Signal-to-background Noise Ratio Research Articles

CZT Detectors-Based SPECT Imaging: How Detector and Collimator Arrangement Can Determine the Overall Performance of the Tomograph

A technical comparison is described between two SPECT systems, one dedicated to cardiovascular studies and one general-purpose, to evaluate the advantages and disadvantages of their use in an organ-specific clinical setting. The comparison was made between a dedicated cardiac SPECT (Alcyone, Discovery NM 530c, GE Healthcare) scanner and a general-purpose one (Discovery NM/CT 670 CZT, GE Healthcare). The two scanners differ in terms of hardware, mainly in the arrangement of the detectors and collimators, which are the main components of SPECT. A standard NEMA phantom was used to characterize the energy resolution, spatial resolution, and sensitivity for the two systems. Then, using a custom-made cardiac phantom, more specific indices were computed to evaluate the quality of cardiac images, such as signal-to-background noise ratio (SBNR), tissue-background contrast-to-noise ratio (TBCNR), and uniformity. Finally, the same indices were computed for clinical images acquired with the two systems from 11 subjects. Alcyone showed superior performance for dedicated cardiac imaging; however, its excellent qualities are aimed only at the study of the heart and only at patients with a low body-mass index, unlike Discovery NM/CT 670 CZT, which can be used for every anatomic district area and for every type of patient.

A 32 × 32-Pixel Flash LiDAR Sensor With Noise Filtering for High-Background Noise Applications

This article introduces a pulsed laser direct time-of-flight (dTOF) flash light detection and ranging (LiDAR) sensor fabricated in 0.18-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> HV CMOS technology. The chip includes <inline-formula> <tex-math notation="LaTeX">$32\times 32$ </tex-math></inline-formula> macro pixels and 1024 time-to-digital converters (TDCs). A noise filtering circuit with different threshold (<inline-formula> <tex-math notation="LaTeX">$\text{N}_{\mathrm {th}}$ </tex-math></inline-formula>) configuration is adopted in each macro pixel [formed by four single-photon avalanche diodes (SPADs)], which can suppress strong background light (BG) induced pile-up. To verify the imaging function and effectiveness of the noise filtering circuit, two systems are implemented (System1 for indoor imaging measurement and System2 for outdoor distance measurement). With the help of the noise filtering circuit and a reasonable signal-to-background noise ratio (SBR), the maximum detection range outdoors with reasonable accuracy can be greatly extended (from 12m &#x0040; N_th &#x003D; 1 of System2 to more than 20m &#x0040; N_th &#x003D; 2 of System2 under 70klux of background noise). The counter in the noise filtering circuit can be reused to get intensity information. A robust 13-bit TDC with a reliable reset is introduced. Thanks to a dedicated START/STOP logic and a Schmitt trigger, large TDC quantization errors can be avoided. It achieves a 200ps resolution (LSB) and exhibits an INL_p-p of 3.55LSB and a DNL_p-p of 0.53LSB. The maximum inter-frame rate can reach 270kfps with 16 IOs operating at speed of 500MHz. Combining 9k inter-frames to get one frame, a frame rate of 30 is achieved for an indoor 3-D imaging. For outdoor measurement, more laser pulses should be accumulated.

Fabrication of Ag nanorods on micropost array for a metal-enhanced fluorescence substrate with a high signal-to-background ratio

Selective fabrication of metallic nanostructures at the spotting area is required to increase the signal-to-background noise ratio (SBR) of the metal-enhanced fluorescence (MEF) substrate. As a simple and cost-effective fabrication method for MEF substrate with high SBR, a glancing angle deposition (GLAD) process of Ag material on the UV-imprinted micropost array (50 μm in height, 300 μm in diameter, and 600 μm in pitch) was proposed to selectively fabricate Ag nanorods on the top of micropost structure (spotting area). Ag nanorod formation at the bottom of the micropost decreased as the deposition angle in Ag GLAD increased. A deposition angle of 89° and deposition thickness of 500 nm were selected as the optimum GLAD conditions to maximize the SBR. The optimum Ag nanorods on micropost array (AgNMPA) MEF substrate provided 71-fold fluorescence signal enhancement and 25-times higher SBR than the bare glass substrate. It also provided 7-times higher SBR than the Ag nanorod MEF substrate, which has a similar Ag nanorod structure but is not selectively formed. The detection limit of AgNMPA was 16- and 4-times lower than that of the amine-functionalized glass substrate and commercial epoxy slide, respectively. Although the fluorescence signal of AgNMPA was similar to that of Ag nanorod substrate, the detection limit was 2-times lower because of the low signal standard deviation caused by the low background noise and clear spot shape.

