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1.
Opt Lett ; 45(17): 4790-4793, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32870858

RESUMO

Optical beams carrying orbital angular momentum are a very active field of research for their prospective applications, especially at short wavelengths. We consider here such beams produced through high-harmonic generation (HHG) in a rare gas and analyze the characterization of their high-charge vortex structure by an extreme ultraviolet Hartmann wavefront sensor. We show that such HHG beams are generally composed of a set of numerous vortex modes. The sensitivity of the intensity and phase of the HHG beam to the infrared laser aberrations is investigated using a deformable mirror.

2.
Opt Lett ; 43(12): 2780-2783, 2018 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-29905687

RESUMO

We demonstrate for the first time, to the best of our knowledge, the ability of extreme ultraviolet (XUV) Hartmann wavefront sensors to characterize high charge vortex beams produced by high-order harmonic generation up to the order of 25. We also show that phase matched absorption limited high harmonic generation is able to maintain the high charge vortex structure of the XUV beam even in a rather long (1 cm) generation medium.

3.
Mol Imaging Biol ; 19(2): 305-314, 2017 04.
Artigo em Inglês | MEDLINE | ID: mdl-27632424

RESUMO

PURPOSE: Human dosimetry studies play a central role in radioligand development for positron emission tomography (PET). Drawing regions of interest (ROIs) on the PET images is used to measure the dose in each organ. In the study aspects related to ROI delineation methods were evaluated for two radioligands of different biodistribution (intestinal vs urinary). PROCEDURES: PET images were simulated from a human voxel-based phantom. Several ROI delineation methods were tested: antero-posterior projections (AP), 3D sub-samples of the organs (S), and a 3D volume covering the whole-organ (W). Inter- and intra-operator variability ROI drawing was evaluated by using human data. RESULTS: The effective dose estimates using S and W methods were comparable to the true values. AP methods overestimated (49 %) the dose for the radioligand with intestinal biodistribution. Moreover, the AP method showed the highest inter-operator variability: 11 ± 1 %. CONCLUSIONS: The sub-sampled organ method showed the best balance between quantitative accuracy and inter- and intra-operator variability.


Assuntos
Algoritmos , Processamento de Imagem Assistida por Computador , Tomografia por Emissão de Pósitrons , Radiometria , Simulação por Computador , Humanos , Variações Dependentes do Observador , Distribuição Tecidual
4.
Opt Lett ; 40(20): 4775-8, 2015 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-26469617

RESUMO

Harmonic seeded operation of a neon-like titanium plasma-based soft x-ray laser is described. The plasma amplifier is pumped with a variation of the grazing incidence technique involving a fast and localized ionization step. We discuss its effect on gain dynamics by measuring the amplifying factor as a function of the delay between pump pulse and harmonic seed. Two different regimes are pointed out, following the pumping scheme used. For one of them, a delay in the gain generation compared with the pumping laser pulse is observed.

5.
Phys Med Biol ; 60(15): 5925-38, 2015 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-26184983

RESUMO

The aim of this work was to evaluate the influence of anatomical variability between subjects and of the partial volume effect (PVE) on the standardized Specific Uptake Ratio (SUR) in [(123)I]FP-bib SPECT studies. To this end, magnetic resonance (MR) images of 23 subjects with differences in the striatal volume of up to 44% were segmented and used to generate a database of 138 Monte Carlo simulated SPECT studies. Data included normal uptakes and pathological cases. Studies were reconstructed by filtered back projection (FBP) and the ordered-subset expectation-maximization algorithm. Quantification was carried out by applying a reference method based on regions of interest (ROIs) derived from the MR images and ROIs derived from the Automated Anatomical Labelling map. Our results showed that, regardless of anatomical variability, the relationship between calculated and true SUR values for caudate and putamen could be described by a multiple linear model which took into account the spill-over phenomenon caused by PVE (R² ≥ 0.963 for caudate and ≥0.980 for putamen) and also by a simple linear model (R(2) ≥ 0.952 for caudate and ≥0.973 for putamen). Calculated values were standardized by inverting both linear systems. Differences between standardized and true values showed that, although the multiple linear model was the best approach in terms of variability (X² ≥ 11.79 for caudate and ≤7.36 for putamen), standardization based on a simple linear model was also suitable (X² ≥ 12.44 for caudate and ≤12.57 for putamen).


