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Abstract(s)
A Tomografia Computorizada por Emissão de Fotão Único (SPECT, do acrónimo em inglês Single Photon Emission Computed Tomography) é uma modalidade de aquisição de imagem em Medicina Nuclear (MN), sensível para a avaliação e quantificação dos processos fisiológicos dos pacientes. No entanto, existem diferentes fatores que afetam, qualitativa e quantitativamente, as imagens SPECT e, consequentemente, a confiabilidade dos dados. São necessários mais estudos relativamente à qualidade de imagem proporcionada por diferentes equipamentos, dado que se tem verificado um grau de variabilidade subjacente ao desempenho intrínseco de sistemas do mesmo ou de diferentes fabricantes, e uma vez que as diferentes configurações das Câmaras Gama (CG) e dos protocolos de aquisição e reconstrução utilizados podem levar à heterogeneização de resultados. O presente trabalho teve como principal objetivo comparar qualitativa e quantitativamente as imagens SPECT obtidas em três CG de três serviços de MN de Lisboa e Vale do Tejo com recurso aos fantomas Jaszczak e NEMA IEC Body, preenchidos com solução homogénea de Tecnécio-99m (99mTc).
Efetuaram-se aquisições, em cada CG, seguindo os protocolos utilizados na prática clínica do respetivo serviço e as imagens foram analisadas e comparadas em termos de resolução espacial, sensibilidade, ruído e contraste (percentagem e recuperação). Posteriormente, os parâmetros de processamento e reconstrução foram harmonizados, de forma a avaliar o seu impacto na uniformização de resultados. Com os protocolos clínicos, as imagens adquiridas com as três CG apresentaram diferenças em termos de resolução espacial, percentagem de ruído e de contraste, sendo que a maior diferença foi verificada a nível da quantificação, dado que a recuperação de contraste média alcançou variabilidades de 0,17 e 0,28, para diferentes concentrações de atividade. Esta variabilidade foi reduzida para 0,09 e 0,08, após alteração dos parâmetros de reconstrução de uma das CG em estudo. Considera-se o presente estudo como mais um passo necessário para a avaliação e interpretação das diferenças verificadas entre imagens adquiridas em diferentes modelos de CG, num ambiente multicêntrico. Concluiu-se que CG de diferentes fabricantes demonstraram a maior heterogeneização de resultados, contudo, eliminando possíveis fontes de variação é possível reduzir as diferenças verificadas entre sistemas.
Single Photon Emission Computed Tomography (SPECT) is a Nuclear Medicine (NM) imaging method, sensitive for the evaluation and quantification of physiological processes in patients. However, there are different factors that affect, qualitatively and quantitatively, the SPECT images and, consequently, the reliability of the data. Thus, further studies are needed regarding the quality of the image provided by different systems, since there has been a degree of variability underlying the intrinsic performance of systems from the same or different manufacturers, and because different Gamma Camera (GC) configurations and different acquisition and reconstruction protocols may lead to heterogeneous results. The main objective of this study was to compare qualitatively and quantitatively SPECT images acquired in three GC from three NM centres in Lisbon and Tagus Valley, using the Jaszczak and NEMA IEC Body phantoms, filled with homogeneous solution of Technetium-99m. Acquisitions were performed in each GC, following the protocols used in clinical practice of the respective NM centre, and the images were analysed and compared in terms of spatial resolution, sensitivity, noise, and contrast (percent and recovery). Subsequently, the processing and reconstruction parameters were harmonised to assess their impact on the standardisation of results. With the clinical protocols, the images acquired with the three GCs showed differences in terms of spatial resolution, noise, and contrast percentage, with the greatest difference being observed in the quantitative accuracy, since the mean contrast recovery has achieved variabilities of 0.17 and 0.28, for different activity concentrations. The inter-system variability was reduced to 0.09 and 0.08 after changing the reconstruction parameters of one of the GCs under study. This study represents a necessary step for the assessment and interpretation of the differences observed between images acquired with different GC models, in a multicentre study. It was concluded that GCs from different manufacturers demonstrated the greatest heterogeneity of results, however, eliminating possible sources of variation it is possible to reduce the differences observed between systems.
Single Photon Emission Computed Tomography (SPECT) is a Nuclear Medicine (NM) imaging method, sensitive for the evaluation and quantification of physiological processes in patients. However, there are different factors that affect, qualitatively and quantitatively, the SPECT images and, consequently, the reliability of the data. Thus, further studies are needed regarding the quality of the image provided by different systems, since there has been a degree of variability underlying the intrinsic performance of systems from the same or different manufacturers, and because different Gamma Camera (GC) configurations and different acquisition and reconstruction protocols may lead to heterogeneous results. The main objective of this study was to compare qualitatively and quantitatively SPECT images acquired in three GC from three NM centres in Lisbon and Tagus Valley, using the Jaszczak and NEMA IEC Body phantoms, filled with homogeneous solution of Technetium-99m. Acquisitions were performed in each GC, following the protocols used in clinical practice of the respective NM centre, and the images were analysed and compared in terms of spatial resolution, sensitivity, noise, and contrast (percent and recovery). Subsequently, the processing and reconstruction parameters were harmonised to assess their impact on the standardisation of results. With the clinical protocols, the images acquired with the three GCs showed differences in terms of spatial resolution, noise, and contrast percentage, with the greatest difference being observed in the quantitative accuracy, since the mean contrast recovery has achieved variabilities of 0.17 and 0.28, for different activity concentrations. The inter-system variability was reduced to 0.09 and 0.08 after changing the reconstruction parameters of one of the GCs under study. This study represents a necessary step for the assessment and interpretation of the differences observed between images acquired with different GC models, in a multicentre study. It was concluded that GCs from different manufacturers demonstrated the greatest heterogeneity of results, however, eliminating possible sources of variation it is possible to reduce the differences observed between systems.
Description
Trabalho final de Mestrado para obtenção do grau de Mestre em Engenharia Biomédica
Keywords
Quantificação em imagem SPECT Resolução espacial Sensibilidade Ruído Quantitative SPECT Spatial resolution Sensitivity Noise Contrast
Citation
GONÇALVES, Maria Inês Rebelo - Avaliação qualitativa e quantitativa da imagem SPECT com recurso a fantomas: estudo em diferentes modelos de Câmara Gama. Lisboa: Instituto Superior de Engenharia de Lisboa, 2022. Dissertação de Mestrado