Zenon Starčuk

In vivo 1H NMR spectroscopy of rat brain at 1 ms echo time

Using optimized, asymmetric radiofrequency (RF) pulses for slice selection, the authors demonstrate that stimulated echo acquisition mode (STEAM) localization with ultra‐short echo time (1 ms) is possible. Water suppression was designed to minimize sensitivity to B1 inhomogeneity using a combination of 7 variable power RF pulses with optimized relaxation delays (VAPOR). Residual water signal was well below the level of most observable metabolites. Contamination by the signals arising from outside the volume of interest was minimized by outer volume saturation using a series of hyperbolic secant RF pulses, resulting in a sharp volume definition. In conjunction with FASTMAP shimming (Gruetter Magn Reson Med 1993;29:804–811), the short echo time of 1 msec resulted in highly resolved in vivo 1H nuclear magnetic resonance spectra. In rat brain the water linewidths of 11–13 Hz and metabolite singlet linewidths of 8–10 Hz were measured in 65 μl volumes. Very broad intense signals (Δν1/2 > 1 kHz), as expected from membranes, for example, were not observed, suggesting that their proton T2 are well below 1 msec. The entire chemical shift range of 1H spectrum was observable, including resolved resonances from alanine, aspartate, choline group, creatine, GABA, glucose, glutamate, glutamine, myo‐inositol, lactate, N‐acetylaspartate, N‐acetylaspartylglutamate, phosphocreatine, and taurine. At 9.4 T, peaks close to the water were observed, including the H‐1 of α‐D‐glucose at 5.23 ppm and a tentative H‐1 resonance of glycogen at 5.35 ppm. Magn Reson Med 41:649–656, 1999.

Quantitation of magnetic resonance spectroscopy signals: the jMRUI software package

The software package jMRUI with Java-based graphical user interface enables user-friendly time-domain analysis of magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) and HRMAS-NMR signals. Version 3.x has been distributed in more than 1200 groups or hospitals worldwide. The new version 4.x is a plug-in platform enabling the users to add their own algorithms. Moreover, it offers new functionalities compared to versions 3.x. The quantum-mechanical simulator based on NMR-SCOPE, the quantitation algorithm QUEST and the main MRSI functionalities are described. Quantitation results of signals obtained in vivo from a mouse and a human brain are given.

Very short echo time proton MR spectroscopy of human brain with a standard transmit/receive surface coil

A method for localized proton spectroscopy of the human brain is proposed which can be used with a standard transmit/receive planar surface coil producing an inhomogeneous RF field. Water suppression is accomplished by a train of full passage adiabatic pulses with optimized frequencies and delays, which account for variation in the water resonance frequency and the spin‐lattice relaxation time. The robust method requires minimal pulse calibration and provides high‐quality spectra even at very short echo times and in the absence of outer volume saturation and, therefore, is well suited for clinical in vivo spectroscopy. Performance of the method is demonstrated on a test object and on MR spectra from the human brain at 3 T. Magn Reson Med 44:964–967, 2000.

Distributed capillary adiabatic tissue homogeneity model in parametric multi-channel blind AIF estimation using DCE-MRI

One of the main challenges in quantitative dynamic contrast‐enhanced (DCE) MRI is estimation of the arterial input function (AIF). Usually, the signal from a single artery (ignoring contrast dispersion, partial volume effects and flow artifacts) or a population average of such signals (also ignoring variability between patients) is used.

Simulation of coupled-spin systems in the steady-state free-precession acquisition mode for fast magnetic resonance (MR) spectroscopic imaging

The steady-state free-precession (SSFP) acquisition mode may be found useful for fast in vivo proton magnetic resonance spectroscopic imaging in high-field MR systems because of the achievable signal-to-noise ratio and the avoidance of RF pulses with large flip angles. Detection of signals from metabolites with coupled-spin systems under SSFP has not yet been accomplished, but should be possible in high field, albeit with substantial signal truncation. It must be expected that the spin system evolution and the spectra will be affected by the steady-state conditions, which prevent the spin systems from returning to the Boltzmann equilibrium. Computer simulation is needed for the experiment design and spectrum quantification. This work outlines a suitable simulation method (QuaM-EPG), which combines and extends two pre-existing approaches: the density matrix calculation, used in high-resolution NMR, and the extended phase graph method, used to describe cyclic excitation in fast MRI of water protons. The method is illustrated by its application to model molecules and myo-inositol, which is one of the clinically relevant target molecules. It is shown that antiphase and multiple-quantum coherences may represent a considerable portion of the steady-state magnetization in a quantum-mechanical sense and that the spectral patterns are affected thereby.

jMRUI Version 4 : A plug-in platform

The software package jMRUI with Java-based graphical user interface enables user-friendly time-domain analysis of magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI), and HRMAS-NMR signals. The version 3.x has been distributed in more than 1000 groups or hospitals world-wide. The new version 4.x is a plug-in platform enabling the users to add their own algorithms. Moreover, it offers new functionalities compared to the versions 3.x.

