Noise Power Spectrum Analysis Research Articles

Noise spectrum analysis of superconducting kinetic inductance detectors

As a newly developed pair-breaking superconducting detector, microwave kinetic inductance detectors are simple to integrate in the frequency domain and have already been used in astronomical detection and array imaging at the (sub)millimeter and optical wavelengths. For these applications, the dark noise level of kinetic inductance detector is one of the key performance indicators. Herein a noise power spectrum analysis method is introduced in detail, which can accurately and effectively analyze the noise spectrum of kinetic inductance detector in a wide frequency range. This method can well balance the noise spectrum resolution and variance performance, by taking the noise data at the resonance frequency with two sampling rates and setting the appropriate frequency resolutions for different frequency bands. This method is used to characterize and compare the noise of aluminum (Al) kinetic inductance detectors made from two different micromachining processes. We deposite a 25-nm-thick aluminum film on high-resistivity silicon substrate for one device, while place one silicon nitride (SiN<sub><i>x</i></sub>) film on the top and one on the bottom of the aluminum film for another device. It is found that the frequency noise of the device with two silicon nitride films is about 25% to 50% of the bare aluminum device. Using this double silicon nitride film fabrication technique, we further fabricate a few groups of lumped-element aluminum kinetic inductance detectors with various inductor and interdigitated capacitor designs. We investigate the noise properties of these devices at different microwave driven power and bath temperatures, and the experimental results show typical two-level system noise behaviors. Our work provides a standard method to characterize the noise power spectrum of kinetic inductor detector, and also paves the way to developing low-noise aluminum kinetic inductance detectors for terahertz imaging, photon-counting and energy-resolving applications.

Improving Image Quality and Reducing Radiation Dose for Pediatric CT by Using Deep Learning Reconstruction.

Background CT deep learning reconstruction (DLR) algorithms have been developed to remove image noise. How the DLR affects image quality and radiation dose reduction has yet to be fully investigated. Purpose To investigate a DLR algorithm's dose reduction and image quality improvement for pediatric CT. Materials and Methods DLR was compared with filtered back projection (FBP), statistical-based iterative reconstruction (SBIR), and model-based iterative reconstruction (MBIR) in a retrospective study by using data from CT examinations of pediatric patients (February to December 2018). A comparison of object detectability for 15 objects (diameter, 0.5-10 mm) at four contrast difference levels (50, 150, 250, and 350 HU) was performed by using a non-prewhitening-matched mathematical observer model with eye filter (d'NPWE), task transfer function, and noise power spectrum analysis. Object detectability was assessed by using area under the curve analysis. Three pediatric radiologists performed an observer study to assess anatomic structures with low object-to-background signal and contrast to noise in the azygos vein, right hepatic vein, common bile duct, and superior mesenteric artery. Observers rated from 1 to 10 (worst to best) for edge definition, quantum noise level, and object conspicuity. Analysis of variance and Tukey honest significant difference post hoc tests were used to analyze differences between reconstruction algorithms. Results Images from 19 patients (mean age, 11 years ± 5 [standard deviation]; 10 female patients) were evaluated. Compared with FBP, SBIR, and MBIR, DLR demonstrated improved object detectability by 51% (16.5 of 10.9), 18% (16.5 of 13.9), and 11% (16.5 of 14.8), respectively. DLR reduced image noise without noise texture effects seen with MBIR. Radiologist ratings were 7 ± 1 (DLR), 6.2 ± 1 (MBIR), 6.2 ± 1 (SBIR), and 4.6 ± 1 (FBP); two-way analysis of variance showed a difference on the basis of reconstruction type (P < .001). Radiologists consistently preferred DLR images (intraclass correlation coefficient, 0.89; 95% CI: 0.83, 0.93). DLR demonstrated 52% (1 of 2.1) greater dose reduction than SBIR. Conclusion The DLR algorithm improved image quality and dose reduction without sacrificing noise texture and spatial resolution. © RSNA, 2020 Online supplemental material is available for this article.

A Third-Generation Adaptive Statistical Iterative Reconstruction Technique: Phantom Study of Image Noise, Spatial Resolution, Lesion Detectability, and Dose Reduction Potential.

