Comparison of IVIS and gamma counter biodistribution measurements for two of the mice. (a) The IVIS biodistribution of [68Ga]GaCl3 in a mouse 65 min after injection. (b) Bar graph comparing the IVIS biodistribution in flux (photons/s) versus the gamma counter measurements of the decay activity (gamma ray counts) normalized to the thigh muscle for two mice 65 min after injection. The intestines, tumor, brain, muscle, and femur bone have similar values, but the heart, lungs, spleen, liver, blood, and kidneys show reduced flux relative to the activity. While the blood had the highest activity of 6.2 times muscle, the Cerenkov light output was only 0.32 times muscle. (c) Ratio of IVIS flux to the gamma counter counts normalized to muscle. Compared to muscle, the ratio of Cerenkov light to radioactivity was only 0.05, demonstrating that blood attenuated much more light than the muscle and other organs.