Impact of beam hardening on CT attenuation values of the lung parenchyma: analysis using computer simulations with voxelized patient models

Accurately assessing health of the lung parenchyma is critically important in the management of patients with chronic obstructive pulmonary disease (COPD). CT attenuation values have been shown to have clinical value for this purpose. However, CT attenuation values lack absolute accuracy due to various physical effects. In this work, we conduct an experimental study to evaluate, realistically and in isolation, the effect of beam hardening errors. Our initial results indicate that spectral interactions between the rib cage and the vertebra induce complex beam hardening error patterns within the lung parenchyma that vary from patient to patient as well as with the slice location. For a difference of 8 HU between healthy and diseased tissue, these variations cause a drop of 0.06 in discrimination performance measured by the area under the ROC curve.