A texture matching method considering geometric transformations in noninvasive ultrasonic measurement of arterial elasticity

Measurement of arterial elasticity can provide an important reference for understanding arterial wall changes that may occur in the early stages of atherosclerosis. Conventional correlation-based methods for evaluating arterial wall movements consider only the translation, ignoring the rotation and deformation, which limits the accuracy of measurement of arterial displacement and its biomechanical properties. This article proposes a novel texture matching method based on ultrasonic B-mode image considering geometric transformations to accurately measure arterial displacement and acquire arterial elasticity noninvasively. The method was validated by simulated images with rotation and deformation and further by measurements in vitro arterial phantom and in vivo common carotid arteries of 20 healthy volunteers. Simulation results demonstrate that the method can improve the accuracy of measurement of arterial displacement. Experimental results show that the elastic modulus of the arterial phantom agrees well with the results obtained from mechanical tests, deviating only 4.1%. The mean elastic modulus of the common carotid arteries is 361.7 ± 93.5 kPa. The texture matching method was shown to be able to measure the displacement and elasticity of the arterial wall with complex geometric transformations and may be clinically useful for early detecting and monitoring atherosclerosis.     

The contribution of vascular smooth muscle, elastin and collagen on the passive mechanics of porcine carotid arteries

The main components responsible for the mechanical behavior of the arterial wall are collagen, elastin, and smooth muscle cells (SMCs) in the medial layer. We determined the structural and mechanical changes in porcine carotid arteries after administration of Triton? X-100, elastase, and collagenase using the inflation-deflation test. The arteries were intraluminarly pressurized from 0 to 200 mmHg, and the outer diameter of the artery was measured. The pressure-strain elastic modulus was determined based on the pressure/diameter ratio. The intima-media thickness, wall thickness, thickness of the tunica adventitia layer, and the area fractions of SMCs, elastin, and collagen within the arterial wall (A(A)(SMC/elastin/collagen, wall)) were measured using stereological methods. The relative changes in the relevant components of the treated samples were as follows: the decrease in A(A)(SMC, wall) after administration of Triton? X-100 was 11% ± 7%, the decrease in A(A)(elastin, wall) after administration of elastase was 40% ± 22%, and the decrease in A(A)(collagen, wall) after the application of collagenase was 51% ± 22%. The Triton? X-100 treatment led to a decrease in the SMC content that was associated with enlargement of the arterial wall (outer diameter) for pressures up to 120 mmHg, and with mechanical stiffening of the arterial wall at higher pressures. Elastase led to a decrease in the elastin content that was associated with enlargement of the arterial wall, but not with stiffening or softening. Collagenase led to a decrease in collagen content that was associated with a change in the stiffness of the arterial wall, although the exact contribution of mechanical loading and the duration of treatment (enlargement) could not be quantified.     

Effects of nitric oxide and sodium nitroprusside on the intrinsic elastic properties of pressurized rat coronary artery

Summary— The study was designed to assess the influence of either nitric oxide (NO) or sodium nitroprusside and the absence of endothelium on the intrinsic elastic properties of coronary arteries from WKY rats. For this purpose, segments of the right interventricular coronary were mounted in an arteriograph where wall thickness and internal diameter were continuously monitored while intraluminal pressure was controlled in the absence of flow. To study the passive properties, pressure-diameter relationships were determined by measuring the corresponding internal diameter for each stepwise increase in intraluminal pressure. Thus, wall stress, strain and incremental elastic modulus (E_inc) were assessed in the following experimental conditions: control, incubation with nitro-L-arginine methyl ester (L-NAME, 100 μM) or L-NAME + L-arginine (L-arg, 100 μM), incubation with sodium nitroprusside (SNP, 100 μM), endothelium removal (CHAPS). The E_inc-stress relationship was not significantly different in the different experimental conditions, but values of E_inc plotted as function of strain were significantly decreased after L-NAME incubation and partly reversed after L-arg addition. The same effect was observed after endothelium destruction but to a lesser extent. After SNP incubation, values of E_inc were significantly decreased for small values of strain and increased for high values of this parameter. These results show that NO synthase inhibition induced, for a given strain, a decrease of elastic modulus in coronary arteries. It can be speculated that functional antagonism exerted by NO against spontaneous contractile tone was reduced. Thus, the smooth muscle cells were in a greater state of activation and probably more strongly involved in the intrinsic elastic properties of this preparation. However, an unexplained effect of NO on wall stiffness cannot be excluded. Conversely, SNP increased the initial diameter and induced an initial decrease in stiffness followed by a subsequent increase. After endothelium destruction, stiffness was significantly decreased compared to control conditions. It can be concluded that NO modulates the intrinsic elastic properties of the coronary arteries through smooth muscle cell relaxation. Furthermore, results with SNP support the hypothesis that the lower the state of activation of the smooth muscle cells, the higher the elastic modulus of the arterial wall in this coronary artery preparation.     

