Hongqi Yu

Fast bi-exponential fluorescence lifetime imaging analysis methods.

A new hardware-friendly bi-exponential fluorescence lifetime imaging (FLIM) algorithm has been proposed. Compared to conventional FLIM software, the proposed algorithms are noniterative offering direct calculation of lifetimes and therefore suitable for real-time applications. They are applicable to single-channel or 2D multichannel time-correlated single-photon counting (TCSPC) systems. The proposed methods have been tested on both synthesized and realistic FLIM data, and we have compared their performances with other recently proposed nonfitting bi-exponential techniques showing promising applications in future massive solid-state TCSPC imagers.

Wide-bandwidth biological impedance spectroscopy system based on the digital lock-in technique

ABSTRACT The spectra of biological impedance can reveal physiological conditions and biological events of biological samples. This paper presents the development of a novel biological impedance spectroscopy system using an improved digital lock-in technique. The hardware of the system mainly consists of a current source, a voltage detector, a clock generator, and a field-programmable gate array (FPGA) device. Digital phase-sensitive detection algorithms including direct digital synthesis, digital multipliers, and digital filters were implemented in the FPGA. Test results show that the proposed spectroscopy has good performance from low frequency to 5 MHz with 1% accuracy. It will be suitable for high-accuracy biological impedance spectra analysis in either in vitro or in vivo conditions.

Artificial neural network approaches for fluorescence lifetime imaging techniques

A novel high-speed fluorescence lifetime imaging (FLIM) analysis method based on artificial neural networks (ANN) has been proposed. In terms of image generation, the proposed ANN-FLIM method does not require iterative searching procedures or initial conditions, and it can generate lifetime images at least 180-fold faster than conventional least squares curve-fitting software tools. The advantages of ANN-FLIM were demonstrated on both synthesized and experimental data, showing that it has great potential to fuel current revolutions in rapid FLIM technologies.

High Accuracy Biological Impedance Measurement System Design and Calibration

The application of biological impedance measurement demands for high-accuracy and fast-speed. A novel measurement system for biological impedance measurement based on automatic balancing bridge is proposed. Besides the improvement on accuracy introduced by bridge method, the utilization of the Least Mean Square (LMS) method guarantees the measurement speed. We designed calibration method to eliminate the error inducted by the practical circuit. The test results reveal the in-phase and quadrature component measurement errors of the proposed system with calibration are respectively lower than 2 percent and 3.2 percent in the range of 1KHz to 1MHz. The system has advantages of high-accuracy and fast-speed which fit for biological impedance measurement applications.

Estimation of Fluorescence Lifetimes Via Rotational Invariance Techniques

Estimation of signal parameters via rotational invariance techniques is a classical algorithm widely used in array signal processing for direction-of-arrival estimation of emitters. Inspired by this method, a new signal model and new fluorescence lifetime estimation via rotational invariance techniques (FLERIT) were developed for multiexponential fluorescence lifetime imaging (FLIM) experiments. The FLERIT only requires a few time bins of a histogram generated by a time-correlated single-photon counting FLIM system, greatly reducing the data throughput from the imager to the signal processing units. As a noniterative method, the FLERIT does not require initial conditions, prior information nor model selection that are usually required by widely used traditional fitting methods, including nonlinear least square methods or maximum-likelihood methods. Moreover, its simplicity means it is suitable for implementations in embedded systems for real-time applications. FLERIT was tested on synthesized and experimental fluorescent cell data showing the potentials to be widely applied in FLIM data analysis.

