COIL FOR NUCLEAR MAGNETIC RESONANCE IMAGING DIAGNOSTIC APPARATUS

Abstract: Mounting structure of an inclined magnetic field coils for a nuclear magnetic resonance (NMR) imaging diagnostic apparatus, wherein the windings (9, 9 ...) of the inclined magnetic field coils (3), (4), (5) are disposed in the magnetic field generated by a main coil (2), and in the first invention, the windings (9, 9 ...) of the inclined magnetic field coils (3, 4, 5) are wound around and held on a bobbin (6) superposed a vibrationproofing material (13) thereon, and in the second invention, the windings (9, 9 ...) and the bobbin (6) are integrally molded with a damping material (15).

Description: TITLE OF THE INVENTION Coil for Nuclear Magnetic Resonance Imaging Diagnostic Apparatus Technical Field The present invention relates to a coil used for a nuclear magnetic resonance (N R) imaging diagnostic apparatus, and more particularly to inclined magnetic field coils used for obtaining the position information at a nuclear magnetic resonance imaging diagnostic apparatus. Background Art Fig. 1 shows a magnetic portion at the conventional superconductive nuclear magnetic resonance imaging diagnostic apparatus, comprising a superconductive main coil 2 contained in a cryostat 1 , inclined magnetic field coils 3/ 4 and 5 disposed inside the main coil 2, a bobbin 6, arid a bed unit 7, so that an examinee is positioned within the bobbin 6. The inclined magnetic field coils comprising two pairs of X-direction inclined magnetic field coils 3, 3 ..., each being a saddle-like shape and disposed transversely, two pairs of Y-direction inclined magnetic field coils 4, 4 ... , each being a saddle-like shape and disposed vertically, and a pair of Z-direction solenoid-type inclined magnetic field coils 5, 5 disposed longitudinally, are mounted on the bobbin 6 formed of a non-conductive material. The inclined magnetic field coils 3, 4, 5 are mounted on the bobbin 6 in such a manner that the windings 9, 9 ... of each inclined magnetic field coil 3, 4 or 5, as shown in Fig. 2, are secured to the bobbin 6 by a band 10, such as a glass fiber tape, or the windings 9, 9 ..., as shown in Fiy. 3, are press-contacted by bolts 12, 12 ... through a pressure plate 11. In the above-mentioned nuclear magnetic resonance imaging diagnostic apparatus, the inclined magnetic coils 3, 4 and 5 are excited in the intense DC magnetic field generated by the main coil 2, at which time a current flow¬ ing in the inclined magnetic field coils 3, 4 and 5, as shown in Fig. 4-(a), is of pulse-like wave form, so that the inclined magnetic field coils 3, 4 and 5 each generates an electromagnetic mechanical force, thereby vibrating as the current varies as shown in Fig. 4-(b). The electromagnetic mechanical force generated in the inclined magnetic field coils 3, 4 and 5 is about similar in wave form to the current shown in Fig. 4-(a). Hence, the frequency component in the mechanical force is distributed in a wide frequency domain of DC to kHz, vibrations and noises caused thereby having the similar frequency component. The conventional inclined magnetic field coil, whose windings are fixed directly to the bobbin, transmits vibrations thereof to the bobbin directly. As a result, a problem has occurred in that noises emitted together with the vibrations from the bobbin cause pain to the examinee positioned inside the bobbin. Disclosure of Invention In order to solve the above problem, the present invention has been designed to provide a coil used for a nuclear magnetic resonance imaging diagnostic apparatus which reduces vibrations and noises. A coil used for the nuclear magnetic resonance imaging- diagnostic apparatus, according to a first invention, comprises inclined magnetic field coils fixed to a bobbin with a vibrationproofing material interposed therebetween. In this invention, the high- frequency component sensitive to audibility among the wide frequency component of the generated noises is attenuated, thereby attenuating the high frequency component among vibrations transmitted from the coil to the bobbin through the vibrationproofing material, such as vibrationproofing rubber. In this case, when the characteristic frequency depending on the mass of coil and on the spring constant of vibrationproofing material is represented by f , the attenuated frequency component is 2 x f or more. In the first invention, by adding a mass body of non¬ magnetic material, such as stainless steel to the inclined magnetic field coils, the mass " of coil increases and the characteristic frequency of coil lowers to expand the frequency domain having the damping effect. A coil for a nuclear magnetic resonance imaging diagnostic apparatus according to a second invention comprises inclined magnetic field coils and a bobbin which are integrally molded by a damping material. In the second invention, since the coils and bobbin are integrally molded by damping material, such as epoxy derivative binary reaction type resin, the damping effect is extremely high, thereby remarkably reducing an abrupt damped vibration generated during the rising and the fall¬ ing of the current. Brief Description of Dawings Fig. 1 is a partially cutway perspective view of the principal portion of the conventional nuclear magnetic resonance imaging diagnostic apparatus. Figs. 2 and 3 are partially sectional views of construction of holding conventional inclined magnetic field coils on a bobbin, Fig. 4 is a wave form chart of a current flowing in the inclined magnetic field coils and vibrations thereof. Fig. 5 is a partially sectional view of an embodiment of a coil used for a nuclear magnetic resonance imaging diagnostic apparatus according to a first invention, Figs. 6 through 8 are partially sectional views of another modified embodiments of the first invention respectively, and Fig. 9 is a partially sectional view of an embodiment of a second invention. Best Mode for Carrying Out the Invention Fig. 5 shows an embodiment of the first invention in which, windings 9, 9... ofinclined magnetic field coils are secured to a bobbin 6 by a band 10 with vibrationproofing rubber 13 interposed therebetween. Fig. 6 shows another modified embodiment of the first invention, in which the windings 9, 9 ... are secured between the bobbin 6 and a pressure plate 11 with vibration¬ proofing rubber 13, 13 interposed between the windings 9, 9 ... and the bobbin 6 and between the windings 9, 9 ... and the pressure plate 11 respectively and fixed to the bobbin 6 by bolts 12, 12 ... through the pressure plate 11. In the above construction, the inclined magnetic field coils whose windings 9, 9 ... are supported to the h>obbin 6 in a vibrationproofing condition are excited and when yenerating an electromagnetic mechanical force, they vibrate in the same way as the conventional, thouyh which the vibrations transmitted to the bobbin 6 are attenuated of the high frequency component and vibrations in the bobbin 6 are reduced, thereby enabling remarkable reduction of noises emitted from ' the bobbin 6. Fig. 7 shows another modified embodiment of the first invention, in which the windings 9, 9 ... are sandwiched between the vibrationproofing rubber 13 and a mass body 14 of non-magnetic material, such as stainless steel, and secured to the bobbin 6 by a band 10. Fig. 8 shows still another modified embodiment of the first embodiment, in which the windings 9, 9 ... are secured to the bobbin 6 by a pressure plate 11 and bolts 12, 12 ... instead of the band 10. In the above constructions, the high requency component of vibrations is attenuated by the vibration- proofing rubber and the characteristic frequency of the coil is also lowered by the mass body 14, thereby enlarging the frequency domain of the damping effect. Fig. 9 shows an embodiment of a second invention, in which a bobbin 6 and windings 9, 9 ... secured thereto are integrally molded with a damping material 15. Ξpoxy derivative binary reaction type resin, for example, is suitable for the damping material. The coils in this embodiment are manufactured .in such a manner that the windings 9, 9 ... are temporarily fixed to the bobbin 6 and a damping material 15 having fluidity prior to reaction, is coated on the entire outer peripheries of the windings 9, 9 ... and bobbin 6 and then cured, thereby integrally securing the windings 9, 9 ... onto the bobbin 6. Thus, the damping material 15 molds the windinys 9, 9 ... and bobbin 6, whereby a layer of damping material 15 of sufficient thickness is formed by effectively using a space between the coil, thereby enabling a large damping effect to be obtained. As a result, it is possible to largely reduce vibrations generated by the inclined magnetic field coils 3 through 5 and bobbin 6 by the electromagnetic mechanical force. The above embodiment is a case when the windings 9, 9 ... are completely molded by the damping material 15, however the windings 9, 9 ... may be exposed in part when the electromagnetic mechanical force is small. Industrial Applicability The present invention is applicable as suppression means for vibrations and noises in the inclined magnetic field coils used for the nuclear magnetic resonance imaging diagnostic apparatus.

