bluuebunny/crossref_metadata_2025 huggingface dataset:
Automated Determination of the Magnitude and Time Delay (“Phase”) of the Cardiac Cycle Dependent Variation of Myocardial Ultrasonic Integrated Backscatter
Authors: Mohr G. A. , Vered Zvi , Barzilai Benico , Perez Julio E. , Sobel Burton E. , Miller J. G.
Published: March 2013

An algorithm for quantitative description of cardiac cycle dependent variation of integrated backscatter (cyclic variation) has been developed and is shown to be suitable for analysis of nonsinusoidal data typical of ultrasonic tissue characterization measurements from myocardium in vivo. The algorithm produces estimates of the magnitude of variation and of the time delay relative to the the electrocardiographically recorded QRS-complex. To validate the algorithm, 246 integrated backscatter measurements were analyzed both manually and by the automated method. The magnitude and time delay estimates from the two methods correlated closely. With a separate set of data, the algorithm produced reasonable descriptions of the cyclic variation for 89 of 101 integrated backscatter measurements. Only modest computational power is required for effective implementation of this algorithm, facilitating inclusion of online automated analysis capabilities in quantitative ultrasonic tissue characterization systems.
Detection of Wall Vibrations by Means of Cepstrum Analysis
Authors: Nowicki Andrzej , Marciniak Artur
Published: March 2013

Preliminary studies on the usefulness of the cepstrum analysis of Doppler signals for detecting vibrations of periodically vibrating structures, such as aortic valves in children with innocent heart murmurs, were carried out in two stages. First, by cepstrum analysis of computer simulated frequency modulated signals, and second, by the analysis of real Doppler signals generated by a vibrating reflector. Simulation and experimental studies were performed for modulating frequencies from 10 Hz to 60 Hz while changing the amplitude of vibrations from 0.2 mm to 1 mm. The striking similarity between computed cepstra for simulated and for real Doppler signals encouraged further studies in patients. Cepstra computed from two Doppler recordings in children with weak innocent vibratory heart murmurs showed characteristic cepstral lines for modulating frequencies at 21 Hz and 30 Hz in the first and second child, respectively, which were interpreted as the vibration frequencies of the aortic valve leaf lets.
A Transaxial Compression Technique (TACT) for Localized Pulse-Echo Estimation of Sound Speed in Biological Tissues
Authors: Ophir J. , Yazdi Y.
Published: March 2013

We describe a new method for the estimation of the speed of sound in soft tissues in the pulse-echo mode. A transducer imparts an accurate transaxial compression to the tissue, and the corresponding change in the arrival time of an echo feature is measured. The ratio between the compressed depth and the difference in arrival time is taken as the estimate of the speed of sound. A second, noncompressing transducer is used to correct for distal tissue movement. We show theoretically and experimentally that accurate speed of sound estimations can be made in overlying and underlying tissue mimicking layers.
Global Breast Attenuation: Control Group and Benign Breast Diseases
Authors: Berger G. , Laugier P. , Thalabard J.C. , Perrin J.
Published: March 2013

This paper deals with the estimation of the slope of attenuation in human breast tissue. The measurement is done in the reflection mode with a short time Fourier analysis. All important factors such as diffraction effect, tissue depth and specular reflectors are taken into account. A population of 49 normal women shows large inter-individual variations of the attenuation coefficient. A multiple linear regression allows correlation of this variation with the duration of the woman's genital life and pregnancies. A preliminary study is done on 10 benign diffuse breast diseases and shows a weak correlation with the type of the breast: normal or pathological. The utility of the quantification is discussed for one case of large fibrocystic disease.
Image Reconstruction by Minimizing Second-Order Moment
Authors: Park Kil-Houm , Park Song-Bai
Published: March 2013

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.
Echographic Tissue Characterization in Diffuse Parenchymal Liver Disease: Correlation of Image Structure with Histology
Authors: Haberkorn Uwe , Zuna Ivan , Lorenz Adolf , Zerban Heide , Layer Günter , van Kaick Gerhard , Räth Ulrich
Published: March 2013

Seventy livers were examined in vitro using a computerized ultrasound B-mode data acquisition and analysis system. For tissue characterization, statistical parameters from pattern recognition algorithms describing image brightness and image structure were used. Reference classification based on histopathology as well as on chemical/morphometrical analysis led to the diagnostic classes of normal, fatty liver, fibrosis/cirrhosis and fatty fibrosis/cirrhosis. Comparing the two reference methods for ultrasound tissue characterization, re-classification based on chemical/morphometrical analysis resulted in a significant increase in diagnostic accuracy. The strong correlations between statistical ultrasound image parameters and morphometrical features reflect the relevance of our statistical approach to ultrasound tissue characterization.
IBR5: An Optimal Measurement of Integrated Backscatter and Cyclic Variation of Integrated Backscatter
Authors: Rhyne T.L. , Sagar K.B.
Published: March 2013

