Flow velocity quantification by exploiting the principles of the Doppler effect and magnetic particle imaging

Changes in blood flow velocity play a crucial role during pathogenesis and progression of cardiovascular diseases. Imaging techniques capable of assessing flow velocities are clinically applied but are often not accurate, quantitative, and reliable enough to assess fine changes indicating the early onset of diseases and their conversion into a symptomatic stage. Magnetic particle imaging (MPI) promises to overcome these limitations. Existing MPI-based techniques perform velocity estimation on the reconstructed images, which restricts the measurable velocity range. Therefore, we developed a novel velocity quantification method by adapting the Doppler principle to MPI. Our method exploits the velocity-dependent frequency shift caused by a tracer motion-induced modulation of the emitted signal. The fundamental theory of our method is deduced and validated by simulations and measurements of moving phantoms. Overall, our method enables robust velocity quantification within milliseconds, with high accuracy, no radiation risk, no depth-dependency, and extended range compared to existing MPI-based velocity quantification techniques, highlighting the potential of our method as future medical application.

Low-cost planar vibration sensor using a modified computer mouse

Purpose The purpose of this study aims to modify a self-mixing laser mouse as an extremely cost-effective displacement sensor to measure the mechanical oscillation of a commercial shaker and a nano-positioning stage. Design/methodology/approach This kind of laser mouse, mostly consisting of a pair of vertical cavity surface emitting lasers, two photodiodes and an integrated signal processing unit, is capable of directly giving the x-axis and y-axis components of the measured vibrating displacement. Based on the laser self-mixing interference, the velocity of the object is coded into the Doppler frequency shift of the feedback light, which allows accurate determination of the vibration of the object. Findings A commercial shaker has been used to provide standard harmonic oscillation to test the displacement sensor. Within a vibrating frequency range of 110 Hz, the experimental results show that the micrometer scale resolution has been achieved at the velocity of up to 2 m/s, which is much improved compared with the image-based optical mouse. Furthermore, the measurements of the two dimensional displacement of a nano-positioning stage are performed as well. The minimum measurable velocity limit for this sensor has been discussed in detail, and the relative measurement error can be greatly reduced by appropriate selection of the modulation frequency of the triangular injection current. Originality/value These results demonstrate the feasibility of this device for the industrial vibration sensing applications.

Resolving velocity ambiguity of two coded pulse in broad-band acoustic Doppler current profiler

Broad-band Acoustic Doppler Current Profiler (BBADCP) adopts short-sequence coded pulse to measure high velocity. Short-sequence coded pulse has large measurable velocity, so it is not easy to have velocity ambiguity. But short coded pulse deteriorates the accuracy of the velocity. To obtain more accurate velocity, we adopt two coded pulse with a time lag. This paper analyzes the ambiguity velocity and velocity standard deviation of two coded pulse and single coded pulse, and gives a solution to resolve velocity ambiguity: single coded pulse which has a large ambiguity velocity due to the short time lag is used to establish a coarse estimate of the velocity, two coded pulsewhich has a long time lag is used to have a high accuracy velocity, then we combine the two velocities in a way to provide an accurate velocity. It has been demonstrated that the two coded pulse can reduce variance of velocity through analyzing numerous experimental data of pool. Meanwhile, the efficiency of method to solve ambiguity has been proved in accordance with multiple sets of data. Compared with the traditional methods, this method has good anti-noise performance and high single measurement accuracy.

Development of Ultrasonic Flowmeter Using Pulsed Doppler Method With Staggered Trigger Pulse

The ultrasonic pulsed Doppler method can be applied to obtain instantaneous velocity distribution along the ultrasonic beam path. This technique has many advantages, and it has been applied for measuring flow rate. However, the method has limitation about the measurable velocity and length. In order to overcome the limitation, a dealiasing method using staggered trigger pulse was applied for measuring velocity profile in a pipe. Furthermore, a multi-wave ultrasonic transducer was proposed for the measurement for improving the velocity measurement accuracy in the near-wall region. The applicability was examined for measuring velocity profile in a pipe with inner diameter of 200 mm. The velocity distributions were accurately obtained over the pipe by combining the velocity distributions at the basic frequency of 8 MHz for the near-wall region and 2 MHz for the region far from the transducer. As a result, it was confirmed that the flow rate measurement was improved by using the multi-wave method.

