bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-Dimensional Arrays for Medical Ultrasound
Authors: Smith S.W. , Trahey G.E. , von Ramm O.T.
Published: March 2013

The design, fabrication and evaluation of two-dimensional transducer arrays are described for medical ultrasound imaging. A 4 × 32, 2.8 MHz array was developed to use new signal processing techniques for improved B-scan imaging including elevation focusing, phase correction and synthetic aperture imaging. Laboratory measurements from typical array elements showed 50 Ω dB, and − dB pulse-echo angular response of 62°. Simulations of pulse-echo beam plots have shown grating lobes 20 dB below the main lobe at ±7° in the elevation direction. The complete 2-D array has been used for measurements of phase aberrations in breast, and the individual 32 element linear arrays have been used to obtain conventional B-scans. Several 16 × 16 arrays have also been developed for high speed volumetric imaging. These include 96 transmit elements and 32 receive channels. With a λ/4 matching layer, laboratory measurements show 50 Ω insertion loss of −72 dB, − dB fractional bandwidth of 63%, interelement crosstalk of &29 dB and − dB angular response of 25°. Pulse-echo sensitivity was improved by 21 dB through the use of integrated circuit preamplifiers of high impedance mounted in the transducer handle. In vivo cardiac, abdominal, and obstetric B-scans with elevation focusing, as well as high speed C-scans, have been obtained with these 2-D arrays.
In Vivo Imaging Using a Copolymer Phased Array
Authors: Goldberg Richard L. , Smith Stephen W. , Brown Lewis F.
Published: March 2013

Phased-array images have been obtained in vivo with a steered copolymer array operating at 2.5 MHz. The array was fabricated using 28 μm copolymer film, λ/4 resonant at 21 MHz, which was bonded to a glass ceramic backing with a thin film bond. The 32 array elements were created by laser ablation of the continuous gold electrode on one side of the film. The transducer was driven by 200 V shock excitation, and the received signal was processed by 32 custom IC preamplifiers that were mounted to the array connector. The amplifiers had a high input impedance compared to that of the array elements and their output impedance matched that of the coaxial cable that connected to the scanner. Because the copolymer transducer had a broad bandwidth, the spectrum of the pulse echo image was modified by the frequency dependent attenuation of tissue and the bandpass of the ultrasound scanner, resulting in a center frequency of 2.5 MHz. The performance of the copolymer array was compared to that of a 3 MHz, PZT array with similar dimensions. On the Duke phased-array scanner, the copolymer sensitivity was 28 dB less than that of PZT. The copolymer elements had a 6 dB pulse-echo angular response of 30°, and the interelement cross-coupling was −35 dB. Phased-array images were made of the heart of a 25 year-old normal male.
Adaptive Imaging in Aberrating Media: A Broadband Algorithm
Authors: Norton Stephen J.
Published: March 2013

An adaptive algorithm is derived for imaging in an aberrating medium based on wideband (time-domain) linear array data. Image reconstructions using simulated scattering data are presented. An analogy is also drawn between broadband array imaging and limited-angle tomography. This analogy suggests some tomographic-like filtering schemes that can be applied to improve the quality of the image. The algorithm is designed for imaging in composite material, although the imaging of other heterogeneous media such as tissue may be feasible under certain conditions.
Elastography: Elasticity Imaging Using Ultrasound with Application to Muscle and Breast in Vivo
Authors: Céspedes I. , Ophir J. , Ponnekanti H. , Maklad N.
Published: March 2013

Changes in tissue elasticity are generally correlated with its pathological state. In many cases, despite the difference in elasticity, the small size of a lesion or its location deep in the body preclude its detection by palpation. In general, such a lesion may or may not posses echogenic properties that would make it ultrasonically detectable. Elastography is an ultrasonic method for imaging the elasticity of compliant tissues. The method estimates the local longitudinal strain of tissue elements by ultrasonically assessing the one dimensional local displacements. This information can be combined with first order theoretical estimates of the local stress to yield a quantitative measure of the local elastic properties of tissue. The elasticity information is displayed in the form of a gray scale image called an elastogram. An experimental system for elastography in phantoms based on a single element transducer has been described previously [1]. Here we introduce a new elastography system based on a linear array transducer that is suitable for in vivo scanning. We describe tissue mimicking phantom experiments and preliminary in vivo breast and muscle elastograms confirming the feasibility of performing elastography in vivo. An elastogram of a breast containing an 8 mm palpable cancer nodule clearly shows the lesion. Elastograms and their corresponding sonograms show some similarities and differences in the depiction of tissue structures.
Reduction of Image Noise in Elastography
Authors: Céspedes Ignacio , Ophir Jonathan
Published: March 2013

