INFLUENCE OF CT IMAGE SIZE AND FORMAT ON ACCURACY OF LUNG NODULE DETECTION

PURPOSE: To evaluate the effect of reducing image size on observers' a bility to detect lung nodules on computed tomographic (CT) scans. MATE RIALS AND METHODS: Stimuli were 80 single sections from 13 normal ches t CT studies. On half of the images, 3-5-mm-diameter nodules were supe rimposed electronically at random locations. Four observed viewed imag es in six formats and sizes that ranged from 6 on 1 (133 x 133 mm) to 80 on 1 (40 x 40 mm). The images were viewed at a fixed distance of 55 cm and at an unrestricted, variable distance. RESULTS: With the fixed viewing distance, nodule detection decreased with smaller images size s. The area under the receiver operating characteristic curve (A) decr eased fro 0.857 for the 6-on-1 format to 0.671 for the 80-on-1 format (P = .0001). With a variable viewing distance, A(2) decreased from 0.8 84 to 0.834 across all formats (difference not statistically significa nt). However, there was a significant drop in performance with the sma llest images (P < .05). Overall, A(2) for the fixed and variable viewi ng distances was significantly different (P < .001). CONCLUSION: Reduc ing image size leads to decreased lung nodule detection on CT scans vi ewed at a fixed distance; however, the observer can compensate for the smaller image by adjusting the viewing distance.