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Pixelated scintillators are commonly used for gamma radiation detection in PET scanners. Dimensions, surface treatment, and reflector thickness affect the resolution and sensitivity of the detector and increase the signal to noise ratio. Pixel arrays fabrication is laborious and expensive, while by including nonscintillating material the active area of the detector is reduced. This process can be simplified and improved by the application of subsurface laser engraving techniques, where a grid of laser-induced microcracks form semitransparent walls inside the scintillator. Conceptual development of such patterns including simulations and photometric measurements is presented as a proof that pixelation without the application of external reflectors is possible, liberating pixel size and shape and allowing detector-specific patterns to be created. To demonstrate this, a case study of a hexagonal grid of pixels of 1.4 mm $^{2}$ size on LYSO monolithic scintillators is proposed and results presented. Depth of interaction is also implemented on same size pixels, through different approaches. Advantages, concerning sensitivity, packing fraction, and cost effectiveness are discussed, supporting the viability of the process as an alternative to conventional pixelated array fabrication techniques which combines advantageous characteristics of both monolithic and pixelated scintillators.

Proceedings of: IPA 2015 / SPIE Biophotonics South America. Rio de Janeiro, Brazil, 22-26 May, 2015 Endoscopy is frequently used in the diagnosis of several gastro-intestinal pathologies as Crohn disease, ulcerative colitis or colorectal cancer. It has great potential as a non-invasive screening technique capable of detecting suspicious alterations in the intestinal mucosa, such as inflammatory processes. However, these early lesions usually cannot be detected with conventional endoscopes, due to lack of cellular detail and the absence of specific markers. Due to this lack of specificity, the development of new endoscopy technologies, which are able to show microscopic changes in the mucosa structure, are necessary. We here present a confocal endomicroscope, which in combination with a wide field fluorescence endoscope offers fast and specific macroscopic information through the use of activatable probes and a detailed analysis at cellular level of the possible altered tissue areas. This multi-modal and multi-scale imaging module, compatible with commercial endoscopes, combines near-infrared fluorescence (NIRF) measurements (enabling specific imaging of markers of disease and prognosis) and confocal endomicroscopy making use of a fiber bundle, providing a cellular level resolution. The system will be used in animal models exhibiting gastro-intestinal diseases in order to analyze the use of potential diagnostic markers in colorectal cancer. In this work, we present in detail the set-up design and the software implementation in order to obtain simultaneous RGB/NIRF measurements and short confocal scanning times. The authors acknowledge support from EC FP7 IMI project PREDICT-TB, the EC FP7 CIG grant HIGH-THROUGHPUT TOMO, the Spanish MINECO project grant FIS2013-41802-R MESO-IMAGING, and TOPUS S2013/MIT-3024 project from the regional government of Madrid Publicado

In vivo imaging using positron emission tomography (PET) is important in the development of new radiopharmaceuticals in rodent animal models for use as biochemical probes, diagnostic agents, or in drug development. We have shown mathematically that, if small animal imaging studies in rodents are to have the same “quality” as human PET studies, the same number of coincidence events must be detected from a typical rodent imaging “voxel” as from the human imaging voxel. To achieve this using the same specifi activity preparation, we show that roughly the same total amount of radiopharmaceutical must be given to a rodent as to a human subject. At high specifi activities, the mass associated with human doses, when administered to a rodent, may not decrease the uptake of radioactivity at non saturable sites or sites where an enzyme has a high capacity for a substrate. However, in the case of binding sites of low density such as receptors, the increased mass injected could saturate the receptor and lead to physiologic effects and non-linear kinetics. Because of the importance of the mass injected for small animal PET imaging, we experimentally compared high and low mass preparations using ex vivo biodistribution and phosphorimaging of three compounds: 2-fluoro-2-deoxyglucos (FDG), 6-fluoro-L-metatyrosin (FMT) and one receptor-directed compound, the serotonin 5HT1A receptor ligand, trans-4-fluoro-N-{2-[4-(2-methoxylphenyl piperazino]ethyl}-N-(2- pyridyl) cyclohexane- carboxamide (FCWAY). Changes in the mass injected per rat did not affect the distribution of FDG, FMT, and FCWAY in the range of 0.6 –1.9 nmol per rat. Changes in the target to nontarget ratio were observed for injected masses of FCWAY in the range of 5–50 nmol per rat. If the specifi activity of such compounds and/or the sensitivity of small animal scanners are not increased relative to human studies, small animal PET imaging will not correctly portray the “true” tracer distribution. These difficultie will only be exacerbated in animals smaller than the rat, e.g., mice. Publicado

