Lessons from intravascular ultrasonography: Observations during interventional angioplasty procedures

This article reviews many of the applications of intravascular ultrasonic imaging for coronary and peripheral arterial disease. In vitro studies demonstrate an excellent correlation between ultrasound measurements of lumen and plaque crosssectional area compared with histologic sections. In vivo clinical studies reveal the enhanced diagnostic capabilities of this technology compared with angiography. Ultrasonic imaging also permits visualization of the atherosclerotic plaque itself for the first time in vivo. In addition to accurately describing the plaque morphology, ultrasonography can identify some of the tissue characteristics of the plaque. During interventional procedures, ultrasonic imaging has been shown to be beneficial for enhanced diagnosis as well as improvement of our understanding of the mechanism of newer interventional devices such as directed atherectomy, rotational or TEC atherectomy, or excimer laser. Initial studies suggest that ultrasound guidance of intravascular stent deployment may be critical for optimizing stent placement. Randomized studies are currently in progress to determine whether the guidance provided by intravascular ultrasonic imaging will alter the results of interventional procedures so that the restenosis rate can be improved. © 1993 John Wiley & Sons, Inc.     

Intravascular ultrasound estimation of arterial stenosis

The evaluation of the degree of reduction in the cross-sectional area of an artery has important pathophysiologic and therapeutic implications. Currently, no technique can easily provide this information. In this in vitro study we evaluated the potential of a new imaging technique, intravascular high frequency ultrasound angioscopy, in the estimation of percentage of cross-sectional area stenosis of an artery. To do this, we compared intravascular high frequency ultrasound to previously-validated external high frequency ultrasound and to anatomic estimation of arterial stenosis. Using a prototype intraluminal imaging catheter with a 20 MHz ultrasound transducer at its tip, we imaged 20 arterial segments of various size (15 to 90 mm2 lumen area by anatomy) in the control state and after experimental stenosis. These arterial segments were also imaged by external high frequency ultrasound. Lumen areas were measured from calibrated ultrasound images in the control state and after stenosis, and percentage of cross-sectional area stenosis was calculated. These data were compared to the percentage of area stenosis derived from calibrated anatomic photographs of the arteries taken in the control state and after stenosis. Both intravascular ultrasound angioscopy and external high frequency ultrasound yielded high-resolution, two-dimensional, circumferential images of the arteries. Alterations in vessel area and shape were apparent after creation of stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Imaging of pulmonary vascular disease by intravascular ultrasound

To assess the ability of intravascular ultrasound (IVUS) to image changes in the pulmonary arterial wall associated with pulmonary hypertension (PHT), 10 subjects requiring diagnostic right and left heart catheterization were studied. In addition to measurements of pulmonary artery pressure and pulmonary vascular resistance and pulmonary angiography, when indicated, all underwent simultaneous IVUS imaging in the pulmonary arterial system using a 20 MHz ultrasound transducer mounted on a 2 mm diameter catheter. Four patients had normal pulmonary artery pressures and 6 had varying degrees of PHT. Satisfactory ultrasound images were obtained in 9 out of the 10 patients. In those with normal pulmonary artery pressures ultrasound showed a thin vessel wall with no destinction between separate layers. In patients with systemic PHT, a threelayered vessel wall was apparent and areas compatible with intimai proliferation were seen. In a patient with pulmonary embolic disease areas consistent with mural thrombus were detected at sites of luminal narrowing on the pulmonary angiogram. IVUS is capable of imaging some of the morphological changes in the wall of the pulmonary artery known to occur in longstanding PHT and may therefore become a useful adjunct to haemodynamic measurements and pulmonary angiography for thein vivo assessement of pulmonary vascular disease.     

