Simulación de rango del positrón y emisiones gamma adicionales en PET

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Atómica, Molecular y Nuclear, leída el 03-04-2014Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

Hybrid Monte Carlo dose algorithm for low energy X-rays intraoperative radiation therapy

Low energy X-rays Intra-Operative Radiation Therapy (XIORT) treatment delivered during surgery (ex: INTRABEAM, Carl Zeiss, and Axxent, Xoft) can benefit from accurate and fast dose prediction in a patient 3D volume

Fully 3D GPU PET reconstruction

Fully 3D iterative tomographic image reconstruction is computationally very demanding. Graphics Processing Unit(GPU) has be enproposed formany years as potential accelerators incomplex scientific problems, but it has not be enuseduntil there cent advances in the programmability of GPU sthat the best available reconstruction code shave started tobe implemented toberunon GPUs. This work presents a GPU based fully 3D PET iterative reconstruction sofware. This new code may reconstruct sinogram data from several commercially available PET scanners. The most important and time consuming part soft he code,the forward and backward projection operations, arebasedonan accurate model of the scanner obtained with the MonteCarlo code PeneloPET and they have been massively parallelize don the GPU.For the PET scanners considered, the GPU based code is more than 70 times faster than asimilar code running on a single core of a fast CPU, obtainingin both cases the same images. The code has been designed to be easily adapted to reconstruct sinograms from any other PET scanner, including scanner prototypes.This work has been supported by MEC(FPA200762216), UCM (Grupos UCM,910059), CPAN(Consolider Ingenio 2010) CSPD 200700042,the RECAVARETIC network, ARTEMISS2009/ DPI 1802, European Regional Development,ENTEPRASE grant, PSE 30000020095 and TEC20080675C0201, Ministerio de Ciencia e Innovación, Spanish Government.Publicad

Validation of peneloPET positron range estimations

Proceeding of: 2010 IEEE Nuclear Science Symposium, Medical Imaging Conference and 17th Room Temperature Semiconductor Detector Workshop (IEEE), Knoxville, Tennessee, USA, October 30 - November 6, 2010Positron range depends on the materials in which positron propagates and on positron emitter isotope. As positron range limits the spatial resolution of PET images, good quantitative estimates of it should be included in any realistic simulation of PET acquisitions. In this work we compare positron range estimates obtained with PeneloPET to previous available simulations and experimental data. PeneloPET was used to simulate the positron range of 18F, 11C, 13N, 15O, 68Ga and 82Rb in the following tissues: cortical bone, soft bone, skin, muscle, brain, water, adipose tissue and lung. The 3D and 1D annihilation Point Spread Functions (aPSF) were calculated for each isotope-material combination. We have studied with more detail the 3D aPSF (radial distributions) and the cumulative fraction of annihilation events. These aPSF distributions were also studied for non-uniform media. Results obtained were consistent with other results previously reported in the literature as well as with experimentally measured data.This work has been supported by MEC (FPA2007-62216), UCM (Grupos UCM, 910059), CPAN (Consolider- Ingenio 2010) CSPD-2007-00042, European Regional Development and ENTEPRASE grant, PSE-300000-2009-5, and the CENIT program project AMIT, Ministerio de Ciencia e Innovación, Spanish Government. Part of the calculations of this work were performed in the “Clúster de Cálculo de Alta Capacidad para Técnicas Físicas” funded in part by UCM and in part by UE under FEDER programme”.Publicad

Positron range effects in high resolution 3D PET imaging

Proceeding of: 2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), Orlando, Florida, 25-31 October 2009Positron range limits the spatial resolution of PET images. It has a different effect for different isotopes and propagation materials, therefore it is important to consider it during image reconstruction, in order to obtain the best image quality. Positron range distribution was computed using Monte Carlo simulations with PeneloPET. The simulation models positron trajectories and computes the spatial distribution of the annihilation coordinates for the most common isotopes used in PET: 18F, 11C, 13N, 15O, 68Ga and 82Rb. Range profiles are computed for different positron propagation materials, obtaining one kernel profile for each isotope-material combination. These range kernels were introduced in FIRST, a 3D-OSEM image reconstruction software, and employed to blur the object during forward projection. The blurring introduced takes into account the material in which the positron is annihilated, obtained for instance from a CT image. In this way, different positron range corrections for each material in the phantom are considered. We compare resolution and noise properties of the images reconstructed with and without positron range modelling. For this purpose, acquisitions of an Image Quality phantom filled with different isotopes have been simulated for the ARGUS small animal PET scanner.This work has been supported in part by MEC (FPA2007 62216), CDTEAM (Programa CENIT, Ministerio de Industria), UCM (Grupos UCM, 910059), CPAN (Consolider Ingenio 2010) CSPD 2007 00042 and the RECAVA RETIC network. Part of the calculations of this work were performed in the “Clúster de Cálculo de Alta Capacidad para Técnicas Físicas” funded in part by UCM and in part by UE under FEDER programme”

