FIG. 4.

^99mTc energy spectrum for interactions in an 11 × 11 group of pixels at the center region of a detector; except for statistics, essentially the same spectrum is obtained if a larger or smaller region is used. The bump near 70 keV is caused by K x rays created from the gold insert on the cylinder aperture or lead and bismuth contained in the Cerrobend of the cylinder aperture when gamma rays interacted in them. The energy resolution is about 10% as measured by full-width-at-half-maximum of the photopeak (140 keV).