Various methods have been developed to measure the coefficient of volume backscatter. For these measures, correction has made for signal energy, instrumentation/transducer filtration, diffraction and bulk loss, while using various square law or log magnitude detectors. Also, tissue backscatter has been measured as a function of frequency and the statistics of the backscatter has been examined. This paper unites methods of measuring a properly scaled (unbiased) estimate of the backscatter coefficient with knowledge of the scattering statistics and frequency response using statistical communications techniques. The maximum likelihood, minimum variance, unbiased estimator for wideband measurement of backscatter is developed together with its performance. The measurement technique has strong implications for system design for measuring cyclic myocardial backscatter.
A Ray Tracing Approach to Restoration and Resolution Enhancement in Experimental Ultrasound Tomography
Authors: Andersen Anders H.
Published: March 2013

Recursive ray tracing is applied for experimental time-of-flight projection data to achieve a resolution enhancement over the initial straight-ray reconstructed velocity image. Curved-ray reconstruction is performed using the dedicated simultaneous algebraic reconstruction technique (SART). Tomographic reconstructions from experimental data are compared to images obtained from simulated projection data for a refractive field mimicking the actual tissue-equivalent phantom. The simulation study adequately explains the macro-structural geometric distortion and loss of resolution in the straight-ray image due to refraction effects that are unaccounted for.
Phase Detection in Acoustic Microscopy
Authors: Levinson Stephen F.
Published: March 2013

The scanning laser acoustic microscope provides a relatively simple means by which speed of sound data can be collected from biological specimens. By employing a phase detection circuit, phase-contour lines can be superimposed on acoustic micrographs and digitized for direct speed of sound calculations. Because of the existence of mild field non-uniformities, the phase reference must be mathematically modeled. This is accomplished by employing a polynomial function and simple linear regression. Scattering can be studied by using a frequency-selective “dark field” approach. Speed of sound maps are readily produced from the phase data by applying the simple geometric relationships of wave propagation; however the theoretical limitations of the technique must be kept in mind. Using this approach, useful data have been obtained.
Transducer Characterization from Pressure Amplitude Distribution Measurements Using a Kalman Filter as Parameter Estimation Algorithm
Authors: Linssen Frans M.J. , Hoeks Arnold P.G.
Published: March 2013

The amplitude and frequency contents of a received ultrasound pulse depends on the spatial pressure amplitude distribution of the sound field, as produced by the transducer in the medium, and on the position and orientation of the reflecting surface in this field. Often, the geometry of the reflecting surface and the acoustical properties of the medium are known or can be estimated. Then it is practical to determine the transducer parameters in order to calculate the distortion of a reflected ultrasound pulse. Apart from geometrical parameters such as size and mechanical focusing, the surface velocity amplitude distribution (SVAD) of a transducer is of major importance. For some transducer configurations this SVAD may be described with a limited number of parameters. This paper presents a method, based on a Kalman filter algorithm, to assess the transducer parameters by measurement of the spatial sound field pressure amplitude distribution in various planes for different emission frequencies. Comparison of the measured pressure amplitudes with those calculated using the estimated values of the parameters shows that this method yields reliable results.
Estimation of Frequency-Dependent Attenuation Based on Parametric Spectral Analysis and Correlation Lags of the Demodulated Echo Signal
Authors: Lymberis A. , Herment A. , Demoment G. , Fric C.
Published: March 2013

Two new methods for estimating frequency-dependent attenuation are proposed which improve the compromise between the estimation variance of this parameter and the analyzed tissue volume: 1) parametric spectral estimation of the demodulated signal, based on fast Kalman filtering (ARC), 2) implementation of a new mean frequency estimator derived from all the available autocorrelation lags (ACn) of the demodulated signal. Both methods are applied to simulated echo signals. The results are compared to those of other already existing estimators. Both ARC and ACn methods provide equivalent results and a better estimation of attenuation (accuracy ranging from 1.3 to 8 %) than the previous methods do (accuracy ranging from 4 to 66 %), for analysis windows ranging from 1.5 to 20 μs.
Experimental Results in Ultrasonic Tomography Using a Filtered Backpropagation Algorithm
Authors: Sponheim Nils , Johansen Ingvild
Published: March 2013

This paper describes an experimental study in diffraction tomography whose main goal was to determine experimentally the performance of the filtered backpropagation algorithm in ultrasound tomography. We have built a simple water tank with a plane wave source and a scanning hydrophone. The test objects have been cylindrical and of a relatively simple structure and made of acrylic and silicone rubber. The resulting reconstructions show that the structure and position of the objects are well reproduced. The velocity of the objects can also be well reproduced if the velocity contrast is not too large. In medical imaging, it is most important to see the structure, and since the velocity change in biological tissue is small, the method should be well suited for medical imaging.
A Method for in Vitro Mapping of Ultrasonic Speed and Density in Breast Tissue
Authors: Yang James N. , Murphy Anthony D. , Madsen Ernest L. , Zagzebski James A. , Gilchrist Kennedy W. , Frank Gary R. , Macdonald Michael C. , Millard Cameron A. , Faraggi Aviva , Jaramillo Carlos A. , Gosset Franz R.
Published: March 2013

