Man Nguyen | University of Pittsburgh (original) (raw)
Papers by Man Nguyen
2015 IEEE International Ultrasonics Symposium (IUS), 2015
Indocyanine green (ICG)-loaded droplets developed for photoacoustic imaging and drug delivery hav... more Indocyanine green (ICG)-loaded droplets developed for photoacoustic imaging and drug delivery have been tested for cavitation imaging in vitro. Perfluoropentane mixed with ICG was vaporized with a short pulse laser and expanded to 3-5 times the initial diameter of 2-5 micron and generated a strong broadband photoacoustic signal. It was found these vaporized droplets could be cavitated and ruptured by a short ultrasound pulses. To test the feasibility of cavitation imaging of laser-triggered droplets, broadband cavitation imaging algorithms were implemented on a commercial ultrasound open platform with a linear array transducer, centered at 5 MHz. Less than 3 cycles ultrasound excitation pulse with a MI of 0.7 was used to insonify a polyethylene tube of 580 μm inner diameter containing droplets to induce inertial cavitation activity. The cavitation imaging was performed before and after vaporizing droplets by laser pulses. Broadband emissions of 5-10 MHz were observed only after droplets were vaporized. These preliminary results demonstrate the feasibility of high resolution cavitation imaging of vaporized droplets using a short ultrasound excitation pulse and could lead to further in vivo experiments.
Fresnel beamforming is a beamforming method with a delay profile similar in shape to a physical F... more Fresnel beamforming is a beamforming method with a delay profile similar in shape to a physical Fresnel lens. The advantage of Fresnel beamforming is the reduced channel count, which consists of four to eight transmit and two analog-to-digital receive channels. Fresnel beamforming was found to perform comparably to conventional delay-and-sum beamforming. However, the performance of Fresnel beamforming is highly dependent on focal errors. These focal errors result in high side-lobe levels and further reduce the performance of Fresnel beamforming in the presence of phase aberration. With the advantages of lower side-lobe levels and suppression of aberration effects, harmonic imaging offers an effective solution to the limitations of Fresnel beamforming. We describe the implementation of tissue harmonic imaging and pulse inversion harmonic imaging in Fresnel beamforming, followed by dual apodization with cross-correlation, to improve image quality. Compared with conventional delay-and-sum beamforming, experimental results indicated contrast-to-noise ratio improvements of 10%, 49% and 264% for Fresnel beamforming using tissue harmonic imaging in the cases of no aberrator, 5-mm pork aberrator and 12-mm pork aberrator, respectively. These improvements were 22%, 57% and 352% for Fresnel beamforming using pulse inversion harmonic imaging. Moreover, dual apodization with cross-correlation was found to further improve the contrast-to-noise ratios in all cases. Harmonic imaging was also found to narrow the lateral beamwidth and shorten the axial pulse length by at least 25% and 21%, respectively, for Fresnel beamforming at different aberration levels. These results suggest the effectiveness of harmonic imaging in improving image quality for Fresnel beamforming, especially in the presence of phase aberration. Even though this combination of Fresnel beamforming and harmonic imaging does not outperform delay-and-sum beamforming combined with harmonic imaging, it provides the benefits of reduced channel count and potentially reduced cost and size of ultrasound systems. (
Because tissues consist of solid and fluid materials, their mechanical properties should be chara... more Because tissues consist of solid and fluid materials, their mechanical properties should be characterized in terms of both elasticity and viscosity. Although the elastic properties of tissue-mimicking phantoms have been extensively studied and well characterized in commercially available phantoms, their viscous properties have not been fully investigated. In this article, a set of 14 tissue-mimicking phantoms with different concentrations of gelatin and castor oil were fabricated and characterized in terms of acoustic and viscoelastic properties. The results indicate that adding castor oil to gelatin phantoms decreases