A Virtual Instrument for Automated Measurement of Arterial Compliance
01 Dec 2010-Journal of Medical Devices-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 4, Iss: 4, pp 045004
TL;DR: A simple instrument for noninvasive in vivo evaluation of arterial compliance using a single element ultrasound transducer that can measure arterial distension with a precision better than 5 and the end-diastolic arterial diameter with an accuracy of 1%.
Abstract: Measurement of arterial distensibility is very important in cardiovascular diagnosis for early detection of coronary heart disease and possible prediction of future cardiac events. Conventionally, B-mode ultrasound imaging systems have been used along with expensive vessel wall tracking systems for estimation of arterial distension and calculation of various estimates of compliance. We present a simple instrument for noninvasive in vivo evaluation of arterial compliance using a single element ultrasound transducer. The measurement methodology is initially validated using a proof of concept pilot experiment using a commercial ultrasound pulser-receiver. A prototype system is then developed around a PXI chassis using LABVIEW software. The virtual instrument employs a dynamic threshold algorithm to identify the artery walls and then utilizes a correlation based tracking technique to estimate arterial distension. The end-diastolic echo signals are averaged to reduce error in the automated diameter measurement process. The instrument allows automated measurement of the various measures of arterial compliance with minimal operator intervention. The performance of the virtual instrument was first analyzed using simulated data sets to establish the maximum measurement accuracy achievable under different input signal to noise ratio (SNR) levels. The system could measure distension with accuracy better than 10 μm for positive SNR. The measurement error in diameter was less than 1%. The system was then thoroughly evaluated by the experiments conducted on phantom models of the carotid artery and the accuracy and resolution were found to meet the requirements of the application. Measurements performed on human volunteers indicate that the instrument can measure arterial distension with a precision better than 5%. The end-diastolic arterial diameter can be measured with a precision better than 2% and an accuracy of 1%. The measurement system could lead to the development of small, portable, and inexpensive equipment for estimation of arterial compliance suitable in mass screening of "at risk" patients. The automated compliance measurement algorithm implemented in the instrument requires minimal operator input. The instrument could pave the way for dedicated systems for arterial compliance evaluation targeted at the general medical practitioner who has little or no expertise in vascular ultrasonography.
Citations
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TL;DR: In this article , deep neural network (DNN) models are employed to perform carotid detection, wall localization, and inner lumen diameter measurement using a noninvasive A-mode ultrasound-based device.
Abstract: Arterial stiffness (AS) of the carotid artery is an early marker of stratifying cardiovascular disease risk. This article aims to improve the performance of ARTSENS, a noninvasive A-mode ultrasound-based device for measuring AS. The primary objective of ARTSENS is to enable the measurement of elastic modulus using A-Mode ultrasound and blood pressure. As this device is image-free, there is a need to automate: 1) carotid detection; 2) wall localization; and 3) inner lumen diameter measurement. This has been performed using conventional signal processing methods in some of the earlier works in this domain. In this article, deep neural network (DNN) models are employed to perform the above three tasks. The DNNs were trained over data acquired from 82 subjects at two different medical centers. Ground-truth labeling was performed by a trained operator using corresponding measurements from the state-of-the-art Aloka e-Tracking system. All three DNN models had significantly lower errors compared to earlier signal processing methods and could perform their measurements using a single A-Mode frame. Using the DNNs, two different machine learning pipelines have been proposed here to measure the elastic modulus; the best among them could achieve an error of 9.3% with the Pearson correlation coefficient of 0.94 ( ). The models were tested on Raspberry Pi and Jetson Nano single board computers to demonstrate real-time processing on low computational resources.
3 citations
01 May 2017
TL;DR: The results validate that the CWTS can be potentially used for mass screening purpose, since the measuring system is very cost-effective, easily portable, includes low signal processing overhead and can be used by any general practitioner with just minimal training.
