Augmented/mixed reality has many potential applications in the medical field. We sought to determine whether a mixed reality ruler capable of measuring the distance between a user’s fingers is sufficiently accurate for making measurements during clinical procedures. A custom virtual ruler application was deployed to the Microsoft HoloLens headset. The custom app calculates the linear distance between the user's fingers. The accuracy of the virtual ruler was tested under various conditions including room brightness and background textures. A set of wires of known length were measured with the virtual ruler. The accuracy of the virtual ruler was dependent on the measurement length. Measurements between 2-15 cm had an error less than 0.5 cm, between 15-30 cm had an error less than 1 cm, and between 30-50 cm had an error less than 1.6 cm. A mixed reality based hand-ruler is sufficiently accurate for making measurements during maximally sterile clinical procedures.
Augmented reality (AR) can enable physicians to “see” inside of patients by projecting cross-sectional imaging directly onto the patient during procedures. In order to maintain workflow, imaging must be quickly and accurately registered to the patient. We describe a method for automatically registering a CT image set projected from an augmented reality headset to a set of points in the real world as a first step towards real-time registration of medical images to patients. Sterile, radiopaque fiducial markers with unique optical identifiers were placed on a patient prior to acquiring a CT scan of the abdomen. For testing purposes, the same fiducial markers were then placed on a tabletop as a representation of the patient. Our algorithm then automatically located the fiducial markers in the CT image set, optically identified the fiducial markers on the tabletop, registered the markers in the CT image set with the optically detected markers and finally projected the registered CT image set onto the real-world markers using the augmented reality headset.The registration time for aligning the image set using 3 markers was 0.9 ± 0.2 seconds with an accuracy of 5 ± 2 mm. These findings demonstrate the feasibility of fast and accurate registration using unique radiopaque markers for aligning patient imaging onto patients for procedural planning and guidance.
Augmented reality (AR) can be used to visualize virtual 3D models of medical imaging in actual 3D physical space. Accurate registration of these models onto patients will be essential for AR-assisted image-guided interventions. In this study, registration methods were developed, and registration times for aligning a virtual 3D anatomic model of patient imaging onto a CT grid commonly used in CT-guided interventions were compared. The described methodology enabled automated and accurate registration within seconds using computer vision detection of the CT grid as compared to minutes using user-interactive registration methods. Simple, accurate, and near instantaneous registration of virtual 3D models onto CT grids will facilitate the use of AR for real-time procedural guidance and combined virtual/actual 3D navigation during image-guided interventions.
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