Measuring Stone Surface Area from a Radiographic Image Is Accurate and Reproducible with the Help of an Imaging Program

Abstract

Background and Purpose:

The surface area of the stone from a radiographic image is one of the more suitable parameters defining stone bulk. The widely accepted method of measuring stone surface area is to count the number of square millimeters enclosed within a tracing of the stone outline on graph paper. This method is time consuming and cumbersome with potential for human error, especially when multiple measurements are needed. The purpose of this study was to evaluate the accuracy, efficiency, and reproducibility of a commercially available imaging program, Adobe Photoshop^® 7.0 for the measurement of stone surface area.

Materials and Methods:

The instructions to calculate area using the software are simple and easy in a Windows-based format. The accuracy of the imaging software was estimated by measuring surface areas of shapes of known mathematical areas. The efficiency and reproducibility were then evaluated from radiographs of 20 persons with radiopaque upper-tract urinary stones. The surface areas of stone images were measured using both graph paper and imaging software. Measurements were repeated after 10 days to assess the reproducibility of the techniques. The time taken to measure the area by the two methods was also assessed separately.

Results:

The accuracy of the imaging software was estimated to be 98.7%. The correlation coefficient between the two methods was R² = 0.97. The mean percentage variation using the imaging software was 0.68%, while it was 6.36% with the graph paper. The mean time taken to measure using the image analyzer and graph paper was 1.9 ± 0.8 minutes and 4.5 ± 1.08 minutes, respectively (P < 0.001)

Conclusion:

The imaging program is accurate, fast, and highly reproducible in estimating two-dimensional stone surface area from radiographs compared with manual measurements using graph paper.