Relation between the elastic properties and intima-media thickness of the common carotid artery

The purpose of the study was to describe the relation between wall elasticity and intima-media thickness in the human carotid artery prior to the development of atherosclerotic plaques. Fifty-eight apparently healthy men, aged 42-65 years (mean 55 years), without symptoms of cardiovascular disease were studied. Thickness and elastic properties of the common carotid artery wall were assessed using ultrasonography and non-invasive arterial pressure measurements. The relation between the calculated intima-media area and the pressure strain elastic modulus was positive and statistically significant on the right but not on the left side. No statistically significant relations were found between the calculated intima-media area and the stiffness or between the intima-media thickness and the elastic modulus or stiffness on either side. Thus, the relations between the common carotid artery intima-media thickness/calculated intima-media area and the common carotid artery elastic modulus/stiffness are weak. In regions without atherosclerotic plaques, the elastic properties of the human carotid artery wall do not seem to be influenced by the wall thickness in an important way.     

Spontaneously hypertensive rat resistance artery structure related to myogenic and mechanical properties

This investigation related arterial structure to myogenic (pressure-dependent) contractile responses in resistance arteries from spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) normotensive control rats under pressurized conditions in vitro. Femoral and mesenteric resistance arteries from either strain were cannulated and pressurized in an arteriograph for the determination of pressure-diameter relationships under passive and active conditions in the range 5-200 mmHg transmural pressure. Arterial geometrical measurements were made under relaxed conditions at 100 mmHg. Media thickness/lumen diameter (M/L) ratios were significantly increased in SHR femoral (5.00+/-0.44% compared with 3.63+/-0.34%; P<0.05) and mesenteric (4.40+/-0.29% compared with 2.62+/-0.23%; P<0.001) arteries compared with those from WKY rats. Maximum myogenic contractions, assessed as minimum normalized diameters, were not significantly different in SHR and WKY rat femoral (0.41+/-0.03 and 0.40+/-0.02 respectively) or mesenteric (0.56+/-0.02 and 0.63+/-0.03 respectively) arteries. Arterial mechanical analyses demonstrated that incremental elastic modulus is reduced in SHR mesenteric arteries, but is not significantly different in SHR femoral arteries, compared with those from WKY rats. Additionally, wall stress at estimated in vivo pressures under passive and active conditions are similar in SHR and WKY rat arteries. These data demonstrate that increased M/L ratios in resistance arteries from SHRs are not associated with increased maximum pressure-dependent contractile responses. Increased M/L ratios in resistance arteries from SHRs are not accounted for by increased vessel wall stiffness, but the hypertension-associated arterial geometrical abnormalities act to normalize wall stress in the face of increased arterial pressure.     

Effects of adrenaline on longitudinal arterial wall movements and resulting intramural shear strain: a first report

Using ultrasound we recently demonstrated that in central elastic arteries as well as in large muscular arteries in humans there is a distinct longitudinal displacement of the arterial wall during the cardiac cycle. Further, for the first time, we also demonstrated that the inner parts of the vessel wall, the intima‐media complex, in these vessels exhibit a larger longitudinal displacement than the outer part of the vessel wall, the adventitial region, introducing the presence of substantial shear strain, and thus shear stress within the vessel wall. The role of these unexplored phenomena is unknown. Here, in a first study on the longitudinal movements of the porcine common carotid artery, we show that administration of adrenaline (epinephrine) might have pronounced effects on the longitudinal displacement of the intima‐media complex. In this experiment the longitudinal displacement of the intima‐media complex increased >200% at the highest blood pressure levels as compared to baseline. Further, shear strain within the wall increased >250%; the longitudinal displacement of the adventitial region being smaller than that of the intima‐media complex. Thus, our results indicate that adrenaline can markedly influence the longitudinal displacement of the arterial wall and the resulting shear strain, and thus shear stress, within the arterial wall. This opens up a new field within cardiovascular research, revealing a previously unknown mechanism in the circulatory system. Further studies on larger materials are needed to confirm our findings and to elucidate the underlying mechanisms and the physiological, pathophysiological and clinical implications of this phenomenon.     

