bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of SMURF Estimation of Shear Modulus in Hydrogels
Authors: McAleavey Stephen , Collins Erin , Kelly Johanna , Elegbe Etana , Menon Manoj
Published: March 2013

A validation study of the Spatially Modulated Ultrasound Radiation Force (SMURF) method for shear modulus estimation is presented. SMURF estimates of uniform gelatin and Zerdine™ phantoms covering a modulus range of 2 to 18 kPa are compared with results obtained by unconfined mechanical compression and sonoelastography. The results show agreement within the measurement uncertainties over the range indicated for all three methods. Repeatability and variation on the order of 5% of the phantom modulus are found for observations made at a single point within the phantom. Averaging of modulus estimates from several adjacent scan lines further decreases the variation. By using multiple radiation force peaks to induce a shear wave of known wavelength and measure the frequency of the wave, SMURF obtains modulus estimates from tracking data acquired along a single A-line. This is significant, as speckle can bias the measured phase of the shear wave. SMURF is shown to be insensitive to a constant phase error in the shear wave measurement. This results in greatly reduced correlated noise in the modulus estimates, in contrast with methods which track at multiple locations and do not cancel phase errors.
ARFI Ultrasound for In Vivo Hemostasis Assessment Postcardiac Catheterization, Part II: Pilot Clinical Results
Authors: Behler Russell H. , Scola Mallory R. , Nichols Timothy C. , Caughey Melissa C. , Fisher Melrose W. , Zhu Hongtu , Gallippi Caterina M.
Published: March 2013

In this second of a two part series, we present pilot clinical data demonstrating Acoustic Radiation Force Impulse (ARFI) ultrasound for monitoring the onset of subcutaneous hemostasis at femoral artery puncture sites (arteriotomies), in vivo. We conducted a randomized, reader-blinded investigation of 20 patient volunteers who underwent diagnostic percutaneous coronary catheterization. After sheath removal (6 French), patients were randomized to treatment with either standard of care manual compression alone or, to expedite hemostasis, manual compression augmented with a p-GlcNAc fiber-based hemostatic dressing (Marine Polymer Technologies, Danvers MA). Concurrent with manual compression, serial ARFI imaging began at the time of sheath removal and continued every minute for 15 min. Serial data sets were processed with custom software to (1) estimate the time of hemostasis onset, and (2) render hybrid ARFI/B-Mode images to highlight displacements considered to correspond to extravasted blood. Images were read by an observer blinded to the treatment groups. Average estimated times to hemostasis in patient volunteers treated with manual compression alone ( n = 10) and manual compression augmented by hemostatic dressing ( n = 9) were, respectively, 13.00 ± 1.56 and 9.44 ± 3.09 min, which are statistically significantly different ( p = 0.0065, Wilcoxon two-sample test). Example images are shown for three selected patient volunteers. These pilot data suggest that ARFI ultrasound is relevant to monitoring subcutaneous bleeding from femoral arteriotomies clinically and that time to hemostasis was significantly reduced by use of the hemostatic dressing.
Shear Modulus Imaging with Spatially-Modulated Ultrasound Radiation Force
Authors: McAleavey Stephen , Menon Manoj , Elegbe Etana
Published: March 2013

The application of Spatially-Modulated Ultrasound Radiation Force (SMURF) to shear modulus imaging is demonstrated in tissue-mimicking phantoms and porcine liver. Scanning and data acquisition was performed with a Siemens Antares ultrasound scanner and VF7-3 linear array operating at 4.21 MHz. Modulus estimates in uniform phantoms of Zerdine with shear moduli of 5.1 and 12.4 kPa exhibited standard deviations within 6% of the mean value. Zerdine spheres 1 cm in diameter (nominally 2.7, 4.7 and 15 kPa) in a 8 kPa (nominal) background are clearly resolved. Cross sectional images of a soft conical inclusion in a gelatin-based phantom indicate a spatial resolution of approximately 2.5 mm. Images of the shear modulus of an ex-vivo sample of porcine liver tissue show an average value of 3 kPa. A stiff lesion induced with 0.5 mL of 10% glutaraldehyde is clearly visible as a region of shear modulus in excess of 10 kPa. A modulus gradient associated with the diffusion of the glutaraldehyde is visible. Two pulse sequences were examined, differing only in the timing of the beams used to generate the shear waves. Details of the beam sequences and subsequent signal processing are presented.
In Vitro Evaluation of Ultrasound-Assisted Thrombolysis Using a Targeted Ultrasound Contrast Agent
Authors: Chen Szu-Chia , Ruan Jia-Ling , Cheng Po-Wen , Chuang Yueh-Hsun , Li Pai-Chi
Published: March 2013

A thrombus-targeted ultrasound contrast agent bound with tirofiban — a glycoprotein (GP) IIb/IIIa antagonist that can specifically bind to activated platelets in the thrombus — was designed to enhance both the image contrast and thrombolysis effect. In this study, we used 76 canine thrombi for investigation. The targeting ability to thrombi was confirmed by microphotography and high-frequency ultrasound (40 MHz) imaging. The effect of the targeted microbubbles on thrombolysis enhancement was investigated using an in vitro flow system: targeted and nontargeted microbubbles flowed through the clot for 30 seconds with a washing step; the microbubbles remained on the clot that were then cavitated by ultrasound (frequency = 1 MHz, MI = 1.2). The extent of thrombolysis was evaluated by weight reduction and histology analysis. The targeted microbubbles reduced the weight of thrombi by a factor of 1.7 times that of the nontargeted microbubbles. (clot weight reduction: 23.1 ± 5.3% versus 13.6 ± 4.9%, p < 0.01 between targeted and nontargeted group), and the signal enhancement was 3.34 ± 0.30 dB (mean ± SD, p < 0.01 compared to control). We conclude that targeted microbubbles are applicable not only for molecular imaging of thrombi but also for improving the effectiveness of ultrasound-assisted thrombolysis.
Small Lesion Detection with Resolution Enhancement Compression
Authors: Linden Paul , Sanchez Jose R. , Oelze Michael L.
Published: March 2013

