Comparison of Instrumented Mouthguard Post-Processing Methods

Abstract

Instrumented head acceleration measurement devices are commonly used in research studies to determine head acceleration exposure in certain populations. Instrumented mouthguards pair directly to the user's teeth and offer six-degree-of-freedom measurements. Though many studies have recently used these devices, post-processing techniques vary by study. Other studies have attempted to label impact quality or coupling status, also with varying methods. This study sought to compare the effect of post-processing and labeling methods on reported exposure distribution characteristics in instrumented mouthguard data from ice hockey players. We collected data from 18 female adolescent ice hockey players on two teams for an entire season. We then post-processed the measured signals using five different techniques: (1) the instrumented mouthguard manufacturer's data output, (2) a 500 Hz linear acceleration filter and a 300 Hz angular velocity filter, (3) HEADSport, (4) a 100 Hz linear acceleration filter and a 175 Hz angular velocity filter, and (5) a salvaging process to detect and remove decoupling based on signal frequency content. The post-processing techniques affected the reported exposure distributions by changing the mean, median, and 95th percentile values of peak linear and angular kinematics. We also compared labeling techniques by measuring agreement and inter-rater reliability between three labeling techniques: the instrumented mouthguard manufacturer's label, Luke et al.'s coupling label, and our classification learner that detects and labels decoupling. We found that the labeling techniques had low agreement about which acceleration events were the best to keep. Labeling technique also influenced the reported distributions' descriptive statistics. Post-processing and event labeling are crucial components of head acceleration event exposure studies. Methods should be described by researchers, and standardization should be sought to allow for better cross-study comparison. Published and publicly available techniques can help move the field toward this ideal. Researchers should be aware of the potential effect post-processing can have on a population's final reported exposure metrics.

Keywords: Artifact; Head impact; Instrumented mouthguard; Labeling; Post-processing; Salvage.

Fig. 1.

Instrumented mouthguard and example signal generated during an accelerative event.

Fig. 2.

Flowchart for our Salvaging method for measured head acceleration events. The Salvaging method consisted of wavelet denoising when decoupling was detected. [24]

Fig. 3.

Overall distributions of iMG-measured acceleration events using different post-processing techniques. Noticeable differences in distribution characteristics, such as mean and scatter, can be observed between the tested post-processing techniques.

Fig. 4.

Scatter plots for each post-processing method against each other, with ordinary least products regression lines, equations, and Pearson correlation coefficient. Severe disagreement in high severity events were seen between the tested techniques. PLA peak linear acceleration.

Fig. 5.

Peak linear acceleration distributions for all impacts in the highest quality category for each labeling technique. Distribution shapes and statistics differed from the original distribution and one another based on which labeling technique was used to select the “best” acceleration events to keep.