Arteriosclerosis and pulse wave velocity

Impairment of the arterial compliance or loss of Windkessel effect of elastic arteries causes increased afterload to the heart and increased pulsatile flow to the peripheral vasculatures. The former induces left ventricular hypertrophy or dysfunction and the latter induces small vessel damage or end organ dysfunction. Thus, the arterial compliance plays important roles in the course of hypertension. Therefore; it is worthwhile to measure the elastic properties of aortoarterial system in patient with hypertension. The velocity of the pressure wave along an arterial system, known as pulse wave velocity(PWV), is related to the average stiffness of an arterial segment between measurement sites. The measurement of PWV is inversely related to arterial wall distensibility, which offers a simple and potential approach. There are numerous reports which PWV is a forceful marker and predictor of the cardiovascular risk in hypertensive or other arteriosclerotic disorders. Thus, PWV measurement is recommended in patients with hypertension for early detection of organ damages or estimation of the cardiovascular risk, as well as for the evaluation of the effectiveness of the treatment as a surrogate marker.     

正常成人上肢动脉彩色多普勒超声测量

目的　应用彩色多普勒超声检查和测量正常上肢动脉 ,以得出上肢动脉的超声正常值。方法　15 3名健康志愿者 3 0 6条上肢动脉 ,每条上肢分 7个节段。测量解剖学和血流动力学参数。结果　获得上肢动脉各节段各参数超声正常值 ,发现上肢动脉从近心至远心段 ,内径减少 ,管壁变薄 ,收缩期峰值流速、收缩期加速度、搏动指数值下降 (P <0 .0 5 ) ;上肢动脉各节段均可表现多种流速曲线形态 ,近心段以双向三峰所占比例大(67%锁骨下动脉段双向三峰 ) ,腋动脉以远段反向峰渐不明显 (4 5 .2 %肱动脉段单向双峰 )。结论　彩色多普勒超声能成功用于检查上肢动脉 ,发现变异和病变。     

Carotid artery involvement in Takayasu's arteritis: evaluation of the activity by ultrasonography.

The purpose of this study was to investigate the ultrasonographic criteria for determining the activity of carotid lesions in Takayasu's arteritis. In 10 consecutive patients, common carotid arteries with active lesions (n = 8) and inactive lesions (n = 9) were included in the study. The activity of the carotid lesions was determined on the basis of clinical and laboratory findings and computed tomographic scans. Special focus was placed on thickness and echogenicity of the involved arterial wall and outer diameter of the involved arterial segment. All 17 common carotid arteries evaluated showed segmental or diffuse circumferential thickening of the involved wall. The wall thickness was 2.5 to 5.0 mm (mean +/- SD, 3.3 +/- 0.8 mm) in active lesions and 1.1 to 2.0 mm (mean, 1.6 +/- 0.4 mm) in inactive lesions. The outer diameter of the involved segment was 7.0 to 15.0 mm (mean, 10.0 +/- 2.4 mm) in active lesions and 4.9 to 9.5 mm (mean, 6.8 +/- 1.4 mm) in inactive lesions. Active lesions showed hyperechogenicity in the full thickness of the involved wall (n = 6) or concentric triple layers with a hyperechoic middle layer (n = 2). Inactive lesions showed hyperechogenicity (n = 7) or isoechogenicity (n = 2) of the involved wall. One active lesion showed intramural arteries. Although precise measurement to tenths of a millimeter is impossible with the transducer used, prominent wall thickening with a maintained outer diameter in the common carotid artery suggests an active lesion, whereas mild wall thickening with a decreased outer diameter suggests an inactive lesion. Triple layers of a thickened wall with intramural arteries can be an ultrasonographic finding of an active lesion.     

