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Abstract: In an ultrasound image-guided High Intensity Focused Ultrasound (HIFU) surgery, reflected HIFU waves received by an imaging transducer should be suppressed for real-time simultaneous imaging and therapy. In this paper, we investigate the feasibility of pulse compression scheme combined with notch filtering in order to minimize these HIFU interference signals. A chirp signal modulated by the Dolph–Chebyshev window with 3–9MHz frequency sweep range is used for B-mode imaging and 4MHz continuous wave is used for HIFU. The second order infinite impulse response notch filters are employed to suppress reflected HIFU waves whose center frequencies are 4MHz and 8MHz. The prototype integrated HIFU/imaging transducer that composed of three rectangular elements with a spherically con-focused aperture was fabricated. The center element has the ability to transmit and receive 6MHz imaging signals and two outer elements are only used for transmitting 4MHz continuous HIFU wave. When the chirp signal and 4MHz HIFU wave are simultaneously transmitted to the target, the reflected chirp signals mixed with 4MHz and 8MHz HIFU waves are detected by the imaging transducer. After the application of notch filtering with pulse compression process, HIFU interference waves in this mixed signal are significantly reduced while maintaining original imaging signal. In the single scanline test using a strong reflector, the amplitude of the reflected HIFU wave is reduced to −45dB. In vitro test, with a sliced porcine muscle shows that the speckle pattern of the restored B-mode image is close to that of the original image. These preliminary results demonstrate the potential for the pulse compression scheme with notch filtering to achieve real-time ultrasound image-guided HIFU surgery. [Copyright &y& Elsevier]

Abstract: Coded tissue harmonic imaging with pulse inversion (CTHI-PI) based on a linear chirp signal can improve the signal-to-noise ratio with minimizing the peak range sidelobe level (PRSL), which is the main advantage over CTHI with bandpass filtering (CTHI-BF). However, the CTHI-PI technique could suffer from motion artifacts due to decreasing frame rate caused by two firings of opposite phase signals for each scanline. In this paper, a new CTHI method based on a nonlinear chirp signal (CTHI-NC) is presented, which can improve the separation of fundamental and harmonic components without sacrificing frame rate. The nonlinear chirp signal is designed to minimize the PRSL value by optimizing its frequency sweep rate and time duration. The performance of the CTHI-NC method was evaluated by measuring the PRSL and mainlobe width after compression. From the in vitro experiments, the CTHI-NC provided the PRSL of −40.6dB and the mainlobe width of 2.1μs for the transmit quadratic nonlinear chirp signal with the center frequency of 2.1MHz, the fractional bandwidth at −6dB of 0.6 and the time duration of 15μs. These results indicate that the proposed method could be used for improving frame rates in CTHI while providing comparable image quality to CTHI-PI. [ABSTRACT FROM AUTHOR]

Abstract: An acoustic guidance method for pedicle screw placement during spine fixation surgery was recently investigated, with a view toward preventing complications such as injury to the spinal cord, thecal sac, and spinal nerve roots due to screw misplacement. The method relies upon the change in the ultrasound amplitude reflected at different sites—from the outer posterior cortex, through the pedicle, and towards the distal ventral cortex. The amplitude change was empirically observed through in vitro measurement of ultrasound amplitude at the different sites by inserting a 2.5-MHz single element transducer into a vertebral body through insertion pathway created by an advancing screw. This paper provides a theoretical and experimental rationale behind these empirical findings and distance-dependent correlation coefficients between amplitude and bone mineral density within the vertebral body, which approached 97%. [ABSTRACT FROM AUTHOR]

