WO2006054187A1

WO2006054187A1 - Magnetic resonance system with reduced noise

Info

Publication number: WO2006054187A1
Application number: PCT/IB2005/053387
Authority: WO
Inventors: Paul R. Harvey; Adrianus M. J. M. Fonken; Patrick W. P. Limpens; Terry M. Doyle; William H. Amor
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2004-11-17
Filing date: 2005-10-14
Publication date: 2006-05-26
Also published as: CN101061390A; JP2008520265A; EP1815263A1

Abstract

A magnetic resonance device includes a main magnet (2, 2a) generating a static magnetic field in an examination space (12) and supported on a floor by a support assembly (3). Gradient generation coil assembly (4) generates a magnetic field gradient in the examination space. Structures (8, 9, 30, 38) are provided for suppressing an effect of vibration generated by the gradient generation coil assembly at least at one of the main magnet and the examination space. A framework (8, 9) supports the gradient generation coil assembly and is connected to the support assembly or to the main magnet near the support assembly. Sound absorbing foam (30, 38) is vibrationally isolated from the gradient generating coil assembly to acoustically isolate the gradient generation coil assembly from the examination space. The gradient generation coil assembly is stiffened to suppress low frequency vibration of the gradient generation coil assembly.

Description

MAGNETIC RESONANCE SYSTEM WITH REDUCED NOISE

DESCRIPTION

The following relates to the magnetic resonance arts. It finds particular application in high magnetic field magnetic resonance imaging, and will be described with particular reference thereto. It finds application more generally in conjunction with magnetic resonance imaging, magnetic resonance spectroscopy, and other magnetic resonance applications at high, intermediate, or low magnetic field.

FIGURE 1 is a diagrammatic sectional view of a prior art magnetic resonance device for performing magnetic resonance imaging or spectroscopy. The plane of the FIGURE 1 corresponds with a vertical cross-section though the axial central axis 1 of the device. The magnetic resonance device includes a main magnet including a hollow cylindrical vessel 2 containing a superconducting static magnet 2a. The superconducting static magnet 2a typically includes windings of superconducting material arranged to produce a substantially uniform static magnetic field in an examination space._' To cool the static magnet 2a, the vessel 2 includes a cryostat containing liquid helium or another coolant. The vessel 2 and the contained static magnet 2a typically comprise the largest and heaviest part of the magnetic resonance device. In some embodiments, a resistive or permanent static magnet is substituted for the superconducting static magnet 2a, in which case the vessel 2 is optionally omitted from the main magnet or is replaced by a liquid nitrogen-cooled, water-cooled, or uncooled vessel or housing. The vessel 2 is supported by the floor upon which the device is installed by support means 3 located at the lower side of the vessel 2. The illustrated support means includes four feet 3 resting on the floor on which the magnetic resonance device is installed. The feet 3 are optionally fixed to the floor by screws or the like. The other parts of the MRI device are connected to, and supported by the vessel 2.

Magnetic field gradient generation means 4, which typically have a hollow cylindrical shape, are located within the hollow cylindrical vessel 2. Typically, the gradient generation means include conductive coils for generating gradients in three orthogonal directions, corresponding shield coils, optional shimming coils, and so forth, mounted on or in one or more cylindrical dielectric formers. Gradient amplifiers 4a deliver selected power to selected conductive coils of the gradient generation means 4 to produce selected magnetic field gradients in the examination space.

At both axial ends, the gradient generation means 4 are connected through support members 5 to both axial ends of the vessel 2. A whole-body radio-frequency coil 6 is optionally located within the gradient generation means 4. The radio-frequency coil 6 typically also has a hollow cylindrical shape, and surrounds the examination space of the magnetic resonance device, into which can be inserted an object to be imaged, spectroscopically analyzed, or otherwise examined. For example, the object to be examined can be a human body or a portion thereof. In FIGURE 1, the radio-frequency coil 6 is not represented in a sectional view, but in a side view. The radio-frequency coil 6 is attached to the gradient generation means 4, so that both the gradient generation means 4 and the radio frequency coil 6 rest through support members 5 on the vessel 2 containing the static magnet 2a. In some embodiments, the whole-body radio-frequency coil 6 is omitted in favor of one or more local radio frequency coils, such as a surface, coil, head coil, or so forth, that is disposed in the examination space.