Intravascular ultrasound imaging following balloon angioplasty

Despite its long history and reliability, contrast angiography has several inherent limitations. Because it is a two-dimensional projection image of the lumen contour, the wall thickness cannot be measured and the plaque itself is not visualized. This results in an underestimation of the amount of atherosclerotic disease by angiography. An assessment of atherosclerosis could be improved by an imaging modality: (1) that has an inherent larger magnification than angiography and (2) that directly visualizes the plaque. Intravascular ultrasound fulfils these criteria. This presentation will provide evidence that intravascular ultrasound may prove complimentary or even superior to angiography as an imaging modality. Intravascular ultrasound demonstrates excellent representations of lumen and plaque morphology ofin vitro specimens compared with histology. There is very close intraobserver and interobserver variability of measurements made from intravascular ultrasound images. Phantom studies of stenoses in a tube model demonstrate that angiography can misrepresent the severity of stenosis when the lumen contour is irregular and not a typical ellipse, whereas intravascular ultrasound reproduces the cross-sectional morphology more accurately since it images the artery from within.In vitro studies of the atherosclerotic plaque tissue characteristics compare closely with the echo representation of fibrosis, calcification, and lipid material. In addition,in vitro studies of balloon angioplasty demonstrate that intravascular ultrasound accurately represents the changes in the structure of artery segments following balloon dilatation.     

Functional magnetic resonance imaging in renal artery stenosis

Renal artery stenosis (RAS) is the leading cause of secondary hypertension. Magnetic resonance (MR) imaging and in particular MR angiography have evolved into important diagnostic tools for the detection and grading of RAS due to the lack of ionizing radiation and nephrotoxic contrast agent. This review describes state-of-the-art MR angiographic techniques and introduces the reader to current concepts of RAS grading with MR angiography. We compare MR angiography with conventional angiography and intravascular ultrasound as a standard of reference. The technical basis of functional imaging techniques such as arterial spin labeling perfusion measurements, contrast-enhanced perfusion measurements, and MR flow measurements are explained. Their value for the grading and detection of RAS and for the differentiation of renovascular from renal parenchymal disease is discussed. An overview about imaging during and after interventional therapy of RAS and an introduction to the current understanding of prediction of successful interventional therapy finishes this review.     

Effects of adaptive speckle filtering on the diagnostic accuracy of ultrasound in vivo tissue characterization

Objective: The purpose of this study was to investigate whether there is an influence of adaptive speckle filtering on ultrasonic tissue characterization. Methods: We have implemented two adaptive two-dimensional speckle filters, the multivariate comparator and the local statistics filter. A tissue characterization system was used to classify ultrasound images showing diffuse liver disease. We compared the classification results achieved before and after speckle filtering. Results: The image texture was completely smoothed out and the classification results got worse when the local statistics filter had been used for adaptive speckle filtering. On the other hand, the image texture was preserved to a certain degree and the classification results were equally good or even slightly improved when the multivariate comparator had been used. In addition, the performance of both filters was demonstrated when they were applied to ultrasound images showing focal liver disease. Conclusion: The two adaptive speckle filters we have investigated differ in their effect on the image texture. The classification results of ultrasonic tissue characterization are reversely influenced by the two adaptive speckle filters. This can be explained with the presence of relevant information in the speckle pattern of homogeneous tissue in ultrasound images.     

血管内超声对粥样硬化冠状动脉成像的研究

研究目的在于评价血管内超声（ＩＶＵＳ）观察粥样硬化冠状动脉（ＣＡ）的安全性和可行性。利用３．５Ｆ，３０ＭＨｚ超声导管对１１例冠心病患者的２０支冠状动脉节段进行了检查，所有病人均顺利接ＩＶＵＳ检查，５例血管造影提示冠脉左主干正常的血管段，ＩＶＵＳ显示有内膜轻度增厚或局灶性斑块，１５支血管造影提示ＣＡ管腔狭窄的血管段，ＩＶＵＳ发现有中至重度的内膜增厚，操作中未发现严重并发症。结论：血管内超声检查是安全可行的，它可提供异常ＣＡ管壁形态学的详细信息。     

