Optimal Measurement Height and Validation of a 2D-Light Detection and Ranging Device-Based Analysis System for Spatiotemporal Gait Parameters

Article information

J Mov Disord. 2024;17(4):459-461

Publication date (electronic) : 2024 August 21

doi : https://doi.org/10.14802/jmd.24134

Seungki Woo^1,2,*, Chaewon Shin^3,*,, Min Young Kim^1,2,

¹School of Electronics Engineering, Kyungpook National University, Daegu, Korea

²Research Center for Neurosurgical Robotic System, Kyungpook National University, Daegu, Korea

³Department of Neurology, Chungnam National University Sejong Hospital, Chungnam National University, Sejong, Korea

Corresponding author: Min Young Kim, PhD School of Electronics Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Korea / Tel: +82-53-950-7233 / Fax: +82-53-950-5505 / E-mail: minykim@knu.ac.kr

Corresponding author: Chaewon Shin, MD, PhD Department of Neurology, Chungnam National University Sejong Hospital, Chungnam National University, 20 Bodeum 7-ro, Sejong 30099, Korea / Tel: +82-44-995-4751 / Fax: +82-44-995-5597 / E-mail: chw.shin@cnu.ac.kr

*These authors contributed equally to this work.

Received 2024 June 14; Revised 2024 August 8; Accepted 2024 August 21.

Dear Editor,

Gait disorders increase with age, accounting for 30% of the total older population and more than 60% of the people over 80 years of age [1]. Gait disorders increase the risk of falling, affect mobility and general conditions, decrease the quality of life of patients and caregivers, and shorten the life of older individuals [2,3]. Light detection and ranging (LiDAR) is a method for determining the distance by targeting an object with a laser and measuring the time of reflection to the receiver. A LiDAR device has the potential to be used as an accurate and portable gait analysis instrument because of its small size and accuracy. Several studies have been conducted to develop a gait analysis system using a LiDAR sensor [4-7]. However, some studies have developed only gait analysis algorithms, whereas others have validated longitudinal spatiotemporal gait parameters without horizontal parameters, such as the step width.

The measurement height of a 2D-LiDAR sensor (GL-310; SOSLAB Co., Gwangju, Korea) is an important factor that influences gait parameters. Intuitively, the lowest height would be the best because spatiotemporal parameters are generated based on the position of the soles of the feet. However, the LiDAR scan can be affected by the shape of the feet or shoes or interrupted by ground objects. To date, there have been no comparative studies regarding the measurement height of the LiDAR sensor. Therefore, this study aimed to validate a 2D-LiDAR-based gait analysis system with a reference system. In addition, the optimal height for the measurement of human gait via the 2D-LiDAR sensor was analyzed.

We compared the gait parameters between the 2D-LiDAR gait analysis system and the reference gait analysis system (GAITRite^®; CIR Systems, Inc., Franklin, NJ, USA) while simultaneously changing the height of the 2D-LiDAR sensor to 10, 12, 14, 16, and 18 cm. Spatiotemporal parameters such as the step length, stride length, step width, and step time were extracted from the two gait analysis systems. The agreement between the parameters was evaluated via the intraclass correlation coefficient (ICC). The detailed methods are described in the Supplementary Material and Supplementary Figure 1 (in the online-only Data Supplement).

Seven healthy adults voluntarily participated in this study (Supplementary Table 1 in the online-only Data Supplement). The Bland‒Altman (BA) plots and scatter plots of the step length, step width, and stride length at each measurement height are presented in Supplementary Figures 2 and 3 (in the online-only Data Supplement). The step time was not presented in the plots because the measurement time of the LiDAR gait analysis system was not continuous, as the resolution limit was 20 Hz. Although there were some outliers, all the parameters agreed appropriately at all the heights in the BA plot. Moreover, all the parameters showed clear linear correlations in the scatter plot.

Table 1 summarizes the mean values, absolute errors, and ICCs of the four parameters at each measurement height of both the LiDAR system and the reference gait analysis system. In the cases of the step length and stride length, very good ICC values of 0.9 or greater were obtained, regardless of the measurement height. However, clear differences were found for the step width. At a measurement height of 10 cm, a satisfactory ICC value of 0.934 (95% confidence interval [CI] 0.882–0.960) was calculated, but as the height increased, the ICC gradually decreased. At a height of 18 cm, only a moderate ICC value of 0.486 (95% CI -0.031–0.819) was calculated. The absolute error was as small as 0.84 ± 0.63 cm at a measurement height of 10 cm but gradually increased to 3.72 ± 1.00 cm at a height of 18 cm. In the case of the step time, the ICC values were moderate at all the measurement heights.

Table 1.

Comparison and concurrent validity of gait parameters between proposed LiDAR gait analysis system and reference system

In this study, the optimal measurement height was confirmed to be 10 cm, which was the lowest. The spatiotemporal parameter that showed the greatest difference among the measurement heights was the step width, which increased significantly as the height increased. This can be explained anatomically by the fact that the center point of the higher height of the LiDAR scan was in the lower calf area, whereas the center point of the measurement height of 10 cm was at approximately the ankle level, which is more similar to the position of the feet in the reference gait analysis system. Because even higher measurement heights showed good agreement in the BA plots (Supplementary Figure 2 in the online-only Data Supplement), the absolute error could be corrected by a simple calculation, if needed. However, 10 cm is still a good option if the environment allows since the calf area may be affected by the muscle volume, which is related to sex and age. Therefore, the use of 10 cm is generally recommended. Only if a measurement at 10 cm is not feasible, would a step width at 12–16 cm be considered. The use of the step width data at a measurement height of 18 cm is not recommended.

In the cases of the step and stride lengths, good agreement was shown regardless of the measurement height. The measurement height can be increased if the users do not need step width data. Depending on its use, the LiDAR system can be simply installed as a portable gait analysis system, such as a portable camera with a tripod.

In a previous study, Iwai et al. [6] compared the spatiotemporal parameters of a gait analysis system with those of GAITRite^® as the gold standard. The ICC values obtained in their study were as follows: for the stance time = 0.74; double support time = 0.56; stride time = 0.89; stride length = 0.83; step length = 0.71; and swing time = 0.23. Fudickar et al. [7] developed a chair that could perform timed up and go tests via a LiDAR sensor and validated the spatiotemporal parameters with GAITRite ® . Gait parameters such as the velocity, cadence, step length, and stride length exhibited good correlation coefficients of 96%–99%. The results of the current study were much better than those of Iwai et al. [6] and similar to those of Fudickar et al. [7] These results can be explained by the following reasons. There is a difference in the angular resolution between LiDAR sensors. The sensors used in the previous studies had 0.25-degree intervals, whereas the sensors employed in this study had 0.18-degree intervals, allowing for more precise measurements. With respect to the software, direct comparisons are not possible because the previous studies did not provide detailed analysis algorithms. However, we meticulously removed the noise from the raw LiDAR data and applied data clustering techniques to obtain meaningful data. This analytical algorithm may have contributed to obtaining more accurate data. Moreover, this study validated the step width, which none of the previous studies has measured and validated.

Compared with the reference system, the 2D-LiDAR-based gait analysis system achieved very good results in measuring the length parameters. However, it is better to minimize the position of the LiDAR sensor as much as possible because of the step width. The optimal sensor height of a LiDAR-based gait analysis system should be determined to balance the advantages of the measuring accuracy and potential disadvantages of ground obstacles of a low height.