GPU-accelerated iterative reconstruction for limited-data tomography in CBCT systems.

BACKGROUND: Standard cone-beam computed tomography (CBCT) involves the acquisition of at least 360 projections rotating through 360 degrees. Nevertheless, there are cases in which only a few projections can be taken in a limited angular span, such as during surgery, where rotation of the source-detector pair is limited to less than 180 degrees. Reconstruction of limited data with the conventional method proposed by Feldkamp, Davis and Kress (FDK) results in severe artifacts. Iterative methods may compensate for the lack of data by including additional prior information, although they imply a high computational burden and memory consumption. RESULTS: We present an accelerated implementation of an iterative method for CBCT following the Split Bregman formulation, which reduces computational time through GPU-accelerated kernels. The implementation enables the reconstruction of large volumes (>10243 pixels) using partitioning strategies in forward- and back-projection operations. We evaluated the algorithm on small-animal data for different scenarios with different numbers of projections, angular span, and projection size. Reconstruction time varied linearly with the number of projections and quadratically with projection size but remained almost unchanged with angular span. Forward- and back-projection operations represent 60% of the total computational burden. CONCLUSION: Efficient implementation using parallel processing and large-memory management strategies together with GPU kernels enables the use of advanced reconstruction approaches which are needed in limited-data scenarios. Our GPU implementation showed a significant time reduction (up to 48 ×) compared to a CPU-only implementation, resulting in a total reconstruction time from several hours to few minutes.

Statistical image reconstruction with beam-hardening compensation for X-ray CT by a calibration step (2DIterBH).

BACKGROUND: The beam-hardening effect due to the polychromatic nature of the X-ray spectra results in two main artifacts in CT images: cupping in homogeneous areas and dark bands between dense parts in heterogeneous samples. Post-processing methods have been proposed in the literature to compensate for these artifacts, but these methods may introduce additional noise in low-dose acquisitions. Iterative methods are an alternative to compensate noise and beam-hardening artifacts simultaneously. However, they usually rely on the knowledge of the spectrum or the selection of empirical parameters. PURPOSE: We propose an iterative reconstruction method with beam hardening compensation for small animal scanners that is robust against low-dose acquisitions and that does not require knowledge of the spectrum, overcoming the limitations of current beam-hardening correction algorithms. METHODS: The proposed method includes an empirical characterization of the beam-hardening function based on a simple phantom in a polychromatic statistical reconstruction method. Evaluation was carried out on simulated data with different noise levels and step angles and on limited-view rodent data acquired with the ARGUS/CT system. RESULTS: Results in small animal studies showed a proper correction of the beam-hardening artifacts in the whole sample, independently of the quantity of bone present on each slice. The proposed approach also reduced noise in the low-dose acquisitions and reduced streaks in the limited-view acquisitions. CONCLUSIONS: Using an empirical model for the beam-hardening effect, obtained through calibration, in an iterative reconstruction method enables a robust correction of beam-hardening artifacts in low-dose small animal studies independently of the bone distribution.

In vivo behavior in rabbit radius bone defect of scaffolds based on nanocarbonate hydroxyapatite.

Bone defects treatment may require the use of biomaterials that behave as a support and promote bone regeneration. Limitations associated with the use of autografts and allografts make it necessary to design new synthetic bone substitutes. Some of the most promising biomaterials currently under investigation are based on nanocarbonate hydroxyapatite (nCHA). In this study, we studied the bone-inducing capacity of nCHA-based scaffolds alone (SAG) and enriched with osteostatin (SAGO) or with bone marrow aspirate(SAGB) after implantation for 12 weeks in a 15-mm long critical defect performed in the radius of New Zealand rabbits. Bone formation obtained was compared with a group with the unfilled defect (CE), as control group, and other with the defect filed with iliac crest autograft (GS), as gold standard. X-ray follow-up was performed at 2, 4, 6 and 12 weeks and µCT and histological studies at 12 weeks. The radiological results showed a greater increment in bone formation in the GS group (75%-100%), followed by the SAG and SAGB groups (50%-75%). µCT results showed an increase of bone volume/tissue volume values in GS group followed by SAG and SAGB groups (0.53, 0.40, and 0.31 respectively) compared with CE group (0.26). Histological results showed limited resorption of the nCHA scaffolds and partial osseointegration in the SAG and SAGB groups. However, in the SAGO group, the presence of connective tissue encapsulating the scaffold was detected. In SAG, SAGB, and increase of bone formation were observed compared with CE group, but less than the GS group. Thus, the investigated materials represent a significant advance in the design of synthetic materials for bone grafting, but further studies are needed to bring their in vivo behavior closer to autograft, the gold standard.

Osteogenic Potential of a Biomaterial Enriched with Osteostatin and Mesenchymal Stem Cells in Osteoporotic Rabbits.

Mesoporous bioactive glasses (MBGs) of the SiO2-CaO-P2O5 system are biocompatible materials with a quick and effective in vitro and in vivo bioactive response. MBGs can be enhanced by including therapeutically active ions in their composition, by hosting osteogenic molecules within their mesopores, or by decorating their surfaces with mesenchymal stem cells (MSCs). In previous studies, our group showed that MBGs, ZnO-enriched and loaded with the osteogenic peptide osteostatin (OST), and MSCs exhibited osteogenic features under in vitro conditions. The aim of the present study was to evaluate bone repair capability after large bone defect treatment in distal femur osteoporotic rabbits using MBGs (76%SiO2-15%CaO-5%P2O5-4%ZnO (mol-%)) before and after loading with OST and MSCs from a donor rabbit. MSCs presence and/or OST in scaffolds significantly improved bone repair capacity at 6 and 12 weeks, as confirmed by variations observed in trabecular and cortical bone parameters obtained by micro-CT as well as histological analysis results. A greater effect was observed when OST and MSCs were combined. These findings may indicate the great potential for treating critical bone defects by combining MBGs with MSCs and osteogenic peptides such as OST, with good prospects for translation to clinical practice.

