Voigt Line Shape Model Research Articles

In vivo characterization of glycogen storage disease type III in a mouse model using glycoNOE MRI.

Glycogen storage disease type III (GSD III) is a rare inherited metabolic disease characterized by excessive accumulation of glycogen in liver, skeletal muscle, and heart. Currently, there are no widely available noninvasive methods to assess tissue glycogen levels and disease load. Here, we use glycogen nuclear Overhauser effect (glycoNOE) MRI to quantify hepatic glycogen levels in a mouse model of GSD III. Agl knockout mice (n = 13) and wild-type controls (n = 10) were scanned for liver glycogen content using glycoNOE MRI. All mice were fasted for 12 to 16 h before MRI scans. GlycoNOE signal was quantified by fitting the Z-spectrum using a four-pool Voigt lineshape model. Next, the fitted direct water saturation pool was removed and glycoNOE signal was estimated from the integral of the residual Z spectrum within -0.6 to -1.4 ppm. Glycogen concentration was also measured ex vivo using a biochemical assay. GlycoNOE MRI clearly distinguished Agl knockout mice from wild-type controls, showing a statistically significant difference in glycoNOE signals in the livers across genotypes. There was a linear correlation between glycoNOE signal and glycogen concentration determined by the biochemical assay. The obtained glycoNOE maps of mouse livers also showed higher glycogen levels in Agl knockout mice compared to wild-type mice. GlycoNOE MRI was used successfully as a noninvasive method to detect liver glycogen levels in mice, suggesting the potential of this method to be applied to assess glycogen storage diseases.

Data Processing Optimization in Untargeted Metabolomics of Urine Using Voigt Lineshape Model Non-Linear Regression Analysis.

Nuclear magnetic resonance (NMR) spectroscopy is well-established to address questions in large-scale untargeted metabolomics. Although several approaches in data processing and analysis are available, significant issues remain. NMR spectroscopy of urine generates information-rich but complex spectra in which signals often overlap. Furthermore, slight changes in pH and salt concentrations cause peak shifting, which introduces, in combination with baseline irregularities, un-informative noise in statistical analysis. Within this work, a straight-forward data processing tool addresses these problems by applying a non-linear curve fitting model based on Voigt function line shape and integration of the underlying peak areas. This method allows a rapid untargeted analysis of urine metabolomics datasets without relying on time-consuming 2D-spectra based deconvolution or information from spectral libraries. The approach is validated with spiking experiments and tested on a human urine 1H dataset compared to conventionally used methods and aims to facilitate metabolomics data analysis.

High-pressure, high-temperature optical cell for mid-infrared spectroscopy

The design, characterization, and operation of a new high-temperature, high-pressure optical cell for infrared spectroscopy is presented. The optical cell uses 16 cm CaF2 window rods to penetrate the temperature gradient between the heated optical path length and the ambient conditions surrounding the system. Along the 21.3 cm optical path length, good temperature uniformity was measured with deviations being less than 2.4% of the mean absolute temperature. Further characterization of the optical cell revealed usable transmission up to ∼ 8 µm and pressure stability from vacuum to over 30 atm. Moreover, stable operation of the optical cell during simultaneous heating and pressurization to 800 K and over 30 atm was demonstrated. To illustrate the utility of the new facility, high-resolution measurements of the R-branch in the fundamental absorption band of nitric oxide near 5.2 µm were collected at several pressures (1-34 atm) and temperatures (294–802 K) using an external cavity quantum cascade laser. The measured spectra were compared with Voigt line shape simulations using the HITRAN/HITEMP databases. At high gas densities, deviations from the Voigt line shape model are observed, emphasizing the need to further study infrared molecular spectra at high temperatures and pressures.

Pressure broadening coefficients in the ν6 band of CH3F in collision with He

In this study we report the first measurements of the pressure line broadening coefficients of 219 lines of CH3F in the PP, RP, RQ, PQ, and RR sub-branches of the ν6 band (8.5 µm-spectral region) at room temperature using a high-resolution Fourier transform spectrometer. The collisional line widths are obtained from the non-linear least-square multi-pressure fitting techniques. A Voigt line shape model was used in the present analysis. Measured values are compared with the results of theoretical calculation based on semi-classical formalism of Robert-Bonamy (RB) model with exact isotropic trajectories. Even with a Smith-Giraud-Cooper intermolecular potential model the calculated values show a quite good agreement with experimental results.