A method has been developed for mapping density and ultrasonic speed in 1 mm thick slices of soft tissue with a resolution of about 1 mm. Tests using phantom sections have verified the accuracy and resolution of the ultrasonic speed maps. The method has been applied to breast tissues of three patients including tumors and surrounding tissue. Fixing a specimen in 5% formaldehyde did not change the degree of local variation in ultrasonic speeds, and raised mean speeds by less than 0.8%. The densities with fixing remained almost unchanged at low tissue densities (0.93 g/cm3), but rose 1.5% for higher tissue density (greater than 1.00 g/cm3).
Ultrasound Tissue Characterization of Breast Biopsy Specimens
Authors: Edmonds P. D. , Mortensen C. L. , Hill J.R. , Holland S.K. , Jensen J. F. , Schattner P. , Valdes A. D. , Lee R. H. , Marzoni F. A.
Published: March 2013

Results of measurements of ultrasound speed and absorption coefficients in the range 3 to 8 MHz in breast tissues at 37 C are reported and analyzed in attempts to identify a set of ultrasound parameters capable of discriminating normal, benign, and malignant tissues. We analyzed 118 tissue regions, comprising 47 normal, 55 benign, and 16 malignant by straight-line fitting of frequency dependence of attenuation. Data for ten additional regions, for a total of 128, became available and were added to the cohort when we subsequently fitted quadratic curves. Sound speed consistently emerged as the variable with greatest discriminating power, particularly for separating normal from benign and malignant tissue. Great difficulty was encountered in discriminating benign from malignant, even when the jackknife technique was used. More success was found with classification and regression trees (CART), although results were sensitive to assigned misclassification costs. Best results from straight-line fits were obtained when discriminating malignant from combined normal/benign data after randomly assigning 75 percent of the data to the learning set and 25 percent to the test set. Then, 23 out of 25 normal/benign and 4 out of 4 malignant cases in the test set were correctly classified. With quadratic fitting, best results were obtained in the three-class case — the false positive rate for malignancy was reduced to zero in the learning (0/31) and test (0/10) sets. Nevertheless, the false negative rate increased to 13 out of 31 (42 percent) in the learning set, while attaining zero (0/4) in the test set.
Speckle Reduction with Edge Preservation in Medical Ultrasonic Images Using a Homogeneous Region Growing Mean Filter (HRGMF)
Authors: Koo Ja I. , Park Song B.
Published: March 2013

In this paper, we propose a new post formation adaptive image filtering technique, to be called the homogeneous region growing mean filter, in order to reduce speckle noise with edge preservation in medical ultrasonic images. First, to find a proper seed region, an initially assumed seed region, which is larger than the average speckle size around a given filtering point, is successively contracted according to a certain local homogeneity criterion. Once the seed region is determined, the next step is to grow the homogeneous region successively based on some measures of local homogeneity and similarity of the neighboring region. The output of the proposed filter for each filtering point is obtained from the arithmetic mean of the grown locally homogeneous region. Several simulation results are presented to illustrate the performance of the proposed filter. They show that the proposed technique effectively smoothes ultrasonic speckle and completely suppresses isolated impulsive noise over the entire texture in addition to preserving the edge information.
Improvement of Lesion Detection by Echographic Image Processing: Signal-to-Noise-Ratio Imaging
Authors: Verhoeven J.T.M. , Thijssen J.M. , Theeuwes A.G.M.
Published: March 2013

Signal-to-noise-ratio (SNR) images were constructed by a sliding window technique. Theoretical derivations of the first order statistical properties of SNR images are given for the case of intensity coding of the original images for low number densities and for the limit case of fully developed speckle. The original images were obtained by realistic simulations of backscattering by homogeneous media, while using a range of number densities of the scatterers (isotropic scattering). The SNR imaging method is illustrated by results obtained from simulated scattering media containing a lesion that is contrasting in reflectivity level or in number density of the scatterers. A considerable improvement in lesion detection is obtained if the primary difference from the background speckle is due to a different number density of the scatterers within the lesion.
Description of Broad-Band Pulsed Doppler Ultrasound Processing Using the Two-Dimensional Fourier Transform
Authors: Wilson L.S.
Published: March 2013

