The effect of increasing the lower energy-window threshold on the sensitivity maps for (a) , (b) ¹¹¹In, and (c) ¹³¹I. The lowest threshold was placed at the Compton backscatter peak for each radionuclide, and the upper threshold was placed at three standard deviations (derived by fitting a Gaussian distribution to the photopeak of the energy spectrum) above the photopeak. The top left corner of each image corresponds to a sensitivity measurement directly in front of the centre of the GDP, while the lower right corner of each image corresponds to a depth of 13 cm and a horizontal displacement of 7 cm.