Reliable quantification of marrow fat content and unsaturation level using in vivo MR spectroscopy.

To develop a novel technique for reliable quantification of bone marrow fat content and composition using in vivo MR spectroscopy (MRS). An MRS quantification method combining both advantages of Voigt line shape model and time-domain analysis was developed. The proposed method was tested using computer-simulated data and in vivo data acquired at lumbar vertebral bodies of 23 subjects (age, 83.8 ± 3.7 y; male, n = 13; female, n = 10) from L1 to L4. Reliability and reproducibility were calculated for the quantification results. Comparisons between the proposed method and some conventional methods were conducted. Low mean absolute percentage errors and low mean coefficients of variation for computer simulations suggest that the proposed method is accurate and precise. By using this method, marrow fat content can be quantified reliably, even for data with low spectral resolution and low signal-to-noise ratio (SNR). Unsaturation level can be reliably quantified for data with moderate spectral resolution and moderate SNR. Results obtained from in vivo data using the proposed method demonstrated better model fit than conventional methods. The method proposed in this study has better performance than conventional methods in the quantification of bone marrow MRS data and has great potential for wide applications of studying marrow fat content and composition. Magn Reson Med 79:1722-1729, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Laser absorption of nitric oxide for thermometry in high-enthalpy air

The design and demonstration of a laser absorption sensor for thermometry in high-enthalpy air is presented. The sensor exploits the highly temperature-sensitive and largely pressure-independent concentration of nitric oxide in air at chemical equilibrium. Temperature is thus inferred from an in situ measurement of nascent nitric oxide. The strategy is developed by utilizing a quantum cascade laser source for access to the strong fundamental absorption band in the mid-infrared spectrum of nitric oxide. Room temperature measurements in a high-pressure static cell validate the suitability of the Voigt lineshape model to the nitric oxide spectra at high gas densities. Shock-tube experiments enable calibration of a collision-broadening model for temperatures between 1200–3000 K. Finally, sensor performance is demonstrated in a high-pressure shock tube by measuring temperature behind reflected shock waves for both fixed-chemistry experiments where nitric oxide is seeded, and for experiments involving nitric oxide formation in shock-heated mixtures of N2 and O2. Results show excellent performance of the sensor across a wide range of operating conditions from 1100–2950 K and at pressures up to 140 atm.

An empirical study on the importance of a speed-dependent Voigt line shape model for tropospheric water vapor profile remote sensing

We use high quality ground-based solar absorption spectra measured in close coincidence with Vaisala RS92 radiosonde in situ water vapor profiles to demonstrate that a Voigt line shape model yields systematic errors in the remotely sensed tropospheric water vapor profiles. We analyse absorption signatures of 4 H 2 16O and 2 HD 16O bands situated between 790 and 4710 cm −1. We find that applying a speed-dependent Voigt line shape model instead of a Voigt line shape model significantly improves the agreement between the water vapor profiles obtained by the radiosondes and by infrared remote-sensing in the different bands. An optimal agreement is obtained for a Γ 2 (relaxation rate for speed-dependence) of 6–21% of Γ 0 (Voigt relaxation rate), which is consistent to the values derived from laboratory experiments. Our study suggests that further extensive laboratory investigations of line shape models are a key for improving the quality of modern water vapor remote sensing products.

Ground-based FTIR water vapour profile analyses

Abstract. Due to a large vertical gradient and strong variability of water vapour, algorithms that are effectively applied for ground-based remote sensing of many different atmospheric trace gases can be insufficient for the retrieval of tropospheric water vapour profiles. We review the most important features of the retrieval and of the radiative transfer modelling required for accurate monitoring of tropospheric water vapour profiles by ground-based FTIR (Fourier Transform Infrared) experiments. These are: a fit of a variety of different water vapour lines with different strength, a logarithmic scale inversion, a speed dependent Voigt line shape model, and a joint temperature profile retrieval. Furthermore, the introduction of an interspecies constraint allows for a monitoring of HDO/H2O ratio profiles.

