Papers by JUAN JOSE VAQUERO
IEEE Transactions on Nuclear Science, 2000
The availability of synthetic realistic data eases design optimization, algorithm evaluation and ... more The availability of synthetic realistic data eases design optimization, algorithm evaluation and verification of any digital system where a significant amount of digital signal processing is performed. The evolution of positron emission tomography cameras towards continuous sampling of individual position-sensitive photomultiplier anodes with processing algorithms implemented on digital programmable logic devices creates a new framework where new approaches to the -event detection are possible. We have developed a system model of the acquisition chain, including multi-layer phoswich, photomultiplier, front-end analog electronics, data acquisition and digital processing. This processing includes estimation algorithms for the most relevant event parameters: energy, layer-of-interaction, time picking-off and event location. The selected simulation platform couples gently to digital hardware simulation tools, in such a way that implemented models may generate real-like stimuli for the digital system under development. The modeling of the whole front-end electronics enables deeper understanding and tuning of different system trade-offs and provides a rapid and soft transition between specification and hardware development.
En este trabajo presentamos un estudio preliminar del diseño de un tomógrafo de emisión de positr... more En este trabajo presentamos un estudio preliminar del diseño de un tomógrafo de emisión de positrones (PET) con geometría octogonal, con el objetivo de evaluar la influencia de varios parámetros críticos en la calidad de la imagen reconstruida. El simulador propuesto está basado en técnicas de Monte Carlo e incluye profundidad de interacción en cristal. Las fuentes de actividad se pueden simular mediante distribuciones paramétricas dentro de campo de visión (FOV). La matriz del sistema también se calcula basándose en modelos estadísticos y simulación de Monte Carlo. Se han empleado algoritmos de reconstrucción iterativos basados en la estimación de máxima verosimilitud MLEM) y regularización bayesiana, así como retroproyección filtrada (FBP).
… Record, 2008. NSS' …, Jan 1, 2009
XIII Mediterranean Conference on Medical and Biological Engineering and Computing 2013, IFMBE Proceedings, 2014
XIII Mediterranean Conference on Medical and Biological Engineering and Computing 2013, IFMBE Proceedings, 2014
ABSTRACT Over the lasts years many works have addressed the potential of compressed sensing techn... more ABSTRACT Over the lasts years many works have addressed the potential of compressed sensing techniques to accelerate acquisition of cardiac MRI. However, most of these works claimed the achievement of acceleration factors solely based on simulated data or on fully sampled acquisition data retrospectively undersampled. In this work the practical feasibility of compressed sensing acquisitions for the acceleration of cardiac cine imaging in small animals is proved with real acquisitions. Our experiments using a combined spatiotemporal technique confirm that high acceleration factors of about 10 are feasible. Future work involving the optimization of undersampling patterns and cardiac artifact correction might further improve this acceleration factor.
Biomedical Optics Express, 2011
Fluorescence diffuse optical tomography (fDOT) is an imaging modality that provides images of the... more Fluorescence diffuse optical tomography (fDOT) is an imaging modality that provides images of the fluorochrome distribution within the object of study. The image reconstruction problem is ill-posed and highly underdetermined and, therefore, regularisation techniques need to be used. In this paper we use a nonlinear anisotropic diffusion regularisation term that incorporates anatomical prior information. We introduce a split operator method that reduces the nonlinear inverse problem to two simpler problems, allowing fast and efficient solution of the fDOT problem. We tested our method using simulated, phantom and ex-vivo mouse data, and found that it provides reconstructions with better spatial localisation and size of fluorochrome inclusions than using the standard Tikhonov penalty term.
