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American Institute of Ultrasound in Medicine Proceedings J Ultrasound Med 32(suppl):S1–S134, 2013times larger than the usual half-wavelength element separation. The sparsedistribution of transducer elements and severe aberration caused by propagationthrough the breast model reduced correlation of waveforms inneighboring transducers that are typically used to estimate arrival time differences.Instead of cross-correlations, waveform 0 crossings in the neighborhoodof the waveform arrival events were used to estimate arrival timedifferences at neighboring transducers. A least mean square estimate ofarrival times was derived from the set of arrival time differences. Waveformsimilarity factors that equal 1 for identical waveforms were calculatedand used to optimize parameters of the estimation method andevaluate the performance of the method.Results—A waveform similarity of 0.10 before compensationwas increased to 0.94 after compensation using estimated arrival times.The 170-nanosecond SD of the arrival time distribution over the whole40-facet array before compensation was decreased to 20 nanoseconds aftercompensation. For a single facet, the 154-nanosecond average SD of thearrival time distribution before compensation decreased to 15 nanosecondsafter compensation.Conclusions—The developed method for arrival time estimationin a sparsely sampled hemispheric array for the described combinationof source and transducer produces accurate estimates of arrival timesfor use in aberration correction methods.1539831 The USAGES Study (Ultrasonographic Study of AlternativeGel Experimental Substances): A Trial of AlternativeSubstances for Use in Clinical Sonographic ImagingDavut Savaser,* Siobhan Gray, Anthony Medak, Virag Shah,Derrick Allen, Eddie Castillo, Mary Beth JohnsonEmergency Medicine, University of California, San Diego,California USAObjectives—We sought to investigate image quality and the diagnosticutility of sonographic images obtained using household productsas alternative conducting media. Tested alternatives included hand sanitizer(HS), hand lotion (HL), liquid detergent (LD), baby shampoo (BS),hairstyling gel (HG), and olive oil (OOi) and were compared to standardultrasound gel (USG).Methods—We conducted a prospective reviewer-blindedcrossover study of healthy volunteers (>18 years) obtaining 7 differentsonographic images on each patient, including the right upper quadrant,subxiphoid, left upper quadrant, bladder, aorta, right lung, and right internaljugular vein views. Six alternative gel substances were tested in additionto standard USG. Images were obtained by a credentialed emergencysonographer and were reviewed and rated by 2 additional credentialedemergency sonographers and a credentialed radiologist. Image quality wasrated on a visual analog scale (VAS) ranging from 0 to 10, and the diagnosticutility of each was assessed and compared to reviewer VAS thresholds.Data were analyzed by calculating image quality VAS means andusing repeated measures analysis of variance to evaluate VAS mean differencesfor each substance.Results—A total of 189 images were obtained. Final VAS meanscores were: HS, 9.2; HL, 8.8; LD, 8.8; BS, 8.3; HG, 8.9; OOi, 8.9; andUSG, 9.6. Compared to control (USG), HS was the only substance to notexhibit a statistically significant mean VAS difference: HS, 0.118 (P =.114); HL, 0.711 (P = .000); LD, 0.696 (P = .000); BS, 0.951 (P = .000);HG, 0.565 (P = .000); and OOi, 0.600 (P = .000). All VAS means for eachsubstance scored above reviewer thresholds for diagnostic utility.Conclusions—Sonographic image quality and the diagnosticutility of HS are similar to those of standard USG. HL, LD, BS, HG, andOOi may still be used as alternatives for clinically useful diagnostic imagingbut are comparatively inferior to images obtained using HS andstandard USG as conducting media.1540013 User-friendly System for Assessing Imaging Performancein the ClinicErnest Madsen,* Chihwa Song, Gary Frank MedicalPhysics, University of Wisconsin, Madison, Wisconsin USAObjectives—One indicator of the effectiveness of a scanner/transducer configuration to delineate the boundary of an abnormal massis the level of detectability it affords for small low-echo cyst-like targets.(A scanner/transducer configuration includes the make and model of thescanner and transducer, foci, depth of field, time-gain compensation, sectorangle, etc). Phantoms with spatially random distributions of 2-, 3.2-, or4-mm-diameter low-echo spheres and scanning windows allowing usewith any shape-emitting surface were reported at the 2012 AIUM meeting.Software allows quantification of sphere detectability as a functionof depth. One objective is to complete refinements in data acquisitionand reduction so that the phantoms and software are easily employed byclinical personnel for comparing scanner/transducer configurations. Anotherobjective is to provide for minimal cost of production for commercialversions.Methods—Current MatLab software is being converted to aform executable on any personal computer with a user-friendly generalizeduser interface (GUI). The large