shear modulus, but increases shear wave dispersion. For 3% gelatin phantoms containing 0%, 10%, 20% and 40% oil, the measured shear moduli are 2.01 ± 0.26, 1.68 ± 0.25, 1.10 ± 0.22 and 0.88 ± 0.17 kPa, and the Voigt-model coupled shear viscosities are 0.60 ± 0.11, 0.89 ± 0.07, 1.05 ± 0.11 and 1.06 ± 0.13 Pa$s, respectively. The results also confirm that increasing the gelatin concentration increases shear modulus. For phantoms containing 3%, 4%, 5%, 6% and 7% gelatin, the measured shear moduli are 2.01 ± 0.26, 3.10 ± 0.34, 4.18 ± 0.84, 8.05 ± 1.00 and 10.24 ± 1.80 kPa at 0% oil and 1.10 ± 0.22, 1.97 ± 0.20, 3.13 ± 0.63, 4.60 ± 0.60 and 8.43 ± 1.39 kPa at 20% oil, respectively. The phantom recipe developed in this study can be used in validating ultrasound shear wave elastography techniques for soft tissues. (
Elastography has become widely used for minimally invasive diagnosis in many tumors as seen with ... more Elastography has become widely used for minimally invasive diagnosis in many tumors as seen with breast, liver and prostate. Among different modalities, ultrasound-based elastography stands out due to its advantages including being safe, real-time, and relatively low-cost. While lung cancer is the leading cause of cancer mortality among both men and women, the use of ultrasound elastography for lung cancer diagnosis has hardly been investigated due to the limitations of ultrasound in air. In this work, we investigate the use of static-compression based endobronchial ultrasound elastography by a 3D trans-oesophageal echocardiography (TEE) transducer for lung cancer diagnosis. A water-filled balloon was designed to 1) improve the visualization of endobronchial ultrasound and 2) to induce compression via pumping motion inside the trachea and bronchiole. In a phantom study, we have successfully generated strain images indicating the stiffness difference between the gelatin background and agar inclusion. A similar strain ratio was confirmed with Philips ultrasound strain-based elastography product. For ex-vivo porcine lung study, different tissue ablation methods including chemical injection, Radio Frequency (RF) ablation, and direct heating were implemented to achieve tumor-mimicking tissue. Stiff ablated lung tissues were obtained and detected with our proposed method. These results suggest the feasibility of pulmonary elastography to differentiate stiff tumor tissue from normal tissue. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/05/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8675 867503-3 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/05/2013 Terms of Use: http://spiedl.org/terms
Fresnel beamforming is a beamforming method that has a delay profile with a shape similar to a ph... more Fresnel beamforming is a beamforming method that has a delay profile with a shape similar to a physical Fresnel lens. With 4 to 8 transmit channels, 2 receive channels, and a network of single-pole/single-throw switches, Fresnel beamforming can reduce the size, cost, and complexity of a beamformer. The performance of Fresnel beamforming is highly dependent on focal errors resulting from phase wraparound and quantization of its delay profile. Previously, we demonstrated that the performance of Fresnel beamforming relative to delayand-sum (DAS) beamforming is comparable for linear arrays at f-number = 2 and 50% bandwidth. However, focal errors for Fresnel beamforming are larger because of larger path length differences between elements, as in the case of curvilinear arrays compared with linear arrays. In this paper, we present the concept and performance evaluation of Fresnel beamforming combined with a novel clutter suppression method called dual apodization with cross-correlation (DAX) for curvilinear arrays. The contrast-to-noise ratios (CNRs) of Fresnel beamforming followed by DAX are highest at f-number = 3. At f-number = 3, the experimental results show that using DAX, the CNR for Fresnel beamforming improves from 3.7 to 10.6, compared with a CNR of 5.2 for DAS beamforming. Spatial resolution is shown to be unaffected by DAX. At f-number = 3, the lateral beamwidth and axial pulse length for Fresnel beamforming with DAX are 1.44 and 1.00 mm larger than those for DAS beamforming (about 14% and 21% larger), respectively. These experimental results are in good agreement with simulation results.
