“…Yet, the ventilation distribution seen on Technegas images could lead to a bigger observed correlation between 81m Krypton and Technegas, since the downscatter originates from the reference tracer. It might be beneficial to use an energy window scatter correction to be able to account for downscatter, as, for example, for 177 Lu [ 23 ] or for Krypton and 99m Tc-MAA [ 24 ]. Nevertheless, significant differences were found in the majority of the results presented here.…”