Claims: CLAIMS 1. A coil for a nuclear magnetic resonance imaging diagnostic apparatus being provided with a main coil and inclined magnetic field coils which are disposed in the magnetic field generated by said main coil and wound around and held on a bobbin, characterized in that a vibrationproofing material is interposed between said inclined magnetic field coils and said bobbin. 2. A coil for a nuclear magnetic resonance imaging diagnostic apparatus as set forth in claim 1 , wherein a mass body formed of a non-magnetic material is added to said inclined magnetic field coils to reduce the character¬ istic frequency of each of said inclined magnetic field coils. 3. A coil for a nuclear magnetic " resonance imaging diagnostic apparatus as set forth in claim 2, wherein said mass body is made of stainless steel. 4. A coil for a nuclear magnetic resonance imaging diagnostic apparatus as set forth in one of claims 1 through 3, wherein said vibrationproofing rαaterial is made of vibrationproofing rubber. 5. A coil for a nuclear magnetic resonance imaging diagnostic apparatus being provided with a main coil and inclined magnetic field coils which are disposed in the magnetic field generated by said main coil and v/ound around and held on a bobbin, characterized in that said inclined magnetic field coils and bobbin are integrally molded with a damping material. 6. A coil for a nuclear magnetic resonance imaging diagnostic apparatus as set forth in claim 5, wherein said damping material is epoxy derivative binary reaction t / ^e resin.

Inventors: KAZUKI MORITSU, KAZUKI, MORITSU
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1986
Main classification: G01N24
IPC codes: G01R33