Accurate Quantification of H Spectra: From Finite Impulse Response Filter Design for Solvent Suppression to Parameter Estimation

A scheme for accurate quantification of ¹H spectra is presented. The method uses maximum-phase finite impulse response (FIR) filters for solvent suppression and an iterative nonlinear least-squares (NLLS) algorithm for parameter estimation. The estimation algorithm takes the filter influence on the metabolites of interest into account and can thereby correctly incorporate a large variety of prior knowledge into the estimation phase. The FIR filter is designed in such a way that no distortion of the important initial samples is introduced. The FIR filter method is compared numerically with the HSVD method for water signal removal in a number of examples. The results show that the FIR method, using an automatic filter design scheme, slightly outperforms the HSVD method in most cases. The good performance and ease of use of the FIR filter method combined with its low computational complexity motivate the use of the proposed method.     

Automatic frequency alignment and quantitation of single resonances in multiple magnetic resonance spectra via complex principal component analysis

Several algorithms for automatic frequency alignment and quantitation of single resonances in multiple magnetic resonance (MR) spectra are investigated. First, a careful comparison between the complex principal component analysis (PCA) and the Hankel total least squares-based methods for quantifying the resonances in the spectral sets of magnetic resonance spectroscopy imaging (MRSI) spectra is presented. Afterward, we discuss a method based on complex PCA plus linear regression and a method based on cross correlation of the magnitude spectra for correcting frequency shifts of resonances in sets of MR spectra. Their advantages and limitations are demonstrated on simulated MR data sets as well as on an in vivo MRSI data set of the human brain.     

Mass transfer characteristics for VOC permeation through flat sheet porous and composite membranes: The impact of the different membrane layers on the overall membrane resistance

In this paper, the mass transfer coefficients for trichloroethylene (TCE), toluene (TOL) and dimethyl sulfide (DMS) are experimentally determined for different porous and composite membranes. For polypropylene/polyvinylidenedifluoride porous layer/thin film polydimethylsiloxane dense layer composite membranes, membrane mass transfer coefficients are 2.55E−03, 2.82E−03 and 2.90E−03 m/s for TCE, TOL and DMS in N₂ at 30.0 ± 0.1 °C, respectively. For polyester/polyacrylonitrile porous layer/thin film polydimethylsiloxane dense layer composite membranes, they are higher, namely 4.28E−03, 4.55E−03 and 4.81E−03 m/s for TCE, TOL and DMS in N₂ at 30.0 ± 0.1 °C, respectively. Analysis of the contribution of the dense layer of both composite membranes to the total membrane resistance for mass transfer, showed that this contribution was small for both composite membranes. The higher mass transfer coefficients of the thin film polydimethylsiloxane composite membranes from this study in comparison to others from the literature are primarily due to improvement of the mass transfer characteristics of the porous layer. Analysis of the mass transfer characteristics of the different porous layers of which the total porous layer is composed, showed that the contribution of the porous “backing” layer for mechanical support can be substantial in comparison to the porous layer in contact with the dense layer.