Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849324
J. Kirkhorn, P. Frinking, N. de Jong, H. Torp
Harmonic power Doppler (HPD) is sensitive for detecting ultrasound contrast agents. In HPD, multiple pulses are transmitted along each beam in the image, and changes from pulse to pulse are detected. The sensitivity of HPD relies on efficient destruction of the contrast agent. Destruction increases with amplitude and pulse length, but amplitude is bounded by safety limitations while long pulses degrade spatial image resolution. To circumvent the implicit trade-off between detection sensitivity and imaging resolution in HPD, the authors propose to combine HPD with a single high energy ultrasound pulse (the release-burst, RE). A few detection pulses are transmitted first, followed by the RE and a second series of detection pulses. The authors propose to combine the pulse sequence with a special polynomial prediction filter to remove clutter. The method has been tested in vitro in a capillary phantom using three different contrast agents, and compared to HPD. The results indicate that the RE can improve the sensitivity of HPD for all agents, also in presence of moving tissue.
{"title":"Improved ultrasound contrast detection combining harmonic power Doppler with a release-burst","authors":"J. Kirkhorn, P. Frinking, N. de Jong, H. Torp","doi":"10.1109/ULTSYM.1999.849324","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849324","url":null,"abstract":"Harmonic power Doppler (HPD) is sensitive for detecting ultrasound contrast agents. In HPD, multiple pulses are transmitted along each beam in the image, and changes from pulse to pulse are detected. The sensitivity of HPD relies on efficient destruction of the contrast agent. Destruction increases with amplitude and pulse length, but amplitude is bounded by safety limitations while long pulses degrade spatial image resolution. To circumvent the implicit trade-off between detection sensitivity and imaging resolution in HPD, the authors propose to combine HPD with a single high energy ultrasound pulse (the release-burst, RE). A few detection pulses are transmitted first, followed by the RE and a second series of detection pulses. The authors propose to combine the pulse sequence with a special polynomial prediction filter to remove clutter. The method has been tested in vitro in a capillary phantom using three different contrast agents, and compared to HPD. The results indicate that the RE can improve the sensitivity of HPD for all agents, also in presence of moving tissue.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130657193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849230
M. Karaman, M. Kozak
A promising approach to reduce the complexity of the front-end hardware of an ultrasound imaging system is to utilize oversampling Delta-Sigma (/spl Delta//spl Sigma/) beamforming. Realization of dynamic receive focusing involves signal resampling of uniformly sampled radio frequency (RF) signals using beamforming timing. The resampling (deleting or repeating samples), however, causes a significant increase in the noise floor of the beamformer output. To overcome this problem, the authors have explored a new digital beamformer employing non-uniform oversampling. To avoid resampling during dynamic focusing, they have used a different sampling clock at each channel to sample RF echo signals non-uniformly at the time instants associated with receive focal points. The performance and validity of the new system are assessed by means of emulations using experimental 3.5 MHz RF data.
{"title":"Digital beamforming using non-uniform oversampling delta-sigma conversion","authors":"M. Karaman, M. Kozak","doi":"10.1109/ULTSYM.1999.849230","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849230","url":null,"abstract":"A promising approach to reduce the complexity of the front-end hardware of an ultrasound imaging system is to utilize oversampling Delta-Sigma (/spl Delta//spl Sigma/) beamforming. Realization of dynamic receive focusing involves signal resampling of uniformly sampled radio frequency (RF) signals using beamforming timing. The resampling (deleting or repeating samples), however, causes a significant increase in the noise floor of the beamformer output. To overcome this problem, the authors have explored a new digital beamformer employing non-uniform oversampling. To avoid resampling during dynamic focusing, they have used a different sampling clock at each channel to sample RF echo signals non-uniformly at the time instants associated with receive focal points. The performance and validity of the new system are assessed by means of emulations using experimental 3.5 MHz RF data.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129259724","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849411
D. Zhang, X. Tong, H. Qin
This paper presents some propagation properties of QLLSAW propagating on Y-rotated cut quartz substrates, such as the substrates at Euler angles [0°, 124°, 50°], [0°, 126°, 50°], [0°, 132°, 50°] etc. The advantages of properties of quasi-longitudinal leaky surface acoustic waves (QLLSAW) along these directions are small propagation attenuation (less than 10-4 dB/λ), small power flow deviation and high phase velocity (can be up from 6,200 m/s to 7,000 m/s). Frequency responses of experimental devices are smooth enough to be applied in practice and the leaky surface shear wave signal cannot be observed in the frequency response. The temperature coefficients on these substrates are also investigated.