Abstract: Background context: In pedicle screw fixation surgery, rigid instruments are inserted into a vertebral body. When the instruments are misdirected within the pedicle or advanced too far beyond it, perforations of the inner or outer cortex can cause damage to the spinal nerve roots and spinal cord. These complications can occur despite the use of imaging modalities, such as radiographs, fluoroscopy, and computerized axial tomography (CAT) scans. A-Mode ultrasound (US), a nonionizing modality, merits study for its possible use in such a type of surgery. Purpose: The purpose of the study was to determine the utility of A-mode US during pedicle screw placement, to characterize the approach to the marrow-cortex interface, and to obtain the signature profiles of cortex perforations. Study design: A-Mode data were generated on insertion of a forward-viewing transducer (FVT) and a side-viewing transducer (SVT) to successively greater drilled depths along the insertion pathway. A-Mode broadband US backscatter (BUB) pedicle screw emulation experiments were conducted with transducers inserted into drilled sheep vertebral bodies. BUB amplitude patterns were observed and analyzed. Descriptive statistics were used. Methods: In vitro acoustic experiments on vertebral bodies in a water bath were performed with two 1-MHz unfocused transducers to measure sound speed, broadband US attenuation, and backscatter coefficients. Micro-CAT scan three-dimensional (3-D) images of 10 disarticulated vertebral bodies were obtained pre- and postdrilling done in 5-mm depth increments with a flat-bottom drill. BUB patterns were noted of transducers inserted through rostral outer cortex, through the pedicle, and advanced to the ventral marrow-cortex interface. 2.5-MHz FVT and SVT were co-advanced in successive 5-mm increments along the insertion pathway, with BUBs measured at each point and the echoes composited into a single figure. Deliberate perforations of ventral cortex were made. Results: Evident patterns or measures indicating the proximity of the ventral marrow-cortex interface were: 1) marrow BUB values increasing in amplitude over three distal peaks in most FVT cases (7 out of 10) and SVT cases (9 out of 10); 2) BUB ratio of marrow-cortex interface to the smallest marrow value greater than 2, in all FVT cases (10 out of 10) with FVT mean of 4.00±1.82 (2.25–8.33); and 3) a ratio of distal BUB value to starting cortex BUB in the 0. 82 to 1.62 range (mean, 0.98±0.30) in 80% of FVT cases. Ventral FVT perforations resulted in a major drop in the BUB value. Conclusions: The increase in the BUB amplitudes in the distal insertion pathway suggests that, at least with a 2.5-MHz transducer, an approximate 1.5-cm US window exists in most cases, by which close approach of the ventral marrow-cortex interface could be anticipated. Other ratios may serve as stop criteria to prevent further drilling. A precipitous drop in BUB amplitude may be an indication of a cortex perforation. [Copyright &y& Elsevier]

Abstract: This paper proposes a frequency compounding method to reduce speckle interferences, where a concentric annular type high-frequency dual element transducer is used to broaden the bandwidth of an imaging system. In frequency compounding methods, frequency division is carried out to obtain sub-band images containing uncorrelated speckles, which sacrifices axial resolution. Therefore, frequency compounding often deteriorates the target-detecting capability, quantified by the total signal-to-noise ratio (SNR), when the speckle’s SNR (SSNR) is not improved as much as the degraded axial resolution. However, this could be avoided if the effective bandwidth required for frequency compounding is increased. The primary goal of the proposed approach, hence, is to improve SSNR by a factor of two under the condition where axial resolution is degraded by a factor of less than two, which indicates the total SNR improvement to higher than 40% compared to that of an original image. Since the method here employs a dual element transducer operating at 20 and 40MHz, the effective bandwidth necessary for frequency compounding becomes broadened. By dividing each spectrum of RF samples from both elements into two sub-bands, this method eventually enables four sets of the sub-band samples to contain uncorrelated speckles. This causes the axial resolution to be reduced by a factor of as low as 1.85, which means that this method would improve total SNR by at least 47%. An in vitro experiment on an excised pig eye was performed to validate the proposed approach, and the results showed that the SSNR was improved from 2.081±0.365 in the original image to 4.206±0.635 in the final compounding image. [Copyright &y& Elsevier]

Abstract: Electrochemical supercapacitive behaviour of polyaniline nanostructures, i.e., nanorods and nanospheres fabricated on aniline-primed conducting indium–tin oxide substrate via electroless surface polymerization using ammonium persulfate as initiator and selenious acid as efficient dopant is investigated. The self-assembled monolayer of urea derivative in presence of 3-(triethoxysilyl)-propyl isocyanate and aniline plays role of aniline-primed substrate. Polyaniline electrode composed of nanorods of excess surface area responsible for large redox reactions has shown 592Fg−1 specific capacitance which is significantly greater than closely compact polyaniline nanospheres, i.e., 214Fg−1. [Copyright &y& Elsevier]