Abstract: Carotid Intima Media Thickness (CIMT) is an established marker of cardiovascular risk with proven utility in early detection. However, conventional B-mode ultrasound imaging based measurement of CIMT is not amenable for deployment in large scale screening due to cost and expertise required to perform the test. We had developed and validated an image -free ultrasound technique for non-invasive, automated evaluation of arterial wall dynamics, called ARTSENS®, for use in vascular screening. Here we present a novel technique to evaluate a carotid artery wall thickness surrogate (CWTS) measure using ARTSENS®, utilizing a single-element 5 MHz ultrasound transducer. The method is based on real time analysis of ultrasound echoes obtained from the far-wall of the common carotid artery. Intelligent algorithms for automated identification of arterial walls, tracking of wall motion, and extraction of far wall structural echoes and measurement of a wall-thickness estimate were developed, and integrated into a prototype ARTSENS® device to enable real time measurement of wall thickness in-vivo. The performance of the system was evaluated using dynamic arterial flow phantoms and in-vivo studies on a set of 7 volunteers. The system could track changes in wall-thickness over a cardiac cycle in both phantoms as well as volunteers in real time. Accuracy of measurements was evaluated in comparison with a reference B-mode ultrasound imaging system. The CWTS measurements showed strong agreement with CIMT values measured with observed error 2.18% and 6.19% in phantom studies and in-vivo measurements respectively. CWTS measurements were also strongly related to CIMT measurements with a R2 value 0.86. While the CWTS is not a replacement for CIMT, but the results validate that it can be potentially used for mass screening purpose, since the measuring system is very cost-effective, easily portable, includes low signal processing overhead and can be used by any general practitioner with just minimal training.
3 citations
01 Jun 2018
TL;DR: Simultaneous assessment of instantaneous variation in arterial pressure, diameter and local PWV using the proposed bi-modal probe has the potential to accurately characterize the elastic behavior of arteries.
Abstract: Arterial pressure or flow wave propagation velocity (pulse wave velocity [PWV]) is inherently dependent on arterial elastic characteristics and distending pressure. Assessment of instantaneous variation in PWV over the cardiac cycle can be noninvasively performed using established biomechanical models by measuring arterial pressure and diameter from the same site. In this work, we explore and validate the viability of a bi-modal probe for local evaluation of PWV variation over the cardiac cycle as a function of arterial pressure. The proposed probe employs singleelement ultrasound transducer (for diameter measurement) and tonometric sensor (for pressure measurement) integrated into a custom probe holder. An application-specific measurement system and dedicated algorithms were used for simultaneous assessment of the desired physiological waveforms. The optimized transducer arrangement in the proposed probe allowed reliable capture of high-fidelity pressure and diameter waveforms from a single arterial site. Real-time assessment of variation in local PWV as a function of arterial pressure was validated on 10 human subjects (age = 31 ± 6 years) using the developed prototype system. Local PWV was found to increase during the systolic phase of each cardiac cycle, and exhibits a non-linear relationship with the arterial pressure. Results from the performed pilot study demonstrated that the proposed ultrasound-tonometer based onepoint method could reliably capture the incremental local PWV over continuous cardiac cycles. Simultaneous assessment of instantaneous variation in arterial pressure, diameter and local PWV using the proposed bi-modal probe has the potential to accurately characterize the elastic behavior of arteries.
3 citations
Cites methods from "A Virtual Instrument for Automated ..."
...The locations of arterial near wall (NW) and far wall (FW) were identified using wall detection algorithm [15]....
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01 Jul 2017
TL;DR: The feasibility of using ARTSENS® for measuring brachial artery stiffness is demonstrated and the capability of the device to perform accurate measurements of carotid artery stiffness has been validated through extensive in-vivo studies.
