Page 72 - Quantitative Imaging of Small Tumours with Positron Emission Tomography

both tumour micro- and macrokinetic parameters, and we observed that partial- volume effects varied over time due to blood pool activity and changing tumour contrast. Hence, the effect of PVC on kinetic parameter estimates was not in full concordance with its effect on simplified metrics (SUV and TBR), and as a consequence PVC was found to affect the validation of SUV using VT both for single measurements and as biomarker of treatment response to a small extent (albeit non-significantly). 3 Application of PVC in oncologic dynamic PET-CT studies is scarce. Mankoff et al. (2003) applied PVC in dynamic FDG-PET of breast cancer patients using a simple method with recovery coefficients, assuming lesions are spherical with homogenous tracer distributions (29). They observed that applying PVC in response measurements reduced changes in metabolic rate of FDG and blood flow of responding patients, reducing significance of parameter changes (albeit still statistically significant). By using this method, however, kinetic parameters were solely corrected for (changes in) tumour size, and no correction for spill-in from blood pool structures and/or heterogeneous tumour background was applied. In 2007, Teo et al. validated the use of iterative deconvolution as an image-based PVC method not requiring anatomical segmentation or knowledge of lesion size, and suggested its potential application in kinetic modeling, which to the best of our knowledge has not been performed to date for oncologic PET-CT (30). PVC in dynamic PET-CT Uncorrected LR LR+HYPR 8 6 4 2 00 5 10 15 20 VT Figure 3.4: Scatter plot of VT versus SUV, without and with PVC. For both LR and LR+HYPR, the Spearman correlation between VT and SUV increased from 0.82 to 0.90 after PVC. 71 SUV