A new circuit design for automatically tuning and matching a saddle coil for small animal imaging is presented. This design allows working at (1)H, (19)F, and (3)He resonance frequencies in a 4.7 T spectrometer. It is based on a balanced circuit with commercial variable capacity diodes controlled by a computer using digital potentiometers. The change between two different frequencies can be accurately performed in a few seconds. System Q is compared, between 140-210 MHz, to the same coil tuned and matched with high Q variable capacitors. Differences lower than 5% were found with a loaded coil. The proposed design has initially been evaluated in (19)F and (1)H NMR images acquired with a five-tube phantom. An application is also shown for the acquisition of (3)He, (19)F, and (1)H lung images in a control rat.

ObjetivoCuantificar el coste de la cirugía menor, realizada en nuestra zona básica de salud durante un año, comparándola según el nivel de facturación. Conocer el grado de correlación clinicopatológica y el número de complicaciones, como indicadores indirectos de calidad.DiseñoEstudio descriptivo, transversal retrospectivo.EmplazamientoAtención primaria, Zona Básica de Salud Río Nacimiento, Abla (Almería).ParticipantesLa población de estudio son todos aquellos usuarios atendidos en el programa de cirugía menor durante el año 2000, incluyendo todos los procesos intervenidos (84 pacientes y 95 procesos).Mediciones principalesLas variables analizadas son: tipo de proceso y procedimiento quirúrgico, correlación clinicopatológica, complicaciones tempranas de la cirugía y coste por proceso. Calculamos el coste de nuestra actividad según: a) factura que ocasionó en el centro de salud; b) lo que facturaría una compañía de seguros médicos; c) lo que facturaría un distrito de atención primaria (AP), y d) lo que facturaría un hospital del Servicio Andaluz de Salud (SAS).ResultadosSe intervinieron 95 procesos en 84 pacientes. Se remitieron 31 muestras a anatomía patológica con una correlación clinicopatológica del 77,42%. No se registraron complicaciones.En nuestro centro el coste es de 817,18 euros; una mutua habría facturado 8.803,63 euros; un distrito de AP, 4.852,03 euros, y un hospital del SAS, 14.015,39 euros.ConclusiónLa cirugía menor realizada en nuestro centro de salud por nuestro equipo es más coste-efectiva que si se llevara a cabo en otros centros públicos o privados, con buenos niveles de calidad.AimTo quantify the cost of minor surgery in our health district during a year, by examining the amounts charged. To find the degree of clinical/pathological correlation and the number of complications, as indirect indicators of quality.DesignDescriptive, cross-sectional, retrospective study.SettingPrimary care, Río Nacimiento Health District, Abla (Almería).ParticipantsThe study included all those patients attended within the minor surgery programme in the year 2000, and all the procedures used (84 patients and 95 procedures).Main measurementsThe variables analysed were: type of procedure and surgery, clinical/pathological correlation, early surgical complications, and cost per procedure. We calculated the cost of our activity on the basis of: a) cost occasioned at the health centre; b) what a medical insurance company would bill; c) what a primary care district would bill, and d) what a health service hospital would bill.Results95 procedures in 84 patients were examined. 31 samples were sent to pathology with a clinical-pathological correlation of 77.42%. No complications were recorded.At our centre the cost was 817.18 euros. An insurance company would have charged 8803.63 euros; a PC district, 4852.03 euros; and a health service hospital, 14 015.39 euros.ConclusionThe minor surgery performed at our health centre by our team was more cost-effective than if it was performed in other public or private centres with high standards of quality.