Considering data from a Doppler sample volume as a two-dimensional function of depth and time, the properties of its two-dimensional fast Fourier transform (2DFFT) are discussed. It is shown that the 2DFFT of idealized Doppler data from moving scatterers is a line whose slope is the velocity of the scatterers. Aliasing, finite bandwidth effects, and spectral broadening due to transit time effects receive simple descriptions in this scheme. Existing processing schemes can be described graphically in this unifying description. Processing of broad band pulsed Doppler ultrasound can incorporate a correction for aliasing if based on the two-dimensional Fourier transform, and this has been tested using data from tissue-mimicking phantom in a tank-based experiment.
A Simulation Study of Echographic Imaging of Diffuse and Structurally Scattering Media
Authors: Jacobs E.M.G.P. , Thijssen J.M.
Published: March 2013

Realistic simulations of echographic image formation were performed. The simulations were based on a focussed single element transducer of 3.5 MHz and linear scanning. The tissue model scanned was composed of a homogeneous, nonattenuating, medium containing point-like scatterers. The scatterers were distributed in space in two different arrangements: randomly with a fixed number density of 7500 per cubic centimeter and regularly in a cubic matrix with a characteristic distance of 1 mm. These two populations of scatterers yielded the diffuse and the structural scattering component, respectively. The B-mode texture was assessed by first and second order statistical parameters. The effects of various modifications of the matrix, i.e., the relative scattering strength, the orientation and the position uncertainty of the scatterers, on the statistical parameters were systematically investigated. Increasing the relative scattering strength yields a monotonic increase of the mean grey level, the ratio of structural over diffuse scattering intensity and a decrease of the signal-to-noise ratio and the autocorrelation lengths. Increasing the position uncertainty to 20 percent reduces these effects practically to zero, except for the lateral ACF's. Rotation of the matrix with respect to the beam axis induces a periodicity in all statistical parameters, which is symmetric around 45 degrees. Again, the effects become statistically insignificant at a position uncertainty of 20 percent, with the exception of length of the lateral ACF. While assuming that in a single clinical B-mode echogram of the liver many orientations of the matrix will be simultaneously present, the B-mode lines of images obtained for a range of orientations were taken together and the overall statistical parameters calculated. The mean, the signal-to-noise ratio of the echo amplitude, SNRA, and the axial and lateral lengths of the ACF for the multirotation condition are significantly different from both the diffuse and the zero degree orientation. The structural backscattering intensity cannot be estimated any more with a reasonable precision. The structural separation distance, however, can still be assessed at a 10 percent level of the position uncertainty, even in the multirotation case and is therefore a robust clinical parameter.
Inverse Scattering Scheme Based on the Moment Method in the Spectral Domain, Part II: Numerical Simulation
Authors: Choi Hyun-Chul , Kim Se-Yun , Ra Jung-Woong
Published: March 2013

A spectral inverse scattering scheme, applying the moment-method procedures with a polynomial basis function for the induced field in each enlarged cell, is implemented numerically and simulated for a simple test geometry. The method provides good results comparable to the discretization of object fine enough to adopt the pulse basis function. The effects of several variables on the reconstructed profile are simulated one by one. Simulation results for the scattered field contaminated by Gaussian random noise show large fluctuations in the reconstructed profiles. The validity of the inversion scheme to regularization of the noise effects is conformed by showing that averaging the reconstructed profile over each cell with a suitable weighting function reduces the reconstruction error to a nearly negligible value.
Phase Aberration Correction Using Echo Signals from Moving Targets I: Description and Theory
Authors: Zhao D. , Bohs L. N. , Trahey G. E.
Published: March 2013

Inhomogeneous acoustic velocity in human tissue introduces phase aberration in ultrasonic imaging systems and degrades image quality. A novel technique that employs echo signals from moving diffuse targets, such as flowing blood, as an image quality factor to compensate for phase aberration is described. Such signals can be obtained by subtracting the images of two consecutive target interrogations. The fundamental statistics of the quality factor and other related parameters are developed to provide a theoretical basis for the technique.
Simulated Capillary Blood Flow Measurement Using a Nonlinear Ultrasonic Contrast Agent
Authors: Schrope B. , Newhouse V.L. , Uhlendorf V.
Published: March 2013

This paper proposes a system for measuring slow, small volume blood flow, such as that found in the capillary beds. The method relies on the injection of a strongly nonlinear echocardiographic contrast agent, whose echoes are then analyzed by a modified Doppler process. The contrast agent is necessary to increase the signal-to-clutter ratio from the small blood volume, and to distinguish the blood movement from other moving structures, such as vessel walls or surrounding tissue. The nonlinear properties of this saccharide-based contrast agent are described, as evidenced by experimental evaluation. The contrast agent and signal processing modality are then tested in a blood flow simulator, at velocities as low as 1.5 mm/s, with good results. In addition, an analysis for applying this technique in vivo is presented, accounting for the dynamic and acoustic parameters of the physiological environment. Finally, some specific applications for this method are discussed, including its limitations.
Segmenting Ultrasound Images of the Prostate Using Neural Networks
Authors: Prater James S. , Richard William D.
Published: March 2013

