Exploring 3D elastic-wave scattering at interfaces using high-resolution phased-array system.

The elastic-wave scattering at interfaces, such as cracks, is essential for nondestructive inspections, and hence, understanding the phenomenon is crucial. However, the elastic-wave scattering at cracks is very complex in three dimensions since microscopic asperities of crack faces can be multiple scattering sources. We propose a method for exploring 3D elastic-wave scattering based on our previously developed high-resolution 3D phased-array system, the piezoelectric and laser ultrasonic system (PLUS). We describe the principle of PLUS, which combines a piezoelectric transmitter and a 2D mechanical scan of a laser Doppler vibrometer, enabling us to resolve a crack into a collection of scattring sources. Subsequently, we show how the 3D elastic-wave scattering in the vicinity of each response can be extracted. Here, we experimentally applied PLUS to a fatigue-crack specimen. We found that diverse 3D elastic-wave scattering occurred in a manner depending on the responses within the fatigue crack. This is significant because access to such information will be useful for optimizing inspection conditions, designing ultrasonic measurement systems, and characterizing cracks. More importantly, the described methodology is very general and can be applied to not only metals but also other materials such as composites, concrete, and rocks, leading to progress in many fields.

High-Selectivity imaging of the closed fatigue crack due to thermal environment using surface-acoustic-wave phased array (SAW PA).

Crack closure can cause the underestimation or misdetection of fatigue cracks in ultrasonic testing (UT). Fatigue-crack closure due to an environmental factor, i.e., high temperature, was found in eddy current testing (ECT), which is used to inspect the vicinity of surfaces. However, its effect and countermeasures have yet to be examined in UT. In this study, we examined the fatigue-crack closure induced by heat processing using a surface-acoustic-wave phased array (SAW PA). SAW PA is a phased-array imaging method using Rayleigh waves, which can sensitively visualize defects in the vicinity of surfaces. As a result, the intensity of crack responses visualized by SAW PA markedly decreased after the heat processing of a fatigue-crack specimen. Furthermore, we demonstrated that the combination of SAW PA with a crack opening method, global preheating and local cooling (GPLC), and a load difference phased array (LDPA) is useful for the high-selectivity imaging of closed fatigue cracks. We also discussed a possible mechanism of the fatigue-crack closure induced by heat processing.

Development of Low-Frequency Phased Array for Imaging Defects in Concrete Structures.

The nondestructive inspection of concrete structures is indispensable for ensuring the safety and reliability of aging infrastructures. Ultrasonic waves having a frequency of tens of kHz are frequently used to reduce the scattering attenuation due to coarse aggregates. Such low frequencies enable the measurement of the thickness of concrete structures and detection of layer-type defects, such as delamination, whereas it causes a lack of sensitivity to crack-type defects. In this paper, to realize the ultrasonic phased array (PA) imaging of crack-type defects, we fabricated a low-frequency (LF) array transducer with a center frequency of hundreds of kHz. To avoid the crosstalk between piezoelectric elements and dampen the vibration of each element, we adopted soft lead zirconate titanate (soft PZT) with a low mechanical quality factor. Subsequently, we optimized the geometry of each piezoelectric element using a finite element method to generate a short pulse. After validating the design in a fundamental experiment using a single-element transducer, we fabricated a 32-element array transducer with a center frequency of 350 kHz. To show the imaging capability of the LF array transducer, we applied it to a concrete specimen with a delamination. As a result, the PA with the LF array transducer clearly visualized the delamination, which could not be visualized using the PA with a 2.5 MHz array transducer. Furthermore, we applied it to a more challenging defect, a slit, which is sometimes used to simulate crack-type defects. As a result, the PA with the LF array transducer clearly visualized a slit of 1 mm width and 40 mm height in a concrete specimen. Thus, we demonstrated the usefulness of the LF array transducer for inspecting crack-type defects.

Nonlinear ultrasonic phased array with fixed-voltage fundamental wave amplitude difference for high-selectivity imaging of closed cracks.