Validation of quantitative analysis of intravascular ultrasound images

This study investigated the accuracy and reproducibility of a computer-aided method for quantification of intravascular ultrasound. The computer analysis system was developed on an IBM compatible PC/AT equipped with a framegrabber. The quantitative assessment of lumen area, lesion area and percent area obstruction was performed by tracing the boundaries of the free lumen and original lumen. Accuracy of the analysis system was tested in a phantom study. Echographic measurements of lumen and lesion area derived from 16 arterial specimens were compared with data obtained by histology. The differences in lesion area measurements between histology and ultrasound were minimal (mean ± SD: ?0.27±1.79 mm², p>0.05). Lumen area measurements from histology were significantly smaller than those with ultrasound due to mechanical deformation of histologic specimens (?5.38±5.09 mm², p<0.05). For comparison with angiography, 18 ultrasound cross-sections were obtainedin vivo from 8 healthy peripheral arteries. Luminal areas obtained by angiography were similar to those by ultrasound (?0.52±5.15 mm², p>0.05). Finally, intra- and interobserver variability of our quantitative method was evaluated in measurements of 100in vivo ultrasound images. The results showed that variations in lumen area measurements were low (5%) whereas variations in lesion area and percent area obstruction were relatively high (13%, 10%, respectively). Results of this study indicate that our quantitative method provides accurate and reproducible measurements of lumen and lesion area. Thus, intravascular ultrasound can be used for clinical investigation, including assessment of vascular stenosis and evaluation of therapeutic intervention.     

Three-dimensional intravascular ultrasonography: Reconstruction of endovascular stents in vitro and in vivo

Background: Intravascular ultrasonography displays an artery in loosely related cross-sectional images with limited axial information. However, intravascular ultrasound images are suited to three-dimensional reconstruction. Methods: A comprehensive intravascular ultrasound imaging system was used to reconstruct planar images in three-dimensions. This system consisted of a 25MHz transducer-tipped rigid probe (for in vitro studies) or a 25MHz transducer-tipped catheter within a 3.9F monorail imaging sheath (for in vivo studies), a motorized catheter pullback device that withdraws the transducer at 0.5mm/s, and an image processing computer that stacks 15 cross-sectional images/mm of stent axial length and then performs thresholding-based three-dimensional image rendering. We imaged 10 stents (4 Palmaz–Schatz, 3 Wiktor, 2 Strecker, and 1 Medinvent) in vitro after implantation in freshly harvested saphenous veins and 37 Palmaz-Schatz stents in vivo, 10 in native coronary arteries and 27 in vein grafts, 21 acutely and 18 on follow-up. Results: Three-dimensional reconstruction of images obtained with this system reproduced the geometry of each stent design. In vitro, images of the Palmaz-Schatz stents showed the expanded diamonds, the central articulation, and flaring of both ends of both halves of the stents. Images of the Wiktor stents showed the sinusoidal wave-shaped coils in their helical configuration. Images of the Strecker stents showed the interlocking-loop design with gaps between the terminal loops at either end of the stent. Images of the Medinvent stent reproduced the woven texture formed by braiding the stent wires. Three-dimensional reconstruction of images obtained in vivo also reproduced the spatial geometry of the Palmaz–Schatz stent. However, reconstruction of in vivo images was limited by cardiac-cycle-linked vessel motion and torsion and the presence of echo-dense tissue that could not be separated completely from the stent itself. Conclusions: Properly acquired intravascular ultrasound images can be used to reconstruct the spatial geometry of endovascular stents. Because stent spatial geometry is known and unambiguous, reconstruction of endovascular stents should be one of the tests of imaging systems designed to perform three-dimensional reconstruction of ultrasound images. © 1993 John Wiley & Sons, Inc.     

Effectiveness of yoga on arterial stiffness: A systematic review

ObjectivesArterial stiffness is a major cardiovascular (CV) risk and an independent strong predictor of CV morbidity and mortality. The aim of this systematic review is to evaluate the clinical or interventional studies that assessed the effectiveness of yoga on arterial stiffness in participants of any age or sex, healthy or with any conditions.DesignSystematic review of clinical trials or interventional studies.Data sourcesCochrane Library, Medline/PubMed, Scopus, and Google Scholar databases.Review methodsDatabases were searched till July 2019 for clinical trials or interventional studies whether controlled or uncontrolled, randomized or non-randomized studies assessing the effects of yoga on arterial stiffness. Quality of the studies was assessed by using Physiotherapy Evidence Database (PEDro) Scale.ResultsSeven full-text articles (total number of participants = 362) that evaluated the effect of yoga on arterial stiffness were included in this review. There were three randomized controlled studies and four were non-controlled studies (single group studies). Four studies have shown significant reduction in arterial stiffness, while three studies did not find any significant change in arterial stiffness. The beneficial effects of yoga intervention on arterial stiffness in young adults and elderly hypertensive patients are encouraging. Methodological quality was good for one study, moderate for two studies and poor for four studies.ConclusionsThis review shows that yoga practice is effective in preventing or reducing the arterial stiffness in young healthy and obese, and elderly hypertensive patients. As the methodology of many studies is of low quality and safety measures were not reported, there is a need of quality randomized controlled trials of yoga effects on arterial stiffness among high risk individuals.     