Modeling and Analysis of a Direct Time-of-Flight Sensor Architecture for LiDAR Applications.

Direct time-of-flight (DTOF) is a prominent depth sensing method in light detection and ranging (LiDAR) applications. Single-photon avalanche diode (SPAD) arrays integrated in DTOF sensors have demonstrated excellent ranging and 3D imaging capabilities, making them promising candidates for LiDARs. However, high background noise due to solar exposure limits their performance and degrades the signal-to-background noise ratio (SBR). Noise-filtering techniques based on coincidence detection and time-gating have been implemented to mitigate this challenge but 3D imaging of a wide dynamic range scene is an ongoing issue. In this paper, we propose a coincidence-based DTOF sensor architecture to address the aforementioned challenges. The architecture is analyzed using a probabilistic model and simulation. A flash LiDAR setup is simulated with typical operating conditions of a wide angle field-of-view (FOV = 40) in a 50 klux ambient light assumption. Single-point ranging simulations are obtained for distances up to 150 m using the DTOF model. An activity-dependent coincidence is proposed as a way to improve imaging of wide dynamic range targets. An example scene with targets ranging between 8–60% reflectivity is used to simulate the proposed method. The model predicts that a single threshold cannot yield an accurate reconstruction and a higher (lower) reflective target requires a higher (lower) coincidence threshold. Further, a pixel-clustering scheme is introduced, capable of providing multiple simultaneous timing information as a means to enhance throughput and reduce timing uncertainty. Example scenes are reconstructed to distinguish up to 4 distinct target peaks simulated with a resolution of 500 ps. Alternatively, a time-gating mode is simulated where in the DTOF sensor performs target-selective ranging. Simulation results show reconstruction of a 10% reflective target at 20 m in the presence of a retro-reflective equivalent with a 60% reflectivity at 5 m within the same FOV.

Detecting impact signal in mechanical fault diagnosis under chaotic and Gaussian background noise

Abstract In actual fault diagnosis, useful information is often submerged in heavy noise, and the feature information is difficult to extract. Traditional methods, such like stochastic resonance (SR), which using noise to enhance weak signals instead of suppressing noise, failed in chaotic background. Neural network, which use reference sequence to estimate and reconstruct the background noise, failed in white Gaussian noise. To solve these problems, a novel weak signal detection method aimed at the problem of detecting impact signal buried under heavy chaotic and Gaussian background noise is proposed. First, the proposed method obtains the virtual reference sequence by constructing the Hankel data matrix. Then an M-order optimal FIR filter is designed, which can minimize the output power of background noise and pass the weak periodic signal undistorted. Finally, detection and reconstruction of the weak periodic signal are achieved from the output SBNR (signal to background noise ratio). The simulation shows, compared with the stochastic resonance (SR) method, the proposed method can detect the weak periodic signal in chaotic noise background while stochastic resonance (SR) method cannot. Compared with the neural network method, (a) the proposed method does not need a reference sequence while neural network method needs one; (b) the proposed method can detect the weak periodic signal in white Gaussian noise background while the neural network method fails, in chaotic noise background, the proposed method can detect the weak periodic signal under a lower SBNR (about 8–17 dB lower) than the neural network method; (c) the proposed method can reconstruct the weak periodic signal precisely.

Bit error rate of RS coded BFSK in broadband powerline channels with background Nakagami and impulsive noise

Power line communication (PLC) systems are being standardized over the globe and some of these standards recommended frequency shift keying (FSK) as their modulation choice. Broadband transmission over a PLC channel is mainly affected by the ever-present background noise and the occasional high-amplitude impulses. It has been recently found that the background noise in PLC can be suitably modelled with Nakagami-m distribution while a standard model for characterizing impulses is to assume Gaussian distributed amplitude and Poisson distributed arrivals. Considering such a model, at first, simple analytical bit error rate (BER) expressions of uncoded binary FSK (BFSK) signals are derived in the paper. The derived expressions are simple, involve only elementary functions, and the analytical BER values match perfectly with computer simulations. Next, a unified analytical framework is presented for evaluating BER when a Reed Solomon (RS) code is used to mitigate the noise effects. The results reveal that when the signal to background noise ratio (SBNR) is low, there is a clear impact of the noise parameter m and the choice of demodulation method (coherent/ non-coherent) on the error performance of the coded system. On the contrary, at higher SBNR, impulsive noise dominates over background noise, and these effects vanish as the BER curves become flat. Numerical evaluations dictated that by allowing a lower code rate (0.7) this error floor may be reduced significantly (up to 10−15). Further, the code gain of the system was found to be an inverse function of the code rate and codeword length.