A support member or table 7 for supporting the object of interest, such as a human body, is present in the substantially cylindrical examination space inside the radio- frequency coil 6 . The table 7 is carried by said support members 5. For example, the support members 5 can be connected to both ends of table 7. A difficulty with the magnetic resonance device is the presence of vibrations during operation of the device which are produced as the gradient generation means 4 rapidly switches magnetic gradient fields. Vibrations produced by the gradient generation means 4 can propagate through other components of the magnetic resonance device, such as the vessel 2, and can propagate through the air as undesirable noise. Vibrations propagating into the vessel 2 can cause a boiling effect in the liquid helium, resulting in dissipation of liquid helium. Vibrations propagating into the table 7 can disturb the human patient or other subject disposed on the table 7. Vibrations propagating as noise through the air can also reach the subject disposed on the table 7. Such noise can be generated by the gradient generation means directly, or can be generated by vibrations of other components, such as the main magnet, caused by propagation of vibration from the gradient generation means into the other components. Various techniques have been disclosed for reducing vibration and noise from the gradient generation means. Designing the gradient generation means to be shorter and stiffer has made them less efficient sound generators. In addition, vibration-isolating materials have been used in mounting the gradient generation means, to reduce vibration propagation to other system components such as the main magnet.

U.S. Patent No. 6,043,653 discloses mechanically uncoupling the gradient generation means from the main magnet, in order to reduce acoustic noise, by providing a separate support structure for supporting the gradient generation means on the floor. The support structure for the gradient generation means is separate from the support means for supporting the main magnet. Using such separate supports has certain disadvantages. Each separately supported portion (such as the gradient coil means and the main magnet) has to be separately installed on the floor, which increases installation time and complexity. The separately supported main magnet and gradient generation means should be precisely aligned with one another, and the attachment points on the floor, as well as the floor itself, should be very flat to make such precise alignment feasible. Still further, it is not possible to pre-assemble the main magnet and the gradient generating means at the manufacturing plant prior to transport to the location where the magnetic resonance device is to be installed. Thus, the precise relative alignment between the main magnet and the gradient generation means must be achieved at the delivery site, rather than at the manufacturing plant.

Vibration and noise tends to be relatively greater for magnetic resonance systems with relatively stronger main magnets. As the static main magnetic field is increased, the applied magnetic field gradients are usually larger, which calls for more power output from gradient amplifiers 4a and typically larger slew rates during magnetic resonance sequences. Thus, for example, noise in a 7 Tesla magnetic resonance system tends to be more problematic than noise in a 3 Tesla magnetic resonance system. The Occupational Safety and Health Administration (OSHA) requires sound pressure levels to be controlled at less than 140 dB.

Propagation of gradient generation noise through the air has also been addressed using soundproofing materials disposed between the gradient generation means and the examination space. U.S. Patent No. 6,414,489 and U.S. Patent No. 6,469,510 disclose such arrangements of soundproofing materials. However, interposing soundproofing material between the gradient generation means and the examination space constricts the examination space, requiring a tradeoff between the amount of soundproofing and the size of the examination space. Moreover, soundproofing materials do not address vibration propagating through the main magnet, the table 7, or other components of the magnetic resonance device.

The following contemplates improvements that overcome the aforementioned limitations and others.

In one optional aspect, gradient generation means are supported by a framework, that is connected to a support means, or to a static magnet means near said support means, for example at the lower side of the static magnet means. In this way, the source of the vibrations in the device is substantially mechanically insulated from other parts of the device. Optionally, the framework comprises flexible elements, for example near locations where it is connected to the support means or the static magnet means, so that vibrations that are propagated in the framework are reduced before they can reach said stable part of the device to which the framework is attached.