The nondestructive evaluation of closed cracks is a challenging subject in ultrasonic testing. Recently, nonlinear ultrasonic phased array with fixed-voltage fundamental wave amplitude difference (fixed-voltage FAD) has been proposed as a practical approach. In this study, the maximum incident wave amplitude, which is one of the most critical parameters in closed-crack imaging, was investigated. First, a theoretical model was formulated to explicitly show the essence of the fundamental principle of FAD and the advantage of fixed-voltage FAD over different-voltage FAD. In experiments, the authors imaged a closed fatigue crack using a nonlinear ultrasonic phased array with fixed-voltage FAD while varying the incident wave amplitude. It was found that when the incident wave amplitude was sufficiently high, the nonlinear image visualized the closed crack tip, which could not be visualized in linear images. In addition, the incident-wave-amplitude dependence of the nonlinear responses was quantified. It was found that different parts within a single fatigue crack showed different nonlinear behaviors. This suggests that fixed-voltage FAD is useful not only for practical application of closed crack imaging but also for examining the nonlinear dynamics at various parts of closed cracks with a high spatial resolution.

Fundamental wave amplitude difference imaging for detection and characterization of embedded cracks.

An ultrasonic technique for imaging nonlinear scatterers, such as partially-closed cracks, buried in a medium has been recently proposed. The method called fundamental wave amplitude difference (FAD) consists of a sequence of acquisitions with different subsets of elements for each line of the image. An image revealing nonlinear scatterers in the medium is reconstructed line by line by subtracting the responses measured with the subsets of elements from the response obtained with all elements transmitting. In order to get a better insight of the capabilities of FAD, two metallic samples having a fatigue or thermal crack are inspected by translating the probe with ultrasonic beam perpendicular (i.e. parallel) to the crack direction which is the most (i.e. less) favorable case. Each time, the responses of the linear scatterers (i.e. conventional image) and nonlinear scatterers (i.e. FAD image) are compared in term of intensity and spatial repartition. FAD exhibits higher detection specificity of the crack with a better contrast than conventional ultrasound imaging. Moreover, we observe that both methods give complementary results as nonlinear and linear scatterers are mostly not co-localized. In addition, we show experimentally that FAD resolution in elevation and lateral follows the same rule as the theoretical resolution of conventional ultrasonic technique. Finally, we report that FAD gives the possibility to perform parametric studies which let the opportunity to address the physical mechanisms causing the distortion of the signal. FAD is a promising and reliable tool which can be directly implemented on a conventional open scanner ultrasound device for real-time imaging. This might contribute to its fast and wide spread in the industry.

The impairment of endocardial radial strain is related to aortic stenosis severity in patients with aortic stenosis and preserved LV ejection fraction using two-dimensional speckle tracking echocardiography.

BACKGROUND: Myocardial function is heterogeneous in different myocardial layers. Recently, two-dimensional speckle tracking echocardiography has been used to define myocardial deformation parameters of the left ventricular (LV) segment. This study aimed to investigate strain in subendocardial and subepicardial layers in patients with aortic stenosis (AS) and preserved LV ejection fraction (LVEF) using speckle tracking echocardiography. METHODS: Parasternal short-axis and apical long-axis views of the left ventricle were acquired at the mid-papillary level in 35 control subjects and 32 patients with AS and preserved LVEF. Radial, circumferential, and longitudinal strain in subendocardial and subepicardial layers at the posterior and anteroseptal segments were calculated. RESULTS: There was no significant difference in circumferential strain in subendocardial and subepicardial layers between the control subjects and the patients with AS. Similarly, there was no significant difference in epicardial radial strain at the posterior and anteroseptal segments between the control subjects and the patients with AS. Longitudinal strain at both the posterior and anteroseptal segments was significantly decreased in the AS group compared with that in the control group. AS patients had significantly decreased values of endocardial radial strain compared with those in controls (anteroseptal: 18.2 ± 11.2 vs. 34.5 ± 14.8, P < 0.005; posterior: 25.2 ± 14.8 vs. 32.6 ± 12.6, P < 0.05). In the AS group, endocardial radial strain in the posterior and anteroseptal segments was significantly correlated with the aortic valve area (posterior: r = 0.41, P < 0.05; anteroseptal: r = 0.33, P < 0.05). CONCLUSION: Patients with AS and preserved LVEF have impaired longitudinal strain and endocardial radial strain, although circumferential strain and epicardial radial strain are preserved. Despite preserved LVEF, endocardial radial strain was associated with AS severity.

