Search

Localized, non-invasive cell stimulation has many applications. Here we show the initial proof-of-concept in vitro study of the photoacoustic cell stimulation approach, which is amenable to high-throughput screening applications. The proposed method is implemented as follows: 1) the localized excitation using the focused pulsed laser delivery on an absorptive material placed inside the well containing the cells, 2) cell stimulation by the photoacoustic pressure generated, and 3) fluorescence quantification of the membrane potential change over time. The preliminary proof-ofconcept in vitro study is conducted with primary neurons isolated from mouse cerebral cortex. The absorptive rubber media generates the photoacoustic pressure by the pulsed laser excitation. The experimental results show the feasibility of photoacoustic cell stimulation approach by indicating the significant membrane potential chance from the photoacoustically-stimulated primary neurons. Otherwise, the sham control without any photoacoustic stimulation shows minimal membrane potential change. We envisage that the proposed approach can allow broad strategies for noninvasive cell stimulation by using the photoacoustic contrasts situated at inside or outside of the body such as external absorptive materials or intravascularly-injected photoacoustic contrast particles.

Recently, a portable US imaging system using smart devices is highlighted for enhancing the portability of diagnosis. Especially, the system combination can enhance the user experience during whole US diagnostic procedures by employing the advanced wireless communication technology integrated in a smart device, e.g., WiFi, Bluetooth, etc. In this paper, an effective post-phase rotation-based dynamic receive beamforming (PRBF-POST) method is presented for wireless US imaging device integrating US probe system and commercial smart device. In conventional, the frame rate of conventional PRBF (PRBF-CON) method suffers from the large amount of calculations for the bifurcated processing paths of in-phase and quadrature signal components as the number of channel increase. Otherwise, the proposed PRBF-POST method can preserve the frame rate regardless of the number of channels by firstly aggregating the baseband IQ data along the channels whose phase quantization levels are identical ahead of phase rotation and summation procedures on a smart device. To evaluate the performance of the proposed PRBF-POST method, the pointspread functions of PRBF-CON and PRBF-POST methods were compared each other. Also, the frame rate of each PRBF method was measured 20-times to calculate the average frame rate and its standard deviation. As a result, the PRBFCON and PRBF-POST methods indicates identical beamforming performance in the Field-II simulation (correlation coefficient = 1). Also, the proposed PRBF-POST method indicates the consistent frame rate for varying number of channels (i.e., 44.25, 44.32, and 44.35 fps for 16, 64, and 128 channels, respectively), while the PRBF-CON method shows the decrease of frame rate as the number of channel increase (39.73, 13.19, and 3.8 fps). These results indicate that the proposed PRBF-POST method can be more advantageous for implementing the wireless US imaging system than the PRBF-CON method.

Ultrasonography has been conducting a critical role in assessing abdominal disorders due to its noninvasive, real-time, low cost, and deep penetrating capabilities. However, for imaging obese patients with a thick fat layer, it is challenging to achieve appropriate image quality with a conventional beamforming (CON) method due to phase aberration caused by the difference between sound speeds (e.g., 1580 and 1450m/s for liver and fat, respectively). For this, various sound speed correction (SSC) methods that estimate the accumulated sound speed for a region-of interest (ROI) have been previously proposed. However, with the SSC methods, the improvement in image quality was limited only for a specific depth of ROI. In this paper, we present the adaptive sound speed correction (ASSC) method, which can enhance the image quality for whole depths by using estimated sound speeds from two different depths in the lower layer. Since these accumulated sound speeds contain the respective contributions of layers, an optimal sound speed for each depth can be estimated by solving contribution equations. To evaluate the proposed method, the phantom study was conducted with pre-beamformed radio-frequency (RF) data acquired with a SonixTouch research package (Ultrasonix Corp., Canada) with linear and convex probes from the gel pad-stacked tissue mimicking phantom (Parker Lab. Inc., USA and Model539, ATS, USA) whose sound speeds are 1610 and 1450m/s, respectively. From the study, compared to the CON and SSC methods, the ASSC method showed the improved spatial resolution and information entropy contrast (IEC) for convex and linear array transducers, respectively. These results indicate that the ASSC method can be applied for enhancing image quality when imaging obese patients in abdominal ultrasonography.

