Ana Maria Marques da Silva

Evaluating the reliability of different preprocessing steps to estimate graph theoretical measures in resting state fMRI data.

With resting-state functional MRI (rs-fMRI) there are a variety of post-processing methods that can be used to quantify the human brain connectome. However, there is also a choice of which preprocessing steps will be used prior to calculating the functional connectivity of the brain. In this manuscript, we have tested seven different preprocessing schemes and assessed the reliability between and reproducibility within the various strategies by means of graph theoretical measures. Different preprocessing schemes were tested on a publicly available dataset, which includes rs-fMRI data of healthy controls. The brain was parcellated into 190 nodes and four graph theoretical (GT) measures were calculated; global efficiency (GEFF), characteristic path length (CPL), average clustering coefficient (ACC), and average local efficiency (ALE). Our findings indicate that results can significantly differ based on which preprocessing steps are selected. We also found dependence between motion and GT measurements in most preprocessing strategies. We conclude that by using censoring based on outliers within the functional time-series as a processing, results indicate an increase in reliability of GT measurements with a reduction of the dependency of head motion.

Dual time point method for the quantification of irreversible tracer kinetics: A reference tissue approach applied to [18F]-FDOPA brain PET.

The Patlak graphical analysis (PGAREF) for quantification of irreversible tracer binding with a reference tissue model was approximated by a dual time point imaging approach (DTPREF). The DTPREF was applied to 18 [18F]-FDOPA brain scans using the occipital cortex as reference region (DTPOCC) and compared to both PGAOCC and striatal-to-occipital ratios (SOR). Pearson correlation analysis and Bland–Altman plots showed an excellent correlation and good agreement between DTPOCC and PGAOCC, while correlations between SOR and PGAOCC were consistently lower. Linear discriminant analysis (LDA) demonstrated a similar performance for all methods in differentiating patients with Parkinson’s disease (PD) from healthy controls (HC). Specifically for [18F]-FDOPA brain imaging, these findings validate DTPOCC as an approximation for PGAOCC, providing the same quantitative information while reducing the acquisition time to two short static scans. For PD patients, this approach can greatly improve patient comfort while reducing motion artifacts and increasing image quality. In general, DTPREF can improve the clinical applicability of tracers with irreversible binding characteristics when a reference tissue is available.

Ambiente colaborativo para formação de pessoal em medicina nuclear

OBJETIVO: Validar a proposta do desenvolvimento de um ambiente colaborativo virtual para formacao de pessoal em medicina nuclear. MATERIAIS E METODOS: No desenvolvimento inicial do ambiente foram levantadas as premissas, restricoes e funcionalidades que deveriam ser oferecidas aos profissionais da area. O prototipo foi desenvolvido no ambiente Moodle, incluindo funcionalidades de armazenamento de dados e interacao. Um estudo piloto de interacao no ambiente foi realizado com uma amostra de profissionais especialistas em medicina nuclear. Analises quantitativas e de conteudo foram realizadas a partir de um questionario semiestruturado de opiniao dos usuarios. RESULTADOS: A proposta do ambiente colaborativo foi validada por uma comunidade de profissionais que atuam nesta area e considerada relevante visando a auxiliar na formacao de pessoal. Sugestoes de melhorias e novas funcionalidades foram indicadas. Observou-se a necessidade de estabelecer um programa de formacao dos moderadores no ambiente, visto que sao necessarias caracteristicas de interacao distintas do ensino presencial. CONCLUSAO: O ambiente colaborativo podera permitir a troca de experiencias e a discussao de casos entre profissionais localizados em instituicoes de diferentes regioes do Pais, possibilitando uma aproximacao e colaboracao entre esses profissionais. Assim, o ambiente pode contribuir para formacao inicial e continuada de profissionais que atuam em medicina nuclear.

ApOtEl: Development of a Software for Electroporation Based Therapy Planning

The objective of this paper is to describe the implementation of a software application, called ApOtEl, developed for needle electrodes positioning optimization for electrochemotherapy procedures in the treatment of cutaneous and subcutaneous tumors. The software was developed using MATLAB®, and it optimizes the needle-type electrodes positioning configurations, through the study of the analytical electric field, using Laplace equation in a homogeneous bi-dimensional environment. The optimization was based on requirements chosen to guarantee the tumor total coverage and to minimize healthy neighboring tissues damage. An optimization function was created to orientate the electrochemotherapy application, and the best option available in all configurations generated by the distance variations between electrodes and positioning orientations was determined. The software provides, by the entry of tumor dimensions, the optimized distances for positioning needle-type electrodes, as well as the representation of the electric field distribution and intensity. Representation of the electrodes positioning and instructions for the procedure to facilitate the procedure planning are provided.