Nonlinear ultrasonic imaging method for closed cracks using subtraction of responses at different external loads.

To improve the selectivity of closed cracks for objects other than cracks in ultrasonic imaging, we propose an extension of a novel imaging method, namely, subharmonic phased array for crack evaluation (SPACE) as well as another approach using the subtraction of responses at different external loads. By applying external static or dynamic loads to closed cracks, the contact state in the cracks varies, resulting in an intensity change of responses at cracks. In contrast, objects other than cracks are independent of external load. Therefore, only cracks can be extracted by subtracting responses at different loads. In this study, we performed fundamental experiments on a closed fatigue crack formed in an aluminum alloy compact tension (CT) specimen using the proposed method. We examined the static load dependence of SPACE images and the dynamic load dependence of linear phased array (PA) images by simulating the external loads with a servohydraulic fatigue testing machine. By subtracting the images at different external loads, we show that this method is useful in extracting only the intensity change of responses related to closed cracks, while canceling the responses of objects other than cracks.

Successful treatment in a case of acute myocardial infarction due to spontaneous coronary artery dissection.

Spontaneous coronary dissection is a rare cause of myocardial ischemia, myocardial infarction, and sudden death. In the present case, we performed stenting only of the severe stenotic lesion of the dissection with a short bare metal stent, and left the remaining long length of dissection vessel untreated. Six months after coronary stenting, follow-up angiography revealed complete healing of the coronary dissection and no significant in-stent restenosis. This case clearly demonstrates the usefulness of intravascular ultrasound (IVUS) imaging in the diagnosis of coronary dissection and IVUS imaging guides to the choice of the best stenting.

Cor triatriatum sinister disclosed after diagnosis of acute myocardial infarction.

We present a case of cor triatriatum sinister diagnosed occasionally after acute anterior myocardial infarction. For management of the acute myocardial infarction (AMI), urgent reperfusion therapy was successfully performed through the left anterior descending coronary artery. Thereafter, no complication associated with AMI occurred. Cor triatriatum sinister was diagnosed and assessed later by means of several modalities. Finally, medical observation was indicated for this patient. This case illustrates the importance of awareness of this congenital disease in an adult when echocardiography shows an abnormal linear echo in the mid portion of the left atrium.

Ultrasonic strain versus coronary flow velocity pattern for predicting regional wall motion recovery after primary coronary intervention for acute myocardial infarction.

BACKGROUND: Strain Doppler echocardiography can detect regional myocardial dysfunction after acute myocardial infarction (AMI). The aim of this study was to assess the utility of strain in predicting regional wall motion recovery after AMI compared with the coronary flow velocity pattern. METHODS: Thirty-three patients with anterior AMIs undergoing successful coronary intervention were included. Longitudinal myocardial strain and coronary flow velocity were measured <24 hours after coronary intervention. Regional wall motion was analyzed by the anterior wall motion score index (A-WMSI). RESULTS: End-systolic strain (r = 0.72, P < .0001), peak strain (r = 0.58, P < .005), and corrected time to peak strain (the time delay from end-systolic to peak strain divided by the RR interval) (r = 0.80, P < .0001) showed good correlations with A-WMSI at 4 weeks. Similarly, diastolic deceleration time was significantly correlated with A-WMSI at 4 weeks (r = 0.69, P < .0001). The diagnostic value in predicting wall motion recovery was compared using a receiver operating characteristic curve. The area under the curve of corrected time to peak strain tended to be larger than that of diastolic deceleration time (0.94 +/- 0.04 vs 0.86 +/- 0.06). CONCLUSION: Strain can predict left ventricular wall motion recovery in patients with AMIs after coronary intervention comparable with predictions using the coronary flow velocity pattern.

Relationship of admission neutrophil count to microvascular injury, left ventricular dilation, and long-term outcome in patients treated with primary angioplasty for acute myocardial infarction.