This paper describes a method for segmenting transrectal ultrasound images of the prostate using feedforward neural networks. Segmenting two-dimensional images of the prostate into prostate and nonprostate regions is required when forming a three-dimensional image of the prostate from a set of parallel two-dimensional images. Three neural network architectures are presented as examples and discussed. Each of these networks was trained using a small portion of a training image segmented by an expert sonographer. The results of applying the trained networks to the entire training image and to adjacent images in the two-dimensional image set are presented and discussed. The final network architecture was also trained with additional data from two other images in the set. The results of applying this retrained network to each of the images in the set are presented and discussed.
Simulation of B-Scan Images from Two-Dimensional Transducer Arrays: Part Ii - Comparisons between Linear and Two-Dimensional Phased Arrays
Authors: Turnbull Daniel H. , Foster F. Stuart
Published: March 2013

Two-dimensional (2-D) arrays have been proposed as a solution to the degradation in medical ultrasound image quality occurring as a result of asymmetric focusing properties of linear phased array transducers. The 2-D phased transducer array is also capable of electronically steering the symmetrically focused ultrasound beam throughout a three-dimensional volume. In a companion paper the potential of 2-D transducer arrays for medical imaging has been investigated using simulated B-scan images. In this paper, the advantages of 2-D over linear transducer arrays is demonstrated by simulating images of spherical cysts embedded in a large scattering volume. The large elevation beamwidth in the nearfield of a 5 MHz linear phased transducer array results in a severe reduction in the image contrast measured between a 4 mm diameter cyst and the surrounding scattering media. By employing a 2-D array with symmetric focusing, the contrast between the cyst and surrounding scatterers is significantly improved. The use of additional elements in the elevation direction of a linear array is also investigated. In this case the additional elements are included only to focus, but not to steer the ultrasound beam. Using the contrast characteristics of a 4 mm diameter cyst, it is shown that relatively few elevation elements are required to significantly improve the nearfield imaging capability of the linear array.
A Comparison Method for Mean Frequency Estimators for Doppler Ultrasound
Authors: Brands Peter J. , Hoeks Arnold P.G.
Published: March 2013

Mean frequency estimators as used in pulsed Doppler ultrasound equipment should provide an accurate (quality) and consistent (robustness) estimate over a wide range of signal conditions. In a simplified signal model, the main parameters to consider are the noise level, mean frequency, bandwidth and power of both the Doppler signal and the stationary component over a given time window. It may be expected that one estimator for a given parameter combination exhibits a good performance while another estimator for the same parameter combination behaves poorly. To allow direct comparison between different types of frequency estimators, a method is introduced to evaluate the quality and robustness of estimators for a common signal space covering a wide range of realistic parameter combinations. The method is illustrated using three different mean frequency estimators: (1) a first order autoregressive estimator in combination with a stationary echo filter; (2) a second order autoregressive estimator; and (3) a complex linear regression estimator in combination with a stationary echo filter. It is concluded that, for the parameter combinations considered, the complex linear regression estimator exhibits the best quality (low variance and bias of the estimate) and robustness (consistent quality for all parameter combinations).
Two Dimensional Ultrasonic Beam Distortion in the Breast: In Vivo Measurements and Effects
Authors: Freiburger P. D. , Sullivan D. C. , LeBlanc B. H. , Smith S. W. , Trahey G. E.
Published: March 2013

Two dimensional arrival time data was obtained for the propagation of ultrasound across the breasts of 7 female volunteers. These profiles were extracted through the use of cross-correlation measurements and a simulated annealing process that maintained phase closure while aligning the data. The phase aberration measured in two dimensions had a larger magnitude than previously reported phase aberration measured in one dimension in the breast A point spread function generation computer program was used to demonstrate the system response degrading effects of the measured phase aberration and the usefulness of current one dimensional phase aberration correction techniques. The results indicate that two dimensional correction algorithms are necessary to restore the system performance losses due to phase aberration.
Modified X Waves with Improved Field Properties
Authors: Song Tai K. , Lu J-y. , Greenleaf J. F.
Published: March 2013

A method to obtain a good compromise between the depth of field and the lateral resolution of “X waves” is proposed. The original X waves are theoretically nondiffracting beams generated by a specially phased infinite transmit aperture. When generated by a finite aperture, X waves are diffracting beams but have a large depth of field, maintaining uniform lateral field profiles. The proposed modification of the wave equation solution for X waves replaces a constant parameter representing the propagation angle of ultrasound with a function of radial distance at the aperture surface, and results in modified X waves that have a larger depth of field than the original X waves. Computer simulations show that a proper choice of the modification function can produce a new beam with improved field properties compared with the original X waves, promising images with higher lateral resolution and increased contrast over a large depth of field in high frame rate medical imaging. Experimental results are presented to verify the simulation results of the proposed method.
Mathematical Simulation of Pressure Pulse Propagation in Biological Tissues
Authors: Adrov Victor N. , chernomordik Victor V.
Published: March 2013