{"title":"Study of propagation properties of quasi-longitudinal leaky surface acoustic wave propagating on Y-rotated cut quartz substrates","authors":"D. Zhang, X. Tong, H. Qin","doi":"10.1109/ULTSYM.1999.849411","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849411","url":null,"abstract":"This paper presents some propagation properties of QLLSAW propagating on Y-rotated cut quartz substrates, such as the substrates at Euler angles [0°, 124°, 50°], [0°, 126°, 50°], [0°, 132°, 50°] etc. The advantages of properties of quasi-longitudinal leaky surface acoustic waves (QLLSAW) along these directions are small propagation attenuation (less than 10-4 dB/λ), small power flow deviation and high phase velocity (can be up from 6,200 m/s to 7,000 m/s). Frequency responses of experimental devices are smooth enough to be applied in practice and the leaky surface shear wave signal cannot be observed in the frequency response. The temperature coefficients on these substrates are also investigated.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129354769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849247
E. Camus, M. Talmant, G. Berger, P. Laugier
Ultrasonic wave propagation in human cortical bone has been investigated in vitro using an axial transmission technique. Two quasi-point source elements, one transmitter and one receiver, were used to generate a wide ultrasonic beam including the longitudinal critical angle and to receive the signals radiated from the sample surface. Validation of the measuring technique was performed on test materials, followed by experiments on human cortical bones. Velocity measurements of the first arriving signal based on time-of-flight determinations were in agreement with reported values of longitudinal velocities for both test materials and bone specimens, and so did the experimental arrival times of the first arriving signal and ray arrival times of the lateral wave. The velocity in cortical bone ranged from 3600 to 4050 m.s/sup -1/. Our results strongly suggest that the first arriving signal corresponds to the lateral wave predicted by theory.
{"title":"In vitro measurements of the lateral wave in human cortical bone","authors":"E. Camus, M. Talmant, G. Berger, P. Laugier","doi":"10.1109/ULTSYM.1999.849247","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849247","url":null,"abstract":"Ultrasonic wave propagation in human cortical bone has been investigated in vitro using an axial transmission technique. Two quasi-point source elements, one transmitter and one receiver, were used to generate a wide ultrasonic beam including the longitudinal critical angle and to receive the signals radiated from the sample surface. Validation of the measuring technique was performed on test materials, followed by experiments on human cortical bones. Velocity measurements of the first arriving signal based on time-of-flight determinations were in agreement with reported values of longitudinal velocities for both test materials and bone specimens, and so did the experimental arrival times of the first arriving signal and ray arrival times of the lateral wave. The velocity in cortical bone ranged from 3600 to 4050 m.s/sup -1/. Our results strongly suggest that the first arriving signal corresponds to the lateral wave predicted by theory.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127770974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849195
K. Ymada, J.-I. Sakamura, K. Nakamura
Performance of ultrasound transducers composed of a piezoelectric plate having a graded parameter is studied theoretically by using an equivalent network model formerly presented by the authors. Transfer functions and impulse responses are calculated for a linearly and an exponentially graded piezoceramic transducer model which has a water load on one side and a matched backing on the other side. The theoretical examinations made for the plates with some typical distributions of the piezoelectric constant e/sub 33/ clearly show the effectiveness of the functionally-graded plates. Some results are also presented for the case that the transducers are excited by a one-cycle sinusoidal electric pulse.
