Measurement error of spiral CT Volumetry: Influence of Low Dose CT Technique

ABSTRACT

PURPOSE: To examine the possible measurement errors of lung nodule volumetry at the various scan parameters by using a small nodule phantom. MATERIALS AND METHODS: We obtained images of a nodule phantom using a spiral CT scanner. The nodule phantom was made of paraffin and urethane and its real volume was known. For the CT scanning experiments, we used three different values for both the pitch of the table feed, i.e. 11, 115 and 12, and the tube current, i.e. 40 mA, 80 mA and 120 mA. All of the images acquired through CT scanning were reconstructed three dimensionally and measured with volumetry software. We tested the correlation between the true volume and the measured volume for each set of parameters using linear regression analysis. RESULTS:For the pitches of table feed of 11, 11.5 and 12, the mean relative errors were 23.3%, 22.8% and 22.6%, respectively. There were perfect correlations among the three sets of measurements (Pearson's coefficient = 1.000, p<0.001). For the tube currents of 40 mA, 80 mA and 120 mA, the mean relative errors were 22.6%, 22.6% and 22.9%, respectively. There were perfect correlations among them (Pearson's coefficient = 1.000, p<0.001). CONCLUSION: In the measurement of the volume of the lung nodule using spiral CT, the measurement error was not increased in spite of the tube current being decreased or the pitch of table feed being increased.