The propagation of pressure pulses of arbitrary time form in inhomogeneous attenuating media with characteristics similar to real biological tissues is considered. A mathematical model using the quasi-optical approximation is developed to solve the wave equation. Such a model proves to be convenient for computer realization. A spectral analysis of known experimental data on frequency dependent backscatter is realized to separate coherent and incoherent components of backscatter from tissues and determine their parameters. The characteristics of the scattering are utilized for digital simulations of ultrasound propagation from an interrogated tissue volume. The results presented describe the expected space distribution of the pressure amplitude and phase near the transducer focus in the presence of an aberrating layer with parameters characteristic of abdominal imaging.
An Efficient Computer Model of Three-Dimensional Speckle Patterns in Dynamically Focused Annular Array
Authors: Park Jong C. , Park Song B.
Published: March 2013

This paper describes an efficient computer method for generating three-dimensional (3-D) ultrasonic speckle patterns for sector scans of an annular array with dynamic focusing in both transmit and receive. Assuming random scatterers in an attenuating medium, the system synthesizes the waveform for each scan line using echo data received at all annular elements of the transducer when short pulses are transmitted by one annulus after another. The amount of echo data needed to synthesize one waveform is tremendously reduced by reducing the 3-D distributions of scatterers to line distributions and by representing scatterers on a small line segment by a single equivalent scatterer taking into account the two-way travel time differences. Furthermore, by a judicious 3-D arrangement of the scatterer lines and scan lines, it is possible to synthesize the waveform for a new scan line with negligible computation overhead. The waveforms of the scan lines are detected to obtain a B-mode image or speckle patterns. The patterns obtained on several differently-oriented image planes showed a good statistical agreement with experimentally obtained patterns.
Deconvolution of in-Vivo Ultrasound B-Mode Images
Authors: Jensen Jørgen Arendt , Mathorne Jan , Gravesen Torben , Stage Bjarne
Published: March 2013

An algorithm for deconvolution of medical ultrasound images is presented. The procedure involves estimation of the basic one-dimensional ultrasound pulse, determining the ratio of the covariance of the noise to the covariance of the reflection signal, and finally deconvolution of the rf signal from the transducer. Using pulse and covariance estimators makes the approach self-calibrating, as all parameters for the procedure are estimated from the patient under investigation. An example of use on a clinical, in-vivo image is given. A 2 × 2 cm region of the portal vein in a liver is deconvolved. An increase in axial resolution by a factor of 2.4 is obtained. The procedure can also be applied to whole images, when it is ensured that the rf signal is properly measured. A method for doing that is outlined.
Improvement of Lesion Detectability by Speckle Reduction Filtering: A Quantitative Study
Authors: Verhoeven J.T.M. , Thijssen J.M.
Published: March 2013

An objective measure (Lesion Signal-to-Noise Ratio) quantifying the detectability of lesions in echographic images was employed. This measure was used to determine the performance of digital speckle reduction filters, which were applied to computer simulated ultrasound B-mode images. One linear (mean filter) and two nonlinear filters (median and L2-mean filters) have been investigated. A comparison was made between fixed and adaptive versions of these filters. The influence of the size of the filter window on the Lesion Signal-to-Noise Ratio was systematically investigated. Also, the effect of the shape of the filter window is illustrated. The difference in performance of the linear and nonlinear filters was found to be small. Adaptive filters did not perform significantly better than fixed filters. The maximum improvement of lesion detectability was in the order of 40 percent. The choice of a correct window size was critical. For all types of filters, an optimum window size appeared to be present in the curves relating the Lesion Signal-to-Noise Ratio to this size.
Application of Neural Networks for the Classification of Diffuse Liver Disease by Quantitative Echography
Authors: Gebbinck M.S. klein , Verhoeven J.T.M. , Thijssen J.M. , Schouten T.E.
Published: March 2013

Three different methods were investigated to determine their ability to detect and classify various categories of diffuse liver disease. A statistical method, i.e., discriminant analysis, a supervised neural network called backpropagation and a nonsupervised, self-organizing feature map were examined. The investigation was performed on the basis of a previously selected set of acoustic and image texture parameters. The limited number of patients was successfully extended by generating additional but independent data with identical statistical properties. The generated data were used for training and test sets. The final test was made with the original patient data as a validation set. It is concluded that neural networks are an attractive alternative to traditional statistical techniques when dealing with medical detection and classification tasks. Moreover, the use of generated data for training the networks and the discriminant classifier has been shown to be justified and profitable.
Characterization of Tissue Microstructure Scatterer Distribution with Spectral Correlation
Authors: Varghese Tomy , Donohue Kevin D.
Published: March 2013

