# Portable RGB-D Camera-Based System for Assessing Gait Impairment Progression in ATTRv Amyloidosis
## 4 Discussion  
Regarding the conformity between the RGB-D camera-based system and the reference system, they were in agreement in most cases for spatiotemporal parameters (65%) and only in some cases for kinematic parameters (38%). These results were expected, since the validity of the Kinect for obtaining spatiotemporal parameters is better when compared with kinematic parameters, according to previous studies with healthy subjects [49] and ATTRV amyloidosis patients [50]. The lower agreement between systems concerning kinematic gait parameters may be explained by the fact that the computation of angle measures involves three joints (most measures used for spatiotemporal involve only one joint) and depends on the relative position of those joints in relation to each other. For these reasons, errors in joint position estimation are expected to have a greater negative impact on the computation of kinematic rather than spatiotemporal gait parameters. Different factors can contribute to the Kinect not being as accurate as the reference system, including a low variable frame rate (\(\approx\)30 Hz) and, in the particular case of our study, the use of a single camera. Using a single camera can lead to occlusions and variable estimation accuracy depending on the subject's distance to the camera (this distance varied during our acquisitions). Although multiple cameras could mitigate some of these problems, it would compromise our goal of achieving a low-cost and easy-to-set-up system that is suitable for use in clinical settings. Another possible reason for lower accordance in the case of kinematic parameters is that the used Kinect configuration (frontal plane view) may not be the most adequate for obtaining accurate kinematic parameters. [PERSON] et al. showed that lower limb angle measures can be obtained with modest accuracy if the Kinect is positioned at a 45\({}^{\circ}\) angle to the longitudinal walking plane [30]. On the other hand, [PERSON] et al. carried out preliminary experiments with different Kinect angles but did not reach any conclusion regarding the best position to obtain particularly accurate kinematic data [36]. Therefore, further studies are needed to investigate whether there is an optimal configuration of the Kinect for obtaining kinematic gait parameters. When considering spatiotemporal parameters, it is possible to see that there was full agreement (i.e., for all patients) between systems for the stride duration, gait speed, and arm swing velocity, and accordance for all patients except one in the case of stride length and foot swing velocity. For gait speed variability, the systems were in accordance for four out of the six patients. There was no accordance for half or more patients in the case of the step, swing, single support and double support duration, step length and width, and TBCM-ML and TBCM-V sway. Concerning the kinematic parameters, spine shoulder angle, and maximum and minimum elbow angles presented the best results (accordance between systems for half of the patients). All other kinematic parameters showed agreement for two patients, except the spine middle angle for which systems were in accordance only for patient P2. It is interesting to note that the six most reliable gait parameters (stride duration, gait speed, arm swing velocity, stride length, foot swing velocity, and gait speed variability) show an almost perfect strength of agreement between systems. Therefore, these parameters can potentially be used to support the clinical gait assessment of ATTRv amyloidosis patients during the course of the disease.