BACKGROUND: The relationship of admission neutrophil count to the degree of microvascular injury, left ventricular (LV) volume, and long-term outcome after acute myocardial infarction (AMI) was examined in the present study. METHODS AND RESULTS: The study group comprised 228 consecutive patients with a first anterior wall AMI who underwent primary angioplasty within 12 h of onset. The degree of microvascular injury was evaluated by Doppler guidewire. Adverse cardiac events were recorded during an average follow-up of 52+/-28 months. Using a receiver-operating characteristic analysis, a neutrophil count >or=7,260 cells/mm(3) was the best predictor of future cardiac events. By regression analysis, the neutrophil count significantly correlated with diastolic deceleration time (r=-0.40, p<0.0001), coronary flow reserve (r=-0.43, p<0.0001), and LV end-diastolic volume at 4 weeks (r=0.32, p<0.0001). Kaplan-Meier survival analysis showed a higher incidence of adverse cardiac events in patients with a high neutrophil count (p=0.002). By multivariate analysis, a neutrophil count >or=7,260 cells/mm(3) was an independent predictor of long-term adverse cardiac events (odds ratio 3.8, p=0.002). CONCLUSION: Neutrophilia on admission is associated with impaired microvascular perfusion, LV dilation, and long-term adverse cardiac events in patients treated with primary angioplasty for AMI.

Effects of smoking cessation on coronary endothelial function in patients with recent myocardial infarction.

BACKGROUND: Smoking is associated with an increased risk and extent of advanced atherosclerotic vascular disease, but few studies have examined the clinical effect of smoking cessation on human coronary endothelial function. OBJECTIVES: We sought to determine the effects of smoking cessation on endothelial function in patients with recent myocardial infarction. METHODS: Infarcted-not-related coronary arteries of 53 patients with acute myocardial infarction undergoing successful angioplasty were examined in two groups: smoking cessation group (n=35, 28 males, mean age 56 years) and non-smoking group (n=18, 10 males, mean age 65 years). We infused acetylcholine into the coronary artery and the diameter was assessed by quantitative angiography at baseline and 6 months after PTCA. RESULTS: The mean % diameter change from baseline was significantly more constricted in the smoking cessation group than in the non-smoking group (38%+/-5 vs. 19%+/-5, p<0.05). However, the response after six months was significantly decreased after smoking cessation (from 38%+/-5 to 28%+/-4, p<0.01). Multiple regression analysis showed smoking cessation (p=0.03) was a significant determinant factor for improvement of endothelial function. CONCLUSIONS: These findings suggest that just 6 months of smoking cessation improves coronary endothelial function in patients with recent myocardial infarction.

Usefulness of coronary flow reserve immediately after primary coronary angioplasty for acute myocardial infarction in predicting long-term adverse cardiac events.

Coronary flow reserve (CFR) evaluated immediately after reperfusion is thought to reflect the degree of microvascular injury and predict left ventricular (LV) functional recovery after acute myocardial infarction. It was hypothesized that CFR immediately after reperfusion would be predictive of the occurrence of long-term adverse cardiac events. Using a Doppler guidewire, CFR was evaluated immediately after primary coronary angioplasty in 118 consecutive patients with first anterior acute myocardial infarctions. Adverse cardiac events combining cardiac death, recurrent myocardial infarction, and congestive heart failure were recorded during an average follow-up period of 62 +/- 32 months. Using receiver-operating characteristic analysis, CFR 1.3 (n = 68). Patients with CFR 1.3. CFR was significantly correlated with the LV ejection fraction at 4 weeks (r = 0.50, p <0.0001) and LV end-diastolic volume at 4 weeks (r = -0.43, p <0.0001). Kaplan-Meier survival analysis showed a higher incidence of adverse cardiac events in patients with CFR

Relation between neutrophil counts on admission, microvascular injury, and left ventricular functional recovery in patients with an anterior wall first acute myocardial infarction treated with primary coronary angioplasty.

