Augmented reality amplifies X-ray images to help surgeons

Approach quickly produces 3-D images that speeds procedures, aids surgeon performance, says Mathias Unberath.

Adding augmented reality to some minimally invasive surgeries can guide the procedures and reduce the number of images needed, according to a new study in the Journal of Medical Imaging.

The study specifically looked at orthopedic surgery, which is often performed through a patient’s skin with small incisions, requiring the use of imaging. The standard imaging technique uses fluoroscopic imaging provided by a C-arm device displaying two-dimensional X-rays to the surgeon on a separate monitor.

However, this technique requires many X-rays for the surgeon to estimate a 3-D image of the patient’s anatomy, and it leaves the surgeon blind in between image acquisitions.

The researchers, from Johns Hopkins University, hypothesized that co-calibrating an optical see-through head-mounted display with the C-arm could render the 2-D X-rays as virtual objects in 3-D to provide surgical guidance. It would be combined with an AI marker projected on the patient for mapping purposes that the C-arm and the head-mounted display would detect. The augmented reality technology would stream interoperative images from the C-arm to the head-mounted display being worn by the surgeon and visualized using a virtual monitor.

The researchers used the ARToolKit, the open source software library for building AR applications to create and calibrate the marker and created a guidance system that connected the C-arm to the head-mounted display, enabling them to recalibrate on the fly. The surgeon would need to take only a few steps to obtain the augmented reality guidance, such as introducing the marker and positioning the C-arm.

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The researchers then simulated orthopedic procedures using the system. The accuracy of the AR system was comparable to the traditional image-guided technique. The system reduced procedure time by almost 10 percent and required only 10 X-rays, compared with more than 90 using the conventional 2-D method. It also simplified the surgeon’s hand-eye coordination.

In addition, while the operating room needed a wireless data-sharing network to stream the images to the head-mounted display, the augmented reality guidance can be used in an “unprepared” environment; no additional hardware other than the head-mounted display on the surgeon, the marker and the X-ray machine is needed, according to Mathias Unberath, the study’s co-author.

Medical augmented reality has been used before but has not been widely accepted. The systems work well but come at the cost of substantial disruptions to the surgical workflow because of complicated setup and calibration, line-of-sight problems and potential increase in procedure time, Unberath says.

“AR guidance must integrate as seamlessly into the surgical workflow as possible to promote wide acceptance among surgeons and thus make a difference. The system proposed [by us] … is one step in this direction,” he says. Next steps include bringing in pre-operative 3-D images, since the system only provides sparse virtual content because of its design, says Unberath.

“In addition to this, we realize that current (head-mounted display-based augmented reality) is not yet sufficiently immersive, which is one of the major challenges future work will have to address,” he says.

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