The unequivocal determination of lactic acid using a one-dimensional zero-quantum coherence-transfer technique

High resolution NMR spectroscopy of rat brain in vivo through indirect zero-quantum-coherence detection

The time evolution of zero-quantum-coherences (ZQCs) is insensitive to magnetic field inhomogeneity. Using a 2D indirect ZQC detection method it is shown that high-resolution (1)H NMR spectra can be obtained from rat brain in vivo at 11.74T that are immune to magnetic field inhomogeneity. Simulations based on the density matrix formalism, as well as in vitro measurements are used to demonstrate the features of 2D ZQC NMR spectra. Unique spectral information which is normally not directly available from regular (1)H NMR spectra can be extracted and used for compound identification or improved prior knowledge during spectral fitting.

Spatially resolved two-dimensional spectroscopy

A method is presented to collect spatially resolved two-dimensional spectra on a conventional clinical scanner. Time-varying gradients during the readout period rapidly sample data simultaneously for two spatial and two spectral dimensions. The k-space trajectories are based on spiral paths that make efficient use of the gradient hardware. A gridding algorithm is used for reconstruction. With the spiral-based readout gradients, current single-voxel two-dimensional techniques can be extended to spatially resolved volumetric acquisitions. The method is demonstrated with a two-dimensional J-resolved acquisition of a phantom with separate compartments of lactic acid and ethyl alcohol in water. Data were acquired with a spatial resolution of 18 x 18 pixels over a 24 cm field of view, 400 Hz spectral bandwidth in the chemical shift dimension with a 3.8 Hz resolution, and 50 Hz spectral bandwidth in the second frequency dimension with a 1.56 Hz resolution.

In vivo lactate and beta-hydroxybutyrate editing using a pure-phase refocusing pulse train

A refocusing pulse train consisting of a semiselective refocusing pulse and a selective inversion pulse to obtain a pure-phase refocusing at the frequency of maximal excitation of the semiselective refocusing pulse is proposed and applied to in vivo lactate and beta-hydroxybutyrate editing using difference spectroscopy. It is shown, using both rotation matrix theory and phantom experiments, that the soft inversion pulse has to be halved to flank the semiselective pulse to obtain perfect refocusing and cancellation of interfering resonances. The editing method is used to obtain lactate and beta-hydroxybutyrate spectra from the occipital cortex of juvenile epilepsy patients before and after ketogenic diet treatment.

Incorporation of lactate measurement in multi-spin-echo proton spectroscopic imaging

An improved multi-slice, multi-spin-echo proton spectroscopic imaging method for human brain is presented. The technique allows the reconstruction of lactate images, along with choline plus creatine, N-acetylaspartate, and lipid images from one single data set processed in three separate ways. The discrimination between resonances of lipid protons and lactate methyl protons is based on homonuclear spin-spin coupling. The reliability of the separation of the lipid and lactate contribution depends on the T2 of the lipid resonances. Measurements were performed on a standard 1.5 Tesla clinical scanner on healthy volunteers and a patient with high grade CNS lymphoma, demonstrating the ability to obtain high quality metabolite maps within 11 min.

A highly sensitive lactate editing technique for surface coil spectroscopic imaging in vivo

A lactate editing sequence based on the use of spin-locking pulses with surface coils is described. The sequence retains more than 90% of the available lactate magnetization and suppresses at least 95% of the lipid signal in a single scan and ca. 99.5% after a simple two step cycle. The technique allows simultaneous observation of lactate and uncoupled metabolites in the range 2 to 3 ppm. The sequence was combined with two-dimensional spectroscopic imaging to obtain a lactate map of an ischemic rat brain in vivo.

A localized in vivo detection method for lactate using zero quantum coherence techniques

A method is described to selectively measure lactate in vivo using proton zero quantum coherence techniques. The signal from lipids is eliminated. A surface coil and additionally slice selective localization are used. The resulting spectra demonstrate the good performance of the method.

Longitudinal spin-order-based pulse sequence for lactate editing

A new pulse sequence which edits proton spectra of lactate with full signal return and gives good suppression of water and fat signals is described. This sequence exploits longitudinal spin-order from lactate to edit lactate from fat. Experimental results from phantoms and excised pig heart are presented.

Spectral editing of tumor 13C MRS in situ

The editing pulse sequence DEPT (D.T. Pegg, D.M. Doddrell, and M.R. Bendall, J. Chem. Phys. 77, 2745 (1982)) was modified using a scheme of various composite pulses and a 16-step phase cycling to obtain proton-decoupled natural-abundance 13C edited subspectra of solid tumors. A solenoidal probe including a Faraday shield and an orthogonal saddle decoupling coil was built for this purpose.

Detection of metabolites in body fluids and biological tissue by a 1D soft COSY technique

With a semi-selective 1D COSY, related to the soft COSY sequence, metabolites with concentrations of a few millimolar can be detected, while highly abundant molecules as water or lipids are efficiently suppressed.