Page 34 - Quantitative Imaging of Small Tumours with Positron Emission Tomography

Introduction Quantitative PET provides clinical oncology with a powerful tool for diagnosis, staging, restaging, and response monitoring (1,2). To allow for appropriate 2 quantification of radioactive tracer uptake, PET data need to be corrected for several physical effects, including decay, scatter, random coincidences, and attenuation. An effect not regularly corrected for, but having a major impact on PET accuracy in small tumours, is the partial-volume effect (PVE) (3). PVE originates from the finite spatial resolution of the PET scanner, described by the point spread function (PSF), and the tissue fraction effect (4). In hot lesions, PVE causes a net spill-out of activity into the background, leading to considerable underestimation of the measured activity concentration (3- 6). Although clinical application of partial-volume correction (PVC) has led to contradictory results to date (7), both accurate and precise PVC methods may have a significant clinical impact and substantially change quantitative reads (8). Many PVC methods have been developed (4,7,9), such as the recovery coefficient method (5,6,10), the geometric transfer matrix (11), the Müller-Gärtner method (12), and iterative deconvolution (13,14). However, each method has its limitations, and new methodology is still being developed. Some are adaptations of the recovery coefficient method (15,16), but others are more refined, such as resolution modeling (17,18), adaptations of iterative deconvolution (19-21), adaptations of the geometric transfer matrix (22,23), and background-adapted PVC algorithms (24). Besides being affected by PVE, PET accuracy is strongly affected by the applied volume-of-interest (VOI) method, noise level, and tumour-to-background ratio (25). In addition, several PVC methods use predefined VOI boundaries to correct for PVE. Hoetjes et al. argued that the performance of PVC methods may benefit from exact (e.g., CT-based) VOI definition (3). We therefore hypothesized that PVC performance, and hence PET accuracy, is strongly affected by VOI definition methodology. Because PVC performance is a function of not only the PVC method and settings but also the VOI method and settings, their interplay may affect the accuracy and precision of PVE-corrected quantitative PET metrics. In the present study, we investigated the effect of several combinations of PVC methods and VOI methods on the accuracy and precision of PET using phantoms and simulations. We also investigated the impact of PVC on the repeatability of 18F-FDG and Accuracy and Precision of PVC 33