Myocardial perfusion imaging with a correlated X-ray CT and SPECT system: an animal study

We have performed a quantitative SPECT study in a porcine model of myocardial perfusion with the correlated X-ray CT transmission and SPECT emission (ETCT) system developed at UCSF. Pixel values in the reconstructed SPECT images were calibrated in units of activity concentration and compared with the activity concentration determined from corresponding excised myocardial tissue samples. An object specific attenuation map was obtained by linear scaling from the X-ray CT. Attenuation maps with lower spatial resolution and higher signal to noise ratio were also derived from the X-ray CT image. The pixel values and intensity distribution in reconstructed myocardial SPECT image was not sensitive to spatial resolution or noise in the transmission map for the given examples. An MLEM algorithm with regularization was used to determine mean and maximum pixel values for ROIs in the myocardial SPECT images. The use of the maximum pixel value did not sufficiently compensate for contrast degradation due to partial volume errors. A separate measurement of the myocardial wall thickness was used to adequately correct for partial volume errors.