A novel coded-excitation method, resolution-enhancement compression (REC), increases the axial resolution and the echo signal-to-noise ratio (eSNR) for an ultrasonic imaging system. The REC technique was examined for its ability to improve lesion detectability. The REC technique was used to double the −3-dB fractional pulse-echo bandwidth of an ultrasonic source in both simulations and experiments. The increase in usable bandwidth increased lesion detectability compared to conventional pulsing (CP) techniques and coded excitation using a linear chirp (LC). Lesion detectibility was quantified through lesion signal-to-noise ratio (lSNR), which is a metric that quantifies the ability of an isolated observer to detect a focal lesion against a background. In simulations, a higher lSNR value was observed using the REC technique for lesions ranging in size from 1 mm to 8 mm in diameter. In addition, the eSNR was increased by almost 15 dB. To validate simulation results, a hydrogel-cone phantom was constructed to provide lesions with +6-dB contrast of different sizes. A transducer was scanned perpendicular to the major axis of the cone at different levels to provide lesions of 3, 5 and 8 mm in diameter. The lSNR was estimated for lesions of different sizes and using the three excitation techniques, i.e., CP, LC and REC. In experiments, the lSNR was observed to be higher using the REC technique than the other pulsing techniques. The lSNR scores for REC were higher by 15%, 45% and 40% for the 3, 5 and 8 mm over the other two excitation techniques. The eSNR was increased by 5.7 dB. Therefore, accrding to the lSNR metric, the improvement in spatial resolution from the REC technique resulted in improved detectability of small lesions.
Minimization of Displacement Estimation Bias Due to High Amplitude-Reflections Using Envelope-Weighted Normalization
Authors: Menon Mnoj , Langdon Jonathan , McAleavey Stephen
Published: March 2013

In elastography, displacement estimation is often performed using cross-correlation-based techniques, assuming fully-developed, homogeneous speckle. In the presence of a local, large variation in echo amplitude, such as a reflection from a vessel wall, this assumption does not hold true, resulting in a biased displacement estimate. Normalizing the echo by its envelope before displacement estimation reduces this effect at the cost of larger jitter errors. An algorithm is proposed to reduce amplitude-dependent bias in displacement estimates while avoiding a large increase in the jitter error magnitude. The algorithm involves ‘Envelope-Weighted Normalization’ (EWN) of echo data before displacement estimation. A parametric analysis was conducted to find the optimum parameters with which this technique could be implemented. The EWN technique was found to significantly reduce the rms error of the displacement estimates, showing the greatest improvements when utilizing longer window lengths and higher ultrasonic frequencies.
Novel Spline-Based Approach for Robust Strain Estimation in Elastography
Authors: Alam S. Kaisar
Published: March 2013

Robust strain estimation is important in elastography. However, a high signal-to-noise ratio ( SNR) and contrast-to-noise ratio ( CNR) are sometimes attained by sacrificing resolution. We propose a least-squares-based smoothing-spline strain estimator that can produce elastograms with high SNR and CNR without significant loss of resolution. The proposed method improves strain-estimation quality by deemphasing displacements with lower correlation in computing strains. Results from finite-element simulation and phantom-experiment data demonstrate that the described strain estimator provides good SNR and CNR without degrading resolution.
Elastography Using Harmonic Ultrasonic Imaging: A Feasibility Study
Authors: Desai Raghavendra Reddy , Krouskop Thomas A. , Righetti Raffaella
Published: March 2013

Tissue Harmonic Imaging (THI) is a relatively new modality that has had a significant impact in the ultrasound field. In the recent past, imaging the mechanical properties of tissues using elastography has also gained great interest. In this paper, we investigate the feasibility of combining these two state-of-the-art ultrasound-imaging modalities. The performance of elastograms obtained using harmonic ultrasonic signals is studied with simulations and compared to the performance of conventional elastograms using standard statistical methods. Experiments are used as a proof of the technical feasibility of generating tissue-harmonic elastograms using experimental harmonic signals.

