The characteristics that make an image suitable for automated delineation are (see Figure 1): i) high spatial resolution ii) high dynamic range iii) low noise level iv) compound imaging and v) harmonic imaging. A) High-resolution image where the intima and adventitia layers are neatly defined, noise is low, and pixel density is high (about 20 pixels/mm) B) image acquired by a medium-end scanner without compound imaging, where LI is hypoechoic C) images acquired by a low-end equipment without harmonic and compound imaging, where LI is almost invisible and pixel resolution is very low (about 12 pixles/mm) D) example of low-resolution image with high level of image noise. ![]() Samples of high-resolution and low-resolution images. This is another example of a low-resolution image. Figure 1D shows an image where noise is very high due to the lack of despeckling filters embedded in the system and the lack of compound and harmonic imaging. ![]() In Figure 1C the LI is almost anechoic and the pixel density is very low. This is an example of a medium-resolution image. However, the noise level is low and the image has a pixel density comparable to Figure 1A. The LI is not focused and it is not well represented. Figure 1B shows an image where the LI is hypoechoic due to lack of compound imaging. This is an example of what we consider a high-resolution image. In Figure 1A the LI and MA interfaces are clearly represented, the line corresponding to the distal LI is echoic and not interrupted, and the noise level is very low ( i.e., the lumen is dark and homogeneous). Figure 1 shows four sample images acquired by a high-level scanner ( Figure 1A), a medium-level scanner ( Figure 1B) and two low-end equipments ( Figure 1C, D). The quality of the image is compromised unless a high-level scanner is used. 21 Therefore, the availability of a computer based IMT measurement algorithm is fundamental. However, manual measurements are discouraged in multicenter and epidemiological studies because they are user-dependent, not fully standardized, subjective, time-consuming and prone to errors. The distance between LI and MA corresponds to the IMT. The operator places a marker in correspondence of the lumen and intima boundary (LI) and another in correspondence of the media and adventitia boundary (MA). The IMT is measured by an expert operator. 19, 20 Also, ultrasound is an imaging modality with low associated costs, minimal invasiveness, and cheap and portable scanners. The ultrasound-based carotid IMT measurement is accurate and reproducible. 18 There are several advantages to the use of carotid IMT as a marker for CVD in epidemiological studies. Carotid IMT is the most widely adopted and validated ultrasonic marker for the assessment of atherosclerosis and cardiovascular risk, 5- 9 and has been used as the principal marker of CVD in studies ranging across Japan, 10 Europe, 8, 9, 11 China, 12 North America 13- 17 and Latin America. 2- 4 Atherosclerosis causes an increase of the arterial intimamedia thickness (IMT). ![]() The earliest manifestation of the possible onset of a CVD is atherosclerosis, which refers to the degeneration of the arterial wall and the deposition of lipids within the latter. Multicenter assessment protocols and epidemiological studies are the basis for understanding the risk factors and for developing public health messages, including in LMIC. Although nowadays CVD is a major problem for high-income countries, WHO forecasts that CVD will also become common in low and middle income countries (LMIC) where it is predicted to be responsible for one third of deaths by 2040. The World Health Organization (WHO) 1 estimated cardiovascular disease (CVD) to be responsible for one third of all global deaths.
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