{"title":"Equivalent network analysis of piezoelectrically-graded broadband ultrasound transducers","authors":"K. Ymada, J.-I. Sakamura, K. Nakamura","doi":"10.1109/ULTSYM.1999.849195","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849195","url":null,"abstract":"Performance of ultrasound transducers composed of a piezoelectric plate having a graded parameter is studied theoretically by using an equivalent network model formerly presented by the authors. Transfer functions and impulse responses are calculated for a linearly and an exponentially graded piezoceramic transducer model which has a water load on one side and a matched backing on the other side. The theoretical examinations made for the plates with some typical distributions of the piezoelectric constant e/sub 33/ clearly show the effectiveness of the functionally-graded plates. Some results are also presented for the case that the transducers are excited by a one-cycle sinusoidal electric pulse.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127960353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849177
S. Hansen, B. Mossawir, A. Sanli Ergun, F. Levent Degertekin, B. Khuri-Yakub
Nondestructive evaluation techniques which use conventional piezoelectric transducers typically require liquid coupling fluids to improve the impedance mismatch between piezoelectric materials and air. Air-coupled ultrasonic systems can eliminate this requirement if the dynamic range of the system is large enough such that the losses at the air-solid interfaces are tolerable. Capacitive micromachined ultrasonic transducers (cMUTs) have been shown to have more than 100 dB dynamic range when used in bistatic transmission mode. This dynamic range, along with the ability to transmit ultrasound efficiently into air, makes cMUTs ideally suited for air-coupled nondestructive evaluation applications. These transducers can be used either in through transmission experiments at normal incidence to the sample or to excite and detect guided waves in aluminum and composite plates. In this paper, we present results of a pitch-catch transmission system using cMUTs that achieves a dynamic range in excess of 100 dB. The pair of transducers is modeled with an equivalent electrical circuit which predicts the transmission system's insertion loss and dynamic range. We also demonstrate the feasibility of Lamb wave defect detection for one-sided nondestructive evaluation applications. A pair of cMUTs excites and detects the so mode in a 1.2 mm-thick aluminum plate with a received signal-to-noise ratio of 28 dB without signal averaging.
{"title":"Air-coupled nondestructive evaluation using micromachined ultrasonic transducers","authors":"S. Hansen, B. Mossawir, A. Sanli Ergun, F. Levent Degertekin, B. Khuri-Yakub","doi":"10.1109/ULTSYM.1999.849177","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849177","url":null,"abstract":"Nondestructive evaluation techniques which use conventional piezoelectric transducers typically require liquid coupling fluids to improve the impedance mismatch between piezoelectric materials and air. Air-coupled ultrasonic systems can eliminate this requirement if the dynamic range of the system is large enough such that the losses at the air-solid interfaces are tolerable. Capacitive micromachined ultrasonic transducers (cMUTs) have been shown to have more than 100 dB dynamic range when used in bistatic transmission mode. This dynamic range, along with the ability to transmit ultrasound efficiently into air, makes cMUTs ideally suited for air-coupled nondestructive evaluation applications. These transducers can be used either in through transmission experiments at normal incidence to the sample or to excite and detect guided waves in aluminum and composite plates. In this paper, we present results of a pitch-catch transmission system using cMUTs that achieves a dynamic range in excess of 100 dB. The pair of transducers is modeled with an equivalent electrical circuit which predicts the transmission system's insertion loss and dynamic range. We also demonstrate the feasibility of Lamb wave defect detection for one-sided nondestructive evaluation applications. A pair of cMUTs excites and detects the so mode in a 1.2 mm-thick aluminum plate with a received signal-to-noise ratio of 28 dB without signal averaging.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128824457","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849442
J. Kondoh, Toshihisa Yamazaki, Y. Matsui, S. Shiokawa
The surface acoustic wave (SAW) on 36YX LiTaO3, the shear-horizontal mode (SH-SAW), can detect liquid properties. This paper describes the new method to identify and estimate components and concentration of ions in aqueous solutions by using a liquid-flow sensing system with the SH-SAW sensor without any selective organic films. The principle of the identification is based on the difference in transient responses. The proposed method includes a new technique for constituting the database of mixing ion solution from that of the single ion solutions.