Abstract: This paper presents a high-speed digital scan converter (DSC) capable of providing more than 400 images per second, which is necessary to examine the activities of the mouse heart whose rate is 5–10 beats per second. To achieve the desired high-speed performance in cost-effective manner, the DSC developed adopts a linear interpolation algorithm in which two nearest samples to each object pixel of a monitor are selected and only angular interpolation is performed. Through computer simulation with the Field II program, its accuracy was investigated by comparing it to that of bilinear interpolation known as the best algorithm in terms of accuracy and processing speed. The simulation results show that the linear interpolation algorithm is capable of providing an acceptable image quality, which means that the difference of the root mean square error (RMSE) values of the linear and bilinear interpolation algorithms is below 1%, if the sample rate of the envelope samples is at least four times higher than the Nyquist rate for the baseband component of echo signals. The designed DSC was implemented with a single FPGA (Stratix EP1S60F1020C6, Altera Corporation, San Jose, CA) on a DSC board that is a part of a high-speed ultrasound imaging system developed. The temporal and spatial resolutions of the implemented DSC were evaluated by examining its maximum processing time with a time stamp indicating when an image is completely formed and wire phantom testing, respectively. The experimental results show that the implemented DSC is capable of providing images at the rate of 400 images per second with negligible processing error. [Copyright &y& Elsevier]

An electrical impedance matching (EIM) network is proposed to achieve the broad bandwidth of a high frequency ultrasound transducer and to improve the signal-to-noise ratio (SNR) of an ultrasound image. The proposed EIM network is based on a general filter structure, i.e., either low-pass filter (LPF) or high-pass filter (HPF) structure composing a capacitor and an inductor. Either filter type can be selected depending on the spectral characteristics of a transducer. The prominent advantage of the proposed method is the capability to broaden the spectrum of a transducer by means of modifying its original spectrum. The values of the electronic components are computed with the measured electrical impedances of a transducer and an imaging system. In this paper, the EIM between a custom-made 50 MHz ultrasound needle transducer and a commercial pulser/receiver system was conducted to verify the characteristics and performance of the proposed method. The experimental results demonstrated that the proposed EIM network is capable of achieving the best performance of the transducer, i.e., broad bandwidth and high SNR that are desirable for the high quality of high frequency ultrasound images. [ABSTRACT FROM AUTHOR]

Abstract: Effective receive beamforming in medical ultrasound imaging is important for enhancing spatial and contrast resolution. In current ultrasound receive beamforming, a constant sound speed (e.g., 1540m/s) is assumed. However, the variations of sound speed in soft tissues could introduce phase distortions, leading to degradation in spatial and contrast resolution. This degradation becomes even more severe in imaging fatty tissues (e.g., breast) and with obese patients. In this paper, a mean sound speed estimation method where phase variance of radio-frequency channel data in the region of interest is evaluated is presented for improving spatial and contrast resolution. The proposed estimation method was validated by the Field II simulation and the tissue mimicking phantom experiments. In the simulation, the sound speed of the medium was set to 1450m/s and the proposed method was capable of capturing this value correctly. From the phantom experiments, the −18-dB lateral resolution of the point target at 50mm obtained with the estimated mean sound speed was improved by a factor of 1.3, i.e., from 3.9mm to 2.9mm. The proposed estimation method also provides an improvement of 0.4 in the contrast-to-noise ratio, i.e., from 2.4 to 2.8. These results indicate that the proposed mean sound speed estimation method could enhance the spatial and contrast resolution in the medical ultrasound imaging systems. [Copyright &y& Elsevier]

