We investigated the temporal dynamics and changes in connectivity in the mental rotation network through the application of spatio-temporal support vector machines (SVMs). The spatio-temporal SVM [Mourao-Miranda, J., Friston, K. J., et al. (2007). Dynamic discrimination analysis: A spatial-temporal SVM. Neuroimage, 36, 88-99] is a pattern recognition approach that is suitable for investigating dynamic changes in the brain network during a complex mental task. It does not require a model describing each component of the task and the precise shape of the BOLD impulse response. By defining a time window including a cognitive event, one can use spatio-temporal fMRI observations from two cognitive states to train the SVM. During the training, the SVM finds the discriminating pattern between the two states and produces a discriminating weight vector encompassing both voxels and time (i.e., spatio-temporal maps). We showed that by applying spatio-temporal SVM to an event-related mental rotation experiment, it is possible to discriminate between different degrees of angular disparity (0 degrees vs. 20 degrees, 0 degrees vs. 60 degrees, and 0 degrees vs. 100 degrees), and the discrimination accuracy is correlated with the difference in angular disparity between the conditions. For the comparison with highest accuracy (08 vs. 1008)...
As árvores desempenham papel fundamental na qualidade ambiental das áreas urbanas. Como a floresta urbana é alvo constante de ações inadequadas de manejo, tais como podas inapropriadas, técnicas que visam avaliar a qualidade dos indivíduos e o risco de queda de árvores são fundamentais para a diminuição de possíveis danos causados aos equipamentos urbanos além de risco aos habitantes das cidades. Os métodos de avaliação visual de árvores desenvolvidos para a identificação de problemas biomecânicos e fitossanitários possibilitaram que avaliações de risco de queda fossem conduzidas. Nesses métodos, inspeções detalhadas a respeito da extensão das lesões presentes no colo e tronco, que podem comprometer sua estabilidade, são recomendadas para os indivíduos. Entre as técnicas utilizadas para o reconhecimento de lesões internas, a tomografia destaca-se por fornecer informações a respeito de toda seção avaliada com apenas uma medição e por gerar uma imagem que permite identificar o posicionamento e a extensão das áreas lesionadas. Por ser um método relativamente novo, são necessários estudos que visem identificar a resposta à tomografia em diferentes espécies, possibilitando desta forma a identificação precisa das áreas lesionadas. O trabalho realizado teve por objetivo testar a confiabilidade das informações geradas pela tomografia de impulso e identificar padrões de resposta em árvores de tipuana (Tipuana tipu (Benth.) O. Kuntze). Trinta e nove indivíduos que apresentaram sinais de injúria...
Há diversas técnicas que utilizam a passagem de ondas através da madeira para obtenção de informações. Dentre elas destaca-se a tomografia de árvores que reconstrói seções transversais de tronco e galhos. A tomografia de impulso, por sua vez, se baseia na cronometragem da viajem de ondas mecânicas sonoras entre sensores anexados em uma seção transversal da árvore, para cálculo da velocidade da onda e construção da imagem tomográfica. Sabe-se que a velocidade de passagem das ondas mecânicas é determinada pelas propriedades físico-mecânicas da madeira. Em especial: o módulo de elasticidade, a densidade e a umidade. Até o momento, há diversos estudos sobre a correlação entre a velocidade de onda (principalmente ultrassom) e o módulo de elasticidade. Os estudos apresentados a seguir se destacam por avaliar a correlação entre a velocidade de onda mecânica, obtida por tomografia de impulso, e a densidade da madeira, com vistas em utilizá-la como ferramenta na estimativa da densidade. Os diversos métodos consagrados para a determinação da densidade se caracterizam por utilizar amostras de madeira, que em muitos casos são de difícil obtenção. Além de serem executados procedimentos laboratoriais que podem levam até semanas. Dessa forma...
