A team St Mary’s Hospital in London, have used Microsoft HoloLens headsets while operating on patients undergoing reconstructive lower limb surgery for the first time.
The HoloLens is a self-contained computer headset that immerses the wearer in “mixed reality” by displaying interactive holographic graphical objects on a visor.
The team, from Imperial College London, used the headsets to overlay images of CT scans – including the position of bones and key blood vessels – onto each patient’s leg, in effect enabling the surgeon to “see through” the limb during surgery.
According to the team trialling the technology, the approach can help surgeons locate and reconnect key blood vessels during reconstructive surgery, which could improve outcomes for patients.
Dr Philip Pratt, a research fellow in the Department of Surgery and Cancer and lead author of the study, said: “We are one of the first groups in the world to use the HoloLens successfully in the operating theatre.
“Through this initial series of patient cases we have shown that the technology is practical, and that it can provide a benefit to the surgical team. With the HoloLens, you look at the leg and essentially see inside of it. You see the bones, the course of the blood vessels, and can identify exactly where the targets are located.”
Reconnecting blood vessels
Reconstructive surgery often requires the use of tissue taken from elsewhere on the body, including the skin and blood vessels, which are used to cover the wound and enable it to close and heal properly.
A vital step in the process is connecting the blood vessels of the ‘new’ tissue with those at the site of the wound, so oxygenated blood can reach the new tissue and keep it alive.
The standard approach for reconstructive surgery has been the use of a handheld scanner which uses ultrasound to identify blood vessels under the skin by detecting the movement of blood pulsing through them, enabling the surgeon to approximate where the vessels are and their course through the tissue.
“Augmented reality offers a new way to find these blood vessels under the skin accurately and quickly by overlaying scan images onto the patient during the operation,” said Dr Pratt.
In the procedures used to trial the technology, five patients requiring reconstructive surgery on their legs underwent CT scans to map the structure of the limb, including the position of bones and the location and course of blood vessels.
Images from the scans were then segmented into bone, muscle, fatty tissue and blood vessels and loaded into intermediary software to create 3D models of the leg.
These models were then fed into specially designed software that renders the images for the HoloLens headset, which in turn overlays the model onto what the surgeon can see in the operating theatre. Clinical staff are able to manipulate these AR images through hand gestures to make any fine adjustments and correctly line up the model with surgical landmarks on the patient’s limbs, such as the knee joint or ankle bone.
However, researchers have highlighted potential limitations of the technology, which could include errors during the modelling stages as well as the potential for the overlaid model to be misaligned.
In addition, the case studies so far have been based on the leg, which has a number of clearly visible surgical ‘landmarks’, such as the ankle or knee. Areas without these rigid landmarks, such as abdomen, may be more complicated with a greater potential for movement of blood vessels.
Dr Pratt added: “In the future we hope to automate the process further. We can use software to improve the alignment and will attach markers to the patient when they have the scan, with the same markers present during the operation to use as additional points of reference.
“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 theatre.”
‘Through the HoloLens looking glass: augmented reality for extremity reconstruction surgery using 3D vascular models with perforating vessels’ by Philip Pratt et al. is published in the journal European Radiology Experimental.