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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 143 out of 330
| Title |
Image and signal processing intravascular ultrasound. |
| Author |
Li WG. |
| Journal |
Thesis(PhD): Erasmus Univ Rotterdam |
| Volume |
|
| Year |
1997 |
| Abstract |
No Abstract Available. |
| Title |
Image degradations in ultrasonic CT. |
| Author |
Itoh T, Choi JS, Kasai C, Nakajima M. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1981 |
| Abstract |
We have developed an experimental data acquisition system for ultrasonic CT. The system reconstructs a velocity distribution and two attenuation constant distributions (one is reconstructed from maximum amplitude and the other from integrated amplitude of the received signals after full-wave rectification). Though we obtained considerably good results in clinical use, the images were degraded by refraction and reflection. The image degradations were also studied by computer simulation and experiments using agar gel phantoms. The phantoms were made by mixing agar gel with graphite powder and saccharose which control attenuation and velocity respectively. In the results, it is obtained that the errors on attenuation images are mainly due to refraction of ultrasound and that they are improved by correcting received intensity loss caused by refraction. |
| Title |
Image matching for pulse echo measurement of ultrasonic velocity. |
| Author |
Robinson DE, Chen CF, Wilson LS. |
| Journal |
Image Vision Comput |
| Volume |
|
| Year |
1983 |
| Abstract |
Diagnostic ultrasound is a pulse echo imaging system similar to radar, sonar or exploration seismology. It has its most widespread use in examination of pregnancy, but also finds routine use in the examination of the organs of the upper abdomen and its use is increasing in other areas. Using current techniques the information obtained is largely anatomical. Information about the propagating properties of the tissue is obtained only indirectly. Recently a system has been developed in which quantitative information about the velocity of propagation may be obtained. The technique uses the amount of apparent shift between the two images of the structure obtained from different directions to deduce the apparent velocity within the tissue. Techniques are described for matching the two images obtained from different scan directions from which the apparent shift in the displayed image can be measured. |
| Title |
Image processing and pre-processing for medical ultrasound. |
| Author |
Lizzi FL,Feleppa EJ. |
| Journal |
Proc Appl Imagery Pattern Rec |
| Volume |
|
| Year |
2000 |
| Abstract |
Much attention is now being focused on techniques to improve the quality and information content of ultrasonic images of the body. Many of these techniques employ digital pre-processing of coherent echo signals prior to image generation. Examples of these procedures include: resolution enhancement; contrast enhancement (using frequency-domain techniques) to suppress speckle; and imaging of spectral parameters (which sense the sizes and concentrations of sub-resolution tissue constituents). Combinations of spectral parameters and ancillary clinical data (e.g., PSA blood levels) are also being used with statistical classifiers (e.g., discriminant analysis neural network) to generate color-coded, images that indicate tissue type (e.g., cancer) or tissue regions responding to therapy. Sets of these images, obtained-from serial-plane scans, promise to be particularly useful when presented in interactive three-dimensional (3-D) formats. |
| Title |
Image reconstruction by minimizing second-order moment. |
| Author |
Park KH, Park SB. |
| Journal |
Acoust Imaging |
| Volume |
|
| Year |
1990 |
| Abstract |
Statistical methods have received much attention in image reconstruction, especially when the projection data are not sufficient in number, since they usually give more reliable results in such a case than other methods. In this paper, we propose a new statistical method which minimizes the second-order moment of an object that indicates the variance and randomness in a statistical structure. By minimizing the second-order moment, the resulting image reflects the statistical structure imposed by the available information and is biased toward a flat gray structure in the absence of information. The computer simulation results show a good convergence behavior of the proposed method. This method was successfully applied to ultrasound attenuation CT using a sponge phantom. |
| Title |
Image staining and differential diagnosis of ultrasound scans based on the mahalanobis distance. |
| Author |
Momenan R, Wagner RF, Garra BS, Loew MH, Insana MF. |
| Journal |
IEEE Trans Med Imaging |
| Volume |
|
| Year |
1994 |
| Abstract |
We have previously reported on the ability to detect and discriminate among several diffuse disease states in human liver using a four-dimensional feature space derived from the statistical physics of ultrasound B-scan speckle. No image resulted from this method of supervised classification. In the present work the covariance matrices associated with each state of health or disease from that study are used as the basis of an image staining display technique for aid in quantitative differential diagnosis. A state of health or disease is chosen by the clinician: this selects the covariance matrix from the data base. A region of interest (ROI) is then scrolled through an abdominal B-scan. For each position of the ROI a point in the four-dimensional feature space is calculated. A natural measure of the distance of this point from the center of mass (multivariate mean) of the disease class is calculated in terms of the covariance matrix of this class; this measure is the Mahalanobis distance. The confidence level for acceptance or rejection of the hypothesized disease class is obtained from the probability distribution of this distance, the T-squared probability law. This confidence level is color coded and used as a color stain that overlays the original scan at that position.