Enriched mesoporous bioactive glass scaffolds as bone substitutes in critical diaphyseal bone defects in rabbits.

In the field of orthopedic surgery, there is an increasing need for the development of bone replacement materials for the treatment of bone defects. One of the main focuses of biomaterials engineering are advanced bioceramics like mesoporous bioactive glasses (MBG´s). The present study compared the new bone formation after 12 weeks of implantation of MBG scaffolds with composition 82,5SiO2-10CaO-5P2O5-x 2.5SrO alone (MBGA), enriched with osteostatin, an osteoinductive peptide, (MBGO) or enriched with bone marrow aspirate (MBGB) in a long bone critical defect in radius bone of adult New Zealand rabbits. New bone formation from the MBG scaffold groups was compared to the gold standard defect filled with iliac crest autograft and to the unfilled defect. Radiographic follow-up was performed at 2, 6, and 12 weeks, and microCT and histologic examination were performed at 12 weeks. X-Ray study showed the highest bone formation scores in the group with the defect filled with autograft, followed by the MBGB group, in addition, the microCT study showed that bone within defect scores (BV/TV) were higher in the MBGO group. This difference could be explained by the higher density of newly formed bone in the osteostatin enriched MBG scaffold group. Therefore, MBG scaffold alone and enriched with osteostatin or bone marrow aspirate increase bone formation compared to defect unfilled, being higher in the osteostatin group. The present results showed the potential to treat critical bone defects by combining MBGs with osteogenic peptides such as osteostatin, with good prospects for translation into clinical practice. STATEMENT OF SIGNIFICANCE: Treatment of bone defects without the capacity for self-repair is a global problem in the field of Orthopedic Surgery, as evidenced by the fact that in the U.S alone it affects approximately 100,000 patients per year. The gold standard of treatment in these cases is the autograft, but its use has limitations both in the amount of graft to be obtained and in the morbidity produced in the donor site. In the field of materials engineering, there is a growing interest in the development of a bone substitute equivalent. Mesoporous bioactive glass (MBG´s) scaffolds with three-dimensional architecture have shown great potential for use as a bone substitutes. The osteostatin-enriched Sr-MBG used in this long bone defect in rabbit radius bone in vivo study showed an increase in bone formation close to autograft, which makes us think that it may be an option to consider as bone substitute.

[Knowledge, beliefs, and attitudes about obesity and overweight in a sample of dietitians-nutritionists in Spain]. / Conocimientos, creencias y actitudes sobre la obesidad y el sobrepeso en una muestra de dietistas-nutricionistas de España.

INTRODUCTION: Introduction: overweight and obesity make up one of the greatest public health challenges worldwide. Dietitians-nutritionists promote the acquisition of healthy habits to adjust weight. There are interesting contributions by psychology to be considered. Objectives: a) to study the link between the variables included in the study and the therapeutic intervention of dietitians in overweight and obesity; b) to collect the opinions of dietitians on the psychological aspects involved; c) to analyze the predictors of therapeutic success. Methods: a descriptive cross-sectional study that, through a survey to dietitians-nutritionists in Spain (n = 266), analyzes demographic, training, and occupational data, as well as knowledge, beliefs, and interventions on obesity and overweight, with emphasis on psychological aspects. Chi-squared analyses were performed for qualitative variables, and a regression analysis was performed to estimate the perception of therapeutic success. Results: specialization in overweight and obesity was linked to nutrition education interventions. The consideration of psychological aspects was associated with addressing emotional and social problems. Nutritional education, number of sessions, and average time per session predicted the perception of therapeutic success, all of these explaining 46.5 % of the variance. Conclusions: the findings documented a highly specific training in obesity, and a limited use of clinical practice guidelines; the cause of obesity is mostly attributable to environmental factors, and teamwork is preferred by most. Psychological factors were considered very necessary in the approach to this problem, with nutritional education being most efficient. The professionals' self-perception of therapeutic success is remarkable.

INTRODUCCIÓN: Introducción: el sobrepeso y la obesidad (SP/OB) conforman uno de los mayores retos de salud pública a escala mundial. Los profesionales de Dietética y Nutrición promueven la adquisición de hábitos saludables para adecuar el peso. Desde la psicología, existen aportaciones interesantes a ser consideradas. Objetivos: a) estudiar el vínculo entre las variables del estudio y la intervención terapéutica de los nutricionistas en el SP/OB; b) recabar las opiniones de los nutricionistas sobre los aspectos psicológicos implicados; c) analizar los factores predictores del éxito terapéutico. Métodos: estudio de corte transversal, descriptivo que, a través de una encuesta a dietistas-nutricionistas de España (n = 266), analiza los datos sociodemográficos, formativos y laborales, así como los conocimientos, las creencias y las intervenciones para el SP/OB, haciendo énfasis en los aspectos psicológicos. Se realizaron análisis del chi cuadrado para las variables cualitativas y análisis de regresión para estimar la percepción del éxito terapéutico. Resultados: la especialización en SP/OB se vinculó a las intervenciones de educación nutricional. La consideración de los aspectos psicológicos se asoció al abordaje de los problemas emocionales y sociales. La educación nutricional, el número de sesiones y el tiempo de atención por sesión predijeron la percepción del éxito terapéutico, explicando en conjunto el 46,5 % de la varianza. Conclusiones: los hallazgos informan de una alta formación específica, un uso limitado de las guías de práctica clínica, la atribución mayoritaria del SP/OB a factores ambientales y la preferencia por el trabajo en equipo. Los factores psicológicos se estiman muy necesarios en el abordaje de mayor preferencia, considerando la educación nutricional como el más eficiente. Es destacada la autopercepción del éxito terapéutico entre los profesionales.

