Page 76 - Quantitative Imaging of Small Tumours with Positron Emission Tomography

regression analyses the impact of PVC-induced increased image noise on kinetic parameter estimation seems negligible. However, it may have significant impact when tumours are analyzed on a parametric level. While the presence of PVE and the consequent need for PVC are well recognized, to date PVC has rarely been applied in oncological PET studies. This may be because to date there is no consensus on the optimal correction strategy and data yielded from application of PVC does not seem to have triggered routine 3 clinical application (12,35). Our study now demonstrates that PVC should not only be performed in future regular static PET-CT studies, but in dynamic PET- CT studies as well, also when simplified quantitative metrics are validated for clinical applications. If not applied, small lesions should preferably be excluded from analyses, as recommended and performed in previous studies using a 2-3cm diameter cut-off to avoid PVE (36,37). Still, our data demonstrate that lesions above these size thresholds are also affected by PVE (Figure 3.2). Only data from 18F-FLT PET-CT was used. However, the current dataset from a widely used whole body TOF PET-CT scanner allowed for both kinetic modeling and extraction of simplified parameters per lesion, at time points used in clinical practice due to the long acquisition time (0-60min post-injection). Also, the dataset included both large and small lesions, both nearby and remote from large blood pool structures. Additionally, it facilitated evaluation of PVCs effect on validation of simplified parameters both in single measurements and during systemic treatment. Since we have demonstrated the significant effect of PVC in kinetic parameter estimation, future dynamic PET studies focusing on other PET- tracers in small tumours (e.g. PSMA-ligand tracers in prostate cancer metastases) should apply PVC as a similar (or larger) impact of PVC may be expected. In the current study no correction was made for potential motion blurring effects, which is another factor possibly affecting accuracy of kinetic parameter estimations (38). Efforts should be made to incorporate both PVC and motion correction methodologies simultaneously for dynamic PET studies. Also, the impact of PVC on parametric kinetic analyses of oncologic dynamic PET warrants further investigation, which will require HYPR denoising to be optimized for this purpose. PVC in dynamic PET-CT 75