Assessment of muscle fatigue using sonomyography: muscle thickness change detected from ultrasound images

Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. As the surface electromyography (SEMG) can be used to estimate the features of neuromuscular activations associated with muscle contractions, it has been widely employed as an objective tool to evaluate muscle fatigue. On the other hand, ultrasound imaging can inherently provide the morphological information of individual muscle, thus the architectural changes of muscles during fatigue can be obtained. In this study, we demonstrated the feasibility of using the dimensional change of muscles detected by ultrasound images, named as sonomyography (SMG), to characterize the behavior of muscles when they were in fatigue. The SEMG signals of the muscles were also recorded simultaneously and used for comparison. The right biceps brachii muscles of 8 normal young male adult subjects were tested for 30s under 80% of the maximal voluntary isometric contraction. The muscle fatigue was indicated by the change of the root-mean-square (RMS) and median frequency (MDF) of the SEMG signals. The results showed that the SEMG RMS had a linear increase with time with a rate of 2.9+/-1.9%/s (mean+/-S.D.), while the MDF decreased linearly with a rate of -0.60+/-0.26Hz/s. The muscle thickness, detected from the ultrasound images, continuously increased during the muscle fatigue but with a nonlinear increase with time, which was rapid during the initial 8.1+/-2.1s with a mean deformation rate of 0.30+/-0.19%/s and then became slower with a rate of 0.067+/-0.024%/s up to 20s after the contraction. The muscle deformation at 20s was 3.5+/-1.6%. The results demonstrated that the architectural change of muscles detected using SMG could potentially provide complementary information for SEMG for the muscle fatigue assessment.     

颈动脉斑块的分割和三维图像显示

人体颈动脉和斑块在亮度分布和形态上有一定交叉和重叠,采用普通方式获得的CT或者MRI数据能清晰地反映斑块在颈动脉中的占位在临床上具有重要意义。本研究提出一种新的参数样条定义切割球簇分割得到颈动脉附近体素,并加强颈动脉和斑块的亮度对比和几何尺度放大,以达到与手术解剖颈动脉斑块基本一致的视觉效果。并将该方法与以血管中心线展开拉伸的血管分割方法进行了比较。实验结果表明本文方法可为颈动脉斑块组织分割提供可视的实时显示,可为相关治疗方法和疗效提供视觉分析。     

Automatic detection of the intima-media thickness in ultrasound images of the common carotid artery using neural networks

Atherosclerosis is the leading underlying pathologic process that results in cardiovascular diseases, which represents the main cause of death and disability in the world. The atherosclerotic process is a complex degenerative condition mainly affecting the medium- and large-size arteries, which begins in childhood and may remain unnoticed during decades. The intima-media thickness (IMT) of the common carotid artery (CCA) has emerged as one of the most powerful tool for the evaluation of preclinical atherosclerosis. IMT is measured by means of B-mode ultrasound images, which is a non-invasive and relatively low-cost technique. This paper proposes an effective image segmentation method for the IMT measurement in an automatic way. With this purpose, segmentation is posed as a pattern recognition problem, and a combination of artificial neural networks has been trained to solve this task. In particular, multi-layer perceptrons trained under the scaled conjugate gradient algorithm have been used. The suggested approach is tested on a set of 60 longitudinal ultrasound images of the CCA by comparing the automatic segmentation with four manual tracings. Moreover, the intra- and inter-observer errors have also been assessed. Despite of the simplicity of our approach, several quantitative statistical evaluations have shown its accuracy and robustness.     

Measurement of the 3D arterial wall strain tensor using intravascular B-mode ultrasound images: a feasibility study

Intravascular ultrasound (IVUS) elastography is a promising tool for studying atherosclerotic plaque composition and assessing plaque vulnerability. Current IVUS elastography techniques can measure the 1D or 2D strain of the vessel wall using various motion tracking algorithms. Since biological soft tissue tends to deform non-uniformly in 3D, measurement of the complete 3D strain tensor is desirable for more rigorous analysis of arterial wall mechanics. In this paper, we extend our previously developed method of 2D arterial wall strain measurement based on non-rigid image registration into 3D strain measurement. The new technique registers two image volumes acquired from the same vessel segment under different levels of luminal pressure and longitudinal stress. The 3D displacement field obtained from the image registration is used to calculate the local 3D strain tensor. From the 3D strain tensor, radial, circumferential and longitudinal strain distributions can be obtained and displayed. This strain tensor measurement method is validated and evaluated using IVUS images of healthy porcine carotid arteries subjected to a luminal pressure increase and longitudinal stretch. The ability of the algorithm to overcome systematic noise was tested, as well as the consistency of the results under different longitudinal frame resolutions.     

