Phantoms and tissues show variation in densities across different scans.

<p>(A) Distribution of densities of three phantoms, air, water, and bone (left to right peaks), with mean densities −927.6 HU, 92.2 HU, and 2612.6 HU, respectively, in one scan. (B) Distribution of densities of the same phantoms as in (A) in a repeated scan six weeks later with mean densities −931.8 HU, 66.5 HU, and 2592.0 HU, respectively. (C) Distribution of densities in the lung parenchyma (white) and soft tissue (gray) from one mouse in one scan with an adaptive threshold at −155 HU. (D) Distribution of densities of the same tissues as in (C) of the same mouse in a repeated scan six weeks later with an adaptive threshold at −190 HU. All scans were acquired at 50 µm with 720 projections. Variations in the density distribution of the phantoms and tissues were observed in repeated scans.