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.
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TL;DR: The feasibility of calibration-free, cuffless BP measurement at an arterial site of interest was demonstrated with a level of acceptable accuracy and the potential utility of the proposed method and system in hypertension screening and local evaluation of arterial stiffness indices was demonstrated.
Abstract: Objective: We propose a calibration-free method and system for cuffless blood pressure (BP) measurement from superficial arteries. A prototype device with bi-modal probe arrangement was designed and developed to estimate carotid BP – an indicator of central aortic pressure. Methods: Mathematical models relating BP parameters of an arterial segment to its dimensions and local pulse wave velocity (PWV) are introduced. A bi-modal probe utilizing ultrasound and photoplethysmograph sensors was developed and used to measure diameter values and local PWV from the carotid artery. Carotid BP was estimated using the measured physiological parameters without any subject- or population-specific calibration procedures. The proposed cuffless BP estimation method and system were tested for accuracy, usability, and for potential utility in hypertension screening, on a total of 83 subjects. Results: The prototype device demonstrated its capability of detecting beat-by-beat arterial dimensions and local PWV simultaneously. Carotid diastolic BP (DBP) and systolic BP (SBP) were estimated over multiple cardiac cycles in real-time. The absolute error in carotid DBP was Conclusion: The feasibility of calibration-free, cuffless BP measurement at an arterial site of interest was demonstrated with a level of acceptable accuracy. The study also demonstrated the potential utility of the proposed method and system in hypertension screening and local evaluation of arterial stiffness indices. Significance: Novel approach for calibration-free cuffless BP estimation; a potential tool for local BP measurement and hypertension screening.
60 citations
Cites background or methods from "A Virtual Instrument for Automated ..."
...Arterial dimensions was measured with a single element ultrasound transducer using the ARTSENS (ARTerial Stiffness Evaluation for Non-invasive Screening) technology – an image-free technique for arterial stiffness evaluation, that has been developed and clinically validated by our group [18]–[20]....
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...6 ns echo pulse width can be obtained while using the present ultrasound transducer (center frequency = 5 MHz), which limits the threshold of DD measurement to 285 μm [18]....
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...Arterial distension waveform (temporal change in arterial diameter as a function of time) was captured from successive ultrasound frames as the sum of relative shift in location of proximal and distal walls with respect to the previous frame [18]....
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...The negative correlation between the proximal and distal wall movement was checked using wall motion negative correlation check (WMNCC) algorithm to ensure that both the walls were in opposite motion [18], [19]....
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TL;DR: The feasibility of the novel ARTSENS device in performing accurate in vivo measurements of arterial stiffness is verified, a device for image free, noninvasive, automated evaluation of vascular stiffness amenable for field use.
Abstract: Vascular stiffness is an indicator of cardiovascular health, with carotid artery stiffness having established correlation to coronary heart disease and utility in cardiovascular diagnosis and screening. State of art equipment for stiffness evaluation are expensive, require expertise to operate and not amenable for field deployment. In this context, we developed ARTerial Stiffness Evaluation for Noninvasive Screening (ARTSENS), a device for image free, noninvasive, automated evaluation of vascular stiffness amenable for field use. ARTSENS has a frugal hardware design, utilizing a single ultrasound transducer to interrogate the carotid artery, integrated with robust algorithms that extract arterial dimensions and compute clinically accepted measures of arterial stiffness. The ability of ARTSENS to measure vascular stiffness in vivo was validated by performing measurements on 125 subjects. The accuracy of results was verified with the state-of-the-art ultrasound imaging-based echo-tracking system. The relation between arterial stiffness measurements performed in sitting posture for ARTSENS measurement and sitting/supine postures for imaging system was also investigated to examine feasibility of performing ARTSENS measurements in the sitting posture for field deployment. This paper verified the feasibility of the novel ARTSENS device in performing accurate in vivo measurements of arterial stiffness. As a portable device that performs automated measurement of carotid artery stiffness with minimal operator input, ARTSENS has strong potential for use in large-scale screening.
