THE WANDERING PROJECTILE: POOR X-RAY TECHNIQUE AND CRITICAL ERRORS

Objectives: When an unstable patient with penetrating thoracic injury arrives, the surgeon must sometimes make operative plans without the benefit of cross-sectional imaging. Plain films are often used to localize missiles within the patient and to guide clinical management. Potential exists for wide variance in technique when obtaining portable x-rays. We hypothesize that poor technique can have significant impact on imaging outcomes.

Methods: A solid anthropomorphic thorax phantom was modified using markers to delineate the anterior cardiac box, posterior cardiac box, and left ventricle (Fig. 1). A GE Revolution x-ray machine was used to project a series of anterior-posterior images onto a digital flat plate. A benchmark film was obtained at 0°, then the x-ray source was moved to -15°, -5°, 5°, and 15° serially in the x- and y- axes, keeping a distance of 40cm at all times. Two different sets of images were performed on two separate days with different radiographic technicians. The radiographic images compared against the reference image and the displacement of each marker was digitally measured at multiple reference points.

Results: There was a direct correlation between degree of rotation and amount of marker displacement. Anterior markers were displaced more than posterior markers. Multiple measurements were made for each point. All of these displacements were statistically significant (p < 0.0001), and different from each other (p < 0.01). Average displacement for markers in the anterior box was 0.29cm/°, and 0.13cm/° for the posterior box.

Conclusion: Single anterior-posterior portable chest x-rays are not adequate to localize foreign bodies or guide clinical management. Minimal changes in angle during radiographic imaging can lead to significant error and missiles located closest to the X-ray source demonstrate greatest displacement. These factors can lead the clinician to erroneous conclusions regarding proximity to vital structures. Knowledge of technique’s effect on imaging results is a critical part of resuscitation bay decision making.