Hayong Jung

Cell Deformation by Single-beam Acoustic Trapping: A Promising Tool for Measurements of Cell Mechanics

We demonstrate a noncontact single-beam acoustic trapping method for the quantification of the mechanical properties of a single suspended cell with label-free. Experimentally results show that the single-beam acoustic trapping force results in morphological deformation of a trapped cell. While a cancer cell was trapped in an acoustic beam focus, the morphological changes of the immobilized cell were monitored using bright-field imaging. The cell deformability was then compared with that of a trapped polystyrene microbead as a function of the applied acoustic pressure for a better understanding of the relationship between the pressure and degree of cell deformation. Cell deformation was found to become more pronounced as higher pressure levels were applied. Furthermore, to determine if this acoustic trapping method can be exploited in quantifying the cell mechanics in a suspension and in a non-contact manner, the deformability levels of breast cancer cells with different degrees of invasiveness due to acoustic trapping were compared. It was found that highly-invasive breast cancer cells exhibited greater deformability than weakly-invasive breast cancer cells. These results clearly demonstrate that the single-beam acoustic trapping technique is a promising tool for non-contact quantitative assessments of the mechanical properties of single cells in suspensions with label-free.

High-resolution harmonic motion imaging (HR-HMI) for tissue biomechanical property characterization.

BACKGROUND Elastography, capable of mapping the biomechanical properties of biological tissues, serves as a useful technique for clinicians to perform disease diagnosis and determine stages of many diseases. Many acoustic radiation force (ARF) based elastography, including acoustic radiation force impulse (ARFI) imaging and harmonic motion imaging (HMI), have been developed to remotely assess the elastic properties of tissues. However, due to the lower operating frequencies of these approaches, their spatial resolutions are insufficient for revealing stiffness distribution on small scale applications, such as cancerous tumor margin detection, atherosclerotic plaque composition analysis and ophthalmologic tissue characterization. Though recently developed ARF-based optical coherence elastography (OCE) methods open a new window for the high resolution elastography, shallow imaging depths significantly limit their usefulness in clinics. METHODS The aim of this study is to develop a high-resolution HMI method to assess the tissue biomechanical properties with acceptable field of view (FOV) using a 4 MHz ring transducer for efficient excitation and a 40 MHz needle transducer for accurate detection. Under precise alignment of two confocal transducers, the high-resolution HMI system has a lateral resolution of 314 µm and an axial resolution of 
147 µm with an effective FOV of 2 mm in depth. RESULTS The performance of this high resolution imaging system was validated on the agar-based tissue mimicking phantoms with different stiffness distributions. These data demonstrated the imaging systems improved resolution and sensitivity on differentiating materials with varying stiffness. In addition, ex vivo imaging of a human atherosclerosis coronary artery demonstrated the capability of high resolution HMI in identifying layer-specific structures and characterizing atherosclerotic plaques based on their stiffness differences. CONCLUSIONS All together high resolution HMI appears to be a promising ultrasound-only technology for characterizing tissue biomechanical properties at the microstructural level to improve the image-based diseases diagnosis in multiple clinical applications.

New modified Butterworth Van-Dyke model for high frequency ultrasonic imaging

For ultrasonic transducers, a number of equivalent circuit models including KLM, Mason and Butterworth Van Dyke (BVD) have been developed. To allow them to be incorporated into design tools for complex integrated circuits, KLM or Mason models are not practical because the discrete components of the equivalent circuits have negative values. Therefore, BVD model appears to be more appropriate but it needs to be improved because the resolution of a high frequency ultrasound system may be severely affected by impedance mismatching between the transducer and the system, as well as attenuation due to parasitic impedances of the systems. A new modified BVD model has been developed and the results demonstrate its usefulness in modeling high frequency ultrasonic transducer and its imaging systems.

Ultrasonic scattering measurements of a live single cell at 86 MHz

Cell separation and sorting techniques have been employed biomedical applications such as cancer diagnosis and cell gene expression analysis. The capability to accurately measure ultrasonic scattering properties from cells is crucial in making an ultrasonic cell sorter a reality if ultrasound scattering is to be used as the sensing mechanism as well. To assess the performance of sensing and identifying live single cells with high-frequency ultrasound, an 86-MHz lithium niobate pressfocused single-element acoustic transducer was used in a highfrequency ultrasound scattering measurement system that was custom designed and developed for minimizing noise and allowing better mobility. Peak-to-peak echo amplitude, integrated backscatter (IB) coefficient, spectral parameters including spectral slope and intercept, and midband fit from spectral analysis of the backscattered echoes were measured and calculated from a live single cell of two different types on an agar surface: leukemia cells (K562 cells) and red blood cells (RBCs). The amplitudes of echo signals from K562 cells and RBCs were 48.25 ± 11.98 mV<;sub>pp<;/sub> and 56.97 ± 7.53 mV<;sub>pp<;/sub>, respectively. The IB coefficient was -89.39 ± 2.44 dB for K562 cells and -89.00 ± 1.19 dB for RBCs. The spectral slope and intercept were 0.30 ± 0.19 dB/MHz and -56.07 ± 17.17 dB, respectively, for K562 cells and 0.78 ± 0.092 dB/MHz and -98.18 ± 8.80 dB, respectively, for RBCs. Midband fits of K562 cells and RBCs were -31.02 ± 3.04 dB and -33.51 ± 1.55 dB, respectively. Acoustic cellular discrimination via these parameters was tested by Students t-test. Their values, except for the IB value, showed statistically significant difference (p <; 0.001). This paper reports for the first time that ultrasonic scattering measurements can be made on a live single cell with a highly focused high-frequency ultrasound microbeam at 86 MHz. These results also suggest the feasibility of ultrasonic scattering as a sensing mechanism in the development of ultrasonic cell sorters.