Elastography is a method for imaging the elastic properties of compliant tissues which produces gray scale elasticity images called elastograms. The elastograms of phantoms with homogeneous elastic properties exhibit a noisy appearance. We demonstrate that this noisy appearance of the elastograms is due to the nonstationary relationship between the pre- and postcompression signals that results in an artifactual modulation of the strain estimates by the amplitude variations of the envelope of the rf signal. We have identified two methods to reduce the strain modulation artifact. The first method consists of reducing the signal amplitude swings within the observation windows by logarithmically or otherwise compressing the rf signal. The sensitivity of this method to amplitude compression strength and the ability to reduce the noise in the elastograms without affecting the spatial resolution are investigated through simulations. The second method to reduce the strain modulation artifact consists of temporal stretching of the signal obtained after physical compression to approximate the shape of the signal obtained before compression. In this paper, we discuss the first method. The results show that significant improvement in image noise can be obtained with logarithmic amplitude compression. This improvement is obtained in conjunction with improved spatial resolution.
Producing Deep Depth of Field and Depth-Independent Resolution in Nde with Limited Diffraction Beams
Authors: Lu Jian-yu , Greenleaf James F.
Published: March 2013

Limited diffraction beams, such as Durnin's J0 Bessel beam, are a class of nonspreading solutions to the isotropic/homogeneous scalar wave equation. These beams can be approximately produced with finite aperture and energy over a deep depth of field. In this paper, we report the application of a broadband J0 Bessel beam to nondestructive evaluation (NDE) of materials. Pulse-echo images of a stainless steel block phantom were obtained with both the Jo Bessel beam and a conventional focused Gaussian beam. Results show that uniformly high resolutions were obtained with the J0 Bessel beam over a large distance. In addition, the lateral resolution of the J0 Bessel beam is almost independent of the speed of sound of the materials inspected. In contrast, the lateral resolution of images obtained with the conventional focused Gaussian beam changes dramatically with the distance and the focal length of the beam in water is greatly reduced by the steel block. Therefore, limited diffraction beams could be useful for nondestructive evaluation of materials of different speeds of sound. Restoration of pulse-echo images obtained with these beams could be simplified.
On Monitoring Structural Changes of Anisotropic Tissues by Means of Statistical Analysis of Ultrasonic Images
Authors: Pecorari C.
Published: March 2013

An investigation into statistical properties of ultrasonic image texture from three-dimensional clusters of anisotropic scatterers is carried out. The structural properties of the clusters are modeled after those of soft biological tissues, such as skeletal muscle tissues, both in their healthy condition and at the early stage of degenerative diseases. The average axial autocorrelation function of the intensity of the image texture is used to characterize and monitor changes of the geometrical properties of the tissue components. A distinct local increase of the autocorrelation is observed within a range of small time shifts, and it is explained in terms of the structure of the time-domain backscattered signal from each individual scatterer. It is shown that such an increase is sensitive to structural variations of the cluster similar to those occurring at the early stage of several muscular diseases.
Improved Detectability with Blocked Element Compensation
Authors: Li Pai-chi , O'Donnell M.
Published: March 2013

The inability of diagnostic ultrasound to detect low contrast lesions deep inside the body has limited its success in cancer diagnosis. To enhance low contrast detectability, two-dimensional, very large arrays (VLA's) providing greatly improved spatial resolution have been proposed. Due to discontinuous acoustic windows into the body, however, a significant fraction of such an array might be blocked resulting in degraded detectability in clinical situations. To compensate for this degradation, an object dependent method utilizing multiple receive beams has been proposed and shown to effectively reduce un-desired beamforming artifacts. To further explore the method's capabilities, simulations have been done quantifying improvements in contrast resolution. Using the contrast-to-noise ratio (CNR) as a performance measure, results show that low contrast detectability is determined by sidelobe energy in the point spread function if the total aperture size is not reduced. Moreover, contrast resolution can be restored using the object dependent method if the number of blocked elements is not very significant. If the number of blocked elements is large, however, the method breaks down and performance improvements are minimal.
Ultrasonic Tomography of Biological Tissue
Authors: Sponheim N. , Gelius L.-J. , Johansen I. , Stamnes J. J.
Published: March 2013

In this paper, quantitative tomographic reconstructions of biological tissue are presented. First, the experimental setup and a hybrid filtered backpropagation (FBP) technique are briefly described. Using this technique, which includes exact backpropagation of data prior to reconstruction by means of the classical FBP algorithm, quantitative velocity maps of relatively large biological objects can be obtained. Since the FBP algorithm is based on a first-order scattering approximation, the deteriorating effects of higher-order scattering in diffraction tomography are also discussed. The higher-order scattering limits the size of the biological object to a few centimeters.
Ultrasound Attenuation Imaging in the Os Calcis: An Improved Method
Authors: Laugier P. , Berger G. , Giat P. , Bonnin-Fayet P. , Laval-Jeantet M.
Published: March 2013