Cluster division is a critical issue in fluor escence micr oscopy-based analytical cytology when preparation protocols do not provide appropriate separation of objects. Overlooking cluster ed nuclei and analyzing only isolated nuclei may dramatically incr ease analysis time or af fect the statistical validation of the r esults. Automatic segmentation of cluster ed nuclei r equir es the implementation of specific image segmentation tools. Most algorithms are inspired by one of the two following strategies: 1) cluster division by the detection of inter nuclei gradients; or 2) division by definition of domains of influence (geometrical approach). Both strategies lead to completely different implementations, and usually algorithms based on a single view strategy fail to corr ectly segment most cluster ed nuclei, or per for m well just for a specific type of sample. An algorithm based on morphological watersheds has been implemented and tested on the segmentation of micr oscopic nuclei clusters. This algorithm pr ovides a tool that can be used for the implementation of both gradient- and domain-based algorithms, and, mor e importantly, for the implementation of mixed (gradient- and shape-based) algorithms. Using this algorithm, almost 90% of the test clusters wer e corr ectly segmented in peripheral blood and bone marr ow pr eparations. The algorithm was valid for both types of samples, using the appr opriate markers and transfor mations. Contract grant sponsor: ARCADIM Project; Contract grant number: CICYT TIC92-0922-C02-01 (Comisión Interministerial de Ciencia y Tecnología); Contract grant sponsor: European Concerted Action CA-AMCA; Contract grant number: BMH1-CT92-1307; Contract grant sponsor: Comunidad Autónoma de Madrid (CAM); Contract grant sponsor: Universidad Politécnica de Madrid (UPM). Publicado

Transnasal administration is one of the most common routes for allergen challenge in mouse models of airway diseases. Although this technique is widely used, neither the amount of allergen that reaches the lung nor its airway distribution has been well established. We used positron emission tomography (PET) and computed tomography (CT) to examine the anatomical distribution of a solution containing a tracer immediately after transnasal delivery and to determine the possible influence of age and administered volume. Procedures: Forty-six female BALB/c mice were divided into three groups according to instillation volume and age: (A) 15 μl, 8–10 weeks old (N=10), (B) 30 μl, 8–10 weeks old (N=20), and (C) 30 μl, 32 weeks old (N=16). Anesthetized animals underwent a dynamic scan in a dedicated small-animal PET scanner immediately after transnasal administration of a solution containing 18FDG. Regions of interest were used to obtain quantitative data. Animals were also imaged with a small-animal CT scanner to obtain complementary anatomical information. Results: Mean±SD (5.69±4.51%) of the solution administered reached the lungs in group A,41.84±8.03% in group B, and 36.65±16.15% in group C. A comparable percentage was delivered to the left and right lungs in all the groups. Analysis of variance revealed a significant difference between the groups in the proportion of the solution that reached the lungs depending on the injection volume (PG0.001), but not depending on animal age. Conclusions: In this first report on quantitative imaging by PET and CT in small animals, we confirmed the suitability of the transnasal route with an instilled volume of 30 μl delivering fluids into the lower airways, although only about 40% of the dose reaches the lungs This work was supported by grants from Ministerio de Ciencia y Tecnología (TEC2004-07052-C02-01), Ministerio de Sanidad y Consumo (CIBER CB06/01/0079 CIBER CB07/09/0031 and FIS 2001/0598), Ministerio de Industria (CDTEAM Project) and Fundación de Investigación Médica Mutua Madrileña Publicado

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 algo rithm 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 independ ent test set of 251 samples labeled manually. Regression analysis showed a good agree ment between automatic and manual methods. A reliable and easy to implement method has been developed to provide an automatic method for quantifying micros copy images of lung histological studies. Results showed similar accuracy to that pro vided by an expert, while allowing analyzing a much larger number of fields in a repea table way Contract grant sponsor: CD TEAM project, CENIT program, Ministerio de Industria Publicado