Manual planimetric measurement of carotid plaque volume using three-dimensional ultrasound imaging

We investigated the utility of three manual planimetric methods to quantify carotid plaque volume. A single observer measured 15 individual plaques from 15 three-dimensional (3D) ultrasound (3D US) images of patients ten times each using three different planimetric approaches. Individual plaque volumes were measured (range: 32.6-597.1 mm3) using a standard planimetric approach (M1) whereby a plaque end was identified and sequential contours were measured. The same plaques were measured using a second approach (M2), whereby plaque ends were first identified and the 3D US image of the plaque was then subdivided into equal intervals. A third method (M3) was used to measure total plaque burden (range: 165.1-1080.0 mm3) in a region (+/- 1.5 cm) relative to the carotid bifurcation. M1 systematically underestimated individual plaque volume compared to M2 (V2 = V1 + 14.0 mm3, r = 0.99, p = 0.006) due to a difference in the mean plaque length measured. Coefficients of variance (CV) for M1 and M2 decrease with increasing plaque volume, with M2 results less than M1. Root mean square difference between experimental and theoretical CV for M2 was 3.2%. The standard deviation in the identification of the transverse location of the carotid bifurcation was 0.56 mm. CVs for plaque burden measured using M3 ranged from 1.2% to 7.6% and were less than CVs determined for individual plaque volumes of the same volume. The utility of M3 was demonstrated by measuring carotid plaque burden and volume change over a period of 3 months in three patients. In conclusion, M2 was determined to be a more superior measurement technique than M1 to measure individual plaque volume. Furthermore, we demonstrated the utility of M3 to quantify regional plaque burden and to quantify change in plaque volume.     

Accurate 3D reconstruction of complex blood vessel geometries from intravascular ultrasound images: in vitro study

We present a technique that accurately reconstructs complex three dimensional blood vessel geometry from 2D intravascular ultrasound (IVUS) images. Biplane x-ray fluoroscopy is used to image the ultrasound catheter tip at a few key points along its path as the catheter is pulled through the blood vessel. An interpolating spline describes the continuous catheter path. The IVUS images are located orthogonal to the path, resulting in a non-uniform structured scalar volume of echo densities. Isocontour surfaces are used to view the vessel geometry, while transparency and clipping enable interactive exploration of interior structures. The two geometries studied are a bovine artery vascular graft having U-shape and a constriction, and a canine carotid artery having multiple branches and a constriction. Accuracy of the reconstructions is established by comparing the reconstructions to (1) silicone moulds of the vessel interior, (2) biplane x-ray images, and (3) the original echo images. Excellent shape and geometry correspondence was observed in both geometries. Quantitative measurements made at key locations of the 3D reconstructions also were in good agreement with those made in silicone moulds. The proposed technique is easily adoptable in clinical practice, since it uses x-rays with minimal exposure and existing IVUS technology.     

Accurate 3D reconstruction of complex blood vessel geometries from intravascular ultrasound images: in vitro study

We present a technique that accurately reconstructs complex three dimensional blood vessel geometry from 2D intravascular ultrasound (IVUS) images. Biplane x-ray fluoroscopy is used to imagethe ultrasound catheter tip at a few key points along its path as the catheter is pulled through the blood vessel. An interpolating spline describes the continuous catheterpath. The IVUS images are located orthogonal to the path, resulting in a non-uniform structured scalar volume of echo densities. Isocontour surfaces are used to view the vessel geometry, while transparency and clipping enable interactive exploration of interior structures. The two geometries studied are a bovine artery vascular graft having U-shapeand a constriction, and a canine carotid artery having multiple branches and a constriction. Accuracy of the reconstructions is established by comparing the reconstructions to (1) silicone moulds of the vessel interior, (2) biplane x-ray images, and (3) the original echo images. Excellent shape and geometry correspondence was observed in both geometries. Quantitative measurements made at key locations of the 3D reconstructions also were in good agreement with those made in silicone moulds. The proposed technique is easily adoptable in clinical practice, since it uses x-rays with minimal exposure and existing IVUS technology.     

