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Research Papers

# Automatic Measurement of End-Diastolic Arterial Lumen Diameter in ARTSENS

[+] Author and Article Information
Ashish Kumar Sahani

Department of Electrical Engineering,
Chennai 600 036, India
e-mail: ee10d043@ee.iitm.ac.in

Jayaraj Joseph

Healthcare Technology Innovation Centre,
Chennai 600 036, India
e-mail: jayaraj@htic.iitm.ac.in

Thambiran Heart and Vascular Institute,
Chennai 600 040, India
e-mail: hemarrk@yahoo.co.uk

Mohanasankar Sivaprakasam

Department of Electrical Engineering,
Chennai 600 036, India;
Healthcare Technology Innovation Centre,
Chennai 600 036, India
e-mail: mohan@ee.iitm.ac.in

1Corresponding author.

Manuscript received October 13, 2014; final manuscript received May 29, 2015; published online August 6, 2015. Assoc. Editor: John LaDisa.

J. Med. Devices 9(4), 041002 (Aug 06, 2015) (11 pages) Paper No: MED-14-1251; doi: 10.1115/1.4030873 History: Received October 13, 2014

## Abstract

Over past few years, we are developing a system for facilitating large scale screening of patients for cardiovascular risk—arterial stiffness evaluation for noninvasive screening (ARTSENS). ARTSENS is an image-free device that uses a single element ultrasound transducer to obtain noninvasive measurements of arterial stiffness (AS) in a fully automated manner. AS is directly proportional to end-diastolic lumen diameter ($Dd$). Multilayered structure of the arterial walls and indistinct characteristics of intima-lumen interface (ILI) makes it quite difficult to accurately estimate $Dd$ 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 $Dd$. 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 $Dd$ obtained from 85 human volunteers using Hitachi-Aloka eTRACKING system. $Dd$ 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, $Dd$ from all methods show significant positive correlation with age.

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## Figures

Fig. 1

(a) The placement of the probe and the hardware block diagram. (b) A typical frame obtained from CCA by ARTSENS hardware. Approximate positions of PW and DW determined by automatic algorithms are marked. Regions of interests Pf and Df are chosen around them. (c) Shifts in the positions of echoes within Pf and Df are tracked over successive frames to obtain the cumulative distension waveform (D).

Fig. 2

(a) A typical frame obtained from ARTSENS. Automatically determined approximate positions of arterial walls ωp and ωd are indicated. Arterial well (ψ) is chosen around ωp and ωd using Eq. (6). (b) The enlarged image of the ψ and its squared envelope (€). The fading characteristics and speckle noise at ILI can be seen. Dl as perceived by an experienced operator is marked by cursors. The central line divides the envelope into left half (Ł) and right half (-R), which are further processed to locate ILI of each half. Ł is flipped such that its origin is at the central line (8a). The expanse of Ł˜ and -R˜, as explained in Eqs. (8c) and (8d), is marked with two-headed arrows. (c) A schematic diagram of the cross-sectional view of the artery illustrating its general layered structure. ILI has been marked on (b) with respect to this figure.

Fig. 3

TSF applied on two halves of envelope of arterial well Ł' and -R'. Lumen diameter is given by IŁ'+I-R'.

Fig. 4

The Gaussian curves GŁ' and G-R' are fitted to two halves of envelope of the arterial well—Ł' and -R', respectively. ILI is located on the basis of standard deviation of the GF and empirically derived multipliers TGl and TGr.

Fig. 5

The squared envelope of the autocorrelation (Д) of ψ is shown on the left. Dl is the distance between the highest peak and the rising point of S3. HA extracted from S3(13d) is shown on the right. The optimal twin segments (LA) and optimal Gaussian curve (GA) are shown.

Fig. 6

The cumulative distension waveform (D), the lumen diameter waveform (-D = D(L)), and the confidence waveform (C// = C/(L)), normalized between 0 and 1, for the TSF method. D is much smoother than -D but there is high positive correlation between them. In this case, the third point of -D has the highest confidence of measurement, and large error in -D at 12th point is quite apparent which has the lowest confidence of measurement. To obtain a better estimate of Dd, we shift whole waveform D based on the third point (marked by the dashed line) such that D(3) = -D(3).

Fig. 7

The screenshots of B-mode and M-mode images and the final results obtained for a volunteer using Aloka eTRACKING system are shown. The reference value of Dd is highlighted with dashed rectangle.

Fig. 8

(a) Mean percentage error in measurement of end-diastolic lumen diameter using GF employing different values of TGl and TGr is shown. The optimal values of multipliers were found to be TGl = 2.6 and TGr = 0.9 for which total percentage error is 6.2%. (b) Mean percentage error in measurement of end-diastolic lumen diameter using AGF employing different values of TA is shown. The optimal value of TA was found to be 2.1 for which total percentage error is 7.0%.

Fig. 9

The linear regression analysis for all four methods. Best line fit between Dd measured using the reference method and the reported methods are shown. The line (y = x) is plotted in each figure as an ideal reference (dotted). A summary of the analysis is given in Table 2.

Fig. 10

The Bland–Altman plots for diameters measured using eTRACKING and ARTSENS for all the four methods are shown. Mean of the reference and estimated diameters are plotted along horizontal axes and their difference are plotted along the vertical axes. The LA are indicated by dashed lines (- - -) and the mean bias is plotted by the continuous line (—).

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