Este trabalho trata da avaliação dos padrões de resposta e da eficácia do método da tomografia de impulso na identificação de lesões e ocos no lenho de árvores de espécies madeireiras da região Amazônica, através do estudo de indivíduos da espécie Manilkara huberi Ducke (Chevalier) (família Sapotaceae). Lesões e ocos resultam do ataque de insetos e fungos e sua ocorrência pode ser favorecida por injúrias como fogo, quebra de galhos e de características do sítio. A colheita de árvores com grandes lesões ou ocos resulta em grande geração de resíduos no campo e na indústria, com impactos ambientais e econômicos negativos. Os métodos tradicionais de verificação de lesões e ocos para seleção de espécies tropicais são muito subjetivos e pouco eficientes, baseados principalmente na experiência dos mateiros e operadores de motosserra. O estudo foi realizado numa área de 3 ha no município de Paragominas, PA. Foram avaliadas 29 árvores de maçaranduba com DAP entre 50 e 130 cm, separadas em 4 grupos, em função do DAP e da ocorrência de oco. A análise da árvore em pé se deu através do tomógrafo de impulso, o qual gerou um gráfico de velocidade e uma imagem da qualidade do lenho. Foram coletadas amostras de solo próximas a cada indivíduo e realizadas análises químicas e físicas para análise da influência do solo na ocorrência de oco. As árvores foram cubadas e feitas estimativas de volume de madeira total (volume da árvore)...
A aplicação de métodos não destrutivos (MND) invasivos - extração de amostras do lenho do tronco das árvores com sondas metálicas - e não invasivos análise do lenho diretamente no tronco - permite a avaliação da qualidade do lenho, dos defeitos internos e sua aplicação como madeira sólida. No presente trabalho são aplicados os MND invasivo (densitometria de raios X) e não invasivo (tomógrafo de impulso) na análise do lenho do tronco de 18 árvores de Pinus caribaea var. hondurensis e 18 de Tectona grandis, com 18 e 52 anos, respectivamente. Os resultados permitem concluir que a (i) estrutura anatômica macroscópica do lenho e dos anéis de crescimento descrita é característica das coníferas (Pinus) e das folhosas (Tectona) e similar à apresentada na literatura; (ii) as imagens tomográficas da seção transversal do lenho indicam um bom estado de sanidade (Pinus) e regiões afetadas do lenho (Tectona); a velocidade de onda é maior na região interna em relação à externa (Pinus) e maior em um dos raios, decrescendo em direção à medula e do raio oposto (Tectona) do lenho, e permite agrupar as árvores em 4 (Pinus) e 6 (Tectona) classes; observa-se a correlação do diâmetro do tronco com o tempo médio da velocidade de onda; (iii) os perfis diametrais de densidade aparente e básica do lenho indicam aumento da medula para a casca e estabilização no lenho externo; os perfis radiais de densidade aparente permitem a precisa demarcação dos anéis de crescimento anuais; os valores médios de densidade agrupam as árvores em 3-2 (Pinus) e 6-5 (Tectona) classes não se observando correlação com o diâmetro do tronco; (iv) os perfis diametrais de teor de umidade do lenho indicam uma diminuição da medula para a casca e estabilização no lenho externo; permitem agrupar as árvores em 3 (Pinus) e 5 (Tectona) classes e não se correlacionam com o diâmetro do tronco; (v) o coeficiente de correlação de Pearson indicou valores negativos e não significativos entre a velocidade de onda e a densidade aparente e básica do lenho (Pinus) e entre a velocidade de onda e a densidade básica do lenho (Tectona); positiva e não significativa para o teor de umidade (Pinus) e positiva e não significativa para o teor de umidade e a densidade aparente (Tectona); negativa entre o teor de umidade e a densidade aparente e básica do lenho; (vi) a velocidade média de onda no lenho é menor e com maior variação das velocidades médias mínima e máxima em Tectona...
