Dual Frequency Probe Research Articles

Brillouin frequency shift measurement by zero-crossing point search in virtually synthesized spectra of Brillouin gain and loss

We demonstrate a method for fast and precise Brillouin frequency shift measurement based on searching for the zero-crossing point of a virtually composed spectrum of Brillouin gain and loss obtained by a dual-frequency probe beam. Simulations and experiments show that searching for the zero-crossing point of a virtually synthesized Brillouin gain spectrum can be easily done without a large error compared with peak search of the Brillouin gain spectrum in the conventional method.

Characterization of an Array-Based Dual-Frequency Transducer for Superharmonic Contrast Imaging.

Superharmonic imaging with dual-frequency imaging systems uses conventional low-frequency ultrasound transducers on transmit, and high-frequency transducers on receive to detect higher order harmonic signals from microbubble contrast agents, enabling high-contrast imaging while suppressing clutter from background tissues. Current dual-frequency imaging systems for superharmonic imaging have been used for visualizing tumor microvasculature, with single-element transducers for each of the low- and high-frequency components. However, the useful field of view is limited by the fixed focus of single-element transducers, while image frame rates are limited by the mechanical translation of the transducers. In this article, we introduce an array-based dual-frequency transducer, with low-frequency and high-frequency arrays integrated within the probe head, to overcome the limitations of single-channel dual-frequency probes. The purpose of this study is to evaluate the line-by-line high-frequency imaging and superharmonic imaging capabilities of the array-based dual-frequency probe for acoustic angiography applications in vitro and in vivo. We report center frequencies of 1.86 MHz and 20.3 MHz with -6 dB bandwidths of 1.2 MHz (1.2-2.4 MHz) and 14.5 MHz (13.3-27.8 MHz) for the low- and high-frequency arrays, respectively. With the proposed beamforming schemes, excitation pressure was found to range from 336 to 458 kPa at its azimuthal foci. This was sufficient to induce nonlinear scattering from microbubble contrast agents. Specifically, in vitro contrast channel phantom imaging and in vivo xenograft mouse tumor imaging by this probe with superharmonic imaging showed contrast-to-tissue ratio improvements of 17.7 and 16.2 dB, respectively, compared to line-by-line micro-ultrasound B-mode imaging.

In Vitro Superharmonic Contrast Imaging Using a Hybrid Dual-Frequency Probe

Superharmonic imaging is an ultrasound contrast imaging technique that differentiates microbubble echoes from tissue through detection of higher-order bubble harmonics in a broad frequency range well above the excitation frequency. Application of superharmonic imaging in three dimensions allows specific visualization of the tissue microvasculature with high resolution and contrast, a technique referred to as acoustic angiography. Because of the need to transmit and receive across a bandwidth that spans up to the fifth harmonic of the fundamental and higher, this imaging approach requires imaging probes comprising dedicated transducers for transmit and receive. In this work, we report on a new dual-frequency probe including two 1.7-MHz rectangular transducers positioned one on each side of a 20-MHz 256-element array. Finite element modeling-based design, fabrication processes and assembly of the transducer are described, as is integration with a high-frequency ultrasound imaging platform. Dual-frequency single-plane-wave imaging was performed with a microbubble contrast agent in flow phantoms and compared with conventional high-frequency B-mode imaging, and resolution and contrast-to-tissue ratio were quantified. This work represents an intermediate but informative step toward the development of dual-frequency imaging probes based on array technology, specifically designed for clinical applications of acoustic angiography.