Accumulation of surficial tidal mud was observed in Muan Bay, Korea, to examine seasonal sedimentary cycles typical of semienclosed bays in contrast with open coast in the southeastern Yellow Sea. One-year monitoring of accumulation rates on the tidal flats indicates that patterns of deposition/erosion can be diverse according to both physiographic setting and seasons. During winter, tidal flats undergo slight deposition to moderate erosion depending on localities. In summer, however, the tidal flats are all consistently subject to stronger erosion. Meteorological data suggest that the erosional effect on the tidal flat might come from heavy rainfall during flooding seasons and possibly typhoon. The enduring rainfall could cause the exposed surface of the tidal flat to be sufficiently weakened for tidal currents alone to strip surficial mud off. [Copyright &y& Elsevier]

• SAF and CFW have been used for enhanced resolution of ultrasound imaging. • We ascertained the effectiveness of SAF and CFW for intravascular ultrasound (IVUS) imaging. • From the results, it was found that SAF is not effective for IVUS imaging. • A focused transducer without SAF and CFW may be the best choice for enhanced resolution. Synthetic aperture focusing (SAF) and coherence factor weighting (CFW) have been used to improve the lateral resolution of ultrasound images. Although the two methods are effective for array-based ultrasound imaging, many researchers have also employed the methods for single-element-based imaging including intravascular ultrasound (IVUS) imaging. For single-element-based imaging, CFW is generally calculated from the scanlines obtained by SAF and applied to the scanline obtained after coherent summation of the SAF delayed scanlines, which is called a SAF-CFW method. In the paper, a theoretical model was derived to explore the effectiveness of SAF and CFW for single-element-based imaging, and the model was used to explain that SAF is not effective for IVUS imaging in terms of enhancing the spatial resolution, although it has the advantage of improving a contrast-to-noise ratio (CNR). This means that the SAF-CFW method is not optimal for improving the spatial resolution of IVUS imaging. In contrast, it was found in simulations and experiments that applying CFW to the target scanline itself is beneficial for the spatial resolution rather than a coherent summed scanline for IVUS SAF imaging, but CNR was not as good as SAF and SAF-CFW. As a result of both simulation and experimentation, it could be concluded that focused IVUS transducers without the application of those methods may be more advantageous to improve the spatial and contrast resolution simultaneously, considering the system complexity in the implementation of such imaging methods. [ABSTRACT FROM AUTHOR]

Exosomes, which are released from all cells and take part in cell-to-cell communication, have been utilized as drug delivery vehicles in many recent studies. Immunotherapy is an emerging technology which uses patients' innate immune systems. In immunotherapy, immune cells are stimulated through antibodies, the other immune cells and genetic modifications for the purposes of, for instance, cancer therapy. In this study, tumor-derived re-assembled exosome (R-Exo) was simultaneously utilized as both a drug delivery carrier and an immunostimulatory agent. A chlorin e6 photosensitizer was loaded into tumor-derived exosomes during exosomal re-assembly. After this modification, R-Exo retains its original average size and has the same membrane proteins, which allows for targeting of tumor cells. Chlorin e6-loaded R-Exo (Ce6-R-Exo) can be visualized by photoacoustic imaging and can efficiently generate reactive oxygen species inside tumor cells under laser irradiation. In addition, Ce6-R-Exo increased the release of cytokines from immune cells, which indicates that these modified exosomes can be used as an immunotherapeutic agent. In conclusion, we developed a novel strategy that enables photoacoustic imaging-guided photodynamic and immune-combination therapy for the treatment of cancer with tumor-derived Ce6-R-Exo. Image 1 [ABSTRACT FROM AUTHOR]

