RESUMEN
A new method for correcting simultaneously the attenuation, scatter and resolution effects in SPECT has been developed for the case of a homogeneous medium. It is based on an effective model of the scatter process. This model depends on only four parameters which are determined experimentally and remain independent of the geometry and of the dimensions of the scatter medium. The method uses the data from the peak events and does not need additional energy windows on the scattered events. An original filter is proposed to remove the noise due to the poor statistics of clinical data. Tests on phantoms varying in size and activity show that the model allows absolute activity determination with an accuracy of a few per cent.
Asunto(s)
Algoritmos , Aumento de la Imagen/métodos , Interpretación de Imagen Asistida por Computador/métodos , Tomografía Computarizada de Emisión de Fotón Único/métodos , Artefactos , Humanos , Fantasmas de Imagen , Reproducibilidad de los Resultados , Dispersión de Radiación , Sensibilidad y Especificidad , Procesos Estocásticos , Tomografía Computarizada de Emisión de Fotón Único/instrumentaciónRESUMEN
A contour detection algorithm for cerebral studies, using the method of Tomitani, has been implemented on a single-photon emission tomographic (SPET) system. It is based on the detetion by threshold of the brain edge in the sinogram and does not depend on the reconstruction algorithm. Thirteen normal subjects underwent an examination on both computed tomography (CT) and SPET using a head holder to ensure the reproducibility of the positioning. The CT scan contour of the brain was drawn manually according to the brain parenchyma limits. The SPET brain contour was obtained by use of the Tomitani algorithm after the threshold had been determined on an active cylindrical phantom. Using a threshold of 37% of the maximum uptake, the length of the contour as well as the area obtained with SPET and CT were not found to be statistically different. The method of Tomitani, which is simpler and faster then previous methods, provides contours which superimpose very well with CT scan images. Application to patients with unilateral pathological defects is possible by requiring that the contour is symmetrical.
Asunto(s)
Algoritmos , Encéfalo/diagnóstico por imagen , Trastornos Cerebrovasculares/diagnóstico por imagen , Procesamiento de Imagen Asistido por Computador , Compuestos de Organotecnecio , Oximas , Tomografía Computarizada de Emisión de Fotón Único/métodos , Adolescente , Adulto , Anciano , Estudios de Casos y Controles , Niño , Femenino , Humanos , Masculino , Persona de Mediana Edad , Reproducibilidad de los Resultados , Exametazima de Tecnecio Tc 99m , Tomografía Computarizada por Rayos XRESUMEN
Single-photon emission tomographic (SPET) reconstruction can be improved, especially for noisy images, by using the iterative expectation-maximization of the maximum-likelihood (EM-ML) algorithm. Its application to clinical routine is, however, hampered by the high number of iterations necessary to achieve acceptable results. Therefore various methods have been developed to accelerate the EM-ML algorithm. In this paper a new accelerated EM-ML-like multiplicative algorithm is proposed for SPET reconstruction. Contrary to some other accelerating methods, it preserves two of the most important properties of the EM-ML, namely pixel positivity inside the patient body and null activity outside. The convergence speed is improved by a factor which can reach 100 in high spatial frequency or low count regions. Good estimates in the low count region are obtained without any smoothing, even at typical routine clinical count rates. The algorithm used in conjunction with the 3D effective one scatter path model provides high-quality SPET images and accurate quantitation.