Radiographic magnification of colon polyps

Radiographic magnification was evaluated on conventional and remote control machinery using a phantom with steel rods positioned at different levels. Depending on the rod-film distance, the range of magnification was 8-47% on remote control and conventional overhead films and 11-82% on conventional fluoroscopic spot-films. Extrapolation to the colon based on cross-sectional anatomic correlation showed a 14-27% variation in the radiographic magnification depending on the machinery used, the segment of the colon considered, and the position of the patient. This implies that substantial inaccuracy in the measurement of colonic polyps is common by barium enema examination, particularly when a conventional fluoroscope is used.