基于三维冠状动脉CTA图像的半自动血管分割方法

目的从患者胸腔部位的计算机断层血管造影(computed tomography angiongraphy,CTA)图像中分离出冠状动脉血管,并实现三维的可视化,以便医生对由冠状动脉病变引起的心血管疾病进行诊断和治疗。方法在传统区域生长的基础上提出一种半自动的血管分割方法。首先采用基于灰度值的主动脉预生长,然后进行基于自适应阈值的冠状动脉生长,最后进行后期处理,得到最终分割结果。结果通过这种半自动的区域生长得到的结果,在三维上进行可视化后能够较清晰地判断出血管的粗细、形状、狭窄等情况,且得到的模型也可用于后期的相关计算。结论基于传统区域生长算法的半自动血管分割方法提高了冠状动脉分割的适应性和有效性,能更好地对冠状动脉CTA图像进分割提取。     

Quantification of vessel wall cyclic strain using cine phase contrast magnetic resonance imaging

In vivo quantification of vessel wall cyclic strain has important applications in physiology and disease research and the design of intravascular devices. We describe a method to calculate vessel wall strain from cine PC-MRI velocity data. Forward–backward time integration is used to calculate displacement fields from the velocities, and cyclic Green–Lagrange strain is computed in segments defined by the displacements. The method was validated using a combination of in vitro cine PC-MRI and marker tracking studies. Phantom experiments demonstrated that wall displacements and strain could be calculated accurately from PC-MRI velocity data, with a mean displacement difference of 0.20±0.16 mm (pixel size 0.39 mm) and a mean strain difference of 0.01 (strain extent 0.20). A propagation of error analysis defined the relationship between the standard deviations in displacements and strain based on original segment length and strain magnitude. Based on the measured displacement standard deviation, strain standard deviations were calculated to be 0.015 (validation segment length) and 0.045 (typical segment length). To verify the feasibility of using this method in vivo, cyclic strain was calculated in the thoracic aorta of a normal human subject. Results demonstrated nonuniform deformation and circumferential variation in cyclic strain, with a peak average strain of 0.08±0.11. © 2002 Biomedical Engineering Society. PAC2002: 8761-c, 8719Uv, 8719Rr, 8757Gg     

Prostate boundary segmentation from 3D ultrasound images

Segmenting, or outlining the prostate boundary is an important task in the management of patients with prostate cancer. In this paper, an algorithm is described for semiautomatic segmentation of the prostate from 3D ultrasound images. The algorithm uses model-based initialization and mesh refinement using an efficient deformable model. Initialization requires the user to select only six points from which the outline of the prostate is estimated using shape information. The estimated outline is then automatically deformed to better fit the prostate boundary. An editing tool allows the user to edit the boundary in problematic regions and then deform the model again to improve the final results. The algorithm requires less than 1 min on a Pentium III 400 MHz PC. The accuracy of the algorithm was assessed by comparing the algorithm results, obtained from both local and global analysis, to the manual segmentations on six prostates. The local difference was mapped on the surface of the algorithm boundary to produce a visual representation. Global error analysis showed that the average difference between manual and algorithm boundaries was -0.20 +/- 0.28 mm, the average absolute difference was 1.19 +/- 0.14 mm, the average maximum difference was 7.01 +/- 1.04 mm, and the average volume difference was 7.16% +/- 3.45%. Variability in manual and algorithm segmentation was also assessed: Visual representations of local variability were generated by mapping variability on the segmentation mesh. The mean variability in manual segmentation was 0.98 mm and in algorithm segmentation was 0.63 mm and the differences of about 51.5% of the points comprising the average algorithm boundary are insignificant (P < or = 0.01) to the manual average boundary.     

In vivo measurement of blood vessel wall thickness.

To understand the mechanical properties of arteries and vascular grafts, it is crucial that the wall thickness in these vessels be known. Unfortunately, all availble methods for measuring this parameter require the removal of the vessel, which precludes the study of such vessels as a function of time. A new radiographic technique for measuring the wall thickness of arteries and vascular grafts in vivo, utilizing contrast materials injected into the vessel lumen and applied to the outer surface of the vessel, is described. Radiographs are obtained with a portable X-ray machine and analyzed using a calibrated microscope. The technique has been successfully applied to the in vivo measurement of wall thickness in canine arteries, veins, and experimental vascular grafts. It is concluded that the method provides better than 95% accuracy in a variety of vessels and that it can be used to study changes in vascular grafts after their implantation into the arterial circulation.     