Simple beam hardening correction method (2DCalBH) based on 2D linearization.

Objective. The polychromatic nature of the x-ray spectrum in computed tomography leads to two types of artifacts in the reconstructed image: cupping in homogeneous areas and dark bands between dense parts, such as bones. This fact, together with the energy dependence of the mass attenuation coefficients of the tissues, results in erroneous values in the reconstructed image. Many post-processing correction schemes previously proposed require either knowledge of the x-ray spectrum or the heuristic selection of some parameters that have been shown to be suboptimal for correcting different slices in heterogeneous studies. In this study, we propose and validate a method to correct the beam hardening artifacts that avoids such restrictions and restores the quantitative character of the image.Approach. Our approach extends the idea of the water-linearization method. It uses a simple calibration phantom to characterize the attenuation for different soft tissue and bone combinations of the x-ray source polychromatic beam. The correction is based on the bone thickness traversed, obtained from a preliminary reconstruction. We evaluate the proposed method with simulations and real data using a phantom composed of PMMA and aluminum 6082 as materials equivalent to water and bone.Main results. Evaluation with simulated data showed a correction of the artifacts and a recovery of monochromatic values similar to that of the post-processing techniques used for comparison, while it outperformed them on real data.Significance. The proposed method corrects beam hardening artifacts and restores monochromatic attenuation values with no need of spectrum knowledge or heuristic parameter tuning, based on the previous acquisition of a very simple calibration phantom.

Optimization of a calibration phantom for quantitative radiography.

OBJECTIVE: Dual energy radiography (DER) makes it possible to obtain separate images for soft-tissue and bony structures (tissue maps) based on the acquisition of two radiographs at different source peak-kilovoltage values. Current DER studies are based on the weighted subtraction method, which requires either manual tuning or the use of precomputed tables, or on decomposition methods, which make use of a calibration to model soft-tissue and bone components. In this study, we examined in depth the optimum method to perform this calibration. METHODS: We used simulations to optimize the calibration protocol and evaluated the effect of the material and size of a calibration phantom composed of two wedges and its positioning in the system. Evaluated materials were water, PMMA and A-150 as soft-tissue equivalent, and Teflon, B-100 and aluminum as bone equivalent, with sizes from 5 to 30 cm. Each material combination was compared with an ideal phantom composed of soft tissue and bone. Our simulation results enabled us to propose four designs that were tested with the NOVA FA X-ray system with a realistic thorax phantom. RESULTS: Calibration based on a very simple and inexpensive phantom with no strict requirements in its placement results in appropriate separation of the spine (a common focus in densitometry studies) and the identification of nodules as small as 6 mm, which have been reported to have a low rate of detection in radiography. CONCLUSION: The proposed method is completely automatic, avoiding the need for a radiology technician with expert knowledge of the protocol, as is the case in densitometry exams. The method provides real mass thickness values, enabling quantitative planar studies instead of relative comparisons.

Tolerance to geometrical inaccuracies in CBCT systems: A comprehensive study.

PURPOSE: The last decades have seen the consolidation of the cone-beam CT (CBCT) technology, which is nowadays widely used for different applications such as micro-CT for small animals, mammography, dentistry, or surgical procedures. Some CBCT systems may suffer mechanical strains due to the heavy load of the x-ray tube. This fact, together with tolerances in the manufacturing process, lead to different types of undesirable effects in the reconstructed image unless they are properly accounted for during the reconstruction. To obtain good quality images, it is necessary to have a complete characterization of the system geometry including the angular position of the gantry, the source-object and detector-object distances, and the position and pose of the detector. These parameters can be obtained through a calibration process done periodically, depending on the stability of the system geometry. To the best of our knowledge, there are no comprehensive works studying the effect of inaccuracies in the geometrical calibration of CBCT systems in a systematic and quantitative way. In this work, we describe the effects of detector misalignments (linear shifts, rotation, and inclinations) on the image and define their tolerance as the maximum error that keeps the image free from artifacts. METHODS: We used simulations of four phantoms including systematic and random misalignments. Reconstructions of these data with and without errors were compared to identify the artifacts introduced in the reconstructed image and the tolerance to miscalibration deemed to provide acceptable image quality. RESULTS: Visual assessment provided an easy guideline to identify the sources of error by visual inspection of the artifactual images. Systematic errors result in blurring, shape distortion and/or reduction of the axial field of view while random errors produce streaks and blurring in all cases, with a tolerance which is more than twice that of systematic errors. The tolerance corresponding to errors in position of the detector along the tangential direction, that is, skew (<0.2°) and horizontal shift (<0.4 mm), is tighter than the tolerance to those errors affecting the position along the longitudinal direction or the magnification, that is, vertical shift (<2 mm), roll (<1.5°), tilt (<2°), and SDD (<3 mm). CONCLUSION: We present a comprehensive study, based on realistic simulations, of the effects on the reconstructed image quality of errors in the geometrical characterization of a CBCT system and define their tolerance. These results could be used to guide the design of new systems, establishing the mechanical precision that must be achieved, and to help in the definition of an optimal geometrical calibration process. Also, the thorough visual assessment may be valuable to identify the most predominant sources of error based on the effects shown in the reconstructed image.