In another optional aspect, the framework comprises a structure at each axial end of the device, by which each structure is connected to said gradient generation means near an axial end of the gradient generation means. The expression "axial" is related to the hollow, typically cylindrical shape of the gradient generation means, which means are coaxial with or aligned with respect to the hollow, typically cylindrical shape of the static magnet means. Optionally, the structures are located along, but at a distance from, the axial ends of the static magnet means.

In another optional aspect, said structures at different ends of the gradient generation means are mutually interconnected, for example by one or more rods or similar members underneath the static magnet means. The rods are optionally part of the support means carrying the whole device. By interconnecting the structures at both ends of the gradient generation means, counteracting forces in the structures compensate each other, substantially reducing vibrations. In another optional aspect, a diagnosis space is surrounded by a radio-frequency coil means, which means are surrounded by the gradient generation means, and around the gradient generation means the static magnet means are located. Optionally, the radio-frequency coil means are supported by said static magnet means and are not connected with said gradient generation means. A substantial reduction of inconvenient vibrations appeared to be obtained by not connecting the radio-frequency coil means with the gradient generation means. The gradient generation means are optionally provided with an opening through which supporting parts can reach, which supporting parts connect the radio-frequency coil means with the static magnet means.

In another optional aspect, in the examination space a table is present for carrying the object of interest. The table is supported by the static magnet means and is free from any connection with said gradient generation means. Optionally, the radio-frequency coil means and the table are connected to each other and have common supporting parts that are attached to the static magnet means.

In another optional aspect, at least a substantial part of the static magnet means and said framework supporting the gradient generation means are enclosed in a cover, for example surrounded by cover plates, so that the radio-frequency coil means and/or the table in the examination space are supported by the cover. The radio-frequency coil means and/or the table are not directly connected to the static magnet means, so that there is no propagation of vibrations between the static magnet means and the radio-frequency coil means and/or the table, thus reducing noise in the examination space. In another optional aspect, an apparatus is provided which is part of a magnetic resonance system. The apparatus comprises static magnet means for generating a static magnetic field in a scanning area defined in an examination space into which an object of interest can be inserted, and gradient generation means for generating a magnetic field gradient in the scanning area. The static magnet means are supported by the floor upon which the apparatus is installed by support means located at the lower side of the static magnet means. The gradient generation means are supported by a framework which is connected to the support means, or to the static magnet means near the support means. Together with other parts of the magnetic resonance system, such as radio-frequency coil means, the above described apparatus can be assembled to form the magnetic resonance system.

In another optional aspect, a magnetic resonance device includes a main magnet for generating a static magnetic field in an examination space into which an associated object of interest can be inserted. The main magnet is supported on an associated floor by support means. Gradient generation means are provided for generating a magnetic field gradient in the examination space. Means is provided for suppressing an effect of vibration generated by the gradient generation means at least at one of the main magnet and the examination space. Optionally, the suppressing means includes a framework supporting the gradient generation means, in which the framework is connected to the support means or to the main magnet near the support means. Optionally, the framework is connected with the support means but not with the main magnet. Optionally, the suppressing means includes sound absorbing foam substantially acoustically sealing the gradient generation means from the examination space, the sound absorbing foam being vibrationally isolated from the gradient generating means. Optionally, the suppressing means includes: (i) a stiffening of the gradient generation means that substantially suppresses lower frequency vibration of the gradient generation means; and (ii) low-pass sound absorbing foam disposed between the gradient generation means and the examination space that substantially absorbs' sound at higher frequencies not suppressed by the stiffening of the gradient generating means.

In another optional aspect, a method is provided for suppressing sound pressure levels in an examination space of a magnetic resonance device. A gradient generation means is stiffened to substantially suppresses lower frequency vibration of the gradient generation means. Higher frequency sound generated by the stiffened gradient generation means is absorbed using a sound absorbing foam disposed between the stiffened gradient generation means and the examination space.