In this paper, we propose a modified electronic Fresnel-based beamforming method for low-cost por... more In this paper, we propose a modified electronic Fresnel-based beamforming method for low-cost portable ultrasound systems. This method uses a unique combination of analog and digital beamforming methods. Two versions of Fresnel beamforming are presented in this paper: 4-phase (4 different time delays or phase shifts) and 8-phase (8 different time delays or phase shifts). The advantage of this method is that a system with 4 to 8 transmit channels and 2 receive channels with a network of switches can be used to focus an array with 64 to 128 elements. The simulation and experimental results show that Fresnel beamforming image quality is comparable to traditional delay-and-sum (DAS) beamforming in terms of spatial resolution and contrast-to-noise ratio CNR) under certain system parameters. With an f-number of 2 and 50% signal bandwidth, the experimental lateral beamwidths are 0.54, 0.67, and 0.66 mm and the axial pulse lengths are 0.50, 0.51, and 0.50 mm for DAS, 8-phase, and 4-phase Fresnel beamforming, respectively. The experimental CNRs are 4.66, 4.42, and 3.98, respectively. These experimental results are in good agreement with simulation results.
The dif fi cul ties as so ci ated with fab ri ca tion and in ter con nec tion have lim ited the d... more The dif fi cul ties as so ci ated with fab ri ca tion and in ter con nec tion have lim ited the de vel op ment of 2-D ul tra sound trans ducer ar rays with a large num ber of el e ments (>5000). In pre vi ous work, we de scribed a 5 MHz cen ter fre quency PZT-P[VDF-TrFE] dual-layer trans ducer that used two per pen dic u lar 1-D arrays for 3-D rec ti lin ear im ag ing. This de sign sub stan tially re duces the chan nel count as well as fab ri cation com plex ity, which makes 3-D im ag ing more re al iz able. Higher fre quen cies (>5 MHz) are more com monly used in clin i cal applications or im ag ing tar gets near trans duc ers, such as the breast, ca rotid and musculoskeletal tissue. In this pa per, we pres ent a 7.5 MHz dual-layer trans ducer ar ray for 3-D rec tilin ear im ag ing. A mod i fied acoustic stack model was de signed and fabricated. PZT el e ments were sub-diced to elim i nate lat eral cou pling. This sub-dic ing pro cess made the PZT into a 2-2 com pos ite mate rial, which could help im prove trans ducer sen si tiv ity and band width. Full syn thetic-ap er ture 3-D data sets were ac quired by in ter fac ing the trans ducer with a Verasonics data-ac qui si tion sys tem (VDAS). Offline 3-D beamforming was then per formed to ob tain vol umes of a multiwire phan tom and a cyst phan tom. The gen er al ized coherence fac tor (GCF) was ap plied to im prove the con trast of cyst im ages. The mea sured -6 dB frac tional band width of the trans ducer was 71% with a cen ter fre quency of 7.5 MHz. The mea sured lat eral beam widths were 0.521 mm and 0.482 mm in az i muth and el e va tion, re spec tively, com pared with a sim u lated beam width of 0.43 mm.
Two-dimensional transrectal ultrasound (TRUS) is being used in guiding prostate biopsies and trea... more Two-dimensional transrectal ultrasound (TRUS) is being used in guiding prostate biopsies and treatments. In many cases, the TRUS probes are moved manually or mechanically to acquire volumetric information, making the imaging slow, user dependent, and unreliable. A real-time three-dimensional (3-D) TRUS system could improve reliability and volume rates of imaging during these procedures. In this article, the authors present a 5-MHz cylindrical dual-layer transducer array capable of real-time 3-D transrectal ultrasound without any mechanically moving parts. Compared with fully sampled 2-D arrays, this design substantially reduces the channel count and fabrication complexity. This dual-layer transducer uses PZT elements for transmit and P[VDF-TrFE] copolymer elements for receive, respectively. The mechanical flexibility of both diced PZT and copolymer makes it practical for transrectal applications. Full synthetic aperture 3-D data sets were acquired by interfacing the transducer with a Verasonics Data Acquisition System. Offline 3-D beamforming was then performed to obtain volumes of two wire phantoms and a cyst phantom. Generalized coherence factor was applied to improve the contrast of images. The measured −6-dB fractional bandwidth of the transducer was 62% with a center frequency of 5.66 MHz. The measured lateral beamwidths were 1.28 mm and 0.91 mm in transverse and longitudinal directions, respectively, compared with a simulated beamwidth of 0.92 mm and 0.74 mm.