Simplified Statistical Image Reconstruction for X-ray CT With Beam-Hardening Artifact Compensation.

CT images are often affected by beam-hardening artifacts due to the polychromatic nature of the X-ray spectra. These artifacts appear in the image as cupping in homogeneous areas and as dark bands between dense regions such as bones. This paper proposes a simplified statistical reconstruction method for X-ray CT based on Poisson statistics that accounts for the non-linearities caused by beam hardening. The main advantages of the proposed method over previous algorithms are that it avoids the preliminary segmentation step, which can be tricky, especially for low-dose scans, and it does not require knowledge of the whole source spectrum, which is often unknown. Each voxel attenuation is modeled as a mixture of bone and soft tissue by defining density-dependent tissue fractions and maintaining one unknown per voxel. We approximate the energy-dependent attenuation corresponding to different combinations of bone and soft tissues, the so-called beam-hardening function, with the 1D function corresponding to water plus two parameters that can be tuned empirically. Results on both simulated data with Poisson sinogram noise and two rodent studies acquired with the ARGUS/CT system showed a beam hardening reduction (both cupping and dark bands) similar to analytical reconstruction followed by post-processing techniques but with reduced noise and streaks in cases with a low number of projections, as expected for statistical image reconstruction.

Automatic quantification of histological studies in allergic asthma.

The evaluation of new therapies to treat allergic asthma makes frequent use of histological studies. Some of them are based on microscope observation of stained paraffin lung sections to quantify cellular infiltrate, an effect directly related to allergic processes. Currently, there is no software tool available for doing this quantification automatically. This paper presents a methodology and a software tool for the quantification of cellular infiltrate in lung tissue images in an allergic asthma mouse model. The image is divided into regions of equal size, which are then classified by means of a segmentation algorithm based on texture analysis. The classification uses three discriminant functions, built from parameters derived from the histogram and the co-occurrence matrix. These functions were calculated by means of a stepwise discriminant analysis on 79 samples from a training set. Results provided a correct classification of 96.8% on an independent test set of 251 samples labeled manually. Regression analysis showed a good agreement between automatic and manual methods. A reliable and easy to implement method has been developed to provide an automatic method for quantifying microscopy images of lung histological studies. Results showed similar accuracy to that provided by an expert, while allowing analyzing a much larger number of fields in a repeatable way.

Enabling tomography with low-cost C-arm systems.

In scenarios where the use of a Computed Tomography (CT) is difficult, such as during surgery or in the ICU, the use of a C-arm system to generate tomographic information could contribute with interesting additional clinical information. Recent days are seeing the development of the so-called cone-beam CT (CBCT) based on advanced motorized isocentric C-arm systems. To be able to make use of more basic C-arm systems, apart from the geometric non-idealities common to any CBCT, we need to address other difficulties. First, the trajectory of the source-detector pair may differ from a circular path and the system may suffer mechanical strains that modify the relative positions of the source and detector for different projection angles. Second, and more importantly, the exact position of the source and detector elements may not be repeatable for consecutive rotations due to low mechanical precision, thus preventing an accurate geometrical calibration of the system. Finally, the limitation of the angular span and the difficulty of obtaining a high number of projections pose a great challenge to the image reconstruction. In this work, we present a novel method to adapt a standard C-arm, originally designed for planar imaging, to be used as a tomograph. The key parts of the new acquisition protocol are (1) a geometrical calibration method to compensate mechanical inaccuracies that prevent an accurate repetition of source-detector position between acquisitions, and (2) an advanced image reconstruction method able to deal with limited angle data, sparse projections and non-circular trajectories. Both methods exploit surface information from the patient, which can be obtained using a 3D surface scanner. The proposed method was evaluated with two real C-arm systems, based on an image intensifier and a flat panel detector respectively, showing the feasibility of the proposal.

Unsupervised CT Lung Image Segmentation of a Mycobacterium Tuberculosis Infection Model.

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis that produces pulmonary damage. Radiological imaging is the preferred technique for the assessment of TB longitudinal course. Computer-assisted identification of biomarkers eases the work of the radiologist by providing a quantitative assessment of disease. Lung segmentation is the step before biomarker extraction. In this study, we present an automatic procedure that enables robust segmentation of damaged lungs that have lesions attached to the parenchyma and are affected by respiratory movement artifacts in a Mycobacterium Tuberculosis infection model. Its main steps are the extraction of the healthy lung tissue and the airway tree followed by elimination of the fuzzy boundaries. Its performance was compared with respect to a segmentation obtained using: (1) a semi-automatic tool and (2) an approach based on fuzzy connectedness. A consensus segmentation resulting from the majority voting of three experts' annotations was considered our ground truth. The proposed approach improves the overlap indicators (Dice similarity coefficient, 94% ± 4%) and the surface similarity coefficients (Hausdorff distance, 8.64 mm ± 7.36 mm) in the majority of the most difficult-to-segment slices. Results indicate that the refined lung segmentations generated could facilitate the extraction of meaningful quantitative data on disease burden.

