bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acoustic Radiation Force Impulse Imaging of In Vivo Vastus Medialis Muscle Under Varying Isometric Load
Authors: Nightingale Kathryn , Nightingale Roger , Stutz Deborah , Trahey Gregg 
Published: March 2013

Acoustic Radiation Force Impulse (ARFI) imaging is a method for characterizing local variations in tissue mechanical properties. In this method, a single ultrasonic transducer array is used to both apply temporally short localized radiation forces within tissue and to track the resulting displacements through time. Images of tissue displacement immediately after force cessation, maximum tissue displacement, the time it takes for the tissue to reach its maximum displacement, and the recovery time constant of the tissue are generated from the ARFI data sets. The information in each of these images demonstrates good agreement with matched B-mode images. The study presented here was designed to evaluate the relationship between changes in these ARFI parameters with known tissue mechanical properties in vivo. Utilizing a modified Siemens Elegra scanner with a 75L40 transducer array, ARFI images of vastus medialis muscle were generated in three of the authors under four levels of activation (0, 5.7, 14.5, and 23.3 N-m). Four ARFI datasets were acquired for each loading condition. The observed trends were that displacement magnitude, the time it took for the tissue to reach its maximum displacement, and recovery time constant decreased with increasing load (i.e., increasing muscle stiffness). Significant differences were observed between load levels and subjects for all parameters (p<0.01). The results indicate that ARFI imaging may be capable of quantifying tissue stiffness in real-time measurements, although further investigation is required.
Experimental Studies of the Thermal Effects Associated with Radiation Force Imaging of Soft Tissue
Authors: Palmeri Mark L. , Frinkley Kristin D. , Nightingale Kathryn R. 
Published: March 2013

Many groups are studying acoustic radiation force-based imaging modalities to determine the mechanical properties of tissue. Acoustic Radiation Force Impulse (ARFI) imaging is one of these modalities that uses standard diagnostic ultrasound scanners to generate localized, impulsive, acoustic radiation force in tissue. This radiation force generates tissue displacements that are tracked using conventional correlation-based ultrasound methods. The dynamic response of tissue to this impulsive radiation force provides information about the mechanical properties of the tissue. The generation of micron-scale displacements using acoustic radiation force in tissue requires the use of high-intensity acoustic beams, and the soft tissue heating associated with these high-intensity beams must be evaluated to ensure safety when performing ARFI imaging in vivo. Experimental studies using thermocouples have validated Finite Element Method (FEM) models that simulate the heating of soft tissue during ARFI imaging. Spatial maps of heating measured with the thermocouples are in good agreement with FEM model predictions, with cooling time constants measured and modeled to be on the order of several seconds. Transducer heating during ARFI imaging has been measured to be less than 1 °C for current clinical implementations. These validated FEM models can now be used to simulate soft tissue heating associated with different transducers, beam spacing, focal configurations and thermal material properties. These experiments confirm that ARFI imaging of soft tissue is safe, although thermal response must be monitored when developing ARFI beam sequences for specific tissue types and organ systems.
A Tutorial on the Use of ROC Analysis for Computer-Aided Diagnostic Systems
Authors: Scheipers Ulrich , Perrey Christian , Siebers Stefan , Hansen Christian , Ermert Helmut 
Published: March 2013