Fresnel beamforming is a beamforming method that has a delay profile with a shape similar to a ph... more Fresnel beamforming is a beamforming method that has a delay profile with a shape similar to a physical Fresnel lens. With 4-8 transmit channels, 2 receive channels and a network of single-pole/single-throw switches, Fresnel beamforming can reduce the size, cost and complexity of a beamformer. The performance of Fresnel beamforming is highly dependent on focal errors due to phase wraparound and quantization of its delay profile. Compared to linear arrays, curvilinear arrays have larger path length differences among elements, which result in larger focal errors. In this paper, we present the concept and performance evaluation of Fresnel beamforming combined with a novel clutter suppression method, dual apodization with crosscorrelation (DAX), for curvilinear arrays. The spatial resolution and contrast-to-noise ratios (CNR) obtained from simulation and experiment show that Fresnel beamforming followed by DAX has higher CNR and comparable spatial resolution compared to delay-and-sum (DAS) beamforming. We also evaluate the performance of Fresnel beamforming in the presence of phase aberration and sound speed error.
This paper presents a new beamforming method that may reduce the size and cost of the system with... more This paper presents a new beamforming method that may reduce the size and cost of the system with minimized image quality tradeoffs. Applying optical Fresnel principles in ultrasound imaging, a system with 4 transmit and 2 receive channels can be used to steer and focus an array with 64 to 128 elements. The spatial resolution and contrast-to-noise ratios obtained from simulation and experiment show that the spatial resolution using an 8-phase Fresnel beamforming method is comparable to those values obtained from traditional delay-andsum beamforming.
In previous work, we successfully developed a 7.5 MHz dual-layer array transducer for 3-D rectili... more In previous work, we successfully developed a 7.5 MHz dual-layer array transducer for 3-D rectilinear imaging. This transducer significantly reduces the fabrication complexity and the channel count compared to fully sampled 2-D arrays, making 3-D imaging more realizable. Also, higher frequency (> 5 MHz) 3-D imaging can provide more accurate volume measurements, detection of cystic or cancerous masses, and also assist in 3-D ultrasound guided biopsy and carotid imaging. In this paper, we present our work toward real-time 3-D imaging with this transducer, including real-time data acquisition with the Verasonics data acquisition system (VDAS), offline beamforming and display for volumetric images. The volume rate was set as 30 volume/sec with a field of view equals to 19.2 x 19.2 x 42.2 mm 3 . Movies were created to present a real-time display of the moving phantoms of multiwire targets or cyst targets.
The difficulties associated with fabricating and connecting 2-D arrays with large numbers of elem... more The difficulties associated with fabricating and connecting 2-D arrays with large numbers of elements have limited the development of arrays with more than 5000 elements. In order to simplify transducer design and system requirements, we proposed a 5 MHz PZT-P[VDF-TrFE] duallayer transducer array design before which used perpendicular 1-D arrays for 3-D imaging of targets near the transducer. This transducer design reduces the fabrication complexity and the channel count. As higher frequencies (> 5 MHz) are more commonly used clinically, in this paper, we present an 8 MHz planar dual-layer transducer array for 3-D rectilinear imaging. Meanwhile, regarding the clinical needs for 3-D transrectal ultrasound (TRUS), we also present a 5 MHz cylindrical duallayer transducer array here, which would be used for visualizing the prostate, guidance of biopsies, and monitoring therapeutic procedures. The flexibility of the copolymer material used in dual-layer scheme also makes it easy to mold around a cylindrical form. Performance of both arrays is verified through simulations and experiments.