53 citations
Cites background or methods from "A Virtual Instrument for Automated ..."
...A smoothened Hilbert envelope of the region of interest (ROI) is used for lumen diameter calculation [17], [18], [24]....
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...The diameter values corresponding to these valley points in the distension array are identified as end diastolic diameters Dd [17]....
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...Digital pulses generated using a microcontroller are translated to high voltage levels and used to excite the transducer in the pulse echo modality [17]....
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...A wall motion negative correlation check running simultaneously along with tracking ensures that tracking is done on near and far walls without fail [17], [23]....
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...We had previously presented the concept of an image-free system for measurement of arterial stiffness [17]–[21] and also demonstrated the accuracy and repeatability of measurements in controlled laboratory settings [22], [23]....
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12 Nov 2012
TL;DR: An imageless portable system for automated estimation of local arterial compliance, designed to be operated by a general medical practitioner with no prior knowledge of ultrasonography, and used for developing an inexpensive cardiovascular screening device for large scale deployment in primary health care centers.
Abstract: Evaluation of arterial compliance is very significant in early detection of coronary heart disease. Here we present an imageless portable system for automated estimation of local arterial compliance, designed to be operated by a general medical practitioner with no prior knowledge of ultrasonography. An algorithm for automatic detection and tracking of the arterial wall locations has been developed to minimize the operator expertise required for measurement. The performance of the automated algorithm was thoroughly characterized using a simulation platform developed for the purpose. Measurements performed on a few human volunteers by untrained personnel clearly illustrated the practical utility of the automatic algorithm during in-vivo tests. The proposed system could be used for developing an inexpensive cardiovascular screening device for large scale deployment in primary health care centers.
50 citations
Cites background or methods from "A Virtual Instrument for Automated ..."
...We had earlier demonstrated the feasibility of a single element ultrasound transducer in the measurement of arterial distension [4]....
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...The approximate locations of the arterial walls ( 1 and 2 obtained as a result of the wall-detection algorithm, is used to initialize a correlation based wall motion tracking algorithm [4]....
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...The movement of the wall echoes in between successive acquisitions is estimated based on a shift and search algorithm utilizing a correlation based technique [4]....
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...The features in the windows are tracked over successive M’ frames using correlation window based technique [4]....
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...From the distension waveform the frame numbers corresponding to the minimum diameter are identified and the diastolic diameter ( ) and systolic diameter ( ) is estimated by method proposed in [4]....
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TL;DR: A novel approach using the autocorrelation of echoes from opposite walls of the artery has been discussed, to bring down the curve fitting time and facilitate processing on low-end processors.
Abstract: Over past few years, we are developing a system for facilitating large scale screening of patients for cardiovascular risk - ARTSENS. ARTSENS is an image-free device that uses a single element ultrasound transducer to obtain non-invasive measurements of arterial stiffness (AS) in a fully automated manner. AS is directly proportional to end-diastolic lumen diameter (�� �� ). Multi- layered structure of the arterial walls and indistinct characteristics of intima-lumen interface (ILI) makes it quite difficult to accurately estimate �� �� in A-Mode radio-frequency (RF) frames obtained from ARTSENS. In this paper, we propose a few methods based on fitting simple mathematical models to the echoes from arterial walls, followed by a novel method to fuse the information from curve fitting error and distension curve to arrive at an accurate measure of �� ��. To bring down the curve fitting time and facilitate processing on low-end processors, a novel approach using the autocorrelation of echoes from opposite walls of the artery has been discussed. The methods were analyzed for their comparative accuracy against reference �� �� obtained from 85 human volunteers using Hitachi-Aloka eTRACKING system. �� �� from all reported methods show strong and statistically significant positive correlation with eTRACKING and mean error of less than 7 % could be achieved. As expected, �� �� from all methods show significant positive correlation with age.
49 citations
Cites methods from "A Virtual Instrument for Automated ..."
...Brief hardware block diagram of the system is illustrated in figure 1(a); details of implementation can be found in our past work [8]....