Melanoma is the most aggressive skin cancer once metastasis begins; therefore, it is important to characterize the molecular players involved in melanoma dissemination. The chemokine receptor CXCR4 and the membrane-bound metalloproteinase MT1-MMP are expressed on melanoma cells and represent candidate molecules for the control of metastasis. Using human melanoma transfectants that either overexpress or silence CXCR4 or MT1-MMP, or that have a combination of overexpression and interference of these proteins, we show that CXCR4 and MT1-MMP coordinate their activities at different steps along melanoma cell metastasis into the lungs. Results from in vivo xenograft mouse models of melanoma lung colonization and mice survival and short-term, homing nested polymerase chain reaction experiments from lung samples indicated that CXCR4 is required at early phases of melanoma cell arrival in the lungs. In contrast, MT1-MMP is not needed for these initial steps but promotes subsequent invasion and dissemination of the tumor with CXCR4. Investigation of potential cross talk between CXCR4 and MT1-MMP revealed that MT1-MMP accumulates intracellularly after melanoma cell stimulation with the CXCR4 ligand CXCL12, and that this process involves the activation of the Rac-Erk1/2 pathway. Subsequent to cell contact with specific basement membrane proteins, MT1-MMP redistributes to the cell membrane in a phosphatidylinositol 3-kinase-dependent manner. These results suggest that combination therapies that target CXCR4 and MT1-MMP should improve the limitations of the current therapies for metastatic melanoma. Copyright © American Society for Investigative Pathology.

Proceeding of: 2008 IEEE Nuclear Science Symposium Conference Record (NSS '08), Dresden, Germany, 19-25 Oct. 2008 A fully 3D statistical image reconstruction algorithm has been developed for a high-resolution coplanar PETtCT scanner based on rotating planar PET detectors. The system matrix has been modeled with custom Monte Carlo techniques optimized for the specific scanner architecture. The system model includes positron range, non-colinearity of gamma rays and crystal interaction modelling with attenuation and Compton scattering effects. Only 0.21 % of the system matrix columns are modeled in detail, obtaining the rest of the values with axial and transaxial voxel-driven symmetries. The iterative algorithm is a fully 3D approach, regularized with the anatomical registered image using a novel version of the minimum cross entropy (MXE) scheme, and accelerated employing ordered subsets. The proposed method has been shown to produce images with superior quality than 3D hybrid (FORE+2D-OSEM) algorithms applied on synthetic GATE data, as well as on real small animal acquisitions This work has been partly funded by the CDTEAM project and CENIT programme (Spanish Ministry of Industry), EMIL (ED Network of Excellence), CIBER CB07/09/0031 and RETIC-RECAVA (Spanish Ministry of Health) and TEC2007-64731/TCM(Spanish Ministry of Education and Science)

Proceeding of: 2007 IEEE Nuclear Science Symposium Conference Record (NSS'07), Honolulu, Hawaii, USA, Oct. 27 - Nov. 3, 2007 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. In this work we review the main differences between PET and CT data and study whether these consistency conditions should be modified in order to take into account the dependence of the probabilities on the distance to the center of the line-of-response. Results from simulations are also presented to illustrate the importance of these effects. They indicate that some consistency conditions can be violated at the 10% level. This work has been partially funded by UCM grant. Part of the computations of this work were done at the 'High capacity cluster for physical techniques' of the Faculty for Physical Sciences of the UCM, funded in part by the UE under the FEDER program and in part by the UCM. This work has been partially funded by CD-TEAM, program CENIT, Ministerio de Industria, Spain.