FUX-Sim: Implementation of a fast universal simulation/reconstruction framework for X-ray systems.

The availability of digital X-ray detectors, together with advances in reconstruction algorithms, creates an opportunity for bringing 3D capabilities to conventional radiology systems. The downside is that reconstruction algorithms for non-standard acquisition protocols are generally based on iterative approaches that involve a high computational burden. The development of new flexible X-ray systems could benefit from computer simulations, which may enable performance to be checked before expensive real systems are implemented. The development of simulation/reconstruction algorithms in this context poses three main difficulties. First, the algorithms deal with large data volumes and are computationally expensive, thus leading to the need for hardware and software optimizations. Second, these optimizations are limited by the high flexibility required to explore new scanning geometries, including fully configurable positioning of source and detector elements. And third, the evolution of the various hardware setups increases the effort required for maintaining and adapting the implementations to current and future programming models. Previous works lack support for completely flexible geometries and/or compatibility with multiple programming models and platforms. In this paper, we present FUX-Sim, a novel X-ray simulation/reconstruction framework that was designed to be flexible and fast. Optimized implementation for different families of GPUs (CUDA and OpenCL) and multi-core CPUs was achieved thanks to a modularized approach based on a layered architecture and parallel implementation of the algorithms for both architectures. A detailed performance evaluation demonstrates that for different system configurations and hardware platforms, FUX-Sim maximizes performance with the CUDA programming model (5 times faster than other state-of-the-art implementations). Furthermore, the CPU and OpenCL programming models allow FUX-Sim to be executed over a wide range of hardware platforms.

A Novel Prior- and Motion-Based Compressed Sensing Method for Small-Animal Respiratory Gated CT.

Low-dose protocols for respiratory gating in cardiothoracic small-animal imaging lead to streak artifacts in the images reconstructed with a Feldkamp-Davis-Kress (FDK) method. We propose a novel prior- and motion-based reconstruction (PRIMOR) method, which improves prior-based reconstruction (PBR) by adding a penalty function that includes a model of motion. The prior image is generated as the average of all the respiratory gates, reconstructed with FDK. Motion between respiratory gates is estimated using a nonrigid registration method based on hierarchical B-splines. We compare PRIMOR with an equivalent PBR method without motion estimation using as reference the reconstruction of high dose data. From these data acquired with a micro-CT scanner, different scenarios were simulated by changing photon flux and number of projections. Methods were evaluated in terms of contrast-to-noise-ratio (CNR), mean square error (MSE), streak artefact indicator (SAI), solution error norm (SEN), and correction of respiratory motion. Also, to evaluate the effect of each method on lung studies quantification, we have computed the Jaccard similarity index of the mask obtained from segmenting each image as compared to those obtained from the high dose reconstruction. Both iterative methods greatly improved FDK reconstruction in all cases. PBR was prone to streak artifacts and presented blurring effects in bone and lung tissues when using both a low number of projections and low dose. Adopting PBR as a reference, PRIMOR increased CNR up to 33% and decreased MSE, SAI and SEN up to 20%, 4% and 13%, respectively. PRIMOR also presented better compensation for respiratory motion and higher Jaccard similarity index. In conclusion, the new method proposed for low-dose respiratory gating in small-animal scanners shows an improvement in image quality and allows a reduction of dose or a reduction of the number of projections between two and three times with respect to previous PBR approaches.

Investigation of different sparsity transforms for the PICCS algorithm in small-animal respiratory gated CT.

Respiratory gating helps to overcome the problem of breathing motion in cardiothoracic small-animal imaging by acquiring multiple images for each projection angle and then assigning projections to different phases. When this approach is used with a dose similar to that of a static acquisition, a low number of noisy projections are available for the reconstruction of each respiratory phase, thus leading to streak artifacts in the reconstructed images. This problem can be alleviated using a prior image constrained compressed sensing (PICCS) algorithm, which enables accurate reconstruction of highly undersampled data when a prior image is available. We compared variants of the PICCS algorithm with different transforms in the prior penalty function: gradient, unitary, and wavelet transform. In all cases the problem was solved using the Split Bregman approach, which is efficient for convex constrained optimization. The algorithms were evaluated using simulations generated from data previously acquired on a micro-CT scanner following a high-dose protocol (four times the dose of a standard static protocol). The resulting data were used to simulate scenarios with different dose levels and numbers of projections. All compressed sensing methods performed very similarly in terms of noise, spatiotemporal resolution, and streak reduction, and filtered back-projection was greatly improved. Nevertheless, the wavelet domain was found to be less prone to patchy cartoon-like artifacts than the commonly used gradient domain.

Funciones ejecutivas y ajuste clínico en adolescentes colombianos policonsumidores / Executive functions and clinical adjustment in Colombian adolescents polydrug

Resumen El estudio tuvo como objetivo analizar el funcionamiento ejecutivo y el ajuste clínico en una muestra de adolescentes colombianos policonsumidores. Se efectuó un estudio ex post facto con 204 participantes entre 12 y 17 años (M = 14,50, DT = 1,71). Se aplicó la Batería Neuropsicológica de Funciones Ejecutivas y Lóbulos Frontales BANFE-2 y para la evaluación clínica se utilizó la Escala de Autoestima de Rosenberg, Cuestionario de Afrontamiento COPE, Escala de Impulsividad de Dickman y Cuestionario de 90 Síntomas SCL-90-R. Se identificó un rendimiento significativamente inferior del grupo policonsumidor en las funciones ejecutivas, bajos niveles de autoestima, altos niveles de impulsividad disfuncional y de diversidad psicopatológica, así como estilo de afrontamiento a través del consumo de sustancias. Así mismo, se detectó un efecto predictor de la interacción edad x tiempo de consumo en el funcionamiento ejecutivo, observándose un menor rendimiento de los policonsumidores más jóvenes a medida que se incrementaba el tiempo de consumo.