Jogo patológico (JP) pode ser definido pela persistência e recorrência do comportamento de apostar em jogos de azar, apesar de prejuízos em diversas áreas da vida decorrentes dessa atividade. O JP é considerado um transtorno do controle de impulso e um modelo de dependência comportamental. Diferentes estudos têm comprovado o envolvimento de vias dopaminérgicas em dependências de substâncias e em jogadores patológicos. O transportador de doamina (DAT) é uma proteína présináptica de neurônios dopaminérgicos nigroestriatais, responsável pela recaptação da dopamina (DA) da fenda sináptica, e tem sido relatada alterações em sua densidade em dependentes de substâncias. O objetivo deste trabalho foi investigar em pacientes com jogo patológico, a densidade de DAT no estriado, através de imagens do exame de SPECT com TRODAT-1- 99mTc verificar por meio de estudo de correlação a associação entre comportamento de jogo (freqüência, tempo, dinheiro, gastos com jogo e fissura/craving) e a densidade DAT em jogadores patológicos. Foram selecionados 15 jogadores e 15 controles normais pareados para gênero, idade e escolaridade. Para inclusão ou exclusão de sujeitos foram utilizados instrumentos de verificação e principais Transtornos Psiquiátricos do Eixo 1 do DSM IV e escalas para depressão e ansiedade; para jogadores patológicos os instrumentos utilizados foram escalas para avaliação do padrão de jogo recente...
The impulse response function of a radioligand is the most fundamental way to describe its pharmacokinetics and to assess its tissue uptake and retention pattern. This study investigates the impulse response function of [11C](+)McN5652, a radioligand used for positron emission tomography (PET) imaging of the serotonin transporter (SERT) in the brain. Dynamic PET studies were performed in eight healthy volunteers injected with [11C](+)McN5652 and subsequently with its pharmacologically inactive enantiomer [11C](−)McN5652. The impulse response function was calculated by deconvolution analysis of regional time-activity curves, and its peak value (fmax), its retention value at 75 minutes (fT), and its normalized retention (frel = fr/fmax) were obtained. Alternatively, compartmental models were applied to calculate the apparent total distribution volume (DVT) and its specific binding component (DVS). Both the noncompartmental (fT, frel) and the compartmental parameters (DV) were investigated with and without correction for nonspecific binding by simple subtraction of the corresponding value obtained with [11C](−)McN5652. The impulse response function obtained by deconvolution analysis demonstrated high tracer extraction followed by a slow decline in the form of a monoexponential function. Statistical analysis revealed that the best compartmental model in terms of analysis of variance F and condition number of the parameter variance-covariance matrix was the one that was based on a single tissue compartment with parameters k1and k2 and that also included the parameter of regional cerebral blood volume (BV). The parameter frel demonstrated low between-subject variance (coefficient of variation [CV] = 19%)...
A three-compartment model is proposed for analyzing magnetic resonance renography (MRR) and computed tomography renography (CTR) data to derive clinically useful parameters such as glomerular filtration rate (GFR) and renal plasma flow (RPF). The model fits the convolution of the measured input and the predefined impulse retention functions to the measured tissue curves. A MRR study of 10 patients showed that relative root mean square errors by the model were significantly lower than errors for a previously reported three-compartmental model (11.6% ± 4.9 vs 15.5% ± 4.1; P < 0.001). GFR estimates correlated well with reference values by 99mTc-DTPA scintigraphy (correlation coefficient r = 0.82), and for RPF, r = 0.80. Parameter-sensitivity analysis and Monte Carlo simulation indicated that model parameters could be reliably identified. When the model was applied to CTR in five pigs, expected increases in RPF and GFR due to acetylcholine were detected with greater consistency than with the previous model. These results support the reliability and validity of the new model in computing GFR, RPF, and renal mean transit times from MR and CT data.
Comprehensive characterization of wideband ultrasonic transducers and specifically optoacoustic detectors is achieved through the analysis of their frequency response as a function of the incident angle. The tests are performed under well-defined, repeatable operating conditions. Backillumination of a blackened, acoustically matched planar surface with a short laser pulse creates an acoustic impulse which is used as a wideband ultrasonic source. Upon illumination with a short laser pulse, the bandwidth of our source shows a −6 dB point of 12 MHz and a low-frequency roll-off around 300 kHz. Using proprietary software, we examine thoroughly the planarity of the emitted wave front within a specified amplitude cutoff and phase incoherence. Analysis of the angular dependence of the frequency response yields invaluable directivity information about the detector under study: a necessary component toward accurate optoacoustic image reconstruction and quantitative tomography. The laser ultrasonic source we developed is the main feature of our directivity measurement setup. Due to its simplicity, it can easily be adapted to various calibration devices. This paper focuses on the development and characterization of the flatness and the bandwidth of our wideband ultrasonic source.
