Simultaneous emission, transmission scan for the measurement of 3-dimensional absolute activity distribution using dual isotope, TEW scatter compensation method and fan beam collimation

Photon attenuation is one of the most important factors degrading the quantitative accuracy of single photon emission computed tomography (SPECT) images. The precise information of attenuation distribution is needed for accurate attenuation compensation. Recently, a lot of methods to measure attenuation distribution using transmission computed tomography (TCT) scans have been reported. The simultaneous SPECT and TCT scan with dual isotopes, which is possible in SPECT systems, but not PET, was investigated as a way to avoid the problems of misalignment and longer scan times for clinical applications. In simultaneous system, however, there are scatter from emission to transmission and from transmission to emission. These scatter must be compensated for quantitative SPECT. To obtain quantitative SPECT images the authors designed and built a simultaneous transmission/emission scan and scatter compensation system (based on a Toshiba GCA-9300A HG triple head SPECT camera) using the TEW method and fan beam collimator for brain SPECT. The analysis of the distribution of the scatter component using the regional energy spectrum is very useful for evaluating scatter compensation. Here, the authors describe the analysis of simulated and measured energy spectrums of TCT scans and three dimensional absolute activity measurement in brain phantoms