A complete assessment of the broadband ultrasonic attenuation (BUA) distribution within the os calcis was made using an ultrasonic mechanical scanning device with focused transducers. Measurements were performed on 12 os calces removed from fresh female cadavers. We present the first images of BUA of the os calcis. Reasonably high quality images were obtained compared to computed tomography. The resolution provided by the focused transducers is approximately 4 or 5 mm in the focal zone. Compared to dual energy X-ray absorptiometry (DEXA) or quantitative computed tomography, ultrasound imaging of the os calcis offers the possibility of controlling the placement, size and shape of the region of interest and to use multiple measurement sites. DEXA was used systematically to measure the bone mineral density (BMD) of the os calces. A highly significant correlation between BMD and BUA was found (r= 0.97 p < 0.001).
Fast Scan Conversion Algorithms for Displaying Ultrasound Sector Images
Authors: Berkhoff A.P. , Huisman H.J. , Thijssen J.M. , Jacobs E.M.G.P , Homan R.J.F.
Published: March 2013

Two fast algorithms for interpolation of ultrasonic sector-scans were developed. Both algorithms are based on line-drawing algorithms and are free from multiplications in the innermost loops. The algorithms were compared to the following conventional interpolators: 2-D windowed sinc, bicubic spline, 4 × 4 point bicubic spline, bilinear, and nearest neighbor. The most accurate of the two new algorithms is about eight times faster than nearest neighbor interpolation. The quantitative errors are of the same order as the errors of the nearest neighbor interpolator. The subjective image quality is between nearest neighbor and bilinear interpolation.
Ultrasonic Measurement of Forced Diameter Variations in an Elastic Tube
Authors: Berrios Javier C. , Pedersen Peder C.
Published: March 2013

This paper presents an ultrasonic measurement technique to determine an elasticity parameter, called the apparent compliance, in a thin-walled tube. The apparent compliance is obtained by ultrasound pulse-echo measurement of the diameter variation in response to an externally applied time-varying pressure function. Specifically, the diameter variation is obtained by tracking the time shift of the echoes from the front and back walls of the tube using a correlation technique. This technique is named the Forced Vibration Method (FVM). This approach to compliance measurement is distinctly different from compliance measurements using the blood function as excitation function, but is closely related to the elastic imaging concept. Two experimental models, termed the rigid wall model and the leg-like model, have been developed. These models allow the amplitude and frequency of the pressure function as well as the dimensions and properties of the tube to be varied. Results for the diameter variations vs. location along the tube and frequency of external pressure function are presented for both models.
Elevational Spatial Compounding
Authors: Li Pai-Chi , O'Donnell M.
Published: March 2013

Spatial compounding has long been explored to reduce coherent speckle noise in medical ultrasound. By laterally translating a one-dimensional array, partially correlated measurements made at different look directions can be obtained and incoherently averaged. The lateral resolution, however, is limited by the sub-array length used for each independent measurement. To reduce speckle contrast without compromising lateral resolution, a new spatial compounding technique using two-dimensional, anisotropic arrays is proposed. This technique obtains partially correlated measurements by steering the image plane elevationally with small inclinations. Incoherent averaging is then performed by adding image magnitudes. Therefore, contrast resolution is improved only at the price of a slightly wider elevational beam. Note that although anisotropic arrays have limited steering capability in elevation, grating lobes are not considered influential since only small inclinations are needed between measurements. Simulations have been performed to show both the change in spatial resolution and the improvement in contrast resolution. Results indicated minimal increase in the correlation length both laterally and axially. It was also shown that detectability can be significantly enhanced by increasing the number of measurements or increasing the differential inclination between measurements. This technique is therefore effective for reducing speckle noise while maintaining in-plane spatial resolution. Furthermore, it demonstrates a new application of two-dimensional anisotropic arrays in spite of their limited elevational steering capability.
Ultrasonic B-Mode Image Enhancement Based on Level-Dependent Spread Functions
Authors: Collaris R.J. , Hoeks A.P.G.
Published: March 2013

The concept of level-dependent spatial summation is applied to the 2-dimensional amplitude distribution comprising an ultrasonic brightness image. The distribution is convolved with a level-dependent kernel. The size (i.e., extent) of the kernel is inversely proportional to the local signal level. The result is a 2-dimensional distribution of Mach bands, accentuating edges and providing useful information for the reduction of speckle. In addition, a small but powerful extension of the processing scheme is presented that supports global edge enhancement and contrast enhancement. The level of improvement has been quantified in terms of an increase in the lesion signal-to-noise ratio on the order of 60 percent. Only two system-dependent parameters have to be supplied for adjustment. The algorithm is rather insensitive to the exact choice of the parameters, making it quite robust. Since only a limited number of simple operations is required for the processing of a frame, the algorithm is expected to be suitable for real time application.
Phase Aberration Correction in Two Dimensions Using a Deformable Array Transducer
Authors: Ries Loriann L. , Smith Stephen W.
Published: March 2013

