Comparison of grey scale median (GSM) measurement in ultrasound images of human carotid plaques using two different softwares

Abstract

Grey scale median (GSM) measured on ultrasound images of carotid plaques has been used for several years now in research to find the vulnerable plaque. Centres have used different software and also different methods for GSM measurement. This has resulted in a wide range of GSM values and cut-off values for the detection of the vulnerable plaque. The aim of this study was to compare the values obtained with two different softwares, using different standardization methods, for the measurement of GSM on ultrasound images of carotid human plaques. GSM was measured with Adobe Photoshop(®) and with Artery Measurement System (AMS) on duplex ultrasound images of 100 consecutive medium- to large-sized carotid plaques of the Beta-blocker Cholesterol-lowering Asymptomatic Plaque Study (BCAPS). The mean values of GSM were 35·2 ± 19·3 and 55·8 ± 22·5 for Adobe Photoshop(®) and AMS, respectively. Mean difference was 20·45 (95% CI: 19·17-21·73). Although the absolute values of GSM differed, the agreement between the two measurements was good, correlation coefficient 0·95. A chi-square test revealed a kappa value of 0·68 when studying quartiles of GSM. The intra-observer variability was 1·9% for AMS and 2·5% for Adobe Photoshop. The difference between softwares and standardization methods must be taken into consideration when comparing studies. To avoid these problems, researcher should come to a consensus regarding software and standardization method for GSM measurement on ultrasound images of plaque in the arteries.

Comparison of diagnostic values of ultrasound micro-flow imaging and contrast-enhanced ultrasound for neovascularization in carotid plaques

“…The GSM technique provides a quantitative and objective evaluation method for the classification of plaques with different echo types, avoiding the subjectivity of judging the plaque echo types by naked eye evaluation. Therefore, the repeatability is high (30–33). According to Mathiesen et al (34), hypoechoic plaques can increase the risk of ischemic cerebrovascular events, which is significantly correlated with the plaque echo type (P=0.015), and detecting the plaque echo type via two-dimensional ultrasound can predict the risk of ischemic cerebrovascular events.…”

The Swedish CArdioPulmonary BioImage Study: objectives and design

“…Atherosclerosis in the carotid arteries is imaged using a standardized protocol with a Siemens Acuson S2000 ultrasound scanner equipped with a 9L4 linear transducer (both from Siemens, Forchheim, Germany). The two-dimensional greyscale ultrasound image is analysed to determine intima-media thickness, plaque size and number of plaques and to differentiate between homogenous and heterogeneous plaque structures and plaques with different echogenicity [32,41]. Participants with moderate-to-large plaques in the carotid arteries (plaque height exceeding 2.5 mm) are asked to return for a third visit to undergo MRI scanning.…”

Influence of Ultrasound System and Gain on Grayscale Median Values

“…Computer‐assisted methods for plaque classification can reduce GSM variability using image normalization procedures, which linearly scale grayscale values in the image between two different reference points available in every subject . However, even after using normalization, there is a wide range (across studies) of GSM values that represent, for example, the lowest echogenicity value/quintile threshold that is associated with an anechoic arterial wall or vulnerable plaque that may rupture or release emboli and thereby contribute to an adverse cerebrovascular event . Although the GSM is a valid research tool, this range limits the transition of the GSM measurement into widespread clinical use.…”

“…These variations may be due to insufficient compensation for differences in hardware and software used for image acquisition and analysis used in textural feature extraction techniques . Changes in the instrumentation settings, such as dynamic range, time‐gain compensation, overall gain, postprocessing map, and imaging frequency, that a sonographer selects for imaging can result in the same tissue appearing brighter or darker and thereby yield different GSM values .…”