a line source. These two extreme cases were studied thoroughly in order to extract specific general conclusions on the imaging system’s response.The point source at the center of the cylindrical phantom case simulates tissues in the human body that demonstrate relatively high uptake values. Such tissues could be malignant tumors where the injected radiopharmaceuticals are targeting. However, the radiopharmaceutical distribution in the human body covers much larger areas that can be extended beyond the axial field of view (FOV) of the system for a certain bed position. This was the main reason for performing a second series of simulations with exactly the same phantom but with a linear source placed along the phantom’s axis. In both cases three series of simulations were carried out, using a cylindrical phantom with three different radii so that three separate patient populations could be studied. This particular modification in the phantom’s geometry gave some useful results and correlations for the total system response and how it can be related to the object’s volume. In case of the point source particularly, it was possible to extract a set of equations that correlate the system’s response with both the phantom’s characteristics and the injected dose. This diploma thesis’ results can be a useful tool for a more advanced and detailed simulation study of the factors that affect the count rate performance of a clinical PET imaging system. Future plans include the introduction of more realistic and complex activity and attenuation maps into our simulation studies. The correlation of these results with real clinical data could give the opportunity to develop a more general imaging protocol for the optimization of the injected dose to patients.Key Terms: Positron Emission Tomography, PET, Nuclear Medicine, simulation, radiopharmaceuticals, dose optimization, Noise Equivalent Count Rate (NECR), Count Rates, phantoms.