Abstract
Purpose
Radiographs are the most common imaging modality used to guide orthopaedic interventions. Ultrasound (US) imaging offers potential advantages for intraoperative imaging by its portability and ability to produce real-time 2D or 3D images without radiation to either the patient or surgical team. Our objective in this study was to determine in a live emergency room setting, if a newly-developed image processing method for 3D US would allow us to accurately extract (reproduce) the surfaces of fractured bones.
Method
We obtained both CT scans and US images from consenting patients admitted to our Level 1 Trauma Centre for radius or pelvic fractures clinically requiring a CT scan. All US examinations in this clinical study were performed with a GE Voluson 730 machine with a 3D RSP5-12 transducer (a mechanized probe in which a linear array transducer is swept through an arc range of 20). Dorsal, volar, and radial views were obtained in the case of radial fractures and iliac crest views in the case of pelvic fractures.
The bone surfaces on CT were extracted using a thresholding algorithm [1]. Standard, clinical 3D reconstructions were also created using GE Voxtool 4.0.1 to serve as a qualitative comparison.
The US images were processed using the phase-processing algorithm described in [2] then registered to the CT images using a manually-supervised anatomical landmark-based rigid registration algorithm. The quality of the resulting surface matching was evaluated by computing the root mean square distance between the two surface representations [2] and by inter-observer agreement of the registered images to the clinical renderings.
Results
Overall, 8 patients were scanned (3 distal radius and 5 pelvic fracture). Quantitative and qualitative outcomes were recorded. The RMS surface fitting error averaged 0.41mm across the 8 patients, with a maximum point-wise error of under 1.0 mm. Qualitatively, clinicians demonstrated a high level of agreement in the ability of the 3D US surfaces to represent the clinical 3D CT reconstructions.
Conclusion
The RMS error in these 8 clinical cases was significantly lower than the threshold of 2–4 mm previously cited as useful for development of clinical fracture care applications in near-real time.
While US has some limitations that prevent it from completely replacing conventional radiography, it may minimize radiation following fracture reduction. The encouraging experimental results of this initial clinical study demonstrate the potential benefits of the proposed method; while, further investigation will define its potential opportunities and limitations.
