Characterization of layered materials by the Lamb wave lens

The Lamb wave lens is a type of lens that can replace the conventional lens of an acoustic microscope for some applications. When it insonifies a layered solid structure, it excites a single mode in the structure, provided that the frequency is properly adjusted. Measuring the return signal as a function of frequency results in a characteristic curve showing the excited modes. Since the number of excited modes, the frequencies at which they are excited, and the efficiency of excitation are highly dependent on the elastic and physical parameters of the layered solid, a characterization method emerges. The authors describe this characterization method for the layered structures using the Lamb wave lens. Theoretical and experimental results are presented

A Lamb Wave Lens for Acoustic Microscopy

In a conventional scanning acoustic microscope the excited leaky modes contributes significantly to the high contrast obtained in the images. However, all such modes exist simultaneously, and the interpretation of the images is not straightforward, especially in layered media. A new lens geometry is proposed that can be used with acoustic microscopes to image layered solid structures. This new lens can focus the acoustic waves in only one of the Lamb wave modes of the layered solid with a high efficiency. V(Z) curves obtained from this lens are more sensitive to material properties compared to that obtained from conventional lens. Measuring the return signal as a function of frequency results in another characteristic curve, V(f). The Lamb wave lens and the associated characterization methods for the layered structures are described. The results presented show that the Lamb wave lens is at least an order of magnitude more sensitive than the conventional lens and can differentiate between a good bond and a disbond in a layered structure easily. © 1992 IEE

Laser-Based Ultrasound for the Inspection of Gas Pipelines

Ultrasonics has proven to be an effective method for detecting a variety of defects in gas transmission pipes including cracks, wall thinning and corrosion pits. The use of Lamb waves for the detection of defects and in situ process monitoring applications has been successfully pursued for many years [1–6]. The use of a laser-based ultrasound (LBU) inspection technique to detecti defects is attractive because of the potential for rapid inspection of large areas and because it is noncontact with large standoff distances. Owing to its noncontacting and remote nature, the LBU technique is being investigated as an alternative technology to piezoelectric transducers or electromagnetic acoustic transducers (EMATs) for the rapid nondestructive inspection of pipelines. Currently, the preferred methods for introducing ultrasonic waves into the pipe are by using a piezoelectric transducer in a liquid-filled wheel or an EMAT. In field use, the wheel or the EMAT is attached to a moveable platform (known as a pig), which travels along the length of the transmission line. The wheel must maintain contact with the pipe wall during the inspection. Although the EMAT is a noncontact sensor, it must be operated close to the pipe’s surface. The contact and near-contact requirements can result in a loss of data when pipe irregularities such as dents or joints between sections cause the wheel or the EMAT to lift off from the surface of the pipe. The liquid-filled wheel uses longitudinal waves that propagate into the wall of the pipe. For a complete inspection of the pipe’s circumference, many wheels must be used. The EMAT generates a Lamb wave in the wall of the pipe that can be directed either circumferentially or axially along the pipe. Although the LBU technique also uses Lamb waves, unlike EMAT systems, the detection sensitivity of the LBU system does not decrease with increased separation from the part. However, a potential difficulty for LBU techniques is that Lamb waves are a family of guided waves that exist in plate-like structures, and a large number of modes of vibration may coexist in a given plate thickness. A laser that has been focused to a spot or line represents a broadband Lamb wave source in both the temporal and spatial frequency domains, which leads to the simultaneous excitation of many modes. Consequently, LBU techniques for generating Lamb waves have generally been pursued only when the lowest order symmetric or asymmetric mode was needed, probably because these modes are generated and detected with the greatest efficiency and thus offer a de facto mode selection mechanism since these modes dominate the others that may be present. We previously demonstrated [7] a mechanism for efficiently generating and selecting a single Lamb wave mode using simulated arrays. In this paper, we describe the implementation of a laser array for the generation of Lamb waves. We also present some preliminary results of a study of the characteristics of Lamb wave modes to identify suitable modes for detecting defects in pipelines. The features that are important include the generation and detection efficiency of the Lamb wave modes, the mode’s energy distribution, and the velocity dispersion of the waves

Fibrinogen storage disease without hypofibrinogenemia associated with estrogen therapy

BACKGROUND: Cytoplasmic inclusion bodies within hepatocytes may have different etiologies, including the Endoplasmic Reticulum Storage Diseases (ERSDs). ERSD is a pathological condition characterized by abnormal accumulation of proteins destined for secretion in the endoplasmic reticulum of hepatocytes; it may be congenital (primary) or acquired (secondary). Fibrinogen storage disease is a form of ERSD. CASE PRESENTATION: We present a case of fibrinogen storage disease secondary to estrogen replacement therapy. Its causal relationship to the drug is shown by histological, immunohistochemical and ultrastructural studies of paired liver biopsies obtained during and after the drug therapy. CONCLUSION: The liver biopsies of patients with idiopathic liver enzyme abnormalities should be carefully evaluated for cytoplasmic inclusion bodies and, although rare, fibrinogen deposits

Significant reduction in restenosis after the use of sirolimus-eluting stents in the treatment of chronic total occlusions