Computed tomography angiography provides limited benefit in the evaluation of patients with pelvic fractures

Introduction

Computed tomography angiography (CTA) has been applied in imaging studies for the assessment of most abdominal and pelvic injuries in some trauma centers. However, in most institutions, CTA is not routinely performed as part of the computed tomography scan protocol. In this study, we aimed to assess the efficiency of CTA in the evaluation of patients with pelvic fractures.

Materials and methods

During the study period, patients with pelvic fracture were retrospectively analyzed. In addition to conventional computed tomography scanning that includes only the single venous phase, CTA with an additional arterial phase was used to obtain more information regarding vascular injuries. Further angiographic examination was performed in the patients with positive results in either the arterial or venous phase. The sensitivity and specificity of the multiphasic CTA images in the evaluation of active arterial hemorrhage were investigated. Furthermore, the results obtained for the arterial and venous phases were also combined to evaluate associated active arterial hemorrhage.

Results

A total of 144 patients with pelvic fractures who underwent CTA were enrolled in this study. Of these patients, 49 (34.0%) had active arterial hemorrhage. The sensitivities of the venous and arterial phase CTA images in the evaluation of active arterial hemorrhage were 100% (49/49) and 89.8% (44/49), respectively. Furthermore, all of the patients with positive results based on the arterial phase images were included in the group of patients with positive results based on the venous phase images. Although there were 4 patients without active arterial hemorrhage based on the angiographic examination, they still underwent embolization.

Conclusions

In the management of patients with pelvic fractures, CTA provides limited benefits in the evaluation of the active arterial hemorrhage. The additional arterial phase may be helpful for distinguishing between arterial and venous hemorrhage. However, this study showed that subsequent treatment was not changed.     

血管内超声溶栓治疗动脉硬化闭塞症的初步研究

目的 探讨经皮血管内超声溶栓再通动脉硬化闭塞症闭塞动脉的可行性。方法 14例有严重下肢缺血症状的动脉硬化闭塞症患者，用血管内超声溶栓仪进行了溶栓治疗。结果 超声溶栓探头在闭塞段血管内重建了通道，所有患者均实现了闭塞血管再通，6例仍有血管狭窄的患者行球囊扩张术。结论 血管内超声溶栓术可以用于再通闭塞的周围动脉，尤其是闭塞范围较长，药物溶栓治疗无效和患者禁忌药物溶栓治疗时，血管内超声溶栓是一种新的可靠的治疗手段。     

Development of a 3 French Dual-Frequency Intravascular Ultrasound Catheter

Coronary plaque morphology, including plaque size and fibrous cap thickness, is thought to contribute to the risk of plaque rupture and future cardiac events. Dual-frequency intravascular ultrasound has been proposed as a possible technique to visualize both large-scale features and superficial detail of coronary plaque; however, it has not been found to be feasible within the constraints of a clinically functional intravascular ultrasound catheter. In this study, we describe the design and fabrication of a dual-frequency catheter using a bidirectional transducer stack with center frequencies of approximately 30 and 80?MHz. We describe how the high-frequency transducer achieves significantly improved axial and lateral resolution (16 and 120?µm, respectively, vs. 50 and 220?µm) at the expense of penetration depth. Finally, imaging of ex vivo human coronary artery segments reveals that the catheter can provide complementary images of the deeper arterial wall and superficial plaque features.     

Variability in ultrasonic measurements of arterial stiffness in the Atherosclerosis Risk in Communities study.

