Fig. 1

Dual isotope energy spectrum. The solid black vertical lines at 80.6 keV (within the orange window) and 140 keV (within the blue window) denote the ¹⁶⁶Ho and ^99mTc photopeak, respectively. The solid green curve is the dual isotope spectrum, recorded when both ¹⁶⁶Ho and ^99mTc were present, and the dashed orange curve represents the ¹⁶⁶Ho spectrum. The dotted blue curve was obtained by subtracting the ¹⁶⁶Ho spectrum from the dual isotope spectrum and represents the ^99mTc spectrum. Energy windows used to estimate the downscatter correction (centered at 118 keV, 12% width and at 170 keV, 12% width) are indicated in gray