A Miniaturized MEMS Motion Processing System for Nuclear Medicine Imaging Applications

Abstract

Cardiac, respiratory, and patient body motion artifacts degrade the image quality and quantitative accuracy of the nuclear medicine imaging which may lead to incorrect diagnosis, unnecessary treatment and insufficient therapy. We present a new miniaturized system including joint micro electromechanical (MEMS) accelerometer and gyroscope sensors for simultaneous extraction of cardiac and respiratory signals. We employ two tri-axial joint MEMS sensors for selecting an optimal trigger point in a cardiac and respiratory cycle. The 6-axis motion sensing helps to detect candidate features for cardiac and respiratory gating in Positron emission tomography (PET) imaging. The aim of this study was to validate MEMS-derived signals against traditional Real-time Position Management (RPM) and electrocardiography (ECG) measurement systems in 4 healthy volunteers. High agreement and correlation were found between cardiac and respiratory cycle intervals. These promising first results warrant for further investigations. IntroductionIn cardiac and oncologic Positron emission tomography (PET)/computed tomography (CT) imaging, cardiac, respiratory, and patient body motions may impair the image quality and the quantitative accuracy of heart imaging [1][2][3]. To reduce motion-related inaccuracies, cardiac and respiratory gating methods are the most common approaches applied in clinical PET imaging [4]. Simultaneous respiratory and cardiac gating, namely dual gating, can reduce motion-related inaccuracies and correspondingly imaging resolution in cardiac PET and oncological applications [5]. Cardiac gating is accomplished by an electrocardiography (ECG) measurement system, while respiratory gating can be performed by external devices such as spirometry, elastic belts (consisting of pressure or load cell sensors) monitors or using optical techniques including a camera and laser sensor that track chest wall or abdomen displacement [3,6,7]. However, respiratory gating devices have been considered for only research purposes due to the need for complex logistics and long data processing which may increase patient discomfort and be laborious for the clinicians [2,3]. Additionally, ECG is able to show only electrical activity of the heart and still fails to trace the instantaneous mechanical state of the heart due to the stirring movements of the myocardium [8]. Thus, these challenges complicate PET imaging protocols and create a serious demand for simultaneous recording of cardiac and respiratory signals in dual gating. Recently, new techniques based on bioimpedance [2, 9] and accelerometers [10] have been suggested for concurrent acquisition of both respiratory and cardiac signals in oncologic and cardiac PET imaging. However, there is still space to optimize these methods, especially in terms of technology, accuracy, and patient comfort. We present a new framework based upon tri-axial microelectromechanical (MEMS) accelerometer and gyroscope sensors to extract cardiac and respiratory signals. Our main objective in this study is t...

Gyrocardiography: A Review of the Definition, History, Waveform Description, and Applications

“…The works published since 2016 use consequently the terms "gyrocardiography" for the method and "gyrocardiogram" for the signal. In the same year Tadi et al published papers on the applications of GCG in PET (positron emission tomography) gating [33,46] and Lahdenoja et al published the first study on heart rate variability (HRV) analysis on gyrocardiograms [47].…”

“…The relationship between SCG waves and cardiac activity is still not fully understood because of the waveform variations in different studies and lack of understanding of the exact sources of SCG waves [70]. However, according to the studies on the relationship between the cardiac cycle and registered vibrations [8,10,11,33,94] and simultaneous recordings of SCG, ECG and echocardiograms [8,10,11,33,94], the SCG signal contains the peaks and valleys of the SCG in the cardiac cycle corresponding to mitral valve opening (MO) and closure (MC), isovolumetric contraction (IVC), rapid ejection (RE), aortic valve opening (AO), closure (AC) [27,95], and also systolic and diastolic velocity [11].…”

“…Another field of application in GCG proposed by Tadi et al [33,46] is PET/CT (positron emission tomography/computed tomography) cardiac and respiratory gating-an approach to enhance the quality of PET/CT images by dividing the PET/CT data into individual bins that correlate with the phases of respiratory and/or cardiac motion [46,109]. The main reason of PET/CT gating are the inaccuracies in image quantification, blurring and other artifacts in cardiac and oncology imaging [110].…”

“…In the second study, Yang et al use band-pass filtering, calculation of the kinetic energy waveform, ensemble averaging and searching for fiducial points [39]. In the same year Tadi et al investigated the feasibility of MEMS cardiac gating in PET/CT in [33,46,113]. Gating is used in PET/CT imaging of the heart and involves determining the occurrence of the heart beats [109].…”

“…Gyrocardiography (GCG) is a technique for recording of three-dimensional angular velocity and displacement of the thorax associated with cardiac activity using a gyroscope placed on a chest wall [8,11,32]. This technique was invented by Meriheinä et al in 2015 [32], and its name was proposed by as the blend of "gyroscope" and "cardiography" [8,33]. The gyroscope is an active sensor which measures its own angular velocity (gyration) and can detect very small angular displacements caused by the cardiac activity [8,32].…”