A new reconstruction strategy is proposed for 3D images acquired with rotating PET scanners. This method is based on the decomposition of the system response matrix (SRM) into a projection and a rotation components that are inverted independently. We present the rationale of the new reconstruction procedure as well as some examples to compare with analytical 3D reconstruction (3DRP) and 3D statistical reconstruction (3D-OSEM)

Proceeding of: 2006 IEEE Nuclear Science Symposium Conference Record, San Diego, CA, Oct. 29 - Nov. 1, 2006 Low-pass filtering sinograms prior to reconstruction is a general practice to reduce noise. Sinograms are generally filtered in the radial direction, although other filtering schemes have been proposed. It is known that the Fourier transform of a sinogram shows a particular shape of the spectral energy distribution (“bow-tie”). In this work, this property has been exploited to perform an adapted filter, whose performance has been compared with previously reported methods: angular, axial and stackgram domain filtering. Stackgram and angular filtering degraded resolution (~16 and ~5.7 % respectively) while no significant enhancement in contrast to noise ratio (CNR) was achieved. Angular filtering resulted in a circle blurring artifact dependant on the distance to the center of the FOV. Bow-tie filtering showed the best results (enhancement of ~26% in resolution and of ~12% in CNR). Axial filtering degraded resolution but enhanced CNR (~14 %), appearing as a good strategy to reduce radial filtering. Experiments on rodent images showed a noticeable image quality enhancement achieved when using bow-tie filtering combined with radial and axial filters. This work was supported in part by from Ministerio de Educación y Ciencia (FIS-PI052583 and TEC2004-07052-C02), Ministerio de Industria (CD-TEAM, CENIT program) and Comunidad de Madrid (GR/SAL/024104).

Proceeding of: 2001 Nuclear Science Symposium and Medical Imaging Conference, november 4-10, 2001, San Diego, California PET scanners designed to image animals the size of rats and mice should possess simultaneously high and uniform spatial resolution and high sensitivity. ATLAS (Advanced Technology Laboratory Animal Scanner), an 11.8 cm diameter aperture, 2 cm axial field-of-view ring-type research scanner seeks these goals by surrounding the animal with eighteen 15 mm deep, LGSO (7 mm) / GSO (8 mm) phoswich detector modules. A Monte Carlo simulation was used to compare the variation of resolution across the field-of-view and the absolute central point source sensitivity (ACS) of ATLAS to similar systems comprised only of LSO arrays of different depths with no depth-of-interaction (DOI) capability. For ATLAS radial spatial resolution deteriorated by 27% from the center to 3 cm off-axis. Scanners comprised of 15 mm deep, 10 mm deep and 7 mm deep LSO crystals deteriorated by 100%, 51%, and 20% respectively, over the same distance. Simulated ACS (absorbed energies > 250 keV) for ATLAS was 2.0% and for the 15 mm, 10 mm deep and 7 mm deep LSO scanners 2.4%, 1.5%, and 0.9%, respectively. Radial resolution loss 3 cm off-axis and ACS measured for the actual ATLAS scanner were similar to the values obtained by simulation (27% resolution loss, 1.8% ACS). The phoswich design thus achieves good resolution uniformity over a 6 cm FOV while preserving sensitivity compared to equivalent non-DOI LSO scanners with a range of crystal depths. Publicado

Proceeding of: Nuclear Science Symposium Conference Record, 2004 IEEE, Rome ,16-22 Oct. 2004 Small animal PET scanners require high spatial resolution (< 1 mm) and good sensitivity. To obtain high resolution images, iterative reconstruction methods, like OSEM, applied to image reconstruction in three-dimensional (3D) positron emission tomography (PET), have superior performance over analytical reconstruction algorithms like FBP. However, the high computational cost of iterative methods remains a serious drawback to their development and clinical routine use. The increase in performance of current computers should make iterative image reconstruction fast enough to attain clinical viability. However, dealing with the large number of probability coefficients for the response of the system in high-resolution PET scanners becomes a difficult task that prevents the algorithms from reaching peak performance. Taking into account all possible axial, in-plane and other symmetries, we have reduced the storage needs what allows us to store the whole response of the system in dynamic memory of ordinary industry standard computers, so that the reconstruction algorithm can achieve near peak performance.

Estimation of the kinetic properties of radiopharmaceuticals from equilibrium data is uncertain. This situation might be improved if the kinetic transport of the compound could be visualized directly. The authors explored this possibility by constructing a physical device, an "H-cell", that by chemical means was made to exhibit three spatially distinct compartments. Transport of a positron-labeled compound across the interfaces and through these compartments was visualized by dynamic positron projection imaging. Results obtained in these initial experiments suggest this technique may yield useful information about tracer kinetics.

