AM-FM Texture Image Analysis of the Intima and Media Layers of the Carotid Artery

Abstract. The purpose of this paper is to propose the use of amplitude modulation-frequency modulation (AM-FM) features for describing atherosclerotic plaque features that are associated with clinical factors such as intima media thickness and a patient's age. AM-FM analysis reveals the instantaneous amplitude (IA) of the media layer decreases with age. This decrease in IA maybe attributed to the reduction in calcified, stable plaque components and an increase in stroke risk with age. On the other hand, an increase in the median instantaneous frequency (IF) of the media layer suggests the fragmentation of solid, large plaque components, which also lead to an increase in the risk of stroke. The findings suggest that AM-FM features can be used to assess the risk of stroke over a wide range of patient populations. Future work will incorporate a new texture image retrieval system that uses AM-FM features to retrieve intima and intima media layer images that could be associated with the same level of the risk of stroke

In vivo Simulation-Based Learning for Undergraduate Medical Students: Teaching and Assessment.

An increasing emphasis on simulation has become evident in the last three decades following fundamental shifts in the medical profession. Simulation-based learning (SBL) is a wide term that encompasses several means for imitating a skill, attitude, or procedure to train personnel in a safe and adaptive environment. A classic example has been the use of live animal tissue, named in vivo SBL. We aimed to review all published evidence on in vivo SBL for undergraduate medical students; this includes both teaching concepts as well as focused assessment of students on those concepts. We performed a systematic review of published evidence on MEDLINE. We also incorporated evidence from a series of systematic reviews (eviCORE) focused on undergraduate education which have been outputs from our dedicated research network (eMERG). In vivo SBL has been shown to be valuable at undergraduate level and should be considered as a potential educational tool. Strict adherence to 3R (Reduce, Refine, Replace) principles in order to reduce animal tissue usage, should always be the basis of any curriculum. In vivo SBL could potentially grant an extra mile towards medical students' inspiration and aspiration to become safe surgeons; however, it should be optimised and supported by a well-designed curriculum which enhances learning via multi-level fidelity SBL

Despeckle Filtering for Multiscale Amplitude-Modulation Frequency-Modulation (AM-FM) Texture Analysis of Ultrasound Images of the Intima-Media Complex

The intima-media thickness (IMT) of the common carotid artery (CCA) is widely used as an early indicator of cardiovascular disease (CVD). Typically, the IMT grows with age and this is used as a sign of increased risk of CVD. Beyond thickness, there is also clinical interest in identifying how the composition and texture of the intima-media complex (IMC) changed and how these textural changes grow into atherosclerotic plaques that can cause stroke. Clearly though texture analysis of ultrasound images can be greatly affected by speckle noise, our goal here is to develop effective despeckle noise methods that can recover image texture associated with increased rates of atherosclerosis disease. In this study, we perform a comparative evaluation of several despeckle filtering methods, on 100 ultrasound images of the CCA, based on the extracted multiscale Amplitude-Modulation Frequency-Modulation (AM-FM) texture features and visual image quality assessment by two clinical experts. Texture features were extracted from the automatically segmented IMC for three different age groups. The despeckle filters hybrid median and the homogeneous mask area filter showed the best performance by improving the class separation between the three age groups and also yielded significantly improved image quality

Ultrasound Imaging Media Layer Texture Analysis of the Carotid Artery

The intima-media thickness (IMT) of the common carotid artery (CCA) is widely used as an early indicator of cardiovascular disease (CVD). It was proposed but not thoroughly investigated that the media layer (ML), its composition and texture, may be indicative for identifying the risk of stroke and differentiating between patients of high and low risk. In this study we investigate the usefulness of texture analysis of the ML of the CCA. The study was performed on 100 longitudinal ultrasound images acquired from asymptomatic subjects at risk of atherosclerosis. The images were separated into three different age groups, namely below 50, 50 to 60, and above 60 years old. A total of 61 different texture features were extracted from the intima-media complex (IMC), ML and the intima layer (IL). The IMC and ML were segmented manually by a neurovascular expert and automatically by a snakes segmentation system. It was shown that texture features extracted from the IL, ML and IMC are significantly different (mean, gray scale median (GSM), standard deviation, contrast, difference variance, periodicity) and that some of them can be associated with the increase (difference variance, entropy) or decrease (GSM) of patient’s age. It was also shown that the GSM of the ML falls linearly with increasing ML thickness (MLT) and with increasing age. Further research on more subjects is required for estimating other features that may provide information for patients at risk of stroke

An integrated system for the segmentation of atherosclerotic carotid plaque

In this paper, we propose and evaluate an integrated system for the segmentation of atherosclerotic plaque in ultrasound imaging of the carotid artery based on normalization, speckle reduction filtering, and four different snakes segmentation methods. These methods are the Williams and Shah, Balloon, Lai and Chin, and the gradient vector flow (GVF) snake. The performance of the four different plaque snakes segmentation methods was tested on 80 longitudinal ultrasound images of the carotid artery using receiver operating characteristic (ROC) analysis and the manual delineations of an expert. All four methods were very satisfactory and similar in all measures evaluated, with no significant differences between them; however, the Lai and Chin snakes segmentation method gave slightly better results. Concluding, it is proposed that the integrated system investigated in this study could be used successfully for the automated segmentation of the carotid plaque