laboratory data acquisition apparatuswill be replaced with a small semiautomatic one to be part of the phantom.Also, minimal data acquisition will be determined for acceptable reproducibility.Results—The methods of data acquisition and reduction willbe described. A transducer holder and stepper motor system provide fortranslation of the transducer in steps of one-fourth of the sphere diameterneeded for determining the centers of the spheres. The procedure for usingthe GUI will be demonstrated. Also, reproducibility of detectability-versus-depthcurves will be demonstrated. Imaging performance comparisonsbetween scanner/transducer configurations will be shown; one interestingresult using a pediatric transducer is that a 4-cm focus resulted in lesser detectabilityoverall than a 3-cm focus.Conclusions—Comparisons will aid in choosing equipmentfor a given set of clinical applications, provide a new means of acceptancetesting, and allow optimization of configurations of installed scannersfor specific applications. The phantoms may also be useful for manufacturersto refine their systems. The cost of production may result in the needfor multiple users to share one commercial form of the system.1541363 Pulse-Echo–Based Sound Speed Estimations Using SpeckleStatisticsIvan Rosado-Mendez, Kibo Nam, Timothy Hall, JamesZagzebski* Medical Physics, University of Wisconsin,Madison, Wisconsin USAObjectives—Speed of sound estimates are required for optimalfocusing and beam forming in medical ultrasound. Moreover, measurementsof tissue sound speeds (c t) have potential diagnostic value. Weinvestigate a method for sound speed estimation using second-orderspeckle statistics to analyze ultrasound image clarity as a function of theassumed sound speed during beam forming (c bf). The size of a region ofinterest (ROI) analyzed can be limited by tissue heterogeneities. This workfocuses on defining a minimum ROI size required to obtain reliable c testimates and on comparing estimates performed near the transmit focuswith values obtained at other depths.Methods—Radiofrequency (RF) echo signals from a “nonfattytissue” (N-F)- and a “fatty tissue” (F)-mimicking phantom were acquiredwith a Siemens S2000 system allowing control over c bf. Excitation frequencieswere 6 and 9 MHz, and the nominal transmit focus was 5 cm.This process was repeated at 5 uncorrelated planes. RF echo signals wereenvelope detected and squared to obtain intensity data. 2D “correlationcell areas” (S c), based on the 2D autocovariance of the intensity data withinthe ROI, was tracked as the ROI size was reduced. Then, S cwas trackedS43
American Institute of Ultrasound in Medicine Proceedings J Ultrasound Med 32(suppl):S1–S134, 2013as c bfvaried from 1350 to 1550 m/s and from 1440 to 1640 m/s whenscanning phantoms F and N-F, respectively, in steps of 10 m/s. The c bfatwhich S cwas minimized was chosen as the c testimate. The c testimatebias was computed as the interplane average of the percentage differencefrom substitution measurements (F phantom, 1452 m/s; N-F phantom,1544 m/s).Results—The minimum required ROI size was 20 pulselengths and 14 uncorrelated scan lines (7 × 9 mm 2 in this experiment). Ingeneral, ct was underestimated by –1.0% ± 0.1% and by –1.3% ± 0.3% forthe F and N-F phantoms, respectively. No significant differences werefound among estimates from different excitation frequencies or amongthose at the physical location or the nominal location of the transmit focus.Conclusions—Results indicate that estimates can be performedwithin 1 cm 2 at the location of the nominal transmit focus, whichcan be a fixed parameter during the in vivo application of this method.The method is being applied in the characterization of liver diseases andlesions.Cardiovascular UltrasoundModerator: John Blebea, MD, MBA1521708 Lagrangian Deformation Tracking of the Left Ventricle forCardiac Ultrasound Strain ImagingChi Ma,* Tomy Varghese Medical Physics, University ofWisconsin, Madison, Wisconsin USAObjectives—Lagrangian description of myocardial tissue structuredeformation is key to accurate regional strain estimation of the leftventricular wall over time. Failure to couple the estimated displacementand strain information with the correct myocardial tissue structures willlead to erroneous result in the displacement and strain distribution overtime.Methods—This study presents a method to obtain Lagrangianbaseddisplacement tracking. Myocardial issue structures are divided intoa fixed number of pixels whose deformation is tracked over the cardiaccycle. An algorithm that uses a polar grid generated between the estimatedendocardial and epicardial contours for the left ventricle in cardiac shortaxisimages is proposed to ensure Lagrangian description of the pixels.Displacement estimations from consecutive radiofrequency frames werethen mapped onto the polar grid to obtain a distribution of the actual displacementthat is mapped to the polar grid over time.Results—The method was validated against a finite-element–based canine heart model coupled with an ultrasound simulation program.Segmental analysis of the accumulated displacement and strain over a cardiaccycle