Time-domain Gating Technique Research Articles

Application of time-domain gating technique in water content measurement of gas-liquid two-phase flow.

This paper introduces an application of the time-domain gating technique in water content measurement of gas-liquid two-phase flow. According to the principle that water and gas have different absorption effects on microwaves, a sensor with transmitting and receiving antennas is designed. Combined with the back propagation neural network, the water content of two-phase fluids can be obtained from the complex transmission coefficient (S21) of antennas. In order to reduce the influence of the sensor structure on antenna measurement, the time-domain gating technique can be used to filter out the interference components in S21 so that the water content can be more easily predicted. Built on the above, an automatic test system is established. In the range of 0%-78%, the absolute test error of the water content is lower than 3%.

Contrast improvement in indocyanine green fluorescence sensing in thick tissue using a time-gating method.

Indocyanine green-based fluorescence imaging techniques are very powerful in clinical applications, but the imaging is restricted to the signal from the near-surface region of tissue. Here, we focus on the method to discriminate the fluorescence signal from the background using a time-domain gating technique. The contrast of the fluorescence image from a fluorescence object at more than 1 cm depth in a meat phantom could be enhanced about 4-5 times relative to the continuous wave method if the time-gate range was properly selected. Further, a Monte Carlo simulation with a simple background model indicates that a shorter source and detector distance is more effective to improve the contrast. The simple time-gating method will enable a highly sensitive fluorescence detection in thick tissue.

SU-E-I-94: External Beam Radiation Cherenkov Emission in Tissue Used for Tissue Oxygen Sensing.

To show that Cherenkov emission is generated by external radiotherapy beam in tissue, and could serve as optical source to excite an oxygen sensitive phosphor, Oxyphor G4, within tissue. The intensity and lifetime of the phosphorescence was measured with a time-gated system and reveals the oxygenation levels in the tissue phantom. A tissue phantom made with PBS, 1% v/v Intralipid-20% (Sigma Aldrich), 1% v/v whole blood and Oxyphor G4 in 1 μM concentration is irradiated by 18MeV external radiotherapy electron beam at a dose rate of 4 Gy/min generated by a medical linear accelerator (Varian LINAC 2100C, Varian Medical Systems). On one side of the phantom, a fiber bundle is used to conduct optical signal to a spectrometer connected to a fast gating ICCD (PI-MAX3, Princeton Instruments). For each oxygenation level, a series of spectrum of phosphorescence at different time points is measured by the time domain gating technique. Lifetime of phosphorescence is analyzed by exponential fitting and is validated by comparison to an independent analysis by frequency domain phosphorimetry. Monte Carlo simulations using GEANT4, of the fiber optic collection of Cerenkov light were performed to decide the sensitivity of the optical system for a range of specified geometries and beam types. Simulation results identify the effective depth within the phantom that is sampled by the optical collection of the Cerenkov signal. Simulations show that we can detect the Cherenkov signals comes from an approximately 5 mm depth from within the tissue phantom. Lifetime of the phosphorescence and pO2 of the phantom could be measured and calculated correctly by the time domain gating system. This work indicates time domain gating techniques combined with an oxygen sensitive phosphor are capable of accurately monitoring tissue oxygenation from a reasonable sampling depth in tissue in vivo during external beam radiotherapy. NIH grant R01CA109558.

SU‐E‐I‐93: External Beam Radiation Cherenkov Emission in Tissue Used for Tissue Oxygen Sensing

Purpose: To show that Cherenkov emission is generated by external radiotherapy beam in tissue, and could serve as optical source to excite an oxygen sensitive phosphor, Oxyphor G4, within tissue. The intensity and lifetime of the phosphorescence was measured with a time‐gated system and reveals the oxygenation levels in the tissue phantom. Methods: A tissue phantom made with PBS, 1% v/v Intralipid‐20% (Sigma Aldrich), 1% v/v whole blood and Oxyphor G4 in 1 μM concentration is irradiated by 18MeV external radiotherapy electron beam at a dose rate of 4 Gy/min generated by a medical linear accelerator (Varian LINAC 2100C, Varian Medical Systems). On one side of the phantom, a fiber bundle is used to conduct optical signal to a spectrometer connected to a fast gating ICCD (PI‐MAX3, Princeton Instruments). For each oxygenation level, a series of spectrum of phosphorescence at different time points is measured by the time domain gating technique. Lifetime of phosphorescence is analyzed by exponential fitting and is validated by comparison to an independent analysis by frequency domain phosphorimetry. Monte Carlo simulations using GEANT4, of the fiber optic collection of Cerenkov light were performed to decide the sensitivity of the optical system for a range of specified geometries and beam types. Simulation results identify the effective depth within the phantom that is sampled by the optical collection of the Cerenkov signal. Results: Simulations show that we can detect the Cherenkov signals comes from an approximately 5 mm depth from within the tissue phantom. Lifetime of the phosphorescence and pO2 of the phantom could be measured and calculated correctly by the time domain gating system. Conclusions: This work indicates time domain gating techniques combined with an oxygen sensitive phosphor are capable of accurately monitoring tissue oxygenation from a reasonable sampling depth in tissue in vivo during external beam radiotherapy. NIH grant R01CA109558

