Malay Ilesh Shah

Ultrasound signal quality parameterization for image-free evaluation of arterial stiffness.

We are in process of developing an image-free, single element ultrasound system for automated evaluation of arterial stiffness, we call it ARTSENS. The lack of a guiding image for arterial visualization necessitates intelligent analysis of ultrasound radio frequency (RF) echo signals to obtain reliable measurements. In this paper, we propose a novel algorithm to parameterize the echo signal received from the common carotid artery (CCA) to improve accuracy and reliability of arterial stiffness measurement. The echo signal quality is parameterized using features such as sharpness of arterial wall and energy ratio. A signal quality score is calculated by integrating the results from each feature. This score is used to triage the set of available echo signals recorded from each subject and select the best signal for computation of stiffness values. The performance of signal quality algorithm is tested using a database of carotid artery echo signals recorded from 28 human volunteers. It was observed that both the accuracy and reliability of the stiffness measurements were improved after triaging using the signal quality parameterization algorithm.

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.

Image-free evaluation of carotid artery stiffness using ARTSENS: a repeatability study.

Evaluation of arterial stiffness is significant in early detection and vascular diagnosis. We have developed and validated an image free system called ARTSENS for evaluation of carotid artery stiffness. In this paper, we present a detailed study on the repeatability of arterial stiffness measurements performed using ARTSENS. The study protocol was designed to emulate typical constraints encountered in field usage of ARTSENS as a screening tool. The intra operator variability (repeatability) of ARTSENS was verified by in-vivo measurements on 18 subjects. Inter operator variability (reproducibility) was also studied. The ability of the instrument to give reliable measurements in both sitting and supine posture of the subject was verified. Further, the variation of arterial stiffness measurements over different times of the day was investigated to verify the ability of the instrument to give a practically usable stable measure of stiffness. The repeatability and reproducibility of ARTSENS measurements was found to be comparable to those provided by state of art image-based systems. Stiffness measurements provided by ARTSENS were found to be stable over a day indicating utility of the instrument in providing a quick and reliable measure of carotid artery stiffness.

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.

ARTSENS® Pen: A portable, image-free device for automated evaluation of vascular stiffness

Evaluation of vascular stiffness is significant in diagnosis for early detection of vascular injury and has potential in screening individuals at risk of future cardiovascular events. State of art techniques use an imaging system for measuring carotid artery stiffness, or rely on carotid-femoral pulse wave velocity (PWV) to evaluate vascular stiffness. These techniques are costly, require expertise to perform and are not amenable for scaling to the population level. To address this gap, we have developed ARTSENS® Pen, a high portable, small, ultrasound based instrument for automated evaluation of carotid artery stiffness. The device has an integrated hardware for ultrasound signal acquisition and digitization that operate along with any Windows tablet for data visualization and result display. Algorithms for real time signal processing and automated artery wall identification and tracking ensures a completely automated measurement of carotid artery stiffness with no operator input. The accuracy of automated arterial dimension measurements performed by ARTSENS®Pen is verified by phantom studies in comparison with a reference ultrasound imaging system. The ability of the device to provide reliable measures of arterial stiffness in-vivo is verified by a systematic study on 29 volunteers. The inter operator and intra-operator variability of stiffness index, β was evaluated to be 17% and 9% respectively. The ARTSENS® Pen was found to be capable of providing accurate and repeatable measures of arterial stiffness in an easy manner and has strong potential in large scale vascular screening.

Arterial compliance probe for calibration free pulse pressure measurement

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.

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.

