Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1991-02-12
1992-11-24
Tokar, Michael J.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324300, G01R 3320
Patent
active
051666162
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for recording spin resonance spectra of test samples having at least two groups of nuclei of the same kind and of substantially identical chemical shift, comprising the step of suppressing the signal of the second group for the purpose of obtaining an isolated image of the signal of the first group.
BACKGROUND OF THE INVENTION
It has been known in practice in the field of spin resonance spectroscopy to "edit" spectra where signals of different groups of nuclei heterodyne one with the other. By "editing" one understands different recording techniques which allow to filter out individual signals from the heterodyning spectra. Usually, this is effected by carrying out series of several measurements using different measuring parameters, and eliminating thereafter the undesirable signal contents by subtraction. Examples of such editing techniques for nuclear magnetic resonance applications have been described in the textbook entitled "Modern NMR Spectroscopy" by Sanders, Jeremy K. M. and Brian K. Hunter, Oxford University Press, 1987, pages 237 to 259. Other methods of this type are described by EP-OS 244 752 and EP-OS 166 559. In the case of these other known methods, uncoupled spins are suppressed by forming the difference between two measurements.
However, all of the techniques described above have the common disadvantage that for recording a single spectrum a plurality of measurements have to be performed successively in time, using different measuring parameters. While this presents no substantial problem to a laboratory in the case of durable chemical samples, considerable problems can result in cases where such nuclear magnetic resonance spectra are to be recorded on biological samples, i.e. on living tissue. This is true above all for in-vivo measurements to be carried out on patients where movement artefacts may lead to adulterations of the measured values.
In addition, subtracting measuring methods are connected with the fundamental drawback that the subtraction of high noise signal amplitudes may give rise to measuring errors which may be in the same range of magnitude as the useful signal.
According to other known methods, nuclear magnetic resonance spectra are recorded in a volume-selective way, i.e. only for a limited, geometrically defined area of a sample. This recording technique has gained particular importance in the fields of biological research and medicine. For, this recording technique enables, for example, a nuclear magnetic resonance spectrum to be recorded for a given, defined point in an inner organ of a patient. The technique of recording volume-selective nuclear magnetic resonance spectra has been known as such. Examples of this technique are found in the textbook entitled "Biomedical Magnetic Resonance Imaging" by Wehrili, Felix W., Derek Shaw and J. Bruce Kneeland, Verlag Chemie, 1988, pages 1 to 45 and 521 to 545.
Other known methods are, for example, the so-called SPARS method, which has been described by the U.S. publication "Journal of Magnetic Resonance", 67 (1986), page 148, and the so-called DIGGER method, described by the U.S. publication "Journal of Magnetic Resonance", 68 (1986), page 367. These known methods are volume-selective methods where the layers outside the selective volume area are saturated to leave only the selected volume area. However, it is the disadvantage of these two known methods, in particular of the DIGGER method, that they require a high r.f. power and that the pre-saturation r.f. pulses must be tuned very exactly in both methods as otherwise additional signals may be generated.
Another special method for volume-selective imaging of nuclear magnetic resonance spectra using three 90.degree. r.f. pulses spaced in time, while applying simultaneously different magnetic gradient field pulses in different coordinate directions, has been described for example by DE-OS 34 45 689. In the case of this known method, conventional stimulated spin echoes are produced.
Finally, it has been known
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Brereton Ian M.
Doddrell David M.
Galloway Grahmam J.
Bruker Analytische Messtechnik GmbH
Tokar Michael J.
Univ of Queensland
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