Contrast Formation for Simple Shaped Objects in Acoustic Microscopy

Various methods can characterize microstructural properties of reservoir rocks with the ultimate goal of relating microstructure to seismic properties. Scanning electron microscopy, transmission electron microscopy, and optical microscopy have traditionally been used for such studies. They have identified lithology, pore space, interconnectivity of pores, grain size, and cementation as the most important factors controlling seismic wave velocity and attenuation. However, these techniques provide qualitative descriptions only. The acoustic techniques presented here, scanning acoustic microscopy (SAM) and acoustic sounding (AS), can map and, more importantly, quantify microstructure as variations in acoustic impedance. Ultrasonic stress waves are sensitive to local variations in elastic properties and are therefore particularly suited for characterizing microstructural properties of reservoir rocks. Reflections from impedance boundaries in grains and between interfaces in the sample are used to construct the microstructural image. This paper will show that acoustic microscopy can be a powerful tool for studying internal structure and pore geometry of reservoir rocks. Acoustic microscopy's basic principle is almost identical to that of reflection seismology. Images of surface and subsurface microstructures are prepared on the basis of reflected acoustic waves—that is, on the impedance changes in the sample. Acoustic waves on a sample are mode converted, partly transmitted into the sample, and partly reflected. The reflection coefficient and with it the signal intensity received by the transducer are determined by the elastic constants of the material. Changes in acoustic impedance in the sample that influence wave reflection characteristics can be studied by mapping the reflected waves. Because the working frequency of the acoustic waves can be varied, their penetration depth into the sample and the resolution of microstructural features can be controlled. I will present results from high-frequency SAM (0.1–2 GHz) and low-frequency AS (25–100 MHz). The resolution of SAM is about 1 μm at 1 GHz; AS …

Examination of cracks and other defects in sodium β & β″-alumina using acoustic, optical and electron microscopy

Medical ultrasound is a diagnostic imaging modality used for visualizing internal organs; the frequencies typically used are 2-10 MHz. Scanning acoustic microscopy (SAM) is a form of ultrasound where frequencies typically exceed 50 MHz. Increasing the acoustic frequency increases the specimen's spatial resolution but reduces the imaging depth. The advantages of using SAM over conventional light and electron microscopy include the ability to image cells and tissues without any preparation that could kill or alter them, providing a more accurate representation of the specimen. After scanning the specimen, acoustic signals are merged into an image on the basis of changes in the impedance mismatch between the immersion fluid and the specimens. The acoustic parameters determining the image quality are absorption and scattering. Surface scans can assess surface characteristics of the specimen. SAM is also capable of elastography, that is, studying elastic properties to discern differences between healthy and affected tissues. SAM has significant potential for detection/analysis in research and clinical studies.

Bulk and subsurface structure analysis of the 319 aluminum casting using acoustic microscopy methods

Spatial resolution is an important factor in ultrasonic materials characterization. Scanning acoustic microscopy [1–2] has proved to be a useful tool for materials evaluation with micrometer-scale spatial resolution. Point-focus-beam (PFB) acoustic microscopy has high spatial resolution and is often used to produce images as well as to probe material inhomogeneity. However, a disadvantage of the PFB technique lies in its insensitivity to material anisotropy. In contrast, line-focus-beam (LFB) acoustic microscopy can provide a directional ultrasonic velocity measurement and is employed for characterization of anisotropic materials [3–5]. But the LFB technique, with its unidirectional spatial resolution, is generally incapable of producing images, and is therefore disadvantageous for probing inhomogeneous materials. In response to this need, a variety of lens designs [6–9] in acoustic microscopy have been proposed for measuring materials, which are both inhomogeneous and anisotropic.

Acoustic methods for interior examination of materials have a well established role in medical imaging and non-destructive testing. Less well known is the field of acoustic microscopy where imaging is achieved on a similar scale to optical microscopy, but where contrast is provided through the elastic properties of the media rather than by reflection and scattering of light. Although acoustic microscopy has been known for over 20 years, and equipment is commercially available, new techniques such as the SLAM (scanning laser acoustic microscope), confocal microscopy, surface waves, phase contrast and wavefront reconstruction have been developed in recent years. This book (in combination with volume 1 (Plenum, 1995)) comprises chapters written by specialists from industry and the research community on selected developments in this field. Particular reference is made to the semiconductor industry and to medical imaging, where the benign, non-invasive character of ultrasonic waves has advantages for non-destructive evaluation. A wide-ranging chapter from Siemens covers applications to product assurance and failure mode analysis in the semiconductor industry. The two principle techniques, SLAM and SAM (scanning acoustic microscopy) are described, and recent results on delamination of IC packages, crack detection, and detection of failed metallization lines or wire contacts are presented with many colourful examples. The excellent chapter on medical imaging describes the historical background to the field, and the present trend towards higher frequencies and higher spatial resolution in scanning acoustic probes. Transducer construction and scanning methods are covered in some detail, including microtransducer construction for internal examination by endoscopy. Examples of clinical applications to skin and eye examination provide a vivid picture of the detail and wealth of information obtainable, and emphasize the importance of data processing and presentation in making effective use of it. The chapter ends with a description of in vivo endoscopic examination of clogged arteries, reminding us not only of relentless mortality, but of the exciting possibilities of micromechanical and microsensor technology in medicine, where acoustics is certain to play an important role. Emphasizing the parallel with optics, the book ends with two interesting chapters on phase-contrast acoustic microscopy, and time reversal in acoustic imaging. Phase contrast enables fine topographical features to be resolved with a resolution dependent on signal-to-noise ratio rather than the wavelength of sound. Examples of nanometre profiling of integrated circuits and low contrast features of biological material are shown, as well as the characterization of elastically non-isotropic materials. Time reversal is a concept with even greater potential, enabling diffraction limited imaging to be obtained through inhomogeneous or scattering media. The principles and technology are described, and although only feasibility has been demonstrated so far, it clearly offers great potential in the medical and non-destructive testing fields for radical improvements in acoustic imaging.