Assuntos
Algoritmos , Compostos Radiofarmacêuticos/farmacocinética , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Interpretação Estatística de Dados , Proteínas da Membrana Plasmática de Transporte de Dopamina/metabolismo , Humanos , Radioisótopos do Iodo/farmacocinética , Método de Monte Carlo , Neostriado/diagnóstico por imagem , Tropanos/farmacocinética
6.
Phys Med Biol ; 60(1): 151-62, 2015 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-25479341

RESUMO

In this work a comparison between experimental and simulated data using GATE and PeneloPET Monte Carlo simulation packages is presented. All simulated setups, as well as the experimental measurements, followed exactly the guidelines of the NEMA NU 4-2008 standards using the microPET R4 scanner. The comparison was focused on spatial resolution, sensitivity, scatter fraction and counting rates performance. Both GATE and PeneloPET showed reasonable agreement for the spatial resolution when compared to experimental measurements, although they lead to slight underestimations for the points close to the edge. High accuracy was obtained between experiments and simulations of the system's sensitivity and scatter fraction for an energy window of 350-650 keV, as well as for the counting rate simulations. The latter was the most complicated test to perform since each code demands different specifications for the characterization of the system's dead time. Although simulated and experimental results were in excellent agreement for both simulation codes, PeneloPET demanded more information about the behavior of the real data acquisition system. To our knowledge, this constitutes the first validation of these Monte Carlo codes for the full NEMA NU 4-2008 standards for small animal PET imaging systems.


Assuntos
Simulação por Computador , Processamento de Imagem Assistida por Computador/métodos , Método de Monte Carlo , Imagens de Fantasmas , Tomografia por Emissão de Pósitrons/instrumentação , Tomografia por Emissão de Pósitrons/normas , Compostos Radiofarmacêuticos , Animais , Camundongos , Software
7.
Phys Med Biol ; 59(24): 7573-85, 2014 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-25415206

RESUMO

It is well-known that in pinhole SPECT (single-photon-emission computed tomography), iterative reconstruction methods including accurate estimations of the system response matrix can lead to submillimeter spatial resolution. There are two different methods for obtaining the system response matrix: those that model the system analytically using an approach including an experimental characterization of the detector response, and those that make use of Monte Carlo simulations. Methods based on analytical approaches are faster and handle the statistical noise better than those based on Monte Carlo simulations, but they require tedious experimental measurements of the detector response. One suggested approach for avoiding an experimental characterization, circumventing the problem of statistical noise introduced by Monte Carlo simulations, is to perform an analytical computation of the system response matrix combined with a Monte Carlo characterization of the detector response. Our findings showed that this approach can achieve high spatial resolution similar to that obtained when the system response matrix computation includes an experimental characterization. Furthermore, we have shown that using simulated detector responses has the advantage of yielding a precise estimate of the shift between the point of entry of the photon beam into the detector and the point of interaction inside the detector. Considering this, it was possible to slightly improve the spatial resolution in the edge of the field of view.