Abstract The research aim was to analyze the executive functioning and the clinical adjustment in a sample of Colombian teen polydrug users. An ex post facto study was carried out with 204 participants, 12-17 years old (M= 14,50, SD = 1,71). The neuropsychological test BANFE-2 was applied for analyzing frontal lobes and executive functioning and the Rosenberg self esteem scale, a COPE questionnaire, the Dickman impulsivity scale and the SCL-90-R questionnaire were used for clinical adjustment respectively. A lower executive functioning throughput were observed in polydrug users. Low self-esteem, high dysfunctional impulsivity, high diverse psychopathologies and coping strategies for drug use were also observed. A predictor effect between age and consumption time on the executive functioning were also determined. A lower throughput in younger polydrug users increase through consumption time.

Accuracy of CT-based attenuation correction in PET/CT bone imaging.

We evaluate the accuracy of scaling CT images for attenuation correction of PET data measured for bone. While the standard tri-linear approach has been well tested for soft tissues, the impact of CT-based attenuation correction on the accuracy of tracer uptake in bone has not been reported in detail. We measured the accuracy of attenuation coefficients of bovine femur segments and patient data using a tri-linear method applied to CT images obtained at different kVp settings. Attenuation values at 511 keV obtained with a (68)Ga/(68)Ge transmission scan were used as a reference standard. The impact of inaccurate attenuation images on PET standardized uptake values (SUVs) was then evaluated using simulated emission images and emission images from five patients with elevated levels of FDG uptake in bone at disease sites. The CT-based linear attenuation images of the bovine femur segments underestimated the true values by 2.9 ± 0.3% for cancellous bone regardless of kVp. For compact bone the underestimation ranged from 1.3% at 140 kVp to 14.1% at 80 kVp. In the patient scans at 140 kVp the underestimation was approximately 2% averaged over all bony regions. The sensitivity analysis indicated that errors in PET SUVs in bone are approximately proportional to errors in the estimated attenuation coefficients for the same regions. The variability in SUV bias also increased approximately linearly with the error in linear attenuation coefficients. These results suggest that bias in bone uptake SUVs of PET tracers ranges from 2.4% to 5.9% when using CT scans at 140 and 120 kVp for attenuation correction. Lower kVp scans have the potential for considerably more error in dense bone. This bias is present in any PET tracer with bone uptake but may be clinically insignificant for many imaging tasks. However, errors from CT-based attenuation correction methods should be carefully evaluated if quantitation of tracer uptake in bone is important.

Relación entre bienestar subjetivo, optimismo y variables sociodemográficas en estudiantes universitarios de la Universidad de San Luis Potosí en México / Relationship between Subjective Well-being, Optimism and Demographic Variables in College Students of the University of San Luis Potosi in Mexico

El objetivo de este estudio fue analizar la relación entre características sociodemográficas, optimismo y bienestar subjetivo (SWB) en estudiantes universitarios mexicanos de la Universidad de San Luis Potosí. Además, identificar qué áreas vitales incidían en mayor medida en el bienestar global y cuánto aportaría el optimismo a esta relación. Se recogió información de 299 estudiantes (17 a 49 años; M = 19.38; DE = 3.19) mediante una entrevista semiestructurada, registrando diversas características sociodemográficas que se consideraron relevantes. El optimismo disposicional se midió empleando el Life Orientation Test Revised (Scheier, Carver & Bridges, 1994) y el bienestar subjetivo mediante diversas medidas: felicidad (Subjective Happiness Scale de Lyubomirsky & Lepper, 1999), satisfacción vital (Satisfaction with Life Scale de Diener, Emmons, Larsen & Griffin, 1985), emociones positivas y emociones negativas (Positive and Negative Affect Schedule de Watson, Clark & Tellegen, 1988) y satisfacción en los dominios vitales de estudios, pareja, salud y ocio (Entrevista semiestructurada de Marrero, Carballeira & Rodríguez, 2007). A través de la Tau-b de Kendall se analizó la relación de las variables sociodemográficas con el optimismo y los indicadores de bienestar, encontrando asociaciones entre género y satisfacción con el trabajo/estudios, satisfacción vital, felicidad y optimismo. Además, tener una relación sentimental se relacionaba con la satisfacción con la pareja y la condición laboral con satisfacción vital. Los análisis correlacionales de Pearson entre los ocho indicadores de bienestar y el optimismo mostraron que todos los indicadores de bienestar se relacionaban entre ellos y el optimismo estaba asociado en mayor medida que las variables sociodemográficas al bienestar, siendo la relación con medidas globales mayor que con los dominios vitales específicos. Para profundizar en esta asociación entre optimismo y bienestar se dividió a los participantes en tres grupos según su nivel de optimismo. A través de un MANOVA se compararon las medias en bienestar encontrando que las personas con optimismo alto y medio informaron de mayor satisfacción vital y emociones positivas, menor emociones negativas y mayor satisfacción en todos los dominios vitales frente a las personas con bajo optimismo El MANCOVA, tomando el género como covariante, indicaba resultados similares. Por último, se aplicaron análisis de regresión múltiple para conocer el peso que tenían las distintas medidas de satisfacción en dominios específicos en los indicadores globales de bienestar, felicidad y satisfacción vital. Los resultados mostraron que todos los dominios son relevantes para ambas variables criterio pero la satisfacción laboral/estudios resultó ser el predictor más poderoso. Cuando se realizaron nuevos análisis de regresión múltiple, incluyendo el optimismo como predictor, se encontró que este explicaba mayor porcentaje de varianza que la satisfacción en dominios específicos, sobre todo en el caso de la felicidad. Estos hallazgos sugieren que el optimismo es un rasgo de personalidad relevante para mejorar el bienestar subjetivo de los individiduos.

