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: 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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14 Oct 2008
TL;DR: The HT-initialized active contours methodology provides a reliable tool to detect the carotid artery wall in ultrasound images and can be used in clinical practice.
Abstract: Automatic segmentation of the arterial lumen from ultrasound images is an important and often challenging task in clinical diagnosis. We previously used the Hough Transform (HT) to automatically extract circles from sequences of B-mode ultrasound images of transverse sections of the carotid artery. In this paper, an active-contour-based methodology is suggested, initialized by the HT circle, in an attempt to extend previous findings and to accurately detect the arterial wall boundary. The methodology is based on the generation of a gradient vector flow field, an approach attempting to overcome conventional active contours constraints. Contour estimation is then achieved by deforming the initial curve (circle) based on the gradient vector flow field. In ten normal subjects, the specificity and accuracy of the segmentation were on average higher than 0.98, whereas the sensitivity was higher than 0.82. The methodology was also applied to four subjects with atherosclerosis, in which sensitivity, specificity and accuracy were comparable to those of normal subjects. In conclusion, the HT-initialized active contours methodology provides a reliable tool to detect the carotid artery wall in ultrasound images and can be used in clinical practice.
61 citations
TL;DR: The significant impact of age on common carotid artery diameter among low risk, middle-aged, black and white men and women suggests arterial remodelling may occur in the absence of identified risk factors.
Abstract: The effect of age on common carotid artery diameter is unclear for varying atherosclerosis risk levels. Cross-sectional data from the Atherosclerosis Risk in Communities Limited Access Data set were used to estimate the association of age with B-mode ultrasound common carotid artery diameter for three atherosclerosis risk levels. Based on information from clinical examinations, B-mode ultrasounds, questionnaires, blood and other tests, participants were categorized into three groups: pre-existing disease (prevalent stroke and/or coronary heart disease), high risk group (no pre-existing disease, but prevalent diabetes, hypertension, plaques/shadowing, body mass index >= 30, current smoking, or hyperlipidemia), and a low risk group (no pre-existing disease, no plaques/shadowing, and no major elevated risk factors). Multivariable linear regression analyses modeled the common carotid artery diameter relationship with age. Age was positively and significantly associated with common carotid artery diameter after risk factor adjustment in the overall sample, but age had a larger effect among persons with evidence of atherosclerosis (interaction p < 0.05). Each year of older age was associated with 0.03 mm larger diameter/year among persons with pre-existing disease, with 0.027 mm larger diameter/year in the high risk group, but only 0.017 mm/year among the low risk group. Results were qualitatively similar using plaques/shadowing status to indicate atherosclerosis severity. The significant impact of age on common carotid artery diameter among low risk, middle-aged, black and white men and women suggests arterial remodelling may occur in the absence of identified risk factors. The significantly larger impact of age among persons with, compared to persons without identified atherosclerosis or its risk factors, suggests that arterial remodelling may be an indicator of exposure duration.
59 citations
TL;DR: The pattern of inhomogeneities in wall distensibility in borderline hypertensives at a relatively young age is similar to that seen in older normotensive subjects, supporting the idea that arteries age faster in hypertensive than in normotensives.
Abstract: AIM To determine whether there are inhomogeneities in arterial wall distensibility with age and hypertension BACKGROUND It has been known for some years that arteries lose their elasticity with increasing age and that they are less distensible in subjects with established and borderline hypertension than in age-matched controls RESULTS OF DATA ANALYSIS In the carotid artery changes in arterial wall properties are not homogeneously distributed along the bifurcation Both in older subjects and in those with borderline hypertension the loss of distensibility is most pronounced in the carotid artery bulb, while in borderline hypertensives the proximal part of the bulb, where the baroreceptors are predominantly located, is more affected than other parts of the bulb The loss of distensibility in the bulb may explain the diminished baroreceptor sensitivity observed in older subjects The pronounced involvement of the proximal part of the bulb in the decreased distensibility in borderline hypertensives suggests that local stiffening, probably leading to disturbed baroreceptor sensitivity, may contribute to the development of hypertension in these patients The pattern of inhomogeneities in wall distensibility in borderline hypertensives at a relatively young age (average 38 years) is similar to that seen in older normotensive subjects (average age 57 years), supporting the idea that arteries age faster in hypertensives than in normotensives CONCLUSION In management of the borderline hypertensive patient, consideration should be given to preventing early ageing of the arterial wall rather than following arterial blood pressure
55 citations
TL;DR: An integrated ultrasound system, capable of detecting both the velocity profile and the wall movements in human arteries, and a clinically relevant variable extracted from the blood velocity profile is the wall shear rate, which represents the spatial velocity gradient near the vessel wall.
55 citations
TL;DR: An ultrasound system to assess diameter, blood flow velocity and volume flow in the brachial artery in man and the results showed that the diameter as assessed with the system compared favorably with the diameter of the tubing in an in vitro set-up.
Abstract: ### 1.1 Introduction
There are always moments in life, inviting to look back on the past. Entering the next millennium is certainly such an occasion, because it happens generally only once in a life-time. Therefore, we very much liked the idea of the Editors to publish a special issue of Cardiovascular Research on the occasion of this event and to explore the impact of the articles in the journal most frequently cited over the years on further developments in the field. We gladly accepted their invitation to evaluate in this respect the article by Levenson et al. published in Cardiovascular Research in 1981 [1].
### 1.2 Content of the article
In this article the authors described an ultrasound system to assess diameter, blood flow velocity and volume flow in the brachial artery in man. The apparatus consisted of an adjustable range-gated pulsed Doppler system, emitter frequency 8 MHz, combined with a double transducer system to accurately determine the angle between ultrasound beam and vessel axis. The latter is a prerequisite for accurate determination of both the velocity in and the diameter of the artery and, hence, for proper calculation of volume flow. The length of the sample volume could be adjusted by varying the length of the reception duration. A small sample volume was used to measure velocity locally in the artery and to determine the diameter of the vessel accurately and a large one to estimate the average velocity over the cross-sectional area of the vessel. A static high-pass filter with a lower cut-off frequency of 250 Hz was used to reduce interference of high amplitude low frequency signals reflected by the arterial walls. The validity of the system was tested in an in vitro set-up and the results showed that the diameter as assessed with the system compared favorably with the diameter of the tubing in …
54 citations