A reproducibility study of a TDI-based method to calculate indices of arterial stiffness

The aim of the study was to investigate the reproducibility of estimation of Young's modulus E and pressure strain elastic modulus Ep, derived from a tissue Doppler imaging (TDI) wall motion technique. Healthy subjects had their arteries insonated at the same sitting by two different observers and at two different sittings by the same observer. From 32 subjects in the reproducibility study, within-scan coefficient of variation (CV) was 4.5%. Intraobserver between-scan CV for E was 12.7% and for Ep 11.0%. Interobserver CVs were 8.3% and 9.3%, respectively. TDI is a reproducible, valid and highly sensitive direct assessment of arterial wall parameters. It is at least as reproducible as other ultrasound based methods for assessing arterial stiffness and also provides increased information about the arterial distension waveform.     

Vascular elasticity from regional displacement estimates

A recently-developed ultrasonic technique for measuring elastic properties of vascular tissue is evaluated using computer simulations, phantom and in vivo human measurements. A time sequence of displacement images is measured over the cardiac cycle to describe the spatial and temporal patterns of deformation surrounding arteries. This information is combined with a mathematical model to estimate an elastic modulus. Computer simulations of ultrasonic echo data from deformed tissues are analyzed to define a signal processing approach. Measurements in flow phantoms, with and without vessel-simulating channel walls, provide an assessment of the accuracy and precision of this technique for vascular elasticity measurements. Finally, preliminary results for the stiffness index (beta) in a study group of healthy human volunteers are compared with previously reported data. We find that careful measurement technique is required to control measurement variability.     

Assessment of the spatial homogeneity of artery dimension parameters with high frame rate 2-D B-mode

To elicit vessel wall inhomogeneities in diameter and distension along an arterial segment, a 2-D vessel wall-tracking system based on fast B-mode has been developed. The frame rate of a 7.5-MHz linear-array transducer (length 36 mm) is enhanced by increasing the pulse-repetition frequency to 10 kHz, decreasing the number of echo lines per frame from 128 to 64, or increasing the interspacing between echo lines with a factor of two or four. Dedicated software has been developed to extract for each echo-line the end-diastolic diameter from the B-mode image and the 2-D distension waveform from the underlying radiofrequency (RF) information. The method is validated in tubes with various focal lesion sizes. Straight segments of presumably homogeneous common carotid arteries have also been tested. The temporal and spatial SD of diameter or distension reveals inhomogeneities in time or space (i.e., inhomogeneities in artery characteristics). The method can be implemented in echo systems supporting high frame rates and real-time processing of radiofrequency data.     

An Inverse Method to Determine Arterial Stiffness with Guided Axial Waves

Many cardiovascular diseases can alter arterial stiffness; therefore, measurement of arterial wall stiffness can provide valuable information for both diagnosis of such diseases in the clinic and evaluation of the effectiveness of relevant drugs. However, quantitative assessment of the in vivo elastic properties of arterial walls in a non-invasive manner remains a great challenge. In this study, we found that the elastic modulus of the arterial wall can be extracted from the dispersion curve of the guided axial wave (GAW) measured using the ultrasound elastography method. It is shown that the GAW in the arterial wall can be well described with the Lamb wave (LW) model when the frequency exceeds a critical value f_c, whose explicit form is determined here based on dimensional analysis method and systematic finite-element simulations. Further, an inverse procedure is proposed to determine both f_c and the elastic modulus of the arterial wall. Phantom experiments have been performed to validate the inverse method and illustrate its potential use in the clinic.     

血管内超声测量血流动力学参数的研究进展

血管内超声显像可在活体中观察血管壁、管腔及斑块形态、性质,甚至斑块成分和管壁功能状态,由此获得的冠状动脉的血流动力学参数(包括管壁的弹性模量和血管壁应力-应变分布等)对于正确诊断冠心病、制定最佳诊疗方案具有重要意义。本文就近年来血管内超声在冠状动脉血流动力学参数测量中的应用进行综述。     

Dynamic behaviour of the common femoral artery: age and gender of minor importance

The distensibility of elastic arteries has been extensively studied, while studies of muscular arteries are sparse. The influences of age and gender on the mechanical properties of the common femoral artery (CFA) were studied. The pulsatile diameter changes of the CFA were noninvasively measured using echo-tracking sonography in 173 healthy volunteers (95 females, 78 males, range 7-81 years). In combination with blood pressure measurements, stiffness (beta) and pressure strain elastic modulus (Ep) were calculated. Neither beta nor Ep was related to age or gender and a considerable interindividual variation was present. The CFA diameter increased with age. In conclusion, the distensibility of this muscular artery is not clearly affected by age or gender, although the diameter increases with age. This indicates remodelling of the arterial wall and an impact of vascular smooth muscles on long-term wall mechanics. Thus, there appear to be fundamental differences in the dynamic behaviour of the common femoral artery when compared to elastic arteries, such as the aorta and the common carotid artery.     