2015 IEEE International Ultrasonics Symposium (IUS), 2015
Indocyanine green (ICG)-loaded droplets developed for photoacoustic imaging and drug delivery hav... more Indocyanine green (ICG)-loaded droplets developed for photoacoustic imaging and drug delivery have been tested for cavitation imaging in vitro. Perfluoropentane mixed with ICG was vaporized with a short pulse laser and expanded to 3-5 times the initial diameter of 2-5 micron and generated a strong broadband photoacoustic signal. It was found these vaporized droplets could be cavitated and ruptured by a short ultrasound pulses. To test the feasibility of cavitation imaging of laser-triggered droplets, broadband cavitation imaging algorithms were implemented on a commercial ultrasound open platform with a linear array transducer, centered at 5 MHz. Less than 3 cycles ultrasound excitation pulse with a MI of 0.7 was used to insonify a polyethylene tube of 580 μm inner diameter containing droplets to induce inertial cavitation activity. The cavitation imaging was performed before and after vaporizing droplets by laser pulses. Broadband emissions of 5-10 MHz were observed only after droplets were vaporized. These preliminary results demonstrate the feasibility of high resolution cavitation imaging of vaporized droplets using a short ultrasound excitation pulse and could lead to further in vivo experiments.
Fresnel beamforming is a beamforming method with a delay profile similar in shape to a physical F... more Fresnel beamforming is a beamforming method with a delay profile similar in shape to a physical Fresnel lens. The advantage of Fresnel beamforming is the reduced channel count, which consists of four to eight transmit and two analog-to-digital receive channels. Fresnel beamforming was found to perform comparably to conventional delay-and-sum beamforming. However, the performance of Fresnel beamforming is highly dependent on focal errors. These focal errors result in high side-lobe levels and further reduce the performance of Fresnel beamforming in the presence of phase aberration. With the advantages of lower side-lobe levels and suppression of aberration effects, harmonic imaging offers an effective solution to the limitations of Fresnel beamforming. We describe the implementation of tissue harmonic imaging and pulse inversion harmonic imaging in Fresnel beamforming, followed by dual apodization with cross-correlation, to improve image quality. Compared with conventional delay-and-sum beamforming, experimental results indicated contrast-to-noise ratio improvements of 10%, 49% and 264% for Fresnel beamforming using tissue harmonic imaging in the cases of no aberrator, 5-mm pork aberrator and 12-mm pork aberrator, respectively. These improvements were 22%, 57% and 352% for Fresnel beamforming using pulse inversion harmonic imaging. Moreover, dual apodization with cross-correlation was found to further improve the contrast-to-noise ratios in all cases. Harmonic imaging was also found to narrow the lateral beamwidth and shorten the axial pulse length by at least 25% and 21%, respectively, for Fresnel beamforming at different aberration levels. These results suggest the effectiveness of harmonic imaging in improving image quality for Fresnel beamforming, especially in the presence of phase aberration. Even though this combination of Fresnel beamforming and harmonic imaging does not outperform delay-and-sum beamforming combined with harmonic imaging, it provides the benefits of reduced channel count and potentially reduced cost and size of ultrasound systems. (
Because tissues consist of solid and fluid materials, their mechanical properties should be chara... more Because tissues consist of solid and fluid materials, their mechanical properties should be characterized in terms of both elasticity and viscosity. Although the elastic properties of tissue-mimicking phantoms have been extensively studied and well characterized in commercially available phantoms, their viscous properties have not been fully investigated. In this article, a set of 14 tissue-mimicking phantoms with different concentrations of gelatin and castor oil were fabricated and characterized in terms of acoustic and viscoelastic properties. The results indicate that adding castor oil to gelatin phantoms decreases shear modulus, but increases shear