Theoretical Analysis of Wavelength Conversion Based on Four-Wave Mixing in Light-Holding SOAs

We propose to use an additional injection beam of short wavelength to enhance the wavelength conversion that utilizes the four-wave-mixing (FWM) effect in a semiconductor optical amplifier (SOA). With this scheme, the assist light can increase the saturation intensity without sacrificing the gain of an SOA, and this leads to an increase in conversion efficiency. A numerical method dealing with various FWM mechanisms, such as amplified spontaneous emission (ASE) noise, longitudinal spatial hole burning, and wavelength-dependent gain spectrum, is developed to predict the static characteristics of our scheme. The carrier densities are nonuniformly distributed along the longitudinal direction of the SOA as a result of the ASE effect, which affects the measurement of the wavelength-dependent transparent current. The effects of an assist light on saturation output power and conversion efficiency are analyzed in detail. The analysis shows that using an assist light can improve both the conversion efficiency and signal-to-background-noise ratio (SBR) for SOAs of different lengths. The degree of improvement depends on the bias condition, assist light wavelength, and the device geometry. The study for the device optimization reveals that a compromise between conversion efficiency and SBR must be made to choose the device length.

Performance of a reconfigurable wavelength converter based on dual-pump-wave mixing in a semiconductor optical amplifier

We report on a wavelength converter based on dual pump wave mixing in an 1-mm-long bulk semiconductor optical amplifier. Very high conversion efficiency (more than 0 dB) and signal-to-background-noise ratio (SBR) (16 dB), for large down- or up-wavelength shifts (30 mn) has been achieved using parallel polarized pumps with low optical power (-13 dBm). Orthogonal polarized pumps result in worse performance, having the advantage of polarization insensitivity for small wavelength spacing between them. The converter operates in a fixed input-tunable output or a tunable input-fixed output mode of operation. In each mode, the measured SBR is almost independent of the wavelength shift for either up- or down-conversion.

Signal Detection for Data Sets with a Signal-To-Noise Ratio of 1 or Less with the Use of a Moving Product Filter

We report on a method to reduce background noise and amplify signals in data sets with low signal-to-noise ratios (SNRs). This method consists of taking a data set with mean 0 and normalized with respect to absolute value, adding 1 to all values to adjust the mean to 1, and then applying a moving product (MP) to the transformed data set (similar to the application of a moving average or 0-order Savitzky–Golay filtering). A data point in the presence of a signal raises the probability of that data point having a value &gt;1, while the absence of a signal increases the probability of that data point having a value &lt; 1. If the autocorrelation lag of the signal is larger than the autocorrelation lag of the associated noise, the use of an MP with window comparable to that of the signal width (i.e., 2–3 times the signal standard deviation) will tend to reduce the values of data points where no signal is present and similarly amplify data points where signal is present. Signal amplification, often to a considerable degree, is gained at the cost of signal distortion. We have used this method on simulated data sets with SNRs of 1, 0.5, and 0.33, and obtained signal-to-background noise ratio (SBNR) enhancements in excess of 100 times. We have also applied this procedure to low SNR measured Raman spectra, and we discuss our findings and their implications. This method is expected to be useful in the detection of weak signals buried in strong background noise.

Coherent Detection of Frequency-Hopped Quadrature Modulations in the Presence of Jamming--Part I: QPSK and QASK Modulations

This paper examines the performance of coherent QPSK and QASK systems combined with FH or FH/PN spread spectrum techniques in the presence of partial-band multitone or noise jamming. The worst-case jammer and worst-case performance are determined as functions of the signal-to-background noise ratio (SNR) and signal-to-jammer power ratio (SJR). Asymptotic results for high SNR are shown to have a linear dependence between the jammer's optimal power allocation and the system error probability performance.