The results of our simulation study indicate that all image quality factors considered in this study (elastographic signal-to-noise ratio, elastographic contrast-to-noise ratio and spatial resolution) may be improved when using harmonic ultrasonic signals, provided that the ultrasound system is characterized by high bandwidth, high sampling frequency and large lateral sampling. Preliminary experimental results suggest that it is technically feasible to generate experimental elastograms using harmonic signals, provided that the sonographic signal-to-noise ratio of the pre- and postcompression harmonic frames is sufficiently high to guarantee reliable values of correlation.
Simulation of Autonomous Robotic Multiple-Core Biopsy by 3D Ultrasound Guidance
Authors: Liang Kaicheng , Rogers Albert J. , Light Edward D. , von Allmen Daniel , Smith Stephen W.
Published: March 2013

An autonomous multiple-core biopsy system guided by real-time 3D ultrasound and operated by a robotic arm with 6+1 degrees of freedom has been developed. Using a specimen of turkey breast as a tissue phantom, our system was able to first autonomously locate the phantom in the image volume and then perform needle sticks in each of eight sectors in the phantom in a single session, with no human intervention required. Based on the fraction of eight sectors successfully sampled in an experiment of five trials, a success rate of 93% was recorded. This system could have relevance in clinical procedures that involve multiple needle-core sampling such as prostate or breast biopsy.
Quantitative Ultrasound Assessment of Cervical Microstructure
Authors: Feltovich Helen , Nam Kibo , Hall Timothy J.
Published: March 2013

The objective of this preliminary study was to determine whether quantitative ultrasound (QUS) can provide insight into, and characterization of, uterine cervical microstructure. Throughout pregnancy, cervical collagen reorganizes (from aligned and anisotropic to disorganized and isotropic) as the cervix changes in preparation for delivery. Premature changes in collagen are associated with premature birth in mammals. Because QUS is able to detect structural anisotropy/isotropy, we hypothesized that it may provide a means of noninvasively assessing cervical microstructure. Thorough study of cervical microstructure has been limited by lack of technology to detect small changes in collagen organization, which has in turn limited our ability to detect abnormal and/or premature changes in collagen that may lead to preterm birth. In order to determine whether QUS may be useful for detection of cervical microstructure, radiofrequency (rf) echo data were acquired from the cervices of human hysterectomy specimens ( n = 10). The angle between the acoustic beam and tissue was used to assess anisotropic acoustic propagation by control of transmit/receive angles from −20° to +20°. The power spectrum of the echo signals from within a region of interest was computed in order to investigate the microstructure of the tissue. An identical analysis was performed on a homogeneous phantom with spherical scatterers for system calibration. Power spectra of backscattered rf from the cervix were 6 dB higher for normal (0°) than steered (±20°) beams. The spectral power for steered beams decreased monotonically (0.4 dB at +5° to 3.6 dB at +20°). The excess difference (compared to similar analysis for the phantom) in normally-incident (0°) versus steered beams is consistent with scattering from an aligned component of the cervical microstructure. Therefore, QUS appears to reliably identify an aligned component of cervical microstructure; because collagen is ubiquitously and abundantly present in the cervix, this is the most likely candidate. Detection of changes in cervical collagen and microstructure may provide information about normal versus abnormal cervical change and thus guide development of earlier, more specific interventions for preterm birth.
Interactive vs. Automatic Ultrasound Image Segmentation Methods for Staging Hepatic Lipidosis
Authors: Weijers Gert , Starke Alexander , Haudum Alois , Thijssen Johan M. , Rehage Jürgen , De Korte Chris L.
Published: March 2013

The aim of this study was to test the hypothesis that automatic segmentation of vessels in ultrasound (US) images can produce similar or better results in grading fatty livers than interactive segmentation. A study was performed in postpartum dairy cows ( N= 151), as an animal model of human fatty liver disease, to test this hypothesis. Five transcutaneous and five intraoperative US liver images were acquired in each animal and a liver biopsy was taken. In liver tissue samples, triacylglycerol (TAG) was measured by biochemical analysis and hepatic diseases other than hepatic lipidosis were excluded by histopathologic examination. Ultrasonic tissue characterization (UTC) parameters — Mean echo level, standard deviation (SD) of echo level, signal-to-noise ratio (SNR), residual attenuation coefficient (ResAtt) and axial and lateral speckle size—were derived using a computer-aided US (CAUS) protocol and software package. First, the liver tissue was interactively segmented by two observers. With increasing fat content, fewer hepatic vessels were visible in the ultrasound images and, therefore, a smaller proportion of the liver needed to be excluded from these images. Automatic-segmentation algorithms were implemented and it was investigated whether better results could be achieved than with the subjective and time-consuming interactive-segmentation procedure. The automatic-segmentation algorithms were based on both fixed and adaptive thresholding techniques in combination with a ‘speckle’-shaped moving-window exclusion technique. All data were analyzed with and without postprocessing as contained in CAUS and with different automated-segmentation techniques. This enabled us to study the effect of the applied postprocessing steps on single and multiple linear regressions of the various UTC parameters with TAG. Improved correlations for all US parameters were found by using automatic-segmentation techniques. Stepwise multiple linear-regression formulas where derived and used to predict TAG level in the liver. Receiver-operating-characteristics (ROC) analysis was applied to assess the performance and area under the curve (AUC) of predicting TAG and to compare the sensitivity and specificity of the methods. Best speckle-size estimates and overall performance ( R2 = 0.71, AUC = 0.94) were achieved by using an SNR-based adaptive automatic-segmentation method (used TAG threshold: 50 mg/g liver wet weight). Automatic segmentation is thus feasible and profitable.
Simulation Study of Amplitude-Modulated (AM) Harmonic Motion Imaging (HMI) for Stiffness Contrast Quantification with Experimental Validation
Authors: Maleke Caroline , Luo Jianwen , Gamarnik Viktor , Lu Xin L. , Konofagou Elisa E.
Published: March 2013

