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Design Innovation

A Virtual Instrument for Automated Measurement of Arterial Compliance

[+] Author and Article Information
Jayaraj Joseph

Department of Electrical Engineering, ESB 317, Measurements and Instrumentation Laboratory, Indian Institute of Technology Madras, 600036, Chennai, Indiajayaraj85@gmail.com

V. Jayashankar

Department of Electrical Engineering, ESB 312, Measurements and Instrumentation Laboratory, Indian Institute of Technology Madras, 600036, Chennai, Indiajshankar@ee.iitm.ac.in

J. Med. Devices 4(4), 045004 (Dec 03, 2010) (13 pages) doi:10.1115/1.4002493 History: Received February 19, 2010; Revised August 17, 2010; Published December 03, 2010; Online December 03, 2010

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 10μm 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.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Noninvasive measurement of arterial compliance

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Figure 2

Measurement system architecture

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Figure 3

(a) Pulse driver circuit and (b) level shifted gate drive signals of MOSFETs

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Figure 4

Conceptual sketch of the carotid artery and expected echo peaks

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Figure 5

Flow chart of the dynamic threshold algorithm

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Figure 6

Gates positioned around the arterial walls

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Figure 7

Arterial wall echoes in successive acquisitions

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Figure 8

Algorithm for automated measurement of arterial distensibility

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Figure 9

Simulated echo signal with four peaks

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Figure 10

Convergence of the dynamic threshold algorithm

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Figure 11

Error in distension measurement

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Figure 12

Error in diameter measurement

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Figure 14

Dynamic phantom model

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Figure 15

Diameter of the dynamic phantom

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Figure 16

B-mode image of the dynamic phantom when the diameter is (a) minimum and (b) maximum

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Figure 17

A-scan of the echoes from the dynamic phantom when the diameter is (a) minimum and (b) maximum

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Figure 18

Ultrasound echo signal (rf) from the human carotid artery

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Figure 19

M is the mode image of the carotid artery

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Figure 20

Carotid diameter waveform

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Figure 21

Longitudinal B-mode image of the carotid artery of volunteer A during diastole and systole. The corresponding lumen diameters measured using on-screen calipers are also indicated.

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Figure 22

The front panel of the virtual instrument showing the automatic measurement of distension from the A-scan signal

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