Optimum Acquisition Time Research Articles

Development of a compact 406 nm diode laser-based cavity-enhanced spectrometer for high-sensitive detection of NO2 levels in exhaust gas

Nitrogen dioxide (NO2) is an important air pollutant due to its environmental impact and adverse effects on human health. It is released into the atmosphere primarily through anthropogenic activities. Here, we report on the development of a simple, compact, and cost-effective robust optical detection method exploiting cavity-enhanced absorption spectroscopy for high-sensitive and selective measurement of NO2 levels in real-time using a visible diode laser operating at 406 nm. A typical detection limit of ∼330 ppb for NO2 was achieved with an optimum acquisition time of ∼3.9 s, at optimal cavity pressure of 100 Torr. The sensor system demonstrates an effective optical path-length of 180 m in a high-finesse 50 cm long optical cavity in an interference-free spectral region and aerosol-free conditions. The spectrometer was optimized, calibrated, and demonstrated for the detection of NO2 levels in vehicular exhaust gases.

18F-NaF PET/CT of Obese Patients on a Lutetium-Yttrium Oxyorthosilicate PET/CT System: Patient Dosimetry, Optimization of Injected Activity, and Acquisition Time.

18F-NaF PET/CT has a rapid single-pass extraction and fast clearance from soft tissues, resulting in a good target-to-background ratio. This study aimed to establish the optimum acquisition time and dosimetry for 18F-NaF PET/CT to evaluate bone metastases in obese patients. A secondary objective was to evaluate the impact of acquisition time on image quality, lesion detection rate, noise level, and radiation burden in this patient group. Methods: In total, 60 patients were included in the study (20 patients with a body mass index (BMI) of 30.0-34.9 kg/m2, 20 with a BMI of 35-39.9 kg/m2, and 20 with a BMI of >40 kg/m2). Images were acquired after intravenous injection of a 2.2 MBq/kg (0.06 mCi/kg) dose of 18F-NaF. Data were acquired in list mode using ordered-subset expectation maximization reconstruction. The raw data were rebinned to simulate scans with acquisition times of 2, 2.5, and 3 min per bed position. The scans were visually analyzed by 2 observers and scored by rank against a panel of parameters (overall image quality, noise level, background soft tissue, and lesion detectability), and the contrast-to-noise ratio (CNR) was calculated. Results: The mean CNR was 20.19 ± 8.39 for a 2-min acquisition, 21.03 ± 8.35 for 2.5 min, and 22.16 ± 8.37 for 3 min. There were no statistically significant differences in CNR among the 3 different acquisition durations (P > 0.05). Lesion delineation was excellent and independent of the acquisition time. All relevant lesions could be identified with all 3 acquisition times. A mean activity of 215.4 ± 31.3 MBq was injected, with estimated mean effective absorbed doses of 4.09 ± 0.59 mSv for 18F-NaF PET and 7.88 ± 1.66 mSv for CT alone. Conclusion: 18F-NaF PET/CT can be beneficial in obese patients because of its good pharmacokinetics. Optimal osseous staging can be achieved with relatively low doses and radiation burden. Lesion delineation was excellent regardless of acquisition time. However, it is recommended that an acquisition of 3 min per bed position be used in patients with a BMI of more than 40.

Portable X-ray Fluorescence (p-XRF) Uncertainty Estimation for Glazed Ceramic Analysis: Case of Iznik Tiles

The aim of this study is to estimate the uncertainty of a portable X-ray fluorescence (p-XRF) instrument for the (semi-quantitative) analyses of tiles with underglaze decoration. Before starting the campaign of on-site measurements, the optimum acquisition time and the most accurate calibration mode were selected. For this purpose, the elemental composition of two glass standards of NIST (SRM610 and SRM612) and a Corning A standard were measured with varied times (5–360 s) and in different calibration modes (Mining, Mining Light Elements, Soil, and Rare Earth Elements). Afterwards, a set of blue-and-white tiles that was unearthed at Iznik Tile Kilns Excavation between the dig seasons of 2015 and 2019 was examined with p-XRF by selecting ten points of measure from each layer (body, transparent glaze, and blue coloured areas). The elemental composition of different layers was evaluated by means of the intragroup and intergroup data. They were also compared to the previous studies and found that the corrosion-free, homogeneous, and non-porous surfaces decrease the relative standard deviation (RSD) by increasing the consistency of the compositional data. The major elements found in the matrix of each layer (Al and Si for the body, Pb and Sn for the glaze) have the lowest value of RSD, as expected. However, the comparison of the data with the analysis of the reference materials showed that the content of Mg and also Si, which belong to the low-Z elements group, is shifted relatively towards the higher compositional values. The impossibility of measuring the elemental composition of sodium does not hinder the classification of the samples. Although the transition metals have very low concentrations, p-XRF measurements appear rather consistent and the intrinsic scattering of the data observed for a single artefact is largely smaller than those observed for the tiles of different historical buildings. Thus, it allows the classification to be made related to the different techniques used.