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...In our earlier publications [8,9], our group had demonstrated the feasibility of measurement of various indices of AS using this setup....
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...had earlier attempted to measure Dl using a simple method based on thresholding and double derivative on the average end-diastolic frame obtained from ARTSENS [8]....
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TL;DR: The study results revealed the sensitivity of ARTSENS® Pen to detect changes in arterial stiffness with age, and the easy-to-use technology and the automated algorithms of the ARtsENS Pen make it suitable for cardiovascular risk assessment in resource-constrained settings.
Abstract: OBJECTIVE The conventional medical imaging modalities used for arterial stiffness measurement are non-scalable and unviable for field-level vascular screening. The need for an affordable, easy-to-operate automated non-invasive technologies remains unmet. To address this need, we present a portable image-free ultrasound device-ARTSENS® Pen, that uses a single-element ultrasound transducer for carotid stiffness evaluation. APPROACH The performance of the device was clinically validated on a cohort of 523 subjects. A clinical-grade B-mode ultrasound imaging system (ALOKA eTracking) was used as the reference. Carotid stiffness measurements were taken using the ARTSENS® Pen in sitting posture emulating field scenarios. MAIN RESULTS A statistically significant correlation (r > 0.80, p < 0.0001) with a non-significant bias was observed between the measurements obtained from the two devices. The ARTSENS® Pen device could perform highly repeatable measurements (with variation smaller than 10%) on a relatively larger percentage of the population when compared to the ALOKA system. The study results also revealed the sensitivity of ARTSENS® Pen to detect changes in arterial stiffness with age. SIGNIFICANCE The easy-to-use technology and the automated algorithms of the ARTSENS® Pen make it suitable for cardiovascular risk assessment in resource-constrained settings.
33 citations
References
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Book•
08 Dec 2010
TL;DR: In this paper, the authors focus on the dynamics and physics of coronary blood flow, and demonstrate how a disruption in these dynamics can affect coronary flow as significantly as can the obstruction of a blood vessel.
Abstract: Coronary blood flow is blood flow to the heart for its own metabolic needs.
In the most common form of heart disease there is a disruption in this flow
because of obstructive disease in the vessels that carry the flow. The subject of
coronary blood flow is therefore associated mostly with the pathophysiology
of this disease, rarely with dynamics or physics. Yet, the system responsible
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dynamical system in which the dynamics and physics of the flow are
as important as the integrity of the conducting vessels. While an obstruction
in the conducting vessels is a fairly obvious and clearly visible cause of disruption
in coronary blood flow, any discord in the complex dynamics of the
system can cause an equally grave, though less conspicuous, disruption in the
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This book is devoted specifically to the dynamics and physics of coronary
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involved, the book focuses on dynamics and physics, approaching the subject
from a strictly biomedical engineering viewpoint. The rationale for this
approach is simply that the coronary circulation involves many issues in dynamics
and physics, as the book will demonstrate. Also, with this particular
focus, the book will complement other books on the subject, that have so far
focused largely on clinical and pathophysiological issues.
A study of the dynamics of the coronary circulation requires far more
information about the system than is currently available. Whether in terms
of anatomical details of the vasculature, system properties such as capacitance
and elasticity of the conducting vessels, or the basic and regulatory conditions
under which the system operates, the information currently available is highly
incomplete. Thus, the scope of this book is limited to dynamical aspects of
coronary blood flow, but within these limits it is also constrained to deal
necessarily with an incomplete picture of these dynamics. In particular, the
book does not include the microcirculation, the venous part of the coronary
circulation, Thebesian veins or the lymphatic system. Also, the many-faceted
regulatory mechanisms of the coronary circulation are not considered in any
systematic or factual way, but only tangentially in how they may affect the
dynamics of the system. These omissions reflect the degree of complexity of
the coronary circulation and serve as a sober reminder that it may never be
possible or practical to deal with this complexity in a single book.