A high-efficiency real-time digital signal averager for time-of-flight mass spectrometry

RATIONALE Analog-to-digital converter (ADC)-based acquisition systems are widely applied in time-of-flight mass spectrometers (TOFMS) due to their ability to record the signal intensity of all ions within the same pulse. However, the acquisition system raises the requirement for data throughput, along with increasing the conversion rate and resolution of the ADC. It is therefore of considerable interest to develop a high-performance real-time acquisition system, which can relieve the limitation of data throughput. METHODS We present in this work a high-efficiency real-time digital signal averager, consisting of a signal conditioner, a data conversion module and a signal processing module. Two optimization strategies are implemented using field programmable gate arrays (FPGAs) to enhance the efficiency of the real-time processing. A pipeline procedure is used to reduce the time consumption of the accumulation strategy. To realize continuous data transfer, a high-efficiency transmission strategy is developed, based on a ping-pong procedure. RESULTS The digital signal averager features good responsiveness, analog bandwidth and dynamic performance. The optimal effective number of bits reaches 6.7 bits. For a 32 µs record length, the averager can realize 100% efficiency with an extraction frequency below 31.23 kHz by modifying the number of accumulation steps. In unit time, the averager yields superior signal-to-noise ratio (SNR) compared with data accumulation in a computer. CONCLUSIONS The digital signal averager is combined with a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS). The efficiency of the real-time processing is tested by analyzing the volatile organic compounds (VOCs) from ordinary printed materials. In these experiments, 22 kinds of compounds are detected, and the dynamic range exceeds 3 orders of magnitude.

Research on Voltage Controlled Current Source for Electrical Impedance Tomography

Electrical Impedance Tomography (EIT) is applied to acquire the impedance characteristic, which is correlative with the physiological and pathological status of a body, and reconstruct the images of impedance distribution. Current injection with voltage measurement phantom is widely adopted in the application of biomedical detection. Voltage controlled current source (VCCS) develops an important part and its performance directly affects the precision of EIT system. In this paper, we design and realize a VCCS using a direct digital synthesizer (DDS) and an improved Howland current source. The detailed simulation and test results and performance analysis are presented. The simulated maxim output impedance achieves 103.41Mohm under frequency from 1KHz to 100KHz and the current source provides broad -3dB bandwidth. In the practical experiment, the driving capability and dynamic performance are tested and analyzed. The actual results show that the VCCS performs stably and provides great output impedance and fine dynamic performance, which are suitable for EIT application.

Single-shot time-gated fluorescence lifetime imaging using three-frame images

Qualitative and quantitative measurements of complex flows demand for fast single-shot fluorescence lifetime imaging (FLI) technology with high precision. A method, single-shot time-gated fluorescence lifetime imaging using three-frame images (TFI-TGFLI), is presented. To our knowledge, it is the first work to combine a three-gate rapid lifetime determination (RLD) scheme and a four-channel framing camera to achieve this goal. Different from previously proposed two-gate RLD schemes, TFI-TGFLI can provide a wider lifetime range 0.6 ~ 13ns with reasonable precision. The performances of the proposed approach have been examined by both Monte-Carlo simulations and toluene seeded gas mixing jet diagnosis experiments. The measured average lifetimes of the whole excited areas agree well with the results obtained by the streak camera, and they are 7.6ns (N2 = 7L/min; O2 < 0.1L/min) and 2.6ns (N2 = 19L/min; O2 = 1L/min) with the standard deviations of 1.7ns and 0.8ns among the lifetime image pixels, respectively. The concentration distributions of the quenchers and fluorescent species were further analyzed, and they are consistent with the experimental settings.

Fast bi-exponential fluorescence lifetime imaging analysis methods: publisher's note.

Table 1 of an earlier paper [Opt. Lett.40, 336 (2015)10.1364/OL.40.000336] contained an incorrect mathematical expression. The error is rectified here.

Parallel Parity Scheme for Reliable Solid-State Disks

Recently, solid-state disks (SSDs) have been extensively applied in many fields. However, with increasing storage density in SSDs, a liability problem has emerged as a significant restriction. A parallel parity scheme is proposed in this paper. This scheme employs a mapping table based on a physical block address and a partial delayed parity update. Experimental results demonstrate the proposed scheme not only improves the reliability of SSDs, but also enhances their performance.