The objective of this study is to show that Harmonic Motion Imaging (HMI) can be used as a reliable tumor-mapping technique based on the tumor's distinct stiffness at the early onset of disease. HMI is a radiation-force-based imaging method that generates a localized vibration deep inside the tissue to estimate the relative tissue stiffness based on the resulting displacement amplitude. In this paper, a finite-element model (FEM) study is presented, followed by an experimental validation in tissue-mimicking polyacrylamide gels and excised human breast tumors ex vivo. This study compares the resulting tissue motion in simulations and experiments at four different gel stiffnesses and three distinct spherical inclusion diameters. The elastic moduli of the gels were separately measured using mechanical testing. Identical transducer parameters were used in both the FEM and experimental studies, i.e., a 4.5-MHz single-element focused ultrasound (FUS) and a 7.5-MHz diagnostic (pulse-echo) transducer. In the simulation, an acoustic pressure field was used as the input stimulus to generate a localized vibration inside the target. Radiofrequency (rf) signals were then simulated using a 2D convolution model. A one-dimensional cross-correlation technique was performed on the simulated and experimental rf signals to estimate the axial displacement resulting from the harmonic radiation force. In order to measure the reliability of the displacement profiles in estimating the tissue stiffness distribution, the contrast-transfer efficiency (CTE) was calculated. For tumor mapping ex vivo, a harmonic radiation force was applied using a 2D raster-scan technique. The 2D HMI images of the breast tumor ex vivo could detect a malignant tumor (20 × 10 mm2) surrounded by glandular and fat tissues. The FEM and experimental results from both gels and breast tumors ex vivo demonstrated that HMI was capable of detecting and mapping the tumor or stiff inclusion with various diameters or stiffnesses. HMI may thus constitute a promising technique in tumor detection (>3 mm in diameter) and mapping based on its distinct stiffness.
Crawling Waves from Radiation Force Excitation
Authors: Hah Zaegyoo , Hazard Christopher , Cho Young Thung , Rubens Deborah , Parker Kevin
Published: March 2013

Crawling waves are generated by an interference of two oscillating waves traveling in opposite directions, with a progressive movement resulting from a frequency difference or a phase difference between the sources. While the idea has been applied to numerous applications, all the previous reports used mechanical sources to vibrate the medium. It is shown, through experiments and simulation, that crawling waves can be generated from focused beams that produce radiation force excitation within the tissue. Some examples are also shown.
Characterizing Stiffness of Human Prostates Using Acoustic Radiation Force
Authors: Zhai Liang , Madden John , Foo Wen-Chi , Mouraviev Vladimir , Polascik Thomas J. , Palmeri Mark L. , Nightingale Kathryn R.
Published: March 2013

Acoustic Radiation Force Impulse (ARFI) imaging has been previously reported to portray normal anatomic structures and pathologies in ex vivo human prostates with good contrast and resolution. These findings were based on comparison with histological slides and McNeal's zonal anatomy. In ARFI images, the central zone (CZ) appears darker (smaller displacement) than other anatomic zones and prostate cancer (PCa) is darker than normal tissue in the peripheral zone (PZ). Since displacement amplitudes in ARFI images are determined by both the underlying tissue stiffness and the amplitude of acoustic radiation force that varies with acoustic attenuation, one question that arises is how the relative displacements in prostate ARFI images are related to the underlying prostatic tissue stiffness. In linear, isotropic elastic materials and in tissues that are relatively uniform in acoustic attenuation (e.g., liver), relative displacement in ARFI images has been shown to be correlated with underlying tissue stiffness. However, the prostate is known to be heterogeneous. Variations in acoustic attenuation of prostatic structures could confound the interpretation of ARFI images due to the associated variations in the applied acoustic radiation force. Therefore, in this study, co-registered three-dimensional (3D) ARFI datasets and quantitative shear wave elasticity imaging (SWEI) datasets were acquired in freshly-excised human prostates to investigate the relationship between displacement amplitudes in ARFI prostate images and the matched reconstructed shear moduli. The lateral time-to-peak (LTTP) algorithm was applied to the SWEI data to compute the shear-wave speed and reconstruct the shear moduli. Five types of prostatic tissue (PZ, CZ, transition zone (TZ) and benign prostatic hyperplasia (BPH), PCa and atrophy) were identified, whose shearmoduli were quantified to be 4.1±0.8 kPa, 9.9±0.9 kPa, 4.8±0.6 kPa, 10.0±1.0 kPa and 8.0 kPa, respectively. Linear regression was per formed to compare ARFI displacement amplitudes and the inverse of the corresponding reconstructed shear moduli at multiple depths. The results indicate an inverse relation between ARFI displacement amplitude and reconstructed shear modulus at all depths. These findings support the conclusion that ARFI prostate images portray underlying tissue stiffness variations.
Improving the Reproducibility of the Cyclic Variation of Myocardial Backscatter
Authors: Lloyd Christopher W. , Holland Mark R. , Miller James G.
Published: March 2013