Improving spectroscopic line parameters by means of atmospheric spectra: Theory and example for water vapor and solar absorption spectra

Current atmospheric remote sensing experiments measuring high resolution spectra apply instruments of similar quality as the laboratory experiments that are especially equipped to derive spectroscopic parameters. We propose a method that uses high quality atmospheric spectra to improve the spectroscopic parameterization. It is an optimal estimation method that applies the uncertainty ranges given in current spectroscopic databases as a priori covariance and the residuals between the simulated and measured atmospheric spectra as new measurements. We test the method by updating the current HITRAN parameters of 49 mid-infrared water vapor lines (situated in 15 spectral windows between 795 and 1330 cm - 1 ) by the information present in high quality ground-based Fourier transform infra-red (FTIR) spectra. We show that the application of a speed dependent Voigt line shape model is important. The updated water vapor parameterization, compared to the original one, leads to lower residuals, larger measurement information content, and better agreement between remotely sensed and coincident in situ water vapor profiles. Using the new line parameterization, a state-of-the-art ground-based FTIR system is able to monitor upper tropospheric water vapor amounts and middle/upper tropospheric HDO / H 2 O ratios.

Line profile study of transitions in the 30012 ← 00001 and 30013 ← 00001 bands of carbon dioxide perturbed by air

In this work we present a line profile study for air-broadened carbon dioxide transitions in the 30012 ← 00001 and 30013 ← 00001 vibrational bands. The room temperature spectra were recorded at a resolution of 0.008 cm −1 using a Fourier Transform spectrometer. The air-broadening, air-shift, and air-line mixing coefficients were derived from a simultaneous fitting of spectra using the Voigt model and a Speed-Dependent Voigt lineshape model. The results obtained are consistent with other studies in addition to the theoretically calculated values. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the relaxation matrix elements.

Line shape parameters measurement and computations for self-broadened carbon dioxide transitions in the 30012 ← 00001 and 30013 ← 00001 bands, line mixing, and speed dependence

Transitions of pure carbon dioxide have been measured using a Fourier transform spectrometer in the 30012 ← 00001 and 30013 ← 00001 vibrational bands. The room temperature spectra, recorded at a resolution of 0.008 cm −1, were analyzed using the Voigt model and a Speed Dependent Voigt line shape model that includes a pressure dependent narrowing parameter. Intensities, self-induced pressure broadening, shifts, and weak line mixing coefficients are determined. The results obtained are consistent with other studies in addition to the theoretically calculated values. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the relaxation matrix elements.

Quantification of MRS data in the frequency domain using a wavelet filter, an approximated Voigt lineshape model and prior knowledge

Quantification of MRS spectra is a challenging problem when a large baseline is present along with a low signal to noise ratio. This work investigates a robust fitting technique that yields accurate peak areas under these conditions. Using simulated long echo time (1)H MRS spectra with low signal to noise ratio and a large baseline component, both the accuracy and reliability of the fit in the frequency domain were greatly improved by reducing the number of fitted parameters and making full use of all the known information concerning the Voigt lineshape. Using an appropriate first order approximation to a popular approximation of the Voigt lineshape, a significant improvement in the estimate of the area of a known spectral peak was obtained with a corresponding reduction in the residual. Furthermore, this improved parameter choice resulted in a large reduction in the number of iterations of the least-squares fitting routine. On the other hand, making use of the known centre frequency differences of the component resonances gave negligible improvement. A wavelet filter was used to remove the baseline component. In addition to performing a Monte Carlo study, these fitting techniques were also applied to a set of 10 spectra acquired from healthy human volunteers. Again, the same reduced parameter model gave the lowest value for chi(2) in each case.

Choice of spectroscopic lineshape model affects metabolite peak areas and area ratios.

The use of Lorentzian model lineshapes leads to systematic errors in the quantification of in vivo (1)H NMR spectra. Experimental lineshapes are better modeled by the Voigt (mixed Lorentzian-Gaussian) function, leading to more accurate fits (reduced chi(2)). In this work, results from a group of 41 subjects are presented. It is shown that not only are the estimated metabolite peak areas affected by the choice of lineshape model, but so too are the metabolite ratios. For example, the NAA/choline ratio was 1.92 +/- 0.06 (mean +/- standard error) using the Lorentzian lineshape model and 1.85 +/- 0.05 using the Voigt lineshape model. The corresponding figures for NAA/creatine were 2.32 +/- 0.06 and 2. 10 +/- 0.05 respectively, which are significantly different for the two lineshape models. An explanation of this previously unreported effect is given. This finding clearly has serious implications for the methodology and reporting of spectroscopic studies.