wave dispersion. For 3% gelatin phantoms containing 0%, 10%, 20% and 40% oil, the measured shear moduli are 2.01 ± 0.26, 1.68 ± 0.25, 1.10 ± 0.22 and 0.88 ± 0.17 kPa, and the Voigt-model coupled shear viscosities are 0.60 ± 0.11, 0.89 ± 0.07, 1.05 ± 0.11 and 1.06 ± 0.13 Pa$s, respectively. The results also confirm that increasing the gelatin concentration increases shear modulus. For phantoms containing 3%, 4%, 5%, 6% and 7% gelatin, the measured shear moduli are 2.01 ± 0.26, 3.10 ± 0.34, 4.18 ± 0.84, 8.05 ± 1.00 and 10.24 ± 1.80 kPa at 0% oil and 1.10 ± 0.22, 1.97 ± 0.20, 3.13 ± 0.63, 4.60 ± 0.60 and 8.43 ± 1.39 kPa at 20% oil, respectively. The phantom recipe developed in this study can be used in validating ultrasound shear wave elastography techniques for soft tissues. (
Elastography has become widely used for minimally invasive diagnosis in many tumors as seen with ... more Elastography has become widely used for minimally invasive diagnosis in many tumors as seen with breast, liver and prostate. Among different modalities, ultrasound-based elastography stands out due to its advantages including being safe, real-time, and relatively low-cost. While lung cancer is the leading cause of cancer mortality among both men and women, the use of ultrasound elastography for lung cancer diagnosis has hardly been investigated due to the limitations of ultrasound in air. In this work, we investigate the use of static-compression based endobronchial ultrasound elastography by a 3D trans-oesophageal echocardiography (TEE) transducer for lung cancer diagnosis. A water-filled balloon was designed to 1) improve the visualization of endobronchial ultrasound and 2) to induce compression via pumping motion inside the trachea and bronchiole. In a phantom study, we have successfully generated strain images indicating the stiffness difference between the gelatin background and agar inclusion. A similar strain ratio was confirmed with Philips ultrasound strain-based elastography product. For ex-vivo porcine lung study, different tissue ablation methods including chemical injection, Radio Frequency (RF) ablation, and direct heating were implemented to achieve tumor-mimicking tissue. Stiff ablated lung tissues were obtained and detected with our proposed method. These results suggest the feasibility of pulmonary elastography to differentiate stiff tumor tissue from normal tissue. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/05/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8675 867503-3 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/05/2013 Terms of Use: http://spiedl.org/terms
Fresnel beamforming is a beamforming method that has a delay profile with a shape similar to a ph... more Fresnel beamforming is a beamforming method that has a delay profile with a shape similar to a physical Fresnel lens. With 4 to 8 transmit channels, 2 receive channels, and a network of single-pole/single-throw switches, Fresnel beamforming can reduce the size, cost, and complexity of a beamformer. The performance of Fresnel beamforming is highly dependent on focal errors resulting from phase wraparound and quantization of its delay profile. Previously, we demonstrated that the performance of Fresnel beamforming relative to delayand-sum (DAS) beamforming is comparable for linear arrays at f-number = 2 and 50% bandwidth. However, focal errors for Fresnel beamforming are larger because of larger path length differences between elements, as in the case of curvilinear arrays compared with linear arrays. In this paper, we present the concept and performance evaluation of Fresnel beamforming combined with a novel clutter suppression method called dual apodization with cross-correlation (DAX) for curvilinear arrays. The contrast-to-noise ratios (CNRs) of Fresnel beamforming followed by DAX are highest at f-number = 3. At f-number = 3, the experimental results show that using DAX, the CNR for Fresnel beamforming improves from 3.7 to 10.6, compared with a CNR of 5.2 for DAS beamforming. Spatial resolution is shown to be unaffected by DAX. At f-number = 3, the lateral beamwidth and axial pulse length for Fresnel beamforming with DAX are 1.44 and 1.00 mm larger than those for DAS beamforming (about 14% and 21% larger), respectively. These experimental results are in good agreement with simulation results.