The goal of myocardial tissue characterization is to augment information provided by two- and three-dimensional echocardiographic imaging, Doppler blood flow and speckle- or Doppler-derived tissue motion. Tissue characterization based on the systematic variation of backscattered ultrasound during the cardiac cycle (‘cyclic variation’) appears to be effective in characterizing both focal and diffuse myocardial pathologies. Unfortunately, comparison of results from different laboratories is difficult because of a lack of consistency among the several reported methods of analyzing the cyclic variation data. The goals of the present work are to present an improved method of analysis and to demonstrate that apparent disagreements are attributable primarily to the distinct approaches employed by different investigators. The improved automated method for determining the magnitude of cyclic variation utilizes binomial smoothing and an average deviation method and was validated using data acquired from 23 patients. This method illustrates a systematic means for resolving differences between laboratories. This resolution facilitates future comparisons between the cyclic variation of myocardial backscatter and measurements derived, for example, from strain-related approaches.
Ultrasonic Multi-Feature Analysis Procedure for Computer-Aided Diagnosis of Solid Breast Lesions
Authors: Alam S. Kaisar , Feleppa Ernest J. , Rondeau Mark , Kalisz Andrew , Garra Brian S.
Published: March 2013

We have developed quantitative descriptors to provide an objective means of noninvasive identification of cancerous breast lesions. These descriptors include quantitative acoustic features assessed using spectrum analysis of ultrasonic radiofrequency (rf) echo signals and morphometric properties related to lesion shape. Acoustic features include measures of echogenicity, heterogeneity and shadowing, computed by generating spectral-parameter images of the lesion and surrounding tissue. Spectral-parameter values are derived from rf echo signals at each pixel using a sliding-window Fourier analysis. We derive quantitative acoustic features from spectral-parameter maps of the lesion and adjacent areas. We quantify morphometric features by geometric and fractal analysis of traced lesion boundaries. Initial results on biopsy-proven cases show that although a single parameter cannot reliably discriminate cancerous from noncancerous breast lesions, multi-feature analysis provides excellent discrimination for this data set. We have processed data for 130 biopsy-proven patients, acquired during routine ultrasonic examinations at three clinical sites and produced an area under the receiver-operating-characteristics (ROC) curve of 0.947±0.045. Among the quantitative descriptors, lesion-margin definition, spiculation and border irregularity are the most useful; some additional morphometric features (such as border irregularity) also are particularly effective in lesion classification. Our findings are consistent with many of the BI-RADS (Breast Imaging Reporting and Data System) breast-lesion-classification criteria in use today.
Performance of New GPU-Based Scan-Conversion Algorithm Implemented Using OpenGL
Authors: Steelman William A. , Richard William D.
Published: March 2013

A new GPU-based scan-conversion algorithm implemented using OpenGL is described. The compute performance of this new algorithm running on a modern GPU is compared to the performance of three common scan-conversion algorithms (nearest-neighbor, linear interpolation and bilinear interpolation) implemented in software using a modern CPU. The quality of the images produced by the algorithm, as measured by signal-to-noise power, is also compared to the quality of the images produced using these three common scan-conversion algorithms.
Combined Ultrasonic Thermal Ablation with Interleaved ARFI Image Monitoring Using a Single Diagnostic Curvilinear Array: A Feasibility Study
Authors: Bing Kristin Frinkley , Rouze Ned C. , Palmeri Mark L. , Rotemberg Veronica M. , Nightingale Kathryn R.
Published: March 2013

The goal of this work is to demonstrate the feasibility of using a diagnostic ultrasound system (Siemens Antares™ and CH6–2 curvilinear array) to ablate ex vivo liver with a custom M-mode sequence and monitor the resulting tissue stiffening with 2-D Acoustic Radiation Force Impulse (ARFI) imaging. Images were taken before and after ablation, as well as in 5- s intervals during the ablation sequence in order to monitor the ablation lesion formation temporally. Ablation lesions were generated at depths up to 1.5 cm from the surface of the liver and were not visible in B-mode. ARFI images showed liver stiffening with heating that corresponded to discolored regions in gross pathology. As expected, the contrast of ablation lesions in ARFI images is observed to increase with ablation lesion size. This study demonstrated the ability of a diagnostic system using custom beam sequences to localize an ablation site, heat the site to the point of irreversible damage and monitor the formation of the ablation lesion with ARFI imaging.
Ultrasonic Attenuation and Backscatter Coefficient Estimates of Rodent-Tumor-Mimicking Structures: Comparison of Results among Clinical Scanners
Authors: Nam Kibo , Rosado-Mendez Ivan M. , Wirtzfeld Lauren A. , Pawlicki Alexander D. , Kumar Viksit , Madsen Ernest L. , Ghoshal Goutam , Lavarello Roberto J. , Oelze Michael L. , Bigelow Timothy A. , Zagzebski James A. , O'Brien William D. , Hall Timothy J.
Published: March 2013

In vivo estimations of the frequency-dependent acoustic attenuation (α) and backscatter (η) coefficients using radiofrequency (rf) echoes acquired with clinical ultrasound systems must be independent of the data acquisition setup and the estimation procedures. In a recent in vivo assessment of these parameters in rodent mammary tumors, overall agreement was observed among α and η estimates using data from four clinical imaging systems. In some cases, particularly in highly-attenuating heterogeneous tumors, multisystem variability was observed. This paper compares α and η estimates of a well-characterized rodent-tumor-mimicking homogeneous phantom scanned using seven transducers with the same four clinical imaging systems: a Siemens Acuson S2000, an Ultrasonix RP, a Zonare Z.one and a VisualSonics Vevo2100. α and η estimates of lesion-mimicking spheres in the phantom were independently assessed by three research groups, who analyzed their system's rf echo signals. Imaging-system-based estimates of α and η of both lesion-mimicking spheres were comparable to through-transmission laboratory estimates and to predictions using Faran's theory, respectively. A few notable variations in results among the clinical systems were observed but the average and maximum percent difference between α estimates and laboratory-assessed values was 11% and 29%, respectively. Excluding a single outlier dataset, the average and maximum average difference between η estimates for the clinical systems and values predicted from scattering theory was 16% and 33%, respectively. These results were an improvement over previous interlaboratory comparisons of attenuation and backscatter estimates. Although the standardization of our estimation methodologies can be further improved, this study validates our results from previous rodent breast-tumor model studies.
Ultrasound Attenuation Measurements Using a Reference Phantom with Sound Speed Mismatch
Authors: Nam Kibo , Rosado-Mendez Ivan M. , Rubert Nicholas C. , Madsen Ernest L. , Zagzebski James A. , Hall Timothy J.
Published: March 2013

