An investigation of dual energy transmission measurements in simultaneous transmission emission imaging

In this study we investigate the feasibility of acquiring dual energy transmission projection data using a conventional gamma camera. Transmission projection data are acquired, simultaneously with ^99m Tc emission data, using the two major photopeaks of ¹⁵³Gd, at 44 keV and 99 keV. The degree of contamination of the data in the 44 keV window, by scattered 99 keV transmission photons, is investigated using Monte Carlo simulations. A modified scaling method is proposed to convert the two attenuation maps, obtained from transmission data acquired at 44 keV and 99 keV, to one appropriate for ^99mTc. This attenuation map is compared to one produced by scaling the 99 keV attenuation map, for the attenuation correction of ^99mTc SPECT images. The use of dual energy transmission imaging is shown to improve the quantitative accuracy of the reconstructed SPECT images compared to a single scale factor method. However, for situations where a dual scaling factor method is possible, this is shown to perform as well as the dual energy method. Dual energy transmission imaging is shown to be more effective at visualizing areas of bone, particularly in regions near the edge of the untruncated field of view