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Current computer-assisted orthopedic surgery (CAOS) systems typically use preoperative computed tomography (CT) and intraoperative fluoroscopy as their imaging modalities. Because these imaging tools use X-rays, both patients and surgeons are exposed to ionizing radiation that may cause long-term health damage. To register the patient with the preoperative surgical plan, these techniques require tracking of the targeted anatomy by invasively mounting a tracking device on the patient, which results in extra pain and may prolong recovery time. The mounting procedure also leads to a major difficulty of using these approaches to track small bones or mobile fractures. Furthermore, it is practically impossible to mount a heavy tracking device on a small bone, which thus restricts the use of CAOS techniques. This article presents a novel CAOS method that employs 2D ultrasound (US) as the imaging modality. Medical US is non-ionizing and real-time, and our proposed method does not require any invasive mounting procedures. Experiments have shown that the proposed registration technique has sub-millimetric accuracy in localizing the best match between the intraoperative and preoperative images, demonstrating great potential for orthopedic applications. This method has some significant advantages over previously reported US-guided CAOS techniques: it requires no segmentation and employs only a few US images to accurately and robustly localize the patient. Preliminary laboratory results on both a radius-bone phantom and human subjects are presented.

Purpose: Ultrasound section-thickness is the out-of-plane beamwidth causing major roles in creating image artifacts normally appearing around the anechoic areas. These artifacts can introduce errors in localizing the needle tips during any ultrasound-guided procedure. To study how section-thickness and imaging parameters can affect observing and localizing needle tips, we have conducted a typical calibration setup experiment. Method: Multiple needles were inserted orthogonal to the axial image plane, at various distances from the transducer. The experiment was conducted on a brachytherapy stepper for a curvilinear transrectal-ultrasound probe. Result: Experiments demonstrated that the imaging parameters have direct impacts on observing needle tips at different axial locations. They suggest specific settings to minimize the imaging artifacts. Conclusion: The ultrasound section-thickness and side lobes could result in misjudgment of needle insertion depth in an ultrasound-guided procedure. A beam profile could assist in considering the likelihood of position errors, when the effects of side lobes are minimized.

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