Ultrasonic attenuation may be measured accurately with clinical systems and array transducers by using reference phantom methods (RPM) to account for diffraction and other system dependencies on echo signals. Assumptions with the RPM are that the speeds of sound in the sample ( csam) and in the reference medium ( cref) are the same and that they match the speed assumed in the system beamformer ( cbf). This work assesses the accuracy of attenuation measurements by the RPM when these assumptions are not met. Attenuation was measured for two homogeneous phantoms, one with a speed of sound of 1500 m/s and the other with a sound speed of 1580 m/s. Both have an attenuation coefficient approximately equal to that of the reference, in which the speed of sound is 1540 m/s. Echo signals from the samples and the reference were acquired from a Siemens S2000 scanner with a 9L4 linear array transducer. Separate acquisitions were obtained with cbf at its default value of 1540 m/s and when it was set at values matching the speeds of sound of the phantoms. Simulations were also performed using conditions matching those of the experiment. RPM-measured attenuation coefficients exhibited spatially-dependent biases when csam differed from cbf and cref Mean errors of 19% were seen for simulated data, with the maximum errors in attenuation measurements occurring for regions of interest near the transmit focus. Biases were minimized (mean error with simulated data was 5.6%) using cbf that matched csam and assuring that power spectra used for attenuation computations in the sample are from precisely the same depth as those from the reference. Setting the transmit focus well beyond the depth range used to compute attenuation values minimized the bias.
Processing of Subharmonic Signals from Ultrasound Contrast Agents to Determine Ambient Pressures
Authors: Dave Jaydev K. , Halldorsdottir Valgerdur G. , Eisenbrey John R. , Forsberg Flemming
Published: March 2013

Subharmonic-aided pressure estimation (SHAPE) is a technique that utilizes the subharmonic emissions, occurring at half the insonation frequency, from ultrasound contrast agents to estimate ambient pressures. The purpose of this work was to compare the performance of different processing techniques for the raw radiofrequency (rf) data acquired for SHAPE. A closed loop flow system was implemented circulating reconstituted Sonazoid (GE Healthcare, Oslo, Norway; 0.2 ml for 750 ml diluent) and the beam-formed unprocessed rf data were obtained from a 4 mm diameter lumen of a Doppler flow phantom (ATS Laboratories, Inc., Bridgeport, CT) using a SonixRP scanner (Ultrasonix, Richmond, BC, Canada). The transmit frequency and incident acoustic pressures were set to 2.5 MHz and 0.22 MPa, respectively, in order to elicit Sonazoid subharmonic emissions that are ambient-pressure sensitive. The time-varying ambient pressures within the flow phantom were recorded by a Millar pressure catheter. Four techniques for extracting the subharmonic amplitude from the rf data were tested along with two noise filtering techniques to process this data. Five filter orders were tested for the noise removing filters. The performance was evaluated based on the least root-mean-square errors reported after linear least-square regression analyses of the subharmonic data and the pressure catheter data and compared using a repeated ANOVA. When the subharmonic amplitudes were extracted as the mean value within a 0.2 MHz bandwidth about 1.25 MHz and when the resulting temporally-varying subharmonic signal was median filtered with an order of 500, the filtered subharmonic signal significantly predicted the ambient pressures ( r2 = 0.90; p < 0.001) with the least error. The resulting root mean square and mean absolute errors were 8.16 ± 0.26 mmHg and 6.70 ± 0.17 mmHg, respectively. Thus, median processing the subharmonic data extracted as the mean value within a 0.2 MHz bandwidth about the theoretical subharmonic frequency turned out to be the best technique to process acoustic data for SHAPE. The implementation of this technique on ultrasound scanners may permit real-time SHAPE applications.
Robust Strain-Estimation Algorithm Using Combined Radiofrequency and Envelope Cross-Correlation with Diffusion Filtering
Authors: Hussain Mohammad Arafat , Alam S. Kaisar , Lee Soo Yeol , Hasan Md. Kamrul
Published: March 2013

In ultrasound elastography, the strain in compressed tissue due to external deformation is estimated and is smaller in harder than softer tissue. With increased stress, the nonaxial motions of tissue elements increase and result in noisier strain images. At high strain, the envelope of the rf signal exhibits robustness to signal decorrelation. However, the precision of strain estimates using envelope signals is much worse compared to that using the rf signals. In this paper, we propose a novel approach for robust strain estimation by combining weighted rf cross-correlation and envelope cross-correlation functions. An applied strain-dependent piecewise-linear-weight is used for this purpose. In addition, we introduce nonlinear diffusion filtering to further enhance the resulting strain image. The results of our algorithm are demonstrated for up to 10% applied strain using a finite-element modelling (FEM) simulation phantom. It reveals that the elastographic signal-to-noise ratio ( SNRe) and the elastographic contrast-to-noise ratio ( CNRe) of the strain images can be improved more significantly than with other algorithms used in this paper. In addition, comparative results in terms of the mean structural similarity (MSSIM) using in vivo breast data show that the strain image quality can be improved noticeably by the proposed method than with the techniques employed in this work.
A Method for Direct Localized Sound Speed Estimates Using Registered Virtual Detectors
Authors: Byram Brett C. , Trahey Gregg E. , Jensen Jørgen A.
Published: March 2013