The main objective of this study was to analyze the relationship between different sociodemographic characteristics, optimism and subjective well-being (SWB) in a sample of Mexican undergraduate students from the University of San Luis Potosi. Additionally, we have tried to identify which specific life domains influenced more on global well-being and how the optimism could explain well-being. Data were collected of 299 participants aged between 17 and 49 years old (M= 19.38; SD= 3.19) through a semi structured interview, considering different relevant sociodemographic characteristics. Dispositional optimism was evaluated using the Life Orientation Test Revised (Scheier, Carver & Bridges, 1994). Subjective well-being included the following measures: Happiness (Subjective Happiness Scale de Lyubomirsky & Lepper, 1999), Life Satisfaction (Satisfaction with Life Scale from Diener, Emmons, Larsen & Griffin, 1985), Positive and Negative Emotions (Positive and Negative Affect Schedule from Watson, Clark & Tellegen, 1988) and Satisfaction with different Life Domains: Job/ Studies, Partner, Health and Leisure (Marrero, Carballeira & Rodríguez, 2007). Through the Test for Kendall's Tau-b, the relationship between sociodemographic variables, optimism and well-being indicators was analysed. The results showed moderate associations between gender and studies satisfaction, life satisfaction, happiness and optimism. Also, the fact of having a sentimental relationship was related to partner satisfaction; and the job situation was associated with life satisfaction. Pearson correlational analyses between the eight well-being indicators and the optimism showed that all the well-being variables were related each other. Optimism was more associated to all the measures of SWB than the sociodemographic variables; and the relationships of optimism with global measures of well-being were greater than those with the specific life domains. In order to deep in this association between optimism and well-being, the sample was split in three groups in function of the level of optimism. A MANOVA was made to compare the means of well-being, finding that those participants with high and medium optimism, vs. those with low optimism, reported more life satisfaction and positive emotions, lower negative emotions and more satisfaction in all the specific life domains. The MANCOVA, taking the gender as a covariant, showed similar findings. Finally, Multiple Regression Analyses were applied to know the influence of the different specific life domains on the global components of well-being: happiness and life satisfaction. The results showed that all the specific domains were relevant for both criteria variables, but studies satisfaction was the more powerful predictor. In the new multiple regression analyses, the optimsm was included and explained a higher percentage of variance than the measures of satisfaction with life domains, especially in the case of happiness as the criteria. These findings suggested that optimism is a relevant personality trait to improve subjective well-being of individuals.

El papel del optimismo y del apoyo social en el bienestar subjetivo / The role of optimism and social support on subjective well-being

Introduction In recent years, a great deal of research has been carried out to identify the aspects that affect subjective well-being. In these studies, different indicators of well-being have been used. While some studies have used satisfaction with life as an indicator, others have focussed on psychological adjustment, while still in some other cases the focus has been on positive emotions and even physical health, understood as the lack of illness, as contributing to well-being. Nevertheless, these indicators have not been directly comparable. The objective of this study is to analyze whether optimism and social support equally affect or not subjective well-being. Subjective well-being has been defined as the global tendency to experience life in a pleasant way. The evaluation that people carry out has two components: a cognitive component, evaluated through life satisfaction, and an affective one, measured through positive and negative affect. Previous research has been centred on analysing the factors which could influence either on positive or negative ways, such as personality, optimism, coping styles, and social support. It has been demonstrated that well-being is determined, in some way, by optimism and social support. However, there has been very little research analysing the relative impact of these variables on the different measures of well-being. Thus, the purpose of this study was to examine the influence of optimism and social support on the different components of subjective well-being. We have analysed: firstly, the relationships of optimism and social support with well-being; second, whether or not optimists feel more subjective well-being; third, social support together with optimism have an enhancer effect on well-being; and four, optimism and social support can differentially predict the several components of subjective well-being. Method This is a cross-sectional study where subjective well-being has been assessed in 477 people from general population between 18 and 66 years old (M=25.66; SD=8.81). The following measures were used: satisfaction with specific life domains (partner, job/studies, health and leisure), life satisfaction, positive emotions, negative emotions, and mental health. Optimism was evaluated through the Life Orientation Test-Revised (LOT-R) and Social Support through the Social Support Questionnaire (SSQ-6). Moreover, certain demographic and physical health characteristics were assessed through a semi-structured interview. In order to analyse the relationships among the variables included in the study, we administered partial correlations, controlling for gender. Also, one-way analyses were conducted to discover any differences in well-being between high, medium, and low optimists. Afterwards, U Mann-Whitney was applied in order to analyze whether optimist people with high social support show more well-being than optimist people without social support. Finally, in order to study the capacity of optimism and social support in predicting the different components of well-being, several multiple regression analyses were applied. Results Results showed that socio-demographic and physical health variables do not influence optimism. There is a close relationship between optimism and all the measures of subjective well-being, with optimists showing more life satisfaction, fewer psychological symptoms, more positive emotions, less negative emotions, and being more satisfied in several specific life domains, such as partner and health. Perceived social support is associated with different signs of well-being, although the extent of the correlation is lower. Participants with more perceived social support show better adjustment, more life satisfaction and partner satisfaction, they have more positive emotions and less negative emotions. There are not significant associations of perceived social support with health satisfaction and with job satisfaction. The amount of social support resources shows low correlations with subjective well-being, particularly with some of the psychological adjustment measures and with life satisfaction. When differences between high and low optimists are analysed, similar results are observed. High optimists have less anxiety, depression, interpersonal sensitivity symptoms, and score lower in the strength disorder index than low optimists. Moreover, high optimists experience more positive emotions and less negative ones, report more satisfaction with their partner, with health and with life in general, and have more perceived social support. So, optimism seems to have an influence on most of the well-being components. On the other hand, when optimism and social support effect on well-being are analyzed altogether, it can be observed that high optimist people with high social support show more positive emotions, more satisfaction with leisure, more life satisfaction; and less negative emotions, depression and interpersonal sensitivity than high optimists with poor social support.