Assuntos
Processamento de Imagem Assistida por Computador/métodos , Modelos Teóricos , Método de Monte Carlo , Imagens de Fantasmas , Tomografia Computadorizada de Emissão de Fóton Único/instrumentação , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Simulação por Computador , Humanos , Compostos de Organotecnécio/metabolismo , Fótons , Reprodutibilidade dos Testes
8.
Phys Med Biol ; 59(16): 4567-82, 2014 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-25069105

RESUMO

SPECT studies with (123)I-ioflupane facilitate the diagnosis of Parkinson's disease (PD). The effect on quantification of image degradations has been extensively evaluated in human studies but their impact on studies of experimental PD models is still unclear. The aim of this work was to assess the effect of compensating for the degrading phenomena on the quantification of small animal SPECT studies using (123)I-ioflupane. This assessment enabled us to evaluate the feasibility of quantitatively detecting small pathological changes using different reconstruction methods and levels of compensation for the image degrading phenomena. Monte Carlo simulated studies of a rat phantom were reconstructed and quantified. Compensations for point spread function (PSF), scattering, attenuation and partial volume effect were progressively included in the quantification protocol. A linear relationship was found between calculated and simulated specific uptake ratio (SUR) in all cases. In order to significantly distinguish disease stages, noise-reduction during the reconstruction process was the most relevant factor, followed by PSF compensation. The smallest detectable SUR interval was determined by biological variability rather than by image degradations or coregistration errors. The quantification methods that gave the best results allowed us to distinguish PD stages with SUR values that are as close as 0.5 using groups of six rats to represent each stage.


Assuntos
Encéfalo/diagnóstico por imagem , Processamento de Imagem Assistida por Computador/métodos , Método de Monte Carlo , Nortropanos , Tomografia Computadorizada de Emissão de Fóton Único , Algoritmos , Animais , Humanos , Ratos
9.
Opt Express ; 20(23): 25391-9, 2012 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-23187356

RESUMO

Experimental results of a two-stage Ni-like Ag soft X-ray laser operated in a seed-amplifier configuration are presented. Both targets were pumped applying the double-pulse grazing incidence technique with intrinsic travelling wave excitation. The injection of the seed X-ray laser into the amplifier target was realized by a spherical mirror. The results show amplification of the seed X-ray laser and allow for a direct measurement of the gain lifetime. The experimental configuration is suitable for providing valuable input for computational simulations.

10.
Phys Rev E Stat Nonlin Soft Matter Phys ; 86(2 Pt 2): 026406, 2012 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-23005868

RESUMO

The accurate characterization of thermal electron transport and the determination of heating by suprathermal electrons in laser driven solid targets are both issues of great importance to the current experiments being performed at the National Ignition Facility, which aims to achieve thermonuclear fusion ignition using lasers. Ionization, induced by electronic heat conduction, can cause the opacity of a material to drop significantly once bound-free photoionization is no longer energetically possible. We show that this drop in opacity enables measurements of the transmission of extreme ultraviolet (EUV) laser pulses at 13.9 nm to act as a signature of the heating of thin (50 nm) iron layers with a 50-nm thick parylene-N (CH) overlay irradiated by 35-fs pulses at irradiance 3×10(16) Wcm(-2). Comparing EUV transmission measurements at different times after irradiation to fluid code simulations shows that the target is instantaneously heated by hot electrons (with approximately 10% of the laser energy), followed by thermal conduction with a flux limiter of ≈0.05.

11.
Rev. esp. anestesiol. reanim ; 59(7): 390-393, ago.-sept. 2012.
Artigo em Espanhol | IBECS | ID: ibc-102482

RESUMO

La equinococosis es una infección endémica en los países cálidos. La afectación cardíaca es rara, pero grave. El riesgo de shock anafiláctico durante la cirugía, precisa de un rápido diagnóstico intraoperatorio y de un tratamiento inmediato. Presentamos el caso de un varón de 35 años, al que se le detectó un quiste hidatídico cardíaco, tributario de cirugía. Previo tratamiento con albendazol oral durante un mes y pauta de anti-H1, anti-H2 y corticoides las 24h previas, se procedió a extirpar el quiste con circulación extracorpórea. Intraoperatoriamente se administraron además, bolus de hidrocortisona y dexclorfeniramina y se protegió el campo quirúrgico con gasas empapadas en suero salino hipertónico. El paciente precisó perfusión de noradrenalina para mantener la estabilidad hemodinámica. Evolucionó sin más complicaciones y fue dado de alta a los 14 días(AU)