Accurate sound speed estimates are desirable in a number of fields. In an effort to increase the spatial resolution of sound speed estimates, a new method is proposed for direct measurement of sound speed between arbitrary spatial locations. The method uses the sound speed estimator developed by Anderson and Trahey. Their least squares fit of the received waveform’s curvature provides an estimate of the wave’s point of origin. The point of origin and the delay profile calculated from the fit are used to arrive at a spatially registered virtual detector. Between a pair of registered virtual detectors, a spherical wave is propagated. By beamforming the data, the time-of-flight between the two virtual sources can be calculated. From this information, the local sound speed can be estimated. Validation of the estimator is made using phantom and simulation data. The set of test phantoms consisted of both homogeneous and inhomogeneous media. Several different inhomogeneous phantom configurations were used for the physical validation. The simulation validation focused on the limits of target depth and signal-to-noise ratio on virtual detector registration. The simulations also compare the impact of two- and three-layer inhomogeneous media. The phantom results varied based on signal-to-noise ratio and geometry. The results for all cases were generally less than 1% mean error and standard deviation. The simulation results varied somewhat with depth and F/#, but primarily, they varied with signal-to-noise ratio and geometry. With two-layer geometries, the algorithm has a worst-case spatial registration bias of 0.02%. With three-layer geometries, the axial registration error gets worse with a bias magnitude up to 2.1% but is otherwise relatively stable over depth. The stability over depth of the bias in a given medium still allows for accurate sound speed estimates with a mean relative error less than 0.2%.
In Vivo Temperature Dependence of Ultrasound Speed in Tissue and its Application to Noninvasive Temperature Monitoring
Authors: Nasoni R. L. , Bowen T. , Connor W. G. , Sholes R. R.
Published: March 2013

Measurements of the speed of ultrasound as a function of temperature in the 35 °C to 45 °C range were made on mammalian (canine) tissue both in vitro and in vivo at 5 MHz using a pulsed transmission technique. Cored samples coinciding with the ultrasonically irradiated tissue were obtained and assayed for water and total lipid content. Results indicate about 2 percent agreement between in vivo and in vitro data, and that, on the basis of kidney data, lipid content and temperature coefficient of ultrasound speed are more highly correlated (0.76 correlation coefficient) than are lipid content and speed of sound (0.17 correlation coefficient).
An Acoustic Gray Scale for Scanning Acoustic Microscopy and Diagnostic Ultrasound
Authors: Weglein R. D.
Published: March 2013

The principle of a true acoustic gray scale standard is presented and experimentally applied to the Scanning Acoustic Microscope (SAM). The implementation is based on the impedance matching property of a quarter wave impedance transformer through which precise changes in reflection coefficient may be produced in a single material. The performance of the first implementation designed for 375 MHz operation is described and the implications of its use are discussed in detail. The application of the principle to diagnostic ultrasound is also treated.
Design of Slotted Transducer Arrays with Matched Backings
Authors: Kino Gordon S. , DeSilets Charles S.
Published: March 2013

A design procedure is described for acoustic transducer arrays suitable for focused acoustic imaging systems. The criteria governing the choice of the width of the individual elements of the array and for broadband matching are discussed. Experimental results on 2.5 MHz arrays are given and are in good agreement with theory.
Improved Ultrasonic Sensitivity Using Pseudo-Random Binary-Code Phase-Modulated Signals
Authors: Chapelon J. Y. , Cathignol D. , Fourcade C.
Published: March 2013

Random signal systems are used in radars, but very seldom in medical and materials ultrasonic applications. Yet, compared with conventional techniques which use the same peak power, pseudo-random signal correlation techniques can easily improve the signal-to-noise ratio by a thousand or more times without sacrificing spatial resolution. To overcome the limitations imposed by the high ratio of peak power to average power, we developed a technique by which the echo energy is integrated with respect to time. As in radar systems, we used a sinusoidal signal which was phase-modulated by the pseudo-random binary code. This approach simplified our apparatus compared to those techniques using noise signals.
Measurements of Young's Modulus of Elasticity of the Canine Aorta with Ultrasound
Authors: Hughes D.J. , Babbs C.F. , Geddes L.A. , Bourland J.D.
Published: March 2013

