An improved echo tracking algorithm for arterial distensibility measurements

Technical Validation of ARTSENS–An Image Free Device for Evaluation of Vascular Stiffness

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.

A Virtual Instrument for Automated Measurement of Arterial Compliance

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.

Arterial compliance probe for calibration free pulse pressure measurement

Abstract: Cardiovascular diseases are the leading cause of death around the world. Non-invasive estimation of arterial parameters is significant in the early detection of cardiovascular diseases. In this work, we present an arterial compliance probe for calibration-free evaluation of carotid pulse pressure. This novel cuffless measurement technique uses dual magnetic plethysmograph (MPG) transducers for carotid local pulse wave velocity (PWV) measurement and single element ultrasound transducer for measuring arterial dimensions. Proposed arterial compliance probe can acquire two blood pulse waveforms and arterial diameter parameters simultaneously, which are then utilized in cycle-to-cycle estimation of arterial local PWV and pulse pressure without any subject or population specific calibration. The design of compliance probe and measurement system was verified by in-vivo trials. Accurate local PWV measurement and calibration free estimation of carotid pulse pressure was also validated by in-vivo studies. Initial results indicate a strong potential of MPG — Ultrasound arterial compliance probe in continuous, cuffless evaluation of blood pressure (BP) from superficial arteries.

Non-invasive estimation of arterial compliance

Abstract: The evaluation of arterial compliance is very important in cardiovascular screening of “at-risk” patients. Existing techniques for local arterial stiffness estimation put a premium on technology and operator expertise. Regional stiffness, measured in terms of the pulse wave velocity, is prone to errors in both path-length and delay estimation. Here, we present a Virtual Instrument (VI) for automated estimation of both local and regional arterial compliance measures. Local arterial compliance is evaluated by utilizing an ultrasound transducer to measure the distension and lumen diameter of the carotid artery. The regional stiffness is estimated from the pulse wave velocity, measured using two magnetic transducers in a dual-channel arrangement. The automated measurement algorithms are thoroughly analyzed, to identify and minimize possible error sources as well as to optimize the design of both the transducer and the virtual instrument. The results of a few human trials are also presented to illustrate the capability of the VI to measure arterial compliance in-vivo.

Vascular Wall Stiffness Indices Detection Using an Accelerometer-Based System

Abstract: The measure of arterial stiffness is significant for the diagnosis of the cardiovascular health. A prototype accelerometer- based system for vascular stiffness indices detection is proposed and experimentally validated. The developed accelerometer-based system could continuously capture the accelerations related to the displacement of the carotid arterial walls. The measured accelerometric waveforms are recorded by a data acquisition card for signal processing and analysis in real-time. The recorded accelerometric signals from the carotid skin surface are double- integrated and calibrated linearly using our clinically validated ARTSENS® (ARTerial Stiffness Evaluation for Noninvasive Screening) device to estimate the subject-specific one-time calibration coefficients. The acquired accelerometric signal with these calibration coefficients was used to estimate the diameter parameters such as arterial distension ($\Delta \textbf{D}$), end-diastolic diameter ($\textbf{D}_{\mathbf {d}}$), and systolic diameter ($\textbf{D}_{\mathbf {s}}$). 12 subjects (7 males, 5 females, age $=25.42\pm 2.5$ years) with no prior history of cardiovascular diseases were enrolled for the in-vivo validation study. The accelerometer-based system could capture continuous distension waveforms for all the recruited subjects. Arterial stiffness indices such as stiffness index (β), arterial compliance (AC) and Peterson's elastic modulus ($\textbf{E}_{\mathbf {p}}$) were calculated using the obtained diameter parameters from the accelerometer-based system. The correlation ($\textbf{R}^{\mathbf {2}}$) for β, AC and $\textbf{E}_{\mathbf {p}}$ observed between ARTSENS reference device and accelerometric system were 0.93, 0.95 and 0.94 respectively. Bland-Altman plots of β, AC, and $E_{\mathbf {p} }$ of ARTSENS reference device and the accelerometric system shows a small mean bias of 0.07, -0.001 and 0.81 respectively. The preliminary results suggest the potential of the accelerometer- based system for vascular wall stiffness indices detection.

Improving Coronary Heart Disease Risk Assessment in Asymptomatic People Role of Traditional Risk Factors and Noninvasive Cardiovascular Tests

Abstract: At least 25% of coronary patients have sudden death or nonfatal myocardial infarction without prior symptoms1 Therefore, the search for coronary patients with subclinical disease who could potentially benefit from intensive primary prevention efforts is critically important The American Heart Association’s (AHA) Prevention V Conference, “Beyond Secondary Prevention: Identifying the High Risk Patient for Primary Prevention,” addressed ways to identify more patients who are asymptomatic and clinically free of coronary heart disease (CHD) but at sufficiently high risk for a future coronary event to justify more intensive risk reduction efforts2 In this report, we amplify on key findings and recommendations of the AHA Prevention V conference, highlight new research since the conference, and propose an approach to the use of office-based testing and additional noninvasive procedures in selected patients to better define their coronary event risk The recommendations are concordant with the recently released approach to risk assessment and management from the third report of the Adult Treatment Panel of the National Cholesterol Education Program (ATP-III)3 Enthusiasm for primary prevention and risk assessment in asymptomatic people has been spurred by recent advances in prevention research Lipid-lowering trials demonstrated that primary prevention of coronary events is feasible, evidenced by the West of Scotland Coronary Primary Prevention Study (WOSCOPS) trial4 of hypercholesterolemic men and by the Air Force/Texas Coronary Atherosclerosis Prevention Study (AFCAPS/TexCAPS) trial5 in average or typical risk men and women with only moderate lipid abnormalities Aspirin6 or ACE inhibitors7 can also reduce risk in selected asymptomatic, high-risk people Emerging coronary risk factors have been described including inflammatory, infectious, and thrombotic markers,8 and there has been a steady flow of reports that focus attention on potential new ways of predicting coronary risk9 In addition, noninvasive tests for subclinical atherosclerotic disease are available …

Carotid artery distensibility: a reliability study.

