Measuring Cerebral and Cerebellar Glutathione in Children Using 1H MEGA-PRESS MRS.

BACKGROUND AND PURPOSE: Glutathione is an important antioxidant in the human brain and therefore of interest in neurodegenerative disorders. The purpose of this study was to investigate the feasibility of measuring glutathione in healthy nonsedated children by using the 1H Mescher-Garwood point-resolved spectroscopy (MEGA-PRESS) sequence at 3T and to compare glutathione levels between the medial parietal gray matter and the cerebellum. MATERIALS AND METHODS: Glutathione was measured using MEGA-PRESS MRS (TR = 1.8 seconds, TE = 131 ms) in the parietal gray matter (35 × 25 × 20 mm3) of 6 healthy children (10.0 ± 2.4 years of age; range, 7-14 years; 3 males) and in the cerebellum of 11 healthy children (12.0 ± 2.7 years of age; range, 7-16 years; 6 males). A postprocessing pipeline was developed to account for frequency and phase variations in the edited ON and nonedited OFF spectra. Metabolites were quantified with LCModel and reported both as ratios and water-scaled values. Glutathione was quantified in the ON-OFF spectra, whereas total NAA, total Cho, total Cr, mIns, Glx, and taurine were quantified in the OFF spectra. RESULTS: We found significantly higher glutathione, total Cho, total Cr, mIns, and taurine in the cerebellum (P < .01). Glx and total NAA were significantly higher in the parietal gray matter (P < .01). There was no significant difference in glutathione/total Cr (P = .93) between parietal gray matter and cerebellum. CONCLUSIONS: We demonstrated that glutathione measurement in nonsedated children is feasible. We found significantly higher glutathione in the cerebellum compared with the parietal gray matter. Metabolite differences between the parietal gray matter and cerebellum agree with published MRS data in adults.

Elucidating Metabolic Maturation in the Healthy Fetal Brain Using 1H-MR Spectroscopy.

BACKGROUND AND PURPOSE: (1)H-MRS provides a noninvasive way to study fetal brain maturation at the biochemical level. The purpose of this study was to characterize in vivo metabolic maturation in the healthy fetal brain during the second and third trimester using (1)H-MRS. MATERIALS AND METHODS: Healthy pregnant volunteers between 18 and 40 weeks gestational age underwent single voxel (1)H-MRS. MR spectra were retrospectively corrected for motion-induced artifacts and quantified using LCModel. Linear regression was used to examine the relationship between absolute metabolite concentrations and ratios of total NAA, Cr, and Cho to total Cho and total Cr and gestational age. RESULTS: Two hundred four spectra were acquired from 129 pregnant women at mean gestational age of 30.63 ± 6 weeks. Total Cho remained relatively stable across the gestational age (r(2) = 0.04, P = .01). Both total Cr (r(2) = 0.60, P < .0001) as well as total NAA and total NAA to total Cho (r(2) = 0.58, P < .0001) increased significantly between 18 and 40 weeks, whereas total NAA to total Cr exhibited a slower increase (r(2) = 0.12, P < .0001). Total Cr to total Cho also increased (r(2) = 0.53, P < .0001), whereas total Cho to total Cr decreased (r(2) = 0.52, P < .0001) with gestational age. The cohort was also stratified into those that underwent MRS in the second and third trimesters and analyzed separately. CONCLUSIONS: We characterized metabolic changes in the normal fetal brain during the second and third trimesters of pregnancy and derived normative metabolic indices. These reference values can be used to study metabolic maturation of the fetal brain in vivo.

SU-E-I-65: Magnetic Resonance Spectroscopy of the Prostate: A Phantom Study of Metabolite Concentrations.

PURPOSE: Magnetic Resonance Spectroscopy (MRS) of the prostate is not used in radiotherapy departments on a regular basis due to a number of issues. The indication and severity of prostate cancer is related to the presence of choline in the prostate, in particular, the ratio of choline (plus creatine) to citrate. In-vivo data supports this theory only marginally but lacks strong correlation with biopsy data. The situation is further complicated by the lack of precise spatial information in biopsy, variation of magnetic susceptibility, and spatial dependence of MRS data on the distance from the endo-rectal coil. The latter also cause low signal-to-noise ratio (SNR). We intend to understand how the level of metabolite concentrations and spatial dependences determine what is observed in MRS. METHODS: A spherical phantom is filled with water solutions containing various amounts of metabolites. It is placed on top of an endo-rectal coil with the balloon filled with per fluorocarbon. MRS data is acquired on a GE 1.5 T MR scanner. The metabolite values, their ratios etc as reported in GE software, FuncTool are studied as functions of metabolite concentrations in the phantom. RESULTS: Analysis of the phantom data indicates that the metabolite ratio reported in FuncTool is approximately linearly correlated to the metabolite concentrations used in the phantom to a certain point and then saturates whereas the largest metabolite value is well correlated with its concentration in the phantom. All metabolite values become weaker and SNR lower as we move away from the coil. CONCLUSIONS: This work indicates the potential of using metabolite values directly provided their spatial dependences on the distance of the voxels from the endo-rectal coil can be accommodated.