Phase aberrations due to tissue inhomogeneities degrade medical ultrasound images by disrupting the ultrasound beam focus. Currently, phase correction algorithms are implemented by adjusting the electronic phase delays used to steer and focus the ultrasound beam. This means that a two-dimensional array is necessary to completely correct two-dimensional aberrations in tissue. However, two-dimensional arrays are a complex option due to their large number of elements and poor sensitivity. Instead of using a full two-dimensional array, a new technique is proposed, similar to one used in adaptive optics, which uses a deformable transducer of significantly fewer channels for two-dimensional phase correction. Phase correction in azimuth is achieved by altering the electronic phase delay of the element. However, phase correction in elevation is achieved by tilting the element in elevation with a piezoelectric actuator. Comparison of simulations of the new phase correction transducer versus the conventional phase correction technique have shown that a deformable 1 × N or 2 × N transducer can approach the image quality of a 4 × N two-dimensional array or greater. A prototype 1 times 32 array with eight low frequency piezoelectric actuators has been constructed such that every four ultrasonic transducer elements in azimuth are mounted on one independently controlled actuator. This prototype transducer was used to test the ability of a deformable array to produce real time phased array scans and to simulate on-line phase correction by tilting the elements in the elevation direction.
Speckle Analysis Using Signal to Noise Ratios Based on Fractional Order Moments
Authors: Dutt Vinayak , Greenleaf James F.
Published: March 2013

The SNR (signal-to-noise ratio) of the echo envelope image is a monotonically-increasing function of scatterer number density. Various SNRs, like amplitude SNR and intensity SNR, can be used to quantify the scatterer density. The problem of using a SNR based on higher order moments like the intensity SNR is that they require large sample sizes to obtain estimates with high confidence (the variance of the estimate becomes large for higher moments). In this paper, we consider SNRs based on fractional order moments (moments of order less than 1), and obtain mathematical analyses of their properties using the K distribution, which has been shown to be a good model for the density function of backscatter echo envelope signal. Statistics of SNRs based on fractional moment are derived and appear to be more robust and useful than the amplitude and intensity SNRs previously studied. The SNRs based on fractional order moments have greater dynamic range and the sample size requirements are smaller than those for integral order moment SNRs, like amplitude SNR or intensity SNR. Thus, SNRs based on fractional order moments could be used to better quantify the variations in scatterer density which can be used for tissue classification problems.
A Method for Estimating an Overlying Layer Correction in Quantitative Ultrasound Imaging
Authors: Lu Z.F. , Zagzebski J.A. , Madsen E.L. , Dong F.
Published: March 2013

A new method is tested to compensate for attenuation losses through the intervening layers in quantitative ultrasound imaging. The method subtracts the echo signal power spectrum acquired from a uniform region beneath the overlying layers from the signal power spectrum obtained from a reference phantom using the same instrumentation system settings. Changes in spectral components with frequency are then used to estimate the attenuation of the overlying layers. Several phantoms were used to test the method, among which was a phantom having three windows, one with no overlying layers and the other two with fat and muscle mimicking layers of different degrees of irregularity. Attenuation losses through the windows were compensated for using the technique, producing backscatter estimator images of a simulated tumor inside the phantom. After applying the method, consistent results for the backscatter estimator of the tumor, as well as the backscatter coefficient of the background material, were obtained from the various windows.
Autoregressive Spectral Estimation in Ultrasonic Scatterer Size Imaging
Authors: Chaturvedi Pawan , Insana Michael F.
Published: March 2013

An autoregressive (AR) spectral estimation method was considered for the purpose of estimating scatterer size images. The variance and bias of the resulting estimates were compared with those using classical FFT periodograms for a range of input signal-to-noise ratios and echo-signal durations corresponding to various C-scan image slice thicknesses. The AR approach was found to produce images of significantly higher quality for noisy data and when thin slices were required. Several images reconstructed with the two techniques are presented to demonstrate difference in visual quality. Task-specific guidelines for empirical selection of the AR model order are also proposed.
Phase Insensitive Homomorphic Image Processing for Speckle Reduction
Authors: Chen Yan , Broschat Shira L. , Flynn Patrick J.
Published: March 2013

Speckle appears in all conventional ultrasound images and is caused by the use of a phase-sensitive transducer. Speckle is an undesirable property as it can mask small but perhaps diagnostically significant image features. In this paper a homomorphic, hybrid nonlinear processing method, based on cancellation of scattering interference, is developed and examined. Experiments with synthetic and real ultrasound imagery show that the proposed method improves the contrast-to-noise ratio in both lesion and cyst areas and preserves edge clarity.
Image Reconstruction with Acoustic Measurement Using Distorted Born Iteration Method
Authors: Lu C. , Lin J. , Chew W. , Otto G.
Published: March 2013

