Magnetic Motion Tracking

Clinical and Virtual Reality

Applications in Healthcare

Neil Schell

Director Business Development

Research and Technology Applications

Polhemus

Colchester, VT, USA

Boston VR Meetup

May 2015

46 Years of Motion Measurement

Started by Bill Polhemus in 1969.

First application was pilot head tracking for the U.S. military - something we still do today.

Over 26,000 Polhemus trackers in the field.

Most common applications:

Biomechanics

Training Simulators

Neuroscience

46 Years of Motion Measurement

This year marks the 20th anniversary of Pixar’s “Toy Story”, the first feature-length animated film.

Polhemus’ 3Space Digitizer was used extensively to digitize many of the characters.

Polhemus was awarded a Technical Achievement Award by the Academy of Motion Pictures that year (1995).

Typical Applications

Biomechanics

Physical Therapy & Rehabilitation

Virtual Reality

Neuroscience research

Motor Control research

Virtual Reality Training Simulators

Welding Simulator

Ultrasound Simulator

Industrial Sprayer Simulator

• All require 6DOF tracked objects (welding torch, ultrasound probe, spray gun) • Some require head tracking as well (welding helmet, and spray paint mask)

Tracker Challenges for High Fidelity Healthcare Sims:

Motion tracking accuracy must be at least that of the procedure being simulated; typically 1-2mm.

Must track position and orientation (full 6DOF).

Must not detract from the native appearance of the device or instrument (invisible/embedded is best).

Latency should be low, particularly if the VR is fully immersive. Latency > 20mS can cause motion sickness.

Independent of fidelity, it should be reliable, repeatable, cost effective, and easy to set up.

Motion Trackers for Simulators

How EM Tracking Works

Magnetic

source

Magnetic Field Lines

Magnetic

sensor

Electronics

unit

Uses the known physics of magnetic fields to compute the position and orientation of a magnetic sensor relative to a magnetic source.

No line-of-sight required (can be embedded)

Full 6DOF

High accuracy

Low latency

High update rate

No drift

Small, portable, reliable and easy to use

Why Use EM Trackers?

Range is limited by the size/strength of the magnetic field produced by the tracker’s source.

• For most training simulators this is not an issue, since the effective range of the magnetic field is on the order of 2 meters. The Polhemus G4 tracker has a range of up to 30 meters using multiple sources simultaneously.

Accuracy can be affected by close proximity to large metal objects.

• Small metal objects like fasteners, jewelry, etc. are not a problem.

• Instruments of medical grade stainless steel are generally not a problem.

• For large metal, keeping the distance between source/sensor small relative to surrounding metal solves this issue in most cases.

Limitations of EM Trackers

Challenge Teach physicians and clinicians to diagnose common and difficult cases using

ultrasound, without waiting for patients with those particular pathologies.

Solution CAE Healthcare’s Vimedix simulator uses Polhemus’ Patriot system for tracking

the 3D movement of the mock ultrasound probes.

Result Medical staff can now practice diagnosing both routine and extraordinary

pathologies on an anatomically correct training mannequin, versus OJT learning on real patients.

Case Study - VR Application

Ultrasound Simulator

Case Study - VR Application

Ultrasound Simulator

Video Courtesy of CAE Healthcare

Challenge

Give the surgeon “eyes” inside the patient’s anatomy for guiding surgical instruments.

Solution

Fastraktm position and orientation data overlaid in real-time on patient’s CT or MRI image.

Result

Improved ENT surgical

outcomes.

Case Study – Clinical

Image Guided Surgery

Originally developed for a cardiac catheterization training simulator. Other applications include:

• Finger tracking

• Head tracking

1.8mm diameter.

Full 6DOF.

Sub-millimeter

accuracy.

New MicroSensor 1.8

Rehabilitation 2.0

VRRS by Khymeia Group. – 3D, Virtual Reality Rehabilitation System

Combines Polhemus G4 motion tracker and rehabilitation specific software.

Fun, interactive app keeps patients motivated.

Much more than Wii Rehab

games. Prescribed, rehabilitation specific exercises are tailored for each patient.

With Polhemus 3D tracking, progress is accurately measured and recorded.

6DOF Tracker

Demo

Summary

Polhemus magnetic motion tracking technology is

enabling products and methods in both clinical and VR medical applications.

AC magnetic tracking delivers performance critical for VR such as sub-millimeter accuracy, full 6DOF, no line-of-sight occlusions, and low latency.

The new MicroSensor 1.8 enables catheter and needle insertion applications, as well as finger and head tracking.