Ashish Kumar Sahani

Automated system for imageless evaluation of arterial compliance

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.

Automatic measurement of lumen diameter of carotid artery in A-Mode ultrasound

Accurate measurement of lumen diameter is essential for correct estimation of arterial compliance. We have been developing a new non-invasive arterial compliance measurement tool using a single element ultrasound transceiver. In this paper we propose a new method for measurement of lumen diameter from single line of Radio-Frequency Signal (RF) obtained from the common carotid artery (CCA). The method is free from fixed thresholds and uses shape fitting to get objective measurement. The accuracy of the algorithm was found to be better than 5 % for software simulated and phantom arteries and better than 10 % in case of data obtained from CCA of human volunteers.

Automatic Measurement of End-Diastolic Arterial Lumen Diameter in ARTSENS

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.

An improved method for detection of carotid walls in ARTSENS.

We have been developing a fully automated ultrasound based imageless system to facilitate mass screening of patients for future risk of cardiovascular diseases. The device shall enable a general medical practitioner to non-invasively measure the local arterial stiffness of common carotid artery (CCA) and has been acronymed ARTerial Stiffness Evaluation for Non-invasive Screening (ARTSENS™). Complete automation of the system requires providing assistance in placement of probe over the CCA location and automatic identification of approximate location of proximal wall (PW) and distal wall (DW) of the CCA. In this paper we propose a method based on temporal motion of PW and DW over successive A-Mode frames to locate the CCA. We evaluated the performance of the algorithm with data obtained from CCA of 30 subjects. It could correctly identify the CCA in more than 70 % of trials. We also propose a method for preprocessing the frames by using the transmitted pulse wavelet. This improved the detection rate significantly. False positives were always less than 6% of total detections.

Carotid and Jugular Classification in ARTSENS

Over past few years our group has been working on the development of a low-cost device, ARTSENS, for measurement of local arterial stiffness (AS) of the common carotid artery (CCA). This uses a single element ultrasound transducer to obtain A-mode frames from the CCA. It is designed to be fully automatic in its operation such that, a general medical practitioner can use the device without any prior knowledge of ultrasound modality. Placement of the probe over CCA and identification of echo positions corresponding to its two walls are critical steps in the process of measurement of AS. We had reported an algorithm to locate the CCA walls based on their characteristic motion. Unfortunately, in supine position, the internal jugular vein (IJV) expands in the carotid triangle and pulsates in a manner that confounds the existing algorithm and leads to wrong measurements of the AS. Jugular venous pulse (JVP), on its own right, is a very important physiological signal for diagnosis of morbidities of the right side of the heart and there is a lack of noninvasive methods for its accurate estimation. We integrated an ECG device to the existing hardware of ARTSENS and developed a method based on physiology of the vessels, which now enable us to segregate the CCA pulse (CCP) and the JVP. False identification rate is less than 4%. To retain the capabilities of ARTSENS to operate without ECG, we designed another method where the classification can be achieved without an ECG, albeit errors are a bit higher. These improvements enable ARTSENS to perform automatic measurement of AS even in the supine position and make it a unique and handy tool to perform JVP analysis.

An Imageless Ultrasound Device to Measure Local and Regional Arterial Stiffness

Arterial stiffness (AS) has been shown to be an important marker for risk assessment of cardiovascular events. Local arterial stiffness (LAS) is conventionally measured by evaluating arterial distensibility at particular arterial sites through ultrasound imaging systems. Regional arterial stiffness (RAS) is generally obtained by evaluating carotid to femoral pulse wave velocity (cfPWV) through tonometric devices. RAS has a better prognostic value than LAS and cfPWV is considered as the gold standard of AS. Over the past few years our group has been developing ARTerial Stiffness Evaluation for Non-Invasive Screening (ARTSENS), an inexpensive and portable device to measure the LAS. It uses a single element ultrasound transducer to obtain A-Mode frames from the desired artery and is fully automated to enable a non-expert to perform measurements. In this work, we report an extension of ARTSENS to enable measurement of cfPWV that now makes it the only fully automatic device that can measure both LAS and RAS. In this paper, we provide a general review of the ARTSENS and compare it with other state-of-the-art AS measurement systems. cfPWV measurement using ARTSENS was cross-validated against SphygmoCor by successive measurements with both devices on 41 human subjects and excellent agreement between both devices was demonstrated (Coefficient of determination and, limits of agreement m/s). The inter-device correlation between ARTSENS and SphygmoCor was found to be better than other similar studies reported in the literature.

Automatic estimation of carotid arterial pressure in ARTSENS

Over past few years our group has been developing ARTSENS®, a low-cost, portable and non-invasive tool for measurement of arterial stiffness (AS). AS of the common carotid artery (CCA) has high prognostic value in stratification of risk of contracting cardiovascular disease (CVD) in future. ARTSENS uses a single element ultrasound transducer to obtain A-Mode frames from the CCA and processes them to obtain the diameter distension waveform. For calculation of AS, any AS measurement system requires the pulse pressure in the artery under investigation. In absence of reliable methods to estimate the carotid arterial pressure (CAP), in conventional AS measurement systems, the brachial arterial pressure (BAP) is used as a surrogate for the CAP to calculate the AS. This can lead to large errors, as there can be large difference in systolic pressures at both sites, especially in young subjects. In this paper we report an extension to the ARTSENS system to estimate the CAP from the BAP. This uses the fact that mean and diastolic pressures at both arterial sites are the same. We made the required hardware to obtain the systolic, mean and diastolic BAP. We then use the diameter distension waveform, obtained by processing ultrasound frames from ARTSENS, as a surrogate for the CAP waveform which is scaled and shifted to obtain the CCA pulse pressure (CPP). BAP and CAP were estimated for 10 human subjects using the new system. Bland-Altman analysis shows that ARTSENS is able to get BAP within acceptable limits of accuracy and pulse pressure is on an average 17 mmHg lower in CCA compared to the brachial artery which is in consonance with findings by other investigators.

Comparison of measurement of the augmentation index from ARTSENS and eTRACKING

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.