PHYSICAL FACTORS AFFECTING QUANTITATIVE SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT)

Abstract

Single Photon Emission Computed Tomography (SPECT) is a technique for studying the biodistribution radioactive tracers introduced into the body, and provides high-contrast three­ dimensional images. SPECT imaging has a number of potential advantages over conventional nuclear medicine planar imaging. However, special attention is needed, and aSPECT system will not produce adequate results unless corrections & very great care is taken in both acquisition and reconstruction ofthe image. Degradation of single photon computed tomography images due to attenuation of photons; and Compton scattering can cause artifacts in clinical images and deteriorate the quantification. This necessitates the implementation of correction techniques in order to obtain accurate quantitative SPECT images. On the other hand for acquisition parameters non circular orbit, 180° acquisition with 64 matrix size is considered standard for cardiac SPECT imaging. Although theoretically, a 360° acquisition orbit with 128 matrix size is preferred because of more complete Fourier spectral information on projection data and better resolution. ECG-gated myocardial perfusion SPECT has allowed the simultaneous assessment of myocardial perfusion and function, particularly for the left ventricular myocardium. This progress has allowed the assessment of both global and regional left ventricular function. As with any technique, it is important to understand the accuracy of the approach, the variables that determine this accuracy, and the causes of errors. The main purpose of this investigation was the evaluation and implementation of a homogeneous attenuation correction (Chang method), with the window subtraction scattering correction of SPECT images by using the Jaszczak cardiac phantom. Homogeneity, contrast and FWHM assessed quantitatively with the differential effect of acquisition orbits ( 180° versus 360°), circular and non circular orbit and the matrix size (64 versus 128).