The distorted Born iterative method (DBIM) is applied to solve electromagnetics and ultrasonics inverse scattering problems. First, we use the DBIM to process the data, which are the scattered fields from two-dimensional cylinders with arbitrary cross section. From this simulation, we confirmed that the first-order Born approximation can be applied to larger objects as long as the phase change of a wave passing through the object due to its presence is smaller than a limit. Then we applied DBIM to process the ultrasonic measurement data. Images for a balloon and an egg that are immersed in water have been reconstructed and compared with those from the first-order diffraction tomography (DT).
A 120-MHz Ultrasound Probe for Tissue Imaging
Authors: Yokosawa Koichi , Shinomura Ryuichi , Sano Shyuzo , Ito Yukio , Ishikawa Shizuo , Sato Yutaka
Published: March 2013

Ultrasound transducers with center frequency above 100 MHz are expected to be used for future diagnostic tissue characterization because of their high lateral resolution. We have fabricated a 120-MHz transducer that consists of a ZnO piezoelectric film on a sapphire substrate that has a concave acoustic lens. The lateral resolution was calculated as 13 μm. The insertion loss of the transducer, defined as the difference between the received voltage and the transmitted one, was −45 dB. The 6-dB bandwidth of the received signal was approximately 40 MHz. The transducer was mounted in a rod-shaped probe to ensure contact with in vivo tissue, because of the low penetration of ultrasound in the high frequency region. While the probe is rotated and moved along its axis mechanically, the transducer receives backscattered ultrasound from the surrounding tissue on a cylindrical plane that is kept a constant distance from the probe surface. The feasibility of this high-frequency tissue imaging probe has been demonstrated by obtaining preliminary images of an in vitro bovine kidney.
A Generalized Hermite Pyramid for Ultrasonic Image Analysis I. Kidney and Liver
Authors: Venkatesh Y. V.
Published: March 2013

Ultrasonic images of the kidney and of the liver are subjected to a multiscale analysis in a generalized Hermite pyramid framework. The gradient images of the multiscale decompositions of the images of healthy and sick kidneys, and of the intraoperative and conventionally imaged livers, exhibit differences, in the structures of gray level regions, which can be interpreted by a medical doctor. These are used as inputs to an unsupervised classifier to automatically classify the images into homogeneous groups, which are found, in the case of the ultrasonic images examined, to correspond to the different physical characteristics of tissues of the organs under study. The main contribution of the paper is believed to be the multiscale tissue characterization along with its display in a manner that has utility as a diagnostic aid to the clinician.
A Generalized Hermite Pyramid for Ultrasonic Image Analysis II. Gallstones
Authors: Venkatesh Y. V.
Published: March 2013

This paper deals with the problem of extracting information regarding the chemical composition of stones in the human gallbladder from in vitro and in vivo B-scan ultrasonic images. The images are subjected to the Hermite pyramid decomposition technique described in Part I (Venkatesh, Y. V., Ultrasonic Imaging, 18, 261–304, 1996). In an attempt to determine the chemical composition of the gallstones, the gradients of the decomposed images are input to an unsupervised classifier. The outputs of the classifier exhibit some interesting patterns that appear to be related to the chemical composition of the gallstones contained in these images.
Computerized Quantification Analysis of Left Ventricular Wall Motion from Echocardiograms
Authors: Chen Tainsong , Chen Tzu-Pei , Tsai Liang Miin
Published: March 2013

Two-dimensional echocardiography (2-D echo) imaging is a more attractive clinical tool than other modalities that either involve radiation exposure or are too slow to image heart motion in real-time. Computer-aided analysis of left ventricular (LV) wall motion provides quantitative parameters for diagnosis. This study presents a computerized model for quantitative analysis of left ventricular wall motion from two-dimensional echocardiography by the application of image processing algorithms, including automatic threshold estimation, contrast stretching, boundary detection and border smoothing. The wall motion measurements rely primarily on sequential changes from end-diastolic to end-systolic frames in the left ventricular contours of apical four-chamber view echocardiograms. Left ventricular wall motion was analyzed on the 30 segments of 5 patients with acute myocardial infarction. The results from the computerized model were compared to those obtained from qualitative analysis of echocardiograms by an experienced clinical cardiologist who was unaware of the results of quantitative data.
Elastographic Dynamic Range Expansion Using Variable Applied Strains
Authors: Konofagou Elisa E. , Ophir Jonathan , Kallel Faouzi , Varghese Tomy
Published: March 2013

In elastography, we want to image the entire range of stiffnesses of the elastic components found in inhomogeneous tissues. In order to achieve this, the elastographic dynamic range should equal the entire stiffness dynamic range in the target. Various sources of noise limit the dynamic range of elastography. The recently-defined strain filter concept offers an analytical and graphical way of observing these limitations. In this paper, we describe a method that achieves the expansion of the elastographic dynamic range. It involves the application of variable strains in combination with selective storage of strain data that have optimal elastographic signal-to-noise ratios. This expands the current dynamic range of elastography by orders of magnitude when compared to single compression elastography. The process is explained theoretically using the strain filter framework, and 1D as well as 2D tissue simulations are used to corroborate the theory.
Adaptive Aberration Correction of Abdominal Images Using PARCA
Authors: Krishnan S. , Rigby K.W. , O'Donnell M.
Published: March 2013