Characterization of tissue microstructure from the backscattered ultrasound signal using the spectral autocorrelation (SAC) function provides information about the scatterer distribution in biological tissue. This paper demonstrates SAC capabilities in characterizing periodicities in A-scans due to regularity in the scatterer distribution. The A-scan is modelled as a cyclostationary signal, where the statistical parameters of the signal vary in time with single or multiple periodicities. This periodicity manifests itself as spectral peaks both in the power spectral density (PSD) and in the SAC. Periodicity in the PSD will produce a well defined dominant peak in the cepstrum, which has been used to determine the scatterer spacing. The relationship between the scatterer spacing and the spacing of the spectral peaks is established using a stochastic model of the echo-formation process from biological tissue. The distribution of the scatterers within the microstructure is modelled using a Gamma function, which offers a flexible method of simulating parametric regularity in the scatterer spacing. Simulations of the tissue microstructure for lower orders of regularity indicate that the SAC components reveal information about the scatterer spacing that are not seen in the PSD and the cepstrum. The echo-formation process is tested by simulating microstructure of varying regularity and analyzing their effect on the SAC, PSD and cepstrum. Experimental validation of the simulation results are provided using in vivo scans of the breast and liver tissue that show the presence of significant spectral correlation components in the SAC.
Measurement of Two-Dimensional Blood Velocity Vectors by the Ultrasonic Speckle Projection Technique
Authors: Wilson L.S. , Gill R.W.
Published: March 2013

A technique has been developed for measuring the two in-plane components of blood velocity using ultrasound. The principle is based on analyzing a time sequence of successive images of the speckle pattern, and forming spatial projections of the resulting three-dimensional data set. The mathematics may be understood in terms of sections through a three-dimensional Fourier transform of the original data. The technique has been tested with data from a computer-controlled scanner using a tissue-mimicking phantom, and with data from a commercial ultrasound scanner using images of flowing blood in a jugular vein. In both cases, velocity vectors with many different orientations were measured, demonstrating the feasibility of the method. A less restrictive real-time implementation is suggested.
In Vivo Study of Online Liver Tissue Classification Based on Envelope Power Spectrum Analysis
Authors: Lang M. , Ermert H. , Heuser L.
Published: March 2013

An ultrasonic imaging and signal analysis system, combining a 3.5 MHz linear array B-scanner and an array processor, has been realized for a clinical liver tissue classification study. Based on the complete unprocessed rf data set of a real time B-image, local envelope power spectra averaged over interactively defined regions are computed. These spectra are partially corrected for several tissue type independent effects that affect comparability. A library containing the in vivo data of 65 patients with known liver tissue states in three groups (normal, cirrhotic, fat) was built up. An algorithm based on numerical optimization of parametrized spectrum characteristics combined with a k-nearest-neighbors classifier, applied to the library, leads to correct classification rates of 85.8 to 87.5 percent in discriminating pathological from normal tissue states. The method can be used for k-weighted color coded tissue type imaging with acceptable spatial resolution.
Two-Dimensional Random Arrays for Real Time Volumetric Imaging
Authors: Davidsen Richard E. , Jensen Jørgen A. , Smith Stephen W.
Published: March 2013

Two-dimensional arrays are necessary for a variety of ultrasonic imaging techniques, including elevation focusing, 2-D phase aberration correction, and real time volumetric imaging. In order to reduce system cost and complexity, sparse 2-D arrays have been considered with element geometries selected ad hoc, by algorithm, or by random process. Two random sparse array geometries and a sparse array with a Mills cross receive pattern were simulated and compared to a fully sampled aperture with the same overall dimensions. The sparse arrays were designed to the constraints of the Duke University real time volumetric imaging system, which employs a wide transmit beam and receive mode parallel processing to increase image frame rate. Depth-of-field comparisons were made from simulated on-axis and off-axis beamplots at ranges from 30 to 160 mm for both coaxial and offset transmit and receive beams. A random array with Gaussian distribution of transmitters and uniform distribution of receivers was found to have better resolution and depth-of-field than both a Mills cross array and a random array with uniform distribution of both transmit and receive elements. The Gaussian random array was constructed and experimental system response measurements were made at several ranges. Comparisons of B-scan images of a tissue mimicking phantom show improvement in resolution and depth-of-field consistent with simulation results.
Efficient Two-Dimensional Blocked Element Compensation
Authors: Li Pai-Chi , O'Donnell M.
Published: March 2013

Very large, two-dimensional, anisotropic arrays have been proposed to improve ultrasound image quality. Due to noncontiguous acoustic windows into the body, however, a significant portion of such an aperture may be blocked. Blocked elements result in high sidelobes in the point spread function, degrading image quality. To compensate for this, an object dependent method using multiple receive beams has been recently proposed. This method is effective in removing undesired sidelobes. However, previous results were for one-dimensional arrays where only lateral beams were used for estimation. With two-dimensional arrays, the distribution of blocked elements can change beam characteristics, both laterally and elevationally. In other words, receive beams must be formed in both directions for better performance. Although straightforward in principle, extension of the algorithm from one dimension to two increases computational complexity dramatically. Furthermore, the restricted elevational steering capability of anisotropic arrays also limits performance. In this paper, several computationally efficient algorithms for two-dimensional blocked element compensation are proposed and evaluated. It is shown that undesired sidelobes can be effectively removed using only a limited number of receive beams. Image quality can therefore be restored in the presence of blocked elements without significantly increasing hardware complexity.
Estimation of in Vivo Pulses in Medical Ultrasound
Authors: Jensen Jørgen Arendt
Published: March 2013