The docking of synaptic vesicles at active zones on the presynaptic plasma membrane of axon terminals is essential for their fusion with the membrane and exocytosis of their neurotransmitter to mediate synaptic impulse transmission. Dense networks of macromolecules, called active zone material, (AZM) are attached to the presynaptic membrane next to docked vesicles. Electron tomography has shown that some AZM macromolecules are connected to docked vesicles, leading to the suggestion that AZM is somehow involved in the docking process. We used electron tomography on the simply arranged active zones at frog neuromuscular junctions to characterize the connections of AZM to docked synaptic vesicles and to search for the establishment of such connections during vesicle docking. We show that each docked vesicle is connected to 10–15 AZM macromolecules, which fall into four classes based on several criteria including their position relative to the presynaptic membrane. In activated axon terminals fixed during replacement of docked vesicles by previously undocked vesicles, undocked vesicles near vacated docking sites on the presynaptic membrane have connections to the same classes of AZM macromolecules that are connected to docked vesicles in resting terminals. The number of classes and the total number of macromolecules to which the undocked vesicles are connected are inversely proportional to the vesicles’ distance from the presynaptic membrane. We conclude that vesicle movement toward and maintenance at docking sites on the presynaptic membrane are directed by an orderly succession of stable interactions between the vesicles and distinct classes of AZM macromolecules positioned at different distances from the membrane. Establishing the number...
The mechanical properties of skin are important tissue parameters that are useful for understanding skin patho-physiology, which can aid disease diagnosis and treatment. This paper presents an innovative method that employs phase-sensitive spectral-domain optical coherence tomography (PhS-OCT) to characterize the biomechanical properties of skin by measuring surface waves induced by short impulses from a home-made shaker. Experiments are carried out on single and double-layer agar–agar phantoms, of different concentrations and thickness, and on in vivo human skin, at the forearm and the palm. For each experiment, the surface wave phase-velocity dispersion curves were calculated, from which the elasticity of each layer of the sample was determined. It is demonstrated that the experimental results agree well with previous work. This study provides a novel combination of PhS-OCT technology with a simple and an inexpensive mechanical impulse surface wave stimulation that can be used to non-invasively evaluate the mechanical properties of skin in vivo, and may offer potential use in clinical situations.
Iterative image reconstruction algorithms for optoacoustic tomography (OAT), also known as photoacoustic tomography, have the ability to improve image quality over analytic algorithms due to their ability to incorporate accurate models of the imaging physics, instrument response, and measurement noise. However, to date, there have been few reported attempts to employ advanced iterative image reconstruction algorithms for improving image quality in three-dimensional (3D) OAT. In this work, we implement and investigate two iterative image reconstruction methods for use with a 3D OAT small animal imager: namely, a penalized least-squares (PLS) method employing a quadratic smoothness penalty and a PLS method employing a total variation norm penalty. The reconstruction algorithms employ accurate models of the ultrasonic transducer impulse responses. Experimental data sets are employed to compare the performances of the iterative reconstruction algorithms to that of a 3D filtered backprojection (FBP) algorithm. By use of quantitative measures of image quality, we demonstrate that the iterative reconstruction algorithms can mitigate image artifacts and preserve spatial resolution more effectively than FBP algorithms. These features suggest that the use of advanced image reconstruction algorithms can improve the effectiveness of 3D OAT while reducing the amount of data required for biomedical applications.
New fast detector technology has driven significant renewed interest in time-resolved measurement of early photons in improving imaging resolution in diffuse optical tomography and fluorescence mediated tomography in recent years. In practice, selection of early photons results in significantly narrower instrument photon density sensitivity functions (PDSFs) than the continuous wave case, resulting in a better conditioned reconstruction problem. In this work, we studied the quantitative impact of instrument temporal impulse response function (TIRF) on experimental PDSFs in tissue mimicking optical phantoms. We used a multi-mode fiber dispersion method to vary the system TIRF over a range of representative literature values. Substantial disagreement in PDSF width – by up to 40% - was observed between experimental measurements and Monte Carlo (MC) models of photon propagation over the range of TIRFs studied. On average, PDSFs were broadened by about 0.3 mm at the center plane of the 2 cm wide imaging chamber per 100 ps of instrument TIRF at early times. Further, this broadening was comparable on both the source and detector sides. Results were confirmed by convolution of instrument TIRFs with MC simulations. These data also underscore the importance of correcting imaging PDSFs for instrument TIRF when performing tomographic image reconstruction to ensure accurate data-model agreement.