Association of self-reported snoring with carotid artery intima-media thickness and plaque

Previous studies have suggested that self‐reported snoring is associated with atherosclerotic vascular diseases. However, the role of self‐reported snoring as an independent risk factor for subclinical atherosclerosis has not been well established. This study aimed to evaluate whether and to what extent self‐reported snoring is associated with subclinical carotid atherosclerosis after adjusting for traditional cardiovascular risk factors. Carotid intima‐media thickness and plaque were investigated with ultrasonography in 1245 urban Chinese aged 50–79 years between September 2007 and November 2007. Information on self‐reported snoring and measurements of traditional cardiovascular risk factors was also collected. A total of 1050 participants were involved in the final analysis. The prevalence of self‐reported snoring habitually (snoring frequency ≥5 days per week) was 31.5, and 64.3% of the participants in this population had a history of snoring. The mean values of the maximum intima‐media thickness of bifurcation and common carotid arteries in snorers were significantly higher than in non‐snorers (1.08 ± 0.14 mm versus 1.04 ± 0.14 mm, P < 0.001, in carotid bifurcation; 1.03 ± 0.15 mm versus 1.00 ± 0.15 mm, P = 0.002, in common carotid artery). After adjustment for traditional cardiovascular risk factors, logistic regression analysis showed that the odds ratio of self‐reported snoring habitually for increased intima‐media thickness and carotid bifurcation plaque was 1.71 [95% confidence interval (CI): 1.22–2.39; P = 0.002] and 3.63 (95% CI: 2.57–5.12; P < 0.001), respectively. In conclusion, the current study suggested that self‐reported snoring is associated significantly with carotid bifurcation intima‐media thickness and the presence of plaque, independent of traditional cardiovascular risk factors.     

Knee cartilage segmentation and thickness computation from ultrasound images

Quantitative thickness computation of knee cartilage in ultrasound images requires segmentation of a monotonous hypoechoic band between the soft tissue-cartilage interface and the cartilage-bone interface. Speckle noise and intensity bias captured in the ultrasound images often complicates the segmentation task. This paper presents knee cartilage segmentation using locally statistical level set method (LSLSM) and thickness computation using normal distance. Comparison on several level set methods in the attempt of segmenting the knee cartilage shows that LSLSM yields a more satisfactory result. When LSLSM was applied to 80 datasets, the qualitative segmentation assessment indicates a substantial agreement with Cohen’s κ coefficient of 0.73. The quantitative validation metrics of Dice similarity coefficient and Hausdorff distance have average values of 0.91 ± 0.01 and 6.21 ± 0.59 pixels, respectively. These satisfactory segmentation results are making the true thickness between two interfaces of the cartilage possible to be computed based on the segmented images. The measured cartilage thickness ranged from 1.35 to 2.42 mm with an average value of 1.97 ± 0.11 mm, reflecting the robustness of the segmentation algorithm to various cartilage thickness. These results indicate a potential application of the methods described for assessment of cartilage degeneration where changes in the cartilage thickness can be quantified over time by comparing the true thickness at a certain time interval.     

Boundary detection in carotid ultrasound images using dynamic programming and a directional Haar-like filter

The intima-media thickness (IMT) of the carotid artery, obtained from B-mode ultrasound images, has recently been proposed as one of the most useful indices of atherosclerosis and can also be used to predict major cardiovascular events. Ultrasonic measurements of the IMT are conventionally obtained by time-consuming manual tracing of the interfaces between tissue layers. We propose a computerized method to detect the boundary of the intima-media complex using a directional Haar-like filter that can account for the slope of the boundary in an image. The directional Haar-like filter extracts a directional boundary feature as an image feature in the region of interest, which is used to compute a cost function. A cost function includes not only the directional Haar-like filtering value but also the geometric continuity that is computed for every pixel in the region of interest. The optimal boundary pixels are detected by using a dynamic programming approach that searches for the pixel that minimizes the cost function in each column of the image. We compared the performance of the proposed method with that of manual methods performed by two radiologists. The results showed that our approach produces very similar results to those based on manual tracing, and there was no statistically significant difference between the IMT measurements segmented manually and those analyzed using our method.     

