Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2002-05-21
2004-10-19
Fulton, Christopher W. (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
Reexamination Certificate
active
06806711
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to the field of magnetic resonance techniques, particularly to the field of imaging magnetic resonance tomography systems.
The invention relates to a high-frequency coil arrangement for examining a subject, particularly a patient, in a magnetic resonance tomography apparatus, particularly in an imaging magnetic resonance tomography apparatus, of the type having a loop coil for receiving an electromagnetic high-frequency signal from the examination subject, the loop coil having at least one conductor loop that is suitable for enclosing the examination subject.
The invention also is directed to a magnetic resonance tomography apparatus for examining a patient, with means for generating a static magnetic field that is vertically oriented with respect to the patient axis.
2. Description of the Prior Art
In a magnetic resonance tomography apparatus for medical applications, particularly for medical diagnosis, the patient to be examined normally is introduced into the examination area with the patient lying flat. The intense static magnetic field, which is required in the examination area, is generated either by a permanent magnet or by an electrical coil that is preferably superconductive. In a magnetic resonance tomography apparatus having a permanent magnet that is used for generating low or medium field intensities, the magnetic field is vertically oriented as a result of the medically required horizontal support of the patient and the installation of the magnet resulting therefrom. This is referred to as a vertical field device. By contrast, the static magnetic field is oriented parallel to the patient axis, (horizontally) when an electrical magnet coil is used for obtaining particularly high field intensities.
A transmission coil or reception coil is used for transmitting high-frequency pulses into the examination subject and for receiving electromagnetic high-frequency signals proceeding from the examination subject. Most of the coils used for these purposes can be divided into two categories regarding their field distribution: These are volume coils, which generate a homogenous magnetic field in an area within the coil, and surface coils, which generate a more or less non-homogeneous magnetic field outside of the coil. With a volume coil, the examination subject, therefore, is normally arranged in the inside of the coil, whereas a surface coil is usually attached to the surface of the examination subject or is placed on the surface of the examination subject. For example, a solenoid is a typical volume coil having a predominantly homogenous field distribution in its interior, namely a wound coil with windings wound on a surface of a cylinder and that is coaxial relative to the patient axis. The solenoid could also be referred to as a loop coil having a number of conductor loops. A loop coil having only one conductor loop or only a few conductor loops could be used as a surface coil, but could also be referred to as a volume coil having a reduced field homogeneity, particularly when the conductor loops enclose the examination subject.
In order to obtain an optimally homogeneous field distribution in the measuring volume, a volume coil or some other antenna having a homogeneous field distribution is normally used for transmitting the high-frequency pulses.
Volume coils have the disadvantage, particularly when only a specific partial area of the examination subject, particularly of the human body, is to be imaged, that the signal-to-noise ratio of the magnetic resonance examination is negatively influenced due to the low filling factor. Therefore, surface coils are used as reception coils, particularly when the partial area to be examined cannot be enclosed by a coil, i.e., the homogeneity of the high-frequency reception characteristic is partially sacrificed for the benefit of a larger filling factor for locally obtaining an optimally efficient signal-to-noise ratio.
In a vertical field device, the imaging electromagnetic high-frequency signal originating from the examination subject is essentially horizontally oriented with respect to its circular polarization (magnetic field component). One method for receiving the circularly polarized high-frequency signal is to separately receive two orthogonal components, e.g. a first polarization component parallel to the patient axis and a second polarization component perpendicular to the patient axis.
A loop coil enclosing the entire patient body or an extremity to be examined can be used for receiving the first polarization component that is oriented parallel to the patient axis. The diameter of the subject to be examined is limited from above due to the interior area that is enclosed by the loop coil. Therefore, loop coils with different diameters have been used, with a suitable coil being selected for the respective patient. This work is laborious for the medical staff since electrical contact connections must be repeatedly made. Moreover, with an extremely adipose patient, it may occur that none of the present coils has a sufficient diameter. This problem particularly occurs when the spine is to be imaged since the loop coil must enclose the entire patient body rather than only an extremity (arm or leg).
SUMMARY OF THE INVENTION
An object of the invention is to provide a high-frequency coil arrangement wherein the number of necessary reception coil changes is reduced, and which is particularly suitable for examining extremely adipose patients. A further object is to provide a magnetic resonance tomography apparatus employing such a high-frequency coil management.
The initial object, with respect to the aforementioned high-frequency coil arrangement, is inventively achieved by providing a surface coil in addition to the loop coil, with the surface coil and the loop coil being fashioned for receiving the same first polarization component of the high-frequency signal.
These terms are used herein consistent with the earlier explanations made in the beginning regarding the terms “surface coil” and “loop coil”. The surface coil of the invention is fashioned in a particularly flat manner and is suitable for placing the examination subject or the patient thereon and is suitable for laterally being placed against the examination subject or patient. The loop coil is particularly suitable for enclosing the examination subject. In this sense, the loop coil also can be referred to as a volume coil. The loop number or number of turns, and therefore the expanse of the loop coil along its central coil axis, is preferably significantly less than the width extent. In other words, the loop coil also is fashioned in a flat manner. For example, it can have a single conductor loop or—particularly with respect to a small coil—2, 3, 4 or up to 10 conductor loops.
Preferably, both coils are simultaneously electrically and/or mechanically connected to the magnetic resonance tomography apparatus. Since a surface coil and a loop coil—optionally or simultaneously—are inventively present in the high-frequency coil arrangement for receiving the same polarization component. The advantage results that at least one usable reception coil is always present even for large-volume examination subjects. This is the surface coil.
The surface coil, however, has the disadvantage that it exhibits a low signal-to-noise ratio compared to the loop coil, particularly with respect to a slim patient. This disadvantage, however, is offset by the particular advantage that the inventive high-frequency coil arrangement, as a result of the presence of the surface coil, provides a high-frequency signal for magnetic resonance tomography examinations even if the loop coil can no longer be used. This is not possible for an especially adipose patient or for a patient with injuries or applied bandage material, for example. Therefore, the inventive high-frequency coil arrangement is not limited, in application by the size or the nature of the patient's dimensions. Moreover, the loop coil can be used
Fulton Christopher W.
Schiff & Hardin LLP
Siemens Aktiengesellschaft
Vargas Dixomara
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