In medical ultrasound imaging, dynamic receive beamforming has been used for improving signal-to-noise ratio (SNR) and spatial resolution. For low-cost portable ultrasound imaging systems, a fractional filter-based receive beamforming (FFRB) method was previously proposed to reduce the hardware complexity compared to conventional interpolation filter-based receive beamforming methods (IFRB). While this new beamforming method substantially reduces the hardware complexity, it yields the nonlinear phase response for high frequencies due to the limited length of fractional filter coefficients, leading to the bias on flow estimation in ultrasound color Doppler imaging. In this paper, to evaluate the FFRB method for ultrasound color Doppler imaging, the Field II simulation and string phantom experiments were conducted. In Field II simulation, the radio-frequency (RF) data were generated by assuming a 7.5-MHz linear array probe with the transmit frequency of 6 MHz, the ensemble size of 8, and the sampling frequencies of 20 MHz. In string phantom experiments, the RF channel data were obtained with a commercial SonixTouch ultrasound scanner equipped with a research package (Ultrasonix Corp., Vancouver, BC, Canada) and a 5-MHz linear array connected to a SonixDAQ parallel system. The ensemble size and the sampling frequency were set to 10 and 20 MHz, respectively. For the Field II simulation and string phantom experiments, only 1.2% and 2.3 % in color Doppler estimation error ratio was observed with mean and standard deviation along the lateral direction. This result indicates that the proposed FFRB method could be utilized for a low-cost ultrasound color Doppler imaging system with lowered hardware complexity and minimized phase errors.

In photoacoustic imaging, an adaptive beamforming method with coherence factor (ABF-CF) was previously introduced for improving spatial resolution and signal-to-noise ratio (SNR) over a conventional delay-and-sum beamforming method (DAS). However, the ABF-CF method is not suitable for being used in practical diagnosis since it is overly-sensitive for off-axis interferences and noises. In this paper, a new adaptive beamforming method with spatially-smoothed coherence factor (ABF-SSCF) is presented for ultrasound and photoacoustic combined imaging to enhance the contrast and spatial resolution while preserving the target information by applying a spatial-smoothing technique into CF coefficients from multiple sub-arrays within an array probe. To evaluate the ABF-SSCF method, computer simulation and ex vivo experiments were conducted. For the computer simulation, 64-channel radio-frequency (RF) data with one channel amplitude-varying off-axis interference was generated. Also, The ex vivo experiments were conducted where 128-channel pre-beamformed RF data were captured from a microcalcification-contained breast core specimen with a commercial ultrasound system equipped with a research package by using a 7-MHz linear array probe (SonixTouch, Ultrasonix Corp., BC, Canada) and an Nd:Yag laser excitation system (Surelite III-10 and Surelite OPO Plus, Continuum Inc., Santa Clara, CA, USA). From the simulation and ex vivo experiments, the proposed ABF-SSCF method provides better contrast and spatial resolutions comparable than the DAS method. Also, compared to the ABFCF method, image information is clearly presented without being degraded by off-axis interferences. These results indicate that the proposed ABF-SSCF method can simultaneously enhance the image quality and efficacy of the ABF method for ultrasound and photoacoustic combined imaging.

In medical ultrasound imaging, a multi-beamforming (MBF) method is used for supporting high frame rate imaging or functional imaging where multiple scanlines are reconstructed from a single excitation event. For efficient MBF, a time-sharing technique (i.e., MBF-TS) can be applied. However, the MBF-TS could degrade image quality due to the decreased beamforming frequency. In this paper, the multi-access register-based MBF (MBF-MAR) method running on the post-fractional filtering (PFF) architecture is presented. In PFF-MBF-MAR, instead of lowering beamforming frequency, a multi-access register at each channel is utilized for generating multiple scanlines simultaneously. To evaluate the performance of the proposed PFF-MBF-MAR method, the phantom experiment was conducted where 64- channel pre-beamformed radio-frequency (RF) data were captured from a tissue mimicking phantom by using a modified commercial ultrasound system (SONOLINE G40, Siemens Inc., USA) using a 3-MHz phased array probe. From the phantom experiment, the PFF-MBF-MAR method showed 4.7 dB and 0.6 improvements in the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR), respectively, compared to the PFF-MBF-TS method, while slightly increasing the hardware complexity (