Simultaneous unbalanced shared local oscillator heterodyne interferometry for high signal-to-noise-ratio, minimally destructive dispersive detection of time-dependent atomic spins

We demonstrate “simultaneous unbalanced shared local oscillator heterodyne interferometry” (SUSHI) a new method for minimally destructive, high signal-to-noise-ratio (SNR) dispersive detection of atomic spins. In SUSHI a dual-frequency probe laser interacts with atoms in one arm of a Mach–Zehnder interferometer, and then beats against a bright local oscillator (LO) beam traversing the other arm, resulting in two simultaneous, independent heterodyne measurements of the atom-induced phase shift. Measurement noise due to mechanical disturbances of beam paths is strongly rejected by the technique of active subtraction, in which antinoise is actively written onto the LO beam via an optical phase-locked loop. In SUSHI, technical noise due to phase, amplitude, and frequency fluctuations of the various laser fields is strongly rejected (i) for any mean phase bias between the interferometer arms, (ii) without the use of piezo actuated mirrors, and (iii) without signal balancing. We experimentally demonstrate an ultralow technical-noise-limited sensitivity of 51  nrad/Hz over a measurement bandwidth of 60 Hz to 8 kHz using a 230 μW probe, and stay within ∼3  dB of the standard quantum limit as probe power is reduced by more than 5 orders of magnitude to as low as 650 pW. SUSHI is therefore well suited to performing quantum nondemolition measurements for preparing spin-squeezed states and for high-SNR, truly continuous observations of ground-state Rabi flopping in cold atom ensembles.

Time Division Multiplexing Optical Time Domain Reflectometry Based on Dual Frequency Probe

A new frequency coding method is proposed and experimentally demonstrated that employs a phase modulator driven by sequential radio frequency and a synchronously controlled acoustooptic modulator to generate time division multiplexing probe pulses for coherent optical time domain reflectometry (C-OTDR). Each probe pulse contains two probe frequencies that are symmetrical regarding the frequency of local oscillator (LO). Heterodyne between the backscattered Rayleigh light of the dual frequency probe pulse and LO generates the same intermediate frequency. Experimental results show that the new C-OTDR, using ten frequency-coded probe pulses, brings an 8.0-dB dynamic range enhancement, compared with conventional C-OTDR.

Dual frequency probe based coherent optical time domain reflectometry

A new approach to enhance the performance of coherent optical time domain reflectometry(C-OTDR) is proposed. In this approach, single frequency light is converted to multi-frequency light using phase modulator (PM), while only two frequencies with the same light power level are adopted as the probe .Coherent heterodyne between the dual frequency probe and original single frequency local oscillator (LO) generates the same intermediate frequency (IF), which equals two IF signals automatically synthesizing in the process of coherent detection other than in IF signal processing circuit, so it doubles measurement speed. Experimental results show that compared with conventional single frequency probe based C-OTDR the dual frequency probe based C-OTDR has more quickly coherent Rayleigh noise (CRN) reduction capability and can bring a 3.0dB dynamic range improvement.

Adjusting the phase of the signals transmitted from dual frequency probe for reducing second harmonic during propagation

During propagation of the ultrasound wave, nonlinearities of the medium, causes rise of higher harmonics that are seen in amplitude spectrum. In ultrasound contrast harmonic imaging this is unwanted effect, since it is expected to image only higher harmonics produced by contrast agents. In previous studies Christopher, Krishnan and Shen proposed transmitting either an inverted signal (collected by hydrophone), transmitting 2nd harmonic with broadband transducer or transmitting third harmonic to reduce the second harmonic at measurement point. Our study uses a dual frequency probe which transmits one wave at frequency f0 and one wave at double frequency 2f0 named second harmonic reduction signal (SHRS) for reducing the second harmonic in the propagating signal. The hardest task is the appropriate adjustment of the phase of the SHRS to reduce second harmonic during propagation in the focal area. We outline how to set phase and established that the phase of the SHRS in not affected by the nonlinear parameter B/A and excitation pressure P0 but rather by the excitation frequency and the ultrasound system geometry (transducer size and distance to focal area). A reduction of 25dB has been obtained in simulation (Po=100kPa, fo=2.25 MHz). Experiments in water tank, have shown the reduction of 2nd harmonic by 30dB.