Positron range estimations with PeneloPET

Technical advances towards high resolution PET imaging try to overcome the inherent physical limitations to spatial resolution. Positrons travel in tissue until they annihilate into the two gamma photons detected. This range is the main detector-independent contribution to PET imaging blurring. To a large extent, it can be remedied during image reconstruction if accurate estimates of positron range are available. However, the existing estimates differ, and the comparison with the scarce experimental data available is not conclusive. In this work we present positron annihilation distributions obtained from Monte Carlo simulations with the PeneloPET simulation toolkit, for several common PET isotopes (18F, 11C, 13N, 15O, 68Ga and 82Rb) in different biological media (cortical bone, soft bone, skin, muscle striated, brain, water, adipose tissue and lung). We compare PeneloPET simulations against experimental data and other simulation results available in the literature. To this end the different positron range representations employed in the literature are related to each other by means of a new parameterization for positron range profiles. Our results are generally consistent with experiments and with most simulations previously reported with differences of less than 20% in the mean and maximum range values. From these results, we conclude that better experimental measurements are needed, especially to disentangle the effect of positronium formation in positron range. Finally, with the aid of PeneloPET, we confirm that scaling approaches can be used to obtain universal, material and isotope independent, positron range profiles, which would considerably simplify range correction.We kindly acknowledge support from Comunidad de Madrid (ARTEMIS S2009/DPI-1802), Spanish Ministry of Science and Innovation (grants FPA2010-17142 and ENTEPRASE, PSE-300000-2009-5), by European Regional Funds, by CDTI under the CENIT Programme (AMITProject) and by CPAN, CSPD-2007-00042@Ingenio2010. Part of the calculations of this work were performed in the “Cluster de Cálculo de Alta Capacidad para Técnicas Físicas” funded in part by UCM and in part by UE under FEDER programme. This is a contribution to the Campus of International Excellence of MoncloaPublicad

Study of CT-based positron range correction in high resolution 3D PET imaging

Positron range limits the spatial resolution of PET images and has a different effect for different isotopes and positron propagationmaterials. Therefore it is important to consider it during image reconstruction, in order to obtain optimal image quality. Positron range distributions for most common isotopes used in PET in different materials were computed using the Monte Carlo simulations with PeneloPET. The range profiles were introduced into the 3D OSEM image reconstruction software FIRST and employed to blur the image either in the forward projection or in the forward and backward projection. The blurring introduced takes into account the different materials in which the positron propagates. Information on these materials may be obtained, for instance, from a segmentation of a CT image. The results of introducing positron blurring in both forward and backward projection operations was compared to using it only during forward projection. Further, the effect of different shapes of positron range profile in the quality of the reconstructed images with positron range correction was studied. For high positron energy isotopes, the reconstructed images show significant improvement in spatial resolution when positron range is taken into account during reconstruction, compared to reconstructions without positron range modeling.This work has been supported by the MEC (FPA2007 62216), the UCM (Grupos UCM, 910059), the CPAN (Consolider Ingenio 2010) CSPD 2007 00042, the RECAVA RETIC network, ARTEMIS S2009/ DPI 1802, the European Regional Development and ENTEPRASE grant, PSE 300000 2009 5 and the Ministerio de Ciencia e Innovación, Spanish Government.Publicad

Real-time 3D PET image with pseudoinverse reconstruction

Real-time positron emission tomography (PET) may provide information from first-shot images, enable PET-guided biopsies, and allow awake animal studies. Fully-3D iterative reconstructions yield the best images in PET, but they are too slow for real-time imaging. Analytical methods such as Fourier back projection (FBP) are very fast, but yield images of poor quality with artifacts due to noise or data incompleteness. In this work, an image reconstruction based on the pseudoinverse of the system response matrix (SRM) is presented. w. To implement the pseudoinverse method, the reconstruction problem is separated into two stages. First, the axial part of the SRM is pseudo-inverted (PINV) to rebin the 3D data into 2D datasets. Then, the resulting 2D slices can be reconstructed with analytical methods or by applying the pseudoinverse algorithm again. The proposed two-step PINV reconstruction yielded good-quality images at a rate of several frames per second, compatible with real time applications. Furthermore, extremely fast direct PINV reconstruction of projections of the 3D image collapsed along specific directions can be implemented.Part of the calculations in this work were performed in the “Clúster de Cálculo para Técnicas Físicas” funded in part by UCM and in part by UE Regional Funds. We acknowledge the support from the Spanish Government (FPA2015-65035-P, RTC-2015-3772-2, and RTI2018-095800-A-I00), Comunidad de Madrid (S2013/MIT-3024 TOPUS-CM, B2017/BMD-3888 PRONTO-CM), and European Regional Funds. This work was also supported by the EU’s H2020 under MediNet, a Networking Activity of ENSAR-2 (grant agreement 654002), and by a NIH R01 CA215700-2 grant. The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505)