Introducción Identificar los factores que inciden en el bienestar de los individuos ha sido uno de los aspectos psicológicos más estudiados en los últimos años. El bienestar subjetivo se ha definido como la tendencia global a experimentar la vida de modo placentero. Esta valoración que hace el individuo tiene dos componentes: el cognitivo, evaluado por medio de la satisfacción vital, y el afectivo, que se basa en la presencia de emociones positivas y emociones negativas. La investigación previa se ha centrado en analizar los factores que inciden en el bienestar subjetivo, pero se han empleado diversas medidas de bienestar que no han sido directamente comparables. En este estudio se analizan conjuntamente los diversos indicadores de bienestar, con el objetivo de estudiar si el optimismo y el apoyo social inciden de manera similar o diferencial en cada uno de ellos. Método Es un estudio transversal con una muestra de conveniencia compuesta por 477 personas entre 18 y 66 años (M=25.66; DT=8.81). Se evalúan distintos componentes del bienestar: satisfacción en áreas específicas como pareja, trabajo/estudios, salud y ocio; satisfacción vital; emociones positivas; emociones negativas y ajuste psicológico. El optimismo disposicional se mide mediante el Test de Orientación Vital Revisado (LOT-R) y el apoyo social por medio del Social Support Questionnaire (SSQ-6). Resultados Los resultados indican que las variables sociodemográficas y las relacionadas con la salud no inciden en el nivel de optimismo. El optimismo guarda relación con la mayor parte de los indicadores de bienestar subjetivo. Las personas optimistas están mejor ajustadas psicológicamente, muestran mayor satisfacción con la vida, experimentan más emociones positivas y menos negativas, y además, informan de mayor satisfacción en algunas áreas de su vida, como la pareja y la salud. Por su parte, las personas con mayor percepción de apoyo se sienten más satisfechas con su vida, muestran más satisfacción con la pareja, están más ajustadas psicológicamente y tienen más emociones positivas y menos negativas. Sin embargo, la cantidad de fuentes de apoyo resulta menos relevante para el bienestar. El análisis de las diferencias entre personas optimistas frente a las poco optimistas confirma el patrón descrito, las optimistas tienen mejor ajuste psicológico, mayor satisfacción en áreas vitales (salvo laboral y de ocio), mayor satisfacción con la vida, experimentan más emociones positivas y menos negativas y tienen más apoyo social percibido. Por otra parte, si se analiza el efecto conjunto del optimismo y del apoyo social en el bienestar se observa que las personas con alto optimismo y alto apoyo muestran más emociones positivas, mayor satisfacción con el ocio y con la vida, menos emociones negativas, menor depresión y menor sensibilidad interpersonal que las personas optimistas con escaso apoyo social. Al analizar la capacidad del optimismo y del apoyo social para predecir el bienestar subjetivo se encuentra que estos factores apenas predicen la satisfacción en áreas específicas pero sí predicen cerca de un 30% de la varianza de la satisfacción vital, un 20.2% del ajuste psicológico y alrededor de un 14% de la varianza de las emociones positivas y emociones negativas. Discusión y conclusiones En general, los resultados avalan la importancia del optimismo y del apoyo social en los distintos indicadores de bienestar subjetivo. Sin embargo, el peso de estos factores no parece ser el mismo en cada uno de los componentes del bienestar. El optimismo guarda relaciones más estrechas con los indicadores de bienestar que el apoyo social, estando más vinculado a la satisfacción vital, a la depresión y al ajuste psicológico que a la satisfacción en dominios específicos. El optimismo, al ser una expectativa global, probablemente incida más en indicadores generales de bienestar que en índices de satisfacción concretos. Por otro lado, el apoyo social percibido tiene más peso a la hora de predecir la satisfacción en áreas específicas. Tal vez, porque en el momento de valorar situaciones de la vida cotidiana resultan más prominentes los otros, y esto incide directamente en el juicio del individuo acerca de su satisfacción en áreas en las que están implicadas las relaciones interpersonales. En investigaciones futuras se precisa profundizar sobre el significado de los distintos componentes del bienestar y qué otros factores, además del optimismo y el apoyo social, pueden estar incidiendo en el mismo.