The application of the receiver operating characteristic (ROC) curve for computer-aided diagnostic systems is reviewed. A statistical framework is presented and different methods of evaluating the classification performance of computer-aided diagnostic systems, and, in particular, systems for ultrasonic tissue characterization, are derived. Most classifiers that are used today are dependent on a separation threshold, which can be chosen freely in many cases. The separation threshold separates the range of output values of the classification system into different target groups, thus conducting the actual classification process. In the first part of this paper, threshold specific performance measures, e.g., sensitivity and specificity; are presented. In the second part, a threshold-independent performance measure, the area under the ROC curve, is reviewed. Only the use of separation threshold-independent performance measures provides classification results that are overall representative for computer-aided diagnostic systems. The following text was motivated by the lack of a complete and definite discussion of the underlying subject in available textbooks, references and publications. Most manuscripts published so far address the theme of performance evaluation using ROC analysis in a manner too general to be practical for everyday use in the development of computer-aided diagnostic systems. Nowadays, the user of computer-aided diagnostic systems typically handles huge amounts of numerical data, not always distributed normally. Many assumptions made in more or less theoretical works on ROC analysis are no longer valid for real-life data. The paper aims at closing the gap between theoretical works and real-life data. The review provides the interested scientist with information needed to conduct ROC analysis and to integrate algorithms performing ROC analysis into classification systems while understanding the basic principles of classification.
Field Computation for Two-Dimensional Array Transducers with Limited Diffraction Array Beams
Authors: Lu Jian-Yu , Cheng Jiqi 
Published: March 2013

A method is developed for calculating fields produced with a two-dimensional (2D) array transducer. This method decomposes an arbitrary 2D aperture weighting function into a set of limited diffraction array beams. Using the analytical expressions of limited diffraction beams, arbitrary continuous wave (cw) or pulse wave (pw) fields of 2D arrays can be obtained with a simple superposition of these beams. In addition, this method can be simplified and applied to a 1D array transducer of a finite or infinite elevation height. For beams produced with axially symmetric aperture weighting functions, this method can be reduced to the Fourier-Bessel method studied previously where an annular array transducer can be used. The advantage of the method is that it is accurate and computationally efficient, especially in regions that are not far from the surface of the transducer (near field), where it is important for medical imaging. Both computer simulations and a synthetic array experiment are carried out to verify the method. Results (Bessel beam, focused Gaussian beam, X wave and asymmetric array beams) show that the method is accurate as compared to that using the Rayleigh-Sommerfeld diffraction formula and agrees well with the experiment.
Real-Time Three-Dimensional Transesophageal Echocardiography for Guiding Interventional Electrophysiology: Feasibility Study
Authors: Pua Eric C. , Idriss Salim F. , Wolf Patrick D. , Smith S.W. 
Published: March 2013

At present, there are limited methods of acquiring three-dimensional visualization of cardiac structure and function in real-time during interventional electrophysiology procedures. Images acquired for integration of computerized tomography and magnetic resonance imaging with electroanatomic mapping systems are static and are obtained earlier in time. The purpose of this study was to test the feasibility of real-time three-dimensional transesophageal echocardiography for the guidance of interventional electrophysiological studies. A matrix array transducer with 504 channels operating at 5 MHz in a 1 cm diameter steerable esophageal probe was used in conjunction with a scanner capable of real-time 3D scanning of pyramidal volumes from 65° to 120° at rates up to 30 volumes per second. This device has a spatial resolution of approximately 3 mm at 5 cm depth. The authors acquired real-time three-dimensional images of anatomic landmarks of value for electrophysiological procedures in five closed chest canines. Real-time, three-dimensional ultrasound imaging was also used for visualization and guidance of interventional catheter devices within the canine heart. Real-time three-dimensional images of the atria, pulmonary veins, and coronary sinus were acquired. Real-time 3-D color flow Doppler was employed to confirm patency. Multiple image planes of image volumes and rendered views were used to track catheter position and orientation. Images of left veno-atrial junctions have been confirmed by dissection. This study has demonstrated the feasiblity of using real-time three-dimensional transesophageal echocardiography for guiding interventional electrophysiology. The technology has the potential to fill a niche as an adjunct modality for cost-effective real-time interventional guidance and assessment, providing catheter and pacing lead visualization simultaneously with functional volumetric cardiac imaging.
3D Strain Imaging Using a Rectilinear 2D Array
Authors: Awad Samer I. , Yen Jesse T. 
Published: March 2013

