Overlaying three-dimensional holograms on its wearer's view of the real world, Microsoft's HoloLens augmented reality headset has allowed users to do everything from reading emotions (sort of) to taking a virtual tour of Mars. More recently, it's also been used to guide British doctors performing lower limb surgery.

The headset was used by a team from Imperial College London at St. Mary's Hospital, in procedures that were performed on five patients who required reconstructive surgery on their legs.

All of the patients first underwent CT scans, to obtain 3D images of the bones and blood vessels in the injured limb. When the HoloLens-wearing doctors were subsequently performing the surgery, those images were superimposed on their view of the leg – to them, it was as if they could actually see through the skin.

This was particularly helpful when they were transplanting flaps of skin and underlying tissue, which were taken from other parts of the body in order to cover open wounds on the leg. In this procedure, blood vessels within the transplanted tissue need to be connected to those at the wound site, in order to provide the flap with oxygenated blood.

Ordinarily, those wound-site blood vessels are located using a handheld ultrasound scanner. Using the HoloLens, however, the surgeons could more quickly and accurately find them, by actually seeing where they were within the leg.

The system works particularly well on body parts such as legs, because users can precisely align the CT scan image with the actual leg by matching up common "landmarks" such as the knee or ankle. While it might be more challenging when applied to wider areas such as the abdomen, this could be remedied by applying markers to the patient's body, that are present both when the CT scan is performed and when they're undergoing surgery.

The project was led by Dr. Philip Pratt, and is described in a paper that was recently published in the journal European Radiology Experimental. Plans now call for the technology to be trialled on a larger set of patients, in procedures carried out at multiple locations.

"There are a number of areas we would like to explore, and further improvements are needed, but the small case series has shown that for reconstructive surgery, this seems to be a valuable tool in the operating theater," say Pratt.

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