Abstract: Central and peripheral arteries stiffening prominently affect hemodynamics thus increasing the risk of coronary heart disease, chronic kidney disease and end stage renal disease. There are several commercially available non-invasive measurement technologies for the evaluation of stiffness that are expensive, demand dedicated expertise and fall short for mass screening. Considering this, we have developed ARTSENS®, a highly compact and portable image-free ultrasound device for evaluation of arterial stiffness. The capability of the device to perform accurate measurements of carotid artery stiffness has been validated through extensive in-vivo studies. In this paper we demonstrate the feasibility of using ARTSENS® for measuring brachial artery stiffness. An inter-operator repeatability study was done based on in-vivo experiments on 9 young healthy subjects. The study included measurement of distension, end diastolic lumen diameter, arterial compliance and stiffness index performed both on carotid artery and brachial artery by two operators successively. The degree of agreement between the measurements made by operators has been investigated based on Bland-Altman plots and paired t-test. The measurements were populated within the limits of agreement. No statistically significant difference (p-values from paired t-test for end-diastolic diameter, distension, stiffness index, arterial compliance were 0.36, 0.24, 0.47 and 0.11 respectively) was seen for the brachial artery measurements performed by the two operators. The correlation between the measurement made by the operators was highly significant (r=0.86, p-value=0.003).
2 citations
Cites background or methods from "A Virtual Instrument for Automated ..."
...Through extensive validation study it has been demonstrated that the device is capable of performing accurate measurements of carotid artery stiffness that meets clinically accepted standards [9][12]....
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...In earlier publications we have presented the technology behind image-free measurement of arterial stiffness and have enlisted various advantages that this system offers when compared to other traditional complex and expensive technologies [8], [9]....
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...The identified wall locations are used and the walls are continuously tracked estimating the shifts in the wall locations based on the correlation based tracking technique [9],[14]....
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TL;DR: It is shown that it is possible to estimate the augmentation index (AIx), a measure of the global arterial mechanics, from the distension waveforms obtained by ARTSENS, a unique device that can measure the three most widely used indices of arterial Mechanics—LAS, RAS and the AIx.
Abstract: Over past few years our group has been developing a fully automated and low-cost device, ARTSENS (ARTerial Stiffness Evaluation for Non-invasive Screening), to enable non-experts to measure arterial stiffness (AS). It uses a single element ultrasound transducer to obtain A-mode frames from a superficial artery such as the common carotid artery (CCA) and analyzes them to obtain the stiffness parameters of the vessel. We have earlier demonstrated that ARTSENS can accurately measure local arterial stiffness (LAS) and regional arterial stiffness (RAS) by tracing the distension waveforms of the CCA and the femoral artery. In this paper, we show that it is possible to estimate the augmentation index (AIx), a measure of the global arterial mechanics, from the distension waveforms obtained by ARTSENS. AIx measurements from ARTSENS are compared against the state-of-the-art Hitachi-Aloka eTRACKING system for 107 volunteers. Both devices show excellent agreement with a correlation coefficient (r) = 0.82 (p < 0.0001), which is comparable to similar studies reported in the literature. This development makes ARTSENS a unique device that can measure the three most widely used indices of arterial mechanics—LAS, RAS and the AIx.
2 citations
References
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TL;DR: This population-based study shows that arterial stiffness is strongly associated with atherosclerosis at various sites in the vascular tree.
Abstract: Background and Purpose—Studies of the association between arterial stiffness and atherosclerosis are contradictory. We studied stiffness of the aorta and the common carotid artery in relation to se...
1,134 citations
TL;DR: The effects of current and future cardiovascular drugs on arterial stiffness are discussed, as is the relationship between arterial elasticity and endothelial function.
Abstract: Investigation of arterial stiffness, especially of the large arteries, has gathered pace in recent years with the development of readily available noninvasive assessment techniques. These include the measurement of pulse wave velocity, the use of ultrasound to relate the change in diameter or area of an artery to distending pressure, and analysis of arterial waveforms obtained by applanation tonometry. Here, we describe each of these techniques and their limitations and discuss how the measured parameters relate to established cardiovascular risk factors and clinical outcome. We also consider which techniques might be most appropriate for wider clinical application. Finally, the effects of current and future cardiovascular drugs on arterial stiffness are also discussed, as is the relationship between arterial elasticity and endothelial function.
