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Abstract
Purpose
With the advent of MSCT, the detection rate of small pulmonary nodules is markedly greater. However, there is no definite diagnostic clue to differentiate between malignant and benign nodules, except for the interval growth in small nodule less than 1 cm in diameter. We evaluated the accuracy of computer-aided volumetry (CAV) and compared it with 4 radiologists' measurement.
Materials and Methods
Fifteen artificial nodules that were embedded in the ex vivo porcine lung were scanned by MSCT. The diameters and volumes of nodules were independently measured three times, at 5-day intervals, and by four radiologists as well as by CAV. We evaluated the accuracy of the measurements on the basis of the true diameter and volume of the nodules. Using a paired t-test and a Bland-Altman plot, we evaluated whether there was a statistically significant difference between the radiologists' measurements and the CAV.
Results
The accuracy of the manual measurements by radiologists revealed a statistically significant difference from the true diameter and volume of the artificial nodules (p<0.01). Conversely, the accuracy of CAV did not show a statistically significant difference with the true nodule diameter and volume (p>0.01).
Figures and Tables
Fig. 1
Tumor phantoms. Axial image of artificial pulmonary nodules (arrows) in air inflated ex vivo porcine lung.
Fig. 2
Histogram for adaptive threshold. Adaptive threshold for each artificial nodule was estimated using mean value of HU value of nodule peak and that of neighborhood peak.
Fig. 3
Graphical user interface of semi-automated volumetry.
A. Selected images are shown on the right side of monitor. To start volumetry, click on the selected nodule, then press the volume button. The calculated volume is visible on the ritgt-lower portion of monitor.
B. Three-dimensional image from 1 mm thickness MSCT data of an artificial nodule
C. The overall workflow for a nodule volume measurement.
Fig. 5
The percentage of error of the volume estimates by radiologists in 15 synthetic nodules. The percentage of error become greater with decreasing nodule size.
Fig. 6
The percentage of error of the volume estimates by CAV algorithm in 15 synthetic nodules. The percentage of error is nearly fixed at -6.6 % with all nodule.
Table 1
Radiologist's Manual Measurement of Longest Diameter of Nodule. The Diameter Estimates and Standard Deviation of Each Artificial Nodule on MSCT Data were Calculated
Table 2
Radiologist's Manual Measurement of Longest Diameter of Nodule. The Diameter Estimates, Standard Deviation and Percentages of Error of Artificial Nodules on MSCT Data were Calculated
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