Diffusion Kurtosis Imaging Detects Microstructural Alterations in Brain of α-Synuclein Overexpressing Transgenic Mouse Model of Parkinson’s Disease: A Pilot Study

Evidence suggests that accumulation and aggregation of α-synuclein contribute to the pathogenesis of Parkinson’s disease (PD). The aim of this study was to evaluate whether diffusion kurtosis imaging (DKI) will provide a sensitive tool for differentiating between α-synuclein-overexpressing transgenic mouse model of PD (TNWT-61) and wild-type (WT) littermates. This experiment was designed as a proof-of-concept study and forms a part of a complex protocol and ongoing translational research. Nine-month-old TNWT-61 mice and age-matched WT littermates underwent behavioral tests to monitor motor impairment and MRI scanning using 9.4 Tesla system in vivo. Tract-based spatial statistics (TBSS) and the DKI protocol were used to compare the whole brain white matter of TNWT-61 and WT mice. In addition, region of interest (ROI) analysis was performed in gray matter regions such as substantia nigra, striatum, hippocampus, sensorimotor cortex, and thalamus known to show higher accumulation of α-synuclein. For the ROI analysis, both DKI (6 b-values) protocol and conventional (2 b-values) diffusion tensor imaging (cDTI) protocol were used. TNWT-61 mice showed significant impairment of motor coordination. With the DKI protocol, mean, axial, and radial kurtosis were found to be significantly elevated, whereas mean and radial diffusivity were decreased in the TNWT-61 group compared to that in the WT controls with both TBSS and ROI analysis. With the cDTI protocol, the ROI analysis showed decrease in all diffusivity parameters in TNWT-61 mice. The current study provides evidence that DKI by providing both kurtosis and diffusivity parameters gives unique information that is complementary to cDTI for in vivo detection of pathological changes that underlie PD-like symptomatology in TNWT-61 mouse model of PD. This result is a crucial step in search for a candidate diagnostic biomarker with translational potential and relevance for human studies.

Blind deconvolution in dynamic contrast-enhanced MRI and ultrasound

This paper is focused on quantitative perfusion analysis using MRI and ultrasound. In both MRI and ultrasound, most approaches allow estimation of rate constants (Ktrans, kep for MRI) and indices (AUC, TTP) that are only related to the physiological perfusion parameters of a tissue (e.g. blood flow, vessel permeability) but do not allow their absolute quantification. Recent methods for quantification of these physiological perfusion parameters are shortly reviewed. The main problem of these methods is estimation of the arterial input function (AIF). This paper summarizes and extends the current blind-deconvolution approaches to AIF estimation. The feasibility of these methods is shown on a small preclinical study using both MRI and ultrasound.

Correction of baseline and lineshape distortions in fourier transform NMR spectroscopy by estimation of missing signals

Abstract Lineshape distortions and baseline undulations are the well-known undesirable effects of the linear phase correction, when applied to signals the initial part of which is corrupted, either duplicated or missing. While the former imperfection can be cured easily by proper time setting, the latter is more principal. It is shown, however, that some general prior knowledge of spectra enables the reconstruction of the missing part of the signal with high fidelity and the removal of most of the distortions appearing in the absorption-mode spectra. For this purpose a simple procedure is proposed yielding good results even after a single iteration step. Simplicity, negligible computational requirements, and its efficacy are the main advantages of this method.

Solvent-peak suppression with a difference hard-pulse technique including solvent presaturation

Abstract A new technique for the solvent-peak suppression is presented which delivers pure absorption-mode spectra. A considerable improvement of the null excitation profile and of the degree of the solvent-signal suppression was reached by incorporating into the hard-pulse scheme the solvent presaturation period. With the use of a difference approach an efficient elimination of the broad solvent signals arising from inhomogeneous parts of the sample was made possible.