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Which tracking device to choose

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Victor Hugo Souza edited this page Mar 23, 2021 · 1 revision

This page is intended to help you choose a tracking device to purchase to neuronavigate with InVesalius Navigator.

What is a spatial tracking device?

A spatial tracker is a devices that measures the spatial coordinates of a sensor in space. The sensors can be attached to an object, like a pointer, a TMS coil, or a surgical instrument. By knowing the position of the object in space we can registrate with the medical images (CT and MRI) and make possible the image-guided navigation. A simple webcam, for instance, can detect a person's face and track its position in space. In surgical applications, specially connected to commercial software programs, the infrared cameras are the most common due to the possibility to use wireless sensors and disposable materials. Other technologies, such as electromagnetic and ultrasound tracking are also available in the market and can be used for a wide range of applications.

With InVesalius Navigator you can choose which spatial tracking devices suits better to your budget and application. Currently, we support devices from 3 different manufacturers, and the development of support for others are also possible and should be straightforward.

Which devices are supported and what are the pros and cons?

The characteristics herein presented are for the use of navigated transcranial magnetic stimulation (TMS), however, navigation for other applications are also possible.

Disclaimer: The authors declare no conflict of interest. No financial support was provided by any of the companies mentioned below and the authors received (or receive) no benefit due to the views expressed in this page.

  1. NDI Polaris is an infrared-based camera that tracks the reflective spheres mounted to some plastic object. It is the device that most commercial navigation software uses (Nexstim, Visor, BrainSight, and others).

  • Pros: wireless, very accurate and stable, you can make one tracking mount for each TMS coil and attach to it permanently, without needing to move the mount every time you work with a different coil.

  • Cons: The most expensive (it costs about US$ 15.000). Also, you have to buy new reflective spheres as they worn out with usage. Our team started to work with this tracker recently and the navigation with Polaris cameras is still under development.

  1. ClaroNav MicronTracker is another camera-based system which does not use cables to connect to the sensors (like the infrared cameras). MicronTracker tracks black and white patterns like QR codes, and not the reflective spheres.

  • Pros: like Polaris, it is wireless and allows one to make one tracking mount for each individual coil (if you have many). Using individual coil markers avoid registering the coil multiple times and saves time. The camera tracks these QR codes-like patterns which one can print at the office in a regular printer, so it is quite easy to make new tracking probes without any cost.

  • Cons: It is less expensive than the Polaris but still not the cheapest (price starting from US$ 10.000). Also, the quality of navigation depends on the lighting of the room, because it uses visible light (it’s like a webcam!), so depending on the marker arrangement and lighting conditions the navigation gets a bit more unstable (shaky).

  1. Polhemus is a different concept than the others, because it is an electromagnetic device. It emits radiofrequency waves from a source to the sensor that is attached to the TMS coil, or other tracked object. We provide support for Polhemus FASTRAK, Polhemus PATRIOT, and Polhemus ISOTRAK

  • Pros: it allows a quite stable navigation and is one of the cheapest available (about US$ 7.000). It is very portable also, you can easily transport from one room to another (the cameras requires better placement relative to the head as they have to “see” the marker to track it). Polhemus is not camera based, so you don’t have the problems of the camera not seeing the coil, which happens quite often in TMS. You can have the coil totally hidden behind the subject and the device still tracks it.

  • Cons: sensors are connected via cable to the unit. This might not be a big issue once the TMS coil is also connected by cable to the stimulator. Also, there is a limited number of sensors, so if you work with multiple TMS coils (circular, figure-of-eight etc) or multiple stimulators (Magstim, MagVenture, etc) you would need to move the sensor from one coil to another when you want to navigate in a different device. As it uses electromagnetic waves, when you give the TMS pulse, there is a “jump” in the navigation, but we are filtering this in the software, and soon, this won’t be visible anymore. Another issue is that too many ferromagnetic materials in the room (chairs, tables, structures, shelves, and so on) might strongly affect the quality of the navigation (sometimes making it impractical).

  1. Webcams: Comming soon!

We recommend you to check our recent research paper on the development and characterization of the InVesalius Navigator combined with different tracking devices for neuronavigation.

Finally, if you have any further questions, do not hesitate to contact us, we will be happy to help you. Here is a contact form.

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