Investigação dos parâmetros dependentes do paciente para a otimização da atividade administrada em exames de PET/CT com 18F-FDG

Abstract

Despite the activities administered to patients during Positron Emission Tomography (PET) scans are guided by methods and reference levels, in clinical practice there is a great discrepancy between these values. Current indications use dependent patient parameters (DPP), such as age and weight, without considering an assessment of the resulting image quality. The purpose of this study is to investigate how the anthropometric and physiological characteristics of patients influence the determination of 18F-FDG activity to be administered in PET/CT scans and image quality. Therefore, we conducted a preliminary study with three simulators of different diameters, representing patients with different sizes, with different values of activity concentration. Subsequently, we performed a retrospective study on a PET/CT image database acquired with 18F-FDG. Image quality indicators (NECR, and NECRN and SNRnorm) of the images of patients were determined for many PDP, namely: body weight, BMI, BSA, fat mass, mass-height ratio and equivalent diameter. The relationship between the administered activity, counts rates and the PDP, with image quality indicators were statistically evaluated. We concluded that the NECRN is the quality indicator which has the best correlation between the PDP, particularly with body mass and BMI. The image quality in can be estimated from the true coincidence events rate (TRUES) during PET/CT acquisition with 18F-FDG, due to the highly linear relationship with NECR for different body mass or BMI ranges, allowing the optimization of the administered activity based on the physical characteristics of the patient.