An algorithm for the estimation of one-dimensional in-vivo ultrasound pulses is derived. The routine estimates a set of ARMA parameters describing the pulse and uses data from a number of adjacent rf lines. Using multiple lines results in a decrease in variance on the estimated parameters and significantly reduces the risk of terminating the algorithm at a local minimum. Examples from use on synthetic data confirms the reduction in variance and increased chance of successful minimization termination. Simulations are also reported indicating the relation between the one-dimensional pulse and the three-dimensional, attenuated ultrasound field for a concave transducer. Pulses are estimated from in-vivo liver data showing good resemblance to a pulse measured as the response from a planar reflector and then properly attenuated. The main application for the algorithm is to function as a preprocessing stage for deconvolution algorithms using parametric pulses.
Simulation of Two-Dimensional Ultrasonic Imaging of Biological Tissues in the Presence of Phase Aberrations
Authors: Adrov Victor N. , Chernomordik Victor V.
Published: March 2013

A simulator of phase aberrations for mathematical modeling of two-dimensional (2-D) ultrasonic medical imaging is developed. Principal characteristics of expected phase aberrations were put into the model to investigate the distorting influence of intervening tissues on the quality of conventional medical B-scan images. Information necessary for numerical simulations, including the form of the phase correlation function, correlation length and distortion magnitude, was obtained from analysis of known experimental data on abdominal and breast imaging in vivo. Examples of simulated acoustical images of some simple phantoms are presented. Improvement of image quality due to one simple phase adaptation algorithm is also presented.
Optimization of Signal-to-Noise Ratio for Multilayer Pzt Transducers
Authors: Goldberg Richard L. , Smith Stephen W.
Published: March 2013

In medical ultrasound imaging, two-dimensional (2-D) array transducers are desirable to implement dynamic focusing and phase aberration correction in two dimensions as well as volumetric imaging. Unfortunately, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance near the resonance frequency. This results in poor signal-to-noise ratio (SNR) of the array elements. It has previously been demonstrated that transducers made from multilayer PZT ceramics have lower electrical impedance and greater SNR than comparable single layer elements. A simplified circuit model has been developed to optimize the SNR for multilayer ceramic (MLC) transducers. In this model, an electronic transmitter excites the array element and in the receive mode, the element drives a coaxial cable load terminated by a high impedance preamplifier. The transducer impedance is Zt/N2, where N is the number of piezoelectric layers. Maximum transmit signal is obtained when N = Ntx such that the transducer impedance, Zt/Ntx2, is matched to the source impedance. Maximum receive signal is obtained when N = Nrx such that the transducer impedance, Zt/Nrx2, is matched to the coaxial cable reactance. For maximum pulse-echo signal, the transducer should be designed with N = [Formula: see text], the geometric mean of Ntx and Nrx. Using this optimization technique, a 1.5-D array was designed with 3 layers for maximum pulse-echo SNR. Results of simulations from the simplified circuit analysis were consistent with those of the KLM model. The 3 layer array was fabricated as well as a single layer control array. The measured transmit signal and receive signal agreed with the simulation results.
Retrospective Dynamic Transmit Focusing
Authors: Freeman S. , Li Pai-chi , O'Donnell M.
Published: March 2013

Dynamically-focused on receive, real-time array systems exhibit image degradation far from the focal zone of the fixed transmit lens. A retrospective filtering technique reducing the effects of the fixed transmitter is presented. The filter deconvolves the defocused transmit pattern producing a new in-focus transmit/receive image, where the filter coefficients are derived with a least-squares method. Experimental results are presented for a 128 channel array system showing the method's performance. A proposed architecture for real-time filtering is also discussed.
Finite Element Analysis and Experimental Studies on the Thickness Resonance of Piezocomposite Transducers
Authors: Qi Wenkang , Cao Wenwu
Published: March 2013

Finite element method (FEA) has been used to calculate the thickness resonance frequency and electromechanical coupling coefficient kt for 2–2 piezocomposite transducers. The results are compared with that of the effective medium theory and also verified by experiments. It is shown that the predicted resonance frequencies from the effective medium theory and the unit cell modeling using FEA deviate from the experimental observations for composite systems with a ceramic aspect ratio (width/length) more than 0.4. For such systems, full size FEA modeling is required which can provide accurate predictions of the resonance frequency and thickness coupling constant kt.