Echinococcosis is an endemic infection in hot countries. Cardiac involvement is rare, but serious. The risk of anaphylactic shock during surgery requires a rapid intra-operative diagnosis and immediate treatment. We present the case of a 35 year-old male in whom a cardiac hydatid cyst was detected that required surgery. He was given preliminary treatment with oral albendazole for one month and prescribed anti-H1, anti-H2 and corticosteroids prior to the removal of the cyst using bypass surgery. During the operation he was also given a bolus of hydrocortisone and dexchlorpheniramine and the surgical area was protected by gauzes soaked in hypertonic saline. The patient required an infusion of noradrenaline to maintain haemodynamic stability. He progressed with no more complications, and was discharged at 14 days(AU)


Assuntos
Humanos , Masculino , Adulto , Equinococose/tratamento farmacológico , Anestesia , Albendazol/uso terapêutico , Corticosteroides/uso terapêutico , Circulação Extracorpórea/métodos , Hidrocortisona/uso terapêutico , Cirurgia Torácica/métodos , Cirurgia Torácica/tendências , Anafilaxia/tratamento farmacológico , Circulação Extracorpórea/tendências , Circulação Extracorpórea , Hemodinâmica , Hemodinâmica/fisiologia
12.
Rev Esp Anestesiol Reanim ; 59(7): 390-3, 2012.
Artigo em Espanhol | MEDLINE | ID: mdl-22789614

RESUMO

Echinococcosis is an endemic infection in hot countries. Cardiac involvement is rare, but serious. The risk of anaphylactic shock during surgery requires a rapid intra-operative diagnosis and immediate treatment. We present the case of a 35 year-old male in whom a cardiac hydatid cyst was detected that required surgery. He was given preliminary treatment with oral albendazole for one month and prescribed anti-H1, anti-H2 and corticosteroids prior to the removal of the cyst using bypass surgery. During the operation he was also given a bolus of hydrocortisone and dexchlorpheniramine and the surgical area was protected by gauzes soaked in hypertonic saline. The patient required an infusion of noradrenaline to maintain haemodynamic stability. He progressed with no more complications, and was discharged at 14 days.


Assuntos
Anestesia Geral/métodos , Cardiomiopatias/cirurgia , Equinococose/cirurgia , Cuidados Pré-Operatórios/métodos , Corticosteroides/uso terapêutico , Adulto , Albendazol/uso terapêutico , Anafilaxia/prevenção & controle , Anti-Helmínticos/uso terapêutico , Antibioticoprofilaxia , Atracúrio , Cardiomiopatias/tratamento farmacológico , Cardiomiopatias/parasitologia , Clorfeniramina/uso terapêutico , Equinococose/tratamento farmacológico , Doenças Endêmicas , Fentanila , Antagonistas dos Receptores Histamínicos/uso terapêutico , Humanos , Hidrocortisona/uso terapêutico , Complicações Intraoperatórias/prevenção & controle , Masculino , Norepinefrina/uso terapêutico , Medicação Pré-Anestésica , Propofol , Ranitidina/uso terapêutico
13.
Opt Express ; 20(9): 10128-37, 2012 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-22535105

RESUMO

The influence on Nickel-like Molybdenum soft-x-ray laser performance and stability of a low energy laser prepulse arriving prior to the main laser pumping pulses is experimentally investigated. A promising regime for 10 Hz operation has been observed. A four times increase in soft-x-ray laser operation time with a same target surface is demonstrated. This soft-x-ray laser operation mode corresponds to an optimum delay between the prepulse and the main pulses and to a prepulse energy greater than 20 mJ. We also show that this regime is not associated with a weaker degradation of the target or any reduced ablation rate. Therefore the role of preplasma density gradient in this effect is discussed.


