Optimal X-ray Beam Angle for Nasal Tangential Radiography: A Phantom Study

Abstract

To determine the optimal caudal X-ray tube angle for nasal tangential radiography using the glabelloalveolar line (GAL) as an anatomical reference and to evaluate the effect of tube angulation on nasal bone visualization in a 3D-printed skull phantom. De-identified facial computed tomography data from 50 adult men were retrospectively reviewed to identify a representative nasal bone length for fabrication of a 3D-printed skull phantom. The phantom was positioned prone and imaged under standardized exposure conditions at caudal tube angles of 15°, 20°, 25°, and 30°. Projected nasal bone length was defined as the straight-line distance from the nasion to the rhinion and was measured using ImageJ. Five experienced radiologic technologists independently assessed image quality using a five-point scale based on five anatomical criteria: symmetry of the nasal bony structures, avoidance of overlap with the upper dentition, separation from the frontal bone, avoidance of overlap with the lower incisors, and alignment of the X-ray beam with the GAL. Quantitative differences among the four tube-angle conditions were evaluated using one-way analysis of variance. Mean projected nasal bone lengths were 11.88 ± 0.12 mm at 15°, 25.23 ± 0.12 mm at 20°, 20.50 ± 0.36 mm at 25°, and 14.39 ± 0.09 mm at 30°. A significant overall difference was observed among the four angles (F = 4369.99, p < 0.001). The 20° caudal angle produced the greatest projected nasal bone length and also received the highest qualitative score for each of the five anatomical image-quality criteria. These findings indicate that the 20° condition provided the most favorable combination of projected nasal bone length and anatomical separation under the standardized phantom conditions. A 20° caudal X-ray tube angle provided the most favorable overall visualization for GAL-based nasal tangential radiography among the four tested conditions. The agreement between the quantitative and qualitative findings supports 20° as a candidate angle for further validation. However, because this study used a single 3D-printed skull phantom and did not assess fracture-detection accuracy or radiation dose, additional clinical studies are required before this angle can be recommended as a universal patient-positioning standard.