2011 IEEE Nuclear Science Symposium Conference Record, 2011
Dynamic cardiac magnetic resonance imaging in small animals is an important tool in the study of ... more Dynamic cardiac magnetic resonance imaging in small animals is an important tool in the study of cardiovascular diseases. The reduction of the long acquisition times required for cardiovascular applications is crucial to achieve good spatiotemporal resolution and signal-to-noise ratio. Nowadays there are many acceleration techniques which can reduce acquisition time, including compressed sensing technique. Compressed sensing allows image reconstruction from
2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 2012
ABSTRACT Respiratory gating is necessary in cardio-thoracic small-animal imaging because of the p... more ABSTRACT Respiratory gating is necessary in cardio-thoracic small-animal imaging because of the physiological motions that are present during scanning. When applying a low-dose protocol, fewer than 180 noisy projections may be left for the reconstruction of each respiratory phase, leading to streak artifacts. The Prior Image Constrained Compressed Sensing (PICCS) algorithm enables accurate reconstruction of highly undersampled data when a prior image is available. We evaluate three CS algorithms based on the Split-Bregman approach, with different transformations of the prior penalty function: Gradient (TV-PICCS), L1-norm (L1-PICCS), and Wavelet Transform (WT-PICCS), on low-dose data acquired on a micro-CT scanner. All CS methods performed very similarly in terms of noise and resolution, greatly improving filtered back-projection (79 % noise reduction) and eliminating streaks. Wavelet domain was found to be sparser and to show a more natural texture than the commonly used gradient domain.
Magnetic Resonance in Medicine, 2013
Self-gated cine sequences are a common choice for cardiac MRI in preclinical applications. The ai... more Self-gated cine sequences are a common choice for cardiac MRI in preclinical applications. The aims of our work were to apply the compressed sensing technique to IntraGateFLASH cardiac MRI studies on rats and to find the maximum acceleration factor achievable with this technique. Our reconstruction method extended the Split Bregman formulation to minimize the total variation in both space and time. In addition, we analyzed the influence of the undersampling pattern on the acceleration factor achievable. Our results show that acceleration factors of up to 15 are achievable with our technique when appropriate undersampling patterns are used. The introduction of a time-varying random sampling clearly improved the efficiency of the undersampling schemes. In terms of computational efficiency, the proposed reconstruction method has been shown to be competitive as compared with the fastest methods found in the literature. We successfully applied our compressed sensing technique to self-gated cardiac cine acquisition in small animals, obtaining an acceleration factor of up to 15 with almost unnoticeable image degradation.
Journal of Biomedical Optics, 2012
Reconstruction algorithms for imaging fluorescence in near infrared ranges usually normalize fluo... more Reconstruction algorithms for imaging fluorescence in near infrared ranges usually normalize fluorescence light with respect to excitation light. Using this approach, we investigated the influence of absorption and scattering heterogeneities on quantification accuracy when assuming a homogeneous model and explored possible reconstruction improvements by using a heterogeneous model. To do so, we created several computer-simulated phantoms: a homogeneous slab phantom (P1), slab phantoms including a region with a two- to six-fold increase in scattering (P2) and in absorption (P3), and an atlas-based mouse phantom that modeled different liver and lung scattering (P4). For P1, reconstruction with the wrong optical properties yielded quantification errors that increased almost linearly with the scattering coefficient while they were mostly negligible regarding the absorption coefficient. This observation agreed with the theoretical results. Taking the quantification of a homogeneous phantom as a reference, relative quantification errors obtained when wrongly assuming homogeneous media were in the range +41 to +94% (P2), 0.1 to -7% (P3), and -39 to +44% (P4). Using a heterogeneous model, the overall error ranged from -7 to 7%. In conclusion, this work demonstrates that assuming homogeneous media leads to noticeable quantification errors that can be improved by adopting heterogeneous models.
2007 IEEE Nuclear Science Symposium Conference Record, 2007
Tomographic Data Consistency Conditions (TDCC) are frequently employed to improve the quality of ... more Tomographic Data Consistency Conditions (TDCC) are frequently employed to improve the quality of PET data. However, most of these consistency conditions were derived from X-ray computerized tomography (CT) and their validity for other imaging modalities has not been well established. For instance, it is well known from (X-ray) CT data that the sum of the projection data from one view of the parallel-beam projections is a constant independent of the view-angle. This consistency condition is based on well-known mathematical properties of the Radon transform and yields good results when employed in noise removal or sinogram restoration. But this consistency condition assumes that emission and detection of radiation occur within a thin (ideally with zero width) line-ofresponse (LOR), with a flat probability distribution of the detection (in PET) or absorption (X-ray) along such LOR. This assumption, being valid for CT, is not realistic for PET acquisitions. Thus, TDCC for PET should be revised in order to check their validity with more realistic detection models.
IEEE Nuclear Science Symposuim & Medical Imaging Conference, 2010
The scatter fraction (SF) in PET data represents the fraction of coincidence events in which at l... more The 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
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Papers by JUAN JOSE VAQUERO