Increased neutrophil counts have been associated with an increased risk of adverse clinical events after acute myocardial infarction (AMI). We examined the association of neutrophil counts on admission with degree of microvascular injury and left ventricular functional recovery after primary coronary angioplasty in AMI. We studied 116 patients with a first anterior wall AMI who underwent primary coronary angioplasty within 12 hours of onset. Patients were categorized into 3 groups based on initial neutrophil count: low (<5,000/mm(3)), intermediate (5,000 to 10,000/mm(3)), and high (>10,000/mm(3)). Coronary flow velocity parameters were assessed immediately after reperfusion using a Doppler guidewire. We defined severe microvascular injury as the presence of systolic flow reversal and a diastolic deceleration time <600 ms. Echocardiographic wall motion was analyzed before revascularization and 4 weeks after revascularization. In patients with a high neutrophil count, systolic flow reversal was more frequently observed, diastolic deceleration time was shorter, and coronary flow reserve was lower. By regression analysis, neutrophil count significantly correlated with diastolic deceleration time (r = -0.38, p <0.0001), coronary flow reserve (r = -0.33, p = 0.0004), and score for change in wall motion (r = -0.36, p = 0.0004). Multivariate analysis showed that neutrophil count on admission was an independent predictor of severe microvascular injury (odds ratio 2.94, p = 0.02). In conclusion, neutrophilia on admission is associated with impaired microvascular reperfusion and poor functional recovery after primary coronary angioplasty.

Usefulness of ultrasonic strain measurements to predict regional wall motion recovery in patients with acute myocardial infarction after percutaneous coronary intervention.

Strain Doppler echocardiography can detect systolic regional myocardial dysfunction. This study assessed whether strain could predict recovery of regional left ventricular function in patients with acute myocardial infarction (AMI) after percutaneous coronary intervention. Forty-three patients with anterior AMI undergoing successful percutaneous coronary intervention of the left anterior descending coronary artery were studied. Longitudinal myocardial strain was measured at the left anterior descending coronary artery territory in the apical long-axis view within 24 hours after percutaneous coronary intervention. Regional wall motion was analyzed by the anterior wall motion score index (A-WMSI). Viable myocardium was defined as a decrease < or = 2.0 in A-WMSI. Patients were categorized as A-WMSI at 4 weeks into a viable group (n = 24) and a nonviable group (n = 19). End-systolic strain and peak strain were significantly lower in the nonviable group than in the viable group (-4.8 +/- 4.8% vs -9.9 +/- 4.7 %, p <0.005; -9.9 +/- 4.6 vs -13.5 +/- 4.1 %, p <0.05). Moreover, corrected time to peak strain (cTPS; time delay from end-systolic to peak strain/RR interval) was significantly longer in the nonviable group than in the viable group (0.19 +/- 0.04 vs 0.13 +/- 0.03, p <0.0001). For prediction of viable myocardium, cTPS <0.15 had a sensitivity of 95% and a specificity of 85%. In conclusion, strain, especially cTPS, is useful for predicting recovery of regional left ventricular function in patients with AMI after percutaneous coronary intervention.

The effects of atorvastatin on coronary endothelial function in patients with recent myocardial infarction.

BACKGROUND: Endothelial dysfunction is a key early event in atherosclerosis that occurs in acute coronary syndrome. It was reported that atorvastatin improves the endothelial function of skeletal muscle vessels, but the effect on the coronary artery is unknown. HYPOTHESIS: The purpose of this study is to determine the effects of atorvastatin on coronary endothelial function in humans. METHODS: Non-infarct-related coronary arteries of 48 patients with acute myocardial infarction who had undergone successful percutaneous transluminal coronary angioplasty were examined. Three groups were studied: hyperlipidemia with use of atorvastatin (Group 1, n=17), hyperlipidemia without statin use (Group 2, n=18), and normal cholesterol level controls (Group 3, n=13). Statin treatment was started at discharge. Acetylcholine (Ach) was infused into the coronary artery and the diameter was assessed by quantitative angiography at baseline and after 6 months. RESULTS: Acetylcholine given in doses of 1, 3, 10, and 30 mg/min increased the coronary artery diameter change in a dose-dependent manner. In the initial study, patients in the three groups had similar responses to Ach. The mean diameter change after 6 months was significantly improved in Group 1 compared with Groups 2 and 3 (-11 +/- 3% vs. -20 +/- 7% and -21 +/- 6%, respectively; p < 0.01 in each case). Multivariate regression analysis showed that atorvastatin (p < 0.01) was the significant determinant for improvement of endothelial function. CONCLUSIONS: These findings suggest that atorvastatin improves endothelial function of the coronary artery in patients with myocardial infarction.