The variability of the calculated features is studied as a function of ROI size, or the spatial resolution of the color coded image, and it is found that for an ROI in the neighborhood of 4 cm-squared most of (speckles) is averaged out, leaving the "noise floor" associated with inter- and intra-patient variability. ROIs on the order of 1 cm-squared may result with technical advances in B-scan resolution. A small number of points on organ boundaries are entered by the user, to fit with arcs of ellipses to be used to switch between organ (liver and kidney) data bases as the ROI encounters the boundary. By selecting in turn various state-of-health or state-of-disease databases, such images of confidence levels may be used for quantitative differential diagnosis. The method is not limited to ultrasound, being applicable in principle to features obtained from any modality or multimodality combination. |
| Title |
Image-guided ex vivo liver ablation by unfocused ultrasound using passive cavitation detection. |
| Author |
Salgaonkar VA, Karunakaran CP, Besse JA, Heinlein G, Datta S, Holland CK, Mast TD. |
| Journal |
Proc SPIE |
| Volume |
|
| Year |
2007 |
| Abstract |
Ablation therapy is used as an alternative to surgical resection of hepatic tumors. In ablation, tumors are destroyed through heating by RF current, high intensity focused ultrasound (HIFU), or other energy sources. Ablation can be performed with a linear array transducer delivering unfocused intense ultrasound (<10 W/cm2). This allows simultaneous treatment and imaging, a feature uncommon in RF ablation. Unfocused ultrasound can also enable faster bulk tissue ablation than HIFU. In the experiments reported here, a 32-element linear array transducer with a 49 mm aperture delivers 3.1 MHz continuous wave unfocused ultrasound at amplitudes 0.7-1.4 MPa during the therapy cycle. It also operates in pulse-echo mode to capture B-scan images. Ex-vivo fresh bovine liver tissue placed in degassed saline is exposed to continuous wave ultrasound interleaved with brief pulsed ultrasound imaging cycles. Tissue exposures range between 5 to 20 minutes. The following measurements are made at intervals of 1 to 3 seconds: tissue temperature with a needle thermocouple, acoustic emissions with a 1 MHz passive unfocused detector, and tissue echogenicity from image brightness. Passively detected acoustic emissions are used to quantify cavitation activity in the ablation experiments presented here. As severity and extent of tissue ablation are related to temperature, this paper will statistically model temperature as a function of tissue echogenicity and cavitation. The latter two quantities can potentially be monitored noninvasively and used as a surrogate for temperature, enabling improved image guidance and control of ultrasound ablation. |
| Title |
Imaging local scatterer concentartions by the nakagami statistical model. |
| Author |
Tsui P,Chang C. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2007 |
| Abstract |
The ultrasonic B-mode image is an important clinical tool used to examine the internal structures of the biological tissue. Due to the fact that the conventional B-scans cannot fully reflect the nature of the tissue, some useful quantitative parameters have been applied to quantify the properties of the tissue. Among various possibilities, the Nakagami parameter was demonstrated to have an outstanding ability to detect the variation of the scatterer concentration. This study is aimed to develop a scatterer concentration image based on the Nakagami parameter map to assist in the B-mode image for tissue characterization. In particular, computer simulations are carried out to generate phantoms of different scatterer concentrations and echogenicity coefficients and their B-mode and Nakagami parametric images are compared to evaluate the performance of the Nakagami image in differentiating the properties of the scatterers. The simulated results show that the B-mode image would be affected by the system settings and user operations, whereas the Nakagami parametric image provides a comparatively consistent image result when different diagnosticians use different dynamic ranges and system gains. This is largely because the Nakagami image formation is only based on the backscattered statistics of the ultrasonic signals in local tissues. Such an imaging principle allows the Nakagami image to quantify the local scatterer concentrations in the tissue and to extract the backscattering information from the regions of the weaker echoes that may be lost in the B-mode image. These findings suggest that the Nakagami image can be combined with the use of the B-mode image simultaneously to visualize the tissue structures and the scatterer properties for a better medical diagnosis. (E-mail: mechang@gate.sinica.edu.tw)©2007 World Federation for Ultrasound in Medicine and Biology.
Key Words: Nakagami distribution, Parametric image, Ultrasonic backscattering.
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| Title |
Imaging microbubbles and tissues using a linear.focussed scanner operating at 20 MHz: possible.implications for the detection of cavitation thresholds. |
| Author |
Watmough DJ, Davies HM, Quan KM, Wytch R, Williams AR. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1991 |
| Abstract |
B-Scan images have been used as a means of detecting the onset of cavitation in tissues. New.echoes appearing during simultaneous sonication with therapeutic ultrasound have often been.attributed to bubble formation. In this study temperature rises up to 15 degrees C W-1 cm2 in.guinea pig leg (post-mortem) were found, which would itself increase the rate of growth of gas.bubbles. It is also hypothesized that a temperature dependent attenuation coefficient predicted by.Bamber and Hill may, at least in part, account for new echoes appearing in tissues. Possible.artefactual echoes in the B-scan images arising from acoustically induced gas bubbles in the.coupling medium are also discussed. |
| Title |
Imaging of the elastic properties of tissue - A review. |
| Author |
Gao L, Parker KJ, Lerner RM, Levinson SF. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1996 |
| Abstract |
Recently, a number of methods have been developed that make it possible to image the elastic properties of soft tissues. Because certain types of tissues such as malignant lesions, for example, have elastic properties that are markedly different from surrounding tissues, elasticity imaging.could provide a significant adjunct to current diagnostic ultrasonic methods. Further, elasticity imaging techniques could be used to augment the study of tissues that change their elastic properties, such as skeletal and cardiac muscle. In this paper, we survey some of the previous work done in the related field of biomechanics, and we review measurement techniques from the 1950s to the 1980s. Different approaches to elastic imaging and signal processing are then discussed and a lexicography for elastic imaging is introduced. It is hoped that this nomenclature will provide a meaningful categorization of various approaches and will make evident the inherent parameters displayed and conditions applied in deriving the resulting images. Key assumptions and signal processing approaches are also reviewed. Finally, directions for future work are suggested. .. |
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