[Partial k-space sampling with zero filling used with phase-contrast flow measurements: in vivo and in vitro validation]. / Partielle k-Raum-Auslesung mit Null-Interpolation bei Phasenkontrast-Flussmessungen: In-vivo- und In-vitro-Validierung.

PURPOSE: To validate the technique of partial k-space sampling and zero filling with phase-contrast flow measurements as compared to measurements with full k-space sampling. MATERIALS AND METHODS: In vitro: A laminar flow phantom was utilized to evaluate the effect of partial k-space sampling on the accuracy, precision and signal-to-noise ratio of phase-contrast flow measurements. In vivo: The effect of partial k-space sampling on the quantification of cardiac output (n = 40 patients) and the duration of the scan were evaluated in the ascending aorta (n = 37) and pulmonary trunk (n = 34) in a prospective study. RESULTS: Partial k-space sampling resulted in an increase in the SNR by 2 % in vitro. The precision was altered by less than 1 %. Flow volumes were systematically overestimated by 3.5 %. No significant differences were found in the in vivo measurements of cardiac output. The scan duration was reduced by 34 % by utilizing partial k-space sampling. CONCLUSION: Partial k-space sampling can be used to reduce scan time without a significant decrease in the accuracy or precision of phase-contrast flow measurements in large arteries.

High-field MR angiography on an in vitro stenosis model determination of the spatial resolution on 1.5 and 3T in correlation to flow velocity and contrast medium concentration.

Since the first description of coronary magnetic angiography (MRA) in the early of 1990, this method seems to be shaped us a promising noninvasive modality to view the coronary arteries. Since several years dedicated high-field MR systems up to 4T are available for human use. The aim of the study was the evaluation of an in vitro vessel model with defined stenoses on 1.5T and 3T. For imaging at 3T, we used a 3d gradient-echo-sequence (fast SPGR). Furthermore, we examined the influence of the flow velocity and the contrast medium concentration on the spatial resolution. The accurate detection of in vitro stenoses was possible in segments up to 0.6 mm at 3T, the best results were obtained at a flow velocity of 40 ml/min and a contrast medium concentration of 0.2 mmol/l. The influence of the contrast medium concentration was statistically not significant. These results show that the spatial resolution can be increased by the use of a high-field MR scanner. Further in vivo studies are necessary to eliminate the method's limitation in visualizing small distal vessel segments.

Comparison of different cardiac MRI sequences at 1.5 T/3.0 T with respect to signal-to-noise and contrast-to-noise ratios - initial experience.

PURPOSE: To compare image quality, signal-to-noise (SNR) and contrast-to-noise ratios (CNR) of different MRI sequences for cardiac imaging at 1.5 T and 3.0 T in volunteers. MATERIAL AND METHODS: 10 volunteers (5 male, 5 female) with a mean age of 33 years (+/- 8) without any history of cardiac diseases were examined on a GE Signa 3.0 T and a GE Signa 1.5 T TwinSpeed Excite (GE Medical Systems, Milwaukee, WI, USA) scanner using a 4-element phased array surface coil (same design) on the same day. For tissue characterization ECG gated Fast Spinecho (FSE) T (1)- (Double IR), T (1)-STIR (Triple IR) and T (2)-weighted sequences in transverse orientation were used. For functional analysis a steady state free precession (SSFP - FIESTA) sequence was performed in the 4-chamber, 2-chamber long axis and short axis view. The flip angle used for the SSFP sequence at 3.0 T was reduced from 45 degrees to 30 degrees to keep short TR times while staying within the pre-defined SAR limitations. All other sequence parameters were kept constant. RESULTS: All acquisitions could successfully be completed for the 10 volunteers. The mean SNR 3.0 T compared to 1.5 T was remarkably increased (p < 0.05) for the T (2) - (160 % SNR increase), the STIR-T (1)- (123 %) and the T (1)- (91 %) weighted FSE. Similar results were found comparing CNR at 3.0 T and 1.5 T. The mean SNR achieved using the SSFP sequences was more than doubled by 3.0 T (150 %), but did not have any significant effect on the CNR. The image quality at 3.0 T did not appear to be improved, and was considered to be significantly worse when using SSFP sequences. Artefacts like shading in the area of the right ventricle (RV) were found to be more present at 3.0 T using FSE sequences. After a localized shim had been performed in 5/10 volunteers at the infero-lateral wall of the left ventricle (LV) with the SSFP sequences at 3.0 T no significant increase in artefacts could be detected. CONCLUSIONS: In all cardiac FSE sequences, SNR and CNR at 3.0 T were found to be increased compared to 1.5 T without any major changes of the sequence parameters. The adjusted SSFP sequences fulfilled the expected increase in SNR at 3.0 T but showed no increase in CNR. On the contrary, the overall image quality did not change or was even found to be significantly lower for the SSFP and the FSE sequences at the free wall of the RV. Nevertheless, the results are encouraging for the use of 3.0 T for cardiac tissue characterization and new applications with progressing use of parallel imaging.