Radionuclide Internal Dosimetry Using GATE and PENELOPE for Experimental Validation in Geometrical Phantoms

The aim of this study is to investigate the use of two freely available Monte Carlo (MC) codes to model simple geometrical radionuclide configurations, which could be compared to experimental measurements or analytical calculus for internal dosimetry. Three spherical geometries were simulated using GATE 7.1 and PENELOPE 2008: (1) a point source centered in a 10 cm radius sphere; (2) a 5 cm radius sphere with homogeneous radioactive distribution inside a 10 cm radius sphere; (3) two separated spheres (5 and 10 cm radius) 5 cm apart, the first acting as source and the second as target. All spheres were filled with water and sources produced 108 primary gamma emissions from 99mTc. Total absorbed doses were analyzed using 3D Dose Point Kernel (DPK). Results obtained with GATE and PENELOPE simulations were, respectively: (1) 15 and 14.25 mGy, with 5.2% difference; (2) 7.4 and 8.51 mGy, showing higher difference (13.04%); (3) 0.93 and 0.97 mGy, in target sphere. Concluding, GATE and PENELOPE MC codes can be easily used to simulate simple geometries, allowing for comparison against experimental measurements or analytical calculations. Further studies are required to compare these simulation results with experimental data designed to the clinical practice.

Image Quality Performance of a Dedicated Cardiac Discovery NM 530c SPECT: Impact of Time Acquisition and Reconstruction Parameters

The aim of this study is to evaluate the impact of acquisition time and reconstruction parameters in image quality in a dedicated cardiac Discovery NM 530c CZT SPECT scanner. Anthropomorphic torso phantom with a cardiac insert and a cold lesion starting with 84 kBq/ml, 62 kBq/ml and 3 kBq/ml in myocardium, liver and background, respectively, simulated high-dose stress 99mTc acquisition. During two half-lives, images were acquired hourly to simulate lower doses, using both 3 and 5 min time acquisition. Reconstruction parameters were used separately per type of acquisition (low-dose and high-dose), according to manufacturer recommendation. Image quality and cold lesion visibility were evaluated using normalized standard deviation (NSD), ventricle-wall cavity contrast (VCC), contrast-to-noise ratio (CNR), and lesion effective contrast (EC). Variations in acquisition time did not affect quality parameters and lesion visibility for the appropriate reconstruction parameters, mainly in higher activities. However, image quality indicators are highly sensitive to the reconstruction parameters, producing significant differences (p < 0.05) in NSD, VCC, CNR and EC. Concluding, the reconstruction parameters need to be chosen carefully, considering patient´s characteristics and administered activity, in order to produce the best relation image quality/lesion visibility and dose.

Investigation of Time-Activity Curve Behavior in Dynamic [ 11 C]-(R)-PK11195 PET in Cortical Brain Regions: Preliminary Results

Dynamic Positron Emission Tomography (PET) allows quantification of underlying physiological processes in a tissue or organ of interest by modeling the radioactivity concentration measured in time (time-activity curve, i.e. TAC). Although the [11C]-(R)-PK11195 PET radiotracer binds to activated microglia and therefore images neuroinflammation, its quantification is still challenging. The aim of this study was to investigate a novel method for analyzing [11C]-(R)-PK11195 TAC behavior from dynamic PET. Seven healthy subjects underwent dynamic 60 min [11C]-(R)-PK11195 PET scans, and TACs were generated for 30 brain cortical regions using the AAL-Merged atlas. The proposed method supposes healthy subjects have similar TACs, which allows the construction of a “healthy template”. Then, TACs of patients can be compared to the healthy template to determine the likelihood that their behavior is abnormal. To evaluate the differences between a healthy region and an inflamed region, a cut-off value for abnormality was created. The method was then tested on a multiple sclerosis (MS) patient. The proposed method was able to identify a number of brain cortical regions with distinct behavior in one MS patient as compared to the healthy template. Further studies are required to evaluate the applicability of the proposed method with additional MS patients, and with data acquired in different scanners and reconstructed with other algorithms.