Estimation of bladder wall location in ultrasound images

A method of automatically estimating the location of the bladder wall in ultrasound images is proposed. Obtaining this estimate is intended to be the first stage in the development of an automatic bladder volume calculation system. The first step in the bladder wall estimation scheme involves globally processing the images using standard image processing techniques to highlight the bladder wall. Separate processing sequences are required to highlight the anterior bladder wall and the posterior bladder wall. The sequence to highlight the anterior bladder wall involves Gaussian smoothing and second differencing followed by zero-crossing detection. Median filtering followed by thresholding and gradient detection is used to highlight as much of the rest of the bladder wall as was visible in the original images. Then a ‘bladder wall follower’—a line follower with rules based on the characteristics of ultrasound imaging and the anatomy involved—is applied to the processed images to estimate the bladder wall location by following the portions of the bladder wall which are highlighted and filling in the missing segments. The results achieved using this scheme are presented.     

A non-invasive study of alterations of the carotid artery with age using ultrasound images

A region-based method for measurement of arterial diameter to find out the elasticity of the vessel is proposed in this paper. Arterial segments are studied by using images obtained through ultrasound scanning in B-mode. Pulsatile changes of the common carotid artery during diastole and systole are computed. To achieve this, thinned segmentation is done by suitably adjusting the contrast of the image. The diameter changes of the artery wall from the centre of artery are calculated. Fifty-three normal subjects with age group 20–40 years are taken for measurement. Measured diameter is plotted as a graph and pulsatile changes of the artery are obtained. Since no atherosclerotic lesions are detected in the studied subjects, it is suggested that the common carotid artery is a highly compliant artery with a strong alteration of viscoelastic properties with age.     

Hormone replacement therapy in postmenopausal women: carotid intima-media thickness and 3-D volumetric plaque quantification.

OBJECTIVE: The relationship between postmenopausal hormone replacement therapy (HRT) and the risk of stroke has been investigated in a number of epidemiological studies. However, data concerning the quantitative effects of HRT on carotid atherosclerosis, as measured by noninvasive ultrasound methods, are sparse. METHODS: In the present case, we examined 55 postmenopausal women (mean age 57.6 +/- 4.2 years) who were treated for 4.7 years with estrogens, either alone (n = 11) or in combination with progestins (n = 44). They were compared to 46 control subjects without HRT who were matched for age, hypertension, and various other vascular risk factors. At the study onset and 1.5 years later, all participants were examined by Doppler ultrasound and B-mode sonography, and plaque visualization, intima-media-thickness (IMT) and volumetric quantification of carotid plaques was performed. RESULTS: The HRT group had a significantly lower incidence of carotid plaques (18%) than the control group (61%). The mean TMT for the HRT subjects was 0.52 mm in the common carotid artery and 0.46 mm in the internal carotid artery, as compared to 0.68 and 0.62 mm, respectively, for the control subjects. No significant changes in IMT were found in either group. 3-D evaluation of carotid plaques showed increased plaque volume in women without HRT compared to women with HRT. CONCLUSION: We have obtained quantitative data using different noninvasive ultrasound techniques which demonstrate that women receiving HRT develop less severe carotid atherosclerosis, an effect which may be mediated by direct hormonal effects on the carotid wall and, in part, by the indirect influence of hormones on lipoproteins. HRT may, indeed, be more effective on existing atherosclerotic plaques.     

Line filtering for surgical tool localization in 3D ultrasound images

We present a method for automatic surgical tool localization in 3D ultrasound images based on line filtering, voxel classification and model fitting. This could possibly provide assistance for biopsy needle or micro-electrode insertion, or a robotic system performing this insertion. The line-filtering method is first used to enhance the contrast of the 3D ultrasound image, then a classifier is chosen to separate the tool voxels, in order to reduce the number of outliers. The last step is Random Sample Consensus (RANSAC) model fitting. Experimental results on several different polyvinyl alcohol (PVA) cryogel data sets demonstrate that the failure rate of the method proposed herein is improved by at least 86% compared to the model-fitting RANSAC algorithm with axis accuracy better than 1 mm, at the expense of only a modest increase in computational effort. The results of this experiment show that this system could be useful for clinical applications.