Synaptic vesicles dock at active zones on the presynaptic plasma membrane of a neuron’s axon terminals as a precondition for fusing with the membrane and releasing their neurotransmitter to mediate synaptic impulse transmission. Typically, docked vesicles are next to aggregates of plasma membrane-bound macromolecules called active zone material (AZM). Electron tomography on tissue sections from fixed and stained axon terminals of active and resting frog neuromuscular junctions has led to the conclusion that undocked vesicles are directed to and held at the docking sites by the successive formation of stable connections between vesicle membrane proteins and proteins in different classes of AZM macromolecules. Using the same nanometer scale 3D imaging technology on appropriately stained frog neuromuscular junctions, we found that ∼10% of a vesicle’s luminal volume is occupied by a radial assembly of elongate macromolecules attached by narrow projections, nubs, to the vesicle membrane at ∼25 sites. The assembly’s chiral, bilateral shape is nearly the same vesicle to vesicle, and nubs, at their sites of connection to the vesicle membrane, are linked to macromolecules that span the membrane. For docked vesicles, the orientation of the assembly’s shape relative to the AZM and the presynaptic membrane is the same vesicle to vesicle...
Soft-tissue sarcomas of the genitourinary tract account for only 1–2% of urological malignancies and 2.1% of soft-tissue sarcomas in general. A 69-year-old male complained of a 4 month history of a painless right groin swelling during routine urological review for prostate cancer follow-up. Clinical examination revealed a non-tender, firm right inguinoscrotal mass. There was no discernible cough impulse. Computed tomography of abdomen and pelvis showed a non-obstructed right inguinal hernia. During elective hernia repair a solid mass involving the spermatic cord and extending into the proximal scrotum was seen. The mass was widely resected and a right orchidectomy was performed. Pathology revealed a paratesticular sarcoma. He proceeded to receive adjuvant radiotherapy. Only around 110 cases of leiomyosarcoma of the spermatic cord have been described in the literature. They commonly present as painless swellings in the groin. The majority of diagnoses are made on histology.
Resolution in diffuse optical tomography (DOT) is a persistent problem and is primarily limited by high degree of light scatter in biological tissue. We showed previously that the reduction in photon scatter between a source and detector pair at early time points following a laser pulse in time-resolved DOT is highly dependent on the temporal response of the instrument. To this end, we developed a new single-photon avalanche photodiode (SPAD) based time-resolved DOT scanner. This instrument uses an array of fast SPADs, a femto-second Titanium Sapphire laser and single photon counting electronics. In combination, the overall instrument temporal impulse response function width was 59 ps. In this paper, we report the design of this instrument and validate its operation in symmetrical and irregularly shaped optical phantoms of approximately small animal size. We were able to accurately reconstruct the size and position of up to 4 absorbing inclusions, with increasing image quality at earlier time windows. We attribute these results primarily to the rapid response time of our instrument. These data illustrate the potential utility of fast SPAD detectors in time-resolved DOT.
Quantitative measures of image quality and reliability are critical for both qualitative interpretation and quantitative analysis of medical images. While, in theory, it is possible to analyze reconstructed images by means of Monte Carlo simulations using a large number of noise realizations, the associated computational burden makes this approach impractical. Additionally, this approach is less meaningful in clinical scenarios, where multiple noise realizations are generally unavailable. The practical alternative is to compute closed-form analytical expressions for image quality measures. The objective of this paper is to review statistical analysis techniques that enable us to compute two key metrics: resolution (determined from the local impulse response) and covariance. The underlying methods include fixed-point approaches, which compute these metrics at a fixed point (the unique and stable solution) independent of the iterative algorithm employed, and iteration-based approaches, which yield results that are dependent on the algorithm, initialization, and number of iterations. We also explore extensions of some of these methods to a range of special contexts, including dynamic and motion-compensated image reconstruction. While most of the discussed techniques were developed for emission tomography...