Proceding of: 2003 IEEE Nuclear Science Symposium Conference Record, Portland, Oregon, USA, 19-25 October, 2003 We present a preliminary study on the design of a small animal positron emission tomograph with octagonal geometry. The main goal is to evaluate the impact of critical design parameters on the quality of the reconstructed images. Monte Carlo simulations take into account the depth of interaction in individual crystals. The activity sources are simulated as parametric distributions within the field of view and images are reconstructed with iterative algorithms based on the estimation of maximum likelihood and Bayesian regularization. The probability system matrix used by these algorithms is also calculated based on statistical models and Monte Carlo simulation. 2D and 3D techniques have been employed. This work has been partly founded by the Spanish Ministry of Science & Technology, (TIC 2001-0175-C03) and by Red Temática IM3 from Spanish Health Ministry (G03/185). Publicado

Proceeding of: 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference, Toronto, Ont., 08 - 14 Nov. 1998 Detector modules in small ring diameter PET scanners must possess depth-of-interaction (DOI) encoding, increased spatial sampling, high sensitivity and the ability to handle high photon input rates without excessive pulse pileup or random coincidences. We created such a module by optically coupling an entrance array of individual LGSO crystals to an exit array of individual GSO (and other) crystals that was, in turn, optically and directly coupled to a miniature PSPMT. DO1 was determined for each event by delayed charge integration (DCI), a technique that exploits differences in light decay time between GSO and LGSO. Spatial sampling in 3D was increased by introducing a half crystal pitch spatial offset between the entrance and exit arrays in both the X and Y directions. Position detection accuracy in both the LGSO and GSO layers, and the accuracy of DO1 assignment of events to either layer was high. These results suggest that this combination of scintillators and acquisition/processing methods may be particularly useful in the design of high performance, small ring diameter PET scanners for small animal imaging Publicado

Proceeding of: 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference, Toronto, Ont., 08 - 14 Nov. 1998 Equilibrium gated blood pool imaging of the heart is a common diagnostic procedure for visualizing cardiac function in human subjects. Recently, this procedure has been modified to evaluate cardiac function in mice. However, the high heart rates encountered in these animals (often greater than 400 beatdmin) can confound R-wave trigger devices, acquisition systems and image processing software containing default conditions tailored specifically to the lower heart rates of human subjects. In order to determine whether data acquisition and processing components of a commercial or self-generated gated blood pool imaging procedure are performing properly, input of known timing and imaging signals that mimic those generated during high heart rate gated blood pool imaging is required. Here, we describe an inexpensive phantom that is suitable for initial evaluation of an unknown system or for ongoing QC of a previously verified system. Publicado

A pair of stationary, opposed scintillation detectors in time coincidence is being used to create planar projection or tomographic images of small animals injected with positronemitting radiotracers. The detectors are comprised of arrays of individual crystals of bismuth germanate coupled to position-sensitive photomultiplier tubes. The system uses FERA (LeCroy Research Systems) charge-sensitive ADCs and a low cost digital YO board as a E R A bus-to-host bridge. In projection mode, the animal is placed within the 55 mm x 45 mm useful field-of-view of the detectors and images are formed from coincidence lines that fall close to the normals of both detectors. In tomographic mode, the animal is placed on a rotation stage between the detectors and rotated around a vertical axis to acquire all possible lines-of-response. Tomographic images are then reconstructed from those lines falling within a user-specified angle of each detector normal. In mice, the system is capable of high-speed, whole-body dynamic projection imaging, and whole body tomographic imaging of slowly varying tracer distributions. An ECG gating capability is also available for evaluating cardiac function. This system is currently being used to study tracer transport in normal and genetically engineered mice. Publicado

High quality compression on cardiac MR images using wavelet based methods have been compared with standard JPEG. Since the latter is an unrestricted algorithm designed for true-color realistic images, its performance compressing gray-level images can be improved with alternate algorithms specifically designed for this purpose. Here the authors present a method based on wavelet transforms and Huffman encoding; Daubechies and Lemarie-Battle wavelets have been used. Different combinations of parameters and transforms have been compared against JPEG with 100, 85, and 75 quality factor. The results show that wavelet based compression performed better in quality and compression rate; differences among the several wavelet based methods implemented have also been found.

