Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
-
A method is introduced that provides improved in vivo spectroscopic measurements of glutamate (Glu), glutamine (Gln), choline (Cho), creatine (Cre), N-acetyl compounds (NAtot, NAA + NAAG), and the inositols (mI and sI). It was found that at 3T, TE averaging, the f1 = 0 slice of a 2D J-resolved spectrum, yielded unobstructed signals for Glu, Glu + Gln (Glx), mI, NA(tot), Cre, and Cho. ⋯ Apparent T1/T2 values were obtained from the raw data, and metabolite tissue levels were determined relative to a readily available standard. A repeatibility error of <5%, and a coefficient of variation (CV) of <10% were observed for brain Glu levels in a study of six normal volunteers.
-
Comparative Study
Cortical depth-dependent gradient-echo and spin-echo BOLD fMRI at 9.4T.
To examine cortical depth-related spatial specificity and signal changes in gradient-echo (GE) and spin-echo (SE) blood oxygenation level-dependent (BOLD) fMRI signals, a well-established cat visual stimulation model was used at 9.4T. The GE BOLD signal percent change is the highest at the surface of the cortex containing pial vessels, and decreases as cortical depth increases. In contrast, the SE BOLD signal is more specific to parenchyma, showing the highest signal change in the middle cortical areas. ⋯ The averaged ratio of DeltaR2* to DeltaR2 in all active regions, including large vessels, is 3.3 +/- 0.5 (N = 6). The averaged ratio of DeltaR2* to DeltaR2 is 8.8 +/- 1.7 (N = 4) on the surface of the cortex with large pial draining vessels, and decreases to 1.9 +/- 0.1 on the middle cortical areas with parenchymal microvessels. DeltaR2*/DeltaR2 is closely related to basal susceptibility effects and can be used to differentiate tissue from vessel regions.
-
One of the most common artifacts for echo-planar imaging is the Nyquist ghost, typically overcome with the aid of a reference scan preceding the actual image acquisition. In this work, a nonlinear phase correction obviating the need for a reference scan is proposed. ⋯ The method's underlying assumption is that the images are dominated by their low frequency and symmetric part. In vivo data demonstrate the effectiveness of the algorithm showing ghost suppression comparable to that achievable with the reference-scan method.
-
Most arterial spin labeling (ASL) techniques apply echoplanar imaging (EPI) because this strategy provides relatively high SNR in short measuring times. Unfortunately, those techniques are very susceptible to static magnetic field inhomogeneities and perfusion signals from organs with fast transverse relaxation might decrease due to the exchange of water molecules in capillaries and organ tissue combined with relatively long echo times of EPI sequences. To overcome these problems a novel imaging technique, FAIR True-FISP, was developed. ⋯ For this reason a sequence structure had to be developed which keeps the advantages of True-FISP and makes the signal intensity sensitive to the FAIR preparation. Breathhold and nonbreathhold examinations of kidneys are presented and possible strategies to quantitative flow measurements are reported. It is shown that correction of spatially inhomogeneous receiver coil characteristics is easily feasible and leads to clinically valuable perfusion examinations of kidneys without application of potentially nephrotoxic contrast media.
-
A 2D multislice spin-lock (MS-SL) MR pulse sequence is presented for rapid volumetric T1rho-weighted imaging. Image quality is compared with T1rho-weighted data collected using a single-slice (SS) SL sequence and T2-weighted data from a standard MS spin-echo (SE) sequence. ⋯ Measurements of T1rho using the saturation-corrected MS-SL data are nearly identical to those measured using an SS-SL sequence. The MS-SL sequence produces quantitative T1rho maps of an entire sample volume with the high-SNR advantages conferred by SE-based sequences.