In this paper, we propose a modified electronic Fresnel-based beamforming method for low-cost por... more In this paper, we propose a modified electronic Fresnel-based beamforming method for low-cost portable ultrasound systems. This method uses a unique combination of analog and digital beamforming methods. Two versions of Fresnel beamforming are presented in this paper: 4-phase (4 different time delays or phase shifts) and 8-phase (8 different time delays or phase shifts). The advantage of this method is that a system with 4 to 8 transmit channels and 2 receive channels with a network of switches can be used to focus an array with 64 to 128 elements. The simulation and experimental results show that Fresnel beamforming image quality is comparable to traditional delay-and-sum (DAS) beamforming in terms of spatial resolution and contrast-to-noise ratio CNR) under certain system parameters. With an f-number of 2 and 50% signal bandwidth, the experimental lateral beamwidths are 0.54, 0.67, and 0.66 mm and the axial pulse lengths are 0.50, 0.51, and 0.50 mm for DAS, 8-phase, and 4-phase Fresnel beamforming, respectively. The experimental CNRs are 4.66, 4.42, and 3.98, respectively. These experimental results are in good agreement with simulation results.
The dif fi cul ties as so ci ated with fab ri ca tion and in ter con nec tion have lim ited the d... more The dif fi cul ties as so ci ated with fab ri ca tion and in ter con nec tion have lim ited the de vel op ment of 2-D ul tra sound trans ducer ar rays with a large num ber of el e ments (>5000). In pre vi ous work, we de scribed a 5 MHz cen ter fre quency PZT-P[VDF-TrFE] dual-layer trans ducer that used two per pen dic u lar 1-D arrays for 3-D rec ti lin ear im ag ing. This de sign sub stan tially re duces the chan nel count as well as fab ri cation com plex ity, which makes 3-D im ag ing more re al iz able. Higher fre quen cies (>5 MHz) are more com monly used in clin i cal applications or im ag ing tar gets near trans duc ers, such as the breast, ca rotid and musculoskeletal tissue. In this pa per, we pres ent a 7.5 MHz dual-layer trans ducer ar ray for 3-D rec tilin ear im ag ing. A mod i fied acoustic stack model was de signed and fabricated. PZT el e ments were sub-diced to elim i nate lat eral cou pling. This sub-dic ing pro cess made the PZT into a 2-2 com pos ite mate rial, which could help im prove trans ducer sen si tiv ity and band width. Full syn thetic-ap er ture 3-D data sets were ac quired by in ter fac ing the trans ducer with a Verasonics data-ac qui si tion sys tem (VDAS). Offline 3-D beamforming was then per formed to ob tain vol umes of a multiwire phan tom and a cyst phan tom. The gen er al ized coherence fac tor (GCF) was ap plied to im prove the con trast of cyst im ages. The mea sured -6 dB frac tional band width of the trans ducer was 71% with a cen ter fre quency of 7.5 MHz. The mea sured lat eral beam widths were 0.521 mm and 0.482 mm in az i muth and el e va tion, re spec tively, com pared with a sim u lated beam width of 0.43 mm.
Two-dimensional transrectal ultrasound (TRUS) is being used in guiding prostate biopsies and trea... more Two-dimensional transrectal ultrasound (TRUS) is being used in guiding prostate biopsies and treatments. In many cases, the TRUS probes are moved manually or mechanically to acquire volumetric information, making the imaging slow, user dependent, and unreliable. A real-time three-dimensional (3-D) TRUS system could improve reliability and volume rates of imaging during these procedures. In this article, the authors present a 5-MHz cylindrical dual-layer transducer array capable of real-time 3-D transrectal ultrasound without any mechanically moving parts. Compared with fully sampled 2-D arrays, this design substantially reduces the channel count and fabrication complexity. This dual-layer transducer uses PZT elements for transmit and P[VDF-TrFE] copolymer elements for receive, respectively. The mechanical flexibility of both diced PZT and copolymer makes it practical for transrectal applications. Full synthetic aperture 3-D data sets were acquired by interfacing the transducer with a Verasonics Data Acquisition System. Offline 3-D beamforming was then performed to obtain volumes of two wire phantoms and a cyst phantom. Generalized coherence factor was applied to improve the contrast of images. The measured −6-dB fractional bandwidth of the transducer was 62% with a center frequency of 5.66 MHz. The measured lateral beamwidths were 1.28 mm and 0.91 mm in transverse and longitudinal directions, respectively, compared with a simulated beamwidth of 0.92 mm and 0.74 mm.
