Abstract
The spill-in counts from neighbouring regions can significantly bias the quantification over small regions close to high activity extended sources. This effect can be a drawback for 18F-based radiotracers positron emission tomography (PET) when quantitatively evaluating the bladder area for diseases such as prostate cancer. In this work, we use Monte Carlo simulations to investigate the impact of the spill-in counts from the bladder on the quantitative evaluation of prostate cancer when using 18F-Fluorcholine (FCH) PET and we propose a novel reconstruction-based correction method. Monte Carlo simulations of a modified version of the XCAT2 anthropomorphic phantom with 18F-FCH biological distribution, variable bladder uptake and inserted prostatic tumours were used in order to obtain simulated realistic 18F-FCH data. We evaluated possible variations of the measured tumour Standardized Uptake Value (SUV) for different values of bladder uptake and propose a novel correction by appropriately adapting image reconstruction methodology. The correction is based on the introduction of physiological background terms on the reconstruction, removing the contribution of the bladder to the final image. The bladder is segmented from the reconstructed image and then forward-projected to the sinogram space. The resulting sinograms are used as background terms for the reconstruction. SUVmax and SUVmean could be overestimated by 41% and 22% respectively due to the accumulation of radiotracer in the bladder, with strong dependence on bladder-to-lesion ratio. While the SUVs measured under these conditions are not reliable, images corrected using the proposed methodology provide better repeatability of SUVs, with biases below 6%. Results also showed remarkable improvements on visual detectability. The spill-in counts from the bladder can affect prostatic SUV measurements of 18F-FCH images, which can be corrected to less than 6% using the proposed methodology, providing reliable SUV values even in the presence of high radioactivity accumulation in the bladder.
Highlights
Positron emission tomography (PET) is a non-invasive imaging technique that visualizes the distribution of different molecules in the body providing functional and molecular information for different tissues
Despite the fact that traditional evaluation is usually performed by visual inspection of the images, the current potential of PET relies on its capability to provide quantitative information (El Naqa et al 2007), usually provided by a semi-quantitative parameter known as Standard Uptake Value (SUV)
An increase in bladder uptake is a counterpart for detectability, so that the tumour with SUV value of 3.03 g l−1 is clearly observed for bladder uptake of 1.01 g l−1 but not for high bladder uptakes
Summary
Positron emission tomography (PET) is a non-invasive imaging technique that visualizes the distribution of different molecules in the body providing functional and molecular information for different tissues. Despite the fact that traditional evaluation is usually performed by visual inspection of the images, the current potential of PET relies on its capability to provide quantitative information (El Naqa et al 2007), usually provided by a semi-quantitative parameter known as Standard Uptake Value (SUV). This parameter provides relatively objective tumour characterization, reliable differential diagnosis, and earlier evaluation and monitoring of treatment response (Boellaard 2009, Adams et al 2010). In this context FDG PET has shown very poor sensitivity and specificity on prostate cancer mainly due to two critical factors: some prostatic tumours do not show an elevated glucose consumption; many infectious processes such as prostatic benign hyperplasia show an increased FDG uptake producing false positives (Salminen et al 2002, Jadvar 2011)
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