Performance and use of current sheet antennae for RF-hyperthermia of a phantom monitored by 3 tesla MR-thermography.

Several MR-compatible current sheet antennae (CSA) of different height (h) (16 cm (l) x 8 cm (w) x 1-5 cm (h)) were built for simulated RF (96 MHz) hyperthermia of a medium-sized (12l) tissue-equivalent phantom inside a 3 tesla whole body tomograph. Prior to use, efficiencies of the CSA were determined by network analysis and by calorimetry. Depending on the height h of the CSA and on the thickness d(bolus) of the water bolus used for RF-coupling of the CSA to the lossy medium, their efficiency varied between 20-70% and the CSA with h = 3 cm was selected for simulated RF hyperthermia. During heating, spatial temperature distributions (20-42 degrees C) of five slices (voxel size 2 x 2 x 10mm(3)) were recorded intermittently within 4 s/slice by measuring the temperature dependent shift of the (1)H resonance frequency (125.32 MHz). A phased array consisting of two identical CSA produced distinctly different spatial temperature distributions at 0 and 180 degrees phase difference between both RF channels feeding the antennae. Within a one-dimensional heat diffusion model, the specific absorption rate (SAR) of the electromagnetic wave generated by a single antenna was deduced from the experimental data resulting in a penetration depth (1/e(2)) of approximately 4 cm.

Human cardiac imaging at 3 T using phased array coils.

Using a two-element phased array receiver coil, single breath-hold, ECG gated cardiac images of signal-to-noise ratios up to 130 and contrast-to-noise ratios exceeding 35 between myocardium and blood were recorded at 3 T. At several locations within the myocardium, T*(2) and B(0) inhomogeneity were determined. Because of shorter T*(2) times and larger B(0) inhomogeneities attributable to enhanced susceptibility effects, real-time cardiac imaging, the use of spiral scans, and echo planar imaging are expected to be considerably more difficult at 3 T.

Comparison of four magnetic resonance methods for mapping small temperature changes.

Non-invasive detection of small temperature changes (< 1 degree C) is pivotal to the further advance of regional hyperthermia as a treatment modality for deep-seated tumours. Magnetic resonance (MR) thermography methods are considered to be a promising approach. Four methods exploiting temperature-dependent parameters were evaluated in phantom experiments. The investigated temperature indicators were spin-lattice relaxation time T1, diffusion coefficient D, shift of water proton resonance frequency (water PRF) and resonance frequency shift of the methoxy group of the praseodymium complex (Pr probe). The respective pulse sequences employed to detect temperature-dependent signal changes were the multiple readout single inversion recovery (T One by Multiple Read Out Pulses; TOMROP), the pulsed gradient spin echo (PGSE), the fast low-angle shot (FLASH) with phase difference reconstruction, and the classical chemical shift imaging (CSI). Applying these sequences, experiments were performed in two separate and consecutive steps. In the first step, calibration curves were recorded for all four methods. In the second step, applying these calibration data, maps of temperature changes were generated and verified. With the equal total acquisition time of approximately 4 min for all four methods, the uncertainties of temperature changes derived from the calibration curves were less than 1 degree C (Pr probe 0.11 degrees C, water PRF 0.22 degrees C, D 0.48 degrees C and T1 0.93 degrees C). The corresponding maps of temperature changes exhibited slightly higher errors but still in the range or less than 1 degree C (0.97 degrees C, 0.41 degrees C, 0.70 degrees C, 1.06 degrees C respectively). The calibration results indicate the Pr probe method to be most sensitive and accurate. However, this advantage could only be partially transferred to the thermographic maps because of the coarse 16 x 16 matrix of the classical CSI sequence. Therefore, at present the water PRF method appears to be most suitable for MR monitoring of small temperature changes during hyperthermia treatment.