Patent No. 4719425 NMR imaging method and apparatus

 

Patent No. 4719425  NMR imaging method and apparatus (Ettinger, Jan 12, 1988)

Abstract

A method and apparatus for imaging the concentration of paramagnetic species inside a sample is disclosed wherein a sample is placed inside an NMR imager and an additional microwave field is introduced. A microwave field is chosen in such a way that there is a simultaneous resonance of nuclear spins (protons) and electrons in the same main magnetic field. The microwave signal is modulated which provides a modulation transfer to the intensity of the NMR signal. The modulation is extracted from the NMR signal to produce an image representative of the local electron spin resonance (ESR) and thereby the concentration of paramagnetic species in the sample. In addition, electrical activity of the brain can be detected and measured by measuring the broadening of the width of NMR spectral lines. A discharging neuron in the brain introduces an inhomogeneity in the magnetic field which reveals itself as a broadening of resonance lines which can be measured to determine the neuron discharge current flux.

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SUMMARY OF THE INVENTION

The present invention is directed to magnetic resonance imaging (MRI) methods and apparatus for measuring and imaging the concentration of paramagnetic species from a sample. In addition, an MRI method is disclosed for detecting and measuring electrical activity of the brain. In one embodiment of the present invention, an imaging technique termed Nuclear Electron Double Resonance (NEDOR) starts with a conventional NMR imaging apparatus and includes a high frequency resonator or radiator such as is used in ESR techniques. A sample, such as a human body, is placed inside the main magnetic field coils of the NMR imager. A radio frequency (RF) pulse is applied via RF coils to excite to resonance a plurality of nuclear spins producing an NMR signal. A microwave (MW) pulse is applied via a high frequency resonator or radiator to excite to resonance a plurality of electron spins within the sample. The RF and MW pulses simultaneously resonate the nuclear and electron spins within the sample. The intensity of the MW signal is modulated, which translates into a modulation of the intensity of the NMR signal. The modulation is extracted from the NMR signal to produce an image representative of the local ESR and thereby the concentration of paramagnetic species in the sample. In a preferred embodiment, the RF coil is also used as the MW resonator.

Electron spin resonance is the study of properties and molecules containing unpaired electrons by observing the magnetic fields at which the electrons come into resonance within an applied radiation field of definite frequency. Nuclear magnetic resonance monitors the reversal of nuclear magnetic moments wherein the nucleus with a net spin has been excited to resonance. For biological and other purposes, it is sometimes necessary to artificially introduce the unpaired electrons, into the sample in the form of paramagnetic tracers. In one embodiment, paramagnetic tracers are introduced into the sample to improve the differentiation between different tissues and improves detection of pathological changes.

In a further embodiment, a plurality of NMR spectral lines having a defined width are derived from the modulated NMR signal. It has been determined by the applicant, that the width of the spectral lines is broadened due to the electric activity in the brain. The discharge of a neuron in the brain introduces an inhomogeneity into the main magnetic field. The contribution of the spectral line width due to the electric activity is measured, which can provide a measurement of the intensity of neuron discharges in the brain.

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While several embodiments of the subject invention have been described and illustrated, it is obvious that various changes and modifications can be made therein without departing from the spirit of the present invention which should be limited only by the scope of the appended claims.