The purpose of this study was to assess image noise, spatial resolution, lesion detectability, and the dose reduction potential of a proprietary third-generation adaptive statistical iterative reconstruction (ASIR-V) technique. A phantom representing five different body sizes (12-37 cm) and a contrast-detail phantom containing lesions of five low-contrast levels (5-20 HU) and three sizes (2-6 mm) were deployed. Both phantoms were scanned on a 256-MDCT scanner at six different radiation doses (1.25-10 mGy). Images were reconstructed with filtered back projection (FBP), ASIR-V with 50% blending with FBP (ASIR-V 50%), and ASIR-V without blending (ASIR-V 100%). In the first phantom, noise properties were assessed by noise power spectrum analysis. Spatial resolution properties were measured by use of task transfer functions for objects of different contrasts. Noise magnitude, noise texture, and resolution were compared between the three groups. In the second phantom, low-contrast detectability was assessed by nine human readers independently for each condition. The dose reduction potential of ASIR-V was estimated on the basis of a generalized linear statistical regression model. On average, image noise was reduced 37.3% with ASIR-V 50% and 71.5% with ASIR-V 100% compared with FBP. ASIR-V shifted the noise power spectrum toward lower frequencies compared with FBP. The spatial resolution of ASIR-V was equivalent or slightly superior to that of FBP, except for the low-contrast object, which had lower resolution. Lesion detection significantly increased with both ASIR-V levels (p = 0.001), with an estimated radiation dose reduction potential of 15% ± 5% (SD) for ASIR-V 50% and 31% ± 9% for ASIR-V 100%. ASIR-V reduced image noise and improved lesion detection compared with FBP and had potential for radiation dose reduction while preserving low-contrast detectability.

PbS Colloidal Quantum Dot Near Infrared Photoconductors: DC and Noise Characterization

High sensitivity photodetectors based on PbS colloidal quantum dots have been demonstrated by several research groups in the last years with performance comparable to commercial III–V semiconductor devices. Nevertheless, investigation of the noise performance of such new photodetectors is still lacking. Here we report on the characterization of PbS colloidal quantum dot near infrared photoconductors including a preliminary analysis of noise power spectra. Devices have been characterized focusing on the low frequency regime (up to 10 kHz) investigating the noise dependence on the voltage bias.

Noise analysis of the turbojet and turbofan engine tests

Aerogine noise leads to environment pollution largely when aerogine is tested. In this paper, the power spectrum analysis method of the aeroengine test noise was discussed, and the noise measurement and analysis experiments of a turbojet engine and a turbofan engine tests were carried out. The noise level, main noise resource, and noise characteristics of the two turbojet and turbofan engines were analyzed. Meanwhile, the indoor noise and far-field noise of the turbojet engine were both measured, the noise spread characteristics were analyzed and the noise reduction performance of the test bench was evaluated. The noise generated by the turbojet engine test had the discrete characteristic of high frequency. The higher frequencies when peak values occurred were the blade passage frequencies and the noises with lower frequencies were the broad band noises, especially the jet noise, and the maximum of the peak values occurred at the basic frequencies or harmonic frequencies of the compressor. Meanwhile, the noises generated by the turbofan engine, focused on the high frequencies and the peak values corresponded to the rotation noise of the fan blades. The experimental results were consistent with the theory basically, which indicated that the aeroengine operating status information could be identified by the noise power spectrum analysis. In addition to the aeroengine noise reduction research, the noise power spectrum analysis could also be used to diagnose the fault of the aeroengine structure and performance. On the other hand, the indoor and far-field noise measurement experimental results implied that the noise was suppressed from 136 dB to 85 dB and could provide the reference to the noise reduction design of the aeroengine test bench.

An Analysis of Noise Power Spectrum Due to Mark Variations of an Optical Disk System

Readout signal and noise power spectrum of an optical disk system were simulated and the results were compared with the measured power spectrum to analyze the major sources of noise in the system. The readout signal and power spectrum were calculated by varying the mark shape and position as well as beam off-track range. The variations of mark length, position and beam off-track range were assumed to have a Gaussian probability distribution. The power spectrum of the readout signal was calculated by executing a discrete fast Fourier transform algorithm. From the fitting of the measured signal power spectrum, the major sources of noise in our optical disk system were deduced to be the variations of mark length, position and beam off-track range.

The analysis of noise power spectrum induced by the semiconductor laser phase noise in fibre-optic interferometers considering optical fibre dispersion

In a fibre-optic interferometer, when the frequency linewidth of the light source is larger than a certain value, the influence of optical fibre dispersion should be considered. In this paper, considering the dispersion effect, we present a theoretical analysis of the output noise power spectrum of the fibre-optic interferometer induced by the random phase noise of semiconductor lasers. The analysis focuses on the noise power spectrum influenced by the first-order dispersion of the single-mode optical fibre. The closed expressions of output noise characteristics are derived. The formulations obtained in this paper can be applied to both a dispersion and a non-dispersion fibre-optic interferometer or optical interferometer.