Evaluation of commercial virtually imaged phase array and Fabry-Pérot based Brillouin spectrometers for applications to biology.

Measuring the complex mechanical properties of biological objects has become a necessity to answer key questions in mechanobiology and to propose innovative clinical and therapeutic strategies. In this context, Brillouin light scattering (BLS) has recently come into vogue, offering quantitative imaging of the mechanical properties without labels and with a micrometer resolution. In biological samples, the magnitude of the spectral changes are typically of a few tens of MHz, and the ability of modern spectrometers to monitor such subtle changes needs to be evaluated. Moreover, the multiplicity of variations in optical arrangements, specific to each lab, requires to set a standard for the assessment of the characteristics of BLS systems. In this paper we propose a protocol to evaluate the precision and accuracy of two commercial spectrometers that is reproducible across labs. For a meaningful comparison, we coupled the spectrometers to the same microscope and to the same laser. We first evaluated the optimum acquisition time and laser power. We evaluated the precision using pure water samples. We determined the accuracy by probing water solutions with increasing concentration of salt and comparing it with theory. Following these quantifications, we applied the VIPA-based spectrometer to tumor spheroids engineered from different cell lines that possess different metastatic potentials and resistance to therapies. On these models, we detected significant changes in the linewidth suggesting that BLS measurements of the viscosity could be used as a read-out to distinguish different levels of drug resistance.

Quantification of nitrous acid (HONO) and nitrogen dioxide (NO2) in ambient air by broadband cavity-enhanced absorption spectroscopy (IBBCEAS) between 361 and 388 nm

Abstract. This work describes an incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for quantification of HONO and NO2 mixing ratios in ambient air. The instrument is operated in the near-ultraviolet spectral region between 361 and 388 nm. The mirror reflectivity and optical cavity transmission function were determined from the optical extinction observed when sampling air and helium. To verify the accuracy of this approach, Rayleigh scattering cross sections of nitrogen and argon were measured and found to be in quantitative agreement with literature values. The mirror reflectivity exceeded 99.98 %, at its maximum near 373 nm, resulting in an absorption path length of 6 km from a 1 m long optical cavity. The instrument precision was assessed through Allan variance analyses and showed minimum deviations of ±58 and ±210 pptv (1σ) for HONO and NO2, respectively, at an optimum acquisition time of 5 min. Measurements of HONO and NO2 mixing ratios in laboratory-generated mixtures by IBBCEAS were compared to thermal dissociation cavity ring-down spectroscopy (TD-CRDS) data and agreed within combined experimental uncertainties. Sample ambient air data collected in Calgary are presented.

Influence of Dynamical Decoupling Sequences with Finite-Width Pulses on Quantum Sensing for AC Magnetometry

Dynamical decoupling sequences of multiple pulses offer filter functions for the time evolution of a qubit superposition state, and thus are indispensable tools for quantum sensing. The authors investigate the effects of sequences of finite-width pulses on ac magnetometry based on nitrogen-vacancy centers in isotopically controlled diamond. This experimental and theoretical study shows that finite pulse width alters the optimum acquisition time, and shows how to correct the resulting frequency shift, providing a guideline for accurate measurement of the frequency, linewidth, and amplitude of an ac field.

Airborne cavity enhanced absorption spectroscopy for high time resolution measurements of atmospheric NO2