Proceeding of: 2000 IEEE Nuclear Science Symposium Conference Record, Lyon, France, October 15 - 20, 2000 Spatially registered PET and CT images of the same small animal offer at .least three potential advantages .over PET alone. First, the CT images should' alIow accurate, nearly noise-free correction of the PET image data for attenuation. Second, the CT images snould permit more certain identification of structures evident in the PET images and third, the CT images provide a priori anatomical information that may be of use with resolution-improving image reconstruction algorithms that model the PET imaging process. Thus far, howeyer, image registration algorithms effective in human studies have not been characterized in the small animal setting. Accordingly,'we evaluated the ability of the AIR algorithm to accurately register PET F-18 fluoride and F-18 FDG images of the rat skull and brain, respectively, to CT images acquired following each PET imaging session. The AIR algorithm was able to register the bone-to-bone images with a maximum error of less than 1.0 mm. The registration error for the brain-to-brain study, however, was greater (2.4 mm) and required additional steps and. user.intervention to segment the brail1 from the head in both data sets before registration. These preliminary results suggest that the AIR algorithm can accurately combine PET and CT images in small animals when the data sets are nearly homologous, but may require additional segmentation steps with increased mis-registration errors when registering disparate, low contrast soft tissue structures.

This communication reviews the use of undersampling techniques to acquire NMR signals. Undersampling transforms bandpass free induction decay (FID) signals, centered at high frequencies, into lowpass signals or bandpass signals centered at much lower frequencies. Consequently, the analog electronic stages that perform the demodulation can be eliminated, gaining in stability and reducing the phase distortion while maintaining an equivalent or better signal to noise ratio when an adequate sampling rate is chosen. The technique has been tested on a BRUKER BIOSPEC BMT 47/40, and the results show that undersampling could be used to process NMR and MRI signals, extending the range of applications of the ‘digital radio’ techniques to NMR and MRI apparatus. © 2001 Elsevier Science B.V. All rights reserved.

Spatially registered positron emission tomography (PET), computed tomography (CT), and magnetic resonance (MR) images of the same small animal offer potential advantages over PET alone: CT images should allow accurate, nearly noise-free correction of the PET image data for attenuation; the CT or MR images should permit more certain identification of structures evident in the PET images; and CT images provide a priori anatomical information that may be of use with resolution-improving image-reconstruction algorithms that model the PET imaging process. However, image registration algorithms effective in human studies have not been characterized in the small-animal setting. Accordingly, the authors evaluated the ability of the automated image registration (AIR) and mutual information (MI) algorithms to register PET images of the rat skull and brain to CT or MR images of the same animal. External fiducial marks visible in all three modalities were used to estimate residual errors after registration. The AIR algorithm registered PET bone-to-CT bone images with a maximum error of less than 1.0 mm, The registration errors for PET brain-to-CT brain images, however, were greater, and considerable user intervention was required prior to registration. The AIR algorithm either failed or required excessive user intervention to register PET and MR brain images. In contrast, the MI algorithm yielded smaller registration errors in all scenarios with little user intervention. The MI algorithm thus appears to be a more robust method for registering PET, CT, and MR images of the rat head Publicado

In certain nuclear magnetic resonance (NMR) applications in which accessibility to the gantry is limited, performing optimal tuning and matching represents a major problem. Here, we discuss a method of tuning NMR probe circuits and matching their impedances which uses cables with different impedance values. This simple but efficien method may be advantageous compared with much more difficul perfect tuning and matching. Spanish Comision Interministerial de Ciencia y Tecnologıa (CICYT) for funding (BIO97– 0543). Publicado

