Image Correlation Between Digitally Reconstructed Radiographs, C-arm Fluoroscopic Radiographs, and X-ray: A Phantom Study

Sebastian Wangler; Janic Hofmann; Helen L Moser; Michael Kuenzler; Rainer J Egli; Michael Schaer

doi:10.7759/cureus.51868

Image Correlation Between Digitally Reconstructed Radiographs, C-arm Fluoroscopic Radiographs, and X-ray: A Phantom Study

Cureus. 2024 Jan 8;16(1):e51868. doi: 10.7759/cureus.51868. eCollection 2024 Jan.

Authors

Sebastian Wangler¹, Janic Hofmann¹, Helen L Moser¹, Michael Kuenzler¹, Rainer J Egli², Michael Schaer¹

Affiliations

¹ Orthopaedic Surgery and Traumatology, Inselspital, Bern University Hospital, University of Bern, Bern, CHE.
² Diagnostic, Interventional, and Paediatric Radiology, Inselspital, Bern University Hospital, University of Bern, Bern, CHE.

Abstract

Objective: Digitally reconstructed radiographs (DRRs) are planar two-dimensional (2D) X-rays derived from a three-dimensional (3D) computed tomography (CT) dataset. DRRs allow the simulation of radiographs of all desired views and facilitate preoperative planning. However, orthopedic surgeons rely on C-arm fluoroscopic imaging during surgery to verify fracture reduction and implant placement. Pincushion distortion represents a technical limitation of fluoroscopic imaging, resulting in a greater distance between points at the periphery of the image compared to the center. This project, therefore, aimed to assess the image correlation between digitally reconstructed radiographs (DRRs) and fluoroscopic imaging (C-arm) using conventional radiographs (X-ray) as a control.

Methods: A 3D-printed cubic prototype and an anatomical humerus bone model were used. C-arm fluoroscopic radiographs and conventional X-ray images were taken in an anteroposterior (AP) view at 10-degree steps while rotating the objects from 0 to 90 degrees. CT scans were made and used to compute and export DRRs in AP view at 10-degree rotational steps from 0 to 90 degrees. The surface area (cm²) was measured and compared between the different modalities. For automated image analysis of the anatomical humerus model, matching (%) between modalities was calculated using the structural similarity index (SSIM).

Results: The overall regression was statistically significant in all models, with an R² >0.99 when comparing all three imaging modalities of the prototype. Surface correlation in the anatomical humerus model was R² 0.99 between X-ray and C-arm and R² 0.95 between C-arm and X-ray to DRRs, respectively. The SSIM was highest for comparing DRR and C-arm images (0.84±0.01%).

Conclusions: The study indicates a strong agreement between digitally reconstructed radiographs and X-ray/C-arm images. DRRs, therefore, represent a valuable tool for research and clinical application.

Keywords: c-arm; ct; digitally reconstructed radiographs; drr; phantom study.