Assuntos
Lasers , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Raios X
14.
Rev. esp. med. nucl. (Ed. impr.) ; 30(5): 286-291, sept.-oct. 2011.
Artigo em Espanhol | IBECS | ID: ibc-90612

RESUMO

Objetivo. Desarrollar un sistema SPECT de animal pequeño utilizando una cámara portátil de bajo coste equipada con colimador de tipo pinhole (con agujero de alfiler), un cristal de centelleo continuo y un tubo fotomultiplicador sensible a la posición. Material y métodos. Se incorporó la gammacámara a un sistema de radio variable que nos permitió optimizar la resolución y la sensibilidad ajustando el radio de rotación al tamaño del objeto. A fin de investigar la capacidad del sistema SPECT para obtener imágenes de animal pequeño se estudió la dependencia de la resolución y los parámetros de calibración con el radio, y se realizaron adquisiciones de maniquí de tamaño pequeño y de ratones. Resultados. Se obtuvieron valores de resolución de 1mm para un radio de 21,4mm hasta 1,4mm para un radio de 37,2mm, justificando el interés en un sistema SPECT de radio variable. Conclusiones. Los resultados de calidad de imagen de los maniquís y animales fueron satisfactorios, confirmando la utilidad del sistema SPECT para realizar estudios de animal pequeño(AU)


Objective. To develop a small-animal SPECT system using a low cost commercial portable gamma camera equipped with a pinhole collimator, a continuous scintillation crystal and a position-sensitive photomultiplier tube. Material and methods. The gamma camera was attached to a variable radius system, which enabled us to optimize sensitivity and resolution by adjusting the radius of rotation to the size of the object. To investigate the capability of the SPECT system for small animal imaging, the dependence of resolution and calibration parameters on radius was assessed and acquisitions of small phantoms and mice were carried out. Results. Resolution values, ranging from 1.0mm for a radius of 21.4mm and 1.4mm for a radius of 37.2mm were obtained, thereby justifying the interest of a variable radius SPECT system. Conclusions. The image quality of phantoms and animals were satisfactory, thus confirming the usefulness of the system for small animal SPECT imaging(AU)


Assuntos
Animais , Masculino , Feminino , Camundongos , Tomografia Computadorizada de Emissão de Fóton Único/instrumentação , Tomografia Computadorizada de Emissão de Fóton Único , Alocação de Custos/economia , Controle de Custos/economia , Custos e Análise de Custo/economia , Elementos Radioativos , Tomografia Computadorizada de Emissão de Fóton Único/tendências , Medicina Nuclear/métodos
15.
Rev Esp Med Nucl ; 30(5): 286-91, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-21640439

RESUMO

OBJECTIVE: To develop a small-animal SPECT system using a low cost commercial portable gamma camera equipped with a pinhole collimator, a continuous scintillation crystal and a position-sensitive photomultiplier tube. MATERIAL AND METHODS: The gamma camera was attached to a variable radius system, which enabled us to optimize sensitivity and resolution by adjusting the radius of rotation to the size of the object. To investigate the capability of the SPECT system for small animal imaging, the dependence of resolution and calibration parameters on radius was assessed and acquisitions of small phantoms and mice were carried out. RESULTS: Resolution values, ranging from 1.0mm for a radius of 21.4mm and 1.4mm for a radius of 37.2mm were obtained, thereby justifying the interest of a variable radius SPECT system. CONCLUSIONS: The image quality of phantoms and animals were satisfactory, thus confirming the usefulness of the system for small animal SPECT imaging.