Validation of NEMA NU4-2008 Scatter Fraction estimation with 18F and 68Ga for the ARGUS smallanimal PET scanner

Proceeding of: 2010 IEEE Nuclear Science Symposium, Medical Imaging Conference, Knoxville, Tennessee, USA, October 30 - November 6, 2010The scatter fraction (SF) in PET data represents the fraction of coincidence events in which at least one of the two emitted photons have been scattered before being detected. It is usually estimated as the ratio of scattered events to total number of coincidences, when the number of random counts is negligible (less than 1% of true rates). SF provides a measurement of the relative sensitivity of the scanner to scattered radiation. It depends on object size, density and location inside the field of view, as well as on detector size, type of detector crystal and energy window. The performance evaluation guideline for smallanimal PET NEMA (National Electrical Manufacturers Association) NU4-2008 proposes the estimation of the SF for three test phantoms made in proportion to the most widely used small animals in the laboratory: mouse, rat and monkey. The method estimates the different coincidence types in sinogram profiles from an off-centered line source inserted in these phantoms. We benchmark the procedure proposed by NEMA to estimate SF with 18F and also with 68Ga, a radionuclide with lager positron range. Real data acquired with the ARGUS smallanimal PET scanner (SEDECAL, Madrid, Spain) as well as simulations of the same scanner with peneloPET are used. The results show that, though SF should be practically the same with both 18F and 68Ga isotopes (and indeed our simulations indicate this) NEMA SF estimations with 68Ga acquisitions are higher. This is due to the fact that 68Ga positron range affects on the width of the line source profiles. Suggestions to modify the protocol to obtain similar SF estimations when using isotopes with larger positron range than 18F are made.This work has been supported by MEC (FPA2007-62216), UCM (Grupos UCM, 910059), CPAN (Consolider-Ingenio 2010) CSPD-2007-00042, European Regional Funds. AMIT Project funded by CDTI (CENIT Programme), ARTEMIS S2009/DPI-1802, European Regional Development and ENTEPRASE grant, PSE-300000-2009-5, Ministerio de Ciencia e Innovación. Spanish Government.Publicad

Viabilidad del uso de fotodetectores SiPM en sistemas PET/IRM

Actas de: XXVIII Congreso Anual de la Sociedad Española de Ingeniería Biomédica (CASEIB 2010). Madrid, 24-26 de noviembre de 2010.El fotomultiplicador de silicio (SiPM) es un detector compuesto por una matriz de fotodiodos funcionando en modo avalancha, también conocido como modo Geiger. Se trata de un dispositivo de alta eficiencia en la detección de fotones que, por tratarse de un semiconductor, es compacto, teóricamente insensible a campos magnéticos, y de bajo coste. Además, la electrónica asociada es sencilla y podría integrarse en el mismo dispositivo. Estas características hacen de este componente un buen candidato para construir detectores de rayos gamma para imagen médica nuclear (PET y SPECT). En este trabajo se evalúan las prestaciones de tres detectores diferentes de 1 x 1 mm2 y una matriz de 2 x 2 SiPMs (6 x 6 mm² área activa total). Se ha analizado la dependencia de los parámetros operacionales del dispositivo en presencia de campos magnéticos estáticos intensos y de los campos de radiofrecuencia generados por un sistema de IRM preclínico, en condiciones extremas de trabajo en cuanto a intensidad y frecuencia de conmutación de los gradientes de campo. Al mismo tiempo se ha verificado que la presencia de estos dispositivos en la zona de imagen de la RM no afecta a la calidad de la misma.Este trabajo ha sido financiado por los proyectos TEC2007-64731, TEC 2008-06715-C02-1 del Ministerio de Ciencia e Innovación, por la RETIC-RECAVA del Ministerio de Sanidad y Consumo, por el programa ARTEMIS S2009/DPI-1802 de la Comunidad de Madrid, por el proyecto europeo FMT-XCT FP7-201792, los programas FPA2007-62216, TEC2008-06715-C02-01, UCM (Grupos UCM; 910059), CPAN (Consolider-Ingenio 2010) y CSPD-2007-00042. Parte de los cálculos realizados en este trabajo se han hecho en el ‘‘High Capacity Cluster for Physical Techniques’’ de la UCM, financiados en parte por la UE bajo el programa FEDER, y en otra parte por la UCM.Publicad