Fresnel beamforming is a beamforming method that has a delay profile with a shape similar to a ph... more Fresnel beamforming is a beamforming method that has a delay profile with a shape similar to a physical Fresnel lens. With 4-8 transmit channels, 2 receive channels and a network of single-pole/single-throw switches, Fresnel beamforming can reduce the size, cost and complexity of a beamformer. The performance of Fresnel beamforming is highly dependent on focal errors due to phase wraparound and quantization of its delay profile. Compared to linear arrays, curvilinear arrays have larger path length differences among elements, which result in larger focal errors. In this paper, we present the concept and performance evaluation of Fresnel beamforming combined with a novel clutter suppression method, dual apodization with crosscorrelation (DAX), for curvilinear arrays. The spatial resolution and contrast-to-noise ratios (CNR) obtained from simulation and experiment show that Fresnel beamforming followed by DAX has higher CNR and comparable spatial resolution compared to delay-and-sum (DAS) beamforming. We also evaluate the performance of Fresnel beamforming in the presence of phase aberration and sound speed error.
This paper presents a new beamforming method that may reduce the size and cost of the system with... more This paper presents a new beamforming method that may reduce the size and cost of the system with minimized image quality tradeoffs. Applying optical Fresnel principles in ultrasound imaging, a system with 4 transmit and 2 receive channels can be used to steer and focus an array with 64 to 128 elements. The spatial resolution and contrast-to-noise ratios obtained from simulation and experiment show that the spatial resolution using an 8-phase Fresnel beamforming method is comparable to those values obtained from traditional delay-andsum beamforming.
In previous work, we successfully developed a 7.5 MHz dual-layer array transducer for 3-D rectili... more In previous work, we successfully developed a 7.5 MHz dual-layer array transducer for 3-D rectilinear imaging. This transducer significantly reduces the fabrication complexity and the channel count compared to fully sampled 2-D arrays, making 3-D imaging more realizable. Also, higher frequency (> 5 MHz) 3-D imaging can provide more accurate volume measurements, detection of cystic or cancerous masses, and also assist in 3-D ultrasound guided biopsy and carotid imaging. In this paper, we present our work toward real-time 3-D imaging with this transducer, including real-time data acquisition with the Verasonics data acquisition system (VDAS), offline beamforming and display for volumetric images. The volume rate was set as 30 volume/sec with a field of view equals to 19.2 x 19.2 x 42.2 mm 3 . Movies were created to present a real-time display of the moving phantoms of multiwire targets or cyst targets.
The difficulties associated with fabricating and connecting 2-D arrays with large numbers of elem... more The difficulties associated with fabricating and connecting 2-D arrays with large numbers of elements have limited the development of arrays with more than 5000 elements. In order to simplify transducer design and system requirements, we proposed a 5 MHz PZT-P[VDF-TrFE] duallayer transducer array design before which used perpendicular 1-D arrays for 3-D imaging of targets near the transducer. This transducer design reduces the fabrication complexity and the channel count. As higher frequencies (> 5 MHz) are more commonly used clinically, in this paper, we present an 8 MHz planar dual-layer transducer array for 3-D rectilinear imaging. Meanwhile, regarding the clinical needs for 3-D transrectal ultrasound (TRUS), we also present a 5 MHz cylindrical duallayer transducer array here, which would be used for visualizing the prostate, guidance of biopsies, and monitoring therapeutic procedures. The flexibility of the copolymer material used in dual-layer scheme also makes it easy to mold around a cylindrical form. Performance of both arrays is verified through simulations and experiments.