Assuntos
Câmaras gama , Tomografia Computadorizada de Emissão de Fóton Único/instrumentação , Animais , Encéfalo/diagnóstico por imagem , Calibragem , Desenho de Equipamento , Processamento de Imagem Assistida por Computador , Pulmão/diagnóstico por imagem , Camundongos , Imagens de Fantasmas , Compostos Radiofarmacêuticos , Agregado de Albumina Marcado com Tecnécio Tc 99m , Tecnécio Tc 99m Exametazima , Tomografia Computadorizada de Emissão de Fóton Único/veterinária
16.
Opt Lett ; 35(9): 1326-8, 2010 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-20436557

RESUMO

We present what we believe to be the first measurement of the spectral properties of a soft x-ray laser seeded by a high-order harmonic beam. Using an interferometric method, the spectral profile of a seeded Ni-like krypton soft x-ray laser (32.8 nm) generated by optical field ionization has been experimentally determined, and the shortest possible pulse duration has been deduced. The source exhibits a Voigt spectral profile with an FWHM of 3.1+/-0.3 mA, leading to a Fourier-transform pulse duration of 4.7 ps. This value is comparable with the upper limit of the soft x-ray pulse duration determined by experimentally investigating the gain dynamics, from which we conclude that the source has reached the Fourier limit. The measured bandwidth is in good agreement with the predictions of a radiative transfer code, including gain line narrowing and saturation rebroadening.

17.
Neuroimage ; 50(4): 1511-8, 2010 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-20083205

RESUMO

Reported values of D(2) receptor occupancy (RO) achieved by antipsychotic drugs tend to be lower when measured with (123)I-IBZM SPECT than with (11)C-Raclopride PET. Image degrading factors such as attenuation, distance-dependent collimator response and scatter could account for this difference. While attenuation correction is routinely applied to SPECT images, the other degradations are not usually accounted for. The aim of this work was to assess the impact of scatter correction on D(2) RO quantification with (123)I-IBZM SPECT, and to compare the results of both corrected and un-corrected SPECT values with (11)C-Raclopride PET measurements. Phantom experiments as well as within-subject human data from a previous study were used for this purpose. SPECT images were reconstructed using filtered back-projection including attenuation correction (FBP(A)), ordered subsets expectation maximization including attenuation and point spread function corrections (OSEM(A+PSF)) and ordered subsets expectation maximization including attenuation, point spread function and scatter corrections (OSEM(A+PSF+SCT)). PET images were reconstructed using the FBP algorithm and corrected for attenuation, scatter, random coincidences and dead time. Quantification of receptor availability was performed using the tissue ratio at pseudoequilibrium for SPECT, and the simplified reference tissue model (SRTM) for PET. Analysis was performed using both occipital cortex (occ) and cerebellum (cer) as reference regions for both modalities. When images were reconstructed using FBP(A), SPECT D(2) RO values were significantly lower as compared with PET leading to a D(2) RO difference of -20% (CI(95%): -13, -27%) (occ) and -23% (CI(95%): -14, -31%) (cer). When images were reconstructed using OSEM(A+PSF), SPECT D(2) RO values were also lower as compared with PET leading to a D(2) RO difference of -21% (CI(95%): -14, -27%) (occ) and -24% (CI(95%): -18, -30%) (cer). When images were reconstructed using OSEM(A+PSF+SCT), the D(2) RO bias was reduced to -6% (CI(95%): 0, -13%) (occ) and -11% (CI(95%): -4, -18%) (cer). These data suggest that the scatter correction plays a major role in explaining the differences between D(2) RO measurements using (123)I-IBZM SPECT and (11)C-Raclopride PET.


Assuntos
Benzamidas , Tomografia por Emissão de Pósitrons/métodos , Pirrolidinas , Racloprida , Receptores de Dopamina D2/metabolismo , Processamento de Sinais Assistido por Computador , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Adulto , Algoritmos , Antipsicóticos/farmacologia , Encéfalo/diagnóstico por imagem , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Mapeamento Encefálico/instrumentação , Mapeamento Encefálico/métodos , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética , Masculino , Modelos Neurológicos , Imagens de Fantasmas , Tomografia por Emissão de Pósitrons/instrumentação , Espalhamento de Radiação , Tomografia Computadorizada de Emissão de Fóton Único/instrumentação
18.
Med Phys ; 36(11): 4903-10, 2009 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-19994499