Clinical images of the abdomen may be degraded by aberrations due to propagation through the abdominal wall, resulting in loss of contrast and reduction in overall image quality. The Parallel Adaptive Receive Compensation Algorithm (PARCA) uses multiple receive beams to compensate for these aberrations. Previous studies have demonstrated that PARCA can restore image quality in tissue-equivalent phantoms scanned with controlled phase and amplitude fluctuations. In this study, PARCA is used to improve clinical images of the abdomen. PARCA processed images show both improved contrast of structures and improved overall image quality.
A Single Bit RF Domain Complex Cross-Correlation Velocity Estimator for Color Flow Mapping
Authors: Brands Peter J. , Hoeks Arnold P.G. , Ledoux Léon A.F.
Published: March 2013

This paper evaluates the performance of a one bit mean frequency estimator to estimate blood flow velocity for ultrasound color flow mapping. This one bit mean frequency estimator, referred to as BC3 estimator, is derived from the recently introduced complex cross-correlation model (C3M) employing the full dynamic data range. The C3M velocity estimator is not suitable for application in color flow mapping because of its high hardware complexity and associated computational load. The BC3 estimator estimates the mean blood flow velocity using only two complex cross-correlation coefficients. For this purpose the latter are computed by means of a complex one bit cross-correlation operation. Each sample of the RF signals is converted into an one bit representation based on the sign of the real and imaginary part of the RF samples. A full derivation and mathematical description of the BC3 estimator is presented. In addition, a thorough performance evaluation of the BC3 estimator in comparison with the full dynamic range C3M velocity estimator is carried out by means of signal simulations to document the effect of signal to noise ratio, sample frequency and bandwidth. For the specific simulation conditions considered the standard deviation of both estimators (C3M and BC3) is comparable. The bias of the BC3 estimator appears to be a function of velocity, while the full dynamic range C3M velocity estimator exhibits no bias. The simulation results are confirmed by evaluation of data from an in vivo measurement. Taking into account the low hardware complexity and computational load in combination with the achieved precision, it may be concluded that the BC3 estimator is well suited for implementation in color flow mapping.
Differential Attenuation Imaging for the Characterization of High Intensity Focused Ultrasound Lesions
Authors: Ribault M. , Chapelon J.Y. , Cathignol D. , Gelet A.
Published: March 2013

High intensity focused ultrasound (HIFU) is an effective technique for creating coagulative necrotic lesions in biological tissue, with a view to treating localized tumors. Although good results have already been obtained, notably in urology, current systems lack a real time monitoring system to check the efficacy of the treatment procedures. This study describes the development and assessment of a noninvasive system for making local measurements of attenuation variations during HIFU treatment procedures.

An apparatus (Ablatherm, Edap-Technomed, France), combining a 2.5 MHz therapeutic transducer and a 5.5 MHz twin plane imaging probe (connected to an ultrasound scanner), was used to produce lesions. The rf signals needed to calculate the attenuation were recorded as outputs from the ultrasound scanner, before and after the high intensity firing sequences, which were performed on ten pieces of porcine liver. Each firing sequence involved producing a lesion volume comprising 42 individual lesions. A number of recordings were also made without producing lesions, in order to test the reproducibility of the measurements. The attenuation function was evaluated locally using the centroid and the multinarrowband methods. Initially, changes in the integrated attenuation αbar; (mean attenuation in the 4–7 MHz range) and the attenuation slope β were examined for the lesion volume. β values did not vary significantly within this range, whereas α values varied significantly (in the region of 86% of the initial level) in comparison to measurements performed without forming lesions. The differential attenuation Δα (representing local variations in α) was subsequently used to generate images revealing the lesion areas. There was a strong similarity between these ‘Δα images’ and the lesion volumes defined by the operator. ‘Δα images’ offer several advantages over existing attenuation imaging techniques. Any problems related to the heterogeneity of the medium are eliminated, since only the change in attenuation is taken into account. Furthermore, there is no need to compensate for diffraction when estimating Δα, as the rf signals are captured in exactly the same positions before and after treatment.

This technique can be used during in vivo treatment procedures. It can be implemented in real time, since the computational algorithms (based primarily on FFT calculations) are very fast. The technique should provide clinical practitioners with valuable qualitative and quantitative information for use in HIFU ultrasound surgery.
Effects of Tissue Anisotropy on the Spectral Characteristics of Ultrasonic Backscatter Measured with a Clinical Imaging System
Authors: Holland Mark R. , Lewis Stephen H. , Hall Christopher S. , Finch-Johnston Ann E. , Handley Scott M. , Wallace Kirk D. , D'sa Alwyn P. , Prater David M. , Perez Julio E. , Miller James G.
Published: March 2013