Nitrogen dioxide (NO2) is an important trace gas in the troposphere and plays a vital role in many aspects of the chemistry of the atmosphere. Accurate measurement of NO2 is the primary step to understand its role in atmospheric chemistry and to establish effective pollution prevention policies. Relatively few measurements of the NO2 profile in troposphere by using point-type instruments with high temporal resolution have been carried out in China. Due to the relatively poor measurement environment on airborne platform, the measurement system requires good anti-vibration ability, stability and environmental adaptability. A home-built incoherent broadband cavity enhanced absorption spectrometer (IBBCEAS) on the airborne platform is presented in this paper, and applied to high temporal resolution observations of the actual atmospheric NO2 spatial distribution. According to the strong absorption of NO2 in a wavelength range from 449 nm to 470 nm, we choose a high-power 457 nm light-emitting diode (LED) as a light source. A Peltier is used to control LED temperature and to stabilize the LED temperature at (200.1)℃. The pure PFA material optical cavity and sampling tube are used to reduce wall loss. And we choose the highly reflecting mirrors (reflectivity R0.9999@440-450 nm) to improve the effective optical path. A 2 m filter is used at the inlet of instrument to remove most of the particulate matter in the sample flows, which reduce the effect of particulate matter on the effective path length. In order to meet the requirement for time resolution in airborne measurement, we use an off-axis paraboloic mirror instead of an achromatic lens to improve the optical coupling efficiency. The reflectivity of the highly reflecting mirror is calibrated by the difference in Rayleigh scattering between He and N2. And the optimum averaging time of the IBBCEAS instrument is confirmed to be 1000 s by the Allan variance analysis. Detection limit (1) of 10 ppt for NO2 is achieved with an optimum acquisition time of 1000 s. Concentrations of NO2 are recorded and compared with data from a long path different optical absorption spectroscopy instrument, and the results show good agreement with each other. The linear correlation coefficient R2 is 0.86 in a slope of 0.92 with an offset of -0.402 ppb. The IBBCEAS system is deployed on an airborne platform, and the detection limit is 95 ppt (1) with a time resolution of 2 s. The profile of tropospheric NO2 by airborne observation is obtained over Shijiazhuang in Northern China. IBBCEAS system in the airborne platform shows good stability.

The detection and quantification of the defects in adhesive bonded joints of the piezoelectric sensors by infrared thermographic nondestructive testing

In this paper, efficacy of pulsed thermography technique has been explored for the first time for the detection and quantification of the subsurface defects present in the rubber-encapsulated piezoelectric sensors. Initial experiments were performed on adhesively bonded joints of the rubber/Al or rubber/PZT control samples to find out an optimum acquisition time for the 3-mm rubber encapsulants. Thermographic measurements were performed in the reflection mode and acquired thermal images were analysed and processed images were described in terms of the phase images. The defective regions are identified as delamination of the adhesive joints at the interface of rubber and PZT stacks, and presence of porosity in the encapsulation in the inspected hydrophone. The defect depths of the observed anomalies were calculated empirically from the plots of the peak time of thermal contrast (tmax) maximum and thermal contrast maximum (Cmax) for a particular defect. The estimated defect depths of the prominent porosity observed in the PZT hydrophone are found nearly 1 mm from the surface.

Incoherent broadband cavity enhanced absorption spectroscopy for measurements of atmospheric HONO

We report the development of an incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) based on an ultraviolet light emitting diode (UV-LED), and the IBBCEAS instrument is used for simultaneously measuring of the atmospheric HONO and NO2. The cavity-enhanced method is characterized by high sensitivity and spatial resolution. The incoherent broadband light is focused into a high-finesse optical cavity, two highly reflecting mirrors form the ends of the cavity, and the light is then trapped between the two highly reflecting mirrors, resulting in long photon residence time and long optical path length. The effects of the Rayleigh scattering of the gases in the cavity and stability of the UV-LED light source were discussed in this paper. The reflectivity of the highly reflecting mirror was calibrated by the difference of Rayleigh scattering of He and N2, and the optimum averaging time of the IBBCEAS instrument was confirmed to be 320 s by the Allan variance analysis. Detection limits (1) of 0.22 ppb for HONO and 0.45 ppb for NO2 were achieved with an optimum acquisition time of 320 s. In order to test the accuracy of measured results by the IBBCEAS instrument, concentrations of HONO and NO2 were recorded during about continuous three days by the IBBCEAS instrument and compared with the results obtained by a different optical absorption spectroscopy (DOAS) instrument. The results of HONO show a linear correction factor (R2) of 0.917, in a slope of 0.897 with an offset of 0.13 ppb; NO2 concentration measured by the IBBCEAS instrument accords well with the result obtained by the DOAS instrument, with a linear correlation of R2 = 0.937, in a slope of 0.914 with an offset of-0.17 ppb.

Time of acquisition and network stability in pediatric resting-state functional magnetic resonance imaging.

Resting-state functional magnetic resonance imaging (rs-fMRI) has been shown to elucidate reliable patterns of brain networks in both children and adults. Studies in adults have shown that rs-fMRI acquisition times of ∼5 to 6 min provide adequate sampling to produce stable spatial maps of a number of different brain networks. However, it is unclear whether the acquisition time directly translates to studies of children. While there are many similarities between the brains of children and adults, many differences are also evident. Children have increased metabolism, differences in brain morphology and connectivity strengths, greater brain plasticity, and increased brain noise. Furthermore, there are differences in physiologic parameters, such as heart and respiratory rates, and compliance of the blood vessels. These developmental differences could translate into different acquisition times for rs-fMRI studies in pediatric populations. Longer scan times, however, increase the subject burden and the risk for greater movement, especially in children. Thus, the goal of this study was to assess the optimum acquisition time of rs-fMRI to extract stable brain networks in school-age children. We utilized fuzzy set theory in 84 six-to-eight year-old children and found that eight networks, including the default mode, salience, frontal, left frontoparietal, right frontoparietal, sensorimotor, auditory, and visual networks, all stabilized after ∼5½ min. The sensorimotor network showed the least stability, whereas the salience and auditory networks showed the greatest stability. A secondary analysis using dual regression confirmed these results. In conclusion, in young children with little head motion, rs-fMRI acquisition times of ∼5½ min can extract the full complement of brain networks.