Spectral Intensity and Lineshape Measurements in the First Overtone Band of HF Using Tunable Diode Lasers

High-resolution absorption lineshapes for theP(3) andP(6) transitions of the first overtone (v= 2–0) band of HF at 296 K have been measured using a pair of distributed feedback diode lasers operating near 1.31 and 1.34 μm, respectively. Spectral line intensities and self-broadening parameters were determined by fitting the measured spectra with Voigt, Galatry, and Rautian lineshape models. Voigt profiles fit the low-pressure (<10 Torr) spectra of theP(3) transition reasonably well due to the relatively strong collisional broadening effect. Lineshape measurements of theP(6) transition (for pressures ranging from 5 to 60 Torr) show significant variation from the Voigt lineshape model due to velocity-changing collisions that effectively reduce the Doppler component of the spectral line. Lineshape models that include motional (Dicke) narrowing effects, Galatry (soft collision) and Rautian (hard collision) profiles yield significant improvements in the spectral lineshape fits compared with Voigt profiles. The collisional broadening coefficient (γ) of theP(6) transition obtained from a Voigt fit is ∼4% lower than those found with either Galatry or Rautian profile fits. The measured intensities and self-broadening coefficients are compared with values in the HITRAN database and previous measurements.

Use of Voigt lineshape for quantification of in vivo 1H spectra.

Quantification of NMR visible metabolites by spectral modeling usually assumes a Lorentzian or Gaussian lineshape, despite the fact that experimental lineshapes are neither. To minimize systematic fitting errors, a mixed Lorentzian-Gaussian (Voigt) lineshape model was developed. When tested with synthetic FIDs, the Voigt lineshape model gave more accurate results (maximum error 2%) than either Lorentzian (maximum error 20%) or Gaussian models (maximum error 12%). The three lineshape models gave substantially different peak areas in an in vitro experiment, with the Voigt model having a much lower chi2 (2.1 compared with 5.2 for the Lorentzian model and 6.2 for the Gaussian model). In a group of 10 healthy volunteers, fitting of 1H spectra from cerebral white matter gave significantly different peak areas between the methods. Even when area ratios were taken, the Lorentzian model gave higher values (+5% for NAA/choline and +2% for NAA/creatine) than the Voigt lineshape model, whereas the Gaussian model gave lower values (-2% and -1%, respectively).

Line parameter measurements and calculations of CO broadened by H 2O and CO 2 at elevated temperatures

Measurements of collisional broadening of four fundamental CO lines in atmospheres of CO 2 and H 2O at 300–600 K were made. The Voigt line-shape model was fitted parametrically to the absorption spectra line-shapes. The results are compared with other experimental studies and with theoretical calculations for CO 2 broadening. Absorption spectra of the exhaust gases of a flat flame were recorded and analyzed to yield CO concentration, temperature, and line half-widths. The flame spectra half-widths were compared with extrapolations of lower temperature data using the simple power law approximation γ(T)=γ(T 0) ( T 0 T ) n . The utility of this approximation in the development of combustion diagnostic techniques is discussed.

Line parameter measurements and calculations of CO broadened by nitrogen at elevated temperatures

Measurements of the line strengths and collisional broadening widths of CO in a N 2 atmosphere were made from 300 to 600 K. The lines studied were the P(2), P(3), P(7), P(12), P(18), and P(22) lines of the fundamental band at 2100 cm −1. The absorption spectra were parametrically fit to a Voigt lineshape model. The band strength was determined to be 250±8 cm −2atm −1. The broadening results are compared to Anderson-Tsao-Curnutte calculations and to other experimental studies. The possibility of using an equation of the form γ(T)=γ(T 0( T 0 T ) n to extrapolate the temperature dependence of the half-widths to flame temperatures is discussed.