Institute Investigacion Sanitarias IDIS

Galicia, Spain

Institute Investigacion Sanitarias IDIS

Galicia, Spain
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Silva-Rodriguez J.,Institute Investigacion Sanitarias IDIS | Dominguez-Prado I.,Complexo Hospitalario Universitario Of Santiago Of Compostela | Pardo-Montero J.,Institute Investigacion Sanitarias IDIS | Pardo-Montero J.,Complexo Hospitalario Universitario Of Santiago Of Compostela | And 5 more authors.
Radiation Physics and Chemistry | Year: 2017

Purpose The aim of this work is to study the effect of physiological muscular uptake variations and statistical noise on tumor quantification in FDG-PET studies. Methods We designed a realistic framework based on simulated FDG-PET acquisitions from an anthropomorphic phantom that included different muscular uptake levels and three spherical lung lesions with diameters of 31, 21 and 9 mm. A distribution of muscular uptake levels was obtained from 136 patients remitted to our center for whole-body FDG-PET. Simulated FDG-PET acquisitions were obtained by using the Simulation System for Emission Tomography package (SimSET) Monte Carlo package. Simulated data was reconstructed by using an iterative Ordered Subset Expectation Maximization (OSEM) algorithm implemented in the Software for Tomographic Image Reconstruction (STIR) library. Tumor quantification was carried out by using estimations of SUVmax, SUV50 and SUVmean from different noise realizations, lung lesions and multiple muscular uptakes. Results Our analysis provided quantification variability values of 17–22% (SUVmax), 11–19% (SUV50) and 8–10% (SUVmean) when muscular uptake variations and statistical noise were included. Meanwhile, quantification variability due only to statistical noise was 7–8% (SUVmax), 3–7% (SUV50) and 1–2% (SUVmean) for large tumors (>20 mm) and 13% (SUVmax), 16% (SUV50) and 8% (SUVmean) for small tumors (<10 mm), thus showing that the variability in tumor quantification is mainly affected by muscular uptake variations when large enough tumors are considered. In addition, our results showed that quantification variability is strongly dominated by statistical noise when the injected dose decreases below 222 MBq. Conclusions Our study revealed that muscular uptake variations between patients who are totally relaxed should be considered as an uncertainty source of tumor quantification values. © 2016 Elsevier Ltd


Silva-Rodriguez J.,Fundacion Ramon Dominguez | Silva-Rodriguez J.,Complexo Hospitalario Universitario Of Santiago Of Compostela | Silva-Rodriguez J.,Institute Investigacion Sanitarias IDIS | Aguiar P.,Fundacion Ramon Dominguez | And 12 more authors.
Medical Physics | Year: 2014

Purpose: Current procedure guidelines for whole body [18F]fluoro-2-deoxy-D- glucose (FDG)-positron emission tomography (PET) state that studies with visible dose extravasations should be rejected for quantification protocols. Our work is focused on the development and validation of methods for estimating extravasated doses in order to correct standard uptake value (SUV) values for this effect in clinical routine. Methods: One thousand three hundred sixty-seven consecutive whole body FDG-PET studies were visually inspected looking for extravasation cases. Two methods for estimating the extravasated dose were proposed and validated in different scenarios using Monte Carlo simulations. All visible extravasations were retrospectively evaluated using a manual ROI based method. In addition, the 50 patients with higher extravasated doses were also evaluated using a threshold-based method. Results: Simulation studies showed that the proposed methods for estimating extravasated doses allow us to compensate the impact of extravasations on SUV values with an error below 5%. The quantitative evaluation of patient studies revealed that paravenous injection is a relatively frequent effect (18%) with a small fraction of patients presenting considerable extravasations ranging from 1% to a maximum of 22% of the injected dose. A criterion based on the extravasated volume and maximum concentration was established in order to identify this fraction of patients that might be corrected for paravenous injection effect. Conclusions: The authors propose the use of a manual ROI based method for estimating the effectively administered FDG dose and then correct SUV quantification in those patients fulfilling the proposed criterion. © 2014 American Association of Physicists in Medicine.


Silva-Rodriguez J.,University of Santiago de Compostela | Silva-Rodriguez J.,Institute Investigacion Sanitarias IDIS | Silva-Rodriguez J.,University of Leeds | Tsoumpas C.,University of Leeds | And 8 more authors.
Physics in Medicine and Biology | Year: 2016

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. © 2016 Institute of Physics and Engineering in Medicine.


Silva-Rodriguez J.,Institute Investigacion Sanitarias IDIS | Silva-Rodriguez J.,University of Santiago de Compostela | Aguiar P.,Institute Investigacion Sanitarias IDIS | Aguiar P.,University of Santiago de Compostela | And 5 more authors.
Revista Espanola de Medicina Nuclear e Imagen Molecular | Year: 2015

Aim: To study in detail the accuracy and repeatability of three commonly used methods for SUV estimation in solitary pulmonary nodules. Material and methods: We have designed a realistic framework based on simulated FDG-PET acquisitions from an anthropomorphic activity model that included solitary pulmonary nodules (different sizes) of well-known SUV. This framework enables us to compare the SUV values obtained from the reconstructed PET images with the real SUV values. Three commonly used methods (SUVmax, SUVmean and SUV50) were used to estimate the tumor activity. Results: Our results showed the tumor activity was overestimated using SUVmax and clearly subestimated using SUVmean. Instead, the quantification of SUV50 showed great agreement with the simulated tumor activity and only slight subestimation was found for very small lesions. On the other hand, SUVmean showed better performance than SUV50 in terms of repeatability, providing variabilities below 5% for all tumor sizes and for injected doses as low as 111 MBq. Conclusions: Our findings showed that SUV50 provided better performance for estimating accurately tumor SUV values in pulmonary nodules, but SUVmean showed better results in terms of repeatability. © 2014 Elsevier España, S.L.U. and SEMNIM.

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