What seems possible at this time is to use known elements or properties
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consider this part of the system in isolation because this is where the largest
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they demonstrate clearly the role of dynamics in the coronary circulation
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flow as significantly as can the obstruction of a blood vessel. This is indeed
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the microcirculation. Each of these must clearly be seen as representing an
important, though equally incomplete, view of the system.
119 citations
TL;DR: The increased vessel diameter in subjects with cardiovascular risk factors may be a sign of attenuated vasoregulation, which could be an important factor during the development of atherosclerosis.
Abstract: Background and Purpose—We investigated whether, in a randomly selected population of 55-year-old men and women, there is a relationship between common carotid artery (CCA) diameter and intima-media...
98 citations
22 Sep 2002
TL;DR: This paper describes an automatic approach to measure LD and IMT based on an active contour technique improved by a multiresolution analysis and shows that the method is a reliable and reproducible way of assessing the LD and far wall IMT in the carotid artery.
Abstract: Carotid vessel ultrasound imaging is a reliable noninvasive technique to measure the arterial morphology. Lumen Diameter (LD), intima-media thickness (IMT) of the far wall, and plaque presence can be reliably determined using B-mode ultrasound. In order to measure the carotid IMT as well as any other more complex quantitative indices of vessel morphology, it is necessary to identify lumen-intima and media-adventitia borders in the ultrasound images. In this paper we describe an automatic approach to measure LD and IMT based on an active contour technique improved by a multiresolution analysis. The measurements of LD and IMT were compared to manual tracing of the vessels border in terms of coefficients of variability (CV) and correlation (R). The results have shown that the method is a reliable and reproducible way of assessing the LD and far wall IMT in the carotid artery.
87 citations
Journal Article•
TL;DR: It is clear that smoking, saturated fat, cholesterol, hypertension, diabetes, central obesity and glucose intolerance alone can not explain the cause of all of the higher CAD among South Indians and study of other risk factors such as insulin resistance and antioxidant vitamins may be necessary.
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74 citations
TL;DR: RCCA diameter is an important correlate of cardiac events, independent of IMT, but adds little to overall risk discrimination after risk factor adjustment.
Abstract: Arterial diameters enlarge in response to wall thickening, plaques, and many atherosclerotic risk factors. We hypothesized that right common carotid artery (RCCA) diameter would be independently associated with cardiac disease and improve risk discrimination. In a middle-aged, biracial population (baseline n = 11225), we examined associations between 1 standard deviation increments of baseline RCCA diameter with prevalent myocardial infarction (MI) and incident cardiac events (MI or cardiac death) using logistic regression and Cox proportional hazards models, respectively. Areas under the receiver operator characteristic curve (AUC) were used to estimate model discrimination. MI was present in 451 (4%) participants at baseline (1987–89), and incident cardiac events occurred among 646 (6%) others through 1999. Adjusting for IMT, RCCA diameter was associated with prevalent MI (female OR = 2.0, 95%CI = 1.61–2.49; male OR = 1.16, 95% CI = 1.04–1.30) and incident cardiac events (female HR = 1.75, 95% CI = 1.51–2.02; male HR = 1.27, 95% CI = 1.15–1.40). Associations were attenuated but persisted after adjustment for risk factors (not including IMT) (prevalent MI: female OR = 1.73, 95% CI = 1.40–2.14; male OR = 1.14, 95% CI = 1.02–1.28, and incident cardiac events: female HR = 1.26, 95% CI = 1.08–1.48; male HR = 1.19, 95% CI = 1.08–1.32). After additional adjustment for IMT, diameter was associated with incident cardiac events in women (HR = 1.18, 95% CI = 1.00–1.40) and men (HR = 1.17, 95% CI = 1.06–1.29), and with prevalent MI only in women (OR = 1.73; 95% CI = 1.37–2.17). In women, when adjustment was limited, diameter models had larger AUC than other models. RCCA diameter is an important correlate of cardiac events, independent of IMT, but adds little to overall risk discrimination after risk factor adjustment.
72 citations