Aquisição e análise quantitativa de imagens PET em camundongos sadios utilizando o radiofármaco 11C-Metionina

Abstract

11C-Methionine is the most widely used radiopharmaceutical in cerebral oncology through Positron Emission Tomography (PET). Due to the high proliferative activity of tumor cells, the transmembrane transport of amino acids is high, which implies in differentiated uptake of the radiopharmaceutical by the tumors. In the Nuclear Technology Development Center (CDTN) pre-clinical studies are being initiated using 11C-Methionine. The aim of this work was to evaluate the uptake profile of 11C-Methionine through the PET imaging. The 11C-Methionine was synthesized using the TRACERlab FX C PRO (GE) automated modulus. The studies were done with healthy male Balb/c mice, aged between 3 and 5 weeks and weighing between 20 and 25g. Mice (n = 3) received 11 to 13 MBq/100μL of 11C- Methionine and were anesthetized with isoflurane. Soon after injection of the radiopharmaceutical, the animals were positioned in the ventral decubitus position. Dynamic images of 30 minutes were acquired in a single bed position. Another mouse (n = 1) was submitted to the acquisition of static image in three bed positions to evaluate the distribution of the whole body. PET software was used to reconstruct the images using the MLEM-2D method. Quantification studies were performed using the PMOD software from the calibration factor determined through a phantom image. Data were expressed as% DI/g. The organ that presented the highest uptake was the pancreas, with 13.6% ID/g in the time of 30 minutes after injection. 11C-Methionine also accumulated in other organs of the abdominal region: liver, stomach, spleen and intestine, with maximum uptakes of 11.4, 8.8, 7.7 and 5.8% DI/g, respectively. Tissues such as muscle and bone presented values of about 2.0% ID/g. The uptake in the brain region was comparable to background. Despite of some limitations, it was possible to follow the profile of radiopharmaceutical capture in the main organs. In principle, 11C-Methionine should not be indicated for studies of organs or tissues of the abdominal region due to the high physiological uptake. The analysis of images confirms the low cerebral uptake of 11C- Methionine, a property that allows the application of this radiopharmaceutical in the detection of brain tumors. PET imaging is a valuable tool that enables noninvasive investigations of small animals. However, improvements to the image acquisition protocols are still required.