Under mechanical compression, tissue movements are inherently three-dimensional. 2-D strain imaging can suffer from decorrelation noise caused by out-of-plane tissue movement in elevation. With 3-D strain imaging, all tissue movements can be estimated and compensated, hence minimizing out-of-plane decorrelation noise. Promising 3-D strain imaging results have been shown using 1 -D arrays with mechanical translation in elevation. However, the relatively large slice thickness and mechanical translation can degrade image quality. Using 2-D arrays, an improved elevational resolution can be achieved with electronic focusing. Furthermore, scanning with 2-D arrays is also done electronically, which eliminates the need for mechanical translation. In this paper, we demonstrate the feasibility of 3-D strain imaging using a 4 cm × 4 cm ultrasonic sparse rectilinear 2-D array operating at 5MHz. The signal processing combinations of 2-D or 3-D beamforming followed by 2-D or 3-D strain imaging are studied and compared to each other to evaluate the performance of our 3-D strain imaging system. 3-D beamforming followed by 3-D strain imaging showed best performance in all experiments.
New Fabrication Techniques for Ring-Array Transducers for Real-Time 3D Intravascular Ultrasound
Authors: Light Edward D. , Lieu Victor , Smith Stephen W. 
Published: March 2013

We have previously described miniature 2D array transducers integrated into a Cook Medical, Inc. vena cava filter deployment device. While functional, the fabrication technique was very labor intensive and did not lend itself well to efficient fabrication of large numbers of devices. We developed two new fabrication methods that we believe can be used to efficiently manufacture these types of devices in greater than prototype numbers. One transducer consisted of 55 elements operating near 5 MHz. The interelement spacing is 0.20 mm. It was constructed on a flat piece of copper-clad polyimide and then wrapped around an 11 French catheter of a Cook Medical, Inc. inferior vena cava (IVC) filter deployment device. We used a braided wiring technology from Tyco Electronics Corp. to connect the elements to our real-time 3D ultrasound scanner. Typical measured transducer element bandwidth was 20% centered at 4.7 MHz and the 50 Ω round trip insertion loss was −82 dB. The mean of the nearest neighbor cross talk was −37.0 dB. The second method consisted of a 46-cm long single layer flex circuit from MicroConnex that terminates in an interconnect that plugs directly into our system cable. This transducer had 70 elements at 0.157 mm interelement spacing operating at 4.8 MHz. Typical measured transducer element bandwidth was 29% and the 50 Ω round trip insertion loss was −83 dB. The mean of the nearest neighbor cross talk was −33.0 dB.
Ultrasonic B-Scan Imaging: Theory of Image Formation and a Technique for Restoration
Authors: Fatemi Mostafa , Kak A. C. 
Published: March 2013

This paper presents a theory for ultrasonic B-scan image formation. Our theory is based on the assumption that imaging is done using broadband signals and that all the information in the returned echos is utilized for image formation, as opposed to only the “video” detected envelopes. We also assume that the image is formed from the backscattered returns caused by inhomogeneities within soft tissue structures. In other words, we do not take into account the contributions from the specularly reflecting surfaces that represent large impedance discontinuities. (Surfaces that only represent small impedance changes and are “visible” to the transducer are accounted for by our theory.) Our main reason for this omission is the fact that although the contributions of the surfaces with large impedance changes are important to the delineation of features in some 3-scan images, it is the presentation of the backscattered echos from small inhomogeneities within the tissues that is more severely distorted by the radiation and the electromechanical properties of the transducer. Also, it is currently believed that the backscattered echoes from the small inhomogeneities within the tissues carry important pathological information. Our theory is also limited to the case of Linearly scanned transducers with unfocused apertures. A major result of our theory is an analytical expression for the point spread function of the image degradation. As expected, this function is position variant. To simplify the computations required for image restoration, we have presented approximations that reduce the point spread function to the position-invariant form. We have shown experimentally that the resulting restoration filters retain their effectiveness over several centimeters of the object thickness. This has led us to conclude that the B-scan images of thick objects may be restored by using piecewise position-invariant techniques.
The Power-Spectrum Centroid Detector: System Considerations, Implementation, and Performance
Authors: Gerzberg Levy , Meindl James D. 
Published: March 2013

