Chest wall motion analysis in healthy volunteers and adults with cystic fibrosis using a novel Kinect-based motion tracking system

Med Biol Eng Comput DOI 10.1007/s11517-015-1433-1 ORIGINAL ARTICLE Chest wall motion analysis in healthy volunteers and adults with cystic fibrosis using a novel Kinect‑based motion tracking system James M. Harte1,2 · Christopher K. Golby1 · Johanna Acosta1 · Edward F. Nash3 · Ercihan Kiraci4 · Mark A. Williams4 · Theodoros N. Arvanitis1 · Babu Naidu3,5 Received: 3 July 2015 / Accepted: 11 December 2015 © The Author(s) 2016. This article is published with open access at Springerlink.com Abstract Respiratory disease is the leading cause of death in the UK. Methods for assessing pulmonary function and chest wall movement are essential for accurate diagnosis, as well as monitoring response to treatment, operative procedures and rehabilitation. Despite this, there is a lack of low-cost devices for rapid assessment. Spirometry is used to measure air flow expired, but cannot infer or directly measure full chest wall motion. This paper presents the development of a low-cost chest wall motion assessment system. The prototype was developed using four Microsoft Kinect sensors to create a 3D time-varying representation of a patient’s torso. An evaluation of the system in two phases is also presented. Initially, static volume of a resuscitation mannequin with that of a Nikon laser scanner is performed. This showed the system has slight underprediction of 0.441 %. Next, a dynamic analysis through the comparison of results from the prototype and a spirometer in nine cystic fibrosis patients and thirteen healthy subjects was performed. This showed an agreement with correlation coefficients above 0.8656 in all participants. The system shows promise as a method for assessing respiratory James M. Harte and Christopher K. Golby have contributed equally to this work. * Christopher K. Golby 1 Institute of Digital Healthcare, WMG, University of Warwick, Coventry, UK 2 Interacoustics Research Unit, c/o Technical University of Denmark, Bldg. 351, Kongens Lyngby 2800, Denmark 3 Heart of England NHS Foundation Trust, Birmingham, UK 4 WMG, University of Warwick, Coventry, UK 5 University of Birmingham, Birmingham, UK disease in a cost-effective and timely manner. Further work must now be performed to develop the prototype and provide further evaluations. Keywords Thoracic wall · Chest wall · Thoracic surgery · Respiratory system diagnostic technique · Medical device design 1 Introduction Respiratory disease, including lung cancer, is the leading cause of death in the UK, accounting for 920,000 disability-adjusted life years lost [10]. It is the most frequent cause of disease in primary care in all age groups and the second most common cause of chronic conditions. For patients who report to A&E, a quick and low-cost method of assessment is required. One process currently used to assess respiratory disease in a low-cost and timeeffective manner is spirometry [14]. Spirometry allows for the measurement of expired airflow from the lungs, enabling physicians to better characterise the cause of breathlessness and to assess progression of respiratory disease over time. However, spirometry can have significant limitations. Firstly, forced spirometric efforts allow assessment of initial diaphragm/muscle strength and can only measure total airflow in and out of the lungs; it therefore provides a limited amount of feedback and does not allow physicians to identify motion at the chest and the relative contribution of different areas of each lung to the subjects’ respiratory function [16]. This is particularly important in subjects with more focal lung abnormalities, such as emphysematous bullae, collapsed lung segments and previous surgical lung resection. Secondly, the effect of chest wall 13 Med Biol Eng Comput abnormalities, such as respiratory muscle weakness and pectus excavatum, as well as diaphragm movement cannot be assessed by spirometry [21]. Thirdly, since it is an effort-dependent procedure, there is a potential for inaccurate results in subjects unable to reliably perform a forced expiratory manoeuvre [12] (e.g. children, the elderly and subjects with hearing impairments, learning difficulties or a language barrier). Fourthly, subjects with facial abnormalities or muscle weakness are often unable to form a tight seal around the mouthpiece, preventing spirometry being accurately performed [8]. As a result of these limitations, there has been increasing interest in the development of alternative methods of assessing respiratory function, including chest wall motion analysis. Systems such as magnetometers [17], respiratory inductance plethysmography [13], optoelectronic plethysmography [1, 4] (OEP) and structured light plethysmography [5] (SLP) have been demonstrated for this purpose; however, these technologies have been shown can be cumbersome, expensive, time consuming, difficult to interpret and not suited to the clinical environment. A more recent method for evaluating chest wall motion is through the use of the Microsoft Kinect technology (a low-cost motion tracking camera). This system is portable, low cost, noninvasive and has been suggested as an alternative for spirometry [3] with positive correlations being shown (Ye et al. 2012 show correlations of r = 0.966 [24]). However, research demonstrating the use of this technology utilises a one-camera version of the system [3, 7, 23, 24]. This method follows a process of monitoring the chest wall only and detecting changes in surface. The issue with this is that motion may affect the sample, particularly large movements during analysis. In addition, it is difficult to compartmentalise different parts of the torso and also calculate volumes of the whole or parts of the torso. This paper reports the development of a low-cost and time-effective novel prototype for capturing dynamic chest wall motion using four Microsoft Kinect sensors. An initial evaluation of this prototype is also presented, involving healthy volunteers and adults with cystic fibrosis (an inherited condition causing progressive respiratory failure) [20]. 2 Methods 2.1 System design This research created a system which was capable of assessing respiratory motion using a low-cost and timeeffective motion tracking device. The device to be used was the Microsoft Kinect, which is a human tracking peripheral used in the gaming industry for the Microsoft Xbox to 13 provide low-cost 3D motion capture capabilities [6]. The device is composed of an infrared (IR) laser projector, an IR camera, a colour camera and a microphone array. The Kinect uses the IR projector to detect distance of an object from the sensor by emitting a single infrared beam which is split to create an invisible pattern of speckles [11]. This pattern is captured by the IR camera and compared against a reference pattern stored in the device to calculate distance from external objects. This study utilised four of these devices to create three-dimensional representations of a subject’s torso o (...truncated)