We assembled a compact detector module comprised of an array of small, individual crystals of lutetium oxyorthosilicate: Ce (LSO) coupled directly to a miniature, metal-can, position-sensitive photomultiplier tube (PSPMT).We exposed this module to sources of 511-keV annihilation radiation and beams of 30- and 140-keV photons and measured spatial linearity; spatial variations in module gain, energy resolution, and event positioning; coincidence timing; the accuracy and sensitivity of identifying the crystal-of-first-interaction at 511 keV; and the effects of intercrystal scatter and LSO background radioactivity. The results suggest that this scintillator/phototube combination should be highly effective in the coincidence mode and can be used, with some limitations, to image relatively low-energy single photon emitters. Photons that are completely absorbed on their first interaction at 511 keV are positioned by the module at the center of a crystal. Intercrystal scatter events, even those that lead to total absorption of the incident photon, are placed by the module in a regular “connect-the-dot” pattern that joins crystal centers. As a result, the accuracy of event positioning can be made to exceed 90%, though at significantly reduced sensitivity, by retaining only events that occur within small regions-of-interest around each crystal center and rejecting events that occur outside these regions in the connect-the-dot pattern. The work was supported in part by a grant from CICYT (Spanish Government). The work of S. Siegel was supported by a grant from the National Research Council. Publicado

In this paper we present the spatial resolution enhancement and noise reduction level achieved with an optimized inductively coupled surface coil specificall designed for our experiments. The technique of designing and implementing customized coils for magnetic resonance imaging of very small structures is described. We have designed a low cost prototype of an inductively coupled circular surface coil, tuned for 1H magnetic resonance imaging at 200 MHz. The coil is mounted on a customized teflo support. The inductive coupling used in this coil improves the signal-to-noise ratio by reducing various loss mechanisms (specially the dielectric losses). Test images have been acquired to determine the evolution of induced articular lesions in a rabbit animal model, as well as brain tumors in rats. The images show high spatial resolution, excellent B1 fiel homogeneity and no ‘‘hot spots’’. Comparing these images with those acquired with conventional coils, one find better spatial resolution and signal-to-noise ratio, as well as larger fiel of view with less intense illumination artifact. The methodology can be used in any application that requires high quality imaging of small structures. Publicado

The Goertzel algorithm is proposed as a method to obtain the first harmonic coefficient of time activity curves from equilibrium gated cardiac studies. The coefficients are used to produce functional images. The algorithm achieves an important reduction in the number of operations and memory accesses needed to compute the coefficients Publicado

Proceedings of: 18th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Amsterdam, 31 Oct. - 03 Nov. 1996. A new family of amplitude-only radiofrequency modulation waveforms for slice selection in Magnetic Resonance Imaging (MRI) is presented. Based on the scaling functions associated to different wavelet families, these new envelope waves provide higher slice selectivity than gaussian or sinc functions. They are also more compact on the time domain, since no truncation is needed, allowing to reduce the time required for the slice selection process. This feature is valuable on multislice-multiecho and fast acquisitions. Their performance has been evaluated both through simulations of the Bloch equations, and by measuring the slice width of real ramp phantoms images. The simulation results show that this amplitude modulation causes a phase behaviour of the resonant protons within the selected volume that is more coherent than with other techniques. This effect can be related to the higher intensity of the images acquired with this slice selection procedure. Publicado

This work describes a systematic evaluation of several autofocus functions used for analytical fluorescent image cytometry studies of counterstained nuclei. Focusing is the first step in the automatic fluorescence in situ hybridization analysis of cells. Thirteen functions have been evaluated using qualitative and quantitative procedures. For the last of these procedures a figure-of-merit (FOM) is defined and proposed. This new FOM takes into account five important features of the focusing function. Our results show that functions based on correlation measures have the best performance for this type of image. Publicado

Proceeding of: 2004 IEEE Nuclear Science Symposium Conference Record, Rome, Italy, 16-22 October 2004 The availability of synthetic realistic data enables 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 γ-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 data processing. This processing includes estimation algorithms for the most relevant event parameters: energy, layerof- 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 reallike 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.