One advantage resides in reduced vibrations and reduced generation of noise. Another advantage is reduced vibrational heating of optional liquid helium coolant of a static magnet Another advantage is a reduction in the number of components.

Another advantage is reduced noise propagation to the floor and to rooms around the room where the magnetic resonance system is installed.

Another advantage is suppressed sound pressure levels in an examination space in which a patient or other object of interest is placed. Another advantage is reduced vibration in an examination space in which a patient or other object of interest is placed. Another advantage is reduced propagation of vibration from a gradient generation means to a main magnet.

Numerous additional advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments.

The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for the purpose of illustrating preferred embodiments and are not to be construed as limiting the invention.

FIGURE 1 diagrammatically shows a prior art magnetic resonance device. FIGURE 2 diagrammatically shows a sectional side view of an example embodiment magnetic resonance device.

FIGURE 3 diagrammatically shows an end view of the magnetic resonance device of FIGURE 2.

FIGURE 4 shows a perspective view of the support structure of the magnetic resonance device of FIGURES 2 and 3.

FIGURE 5 diagrammatically shows a sectional side view of another example embodiment magnetic resonance device. FIGURE 6 diagrammatically shows a sectional side view of another example embodiment magnetic resonance device.

FIGURE 7 diagrammatically shows a side sectional view of a portion of another example magnetic resonance device, which example magnetic resonance device includes noise suppressing foam. FIGURE 8 diagrammatically plots typical foam absorption and typical gradient coils amplifier power as a function of frequency. The fundamental, first, and second vibrational modes (fo, ft, f₂) of typical gradient coils are also shown.

FIGURE 9 diagrammatically plots typical foam absorption and typical gradient coils amplifier power as a function of frequency. The fundamental, first, and second vibrational modes (fo, ft, f₂) of stiffened gradient coils are also shown. FIGURE 2 diagranimatically shows a magnetic resonance device in which vibrations originating from the gradient generation means 4 are reduced. To achieve such reduction, the gradient generation means 4 are not attached to the vessel 2 containing the static magnet 2a, but rather are connected to the support means 3 through a framework comprising supporting structures 8 at each axial end of the magnetic resonance device. The structures 8 are not connected to the vessel 2 of the main magnet. Propagation of vibrations from the gradient generation means 4 to other parts of the magnetic resonance device through the support means 3 is limited, because the support means 3 (which in the illustrated example include four base members or feet) are firmly clamped to the floor by the weight of the magnetic resonance device and optionally by additional fixation elements such as screws. The floor on which the magnetic resonance device is installed is usually made of solid concrete in order to carry the heavy weight of the device, so that the support means 3 have limited freedom to vibrate. Furthermore, there is optionally a flexible or elastic connection between the structures 8 and the support means 3, in order to reduce the propagation of vibrations from the structures 8 to the support means 3.

To further reduce the vibration of the support means 3, there is optionally provided a connecting member, such as the illustrated connecting rod 9, in axial direction of the magnetic resonance device. The rod 9 connects the lower ends of the structures 8 at either axial ends of device. A substantial portion of the vibrations at the lower ends of the structures 8 will be directed axially or will have an axial component, and such vibrations will be counteracting at both support means 3, so that the connecting rod 9 will considerably extinguish such vibrations. Furthermore, it has appeared that the presence of rods 9 also reduces vibrations in other directions.

The other parts of the MRI device, such as the radio-frequency coil 6 and the table 7, are connected to the vessel 2 by means of common supporting parts 10. These supporting parts 10 pass through openings in the gradient generation means 4. The table 7 is attached to the supporting parts 10, and the radio-frequency coil means 6 are attached to the supporting parts 10 via a bridge member 11 extending between the supporting parts 10.