Arterial stiffness is emerging as an important risk marker for cardiovascular disease. Ultrasound-based measurements of arterial stiffness are in use by several large epidemiological studies. The reliability of ultrasonic measurements of arterial stiffness was assessed as part of one of these, the Atherosclerosis Risk in Communities (ARIC) study. ARIC, a prospective, four-center epidemiological study, used B-mode ultrasound with an electronic tracking device to measure arterial stiffness of the carotid artery. Oscillometric blood pressure measures were obtained before and after the arterial wall tracking. Measurement variability was estimated in 36 volunteers who were scanned at three visits conducted at 7- to 14-day intervals. Between- and within-person components of variation were estimated for arterial diameter and blood-pressure measurements. The correlation (R) between repeated measurements for pulse pressure, the percent change in arterial diameter (strain), and the percent and absolute change in the arterial area were 0.69, 0.67, 0.66 and 0.81, respectively. The R for the stress-strain elastic modulus (Ep), arterial distensibility, and arterial compliance were 0.66, 0.67, and 0.77, respectively. The R for the pressure-adjusted diameter change (i.e., diameter change adjusted for diastolic and pulse pressures) was 0.75. In summary, the ultrasonic measurements of arterial stiffness employed in the ARIC study demonstrate excellent short-term repeatability, demonstrating their utility in field settings.     

基于二维超声图像纹理分析判断HIFU凝固性坏死

目的 探讨在高强度聚焦超声(HIFU)治疗中,利用二维超声监控图像在多分辨率下的纹理参数,对HIFU所致凝固性坏死组织进行评价,提高对凝固性坏死判断的敏感度.方法 在相同声强、功率和深度条件下,选用点打的方式辐照新鲜离体牛肝,采集辐照前以及辐照后即刻、1 min、2 min和3 min的二维声像图和灰度图像,利用小波变换提取二维超声图像在多分辨率下的纹理参数,建立支撑矢量机(SVM),对样本进行分析判断.结果 多分辨率下的纹理参数比灰度对HIFU凝固性坏死的判断敏感度要高,且差异有统计学意义(P<0.05).结论 利用多分辨率下的纹理参数来评价HIFU凝固性坏死的方法是可行的,且敏感度高于灰度对凝固性坏死的评价.     

Real-time texture analysis for identifying optimum microbubble concentration in 2-D ultrasonic particle image velocimetry

Many recent studies on ultrasonic particle image velocimetry (Echo PIV) showed that the accuracy of two-dimensional (2-D) flow velocity measured depends largely on the concentration of ultrasound contrast agents (UCAs) during imaging. This article presents a texture-based method for identifying the optimum microbubble concentration for Echo PIV measurements in real-time. The texture features, standard deviation of gray level, and contrast, energy and homogeneity of gray level co-occurrence matrix were extracted from ultrasound contrast images of rotational and pulsatile flow (10 MHz) in vitro and in vivo mouse common carotid arterial flow (40 MHz) with UCAs at various concentrations. The results showed that, at concentration of 0.8∼2 × 10³ bubbles/mL in vitro and 1∼5 × 10⁵ bubbles/mL in vivo, image texture features had a peak value or trough value, and velocity vectors with high accuracy can be obtained. Otherwise, poor quality velocity vectors were obtained. When the texture features were used as a feature set, the accuracy of K-nearest neighbor classifier can reach 86.4% in vitro and 87.5% in vivo, respectively. The texture-based method is shown to be able to quickly identify the optimum microbubble concentration and improve the accuracy for Echo PIV imaging.     

Advances in diagnostic imaging for peripheral arterial disease

Refinements in both noninvasive and invasive imaging techniques have led to significant improvements in both the diagnosis and treatment of peripheral arterial disease. Multiple complementary imaging modalities are available for evaluating these patients. This article reviews the advantages, disadvantages and recent advances in the commonly used clinical applications of duplex ultrasonography, magnetic resonance angiography, computed tomographic angiography, digital subtraction angiography and intravascular ultrasound for arterial imaging in the lower extremities. It also discusses experimental imaging techniques more recently applied to peripheral arterial disease such as PET, hyperspectral imaging and molecular imaging of atherosclerosis. As more is understood about both lesion and patient characteristics that affect their response to peripheral interventions, clinician selection of the various imaging modalities as well as different peripheral interventions will allow for more effective treatment of patients with peripheral arterial disease.     