Development and deployment of a cavity enhanced UV-LED spectrometer for measurements of atmospheric HONO and NO2 in Hong Kong

An optical analytical instrument based on light emitting diode (LED) incoherent broadband cavity enhanced absorption spectroscopy (LED-IBBCEAS) was developed for simultaneous measurements of HONO and NO2 in ambient air. Detection limits (for signal-to-noise ratio, SNR = 2) of 0.6 ppbv for HONO and 2 ppbv for NO2 were achieved with an optimum acquisition time of 120 s. Field intercomparison campaign at a suburban site of Tung Chung in Hong Kong was carried out. Daytime and nighttime concentrations of HONO and NO2 were recorded and compared with data from a long path absorption photometer (LOPAP) and a NOx analyzer equipped with a blue light converter. The test of such a LED-IBBCEAS setup by the measurement intercomparison with the well established HONO and NO2 measurement instruments, for the first time, in a real atmospheric environment, demonstrated the feasibility of the proposed technique for the measurement of environmental HONO and NO2 concentrations in a manner that is free of chemical and spectral interference. During the measurement period from 12:32 on May 12th to 12:32 on May 14th, 2012, the quantitative assessments from these techniques showed well agreed data. High temporal correlations of HONO with NOx and CO were observed, and possible formation sources of HONO are discussed. Occasional inconsistencies in the quantitative assessment of HONO were observed during the in-field campaign. The problems encountered by the IBBCEAS technique applied to field observation and the further improvements are discussed.

Development of an open-path incoherent broadband cavity-enhanced spectroscopy based instrument for simultaneous measurement of HONO and NO2 in ambient air

We report on the development of an optical instrument based on incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) for simultaneous open-path measurements of nitrous acid (HONO) and nitrogen dioxide (NO2) in ambient air using a UV light emitting diode operating at ∼366 nm. Detection limits of ∼430 pptv for HONO and ∼1 ppbv for NO2 were achieved with an optimum acquisition time of 90 s, determined by an Allan variance analysis. Based on a 1.85 m long high optical finesse open-path cavity, the effective optical path length of 2.8 km was realized in aerosol-free samples or in an urban environment at modest aerosol levels. Such a kilometer long optical absorption is comparable to that achieved in the well established differential optical absorption spectroscopy (DOAS) technology while keeping the instrument very compact. Open-path detection configuration allows one to avoid absorption cell wall losses and sampling induced artifacts. The demonstrated sensitivity and specificity shows high potential of this cost-effective and compact infrastructure for future field applications with high spatial resolution.

Comparison of deuterium NMR imaging methods and application to plants

FID, gradient-echo, and spin-echo imaging sequences have been compared id order to determine the imaging sequence optimally suited for deuterium MRI. Each sequence was investigated for the polar and Cartesian spatial encoding mode. Analytical expressions for the SNR per unit time were derived. The most favorable imaging parameters, in particular the optimum acquisition time and repetition time for each sequence, were deduced. The sensitivities per unit time of the selected sequences at individually optimized parameters were compared. While the FID sequence (in polar mode) provides the optimum SNR, and is thus favorable for imaging at very low deuterium concentrations, this method is also very susceptible to artifacts and yields poor spatial resolution. In standard situations one will therefore choose the gradient-echo sequence in the Cartesian encoding mode, with a simple spoiling gradient interval. The 20% lower sensitivity of this sequence is compensated for by its significantly better overall image quality. Optimal parameters of this sequence with respect to SNR per unit time include an acquisition time of 0.7T 2 ∗ and a repetition time of 0.7 T 1. When deuterium MRI was applied to small plants, it was possible to demonstrate that (i) spatial structures of 0.3 mm can be resolved at high D 20 concentrations, (ii) concentrations as low as 20 m M can be imaged at spatial resolution of 5 mm, and (iii) time resolution can be chosen as low as 3 min in projectional images at a spatial resolution of 0.5 mm, if tracer concentrations in the range of 50% D 20 are applied. In kinetic image series the distribution patterns, the transport pathways, and the transport velocity of water in plants could be determined.