[Size and density determination by thin-layer CT in relation to structural diameter and the contrast of the...

The reliability of CT size and density measurements has been examined by using phantom measurements with constant examination and reconstruction parameters (Somatom DRH/Siemens). Ten plexiglass rods with diameters from 2 to 15 mm. were measured singly in (1) air, (2) isodense (146 Hu) and (3) hyperdense medium (985 Hu) using 2 mm. sections. In the isodense medium there was only small variation in density measurements (124 to 131 Hu). Measurements of size showed a maximum error up to -35%. Density measurements in the hyperdense medium produced raised values (197 +/- 17 Hu at 15 mm.). There was an even greater increase for rods smaller than 5 mm. Measurement of size was correct, as it was in air (maximum deviation 8%). Density measurements in air for diameters less than 6 mm. were significantly reduced.