With the advent of high-resolution CT, three-dimensional (3D) methods for nodule volumetry have been introduced,
with the hope that such methods will be more accurate and consistent than currently used planar measures of size.
However, the error associated with volume estimation methods still needs to be quantified. Volume estimation error is
multi-faceted in the sense that there is variability associated with the patient, the software tool and the CT system. A
primary goal of our current research efforts is to quantify the various sources of measurement error and, when possible,
minimize their effects. In order to assess the bias of an estimate, the actual value, or "truth," must be known. In this
work we investigate the reliability of micro CT to determine the "true" volume of synthetic nodules. The advantage of
micro CT over other truthing methods is that it can provide both absolute volume and shape information in a single
measurement. In the current study we compare micro CT volume truth to weight-density truth for spherical, elliptical,
spiculated and lobulated nodules with diameters from 5 to 40 mm, and densities of -630 and +100 HU. The percent
differences between micro CT and weight-density volume for -630 HU nodules range from [-21.7%, -0.6%] (mean=
-11.9%) and the differences for +100 HU nodules range from [-0.9%, 3.0%] (mean=1.7%).