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Computación y Sistemas

Print version ISSN 1405-5546

Comp. y Sist. vol.7 n.3 México Jan./Mar. 2004

 

Artículo

 

Emission Tomography: SPECT and PET

 

Tomografia por Emissão: SPECT e PET

 

Cecil Chow Robilotta

 

Departamento de Física General – Instituto de Física Universidade de São Paulo Rua do Matão, Travessa R, 187 – Cidade Universitária, 05508–900, São Paulo, S.P. – Brasil Tel: (55)(11)3091–6805 Fax: (55)(11) 813–4334. E–mail: cecilcr@if.usp.br

 

Article received on december 20, 2003
Accepted on february 02, 2004

 

Abstract

Emission tomography is a medical image modality that utilizes molecules labelled with radionuclides, the radiopharmaceuticals, to obtain functional information about specific tissues or systems.

In SPECT, Single Photon Emission Computerized Tomography, the radionuclide decays by emitting one or more photons, while in PET, Positron Emission Tomography, the radionuclide emits a positron, in order to reach a lower energy level. Although the forms of energy emitted are different, the images are reconstructed from the information acquired by external detection of the emitted photons (SPECT) and the pair of annihilation photons (PET) in coincidence.

Due to the specificity and characteristics of these images, their information can be quantified, so that functional or metabolic parameters can be obtained for diagnostic or therapeutic purposes. However, in order to achieve reliable results, factors related to the instrumentation and patient conditions, as well as to the interactions between radiations and tissues and the reconstruction methods have to be considered carefully. In this lecture, after the introduction of the fundamentals of nuclear medicine imaging, the basis of emission tomography acquisition and reconstruction will be presented. Some correction methods will be introduced in order to exemplify the current quantifications adopted in the clinical routine of molecular imaging.

Keywords: Emission tomography, functional imaging, iterative reconstruction, nuclear medicine, PET, quantification, SPECT.

 

Resumo

Tomografia por emissão é uma modalidade de imagem médica que utiliza moléculas marcadas com radionuclídeos, os radiofármacos, para obter informação funcional sobre tecidos ou sistemas específicos. Em SPECT (Single Photon Emission Computerized Tomography), tomografia por emissão de fóton único, o radionuclídeo decai emitindo um ou mais fótons, enquanto que em PET (Positron Emission Tomography), o radionuclídeo emite um pósitron para alcançar um nível energético mais baixo. Apesar de as formas de energia emitida serem diferentes, as imagens são reconstruídas a partir das informações adquiridas pela detecção externa dos fótons emitidos (em SPECT) e do par de fótons de aniquilação (PET) em coincidência.

Devido à especificidade e às características dessas imagens, suas informações podem ser quantificadas, de modo que os parâmetros funcionais ou metabólicos possam ser obtidos para fins de diagnóstico ou terapia. Entretanto, para se conseguir resultados confiáveis, fatores relacionados à instrumentação e às condições do paciente, assim como as interações entre as radiações e tecidos e os métodos de reconstrução, devem ser considerados cuidadosamente. Nesta palestra, após uma introdução aos fundamentos da formação de imagem de medicina nuclear, serão apresentadas as bases da aquisição e da reconstrução tomográfica. Alguns métodos de correção serão introduzidos para exemplificar as quantificações correntemente adotadas na rotina clínica do imageamento molecular.

Palavras–chave: Tomografia por emissão, imageamento funcional, reconstrução iterativa, medicina nuclear, PET, quantificação, SPECT.

 

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