Geração de Imagens PET Estáticas com [11C]-(R)-PK11195: Definição do Intervalo Temporal

O radiotracador [ 11 C]-( R )-PK11195 mostra afinidade com a microglia em imagens PET in vivo e vem sendo utilizado como indicador de doenca inflamatoria cerebral, como a esclerose multipla (EM). Atualmente, nao ha consenso sobre o intervalo temporal adequado para gerar imagens PET estaticas com [ 11 C]-( R )-PK11195. O objetivo deste trabalho e determinar o intervalo temporal mais adequado para a geracao de imagens PET cerebrais estaticas adquiridas com [ 11 C]-( R )-PK11195 para a quantificacao. Foram geradas imagens PET estaticas com [ 11 C]-( R )-PK11195 nos intervalos de: 0-60min, 5-20min, 5-30min, 10-60min, 30-60min e 40-60min. Para quantificacao das imagens foi utilizado o metodo da razao entre a media do SUV ( Standard Uptake Value ) nas regioes justacortical e periventricular e na substância branca, denominado SUVR WM . Os resultados mostram grande variacao do SUVR WM nos intervalos que incluem o periodo de perfusao do radiotracador. Existe uma maior estabilidade do SUVR WM nos ultimos intervalos avaliados (30-60min e 40-60min), tanto para o grupo controle, como para os pacientes com EM. Conclui-se que o melhor intervalo para aquisicao da imagem PET estatica para quantificacao e de 40 a 60 minutos apos a administracao, o que significa uma imagem adquirida 40 min apos a injecao do radiotracador [ 11 C]-( R )-PK11195, por um periodo de 20 min.

Dual time-point imaging for post-dose binding potential estimation applied to a [11C]raclopride PET dose occupancy study

Receptor occupancy studies performed with PET often require time-consuming dynamic imaging for baseline and post-dose scans. Shorter protocol approximations based on standard uptake value ratios have been proposed. However, such methods depend on the time-point chosen for the quantification and often lead to overestimation and bias. The aim of this study was to develop a shorter protocol for the quantification of post-dose scans using a dual time-point approximation, which employs kinetic parameters from the baseline scan. Dual time-point was evaluated for a [11C]raclopride PET dose occupancy study with the D2 antagonist JNJ-37822681, obtaining estimates for binding potential and receptor occupancy. Results were compared to standard simplified reference tissue model and standard uptake value ratios-based estimates. Linear regression and Bland–Altman analysis demonstrated excellent correlation and agreement between dual time-point and the standard simplified reference tissue model approach. Moreover, the stability of dual time-point-based estimates is shown to be independent of the time-point chosen for quantification. Therefore, a dual time-point imaging protocol can be applied to post-dose [11C]raclopride PET scans, resulting in a significant reduction in total acquisition time while maintaining accuracy in the quantification of both the binding potential and the receptor occupancy.

SHIELD 1.0: desenvolvimento de um programa de cálculo de blindagem em radiodiagnóstico

No calculo de blindagem em instalacoes radiologicas, diversos parâmetros sao requeridos, tais como fator de ocupacao, fator de uso, numero de pacientes, distância fonte-barreira, tipo de area (livre ou controlada), radiacao (primaria ou secundaria) e material utilizado na barreira. A otimizacao do projeto de blindagem exige a analise de diversas opcoes de estruturacao fisica do ambiente e, principalmente, a obtencao da melhor relacao custo-beneficio do material utilizado na barreira. Para facilitar o desenvolvimento deste tipo de projeto, foi implementado um programa para calculo de blindagem em radiodiagnostico, com base em dados e limites estabelecidos pela National Council on Radiation Protection and Measurements (NCRP) 147 e Portaria SVS-MS 453/98. O programa foi desenvolvido na linguagem C# e apresenta uma interface grafica para entrada de dados pelo usuario e emissao de relatorios. O modulo implementado inicialmente, denominado SHIELD 1.0, refere-se ao calculo de barreiras para salas de raios X convencionais. A validacao do programa foi realizada atraves da comparacao com os resultados de exemplos de calculos de blindagem apresentados na NCRP 147.