• Ultrasound therapy requires real-time monitoring during treatment. • The use of focused ultrasound (FUS) transducers for the purpose is limited due to their inability to provide high quality of images. • The proposed coded excitation and Wiener deconvolution can enhance the resolution, SNR, and CNR of images acquired by FUS transducers. • The performance of the proposed method was confirmed by imaging experiments. To enhance the effectiveness and safety of focused ultrasound (FUS) therapy, ultrasound image-based guidance and treatment monitoring are crucial. However, the use of FUS transducers for both therapy and imaging is impractical due to their low spatial resolution, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). To address this issue, we propose a new method that significantly improve the quality of images obtained by a FUS transducer. The proposed method employs coded excitation to enhance SNR and Wiener deconvolution to solve the problem of low axial resolution resulting from the narrow spectral bandwidth of FUS transducers. Specifically, the method eliminates the impulse response of a FUS transducer from received ultrasound signals using Wiener deconvolution, and pulse compression is performed using a mismatched filter. Simulation and commercial phantom experiments confirmed that the proposed method significantly improves the quality of images acquired by the FUS transducer. The −6 dB axial resolution was improved 1.27 mm to 0.37 mm that was similar to the resolution achieved by the imaging transducer, i.e., 0.33 mm. SNR and CNR also increased from 16.5 dB and 0.69 to 29.1 dB and 3.03, respectively, that were also similar to those by the imaging transducer (27.8 dB and 3.16). Based on the results, we believe that the proposed method has great potential to enhance the clinical utility of FUS transducers in ultrasound image-guided therapy. [ABSTRACT FROM AUTHOR]

Biomedical imaging-guided cancer therapy should have capabilities of both accurate tumor diagnosis and high therapeutic efficacy for the personalized treatment. Various biomedical imaging-guided cancer therapies are currently being investigated to overcome current limitations that include low sensitivity of diagnosis and poor drug delivery to the tumor site. Here, we report the development of a multifunctional theranostic contrast agent demonstrating high sensitive photoacoustic and ultrasound imaging and effective local delivery of anticancer drug to a tumor site. A microbubble (porphyrin-MB) was developed using phospholipid–porphyrin conjugates to enhance ultrasound and photoacoustic signal intensities simultaneously. Paclitaxel-loaded human serum albumin nanoparticles (PTX-HSA-NPs) were then conjugated onto the surface of the microbubble. The developed PTX-HSA-NPs conjugated porphyrin-MB (porphyrin-MB-NPs) provided sensitive, dual modal images of a tumor at 700 nm optimal laser wavelength for photoacoustic imaging and 5–14 MHz operating frequency for the ultrasound imaging. In addition, porphyrin-MB-NPs efficiently suppressed tumor growth by ultrasound exposure. Exposure to the focused ultrasound triggered the collapse of porphyrin-MB-NPs, resulting in the local release of PTX-HSA-NPs and enhanced penetration into the tumor site. The increased preferential accumulation and penetration of PTX-HSA-NPs suppressed tumor growth 10-fold more than without exposure to ultrasound. In conclusion, the developed porphyrin-MB-NPs establish a new paradigm in simultaneous bi-functional ultrasound/photoacoustic imaging diagnosis and locally triggered release of nanomedicine and enhanced chemotherapy efficiency. [ABSTRACT FROM AUTHOR]

Photoacoustic imaging is the latest promising diagnostic modality that has various advantages such as high spatial resolution, deep penetration depth, and use of non-ionizing radiation. It also employs a non-invasive imaging technique and optically functionalized imaging. The goal of this study was to develop a nanomedicine for simultaneous cancer therapy and diagnosis based on photoacoustic imaging. Human serum albumin nanoparticles loaded with melanin and paclitaxel (HMP-NPs) were developed using the desolvation technique. The photoacoustic-based diagnostic and chemotherapeutic properties of HMP-NPs were evaluated through in vitro and in vivo experiments. The size and zeta potential of the HMP-NPs were found to be 192.8 ± 21.11 nm and − 22.2 ± 4.39 mV, respectively. In in vitro experiments, HMP-NPs produced increased photoacoustic signal intensity because of the loaded melanin and decreased cellular viability because of the encapsulated paclitaxel, compared to the free human serum albumin nanoparticles (the control). In vivo experiments showed that the HMP-NPs efficiently accumulated inside the tumor, resulting in the enhanced photoacoustic signal intensity in the tumor site, compared to the normal tissues. The in vivo chemotherapy study demonstrated that HMP-NPs had the capability to treat cancer for an extended period. In conclusion, HMP-NPs were simultaneously capable of photoacoustic diagnostic and chemotherapy against cancer. [ABSTRACT FROM AUTHOR]