Scanning acoustic microcopy (SAM) method with inverted inspection direction has been successfully develop and evaluate the quality of flip chip underfill and interconnect bonds in manufacturing of microelectronic components. Acoustic microscopes utilize high frequency ultrasound transmitting through the silicon chip backside in one scan to access and examine the internal structures in optically opaque materials. These non-destructive methods relatively enable the defect localization which leads microstructural examinations involving destructive analysis sample preparation. For the justification of accuracy of SAM method analysis, a destructive cross-sectioned and mechanical lapping physical analysis were performed for preparing the samples and examine by optical microscope and Scanning Electron Microscope (SEM) for defect verification. Cases studies have been demonstrated that the capabilities of conventional SAM inspection and advantages over other analysis method.

Ahrmct-The use of a versatile digital image storage and processing system for scanning acoustic micrmcopy is described. In addition to the data capture and storage functions, different types of image processing functions of particular relevance to scanning acoustic microscopy have been incorporated These ipclude real-time grey scale enhancement and a variety of ofStine edge enhancement, spatial fdtering, and pseudocolor processing algorithms. These facilities can enhance particular aspects of the image or 6lter out unwanted artifacts. Typical results are presented. The further potential of digital processing for scanning acoustic microscopy is discussed. recurring problem associated with the use of imaging apparatus is the production of a display which will do justice to the quality of the data acquired and which is able to take advantage of the powerful electronic techniques for image storage and processing. The image processing described in this paper arose out of necessity, in the course of working with a relatively new form of imaging-scanning acoustic microscopy. Our approach has therefore been to present our results as an example of the application of general image processing techniques to a set of specific problems, arising from this form of microscopy. The scanning acoustic microscope (SAM) was first demonstrated by Quate and Lemons in 1973 [l]. Since then it has been developed sufficiently to allow its use as a tool for investigation of a wide range of materials as well as biological samples. It is particularly appropriate for the examination of the interior of optically opaque media [2] - [4]. In the basic operation of a SAM (reflection or transmission) [5], the object is immersed in a liquid (normally water) and place at the focal plane of an acoustic lens where it is interrogated by a focused ultrasonic beam. The object is subsequently scanned over the entire field of view in a raster manner so that the image is formed point by point. In a typical instrument the two orthogonal displacements of the scanner are measured by means of position encoders. Both amplitude and phase data may be recorded at each point in the scan. As the information and the position encoder outputs are produced in an analog form it was, until recently, accepted practice to resort

This paper describes our newly designed scanning acoustic microscope (SAM). Our concern is to determine the mechanical properties of each histological component of the vocal fold in normal and varying pathological states.Generally speaking, the images obtained by means of an acoustic microscope not only present structure of the object to be investigated but also reflect its mechanical properties. Our present SAM has the following features.1) The frequency of ultrasonic waves is variable between 100 and 200 MHz. The best resolution is about 5μm(at 200MHz).2) This single device can function as three different types of SAM: i. e. reflection-, transmission-, and interference-type.3) Linear and logarithmic conversions of the image intensity are available. The range of the intensity covered by linear conversion is about 20dB, whereas, by logarithmic conversion, it is about 40dB.4) Tilting mechanism is installed to the sample bed so as to adjust the angle of specimen to be parallel to focal plane of the acoustic lens.5) As far as one direction is concerned, consecutive images are obtained easily by simply pushing a button.6) The image stored in the digital memory can be recorded by an ordinary video recorder.Also, as concerns the reflected image, a brief explanation of the preparation of the specimen and the operation of the device are presented.In Discussion, several advantages of the acoustic image compared with the optical image are mentioned. Then, a method of quantifying the mechanical property of biological tissues based on the acoustic image is briefly explained. A preliminary result on the vocal fold tissue shows that the 'hardness' increases in the order of the ground substance, the epithelium, and the fibrous components (a mixture of elastic and collagenous fibers).