Harmonic distortion reduction technique of the power amplifier for very high frequency ultrasonic transducer applications

Power amplifiers are used to trigger the transducers in order to generate the acoustic waves into the desired target. The resolution of the ultrasound imaging systems is related with the sensitivity of the transducers so the high voltage output signals of the power amplifiers are required to be used to drive the transducers. Therefore, a linear power amplifier is more attractive choice because of its higher dynamic range of the output signals. The novel pre-distortion circuit using the passive resistor, capacitor and inductor components with a power MOSFET device was designed to enhance the dynamic range of the power amplifiers. The dynamic range of the power amplifiers is defined as the characteristic to amplify an input signal with less distortion. This characteristic can be improved by reducing the harmonic distortion components of the high voltage signals produced by the power amplifiers.

Functional Assay of Cancer Cell Invasion Potential Based on Mechanotransduction of Focused Ultrasound

Cancer cells undergo a number of biophysical changes as they transform from an indolent to an aggressive state. These changes, which include altered mechanical and electrical properties, can reveal important diagnostic information about disease status. Here, we introduce a high-throughput, functional technique for assessing cancer cell invasion potential, which works by probing for the mechanically excitable phenotype exhibited by invasive cancer cells. Cells are labeled with fluorescent calcium dye and imaged during stimulation with low-intensity focused ultrasound, a non-contact mechanical stimulus. We show that cells located at the focus of the stimulus exhibit calcium elevation for invasive prostate (PC-3 and DU-145) and bladder (T24/83) cancer cell lines, but not for non-invasive cell lines (BPH-1, PNT1A, and RT112/84). In invasive cells, ultrasound stimulation initiates a calcium wave that propagates from the cells at the transducer focus to other cells, over distances greater than 1 mm. We demonstrate that this wave is mediated by extracellular signaling molecules and can be abolished through inhibition of transient receptor potential channels and inositol trisphosphate receptors, implicating these proteins in the mechanotransduction process. If validated clinically, our technology could provide a means to assess tumor invasion potential in cytology specimens, which is not currently possible. It may therefore have applications in diseases such as bladder cancer, where cytologic diagnosis of tumor invasion could improve clinical decision-making.

Wideband portable power amplifier design for very high frequency ultrasonic transducer applications

This paper describes the design of Class A wideband power amplifier (PA) for very high frequency ultrasonic transducer applications with power field-effect transistor (FET). The PA is a one-stage common-source amplifier with 28 V supply voltage. The measured gain of the PA is 15.8 ~ 17.8 dB in the range of 100 to 250 MHz and current consumption of the PA is 0.3 ~ 0.4 A. The measured 3rd-order input and output inter-modulation points (IIP3 and OIP3) of the PA are 12.25 dBm and 27.25 dBm, respectively and the measured noise figure of the PA is 2.14~2.98 dB in the range of 80~120MHz.

Characterizing Deformability of Drug Resistant Patient-Derived Acute Lymphoblastic Leukemia (ALL) Cells Using Acoustic Tweezers

The role of cell mechanics in cancer cells is a novel research area that has resulted in the identification of new mechanisms of therapy resistance. Single beam acoustic (SBA) tweezers are a promising technology for the quantification of the mechanical phenotype of cells. Our previous study showed that SBA tweezers can be used to quantify the deformability of adherent breast cancer cell lines. The physical properties of patient-derived (primary) pre-B acute lymphoblastic leukemia (ALL) cells involved in chemotherapeutic resistance have not been widely investigated. Here, we demonstrate the feasibility of analyzing primary pre-B ALL cells from four cases using SBA tweezers. ALL cells showed increased deformability with increasing acoustic pressure of the SBA tweezers. Moreover, ALL cells that are resistant to chemotherapeutic drugs were more deformable than were untreated ALL cells. We demonstrated that SBA tweezers can quantify the deformability of nonadherent leukemia cells and discriminate this mechanical phenotype in chemotherapy-resistant leukemia cells in a contact- and label-free manner.

Integrated high frequency linear transducer array for needle biopsy probe

We are developing a high frequency ultrasound imaging array for a needle biopsy probe. The goal of this work is to integrate a 64 channel high frequency linear array fabricated using PMN-PT transducer material alongside a high voltage CMOS ASIC. The ASIC is designed to multiplex the signals from the array to a single cable for synthetic aperture imaging. In this paper we discuss some of the challenges in this development and present initial results. The 64 channel transducer array was first assembled to a single layer flex circuit using gold bumps and silver-loaded epoxy. Pulse/echo data was obtained for this first prototype assembly. In addition to the gold bumped assembly, we have used silver coated glass beads and silver epoxy for assembly, and present initial results for this assembly as well.

Design of a high voltage 1 to 64 Mux/De-Mux for high frequency synthetic aperture imaging

In this paper, a high voltage 1 to 64 Mux / De-Mux is proposed using a high voltage CMOS process for a high frequency synthetic aperture imaging system. The controlling stage is made up of a low voltage 6 to 64 decoder with additional enable controlling logic. A low voltage (0V~3.3V) to high voltage (-18V~+18V) level shifter structure is used to change the controlled voltage potential. The high voltage Mux/De-Mux is comprised of two source-connected DNMOS pairs at each channel as a switch. The experimental results show that the switch has a 3-dB bandwidth over 70 MHz, and 180 ohms of on-resistance, -2.635 dB of insertion loss, and -26.5261 dB of off-isolation at 70MHz.