Flat panel detector-based volumetric CT: prototype evaluation with volumetry of small artificial nodules in a pulmonary phantom.

PURPOSE

To evaluate amorphous silicone-based flat panel detector volumetric CT (VCT) in volumetric assessment of small nodules in a pulmonary phantom, and to perform comparative experiments with 4-row multislice CT (MSCT).

MATERIALS AND METHODS

Seventy synthetic nodules (volume range (VR): 0.99-185.77 mm; estimated diameter range (ED): 1.4-7.8 mm) were scanned in spherical shape and after iso-volumetric deformation with VCT and MSCT using 0.63 mm (MSCT I) and 1.25 mm (MSCT II) collimations. Measured volumes and percent measurement errors (PME) were compared between the 3 CT modes before and after nodule deformation. For each measurement pair before and after deformation, the post-deformation relative volumetric inaccuracy (RIA) was determined. Volume, PME, and RIA differences were tested using Wilcoxon and Friedman methods.

RESULTS

The volumes of the smallest nodules (VR = 0.99-2.83 mm, ED = 1.4-1.9 mm) were computable only from VCT scans. In VCT, measured volumes and PMEs before and after deformation differed significantly less compared with MSCT (VCT: P = 0.06 and 0.56, respectively; MSCT I: P = 0.0012 and 0.006, respectively; and MSCT II: P < 0.0001 for measured volumes and PMEs). In VCT PMEs of 5.51-32.21 mm nodules (ED = 2.4-4.1 mm) before and after deformation were significantly below MSCT (VCT averages = 1.43-1.91% and 1.98-3.48%, for spherical and deformed nodules, respectively; MSCT I averages = 9.97-26.1% and 12.16-38.10%, respectively; MSCT II averages = 17.79-46.18 and 18.14-54.66%, respectively, P < 0.0001) and RIAs in VCT were significantly below MSCT (VCT: 0.50-2.62%, MSCT I: 3.35-15.97%, and MSCT II: 4.29-18.46%; P = 0.0001-0.0039).

CONCLUSION

VCT volumetry is highly accurate in volumetry of smallest nodules with estimated diameters of 1.4-4.1 mm.