ACE: a single-shot method for water-suppressed localization and editing of spectra, images, and spectroscopic images

Alanine peak in central neurocytomas on proton MR spectroscopy

INTRODUCTION

We present three consecutive patients with central neurocytoma in whom proton MRS demonstrated the presence of alanine.

MATERIALS AND METHODS

Three patients in the age range 24 to 30 years underwent MRI and proton MRS using a 1.5-T system. MRS was performed with the multivoxel PRESS sequence. All three patients underwent surgery and the diagnosis of central neurocytoma was established by histopathological examination and immunostaining.

RESULTS

With an echo time of 135 ms glycine, high choline, small NAA and alanine were observed in all three patients.

CONCLUSION

Alanine may be observed in central neurocytomas as it is in meningiomas. Other spectral peaks such as those for glycine and NAA should help to identify this tumor correctly.

Transmit/receive headcoil for optimal 1H MR spectroscopy of the brain in paediatric patients at 3 T

(1)H magnetic resonance (MR) spectroscopy is a useful tool to obtain metabolic information from the brain in paediatric patients. To detect signals of metabolites at low concentrations or from small volumes, the signal-to-noise ratio (SNR) has to be optimized. The SNR can be increased by going to higher field strengths. However, this leads to higher spectral bandwidths, which increases the chemical shift artefact. Here we present a transmit/receive headcoil which is adapted to the dimensions of the paediatric head and enables PRESS localization with high radio-frequency (RF) bandwidths that minimize the chemical shift displacement to only 5%. In addition, since the pulse lengths are shorter with higher RF bandwidths, the echo time can be reduced to 10 ms improving SNR as well.

Stimulated anti-echo selection in spatially localized NMR spectroscopy

Spectral localization using the stimulated-echo acquisition mode (STEAM) is one of the most popular methods in volume-localized in vivo NMR spectroscopy. The localized volume signal is generated via stimulated echoes from spins excited by three 90 degrees RF pulses, and the conventional STEAM sequence detects the stimulated-echo signal. From an analysis of the STEAM pulse sequence using the coherence transfer pathway formalism, stimulated anti-echoes are also formed by the same pulse sequence, which constitute the other half of the localized signal in the STEAM experiment. A new scheme of pulsed field gradients for the selection of stimulated anti-echoes was proposed, and localized spectroscopy in the stimulated anti-echo selection mode was achieved on a phantom and from in vivo rat brain.

Three dimensional outer volume suppression for short echo time in vivo 1H spectroscopic imaging in rat brain

Three-dimensional in vivo spectroscopic imaging in rat brain requires additional localization to reduce the effects of lipid contamination. Outer volume suppression has been shown to be effective in two dimensions. We have extended this approach to three dimensions with additional outer volume suppression conforming to the shape of the rat brain. The technique suppresses the pericranial lipid effectively, allowing sampling of volumes close to the skull and effective localized shimming. These benefits permit three-dimensional 1H magnetic resonance spectroscopic imaging to be performed over most of the brain at shorter echo times, providing spectra more amenable to quantitative analysis.

Mapping of cerebral metabolites in rats by 1H magnetic resonance spectroscopic imaging. Distribution of metabolites in normal brain and postmortem changes

The goal of this study was to examine metabolic differences between cortex and basal ganglia in normal rat brain and to determine postmortem changes using in vivo 1H magnetic resonance spectroscopic imaging at 300 MHz. The resonances observed were: choline, creatine + phosphocreatine, N-acetyl aspartate (NAA), lactate (Lac), and three small resonances in the amino acid region which included resonances from aspartate + NAA (Asp), glutamine + NAA (Gln), and glutamate + GABA (Glu). A previously unassigned resonance was observed at 1.13 ppm in brain of rats anesthetized with pentobarbital. Spectroscopic images in normal brain demonstrated increased NAA and Gln and decreased Glu in cortex compared to basal ganglia. The major postmortem changes were an increase of Lac, Glu and Cho and a decrease of NAA and Asp. The rise in Lac was significantly higher in cortex than in basal ganglia.

Application of high field localised in vivo 1H MRS to study biochemical changes in the thiamin deficient rat brain under glucose load

In vivo, volume-selected 1H NMR spectroscopy employing the SPACE technique was used to monitor biochemical changes in the thiamin deficient rat brain in response to glucose loading. The concentrations of brain N-acetylaspartate, glutamate/glutamine/gamma-aminobutyric acid, lactate and glucose differed significantly from those of control animals. The results are consistent with a metabolic block at the reaction catalyzed by the thiamin dependent enzyme alpha-keto glutarate dehydrogenase soon after the onset of neurological symptoms of thiamin deficiency, and a further block at pyruvate dehydrogenase arising late in the course of thiamin deficiency.

In vivo localized proton NMR spectroscopy of silicone

1H NMR localized spectroscopy (STEAM) can assess unambiguously the presence of free chemically unchanged silicone in animal tissue after injection of silicone oil. Although the signal-to-noise ratio obtained in 1H imaging is sufficient to detect the distribution of relatively large amounts of silicone in vivo, the specificity of silicone detection can be improved by using 1H localized spectroscopy techniques. The sensitivity of the STEAM experiments is sufficient to detect silicone at a concentration of 0.5% in a voxel of 27 mm3. Preliminary results from rats with silicone gel-filled implants show no detectable amounts of silicone in sites such as lymph nodes, the liver or the spleen, 3 or 6 months after implantation.

Three-dimensional 1H spectroscopic imaging of cerebral metabolites in the rat using surface coils

Three dimensional metabolite maps of protonated metabolites were obtained using 1H magnetic resonance spectroscopic imaging at 7 T. Surface coils were used to increase sensitivity and spatial resolution significantly over a volume coil two-dimensional acquisition. Adiabatic pulses were employed to provide homogeneous B1 excitation and frequency selective refocusing over the volume of the rat brain. These techniques were employed to obtain three-dimensional spectroscopic imaging spectra from nominal voxel volumes of 9-30 microliters from rat brain. The improved spatial resolution and sensitivity are also demonstrated with studies of focal ischemia in the rat.