A Real-Time Microscopic PIV System Using Frame Straddling High-Frame-Rate Vision

In this paper, we propose a novel concept of realtime microscopic particle image velocimetry (PIV) for apparent high-speed microchannel flows in lab-on-achip (LOC). We introduce a frame-straddling dualcamera high-speed vision system that synchronizes two different camera inputs for the same camera view with a submicrosecond time delay. In order to improve upper and lower limits of measurable velocity in microchannel flow observation, we designed an improved gradient-based optical flow algorithm that adaptively selects a pair of images in the optimal frame-straddling time between the two camera inputs based on the amplitude of the estimated optical flow. This avoids large image displacement between frames that often generates serious errors in optical flow estimation. Our method is implemented using software on a frame-straddling dual-camera high-speed vision platform that captures real-time video and processes 512 × 512 pixel images at 2000 fps for the two camera heads and controls the frame-straddling time delay between them from 0 to 0.25 ms with 9.9 ns step. Our microscopic PIV system with frame-straddling dualcamera high-speed vision simultaneously estimates the velocity distribution of high-speed microchannel flow at 1 × 108pixel/s or more. Results of experiments using real microscopic flows on microchannels thousands of µm wide on LOCs verify the performance of the real-time microscopic PIV system we developed.

Mountain glacier velocity variation during a retreat/advance cycle quantified using sub-pixel analysis of ASTER images

Coverage of ice velocities in the central part of the Southern Alps, New Zealand, is obtained from feature tracking using repeat optical imagery in 2002 and 2006. Precise orthorectification, co-registration and correlation is carried out using the freely available software COSI-Corr. This analysis, combined with short times between image acquisitions, has enabled velocities to be captured even in the accumulation areas, where velocities are lowest and surface features ephemeral. The results indicate large velocities for mountain glaciers (i.e. up to ∼5 m d−1) as well as dynamic changes in some glaciers that have occurred between 2002 and 2006. For the steep and more responsive Fox and Franz Josef Glaciers the speed increased at the glacier snout during the advance period, while the low-angled and debris-covered Tasman Glacier showed no measurable velocity change. Velocity increases on the steeper glaciers are the result of an observed thickening and steepening of the glacier tongues as they moved from a retreat phase in 2002 to an advance phase in 2006. This contrasting behaviour is consistent with historic terminus position changes. The steeper glaciers have undergone several advance/retreat cycles during the observation period (1894 to present), while the low-angled glacier showed little terminus response until retreat resulting from the accelerating growth of a proglacial lake commenced in 1983.

Doppler Optical Coherence Tomography: Real-Time Optical Sectioning for Microfluidics

Doppler optical coherence tomography (DOCT) is an emerging imaging modality demonstrated in 1991 for the first time and is a functional extension of optical coherence tomography (OCT) to including flow measurement. DOCT allows not only high-resolution, non-invasive, cross-sectional imaging but also simultaneous real-time visualization of sample structure and flow. DOCT is often compared to clinical Doppler ultrasound. However, the spatial resolution of clinical Doppler ultrasound is limited to approximately 100 μm due to the relatively long wavelength of acoustic waves. DOCT takes advantage of the short coherence length of broadband light sources in order to achieve cross-sectional images with micrometer (2–10 μm) scale resolution. DOCT is also superior to ultrasound in that DOCT is operated in non-contact-mode. The last four years have witnessed an era of technology revolution in DOCT, introduced by the Fourier-domain technology that shows tremendous advantage over time-domain DOCT. Fourier-domain Doppler optical coherence tomography (FDDOCT) instruments have higher imaging speed and higher system sensitivity which are able to overcome motion artifacts and enhance minimum measurable velocity, respectively. Because of the aforementioned merits, FDDOCT has a broad range of clinical applications including ophthalmology, cardiology, urology, etc with information of tissue microstructure and blood flow. However, FDDOCT has seldom been applied to diagnose microfluidic devices. In this keynote paper, system configuration, principle behind, and applications of FDDOCT for microfluidics will be covered.