Quantitative CT applications: comparison of current scanners

Quantitative computed tomography (QCT) has been used with variable success to measure the density of lung nodules, bone, and kidney stones and to determine volumes of tumor. Commercially available CT scanners vary in their ability to quantify high-atomic-number (high-Z) and low-Z components accurately and reproducibly. Sixteen models of CT scanners from eight manufacturers were compared as to their capability for QCT. Field uniformity was determined in phantoms simulating the human torso. For high-Z (250 HU) materials, the difference in CT numbers from the center to a radial distance of 13 cm ranged from 1 to 50 HU (mean, 15 HU); for water, the range was 0-15 HU. Accuracy of computed radiographic localizer systems ranged from +/- 0.5 to +/- 2.0 mm without gantry angulation and up to +/- 4 mm with an angled gantry. A variety of artifacts also reduced QCT accuracy and reproducibility. Thus, not all CT scanners are equally suited to QCT, and results on one machine may not be comparable to those of another unless correction factors are used.