Operation of the √f centroid detector with various doppler systems is discussed, and its design, implementation, and performance are described. It is determined that the detector can be employed in directional detection schemes to measure spectral moments and centroids with correct polarity and with no degradation in accuracy. Narrow- and wideband deterministic signal detection of both stationary and FM information is investigated, and it is found that the centroid detector can also serve as an FM demodulator with high AM rejection. A versatile √f detector was realized in discrete form and evaluated with deterministic and random signals, and its measured variance agreed closely with the theoretical values. The validity and application of the noise-reduction method was verified on deterministic and random doppler signals. Applications of the detector and the noise-reduction method to blood-flow and velocity measurements are demonstrated.
The Conical Scanner: A Two Transducer Ultrasound Scatter Imaging Technique
Authors: Foster F. S. , Patterson M. S. , Arditi M. , Hunt J. W. 
Published: March 2013

A new two transducer ultrasound scatter imaging system has been developed. In operation, a large conical transducer generates an ultrasound beam that converges to a sharp line focus in the tissue being imaged. The second transducer is aimed along the axis of the cone and detects scattered ultrasound as a function of time, converting this information into a high resolution image. Excellent focusing properties are maintained over a large depth of field with no increase in the complexity of standard B-scanner electronics. As well, no increase in time is required to generate the image. The performance of a 45° conical scanner is examined theoretically and experimentally. The FWHM of the lateral point response of the scanner remains 0.25 mm over a 5 cm depth of field. Images of phantoms and in vitro breast tissue demonstrate a great improvement in image quality compared with conventional pulse-echo imaging.
An Annular Array System for High Resolution Breast Echography
Authors: Arditi M. , Taylor W.B. , Foster F.S. , Hunt J.W. 
Published: March 2013

Ultrasound B-mode imaging with electronically focused annular arrays has been associated in the past with fairly complex and expensive electronic circuits. When image quality rather than scanning speed is the prime concern, the concept of switched zone focusing offers an attractive alternative to true dynamic focusing previously reported. Strongly focused apertures used in both transmit and receive modes allow improved lateral resolution, lower side lobe levels, higher sensitivity, as well as simplified electronics. This approach was investigated for the particular case of breast imaging. We outline some general design considerations for water path imaging with annular arrays, and describe the system adopted in the development of a high resolution breast scanner using a sealed, water filled head. Experimental results are compared to theoretical predictions, and grey scale images are presented to illustrate the performance of the instrument.
Imaging the Nonlinear Ultrasonic Parameter of a Medium
Authors: Ichida Nobuyuki , Sato Takuso , Linzer Melvin 
Published: March 2013

A technique for imaging the nonlinear ultrasonic parameter B/A has been developed. The nonlinear parameter describes the dependence of ultrasonic velocity on pressure and may well provide a new and powerful tool for characterizing both biological and nonbiological media. Our approach is based on observing the interaction of two ultrasonic waves with different frequencies and power levels. A low frequency pump wave, with power level suitable for medical diagnosis (1 mW/cm2), is used to sinusoidally modulate the sound pressure over the region of interest. A much lower intensity high-frequency probe beam is propagated perpendicularly to the pump beam. The phase of the probe wave is modified in proportion to the integral of the product of the nonlinear parameter B/A and the pressure of the pump wave, which varies sinusoidally along the probe beam. This phase change provides a Fourier component of the distribution of the nonlinear parameter B/A for the spatial frequency corresponding to the inverse of the pump wavelength. By changing the frequency of the pump waves, the spatial frequency is changed and a set of spatial Fourier coefficients of the distribution of the nonlinear parameter B/A is obtained. An inverse operation then gives the one-dimensional image along the probe beam. If the probe beam is scanned mechanically, the entire cross-sectional image is obtained. Several images of the nonlinear parameter of biological objects were generated with our system. To our knowledge, these represent the first images of the nonlinear parameter to be reported in the literature. The nonlinear parameter of water was also measured and agreed well with values obtained by other techniques.
Nonlinear Parameter Tomography System Using Counterpropagating Probe and Pump Waves
Authors: Sato Takuso , Fukusima Akira , Ichida Nobuyuki , Ishikawa Hiroyuki , Miwa Hirohide , Igarashi Yutaka , Shimura Takaki , Murakami Keiichi 
Published: March 2013