RESUMO

PURPOSE: Image registration is important in functional image analysis. In neurotransmission single photon emission tomography (nSPECT), specific uptake sites can be accurately localized by superimposing the SPECT study onto a high-resolution structural image such as a magnetic resonance (MR) of the subject. Mutual-information (MI)-based algorithms are usually employed for this purpose. Nevertheless, nSPECT/MR registration using MI is often limited by the low count rates present in nSPECT. Several works have proposed extensions of the MI measures to include gradient information (GI) from the images but their performance has not been evaluated in SPECT studies. METHODS: In this work, the accuracy of the MI including gradient information (MIG) was compared with the standard MI using data from healthy volunteers and data simulating a specific uptake reduction using three different radioligands: 123I-IBZM, 123I-ADAM, 123I-R91150. RESULTS: The results showed that MIG-based registration yielded better accuracy than MI. The MIG-based similarity measures were less sensitive to sparse sampling and diminished computational time without a substantial decrease in registration accuracy. CONCLUSIONS: Accuracy of nSPECT/MR registration is improved when gradient information is included in the MI-based algorithm, which makes MIG-based registration potentially useful for clinical applications.


Assuntos
Processamento de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Algoritmos , Benzamidas , Encéfalo/diagnóstico por imagem , Simulação por Computador , Humanos , Teoria da Informação , Radioisótopos do Iodo , Piperidinas , Pirrolidinas , Estudos Retrospectivos , Fatores de Tempo
19.
Opt Lett ; 34(17): 2640-2, 2009 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-19724517

RESUMO

Plasma-based seeded soft x-ray lasers have the potential to generate a high-energy, highly coherent, short pulse beam. Owing to their high density, plasmas created by interaction of an intense laser with a solid target should store the highest amount of energy among all plasma amplifiers. However, to date output energy from seeded solid amplifiers remains as low as 60 nJ. We demonstrated that careful tailoring of the plasma shape is crucial for extracting energy stored in the plasma. With 1-mm-wide plasma, energy as high as 20 microJ in sub-ps pulses is achievable. With such tailored plasma, gain and pumping efficiency have been increased by nearly a factor of 10 as compared to the narrower plasma amplifiers studied here.

20.
Neuroimage ; 39(3): 1121-8, 2008 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-18042402

RESUMO

Statistical parametric mapping (SPM) has become the standard technique to statistically evaluate differences between functional images. The aim of this paper was to assess the effect of anatomical variability of skull, the reconstruction algorithm and the scattering of photons in the brain on the output of an SPM analysis of brain PET studies. To this end, Monte Carlo simulation was used to generate suitable PET sinograms and bootstrap techniques were employed to increase the reliability of the conclusions. Activity distribution maps were obtained by segmenting thirty nine T1-weighted magnetic resonance images. Foci were placed on the posterior cingulate cortex (PCC) and the superior temporal cortex (STC) and activation factors ranging between -25% and +25% were simulated. Preprocessing of the reconstructed images and statistical analysis were performed using SPM2. Our findings show that intersubject anatomical differences can cause the minimum sample size to increase between 10 and 42% for posterior cingulate Cortex and between 40 and 80% for superior temporal cortex. Ideal scatter correction (ISC) allowed us to diminish the sample size up to 18% and fully 3D reconstruction reduced the minimum sample size between 8 and 33%. Detection sensitivity was higher for hypo-activation than for hyper-activation situations and higher for superior temporal cortex than for posterior cingulate cortex.


Assuntos
Algoritmos , Mapeamento Encefálico/métodos , Encéfalo/anatomia & histologia , Encéfalo/diagnóstico por imagem , Processamento de Imagem Assistida por Computador/estatística & dados numéricos , Encéfalo/fisiologia , Córtex Cerebral/anatomia & histologia , Córtex Cerebral/fisiologia , Humanos , Método de Monte Carlo , Fótons , Tomografia por Emissão de Pósitrons , Espalhamento de Radiação
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