Abstract: Arterial distensibility is a measure of the arterial ability to expand and contract with cardiac pulsation and relaxation.1 A decrease of arterial distensibility (increased artery wall stiffness) seems to be a common pathologic mechanism for many factors that lead to the occurrence and progression of the vascular changes associated with cardiovascular disease (CVD).2,3 Functional impairment of the arterial wall may occur in an early stage of the atherosclerotic process before structural wall changes become detectible as well as before the occurrence of clinical symptoms of CVD.3 Early detection of this impairment can lead to more effective strategies for the prevention of CVD. This concept that early changes in functional properties of the arterial wall precede the clinical stage of atherosclerosis has been investigated in peripheral arteries (femoral and brachial) and in the aorta for many years. Recent development of high-resolution and high-definition sonography has focused new investigations on the carotid arteries. With these techniques, arterial wall and vessel diameters can be assessed in a dynamic fashion through-out the cardiac cycle as the artery expands and contracts with each cardiac pulsation and relaxation.2,3 Arterial distensibility is, however, only an estimate of the mean strain and modulus at best because the entire soft tissue surrounding the vessel is responding to the change in the volume of the vessel, and the standard boundary identification methods of the vessel wall may not be as reliable as speckle-tracking methods.4 Carotid distensibility (CD) has been introduced as a novel risk factor for CVD in cross-sectional study designs from population-based cohorts, including Atherosclerosis Risk in Communities (ARIC), Second Manifestations of Arterial Disease (SMART), the Rotterdam Study, the Baltimore Longitudinal Study of Aging (BLSA), and the Multiethnic Study of Atherosclerosis (MESA).5–9 Nevertheless, the value of CD in predicting future stroke is currently under debate.10,11 The discrepancy over CD and its relationship to atherosclerosis seems to arise from several plausible factors, such as small sample sizes, different clinical characteristics of the study populations, analyses of CD restricted to different vascular beds, and measurement variability. Additionally, there is a lack of information regarding the reliability of CD measures. Therefore, we sought to evaluate the inter-reader reproducibility of the common carotid artery (CCA) diameters and distensibility measurements in a sample of 118 stroke-free subjects derived from a multiethnic population of northern Manhattan.

Noninvasive vascular ultrasound: an asset in vascular medicine.

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 …

388 Normal vascular aging evaluated by a new tool: e-tracking

Abstract: ; BP 126±15/76±10 mm Hg), free of heart disease, HBP, diabetes, dyslipidemia were studied. LV pump function (CO and EF) was assessed by 2D Echo. Arterial mechanics was evaluated at carotid level by vascular ultra- sound (Aloka SSD-5500) implemented with a double beam tracking system providing distension waveforms, diameter-derived pressure and flow. Pres- sure independent stiffness index (s) and pulse wave velocity (PWV) were estimated. By wave intensity analysis (time-dependent product of first de- rivatives of BP and flow), an index of LV inotropic function was obtained by the amplitude of the early-systolic peak (forward compression wave, FCW). Insulin sensitivity was estimated from plasma glucose and insulin responses to O-GTT (OGIS index). Results: Waist to hip ratio (W/H) correlated directly with MBP, CO, PWV, b (r: 0.34-0.41, p<0.01), but not with EF and FCW. OGIS correlated inversely with W/H, CO, MBP (r: -0.45 to -0.47, p<0.005) but not with stiffness. PWV and s correlated directly with age and MBP (r: 0.35-0.63), but not with OGIS. In a sex-adjusted multivariate model, age and MBP were independent pre- dictors of stiffness (adjusted r2: 0.57). Both PWV and s were inversely re- lated to FCW (r: -0.27 for both, p<0.05), but not to CO and EF. Conclusions: In otherwise healthy subjects from lean to morbid obesity, visceral adiposity is associated with increase in CO, BP and carotid stiff- ness. Visceral adiposity and changes in systemic hemodynamics are asso- ciated with IR. Increased carotid stiffness paralleling visceral adiposity re- sults from increased BP more than from an independent effect of IR. WI analysis, but not established indices of LV performance, discloses an unfavorable VA coupling in obesity.

A PC based system for non-invasive measurement of carotid artery compliance

Abstract: A PC based system for non-invasive, in-vivo measurement of carotid artery compliance is proposed here. The equipment is a low cost and reliable alternative to the expensive B-mode scanner for vessel wall tracking and stiffness measurement of the artery. The system gives an accurate recording of the distensibility waveform of the carotid artery that could then be used to estimate the various measures of arterial compliance. The system is tested with phantom models of the carotid artery and the accuracy and resolution has been found to meet the requirements of the application. Results obtained from human trials have also been presented to illustrate the capability of the instrument to accurately measure carotid artery compliance.