In this paper, we report the effects of inherent tissue anisotropy on the spectral properties of backscattered ultrasound when measured with a commercially-available imaging system. We insonified five specimens of bovine tendon immersed in a water tank and rotated in 10° increments while being imaged with a Hewlett-Packard Sonos 1500 system. The backscattered RF signals corresponding to each angle of insonification were digitized and the spectral characteristics of the backscattered ultrasound were determined. The mean anisotropy, defined as the average difference between values at perpendicular and parallel insonification, for band-limited estimates of backscattered power, centroid frequency, upper-band to lower-band power ratio, and upper-band to total-band power ratio were found to be 24.6 ± 1.1 dB, 142 ± 27 kHz, 32 ± 13%, and 22 ± 5%, respectively (mean ± SE). The magnitude of each of these backscatter spectral parameters was larger at perpendicular insonification compared with the corresponding values at parallel insonification, consistent with previous measurements of the inherent anisotropy of ultrasonic attenuation and backscatter in tissue.
Modeling of the Correlation of Analytic Ultrasound Radiofrequency Signals for Angle-Independent Motion Detection
Authors: Ledoux Léon A.F. , Willigers Jean M. , Brands Peter J. , Hoeks Arnold P.G.
Published: March 2013

Conventional pulsed ultrasound systems are able to assess motion of scatterers in the direction of the ultrasound beam, i.e., axial motion, by determining the lag at which the maximum correlation occurs between consecutively-received radiofrequency (rf) signals. The accuracy, resolution, and processing time of this technique is improved by making use of a model for the correlation of rf signals. All previously-described correlation models only include axial motion, but it is common knowledge that lateral motion, i.e., motion in the plane perpendicular to the beam axis, reduces the correlation of rf signals in time. In the present paper, a model for the correlation of analytic rf signals in depth and time is derived and verified. It also includes, aside of some signal and transducer parameters, both axial and lateral motion. The influence of lateral motion on the correlation of (analytic) rf signals is strongly related to local phase and amplitude characteristics of the ultrasound beam. It is shown how the correlation model, making use of an ultrasound transducer with a circular beam shape, can be applied to estimate, independent of angle, the magnitude of the actual motion. Furthermore, it is shown that the model can be applied to estimate the local signal-to-noise ratio and rf bandwidth.
Determination of Ultrasonic Parameters Based on Attenuation and Dispersion Measurements
Authors: He Ping
Published: March 2013

In the measurement of acoustic attenuation that obeys a power-law α = β f, the traditional through-transmission method uses only the amplitude information of the recorded pulses to determine the two parameters, β and n. In this paper, we propose a new method that utilizes both the amplitude and phase information of the pulses to determine the two parameters. According to this method, the two parameters are estimated by simultaneously performing a least squares fit to the attenuation data that are derived from the amplitude spectra of the pulses, and to the dispersion data that are derived from the phase spectra of the pulses. By fully utilizing the information contained in the recorded pulses and imposing additional constraints on the two parameters, the estimation uncertainty can be reduced. Experimental results from two specimens, one having a linear attenuation and one having a nonlinear attenuation, demonstrate that the new method produces a moderate variance reduction in the case of linear attenuation, and a significant variance reduction in the case of nonlinear attenuation.
A Method for Experimental Characterization of the Noise Performance of Elastographic Systems
Authors: Varghese Tomy , Ophir Jonathan
Published: March 2013

Characterization of the noise performance of the elastographic system is necessary to evaluate the accuracy and precision of the estimated strain. The elastographic system includes the ultrasonic scanner, the computer controlled compression device and the strain estimation algorithm. In this paper, we present a method of characterizing the elastographic system experimentally using a uniformly elastic homogenous tissue-mimicking phantom. The strain response of the elastographic system is evaluated by characterizing the accuracy and precision of the strain estimates for a large range of input strains. The experimental results obtained follow the theoretical predictions obtained using the Strain Filter (SF) concept for the cross-correlation based strain estimator. In this paper, we illustrate the application of the Experimental Strain Response (ESR) to characterize strain estimation at the focus of the transducer and the axis of symmetry of the phantom.
Validation of Theoretical Diffraction Correction Functions for Strongly Focused High Frequency Ultrasonic Transducers
Authors: Machado J.C. , Foster F.S.
Published: March 2013

Adequate correction for diffraction effects is critical to the measurement of device-independent acoustical parameters. This correction is especially important in situations where strongly focused beams are used in the measurements. Diffraction correction function profiles, for two spherically-focused high frequency transducers (50 MHz, focal distance 5.7 mm, f/number of 1.7 and 29 MHz, focal distance 10.0 mm, f/2), were determined using experimental and theoretical approaches. Experimental measurements are based on established approaches using the power backscattered by an ultrasonic tissue-equivalent calibrating phantom. These results are compared to a recently-published theoretical model. Excellent agreement between the experiment and theory is achieved. No statistically-significant difference in mean backscattered power is found between the experimental and theoretical approaches. The use of a simple normalization procedure (termed ‘diffraction correction’) involving the ratio of the mean power backscattered from the sample to the power for reflection from a plane reflector at the same depth, is shown to introduce significant errors.
Quantitative Analysis of Ultrasonic B-Mode Images
Authors: Coolen J. , Engelbrecht M.R. , Thijssen J.M.
Published: March 2013