SUMMARYSurface cracks can be detected with great sensitivity in an acoustic microscope, even when the width of the crack is much less than the acoustic wavelength. This is because of the strong excitation and scattering of Rayleigh waves. Cracks in a variety of materials, including cracks from indents in several different ceramics, have been studied by acoustic microscopy, and the results compared with images from light and scanning electron microscopes. No crack or part of a crack that was seen by the other two techniques failed to be seen by acoustic microscopy. The contrast of a crack in an acoustic microscope showed no sign of fading as the crack became thinner towards its tip, and diffraction from tips suggests that they are acoustically well‐defined points on the surface. Although theoretically the acoustic contrast from a crack might be expected to diminish when the crack width is smaller than the shear‐wave decay length in the fluid, in practice this is so small that for many purposes it may be considered that there is almost no limit to how fine a crack can be and still be detected in an acoustic microscope.

A new high-frequency time-resolved acoustic microscope was developed at the Fraunhofer-Institute for Biomedical Engineering. It is based on an optical microscope from olympus and it operates in reflection mode. The duration of the pulse is 5 ns and the central frequency is 860 MHz. The new microscope permits fluorescence microscopy and scanning acoustic microscopy at the same time, which are used for synchronous optical and acoustical investigation of cell components with changing cellular stiffness.

<i>Objectives:</i> The purpose of this study was to characterize human breast cancer tissues by the measurement of microacoustic properties. <i>Methods:</i> We investigated eight breast cancer patients using acoustic microscopy. For each patient, seven blocks of tumor tissue were collected from seven different positions around a tumor mass. Frozen sections (10 micrometer, &mu;m) of human breast cancer tissues without staining and fixation were examined in a scanning acoustic microscope with focused transducers at 80 and 200 MHz. Hematoxylin and Eosin (H and E) stained sections from the same frozen breast cancer tissues were imaged by optical microscopy for comparison. <i>Results:</i> The results of acoustic imaging showed that acoustic attenuation and sound speed in cancer cell-rich tissue regions were significantly decreased compared with the surrounding tissue regions, where most components are normal cells/tissues, such as fibroblasts, connective tissue and lymphocytes. Our observation also showed that the ultrasonic properties were influenced by arrangements of cells and tissue patterns. <i>Conclusions:</i> Our data demonstrate that attenuation and sound speed imaging can provide biomechanical information of the tumor and normal tissues. The results also demonstrate the potential of acoustic microscopy as an auxiliary method for operative detection and localization of cancer affected regions.

Scanning acoustic microscopy (SAM) is a label-free imaging technique used in biomedical imaging, non-destructive testing, and material research to visualize surface and sub-surface structures. In ultrasonic imaging, noises in images can reduce contrast, edge and texture details, and resolution, negatively impacting post-processing algorithms. To reduce the noises in the scanned image, we have employed a 4D block-matching (BM4D) filter that can be used to denoise acoustic volumetric signals. BM4D filter utilizes the transform domain filtering technique with hard thresholding and Wiener filtering stages. The proposed algorithm produces the most suitable denoised output compared to other conventional filtering methods (Gaussian filter, median filter, and Wiener filter) when applied to noisy images. The output from the BM4D-filtered images was compared to the noise level with different conventional filters. Filtered images were qualitatively analyzed using metrics such as structural similarity index matrix (SSIM) and peak signal-to-noise ratio (PSNR). The combined qualitative and quantitative analysis demonstrates that the BM4D technique is the most suitable method for denoising acoustic imaging from the SAM. The proposed block matching filter opens a new avenue in the field of acoustic or photoacoustic image denoising, particularly in scenarios with poor signal-to-noise ratios.

Scanning acoustic microscopy (SAM) was applied to assess the change of shape and acoustical parameter of the endothelium after exposure to the shear stress. SAM is useful for assessing the properties of the living cells since it can detect morphological and acoustical changes without pathological staining or fixation techniques.

The laser shaping of thin alumina ceramic plates appears to be an advantageous manufacturing method. Unfortunately, the failure rate for using this technique is high because of crack initiation during the application of a high power laser. We address the issue of crack initiation with the use of in-process and post-process analysis. This article reports our results on the evaluation of the surface and interior cracks with optical, scanning laser, scanning electron and scanning acoustic microscopy. We present images of surface and subsurface micro-cracks generated at different power levels of a high power CO2 laser system. The spatial variation of the Rayleigh wave velocity is measured by the V(z) curve technique. These preliminary data suggest that, some with improvement, the V(z) technique may detect residual stress with high spatial resolution. The obtained results may contribute to the understanding of the fracture mechanism, and can eventually provide guidance for the choice of laser parameters (e.g., power, focus, scanning rate, emitting duration, or the like) in laser shaping apparatus.