Case study evaluating two positioning aids

Head immobilization during fMRI with
galvanic vestibular stimulation
Prof. Peter zu Eulenburg, Ludwig Maximilian University Munich, 2017

BackgroundIn neuroradiology, head movement during MRI is a significant issue. Uncooperative patients, challenging examination positions and lack of time to achieve correct
patient immobilization often lead to movement artifacts.
If imaging sequences contain artifacts it is more difficult to analyze the results and there is potential formisdiagnosis.
A variety of positioning aids are currently used to minimize head movement. This case study at the Ludwig
Maximilian University in Munich examined the effect ofusing two different positioning aids on optimal head
immobilization during fMRI.

In galvanic vestibular stimulation, the vestibular apparatus which controls balance is artificially stimulatedusing an electric current so the subject perceives theirhead to be shaking from side to side. The subject thenswiftly and reflexively attempts to counteract this sensation by moving the head inside the coil.
The results were evaluated after the procedure to assess the movement permitted in the three different
planes (transverse, frontal, saggital) and the extent of
cumulative positional change by the subjects during
the sequences was compared for the two different positioning aids.

Movement profile for conventional foam

Objective
In this study, the Pearltec positioning system was compared with conventional foam cushioning for head immobilization. The aids were used to immobilize the head
during vestibular fMRI in order to evaluate the extent towhich each aid was able to suppress head movement
and to improve the analysis of the results.

Material and Methods
10 subjects underwent an fMRI scan during which theyexperienced galvanic vestibular stimulation (3T Siemens Verio, Erlangen, Germany; 32-channel head coil).
Head immobilization was achieved using conventionalfoam cushioning or the Pearltec positioning system.

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Fig. 1: Spatial resolution improved from 5.6 mm to 4.9 mm and theaverage positional shift from one image to the next decreased byalmost 40% from 0.17 mm to 0.105 mm.

info@pearl-technology.ch
www.pearl-technology.ch
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ResultsConclusion

It was found that immobilization using the Pearltec positioning system resulted in significantly better image
quality and improved signal exploitation. The signal-to-noise ratio increased by 20%, spatial resolution
improved from 5.6 mm to 4.9 mm and the average positional shift from image to image within a sequence
decreased by almost 40% from 0.17 mm to 0.105 mm.

With the Pearltec positioning system, the dominant movement could be almost fully suppressed in the threeplanes, which led to an improvement in image quality
and better resolution in the measurement of brain activity. In particular, artifacts induced by movement responses to artificial stimulation could be suppressed,
which significantly improved the fMRI signal.

BOLD-localization conventional foam

BOLD-localization Pearltec

Fig. 2: More precise and significant localization of BOLD signals in
the cerebral cortex during fMRI investigation using the Pearltec positioning system to immobilize the head.

About Pearltec
Positioning System
The patented technology was originally developed inorder to create a positional aid for high-resolution pQCT
systems for rheumatoid arthritis patients and stands
out primarily due to its high level of flexibility, evenly distributed pressure and adaptive immobilization. It wasdeveloped in collaboration with the Zurich Federal Institute of Technology (ETH).
The technology, which is available in a variety of product versions, reliably suppresses movement, is easy
to clean and provides a high level of patient safety andcomfort.