813 citations
TL;DR: Common carotid IMT anddistensibility are clear markers of cardiovascular risk in patients who already have vascular disease or atherosclerotic risk factors and IMT appears to discriminate between low- and high-risk patients better than distensibility.
Abstract: Background—Common carotid intima-media thickness (IMT) and distensibility are markers of structural and functional vessel wall properties. Both parameters have been found in population-based studies to be associated with cardiovascular risk factors and prevalent cardiovascular disease. We investigated cross-sectionally whether IMT and distensibility are associated with cardiovascular risk in patients who already have vascular disease or atherosclerotic risk factors and evaluated the diagnostic ability of IMT and distensibility to discriminate between low- and high-risk patients. Methods and Results—IMT and distensibility (change of diameter) of the left and right common carotid arteries were measured in the first 570 patients (537 for distensibility) enrolled in the Second Manifestations of ARTerial disease (SMART) study, a cohort study among patients with a manifestation of vascular disease or cardiovascular risk factors. Three risk scores were used to classify each patient’s vascular risk. Areas under t...
378 citations
TL;DR: An overview of time-domain techniques that have appeared in the literature over the past few years is presented, and their potential advantages over Doppler are examined, and the individual techniques are compared.
Abstract: The Doppler technique has traditionally been the method used to extract motion information from ultrasonic echoes reflected by moving tissues. The Doppler technique has been around for a long time, and has been extensively reviewed and analyzed in the literature. Recently, time-domain methodologies for estimating tissue motion have gained in popularity. Time-domain methods have advantages over Doppler methods in many applications, and as of yet have not been comprehensively reviewed. An overview of time-domain techniques that have appeared in the literature over the past few years is presented. Their potential advantages over Doppler are examined, and the individual techniques are compared. >
340 citations
TL;DR: Under controlled experimental conditions there was good repeatability of measurements of indices between sessions of both intrinsic and functional arterial mechanical properties (central and carotid arterial compliance, intima-media thickness and brachial flow-mediated dilation).
Abstract: 1. Repeatability of measurements of arterial compliance and flow-mediated dilation of the brachial artery has been infrequently reported, despite increasing use in interventional and risk-factor modification studies. Furthermore, little is known about the interrelationships of the various indices. The purposes of this study were to determine the repeatability and interrelationships of a range of arterial indices.2. Fifty healthy volunteers, 20 men and 30 women, aged 20-70 (mean 46.5) years, were studied on two occasions, using an identical protocol, at a mean interval of 2.5 weeks. Tonometry, ultrasound and Doppler technique were used to measure the following: carotid wall intima-media thickness (IMT), total systemic artery compliance (SAC), arterial pulse wave velocity [PWV aorto-femoral (A-F), and femoral-dorsalis pedis (F-D)], carotid distensibility coefficient (DC) and carotid augmentation index (AI). Brachial flow-mediated dilation was measured in 30 subjects with analysis of diameter change for 4 min post ischaemia.3. There were no systematic differences over the observed range of measurements for any of the reported parameters. Coefficients of variation were as follows: IMT 2.8%, SAC 9.2%, PWV(A-F) 3.2%, PWV(F-D) 5.0%, DC 10.0%, AI 1.3%. Brachial flow-mediated dilation curves were not different between visits; changes were maximum 60-s post ischaemia. All indices of arterial compliance were significantly correlated with age. The three different indices of central arterial compliance [SAC, PWV(A-F) and AI] were significantly correlated with carotid intima-media thickness.4. Under controlled experimental conditions there was good repeatability of measurements of indices between sessions of both intrinsic and functional arterial mechanical properties (central and carotid arterial compliance, intima-media thickness and brachial flow-mediated dilation). Sample size tables for clinical trials using these indices are presented.
316 citations