Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1995-06-06
1997-07-08
O'Shea, Sandra L.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
G01V 300
Patent
active
056465297
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Introduction and description of the system used
Magnetic Resonance (MR) is a method of investigation which allows observation of the interaction of a system of nuclei in the presence of a magnetic field. The information obtained relate to the concentration of the nuclei themselves, their chemical surroundings, and the interactions within the system.
The first applications were found to be extremely useful in the physical and chemical fields. Subsequent developments in technique also led to applications in the field of biology, and finally in that of medicine. In the latter field, MR makes it possible to obtain images representing planar cross-sections of the human body, of a quality comparable with that of X-ray tomography. MR is at present the most widely used technique for the diagnosis and study of neurological diseases, and its use is spreading rapidly to other areas of diagnosis. MR images in medicine are based on the resonance of the Hydrogen nuclei found in water and lipids.
The only physical dimension which can be measured is the duration in time of an electric signal; the image is therefore built up from a group of signals, measured according to the following.
With the object of producing an MR image, representing a planar cross-section of an three-dimensional physical object, the object to be examined is placed in an area having a strong static and homogeneous magnetic field, of an intensity equivalent to 0.5-1.5 T (see FIG. 2). Following this, the magnetic field is perturbed, by adding to the static and homogeneous field an oscillating field, known as a radio frequency impulse, which is perpendicular to the former and at a much lower intensity. The frequency spectrum of the radio frequency impulse is centered around the resonance frequency of the nuclei--static field system, which for the Hydrogen nucleus and with a field of 1.5 T is equivalent to approximately 64 Mhz, with a bandwidth of around one kHz. In this way, the system of nuclei of the object, on absorbing the energy transported by the impulse, is excited.
With the aim of exciting only those nuclei contained within a thin portion around the section under consideration, the following method is used. Simultaneously with the radio frequency impulse, a further static field is added, directed like the static and homogeneous one, whose value is linearly proportional to the height with respect to the plane of the cross-section, with a typical gradient value of approximately 5.10.sup.-3 T/m (see FIG. 3). Since the resonance frequency of the nuclei--static field system is linearly proportional, with a constant known as the gyromagnetic ratio, to the value of the static field, during the impulse said frequency will depend in a linear manner on the height with respect to the plane of the cross-section (see FIG. 4). From quantum mechanics it is known, furthermore, that, in order for the nuclei to absorb energy through the impulse, the resonance frequency must be within the frequency band of the impulse spectrum. There is therefore a portion of space, between two planes parallel to the cross-section and opposite to it, in which the resonance frequency lies within the impulse frequency band, while this does not occur outside said portion. Therefore, the nuclei excited by the impulse are only those within said portion. The thickness of the portion can be calculated by dividing the bandwidth of the impulse spectrum by the gyromagnetic ratio, and is typically equal to 0.005-0.01 m. By means of the radio-frequency impulse, applied in the presence of a gradient in the static field, only the nuclei contained in a thin portion of space around the cross-section plane have thus been excited (see FIG. 5).
If, at this point, the nuclei are left in the presence of the static and homogeneous field alone, they will all have the same resonance frequency and will emit the energy previously absorbed, in the form of electromagnetic radiation with a spectrum concentrated around said frequency. This can be detected using a receiving circuit, within which an
REFERENCES:
patent: 5086275 (1992-02-01), Roemer
patent: 5157330 (1992-10-01), Kaufman et al.
patent: 5285157 (1994-02-01), Zur
patent: 5427102 (1995-06-01), Shimode et al.
Smith et al, "Magnetic Resonance Image Noise Reduction and Resolution Enhancement Using Parametric Techniques" Control & Computers vol. 15, No. 2, pp. 75-99 (1987).
Sano et al, "MR Image Reconstruction From Half the Data Using a Phase Map." Systems & Computers in Japan vol. 20, No. 2 pp. 60-66 (Feb. 1989).
Barone Piero
Sebastiani Giovanni
Consiglio Nazionale Delle Ricerche
Mah Raymond Y.
O'Shea Sandra L.
LandOfFree
System for producing high-resolution magnetic resonance images w does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System for producing high-resolution magnetic resonance images w, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System for producing high-resolution magnetic resonance images w will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2410640