Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1990-03-26
1992-05-05
Tokar, Michael J.
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
324309, G01R 3320
Patent
active
051111470
DESCRIPTION:
BRIEF SUMMARY
An object of the present invention is a system of gradient coils for nuclear magnetic resonance (NMR) machines. It is due to the collaboration of the Service National des Champs Intenses (Director: Mr. Guy AUBERT). This system of gradient coils is designed to create a magnetic field gradient in a volume of interest of an NMR instrument. The invention can be applied more particularly in the medical field where imaging by nuclear magnetic resonance is unanimously recognized as a diagnostic aid. It can clearly be implemented in other fields. The aim of the present invention is to contribute to the creation of images, of a body to be examined, that are more faithful as well as more precise in their resolution.
A nuclear magnetic resonance imaging instrument essentially has three types of coils. Coils of a first type (which may be replaced, as the case may be, by permanent magnets) are designed to create an intense, homogeneous magnetic field B.sub.0 in a predetermined field of interest. Coils of a second type, called a radio-frequency coils, are aimed at subjecting a body, examined and placed under the influence of the field of the first coils, to radio-frequency excitation sequences, and to measure a radio-frequency signal re-emitted in return by particles of the body following the excitation. The radio-frequency response is a response in volume: all the particles of a region of the body subjected to the examination emit their radio-frequency response at the same time. To create an image, these responses have to be differentiated. To this end, the imaging instruments have coils of a third type, called gradient coils, to superimpose additional magnetic fields on the intense homogeneous field. The value of these fields depends on the spatial coordinates of their place of application. In standard practice, it is proposed to organize this differentiation along three orthogonal axes X, Y, Z. By convention, the axis Z is even generally taken to be colinear with the intense field created by the first type of coils. In other words, each location of space may be encoded at a different field value: the modifications resulting therefrom in the re-emitted signal are exploited to create the image.
Gradient coils are generally divided into three classes: those that create a gradient along X, those that create a gradient along Y and those that create a gradient along Z. For example, a magnetic field gradient along X is a magnetic field for which the distribution of the component colinear to the intense field (Z), in space, is a function solely of the coordinate x.sub.i of its place of application. In practice, it is preferably even proportionate thereto. This means that all the particles of a body to be examined, located in a plane parallel to Y-Z and with a given abscissa x.sub.i, are subjected to one and the same total field B.sub.0 +G.sub.x.x.sub.i. The gradient G.sub.x is the slope of the variation of the component along Z of the additional field provided by these gradient coils X.
The acquisition of an image thus requires the application of field gradient sequences in conjunction with the application of the radio-frequency excitation sequences. The field gradient sequences depend on the imaging method implemented. This method may be, for example, of the 2DFT type described by A. KUMAR and R. ERNST or, for example, of the back projection type prepared by P. C. LAUTERBUR. Irrespectively of the type of imaging chosen, one characteristic of the field gradients is that they are pulsed. They are set up, they persist for a short duration, then they are cut off. This may occur one or more times during each sequence. The consequence of this particular feature is that the working of the coils that produce them must be studied not only in permanent operation, during the application of the gradients, but also during the transient phenomena resulting from their being set up and their being cut off.
Another major characteristic of the field gradients concerns their homogeneity. Homogeneity means the condition where a real field grad
REFERENCES:
patent: 4761612 (1988-08-01), Holland et al.
patent: 4833434 (1989-05-01), Takechi
patent: 4864241 (1989-09-01), Goldie
patent: 4876510 (1989-10-01), Siebold et al.
patent: 4881032 (1989-11-01), Bottomley et al.
patent: 4881035 (1989-11-01), Siebold
patent: 4905316 (1990-02-01), Okamoto
patent: 4910460 (1990-03-01), Sebok
patent: 4920316 (1990-04-01), Egloff
patent: 4965521 (1990-10-01), Egloff
patent: 4980641 (1990-12-01), Breneman et al.
Centre National de la Recherche Scientifique
Tokar Michael J.
LandOfFree
Gradient coil system for NMR machines does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gradient coil system for NMR machines, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gradient coil system for NMR machines will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1415448