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.

ARTSENS - An image-free system for noninvasive evaluation of arterial compliance

“…The artery detection algorithm has been validated to be capable of detecting artery locations with sensitivity more than 90 % even for SNR as low as 5 dB in the normal range of expected wall motion frequencies between 0.5 -4 Hz [7]. The correlation based wall tracking algorithm has also been independently shown have error less than 10 % [6]. ARTSENS performs synchronized transducer excitation and data capture, and integrates wall detection and tracking algorithms along with on-the-fly distension waveform analysis to enable quick in-vivo measurements.…”

“…A detailed explanation of the various steps in the automated measurement algorithm may be found elsewhere [6], [7]. The artery detection algorithm has been validated to be capable of detecting artery locations with sensitivity more than 90 % even for SNR as low as 5 dB in the normal range of expected wall motion frequencies between 0.5 -4 Hz [7].…”

“…The performance of the wall-detection, tracking and automated measurement algorithms have already been extensively characterized by simulation studies, and experiments conducted using artery phantoms [6], [7]. To evaluate the practical feasibility of performing image-free evaluation of arterial compliance in-vivo, the prototype ARTSENS device was utilized to perform measurements on more than 100 healthy volunteers.…”

“…Every 5 successively obtained cardiac cycles are analysed to detect the time instants corresponding to the end-diastole. The corresponding radiofrequency echo signals are extracted from the data buffer and used to measure the end-diastolic diameter using a dynamic threshold based lumen diameter measurement algorithm [6]. The values of the diastolic time instants calculated in the previous step are also used to split the distension waveform into a set of 5 individual cycles from which the arterial compliance measurements are performed.…”

“…The practical feasibility of an image-free modality for evaluation of arterial compliance in controlled settings has also been demonstrated [6].…”