THE ACCURACY OF MEASUREMENTS OF 3-DIMENSIONAL COMPUTED-TOMOGRAPHY RECONSTRUCTIONS

Purpose: The purpose of this study was to evaluate the accuracy and re producibility of linear measurements obtained from three-dimensional r econstructions of computed tomography (CT) scans. Materials ana Method s: Ten rectangular acrylic blocks were prepared with titanium molybden um alloy (TMA) markers spaced from 1 to IO mm, respectively. A plastic sphere was prepared with 10 sets of TMA markers spaced at variable in tervals of 1 to 10 mm, Each object was scanned three times at 3-mm sli ce thicknesses and 1.5 mm with 0.5 mm overlap slice thicknesses, as we ll as positioned in the GT scanner in two different directions (perpen dicular and parallel) to the scanning beam. Intermarker distances of t he reconstructed objects were then measured using the measurement tool of the MediCAD software and compared with measurements taken by hand with a vernier caliper. Results. Using the 3-mm cut protocol, the data indicated that inconsistency exists between intermarker distance in t he scans when the rectangular objects were scanned parallel to the sca nning beam. This finding was not seen using the 1.5-mm with 0.5-mm ove rlap slice thickness protocol, The intermarker distances for objects s canned perpendicular to the scanning beam were consistent but subject to demagnification in the range of 17% to 20% for both scanning protoc ols, Conclusion: The orientation of the object to the scanning beam an d slice thickness protocol appear to have an impact on the accuracy an d variability of linear measurements taken in the x, y, z axes.