Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2001-04-17
2003-07-01
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000
Reexamination Certificate
active
06586934
ABSTRACT:
BACKGROUND OF THE APPLICATION
1. Field of the Invention
The invention relates to a method of Nuclear Magnetic Resonance imaging, which method includes the following steps:
a) generating a static magnetic field having appropriate intensity and homogeneity characteristics in a predetermined imaging volume;
b) introducing a body or a part of said body in said imaging volume for examination;
c) generating magnetic field gradients in several different spatial directions to select the scan slice of the body under examination and to univocally phase-encode nuclear spins in the selected slice;
d) generating sequences of electromagnetic signals to excite the nuclear spins of the body or of the body part introduced in the imaging volume;
e) receiving the resonance signals emitted by nuclear spins and processing them to extract information therefrom and reconstruct the corresponding images which images relates only to a predetermined limited region of the body or of a part thereof to be examined;
f) displacing the body or the part thereof to be examined to a predetermined extent from said first imaging position to at least a second imaging position, the above steps being repeated for further regions of the body part under examination corresponding to further relative positions between the body or part thereof and the imaging volume, by displacing the body or the part thereof in predetermined directions relative to the imaging volume or vice versa.
2. Discussion of Related Arts
These methods are currently well-known and widely used. In most prior art systems imaging volumes are generated, i.e. regions of space permeated by a static magnetic field with the characteristics required for proper imaging, particularly intended for diagnostic purposes. This is aimed at obtaining considerably large imaging volumes, to allow imaging of relatively wide regions of the body under examination, particularly to find the region of the body part which is relevant for diagnostic purposes. The provision of these comparatively large imaging volumes requires apparatuses having large-sized magnetic structures. In addition to their high purchase cost, these apparatuses are expensive to install and need to be located in appropriate facilities.
EP 654 675 discloses an apparatus having a simplified “total body” construction for Nuclear Magnetic Resonance tomography. According to this document, a magnetic field is generated for Nuclear Magnetic Resonance imaging, which permeates a substantially cylindrical volume whose axial dimension equals from 10 to 15 cm. The body under examination is displaced in the direction of the cylindrical body axis, to allow imaging of successive slices in different regions of the body. The processed images or received signals are stored sequentially and in relation to the scan slice of the body wherefrom they were generated to provide a virtual three-dimensional image in the memory. In order to limit scanning time, particular and relatively fast sequences are used, such as those named echo-planar sequences. During the scanning operation, the information relating to the whole scanning cross section of the body is detected, processed and stored. Once the data obtained by scanning the successive slices are stored, they may be recalled and displayed. The construction of the apparatus derives from that of the so-called total-body apparatuses and, with respect to the latter, the ring-like magnetic structure is only axially shortened depending on whether the volume permeated by the imaging static field is selected as being an axially short cylinder or a thin disk.
EP 430 222 discloses a method for Nuclear Magnetic Resonance tomography imaging of the same type as radiological scanograms. Here again the magnetic structure derives from “total body” constructions, i.e. those designed for imaging the whole body or a considerable part thereof. The method disclosed in this document equally provides that a succession of different slices of the body under examination are scanned, by displacing the body under examination relative to the useful volume permeated by the static magnetic field. However, unlike the method of EP 654 675, this method provides the selection of a slice plane parallel to the longitudinal extension of the body under examination and parallel to the displacement direction of said body, by applying dephasing sequences, e.g. for saturating the nuclear spins of each cross section beyond the slice oriented in the direction of advance of the body, to limit the detection of echo signals to those actually emitted by the spins of the slice and/or section of the body oriented in the displacement direction. Here again the images are processed and generated at the end of the whole scanning process.
Hence, according to both prior art methods, images are displayed after the whole body or region of interest thereof have been scanned.
Now apparatuses are known, in which the magnetic structure is drastically limited in size, with a consequent reduction of the volume in which the magnetic field has the characteristics required for proper imaging. These apparatuses provide considerable advantages in terms of money savings, but do not allow to obtain relatively wide images of the relevant region, or not at a high quality level.
Moreover, in these apparatuses the problem exists of finding the region of the body which is of relevance or of diagnostic interest. Hence, repeated scanning operations of different regions of a body part are required to frame the region of diagnostic interest. For instance, for a diagnosis on a meniscus, several different scans of the knee may be required to obtain the proper, best shot of the meniscus region.
These scans are currently made with sequences adapted to provide the best image in terms of definition and contrast, but these sequences are comparatively long and complex, so much longer scanning times are requested. Even in total body apparatuses, or the like, in which the structure allows for relatively wide imaging volumes, the sequences are adapted to ensure the best image quality, resulting in a long scanning and processing time.
Moreover, even in the so-called “total body” apparatuses, the quality of the image might not be consistent all over the volume and anyway imaging time tends to be comparatively long when obtaining wide images.
Imaging sequences for generating high quality images, besides being time-consuming, also involve considerable costs as regards the construction of the apparatus, which has to be configured to execute them within acceptable times.
Prior art apparatuses have such characteristics that they do not allow a real time, or almost real time display of the detected images, moment by moment, e.g. while the body under examination is displaced. This is a drawback when imaging is performed in transient conditions of the body under examination, which may be either pathologic or physiologic or induced by relatively invasive techniques, such as the use of substances, injected into the body under examination, designed to improve the signals received from the body under examination or parts thereof, such as contrast agents for Nuclear Magnetic Resonance.
OBJECTS AND SUMMARY
The invention is based on the acknowledgement that, in practice, no excessively wide image of the body, limb, or region thereof is required for the purpose of finding the specific shot for diagnosis or for a specific examination and for finding the right acquisition moment with reference to induced transient conditions. Images of wide portions of the body, the so-called panoramic images are used to provide an overall view of the situation. Certain “total body” apparatuses use sequences which allow almost real time imaging upon introduction of the patient in the imaging cavity, i.e. as the patient gradually enters the magnet cavity. These techniques are highly complex and require heavy and fast processing, which may be only performed in advanced and costly hardware structures, contained both in the NMR apparatus and in the processing unit.
The invention has an object of providing a
Biglieri Eugenio
Palazzolo Marino
Satragno Luigi
Burns Doane Swecker & Mathis L.L.P.
Esaote S.p.A.
Lefkowitz Edward
Shrivastav Brij B.
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