Investigating the Effects of Image Scaling Techniques in Radiographic Measurements of Spinal Alignment and Motion: A Comparative Analysis.

Radiographic measurements from spinal radiographs are crucial in many diagnostic and therapeutic decisions. However, widely used manual line drawing techniques in DICOM viewers are associated with significant errors, partly due to the unreliability of DICOM scale factors. A recently developed algorithm has been engineered to scale radiographs using assumed vertebral endplate widths (EPWs). Use of EPW to scale radiographs can eliminate the need to determine image magnification. This study was designed to (1) quantify the measurement error associated with the standard of care DICOM scale factor and (2) evaluate the efficacy of the EPW scaling algorithm. Previously collected cervical and lumbar lateral radiographs with a calibration marker of known size were used to collect radiographic measures of spinal alignment and spinal motion. Three different scale factors were used to acquire mm-based measurements: (1) the ground truth scale factor; (2) the DICOM scale factor; and (3) the EPW scale factor. DICOM and EPW scaled measurements were compared with respect to ground truth measurements. The DICOM scaled radiographic measurements demonstrated significantly more error compared to the EPW scaled radiographic measurements across multiple X-ray types: 19.6% vs. 9.7% in cervical neutral lateral (p < 0.001), 19.8% vs. 9.9% in cervical flexion/extension (p < 0.001), 35.0% vs. 7.5% in lumbar neutral lateral (p < 0.001), and 35.7% vs. 7.7% in lumbar flexion/extension (p < 0.001). The EPW algorithm provides adequate scaling accuracy for many clinical applications and is associated with considerably lower error than traditional DICOM scaled measurements. Clinicians should be aware of the potential scale factor inaccuracies in their imaging and be cautious when making diagnostic and therapeutic decisions based on improperly scaled radiographs.