Various sources of variability, such as speckle noise, depth dependence and inhomogeneous intervening tissue, are involved in B-mode images, even when using the same ultrasonic equipment with fixed settings. The behavior of these sources of variability was investigated by texture analysis of images obtained from simulations and from a tissue-mimicking phantom, a normal adult liver and a pediatric renal (Wilms') tumor. First-order statistics (MEAN and SNR) and second-order statistics from the co-occurrence matrix (ENT and COR) were calculated. In a phantom, the SNR and ENT show a clear depth dependence. In biological tissue, the variability is mainly caused by the speckle noise and inhomogeneous intervening tissue. In addition, almost the entire range of the COR feature is present in images of liver and tumor. Furthermore, all the features calculated in windows of 1 cm2 exhibit an overlap among the different media. With the second-order features, it is possible to discriminate 85% reliable (average) between the normal, adult, liver and the pediatric renal tumor above a window size of 9 cm2. The SNR can not discriminate between these tissues. The maximum resolution of 9 cm2 reveals a serious limitation of parametric imaging. Finally, the features reproduce well in the case of follow-up of an abdominal tumor during chemotherapy.
Angle-Independent Motion Measurement by Correlation of Ultrasound Signals Assessed with a Single Circular-Shaped Transducer
Authors: Ledoux Léon A.F. , Willigers Jean M. , Brands Peter J. , Hoeks Arnold P.G.
Published: March 2013

In medicine, pulsed ultrasound is a widespread noninvasive technique that measures motion in the direction of the ultrasound beam, i.e., axial motion. The magnitude of the actual motion can be determined only if the angle between the ultrasound beam and the direction of motion (transducer-to-motion angle) is known. For blood flow measurements, current pulsed ultrasound systems assume this angle to be equal to the angle between the ultrasound beam and the longitudinal direction of the vessel, as can be estimated from a two-dimensional brightness-mode (B-mode) image that is obtained prior to the blood flow measurement. For tissue motion measurements, current pulsed ultrasound systems are mostly unable to determine the transducer-to-motion angle. Recently, a model has been derived for the correlation of (analytic) radiofrequency (rf) signals, assessed with a circularshaped ultrasound transducer along the same line of observation. In the present paper, this model is used to derive estimators, requiring only the calculation of a few correlation coefficients, for the motion components (axial, lateral and actual) and for some of the signal parameters (center frequency, bandwidth and signal-to-noise ratio) of the assessed rf signals. The transducer-to-motion angle can be derived from the estimated motion components. For the evaluation of the estimators, rf signals were acquired with a motion-controlled experimental arrangement. The results of the evaluation study show that the transducer-to-motion angle can be estimated with a mean standard deviation of less than 2°.
Strategies for justifying counter-arguments in Q&A discussion
Authors: Savolainen Reijo
Published: March 2013

This study examines the strategies employed in justifying counter-arguments against answers provided in Q&A (question and answer) discussion. The study also explores how information sources are used in support of such arguments. The findings draw on the analysis of 100 discourse episodes focusing on global warming – a controversial topic eliciting competing answers from the participants. The empirical data were downloaded from Yahoo! Answers. Four strategies were identified. Of them, questioning the validity of answers and questioning the background assumptions of answers were used most frequently. While justifying counter-arguments, the participants also drew on emotional appeals and questioned the contributor’s motives. To support the counter-arguments, the participants mainly drew on internet-based sources of information. The controversial nature of the discussion topic was reflected in the debate about the most authoritative information sources: persuasive material advocating a particular viewpoint to global warming vs objective research reports.
Choosing Wisely: Our List
Authors: Robertson Peter J. , Brereton Jean M. , Roberson David W. , Shah Rahul K. , Nielsen David R.
Published: March 2013

In February 2013, the American Academy of Otolaryngology–Head and Neck Surgery Foundation (AAO‐HNSF) released its list of 5 recommendations of diagnostic and therapeutic interventions that physicians and patients should question, as part of the American Board of Internal Medicine (ABIM) Foundation's Choosing Wisely campaign. This commentary outlines the impetus for the AAO‐HNSF to join the campaign, our list of 5 recommendations, how they were developed, and our future involvement with the campaign. The AAO‐HNSF's 5 recommendations are (1) don't order a computed tomography (CT) scan of the head/brain for sudden hearing loss, (2) don't prescribe oral antibiotics for uncomplicated acute tympanostomy tube otorrhea, (3) don't prescribe oral antibiotics for uncomplicated acute external otitis, (4) don't routinely obtain radiographic imaging for patients who meet diagnostic criteria for uncomplicated acute rhinosinusitis, and (5) don't obtain CT or magnetic resonance imaging in patients with a primary complaint of hoarseness prior to examining the larynx.