Measurement of CT section thickness by using the partial volume effect.

A method to calculate section thickness from mean computed tomographic (CT) numbers of two materials in a section (and by varying the ratio of their volume) was developed. A cylindrical water phantom with an acrylic rod at the center was used, and section thickness was measured with two CT scanners. At actual section thicknesses of more than 4 mm, results with this method differed from results of the aluminum ramp method by only about 10%. At section thicknesses of 1-2 mm, however, the difference was about 30%-50%. Measurement with this method was not influenced by filter function and therefore was more accurate than with the aluminum ramp method.