Effect of adhesion force between crack planes on subharmonic and DC responses in nonlinear ultrasound.

Subharmonic and DC responses in nonlinear ultrasound have been expected as a possible means of detecting closed cracks. Recently, it has been reported that subharmonics in a closed crack markedly increases above a certain input wave amplitude. Such a phenomenon is called "threshold behavior". However, the mechanism of threshold behavior has yet to be elucidated. To clarify this, we introduced adhesion force as a short-range force into the previous analytical model, which expresses the nonlinear contact vibrations of crack planes with intense ultrasound and provides a DC displacement as an approximation of the subharmonic response. Consequently, upward convex curves of displacement against input wave amplitude above the threshold were reproduced for the first time. The validity of the derived analytical solution is discussed by comparison with experimentally observed subharmonics.

Acute myocardial infarction caused by simultaneous occlusion of the right coronary artery and the left anterior descending coronary artery probably due to coronary spasm: a case report.

A 56-year-old man had an attack of chest pain associated with ST-segment elevation in both the inferolateral and anteroseptal leads on electrocardiography. Emergency coronary angiography showed thrombus in the mid right coronary artery and total occlusion in the distal left anterior descending coronary artery. Intravenous heparin infusion and antiplatelet therapy were given without other coronary intervention. After 1 week, repeat coronary angiography showed neither significant stenosis nor thrombus in the coronary arteries. Severe coronary artery spasm in the left coronary artery was induced by the provocation test with intracoronary injection of 50 microg acetylcholine. He had an uneventful hospital course. This unique case demonstrated intracoronary thrombus formation in the right coronary artery and left anterior descending coronary artery simultaneously due to suspected coronary spasm.

Ultrasonic tissue characterization predicts left ventricular remodeling in patients with acute anterior myocardial infarction after primary coronary angioplasty.

OBJECTIVES: The aim of this study was to assess the role of cyclic variation (CV) of myocardial integrated backscatter (IBS) in the prediction of left ventricular (LV) remodeling in patients with anterior acute myocardial infarction (AMI) after primary coronary angioplasty. BACKGROUND: Some studies have shown that the CV of myocardial IBS predicts myocardial viability for patients with AMI. METHODS: We recorded short-axis IBS images within 24 hours of angioplasty in 80 patients with anterior AMI. Two parameters were measured: the magnitude of CV and the normalized time delay (NTD). The increase in LV end-diastolic volume (LVEDV) at 4 weeks (DeltaLVEDV) was defined as LV remodeling (>20% increase from baseline). RESULTS: Patients were divided into two groups according to LV remodeling status: the remodeling group (n = 41) and the nonremodeling group (n = 39). There was a significant difference in the magnitude of CV between the two groups (5.11 +/- 1.47 vs 5.96 +/- 189 dB, P < .05), and the NTD was significantly different in the two groups (1.57 +/- 0.31 vs 1.23 +/- 0.32, P < .0001). The correlation between the magnitude of CV and DeltaLVEDV was significant but weak (r = -0.338, P < .01). There was significant correlation between NTD and DeltaLVEDV (r = 0.443, P < .0001). Using NTD greater than 1.35 as the optimal cutoff, the sensitivity, specificity, and positive and negative predictive values to predict LV remodeling were 82%, 86%, 87%, and 80%, respectively. CONCLUSIONS: Myocardial IBS, especially NTD, is useful for predicting LV remodeling in patients with AMI after primary coronary angioplasty.

Left ventricular free wall rupture in transient left ventricular apical ballooning.

A 79-year-old woman presented with chest pain. Her symptoms, combined with the results of an electrocardiogram, echocardiogram and laboratory investigations were compatible with an extensive acute anterior myocardial infarction. However, emergency coronary angiography showed no stenotic lesion in any coronary artery, but left ventriculography revealed apical ballooning akinesis and basal hyperkinesis and she was diagnosed as having transient left ventricular apical ballooning. After 7 days, she suddenly went into cardiopulmonary arrest because of cardiac tamponade. The autopsy revealed a free wall rupture. Generally, the prognosis in transient left ventricular apical ballooning is good; left ventricular free wall rupture is very rare.