peer-reviewed; Abdominal Aortic Aneurysms (AAAs) is a permanent and irreversible dilation of the
infrarenal section of the aorta. AAA’s are generally asymptomatic, until rupture of the
AAA wall occurs. Rupture can lead to large abdominal bleeding and death within a
short period of time. AAA formation affects the integrity of the aortic wall, leading to a
decrease in compliance and tensile strength, increased wall stiffness and a progressive
dilation of the wall. From a biomedical engineering perspective, rupture of an AAA
occurs when, locally, the wall stress surpasses the strength of the wall. This suggests it
is of importance to have wall property information and perform wall stress analysis
which can assess the risk of rupture reliably. Noninvasive assessment of aneurysm wall
properties would improve insight into the vascular changes, preceding rupture. This
thesis aims to explore noninvasive methods of characterising aortic wall properties and
the effectiveness of these techniques to aid in clinical assessment. In this study, the
efficacy of acoustic radiation force impulse (ARFI) imaging for determination of aortic
changes in vitro was reported. The study successfully developed an artificial aneurysm
in excised tissue and the changes induced by aneurysm development were detected
using ARFI. A feasibility case study demonstrated a method for estimation of in vivo
tissue properties using ARFI and exhibited the viability of translation of this modality to
AAA clinical use. Most preoperative imaging protocols use computerised tomography
(CT) angiography with three dimensional (3D) reconstructions for sizing and planning.
The resulting images are static images...
Iterative image reconstruction algorithms for optoacoustic tomography (OAT),
also known as photoacoustic tomography, have the ability to improve image
quality over analytic algorithms due to their ability to incorporate accurate
models of the imaging physics, instrument response, and measurement noise.
However, to date, there have been few reported attempts to employ advanced
iterative image reconstruction algorithms for improving image quality in
three-dimensional (3D) OAT. In this work, we implement and investigate two
iterative image reconstruction methods for use with a 3D OAT small animal
imager: namely, a penalized least-squares (PLS) method employing a quadratic
smoothness penalty and a PLS method employing a total variation norm penalty.
The reconstruction algorithms employ accurate models of the ultrasonic
transducer impulse responses. Experimental data sets are employed to compare
the performances of the iterative reconstruction algorithms to that of a 3D
filtered backprojection (FBP) algorithm. By use of quantitative measures of
image quality, we demonstrate that the iterative reconstruction algorithms can
mitigate image artifacts and preserve spatial resolution more effectively than
FBP algorithms. These features suggest that the use of advanced image
reconstruction algorithms can improve the effectiveness of 3D OAT while
reducing the amount of data required for biomedical applications.
This is the author accepted manuscript. The final version is available from Society for Neuroscience via http://doi.org/10.1523/JNEUROSCI.3890-14.2015; We have previously shownthat impulsivity in rats is linkedto decreased dopamine D2/3 receptor availability inthe ventral striatum. In the
present study, we investigated, using longitudinal positron emission tomography (PET), the effects of orally administered methylphenidate
(MPH), a first-line treatment for attention deficit hyperactivity disorder, on D2/3 receptor availability in the dorsal and ventral
striatum and related these changes to impulsivity. Rats were screened for impulsive behavior on a five-choice serial reaction time task.
After a baseline PET scan with the D2/3 ligand [18F]fallypride, rats received 6 mg/kg MPH, orally, twice each day for 28 d. Rats were then
reassessed for impulsivity and underwent a second [18F]fallypride PET scan. Before MPH treatment, we found that D2/3 receptor availability
was significantly decreased in the left but not the right ventral striatum of high-impulse (HI) rats compared with low-impulse (LI)
rats. MPH treatment increased impulsivity in LI rats, and modulated impulsivity and D2/3 receptor availability in the dorsal and ventral
striatum of HI rats through inverse relationships with baseline levels of impulsivity and D2/3 receptor availability...