The analysis of noise power spectrum induced by the semiconductor laser phase noise in fibre-optic interferometers considering optical fibre dispersion

The analysis of noise power spectrum induced by the semiconductor laser phase noise in fibre-optic interferometers considering optical fibre dispersion

Technical note: compensation for field non-uniformity on a mammographic X-ray unit.

A well observed phenomenon in diagnostic radiology is that of the anode heel effect. The heel effect is caused by target absorption of X rays emitted from an electron impact site at angles more nearly parallel to the anode face (Curry et al, 1984). This has the consequence of producing a non-uniform exposure profile in the image plane (Figure 1). Other non-uniformities may be caused by imperfections in any pre-filtration foils (IPSM, 1989). Although non-uniformity is tolerated and to a large extent is of no clinical concern, there are applications where a uniform field exposure is required. One such area is where quantitative measurements need to be made at different spatial positions. Additionally it may prove advantageous to use a flat field exposure in mammographic examination of women with very large breasts where areas towards the breast periphery may get a significantly lower exposure than at the chest wall, reducing image contrast in that region. As part of a Department of Health evaluation into the use of computed radiography (CR) in mammography (see, for example, Takeno et al, 1987) the authors have been investigating the mammographic imaging performance of CR using quantitative measurement techniques. One such technique is noise power spectrum analysis. Because this technique requires uniform exposure distribution over a large field area (12 cm × 12 cm) it was necessary to develop a technique to compensate for X-ray beam non-uniformity on a clinical mammography unit (Philips Diagnost UC).

Simulation study of cerebral blood flow measurements in xenon‐CT: Evaluation of washin/washout procedures

Simulation programs have been created that allow one to vary image pixel noise, the number and the distribution of scans with time, cerebral tissue parameters, and the type of xenon CT inhalation procedure in order to investigate CBF measurements with respect to accuracy and signal-to-noise ratio (SNR). In particular, standard washin studies were compared to washin/washout studies. Based on the results of these simulations, a new protocol is suggested; it consists of only 3 min of xenon inhalation (washin phase) and 3 min of washout, monitored by one reference and six enhancement scans taken at 1-min intervals. Compared with a standard 8-min washin study of equal total dose, flow standard deviation (s.d.) for an unconstrained least-squares algorithm is reduced by factors of 2.2 and 1.2 for gray and white matter, respectively; for flow distributed uniformly from 20 to 80 ml/min/100 g, an average s.d. reduction factor of 1.7 is achieved. This was confirmed experimentally in a volunteer study using noise power spectrum analysis. In addition, effects of tissue heterogeneity have been investigated; both the bias and s.d. of flow estimates due to varying proportions of white and gray matter in a given volume element are reduced in washin/washout protocols. When compared to a short washin-only study of 4.5 min, the 3-min washin/3-min washout study provides an improvement of flow s.d. by a factor of 1.6 and 1.9 for gray and white matter, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Fast Fourier digital quantum mottle analysis with application to rare earth intensifying screen systems.

The advent of fast Fourier techniques has greatly facilitated the digital analysis of noise power spectra (Wiener spectra) by circumventing the need for the autocorrelation function. We are now able to Fourier analyze film data at about the same rate the microdensitometer-computer system can collect it (1000 points/sec). The new technique has been applied to the analysis of the quantum mottle of several rare earth intensifying screen systems confirming earlier estimates from our pilot studies that such screens are capable of reducing exposure by a factor of about 2 with imaging parameters comparable to those of conventional calcium tungstate systems.

Application of a laser self-beat spectroscopic technique to the study of solutions of human plasma lipoproteins

The technique of self-beat or homodyne spectroscopy in conjunction with a He–Ne (50 mW) laser has been applied to the determination of the translational diffusion constants of human plasma lipoproteins. The photo power spectrum of the laser light scattered by the particles was analyzed in the frequency domain by noise power spectrum analysis and in the time domain by autocorrelation. The results were corroborated by the spectral analysis of polystyrene latex spheres of known diameters. The precision of these measurements was 3 % and accuracy 5 %. The following results were obtained, for the very low density lipoproteins, D of 5.4 × 10–7 cm2 s–1, and a mean diameter of 792 ± 30 Å, for the low density lipoproteins, D of 1.8 × 10–7 cm–2 s–1 and a mean diameter of 265 ± 13 Å, for the high density lipoprotein, D of 0.72 × 10–7 cm2 s–1, and a mean diameter of 110 ± 10 Å. Results from the two methods of analysis were in good agreement and were comparable to those reported previously in the literature. Whereas the noise power spectrum required recording in the order of hours, autocorrelation can be conveniently done in minutes. As compared with more conventional methods, autocorrelation in conjunction with laser self-beat spectroscopy provides a rapid technique for the physical characterization of lipoprotein particles in solution.