Coffee-filled tracking cap

Coffee-filled cap improves precision of tracking for surgery

Image credit: Joe Howell, Vanderbilt University

Engineers from Vanderbilt University in Nashville, Tennessee have developed a stretchy “granular jamming cap” filled with coffee grounds which improves the reliability of the tracking system that surgeons use for nose and throat operations.

Before these delicate procedures begin, surgeons perform “registration”, in which a scanner is used to map the location of reflective dots attached to the patient’s head. This allows a tracking system to observe the dots with a camera and identify the position of the patient’s head when the surgeon repositions it.

This information is used to compile a CT scan, which provides a real-time 3D view of the bone, soft tissue and surgical tools inside the patient.

“These are very delicate operations and a sophisticated image guidance system has been developed to help the surgeons, but they don’t trust the system because it is spot on and other times it is off the mark,” said Professor Robert Webster of Vanderbilt University, who is also developing a surgical robot for endonasal operations.

“When we heard about this, we began wondering what was causing these errors and we decided to investigate.”

The researchers found that these problems were being caused by the reflective markers slipping and being nudged during operations by up to half an inch. This requires the surgeon to repeat the registration process.

The Vanderbilt team decided to develop a non-invasive method to attach these critical markers firmly on the patient. Inspired by the use of vacuum-pumped bladders filled with coffee grounds – which have been used to help robots grip irregularly shaped objects – they decided to see if this could be applied to the problem.

They worked through several different designs, beginning with headbands filled with coffee grounds, before coming around to the elastic cap design. This fits tightly to the head, and can be covered all over with markers, increasing the efficiency of the system. It is filled with six cups of coffee grounds. The cap is attached to a vacuum pump, which jams the grounds together to form a rigid layer snug to the shape of the patient’s head. This is the same process that turns vacuum-packed coffee into solid bricks for transport.

In testing, the cap proved to be extremely effective, reducing targeting errors by 83 per cent.

 “It’s a very clever way – that doesn’t involve drilling holes in patient’s skulls – to greatly improve the accuracy of the guidance system when we are operating in the middle of a person’s skull: a zone where the accuracy of the current system is inadequate,” said Professor Paul Russell, who collaborated on the project at Vanderbilt University.

The researchers have applied for a patent on the design, and are presenting their design at the International Conference on Information Processing in Computer-Assisted Interventions in Barcelona.

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