Trandolapril treatment at low dose improves mechanical and functional properties in perfused coronary arteries of spontaneously hypertensive rat

The ex-vivo effects of a 1-month treatment period with trandolapril at a low dose (0.3 mg/kg/day) were assessed on the mechanical and functional alterations observed in SHR coronary arteries. The in-vitro intrinsic elastic properties of the wall in treated SHR coronary arteries were determined in comparison to those of SHR rats. In preconstricted preparations, agonist- and flow-induced dilatations were investigated in arteries of both groups. Arterial segments were cannulated at both ends using an arteriograph system. Internal diameter and wall thickness were continuously monitored while intraluminal pressure and flow were controlled. Wall thickness was reduced in arteries of treated rats compared to those in control SHR (mm): 52 +/- 2 vs. 41 +/- 2, P < 0.001, respectively. Arterial stiffness, expressed by the incremental elastic modulus-stress relationship, was significantly lower in arteries of treated compared to control SHRs. In preconstricted preparations, dilatations induced by bradykinin were significantly greater in treated SHR compared to control SHR arteries whereas dilatations induced by acetylcholine were slightly but not significantly increased. On the other hand, starting flow at the plateau of 5-HT-induced constriction led to dilatations which were not significantly different in the treated compared to the control group. The maximal dilatation induced by flow in arteries of treated rats was obtained for the same value of shear stress compared to that determined in preparations of control SHRs: (dyn/cm2) 63 +/- 3 vs. 61 +/- 2, respectively, NS. These results show that together with hypertrophy, the abnormal mechanical properties observed in the coronary arterial wall of SHR were improved by a low dose of trandolapril treatment. However, differential effects of trandolapril treatment were observed on agonist and flow-induced dilatations. Although flow-induced dilatation seemed to remain unaffected, acetylcholine-induced dilatation was slightly improved and bradykinin-induced dilatation was markedly increased by trandolapril treatment.     

The aging of elastic and muscular arteries: a comparison of diabetic and nondiabetic subjects

OBJECTIVE: To compare age-related changes in the mechanical properties of different arterial segments in normal volunteers and subjects with type 2 diabetes. RESEARCH DESIGN AND METHODS: In 169 subjects (diabetic n = 57 and nondiabetic n = 112), we assessed the mechanical properties of three arterial segments of differing wall composition. Pulse wave velocity (PWV) was measured noninvasively in a thoraco-abdominal segment (carotid femoral PWV [PWV(cf)]), in an upper limb muscular artery (carotid radial PWV [PWV(cr)]), and from the aorta to the finger (PWV from the aorta to the finger [PWV(fin)]). Central aortic compliance (CAC) was also measured. RESULTS: Average CAC was lower (0.662 vs. 0.850, P < 0.05) and all measures of PWV tended to be faster in diabetic subjects despite the fact that they were, on average, 10 years younger. However, these measures were not related to age in diabetic subjects. After correcting for blood pressure, only PWV(cf) was associated with age in nondiabetic subjects (P < 0.001). Expressing results as ratios of nonelastic to elastic arterial segments (i.e., PWV(cr)-to-PWV(cf) and PWV(fin)-to-PWV(cf)) improved the relationship with age. Both PWV(cr)-to-PWV(cf) and PWV(fin)-to-PWV(cf) were significantly associated with age in nondiabetic subjects (r = -0.59, P < 0.001; r = -0.57, P < 0.001) but not in diabetic subjects (r = -0.15, P = 0.302; r = -0.24, P = 0.129). Multivariate analysis showed that the ratios were not associated with systolic blood pressure. CONCLUSIONS: There are significant differences in the rate of age-related decline in vascular stiffness in elastic arteries of nondiabetic compared with diabetic arteries. Diabetic arteries appear to age at an accelerated rate at an earlier age and then reach a functional plateau.     