Arterial compliance probe for cuffless evaluation of carotid pulse pressure

Objective Assessment of local arterial properties has become increasingly important in cardiovascular research as well as in clinical domains. Vascular wall stiffness indices are related to local pulse pressure (ΔP) level, mechanical and geometrical characteristics of the arterial vessel. Non-invasive evaluation of local ΔP from the central arteries (aorta and carotid) is not straightforward in a non-specialist clinical setting. In this work, we present a method and system for real-time and beat-by-beat evaluation of local ΔP from superficial arteries—a non-invasive, cuffless and calibration-free technique. Methods The proposed technique uses a bi-modal arterial compliance probe which consisted of two identical magnetic plethysmograph (MPG) sensors located at 23 mm distance apart and a single-element ultrasound transducer. Simultaneously measured local pulse wave velocity (PWV) and arterial dimensions were used in a mathematical model for calibration-free evaluation of local ΔP. The proposed approach was initially verified using an arterial flow phantom, with invasive pressure catheter as the reference device. The developed porotype device was validated on 22 normotensive human subjects (age = 24.5 ± 4 years). Two independent measurements of local ΔP from the carotid artery were made during physically relaxed and post-exercise condition. Results Phantom-based verification study yielded a correlation coefficient (r) of 0.93 (p < 0.001) for estimated ΔP versus reference brachial ΔP, with a non-significant bias and standard deviation of error equal to 1.11 mmHg and ±1.97 mmHg respectively. The ability of the developed system to acquire high-fidelity waveforms (dual MPG signals and ultrasound echoes from proximal and distal arterial walls) from the carotid artery was demonstrated by the in-vivo validation study. The group average beat-to-beat variation in measured carotid local PWV, arterial diameter parameters—distension and end-diastolic diameter, and local ΔP were 4.2%, 2.6%, 3.3%, and 10.2% respectively in physically relaxed condition. Consistent with the physiological phenomenon, local ΔP measured from the carotid artery of young populations was, on an average, 22 mmHg lower than the reference ΔP obtained from the brachial artery. Like the reference brachial blood pressure (BP) monitor, the developed prototype device reliably captured variations in carotid local ΔP induced by an external intervention. Conclusion This technique could provide a direct measurement of local PWV, arterial dimensions, and a calibration-free estimate of beat-by-beat local ΔP. It can be potentially extended for calibration-free cuffless BP measurement and non-invasive characterization of central arteries with locally estimated biomechanical properties.

iQuant™ Analyser: A rapid quantitative immunoassay reader

Lateral flow immunoassays (LFIA) used in rapid quantitative point of care testing require an accurate, reliable and easy to operate instrument to read the LFIA kit and calculate the quantitative result value. We present iQuant® Analyser, an immunoassay reader designed for reading the Quanti® range of LFIA test kits for key markers such as HbA1C, Vitamin D, TSH etc. The instrument utilizes a laser based confocal optics system to capture the test and control lines from the LFIA kit, digitizes the fluorescent signal with high spatiotemporal resolution, computes necessary peak area ratios, applies calibration curves and declares the final result in an automated manner with minimal operator input. The instrument uses kit specific calibration information embedded on each LFIA test kit, to compute the final clinical parameter without using any external calibration chip. An intuitive icon based interface enables easy operation with minimal key presses, suited for point of care applications. The technology is designed in a modular manner to enable the instrument to perform tests on various parameters such as HbA1C, TSH, and Vitamin D etc without any hardware changes, using test-specific LFIA kits. The functional performance of the iQuant Analyser was verified over the range of expected area ratio values with standard reference cartridges that provided stable fluorescent lines. Repeatability of the instrument was found to be excellent with coefficient of variation (CoV) of area ratios found to be less than 1%. The inter-instrument reproducibility was also found to be good with CoV less than 4 %. Tests using blood samples with Quanti LFIA kits verified the accuracy of HbA1C results to be acceptable as per international standards with errors < 4 %. The iQuant Analyser is a portable, easy to use rapid quantitative immunoassay reader best suited for point of care applications.

ImageQuant: An image-based quantitative Immunoassay Analyzer

Lateral flow immunoassay (LFIA) is popularly employed in point-of-care (PoC) diagnostics for quantitative estimation of a particular analyte present in a sample. Here, we present a compact, affordable and easy-to-use quantitative LFIA reader: ImageQuant Analyzer. This is an image-based analyzer for LFIA test kits. It gives a quantitative estimate of the target analyte — a good improvement over existing semi-quantitative or qualitative image-based LFIA readers. The instruments hardware architecture and software are described in this paper. The Coefficient of Variation (CoV) for repeatability and reproducibility of the measurements was verified with four stable fluorescence cartridges. The CoV for repeatability test across all four reference cartridges was found to be less than 1 %. The variation observed for the reference cartridges across two instruments was also found to be good — 2.3 % for reproducibility test. The instrument was tested with human blood and serum samples on two distinct LFIA tests; Glycated Hemoglobin (HbA1c) and Vitamin D. The tests using blood/serum samples with both LFIA kits demonstrated excellent correlation. The correlation between the value measured by standard lab reference instrument and ImageQuant ratio-metric calculated output was 0.97 and 0.95 for HbA1C and Vitamin D tests respectively. The ImageQuant Analyzer can be a good substitute over traditional bulky, expensive LFIA Analyzers overcoming the many challenges posed by the latter in POC applications.