Peter R. Luyten

1H MR spatially resolved spectroscopy of human tissues in situ.

SPAtially Resolved Spectroscopy (SPARS) has been developed as a method to obtain localized MR spectra in a whole body MRI system. It is based upon a combination of selective and non-selective pulses such that longitudinal magnetization is preserved in a particular volume of interest (VOI), whereas outside this volume the magnetization is dephased in the transversal plane. After this selection phase the spectrum of the VOI can be obtained after a single excitation pulse. In this respect it is similar to the VSE sequence as proposed by Aue et al. The difference is that even by using relatively large body and head coils the SPARS sequence requires much lower rf powers levels, such that it can be implemented on a whole body MRI system.

Reduced lipid contamination in in vivo 1H MRSI using time-domain fitting and neural network classification

It is a well-known problem that metabolite maps, reconstructed from in vivo 1H MRSI data sets, may suffer from contamination caused by the presence of strong lipid signals. In the present investigation, the lipid problem was addressed by applying specific signal processing and data-analysis techniques, combined with pattern recognition based on the concept of the artificial neural network. In order to arrive at images, cleaned from lipid artifacts, we have applied our previously introduced iterative and noniterative time-domain fitting procedures. Furthermore, reduction in computational time of the image reconstructions could be realized by using information provided by a neural network classification of the spectra, calculated from the MRSI data sets.

In vivo monitoring of fructose metabolism in the human liver by means of 31P magnetic resonance spectroscopy

It has been shown that fructose metabolism in the human liver can be monitored quantitatively by means of 1H image-guided 31P MRS, implemented on a clinical MR imaging system equipped with surface coils and with appropriate data processing software. Temporal resolution of the 31P MRS measurements is of the order of 2 min.

METHOD OF DETERMINING A NUCLEAR MAGNETIZATION DISTRIBUTION OF A SUB-VOLUME OF AN OBJECT, METHOD OF SHIMMING A PART OF A STEADY FIELD IN WHICH THE OBJECT IS SITUATED, AND MAGNETIC RESONANCE DEVICE FOR PERFORMING SUCH A METHOD

An MRI method for spectroscopy utilizes a sequence which includes four RF electromagnetic pulses (p1, p2, p3, p4), three of which are spatially selective to generate a resonance signal (e) from a sub-volume of an object. The phase difference between the first and the second 90° excitation pulse amounts to 90°. The waiting period (dt1) between the first and the second pulse (p1, p2) is chosen so that the second pulse (p2) selectively resets the nuclear spins excited by the first non-selective pulse (p1) in the longitudinal direction. The selectively reset magnetization, for example of fat, is recalled, after the dephasing of the non-reset magnetization, for example of water, by the further pulses (p3, p4). A spectrum is determined from the resonance signal (e). In a modified version in which the phases of the first and the second pulse are the same, the sequence is used for shimming a local field around the sub-volume.

Method of heteronuclear decoupling in magnetic resonance spectroscopy, and device for determining a spectrum.

A method of heteronuclear decoupling in magnetic resonance spectroscopy and a device for determining a spectrum where spectra of a first type of nucleus which is spin-coupled to a second type of nucleus are decoupled inter alia in order to obtain a higher resolution. In inter alia phosphorous spectroscopy, during signal acquisition of resonance signals of the first type of nucleus, decoupling pulses are applied to the second type of nucleus, which decoupling pulses have been modulated in amplitude as well as in frequency or phase. The decoupling pulses need hardly be optimized. Very good decoupling is achieved, notably when use is made of surface coils for the transmitter and receiver coils exhibiting a substantial field inhomogeneity. When surface coils are used, suitable decoupling is achieved across a comparatively large volume.

1H NMR Spectroscopy and Spectroscopic Imaging of The Human Brain

The first high field 1H NMR spectroscopy studies of the animal brain were performed in 1983 [1]. These studies showed that 1H NMR spectroscopy allows in vivo observation of a number of brain compounds, including different aminoacids, creatine, choline residues, and—under certain perturbations—of lactate. Those initial studies have given rise to a large number of studies which apply 1H NMR spectroscopy to different aspects of brain metabolism, under different kind of perturbations [2]. These studies have shown that a wealth of information can be obtained about cerebral metabolism and physiology by 1H NMR spectroscopy of the animal brain.

Humans under the spectrometer

The introduction of nuclear magnetic resonance (NMR) in medicine has had an enormous impact on diagnostic radiology. Images of all kinds of (soft) tissues in the human body are currently reconstructed using the radiofrequency signals of the nuclear spins of hydrogen nuclei contained in water and fat. Already, magnetic resonance imaging (MRI), as this application is called, has become the preferred technique for the diagnosis of common diseases. However, the medical potential of NMR is not limited to spatial imaging. It turns out that certain elements produce characteristic signals which depend not only on their particular chemical state but also on the environment in which they are located. Nuclear magnetic resonance spectra can now be used to monitor biochemical reactions in intact tissues and may soon provide a unique tool to study in situ human biochemistry non-invasively and without any hazardous irradiation.

Proton Spectroscopic Imaging in Cerebral Ischaemia Where we Stand and What Can be Expected

Cerebrovascular research is traditionally focused on the effects of changes in blood flow on neurological function. With the improvement of technical developments it became possible to correlate local cerebral blood flow (CBF) with focal neurological deficits. From local CBF measurement we learned that perfusion above the threshold of 20 ml/100 mg/min does not always mean that metabolism and function are still intact. Over the past ten years research interest in cerebral ischaemia showed a gradual shift towards cellular biology and pathophysiology. Changes in brain metabolism were considered to be more important than differences in blood flow. The development of new techniques in vitro and in vivo allowed to investigate many different aspects of cellular metabolism. Positron emission tomography was the first in vivo technique which proved that it was possible to obtain regional metabolic information with an acceptable local resolution. Nuclear magnetic resonance, which was introduced in medical research only fifteen years ago, has become a major tropic in brain research. Actually it has become an entire research field with many aspects, including imaging, angiography, and CBF-, energy metabolism-, and intracellular pH-measurement. Several brain metabolites, among which lactate (Berkelbach v. d. Sprenkel 1988 a), can be studied in vivo with proton nuclear magnetic resonance imaging (MRS).

Observation of Fructose Metabolism in the Human Liver by Means of 1H Image-Guided Localized 31P MR Spectroscopy

When comparing 31P magnetic resonance (MR) spectra from biological tissues of one particular type, variations in the spectral patterns may be observed. These can be due to biological variability but also to instrumental factors such as magnetic field homogeneity and the experimental protocol applied. Therefore, tissue characterization by means of 31P MR spectroscopy is often ambiguous.