demonstrated excellent agreement between the ideal result obtaineddirectly from the finite-element model and our Lagrangian approachto strain estimation. Traditional Eulerian-based estimation results, on theother hand, showed a significant deviation from the ideal result. An in vivocomparison of the displacement and strain estimated using parasternalshort-axis views is also presented.Conclusions—Lagrangian strain estimation using a polar griddemonstrates accurate results when validated in a finite-element cardiacmodel. In addition to the cardiac application, this approach can also beapplied to transverse scans of arteries, where a polar grid can be generatedbetween the contours delineating the outer and inner walls of the vesselsfrom the blood flowing though the vessels. (Supported by National Institutesof Health grants 5R21EB010098 and R01CA112192-S103.)S441509371 Effects of Respiration on Estimation of Systolic PulmonaryArtery Pressure in Patients With Right Ventricle SystolicDysfunctionXiao-Yong Zhang,* Tie-Sheng Cao, Li-Jun Yuan UltrasoundDiagnostics, Tangdu Hospital, Fourth Military MedicalUniversity, Xi’an, ChinaObjectives—We investigated the effects of respiration on thepeak velocity of tricuspid regurgitation (TR) and estimation of systolicpulmonary artery pressure (SPAP) in patients with right ventricle (RV)systolic dysfunction by Doppler echocardiography.Methods—Continuous wave Doppler spectra of TR wererecorded in 32 patients with and 28 controls without RV systolic dysfunction.Electrocardiography and respiratory tracing were recorded simultaneously.The expiratory and inspiratory peak velocities of TR wereacquired and averaged for 5 consecutive respiratory cycles. The SPAPduring expiration and inspiration was calculated.Results—The velocity of TR and SPAP did not vary significantlybetween expiration and inspiration in controls (2.77 ± 0.23 and 2.82 ± 0.26m/s; P = .776; 35.94 ± 4.96 and 36.18 ± 5.12 mm Hg; P = .747), whereasthe velocity of TR and SPAP decreased significantly from expiration to inspirationin patients with RV systolic dysfunction (3.27 ± 0.35 and 2.59 ±0.22 m/s; P < .001; 53.72 ± 7.39 and 38.45 ± 5.63 mm Hg; P < .001).Conclusions—Respiration has significant effects on the velocityof TR and SPAP in patients with RV systolic dysfunction, and the measurementshould be carried out when patients are at the end of expiration.1541517 High–Frame Rate Lateral Strain Estimation Using VirtualBeam Focusing in Canine and Human Hearts In VivoEthan Bunting, 1 * Jean Provost, 1 Elisa Konofagou 1,21Biomedical Engineering, 2 Radiology, Columbia University,New York, New York USAObjectives—Ultrasonic strain imaging is capable of providing clinicianswith useful information regarding cardiac function in a fast, noninvasivemanner. Lateral strain estimation is required to obtain the full 2D straintensor of the heart and accurately represent the cardiac deformation within theimage plane. Previous work has shown that 2 major parameters influencingthe quality of lateral strain estimation are the motion estimation rate and beamdensity (Provost et al. Phys Med Biol 2011). Using element channel data,virtual beam focusing can be used to reconstruct a large number of beamsfrom only a few acoustic interrogations. Furthermore, the rate of motion estimationcan be increased by using temporally unequispaced acquisition sequences(TUAS), a technique developed previously by our group, whichincreases the motion estimation rate while reducing the motion sampling rate.Methods—Using a Verasonics scanner with a custom TUASand virtual beam focusing, we have acquired short-axis views of human(n = 1) and open-chest canine (n = 3) hearts. Virtual beam focusing wasused to reconstruct 156 radiofrequency (RF) lines from 12 focusedacoustic transmits. Lateral displacement estimation was performed usingRF cross-correlation, and strain was computed using a least squares strainestimator. The quality of strain estimation was evaluated by using the elastographicsignal-to-noise ratio (SNRe).Results—We first show that lateral strain estimation can beachieved in vivo using virtual beam focusing and that the results are similarto conventional beam focusing. Also, we show that it is possible touse TUAS to estimate strain using a wide range of frame rates (57, 130,447, 894, 1788, and 2682 Hz) while maintaining this high beam density.The SNRe for lateral strain was found to range from 2 to 10 and be optimalat a motion estimation rate of 894 Hz.Conclusions—In conventional scanners, there is a trade-off betweenthe beam density and motion estimation rate, leading to a theoreticallimit on the quality of strain estimation. The use of virtual beamfocusing and TUAS techniques for lateral strain imaging was shown toeliminate this tradeoff and lead to good-quality lateral strain estimation athigh frame rates.
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Small-Animal Preclinical High-Frequ
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2013 AIUM Award WinnersJoseph H. Ho
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2013 AIUM Award WinnersDistinguishe
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