Neuroscience
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Objectively Assessing Sports Concussion Utilizing Visual Evoked Potentials
Chapters
Summary April 27th, 2021
A portable system capable of measuring steady-state visual-evoked potentials was developed and trialed on 65 amateur rugby players over 18 weeks to investigate SSVEP as a potential electrophysiological biomarker for concussion. Players' baselines were measured pre-season, with retesting for reliability, concussion, and recovery assessment being conducted within controlled time-periods, respectively.
Transcript
A VEP is a type of quantitative electroencephalography signal that provides information related to brain health. This protocol provides initial feasibility data to support the Nurochek headset as an objective, portable, and accessible method for collecting data of this nature. This protocol enables fast and easy acquisition of VEPs at the point of care, with potential applications in various fields, without the need for a complex neurophysiological testing set up or highly skilled device operators.
To our knowledge, this is the first consumer device that allows this. The ability to collect VEPs using the Nurochek technology will allow clinicians to compare objective clinical findings in neurological function before and after injury or illness, during recovery, and longitudinally over the course of life. The system may be applicable to other diseases and conditions, and its relatively modest cost means that researchers can utilize it either alone or with other modalities to engage in low cost discovery.
The Nurochek system is straightforward and easy to use. The technology intuitively guides the user through the different steps of donning the technology, performing the necessary sensor checks for signal fidelity, and completing the assessment. Begin by fitting a charged LCD smartphone into a VR frame.
Generate an mp4 video file consisting of a sequence of black and white screens alternating at a frequency of 15 hertz for a total of 30 seconds. Place a random number in the center of the video frame, ensuring that the number is altered at five second intervals. Install the saturated sensors into the black plastic arms of the headset by gently turning each sensor clockwise until a click is felt and the sensor feels secure.
Completely saturate the supplied felt sensors with saline solution. Ask consented participants to be seated in a chair in a quiet enclosed environment with natural ambient light such an office room. While the participants are seated, fit the 14 channel EEG headset to the participant's heads by sliding the headband down fro the top of their head.
Arrange the electrodes according to the international 10-20 system. Position the two front sensors of the headset in line with the participant's hairline or roughly three finger widths above the participant's eyebrows. Ask the participants to hold the testing smartphone within the VR frame up to the eyes, flush against their faces and nasal bridge, ensuring both eyes are completely covered and confirming that the focal number is visible at the center of the screen and that the frame is blocking out environmental light.
Inform the participants that they are to focus on the focal number and remain still and quiet during the SSVEP testing. Initiate the visual stimulus video by pressing the play button on the smartphone screen. Then have the participants place the VR frame on their face in the correct position.
Begin a countdown stopwatch for 30 seconds. Then select the start recording button on the 14 channel EEG headset software to begin recording. Ensure that any impact on the field suspected to be a concussion is recorded and reported back to the study investigator by either the team physician or player.
Have the team physician perform a neurological exam in addition to using elements of the SCAT to determine the player's state of consciousness or the presence of any of the common signs and symptoms associated with concussion. Compare the mean SNR between all three assessment groups using paired T-tests for players who experienced all three types of assessments, ensuring that a multiple comparison correction is applied by utilizing a Bonferroni correction. Obtain a portable SSVEP system that contains a visual stimulus and electrode configuration as described in the text manuscript.
Generate subject accounts on the iOS application by following the IFU of the portable SSVEP system. Open the app, select the subjects tab, then press the add new subject button. Set up the SSVEP headset according to the IFU.
Fully charge the headset, then Bluetooth pair it to the SSVEP iOS application. Insert the supplied polyurethane sensor cylinders into the electrode channels and saturate them using normal saline solution. Place the SSVEP headset on the participant's head with the inferior of the rear housing unit situated directly above the participant's inion, the front visor housing placed securely over their eyes and nasal bridge, and the headset tightened via the elastic adjustment straps and securing buckles.
Check the SSVEP iOS application's impedance green indicator to ensure an adequate connection between the headset and the participant's head before testing. Ensure that the participant is comfortable and instruct them to remain still, calm, and quiet while seated, and gazing forward into the lights, and to only blink when required. Initiate the visual stimulus by pressing the begin test button on the iOS application.
When prompted, press the continue button to move to the next stage of testing. Following completion of the SSVEP assessment, remove the SSVEP headset from the participant's heads. Allow the subjects to relax for a minimum of 30 seconds.
To obtain a test retest reliability value, repeat the SSVEP assessment protocol with the SSVEP system after a rest period. Allow the participants to rest for five minutes before proceeding with the next EEG system. Once the pair of SSVEP assessments have successfully completed, have the participant remove the front visor from their eyes and carefully detach the electrode patches from their scalp.
Ask the participant whether they experienced any abnormal reactions to the stimulus, including the presence of a headache or dizziness. Record their responses in a study log before informing them they have completed their participation in the study. Download the raw SSVEP values of both SSVEP primary test sets from the iOS device using a mobile management utility software outputted as comma separated value files.
Save the files using the name and date. Use the SNR of each SSVEP reading to compare the results of the different tests, and estimate test retest reliability. Outline the criteria for determining whether an SSVEP was detected by the EEG system as described in the text manuscript.
Create a PSD of both system's normalized average SNR results between zero and 25 hertz. Participant's hair or skin potentially impact the EEG system's ability to obtain clean SSVEP, which was corrected by using saline saturated electrodes. The average SSVEP values of a separate control group produced by the same visual stimulus but recorded with a different EEG system were graphed as a PSD, which allowed for a clear control to be set for a SSVEP response of a non-concussed player to the investigative setup.
The all-in-one portable SSVEP system was also used on healthy control subjects from the general population, non-specified to the sport of rugby with a different electrode system and slightly varied stimuli from the initial SSVEP setup. Hence, their median and average SNR values were not valid for comparison. Additionally, the accuracy of the system's EEG technology was validated through an agreement study against a traditional clinical grade EEG system, which returned a similar ICC value of 0.83.
The PSD of a single control participant's SSVEP response was measured by the SSVEP system and the clinical EEG system. In second repetition, the overall accuracy of the two systems to produce an SSVEP depicted that both systems have a prominent SNR solely at the 15 hertz frequency. Proper positioning of the Nurochek headset on the subject is critical to obtain a clean reading.
And if you have any issues, the system is so simple that repeating the reading is seldom a problem. Following the development of Nurochek with its ability to take the recording of visual evoked potentials from the distant realms of a major hospital, several neurological conditions of patients can be tracked before and after injuries, and their progress can be followed for years.
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