Performance Evaluation of Active Contour Models for Carotid Plaque Segmentation

In this paper we compare four different snakes segmentation methods for segmenting the athrerosclerotic carotid plaque from longitudinal ultrasound images of the carotid artery. The accuracy and reproducibility of the methods were tested on 80 images and the results were compared with the manual delineations of an expert. The comparison showed that the Lai&Chin snakes segmentation method gave better results with the true positive fraction, TPF, true negative fraction TNF, Williams index, KI, and overlap index, to be 82.70%, 80.89%, 80.66%, and 69.30% respectively. Better false negative fraction, FNF, and false positive fraction, FPF, were given by the Balloon method with 13.90% and, 5.40% respectively

Atherosclerotic carotid plaque texture variability in ultrasound video

Ultrasound video of the common carotid artery (CCA) combined with texture feature analysis has the potential in differentiating between asymptomatic and symptomatic atherosclerotic carotid plaque and is used widely for the assessment of cardiovascular disease. Texture features were extracted from the segmented atherosclerotic carotid plaque for each video frame, from 10 ultrasound videos of the CCA, acquired from 5 asymptomatic and 5 symptomatic subjects. All videos were resolution normalized, despeckled and the plaque was automatically segmented by snakes. The cardiac cycle in each video was identified and the M-mode was generated, thus identifying systolic and diastolic states. From the segmented plaque, different texture features were extracted and studied throughout the cardiac cycle. It is shown that: (i) the plaque gray-scale median (GSM) for the asymptomatic group was significantly higher when compared to the symptomatic group and the same applies for the %CV and the %MAE; (ii) similar to this trend was also the case for features angular second moment, contrast, entropy, and difference variance; (iii) there is plaque GSM variability per frame throughout the cardiac cycle, and this variability differs between the systolic and diastolic states. It is anticipated that the proposed method may help the physician in the assessment of cardiovascular video analysis. However, exhaustive evaluation has to be carried out with more videos and texture features

Manual and automated media and intima thickness measurements of the common carotid artery

The intima-media thickness (IMT) of the common carotid artery (CCA) is widely used as an early indicator of the development of cardiovascular disease (CVD). It was proposed but not thoroughly investigated that the media layer (ML) thickness (MLT), its composition, and its texture may be indicative of cardiovascular risk and for differentiating between patients with high and low risk. In this study, we investigate an automated method for segmenting the ML and the intima layer (IL) and measurement of the MLT and the intima layer thickness (ILT) in ultrasound images of the CCA. The snakes segmentation method was used and was evaluated on 100 longitudinal ultrasound images acquired from asymptomatic subjects, against manual segmentation performed by a neurovascular expert. The mean +/- standard deviation (sd) for the first and second sets of manual and the automated IMT, MLT, and ILT measurements were 0.71 +/- 0.17 mm, 0.72 +/- 0.17 mm, 0.67 +/- 0.12 mm; 0.25 +/- 0.12 mm, 0.27 +/- 0.14 mm, 0.25 +/- 0.11 mm; and 0.43 +/- 0.10 mm, 0.44 +/- 0.13 mm, and 0.42 +/- 0.10 mm, respectively. There was overall no significant difference between the manual and the automated IMC, ML, and IL segmentation measurements. Therefore, the automated segmentation method proposed in this study may be used successfully in the measurement of the MLT and ILT complementing the manual measurements. MLT was also shown to increase with age (for both the manual and the automated measurements). Future research will incorporate the extraction of texture features from the segmented ML and IL bands, which may indicate the risk of future cardiovascular events. However, more work is needed for validating the proposed technique in a larger sample of subjects

Ultrasonic Imaging of Carotid Atherosclerosis

Ultrasound is widely used in vascular imaging because of its ability to visualize, in real-time, the arterial lumen and wall in a noninvasive and harmless way. Monitoring of the arterial characteristics like the vessel lumen diameter, the intima media thickness of the near and far wall, and the morphology of atherosclerotic plaque are very important in order to assess the severity of atherosclerosis and evaluate its progression. Quantitative image analysis based on despeckle filtering, automated or semiautomated segmentation of the intima media or the atherosclerotic plaque, texture feature extraction and selection, and classification support computer-aided diagnosis, enabling early diagnosis, disease monitoring, and better treatment. Emerging techniques in vascular imaging include 3-D imaging, which attempts to provide the physician with a more realistic reconstruction and visualization of the 3-D structure under investigation, telemedicine and ultrasound video compression, and others. Furthermore, it is hoped that once genes contributing to atherosclerosis have been identified, combined with DNA-based tests, risk factors and quantitative ultrasound vascular imaging will contribute toward the implementation of the most effective strategy to minimize cardiovascular death