{"title":"Identification of ion species in electrolytic solutions using surface acoustic wave liquid flow sensing system based on new pattern recognition method","authors":"J. Kondoh, Toshihisa Yamazaki, Y. Matsui, S. Shiokawa","doi":"10.1109/ULTSYM.1999.849442","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849442","url":null,"abstract":"The surface acoustic wave (SAW) on 36YX LiTaO3, the shear-horizontal mode (SH-SAW), can detect liquid properties. This paper describes the new method to identify and estimate components and concentration of ions in aqueous solutions by using a liquid-flow sensing system with the SH-SAW sensor without any selective organic films. The principle of the identification is based on the difference in transient responses. The proposed method includes a new technique for constituting the database of mixing ion solution from that of the single ion solutions.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125660761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849461
G. Mansfeld, S. Alekseev, Y. Gulyaev, Z. Kosakovskaya
The BAW spectroscopy method for the acoustic characterization of carbon nanotubes was applied. The material density and the elastic constants for carbon nanotube films were evaluated directly. The effect of the increase in the electric field near the electrodes with nanotube thin films may be conveniently used in electrostatic transducers for acoustic wave excitation in nonpiezoelectric solids and liquids.
{"title":"Microwave HBAR spectroscopy and transducer application of carbon nanotube films","authors":"G. Mansfeld, S. Alekseev, Y. Gulyaev, Z. Kosakovskaya","doi":"10.1109/ULTSYM.1999.849461","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849461","url":null,"abstract":"The BAW spectroscopy method for the acoustic characterization of carbon nanotubes was applied. The material density and the elastic constants for carbon nanotube films were evaluated directly. The effect of the increase in the electric field near the electrodes with nanotube thin films may be conveniently used in electrostatic transducers for acoustic wave excitation in nonpiezoelectric solids and liquids.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"115 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123191341","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849184
E. Kuhnicke
Because the refracted sound field of a finite beam extremely depends on the size and on the frequency of the generating element, Snell's law is not applicable to calculate the refraction angle of a finite beam. Approaches using plane reflection and transmission coefficient in connection with a discretization of the source into elementary point sources are more exact. This paper demonstrates that the application of plane reflection and transmission coefficients requires a point to point distance smaller than a half wavelength, in order to obtain an accurate sound field of the refracted beam.
{"title":"The limitations of Snell's law in the design of ultrasound transducers","authors":"E. Kuhnicke","doi":"10.1109/ULTSYM.1999.849184","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849184","url":null,"abstract":"Because the refracted sound field of a finite beam extremely depends on the size and on the frequency of the generating element, Snell's law is not applicable to calculate the refraction angle of a finite beam. Approaches using plane reflection and transmission coefficient in connection with a discretization of the source into elementary point sources are more exact. This paper demonstrates that the application of plane reflection and transmission coefficients requires a point to point distance smaller than a half wavelength, in order to obtain an accurate sound field of the refracted beam.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126116695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-10-17DOI: 10.1109/ULTSYM.1999.849467
Jian-jun Chen, Y. Mao, Yan Zhang, Wen‐hua Jiang, D. Zhang
The generation of reflected freely-propagating second harmonic SV wave at solid-solid interface is an interface nonlinear effect. It is anticipated that the bonding state of the interface will affect the effect. In this paper, the influence of the vibrating interface on the effect is studied. It is observed that the nonlinear reflective SV wave becomes amplitude modulation due to the vibration of the refractive media (PZT), whereas no modulation takes place for the linear reflective SV wave.
{"title":"A nonlinear amplitude modulation phenomenon","authors":"Jian-jun Chen, Y. Mao, Yan Zhang, Wen‐hua Jiang, D. Zhang","doi":"10.1109/ULTSYM.1999.849467","DOIUrl":"https://doi.org/10.1109/ULTSYM.1999.849467","url":null,"abstract":"The generation of reflected freely-propagating second harmonic SV wave at solid-solid interface is an interface nonlinear effect. It is anticipated that the bonding state of the interface will affect the effect. In this paper, the influence of the vibrating interface on the effect is studied. It is observed that the nonlinear reflective SV wave becomes amplitude modulation due to the vibration of the refractive media (PZT), whereas no modulation takes place for the linear reflective SV wave.","PeriodicalId":339424,"journal":{"name":"1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)","volume":"163 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1999-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125915894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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