New approaches for the assessment of vessel sizes in quantitative (cardio-)vascular X-ray analysis

This paper presents new approaches for the assessment of the arterial and reference diameters in (cardio-)vascular X-ray images, designed to overcome the problems experienced in conventional quantitative coronary and vascular angiography approaches. In single or “straight” vessel segments, the arterial and reference diameter directions were made independent of each other in order to be able to measure the minimal lumen diameter (MLD) more accurately, especially in curved vessel segments. For ostial segments, an extension of this approach was used, to allow measurement of ostial lesions in sidebranches more proximal than using conventional methods. Furthermore, two new bifurcation approaches were developed. The validation study shows that the straight segment approach results in significant smaller MLDs (on average 0.032 mm) and the ostial approach achieves on average an increase in %DS of 3.8% and an increase in lesion length of 0.59 mm due to loosening the directional constraint. The validation of our new bifurcation approaches in phantom data as well as clinical data shows only small differences between pre- and post-intervention measurements of the reference diameters outside the bifurcation core (errors smaller than 0.06 mm) and the bifurcation core area (errors smaller than 1.4% for phantom data). In summary, these new approaches have led to further improvements in the quantitative analyses of (cardio-)vascular X-ray angiographies.     

In vitro examination of the coronary artery wall after balloon angioplasty using intracoronary ultrasound

After autopsy 12 human coronary arteries were investigated by intracoronary ultrasound in order to measure the vessel wall dimensions and to detect damage on the vessel wall architecture after balloon angioplasty. Histology revealed artherosclerosis in 11/12 arteries. A total of 41 representative coronary segments were selected for further off-line ultrasound and histological analysis. Intracoronary ultrasound and histological measurements of the vessel wall thickness after balloon dilatation demonstrated a good correlation between the maximum thickness of the intima (histology 0.62 mm vs. intracoronary ultrasound 0.65 mm, r = 0.87) and the intima-media complex (0.80 mm vs. 0.83 mm, r = 0.87), in contrast to a weak one between the minimum thickness (r = 0.46 and r = 0.37). A total of 21 cases of damage occurred during angioplasty; intracoronary ultrasound detected 17. Further analysis showed that it imaged 10 of 11 cases of damage involving more than 30° of the vessel circumference and 7 of 10 cases of damage involving less than 30° of the vessel circumference. After balloon angioplasty of diseased coronary arteries, intracoronary ultrasound is therefore reliable in measuring the maximum wall thickness and in imaging damage involving more than 30° of the vessel wall circumference.     

磁共振黑血序列冠状动脉管壁成像评价粥样硬化斑块初步研究结果:与血管内超声对照研究

目的与血管内超声（IVUS）对照,探讨磁共振黑血序列冠状动脉管壁成像评价冠状动脉斑块的可行性及准确性。方法拟行IVUS检查及行IVUS检查而未行支架植入术的患者11例,分别于IVUS术前及术后10日内行磁共振检查。成像序列采用二维横截面、双反转恢复、呼吸导航心电门控触发、压脂TSE序列,采集自病变冠脉开口至中段无间隔连续扫描,测量以下数据：血管横截面积（CSA）、管腔CSA、斑块负荷、管壁信噪比（SNR）及对比噪声LL（CNR）。在IVUS上将靶冠脉白开口分为每5mm节段,与MRI管壁横截面一一对应。当冠状动脉管壁厚度≥0．5mm时考虑存在斑块。结果共9例病人,9支冠脉,37个层面纳入分析;2例病人被排除（因扫描时间长,病人无法坚持1,扫描成功率82％。37个层面中有20个有斑块。斑块层面的斑块负荷、SNR、CNR大于非斑块层面（分别为0．70±0．11vs0．58±0．14,1．95±0．39vs1．48±0．21,5．47±2．06vs2．99±0．78,P〈0．05）。MRI斑块层面血管CSA、管腔CSA及斑块负荷与IVUS比较,具有良好的相关性（13．66±4．52vs14．92±6．37,4．62±2．23vs6．03±3．85,0．63±0．13vs0．60±0．14,P〈0．05）。结论冠状动脉黑血管壁成像可以发现冠状动脉近中段的粥样硬化斑块,且能够相对评价狭窄段血管面积和管腔面积。