In this paper, a novel tomographic system for imaging the nonlinear parameter (B/A) of biological objects is described. This parameter is closely related to the detailed properties of tissue, and may well provide a new powerful tool for ultrasonic tissue characterization. In our new system, an impulsive, relatively high power (10 mW/cm2), low frequency pump wave is applied from the opposite direction of a cw low intensity probe wave of high frequency (5 MHz) so that the phase of the probe wave is modulated sequentially by the product of the nonlinear parameter (B/A) along the beam (x axis) and the pressure of the impulsive pump wave. This modulated probe wave is detected and demodulated to derive the distribution of (B/A) along the x axis. Many responses are averaged to increase the S/N ratio. Inverse or other filtering operations are applied to widen the frequency bandwidth of the pump wave. The entire system is realized in hardware. The counterbeam orientation makes the imaging system compact, with easy access to many parts of the human body. Its resolution is two times that of the perpendicular system proposed previously by us and the attenuation of the pump wave can also be compensated for easily. A practical system aimed at breast and liver diagnosis is described. The principle of the method and the system construction are described. B/A images of several objects are given.
Ultrasonic Reflex Transmission Imaging
Authors: Green Philip S. , Arditi Marcel 
Published: March 2013

Reflex Transmission Imaging (RTI) is a new imaging method by which orthographic transmission images can be made using augmented B-mode equipment. Conventional transmission imaging requires acoustic coupling to large areas on both sides of the body, whereas RTI can be performed from one side with a single, small transducer probe. In this mode, transmission images in a plane normal to the beam are made by integrating the reverberations from beyond the focal zone of the transducer. These reverberations provide, in essence, a source of incoherent insonification from behind the focal plane. Preliminary in-vitro images have been made using a computer-interfaced rectilinear scanner with a 1-inch diameter f/2.8 transducer. The images have good resolution and signal-to-noise ratio, and a short depth-of-field. Backscatterer inhomogeneity is well smoothed. Transmission images provide information that is complementary to B-scans. RTI will allow both to be made with the same instrument and presented on the same display. A time-gated reflection C-scan could be generated simultaneously. Other RTI modes, including an attenuation B-mode, also are discussed.
Elastic and Acoustic Properties of Vessel Mimicking Material for Elasticity Imaging
Authors: de Korte C.L. , Céspedes E.I. , van der Steen A.F.W. , Norder B. , te Nijenhuis K. 
Published: March 2013

The mechanical and acoustic properties of agar-gelatin gels, used to construct vessel mimicking phantoms for ultrasonic elasticity studies, were investigated. Gels with varying compression moduli were made using a gelatin solution (8% by weight) with a variable amount of agar(1%-3% by weight). Carborundum particles were added as scattering material. The compression modulus was determined using a dynamic mechanical analyzer. The dependence of the compression modulus and the acoustic parameters on the agar concentration, as well as on the age and the temperature of the samples, was investigated. The results show that the compression modulus is strongly influenced by these factors, while the effect on the acoustic parameters is less. Compression moduli spanning a useful range for vascular phantom construction with realistic acoustic parameters can be achieved by varying the amount of agar. Phantoms constructed from these gels are well suited to serve as a model for plaque containing vessels.