Compton scatter image simulating jugular venous reflux

In a radionuclide cerebral angiographic study, Tc-99m photons from the subclavian vein may scatter in the superficial tissues of the neck and head, resulting in an image simulating the jugular venous reflux. In a scintillation camera peaked at 140 keV with a 20% window, any scattered photons with a scatter angle of less tha 53.5 degrees may be counted in the Tc-99m window. This scatter angle is large enough to allow counting of many secondary photons from Compton collisions in an area quite distant from the radioactive source to be counted, provided the scatter area and source are separated by air.