Time-Reversal MUSIC Imaging with Time-Domain Gating Technique

A time-reversal (TR) approach with multiple signal classification (MUSIC) provides super-resolution for detection and localization using multistatic data collected from an array antenna system. The theory of TR-MUSIC assumes that the number of antenna elements is greater than that of scatterers (targets). Furthermore, it requires many sets of frequency-domain data (snapshots) in seriously noisy environments. Unfortunately, these conditions are not practical for real environments due to the restriction of a reasonable antenna structure as well as limited measurement time. We propose an approach that treats both noise reduction and relaxation of the transceiver restriction by using a time-domain gating technique accompanied with the Fourier transform before applying the TR-MUSIC imaging algorithm. Instead of utilizing the conventional multistatic data matrix (MDM), we employ a modified MDM obtained from the gating technique. The resulting imaging functions yield more reliable images with only a few snapshots regardless of the limitation of the antenna arrays.

High Resolution 3-D Imaging

A three dimensional radar image can be constructed from scanning microwave measurements. A Vector Network Analyzer has been used for wideband phase and magnitude measurements of radar return. Quasi-monostatic horn antenna configuration is chosen to transmit and receive the electromagnetic wave. Measured target is placed on a polystyrene foam pedestal at 5 meters distance away from the 2-D planar scanner. A wide bandwidth, ranging from 3 GHz to 18 GHz gives rise to very fine range resolution. A time domain gating technique is used to remove spurious signals from the desired signal of the radar target. Range Migration Technique has been used to produce a 3-D radar image. Indoor measurements have been performed on conducting spheres to validate the software. A high resolution 3-D radar image for spheres has been obtained. Analysis of the radar cross-sections shows good correlation with theoretical values. Subsequently, the radar cross-section of an oil palm tree was measured and analyzed.

Polarimetric RCS Calibration using Reference Reflectors

A new polarimetric radar cross section (RCS) calibration technique using two reference reflectors is developed and verified experimentally in the anechoic chamber of Multimedia University. The antenna system and the two orthogonal channels are modeled as a two-port network. The technique utilizes two electrically large reflectors, namely a rectangular flat plate and a 45° rotated dihedral corner reflector as the calibration targets to provide large reflections for co-polarization and cross-polarization returns, respectively. The orientation of the reflectors is not critical, and their theoretical RCS are not required in the calibration process. Therefore the alignment problem and uncertainties in the computation of the theoretical responses are eliminated. A metallic sphere with known theoretical RCS is used to verify the calibration accuracy and determine the correction factor for absolute RCS measurement. Scattering measurements are performed using a Vector Network Analyzer (VNA). Raw data are acquired and stored in the PC for further processing. Time domain gating technique is applied to remove the target-chamber coupling effect in the measurements.

A broadband free-space dielectric properties measurement system at millimeter wavelengths

A free-space system operating in the 75 GHz to 95 GHz range for measurement of the complex permittivity of matter is presented. The complex transmission coefficient of a parallel polarized quasiplane wave through a planar sample is determined for different incidence angles. The quasiplane wave is realized by a collimated Gaussian beam. The complex permittivity is subsequently calculated from the measured data by applying a nonlinear least-squares method. Errors induced by multiple reflections between the transmitting and receiving horn antennas are removed by a time-domain gating technique. The design of the quasioptical measurement setup is based on Gaussian beam optics. A dielectric lens collimates the beam of the transmitting horn antenna for minimization of diffraction effects at the edges of the sample. In order to verify the Gaussian beam and thin lens approximations at millimeter wavelengths, the far-field pattern of the horn antenna and the dielectric lens system has been measured. The performance of the measurement setup has been tested using glass samples.