We have developed an ultrasonic technique for determining the dynamic Young's modulus of elasticity (E) of the canine aorta in vivo. Young's modulus was measured in the descending thoracic aorta (DTA) and the abdominal aorta (AA) of 12 dogs over a range of mean blood pressures from 40 – 200 mm Hg. The vessels were excised and dynamic moduli were determined in vitro post-mortem from pressure-volume curves. The data so obtained were compared to the in vivo values. In vivo and in vitro moduli increased exponentially with mean distending pressure (P). The equation of best fit for these data was of the form E = R0 exp(aP). E0 and a depend on the site of measurement (AA or DTA) and upon the particular animal. In vivo and in vitro moduli were not significantly different in the AA (AA: in vivo E0 = 667 ± 382 mm Hg, a = 0.017 ± 0.004 mm Hg-1 in vitro E0 = 888 ± 367, a = 0.016 ± 0.002). However, in vivo moduli exceeded in vitro moduli in the DTA. (DTA: in vivo E0 = 687 ± 241, a = 0.016 ± 0.004 in vitro E0 = 349 ± 64, a = 0.018 ± 0.003). The increased stiffness of the DTA compared to the AA in vivo may be due to the in situ tethering of the aorta to the spine by the parietal pleura.
A Limitation on Ultrasonic Transmission Tomography
Authors: McKinnon G. C. , Bates R. H. T.
Published: March 2013

Ultrasonic propagation can often be usefully described in terms of rays. As these rays are in general curved, transmission tomography is more complicated for ultrasound than for x-rays. It is shown here that in most media there are “forbidden” regions which are not intersected by any “minimum propagation time” rays. It is concluded that it is seldom feasible to obtain better images than those reconstructed on the assumption that the ultrasonic rays travel along straight lines.
Characterization of Multielement Acoustic Arrays by Acousto-Optic Diffraction Methods
Authors: Hanafy Amin
Published: March 2013

The characterization of multielement acoustic arrays for diagnostic ultrasound has always been a thorny problem. This paper describes optical techniques for determining the essential parameters of wideband multielement arrays. These parameters which are measured are the spatial frequency response of both the single element and full array, the acoustic cross-coupling between elements, the focusing properties of the array, and the acoustic field intensity.
Ultrasound Characterization of Fetal Growth
Authors: Birnholz Jason C.
Published: March 2013

Fetal weight is estimated in vivo from ultrasound image measurements. Serial study of weight growth defines a trajectory which has physiologic and clinical significance. Low order polynomial fits to these data provide a functional description of the growth process which may be used for recognition and characterization of distinct growth patterns.
Estimating Ultrasound Propagation Velocity in Tissues from Unwrapped Phase Spectra
Authors: Gupta V. N. , Bhagat P. K. , Fried A. M.
Published: March 2013

A digital computer-based technique for estimating the velocity of sound in tissue is proposed. The technique utilizes the unwrapped phase spectra of full band reference and attenuated ultrasonic pulses normally used in attenuation measurements. In addition, it does not require explicit measurement of pulse-transit-times. The accuracy of the technique was tested on several computer simulated models, on specimens of known velocities (aluminum and plexiglass), and on formalin-fixed rabbit kidneys. The results indicate that the technique has an accuracy comparable to the pulse-transit-time method.
Matched Gaussian Apodization of Pulsed Acoustic Phased Arrays
Authors: Duerinckx Andre J.
Published: March 2013

Gaussian apodization weighting functions matched to the time delay distribution for focusing of phased arrays are introduced. The matching concept is based upon the theory of eigenmodes of freely propagating acoustic beams with a finite cross-section. The effect of this matched gaussian apodization on the beam cross-section is analysed for several acoustic phased array configurations generating acoustic wavefronts in a weakly attenuating and homogeneous medium. A strength of focusing parameter is introduced. The relation between apodization parameters and the strength of focusing is analyzed and illustrated. For strong focusing the parameters of the gaussian matched apodization become independent of the focal range. A simulator was developed which allows the study of acoustic pressure waves in the near-field and far-field generated by a linear phased array excited with short pulses. The simulator provides 2-D and 3-D representations of acoustic wave fronts generated by a pulsed phased array, illustrating the effects of apodization for pulsed acoustic beams in the time-space domain.
Tomographic Imaging of Attenuation with Simulation Correction for Refraction
Authors: Farrell Edward J.
Published: March 2013

Beam refraction in soft tissue and phase cancellation at the receiver can cause large errors and prevent tomographic reconstruction of attenuation. The method developed in this study incorporates simulation of ultrasound propagation into tomographic imaging to correct these effects. The method is based on input scan data of time-of-flight and received signal amplitude. The speed of propagation is estimated from the time-of-flight scan data. Based on this estimate, the simulation generates scan data of signal amplitude. This scan data represents the loss from refraction and phase cancellation with zero attenuation, and is used to correct the input amplitude scans. We evaluate the accuracy of the method, and investigate the trade-off between various scanning and filtering parameters. The evaluation is based on scan data generated by a comprehensive simulation including refraction, attenuation, phase cancellation, finite beam width, several target shapes and sizes with sound parameters consistent with biologic values, and discrete translational and rotational transducer positions. In several cases with large refraction distortions, attenuation images are accurately reconstructed which are not feasible using standard tomographic methods.
Discriminant Analysis of Ultrasonic Texture Data in Diffuse Alcoholic Liver Disease: 1. Fatty Liver and Cirrhosis
Authors: Lerski R. A. , Smith M. J. , Morley P. , Barnett E. , Mills P. R. , Watkinson G. , MacSween R. N. M.
Published: March 2013

In previous work by our group, it has been shown that the use of texture analysis on digitally recorded radio-frequency ultrasonic signals can provide useful diagnostic information in diffuse liver disease. A rigorous multivariate analysis and the addition of new texture parameters has confirmed the efficacy of the technique. Discriminant functions have been produced to provide excellent accuracies in the detection of diffuse liver disease.