AbstractObjectivesThe aim of this study was to assess sirolimus-eluting stent (SES) implantation for the treatment of chronic total coronary occlusions (CTO).BackgroundLong-term results after percutaneous coronary intervention (PCI) in the treatment of CTOs is hindered by a significant rate of restenosis and reocclusion. In the treatment of relatively simple nonocclusive lesions, SESs have shown dramatically reduced restenosis rates compared with bare metal stents (BMS), but whether these results are more widely applicable is unknown.MethodsFrom April 2002, all patients at our institution were treated with SES as the device of choice during PCI. During the first six months, 563 patients were treated solely with SES, with treatment of a de novo CTO in 56 (9.9%). This CTO cohort was compared with a similar group of patients (n = 28) treated in the preceding six-month period with BMS.ResultsAt one year, the cumulative survival-free of major adverse cardiac events was 96.4% in the SES group versus 82.8% in the BMS group, p < 0.05. At six-month follow-up, 33 (59%) patients in the SES group underwent angiography with a binary restenosis rate (>50% diameter stenosis) of 9.1% and in-stent late loss of 0.13 ± 0.46 mm. One patient (3.0%) at follow-up was found to have reoccluded the target vessel.ConclusionsThe use of SESs in the treatment of chronic total coronary occlusions is associated with a reduction in the rate of major adverse cardiac events and restenosis compared with BMS

Virological and clinical characteristics of hepatitis delta virus in South Asia

<p>Abstract</p> <p>Background & Aims</p> <p>There is a paucity of data on the impact of hepatitis D virus (HDV) in patients with hepatitis B virus (HBV) infection from South Asia. We studied the impact of HDV co-infection on virological and clinical characteristics.</p> <p>Methods</p> <p>We collected data of 480 patients with HBsAg positive and a detectable HBV DNA PCR, who presented to the Aga Khan University, Karachi and Isra University in Hyderabad, Pakistan in the last 5 years. HDV co-infection was diagnosed on the basis of anti-HDV. ALT, HBeAg, HBeAb and HBV DNA PCR quantitative levels were checked in all patients. We divided all patients into two groups based on anti-HDV, and compared their biochemical, serological & virological labs and clinical spectrum. Clinical spectrum of disease included asymptomatic carrier (AC), chronic active hepatitis (CAH), immuno-tolerant phase (IP), and compensated cirrhosis (CC).</p> <p>Results</p> <p>HDV co-infection was found in 169 (35.2%). There were 164 (34.6%) HBeAg positive and 316 (65.4%) HBeAg negative patients. Mean ALT level was 66 ± 73 IU. 233 (48.5%) had raised ALT. HBV DNA level was ≥ 10e5 in 103(21.5%) patients. Overall, among HBV/HDV co-infection, 146/169 (86.4%) had suppressed HBV DNA PCR as compared to 231/311 (74.3%) patients with HBV mono-infection; p-value = 0.002. Among HBeAg negative patients 71/128(55.5%) had raised ALT levels among HBV/HDV co-infection as compared to 71/188 (37.8%) with HBV mono-infection (p-value = 0.002); levels of HBV DNA were equal in two groups; there were 27/128 (21%) patients with CC among HBV/HDV co-infection as compared to 23 (12%) in HBV mono-infection (p-value = 0.009); there were less AC (p-value = 0.009) and more CAH (p-value = 0.009) among HBV/HDV co-infection patients. Among HBeAg positive patients, serum ALT, HBV DNA levels and the spectrum of HBV were similar in the two groups.</p> <p>Conclusions</p> <p>HBV/HDV co-infection results in the suppression of HBV DNA. A fair proportion of HBV/HDV co-infected patients with HBeAg negative have active hepatitis B infection and cirrhosis as compared to those with mono-infection.</p

Revised cutoff values of ALT and HBV DNA level can better differentiate HBeAg (-) chronic inactive HBV patients from active carriers

<p>Abstract</p> <p>Background and Aims</p> <p>ELISA is still used as primary test for diagnosis HBV disease. However, ELISA-positive patients were marked as HBV inactive after confirmation with PCR and vice versa. Our aim was to assess the performance of new cut-off value of ALT, HBV DNA load and significance of AST as screening tool for HBeAg (-) chronic active or inactive patients in Pakistani population.</p> <p>Materials and methods</p> <p>In a cross-sectional, cohort study, 567 HBeAg (-) patients followed for one year were selected. Patients with persistent elevated ALT than normal and HBV DNA ≥ 100,000 copies/mL were taken as active chronic. Diagnostic values for ALT, AST and HBV DNA load in HBV HBeAg (-) chronic active and inactive patients compared using receiver operation characteristic (ROC) curves.</p> <p>Results</p> <p>Of 567 HBeAg (-) patients, 228 were classified as chronic inactive and 339 as active. HBV infection was dominant in male. Serum ALT, AST and HBV DNA levels showed significant and high AUROC to differentiate chronic HBeAg (-) inactive patients from active. AUROC for Serum ALT, AST and HBV DNA were observed 0.997, 0.969 and 1.000, respectively. For revised cut off value for ALT (30 IU/L for male and 19 IU/L for female) and HBV DNA load ≥100,000 copies/mL, a PPV of 97%, NPV of 94%, a sensitivity of 98%, and a specificity of 92% was observed to discriminate active carriers from inactive carriers. We also observed 93.5% specificity, 83.1% sensitivity, 82% PPV and 89.5% NPV for AST ≤20 IU/L to differentiate inactive carriers from active ones in our study group.</p> <p>Conclusions</p> <p>Revised cut off value of ALT and NIH derived HBV DNA value can better discriminate between HBeAg (-) chronic active and inactive patients.</p

Hepatitis B and Renal Disease

Glomerulonephritis is an important extrahepatic manifestation of chronic hepatitis B virus (HBV) infection. The uncommon occurrence, variability in renal histopathology, and heterogeneity in clinical course present challenges in clinical studies and have resulted in a relative paucity of data and uncertainty with regard to the optimal management of HBV-related glomerular diseases. The advent of nucleos(t)ide analogue medications that effectively suppress HBV replication has markedly altered the clinical outcomes of kidney transplant recipients with HBV infection, but the emergence of drug resistance is an escalating problem. This article reviews the recent knowledge of the pathogenesis and treatment of HBV-related membranous nephropathy, and discusses the management of hepatitis B in kidney transplant recipients, which is continuously evolving