Letter to the Editor on “Augmented Reality Based Navigation for Computer Assisted Hip Resurfacing: A Proof of Concept Study”

Abstract

To the Editor, I read with great interest the article ‘‘Augmented Reality Based Navigation for Computer Assisted Hip Resurfacing: A Proof of Concept Study’’. In the paper, the authors propose an augmented reality (AR) based surgical navigation system for hip resurfacing. The ambition of the work is to conceive a solution that can overcome the limits of traditional image-guided surgery (IGS) systems thanks to the advantages offered by a commercial optical see-through (OST) AR visor (i.e., Microsoft Hololens). Thereby, I would like to open a productive discussion concerning some of the technical and human-factor flaws that still hinder the adoption of OST head-mounted displays (HMDs) in IGS. First and foremost, the authors should be complemented for their pioneering procedure, which combines a markerless image-to-anatomy registration, yielded by depth sensing technology and robotic assistance, with an ergonomic AR visualization. The emerging of modern medical imaging technologies together with the need to reduce the invasiveness of the surgical procedures is increasingly encouraging the research for new 3D visualization modalities that could act as tools for diagnosis and surgical guidance. Nevertheless, standard IGS systems have a few pitfalls that hinder their profitable integration into the surgical workflow: they generally increase the surgical time needed for system setup and management, they increase the technical complexity of the surgical procedure, they limit the surgeon’s depth perception, and they arise problems of eye-hand coordination. For this reason, I entirely support the authors’ claim that visual AR technology could represent a significant breakthrough in IGS, as it is capable of providing the surgeon with the ability to access the radiological images and surgical planning contextually to the real patient anatomy (e.g., in situ). Wearable AR systems based on HMDs particularly offer the most ergonomic and reliable solution for aiding those surgical tasks manually performed under the surgeon’s direct vision since they preserve the user’s egocentric viewpoint and smoothly augment the visual perception of the working area. AR HMDs have gained significant interests in recent years and stimulated the technological growth for a broad range of consumer applications. In AR HMDs, the see-through capability can be accomplished either through the video seethrough (VST) or through the OST paradigm. In binocular VST HMDs, the view of the real world is mediated by a pair of stereo cameras rigidly anchored to the visor with an anthropometric interaxial distance. The stereo views of the world are presented onto the binocular micro displays of the HMD after being digitally blended with the virtual content. By contrast, in OST HMDs, the user’s direct view of the world is mostly preserved. As stated by the authors, this aspect confers a clear advantage over VST solutions, particularly when used to interact with objects in the intimate space, since it allows the user to maintain almost unaltered his/her own natural visual experience. The OST paradigm in HMDs is fundamentally still the same as described by Benton back in 2001 and successfully proposed in a wide range of commercial AR visors. The user’s own view is augmented by rendering the virtual content on a two-dimensional (2D) micro display and by sending it to an optical combiner. Enlarging optics are placed between the combiner and the display to focus the virtual 2D image so that it is perceived at a comfortable viewing distance on a semitransparent surface of projection. Although OST HMDs are, to this day, at the leading edge of the AR research, mass adoption is still far Address correspondence to Fabrizio Cutolo, Department of Information Engineering, University of Pisa, Pisa, Italy. Electronic mail: [email protected] Annals of Biomedical Engineering, Vol. 47, No. 11, November 2019 ( 2019) pp. 2151–2153 https://doi.org/10.1007/s10439-019-02299-w BIOMEDICAL ENGINEERING SOCIETY