Figure 5:
Patient size and image truncation. A, Maximal FOV axial reconstructions in the thorax and, B, those in the pelvis for patients with comparable manually measured Deff. While the physical areas of these two axial cross sections are similar, the DW is 15% higher in the pelvis (B) than in the thorax (A) because of the aerated lungs, corresponding to a 32% higher tissue attenuation in the pelvis (contained attenuation scales as the square of the diameter). Physical dimensions such as Deff do not capture this underlying attenuation difference. C, D, Axial image reconstructions performed in clinical routine with a limited FOV have expected decreases in the measured DW, compared with reconstructions in A and B. Image C is truncated version of A; image D is truncated version of B. Use of the air border proportion as a measure of truncation allows for the correction of DW values that more closely approximate maximal FOV images.