Advances in diagnostic imaging for peripheral arterial disease

Refinements in both noninvasive and invasive imaging techniques have led to significant improvements in both the diagnosis and treatment of peripheral arterial disease. Multiple complementary imaging modalities are available for evaluating these patients. This article reviews the advantages, disadvantages and recent advances in the commonly used clinical applications of duplex ultrasonography, magnetic resonance angiography, computed tomographic angiography, digital subtraction angiography and intravascular ultrasound for arterial imaging in the lower extremities. It also discusses experimental imaging techniques more recently applied to peripheral arterial disease such as PET, hyperspectral imaging and molecular imaging of atherosclerosis. As more is understood about both lesion and patient characteristics that affect their response to peripheral interventions, clinician selection of the various imaging modalities as well as different peripheral interventions will allow for more effective treatment of patients with peripheral arterial disease.     

Longitudinal displacement of the carotid wall and cardiovascular risk factors: associations with aging, adiposity, blood pressure and periodontal disease independent of cross-sectional distensibility and intima-media thickness

The recently discovered longitudinal displacement of the common carotid arterial wall (i.e., the motion along the same plane as the blood flow), may be associated with incident cardiovascular events and represents a novel and relevant clinical information. At present, there have only been a few studies that have been conducted to investigate this longitudinal movement. We propose here a method to assess noninvasively the wall bi-dimensional (two-dimensional [2-D], cross-sectional and longitudinal) motion and present an original approach that combines a robust speckle tracking scheme to guidance by minimal path contours segmentation. Our method is well suited to large clinical population studies as it does not necessitate strong imaging prerequisites. The aim of this study is to describe the association between the longitudinal displacement of the carotid arterial wall and cardiovascular risk factors, among which periodontal disease. Some 126 Indigenous Australians with periodontal disease, an emerging risk factor, and 27 healthy age- and sex-matched non-indigenous control subjects had high-resolution ultrasound scans of the common carotid artery. Carotid intima-media thickness and arterial wall 2-D motion were then assessed using our method in ultrasound B-mode sequences. Carotid longitudinal displacement was markedly lower in the periodontal disease group than the control group (geometric mean (IQR): 0.15 mm (0.13) vs. 0.42 mm (0.30), respectively; p < 0.0001), independent of cardiovascular risk factors, cross-sectional distensibility and carotid intima-media thickness (p < 0.0001). A multivariable model indicated that the strongest correlates of carotid longitudinal displacement in adults with periodontal disease were age (β-coefficient = −.235, p = .03), waist (β-coefficient = −.357, p = 0.001), and pulse pressure (β-coefficient = .175, p = 0.07), independent of other cardiovascular risk factors, cross-sectional distensibility and pulse wave velocity. Carotid longitudinal displacement, estimated with our approach, is impaired in the periodontal disease group, independent of established cardiovascular risk factors and other noninvasive measures of arterial stiffness, and may represent an important marker of cardiovascular risk.     

Imaging Microvasculature with Contrast-Enhanced Ultraharmonic Ultrasound

Atherosclerotic plaque neovascularization was shown to be one of the strongest predictors of future cardiovascular events. Yet, the clinical tools for coronary wall microvasculature detection in vivo are lacking. Here we report an ultrasound pulse sequence capable of detecting microvasculature invisible in conventional intracoronary imaging. The method combines intravascular ultrasound with an ultrasound contrast agent, i.e., a suspension of microscopic vascular acoustic resonators that are small enough to penetrate the capillary bed after intravenous administration. The pulse sequence relies on brief chirp excitations to extract ultraharmonic echoes specific to the ultrasound contrast agent. We implemented the pulse sequence on an intravascular ultrasound probe and successfully imaged the microvasculature of a 6 days old chicken embryo respiratory organ. The feasibility of microvasculature imaging with intravascular ultrasound sets the stage for a translation of the method to studies of intra-plaque neovascularization detection in humans.