G Chadzynski

Differentiation between idiopathic and atypical parkinsonian syndromes using three-dimensional magnetic resonance spectroscopic imaging

Objectives Degeneration of dopaminergic neurons in the substantia nigra (SN) pars compacta is the primary cause of idiopathic Parkinsons disease (iPD). In early stages of disease in particular, presentation of symptoms is non-specific leading to difficulties in differentiating between iPD and atypical parkinsonian syndromes (aPS). The aim of this study was to evaluate the feasibility of three-dimensional magnetic resonance spectroscopic imaging (MRSI) of the SN region for differentiation between iPD and aPS. Methods 20 patients with iPD, 10 with aPS and 22 controls were examined on a 3 T MR scanner using three-dimensional MRSI with a voxel size of 0.252 ml and an echo time of 30 ms. Excitation volume was positioned in such a way that in each hemisphere 1 voxel defines the rostral and 1 voxel the caudal SN region. Using a fully automatic spectra evaluation, the metabolite ratios of N-acetyl aspartate/creatine (NAA/Cr) were calculated. Results In all cases spectra with good quality were obtained. Differences in rostral to caudal NAA/Cr ratios were significant between controls and iPD patients, as well as between iPD and aPS patients (p<0.001 for both). For controls, rostral NAA/Cr was greater than caudal, whereas in iPD patients this ratio was reversed. aPS patients showed similar ratios as controls. Conclusions Typical reversed rostral to caudal NAA/Cr ratios in iPD patients suggests that they could be linked to specific pathology of neuronal loss in the SN pars compacta. Therefore, the results suggest that MRSI may support the differential diagnosis of patients with clinically unclassifiable parkinsonian syndromes who do not yet fulfil the established clinical criteria.

Chemical shift imaging without water suppression at 3 T

PURPOSE Proton magnetic resonance spectroscopy without water suppression is possible but is hampered by the presence of sideband artifacts. The aim of this study was to develop a chemical shift imaging method without water suppression for clinical routine with reduced sideband artifacts. MATERIALS AND METHODS Spectra from ten healthy volunteers were acquired using a 3T (TimTrio, Siemens, Erlagen, Germany) scanner with a Point RESolved Spectroscopy sequence for volume selection. Postprocessing was performed in three steps: correcting the water peak position in all spectra (chemical shift correction), subtracting the Gaussian convolution of all free induction decay signals (FIDs) (water signal reduction), and subtracting the FID of a water phantom from the volunteers FID signal (reduction of sidebands). For the postprocessing customized software was developed with Matlab 2007b. RESULTS The described technique provides spectra with reduced water signal and sidebands. Quantitative analysis showed that there is a good agreement between spectra obtained with water suppressing radiofrequency pulses and the new method. Moreover, spectra obtained with the new method do not need phase correction. CONCLUSION The new method offers sufficient reduction of the water peak and sidebands. Its simplicity allows its use in clinical applications.

Tissue specific resonance frequencies of water and metabolites within the human brain.

Chemical shift imaging (CSI) without water suppression was used to examine tissue-specific resonance frequencies of water and metabolites within the human brain. The aim was to verify if there are any regional differences in those frequencies and to determine the influence of chemical shift displacement in slice-selection direction. Unsuppressed spectra were acquired at 3T from nine subjects. Resonance frequencies of water and after water signal removal of total choline, total creatine and NAA were estimated. Furthermore, frequency distances between the water and those resonances were calculated. Results were corrected for chemical shift displacement. Frequency distances between water and metabolites were consistent and greater for GM than for WM. The highest value of WM to GM difference (14ppb) was observed for water to NAA frequency distance. This study demonstrates that there are tissue-specific differences between frequency distances of water and metabolites. Moreover, the influence of chemical shift displacement in slice-selection direction is showed to be negligible.

MR spectroscopy for in vivo assessment of the oncometabolite 2-hydroxyglutarate and its effects on cellular metabolism in human brain gliomas at 9.4T.

To examine in vivo metabolic alterations in the isocitrate dehydrogenase (IDH) mutated gliomas using magnetic resonance spectroscopy (MRS) at magnetic field 9.4T.

Fast and efficient free induction decay MR spectroscopic imaging of the human brain at 9.4 Tesla

The purpose of this work was to develop a fast and efficient MRSI‐FID acquisition scheme and test its performance in vivo. The aim was to find a trade‐off between the minimal total acquisition time and signal‐to‐noise ratio of the acquired spectra.

Ultrashort‐TE stimulated echo acquisition mode (STEAM) improves the quantification of lipids and fatty acid chain unsaturation in the human liver at 7 T

Ultrahigh‐field, whole‐body MR systems increase the signal‐to‐noise ratio (SNR) and improve the spectral resolution. Sequences with a short TE allow fast signal acquisition with low signal loss as a result of spin–spin relaxation. This is of particular importance in the liver for the precise quantification of the hepatocellular content of lipids (HCL). In this study, we introduce a spoiler Gradient‐switching Ultrashort STimulated Echo AcqUisition (GUSTEAU) sequence, which is a modified version of a stimulated echo acquisition mode (STEAM) sequence, with a minimum TE of 6 ms. With the high spectral resolution at 7 T, the efficient elimination of water sidebands and the post‐processing suppression of the water signal, we estimated the composition of fatty acids (FAs) via the detection of the olefinic lipid resonance and calculated the unsaturation index (UI) of hepatic FAs. The performance of the GUSTEAU sequence for the assessment of UI was validated against oil samples and provided excellent results in agreement with the data reported in the literature. When measuring HCL with GUSTEAU in 10 healthy volunteers, there was a high correlation between the results obtained at 7 and 3 T (R2 = 0.961). The test–retest measurements yielded low coefficients of variation for HCL (4 ± 3%) and UI (11 ± 8%) when measured with the GUSTEAU sequence at 7 T. A negative correlation was found between UI and HCL (n = 10; p < 0.033). The ultrashort TE MRS sequence (GUSTEAU; TE = 6 ms) provided high repeatability for the assessment of HCL. The improved spectral resolution at 7 T with the elimination of water sidebands and the offline water subtraction also enabled an assessment of the unsaturation of FAs. This all highlights the potential use of this MRS acquisition scheme for studies of hepatic lipid composition in vivo. Copyright