Super harmonic imaging: a new imaging technique for improved contrast detection

For ultrasound contrast agents (UCA), nonlinear imaging now has become fundamental. All of the current contrast-imaging methods are dominantly based on the nonlinear response of UCA bubbles. The discrimination between the perfused tissue and the UCA is the challenge in the field of UCA-imaging. This differentiation is usually associated or expressed by the ratio of the scattered power from the contrast agent to the scattered power from the tissue and is termed “contrast-to-tissue ratio” (CTR). Second harmonic imaging showed a better discrimination between tissue and UCA than fundamental imaging because of a higher CTR. We demonstrate, in this study, that the CTR increases as a function of the order of the harmonic frequency. Currently, due to the limited bandwidth of the transducers, only the second harmonic is selectively imaged, resulting in images with a superior quality to fundamental images, but still degraded and not optimal because of the harmonic generation in the underlying tissue (due to nonlinear propagation) and hence giving a limited CTR. To increase the CTR and to take advantage of the higher harmonics (third, fourth, fifth and the ultraharmonics and termed here super harmonics), we have developed a new phased array transducer. The array transducer contains two different types of elements arranged in an interleaved pattern (odd and even elements). The total number of elements is 96. The elements can operate separately and at a distinct frequency, enabling separate transmission and reception modes. The odd elements (48) operate at typically 2.8 MHz center frequency and 80% bandwidth. The even elements (48) have a center frequency of 900 kHz with a bandwidth of 50%. In vitro measurements using the dual frequency probe show an increase of 40 dB in the CTR for super harmonic components over the conventional second harmonic system. The increase in CTR is in agreement with the calculations using existing models for the response of encapsulated bubbles and known theory of nonlinear propagation. Animal experiments have demonstrated the feasibility of this approach using commercially available UCA and showed a similar increase of the CTR (E-mail: bouakaz@tch.fgg.eur.nl).

A dual frequency ultrasonic probe for medical applications

A dual frequency probe using a multilayer ceramic is proposed for simultaneously obtaining a high resolution B mode and a high sensitivity Doppler mode image. This ceramic consists of two layers in which the poling directions are opposite and the individual thicknesses are different. It is possible to control the values of relative electromechanical coupling factors in the fundamental and the second harmonic by changing the thickness ratio. A thickness ratio of 1:0.7 was decided from computer simulation based on the Mason's model. A sufficient resolution has been shown from the fact that the intima of the carotid artery could be distinguished by an actually fabricated probe with dual frequencies of 3.75 and 7.5 MHz. Also, the sensitivity of this probe in the Doppler mode at 5 cm depth from the surface has been improved as much as 5 dB over that of a conventional one. >

A dual frequency ultrasonic probe for medical application.

A dual frequency probe employing two ceramic layers for medical ultrasonic diagnostic equipment has been developed for simultaneously obtaining both a high-resolution tomogram and a high S/N Doppler mode image. This ceramic vibrator, which has opposite poling directions and different individual thicknesses, has enabled the excitement of a second harmonic in addition to the fundamental resonance. Therefore, only a pair of electrical terminals are enough to excite dual frequencies. Ultrasonic attenuation in a human body is reduced, since the Doppler reference frequency can be set below the tomogram center frequency. Moreover, the two relative resonant levels are widely controllable by changing the thickness ratio of the two layers. An optimum thickness ratio of 1:0.7 has been obtained by computer simulation under Mason’s model. A cofiring multilayer method has been developed to achieve a multilayer ceramic with a large adhesive strength. As a result, the S/N of the Doppler mode has been improved as much as 5 dB over that of a conventional probe at an artery located 5 cm deep from the surface.

A Dual Frequency Ultrasonic Probe

A dual frequency probe using a multilayer ceramic is proposed for simultaneously obtaining a high resolution B mode and a high S/N Doppler mode image. This ceramic consists of 2 layers in which the poling directions are opposite and the individual thicknesses are different. It has been shown that the intima of the carotid artery can be distinguished by an actually fabricated probe with dual frequencies of 3.75 and 7.5 MHz. Also, the S/N of this probe in the Doppler mode has been improved as much as 5 dB over that of a conventional one at the popliteal artery located 5 cm deep from the surface.