FIGURE 3 is a diagrammatic front view (in the axial direction) of the magnetic resonance device of FIGURE 2. The front view of FIGURE 3 shows the vessel 2 which contains the static magnet 2a, the gradient generation means 4, and the radio-frequency coil 6, all of which have a hollow cylindrical shape. The examination space 12 is located inside the radio-frequency coil 6, and the examination space 12 is provided with the table 7 for supporting the object of interest, for example a human body or portion thereof extending in axial direction of the magnetic resonance device. The table 7 is carried by supporting parts 10 which are also connected with the radio-frequency coil 6 and with the vessel 2. The supporting parts 10 pass through openings in the gradient generation means 4. The vessel 2 is supported by the floor by means of support means 3 at the lower side of the vessel 2.

The supporting structures 8 that support the gradient generation means 4 include portions at the front and back sides of the magnetic resonance device. The gradient generation means 4 optionally rests on the supporting structures 8 through a layer 13 of a material which reduces or damps the transmission of vibrations, such as a flexible material, in order to reduce the propagation of vibrations from the gradient generation means 4 to the supporting structures 8. The connection between the supporting structures 8 and the feet 3 is also optionally through flexible material to further reduce propagation of vibrations.

FIGURE 4 shows the framework by which the gradient generation means 4 is supported, comprising the two supporting structures 8 and the two rods 9. The gradient generation means 4 rest on surfaces 14, or on the flexible material 13 (shown in FIGURE 3 but not in FIGURE 4) optionally present between said surfaces 14 and the gradient generation means 4. At locations 15, the framework 8, 9 connects to the four feet 3, optionally also through flexible material.

FIGURE 5 is a diagrammatic view of another magnetic resonance device, in which similar parts are indicated with the same reference numerals as in the FIGURES 2-4 of the first embodiment. The gradient generation means 4 in this second embodiment is supported by supporting structures 8 as in the first embodiment. However, the support of the radio- frequency coil 6 and the table 7, both located inside the gradient generation means 4, is different.

In the second embodiment, the radio-frequency coil 6 is suspended from a bridge member 17 at the top side of it. Bridge member 17 is connected to the vessel 2 by supporting parts 18 at each axial end of the device. The table 7 is connected to the radio- frequency coil 6 inside said means. In this second embodiment the supporting parts 10 of the first embodiment which pass through openings in the gradient generation means 4 are thus omitted.

FIGURE 6 is a diagrammatic view of a third example magnetic resonance device, in which a cover or covering shell 19 surrounds most parts of the device. In the other example embodiments the described parts of the device may also be enclosed in a cover shell. In the embodiment of FIGURE 6, however, the cover shell 19 has a supporting function.

The cover shell 19 surrounds the parts of the magnetic resonance device, except for the table 7 and the four feet 3. At the inner side, the cover shell 19 is provided with or incorporates vibration reducing material that is preferably soft and preferably has a relatively large weight. The vibration reducing material is suitably attached to the inner side of the cover shell 19 by means of glue or the like.

In the embodiment of FIGURE 6, both the radio-frequency coil 6 and the table 7 are supported by the cover shell 19. The radio- frequency coil 6 is fixed to the inner side of the cover shell 19, and the table 7 is secured to the cover shell 19 by fixation means 20 at either axial end of the table 7.

FIGURE 7 shows a sectional view of a magnetic resonance device including portions of the vessel 2 containing the static magnet 2a, the gradient generation means 4, and the examination space 12. In FIGURE 7, the optional bore-mounted radio frequency coil 6 and the table 7 are omitted for clarity. In the embodiment of FIGURE 7, the gradient generation means 4 is secured to the vessel 2 by vibration-isolating mounts 24.

Alternatively, the supporting structures 8 of the previous embodiments can be used to support the gradient generation means 4 independently from the vessel 2. The vessel 2 and the gradient generation means 4 are generally cylindrical and define a hollow, round central bore. The central bore axis 1 defined by the cylindrical vessel 2 and cylindrical gradient generation means 4 is also drawn in FIGURE 7.

In the magnetic resonance device of FIGURE 7, a shell, casing, or housing of the device includes a bore tube 28 that is also typically hollow and cylindrical, and is placed concentrically within the hollow and cylindrical gradient generation means 4. A sound absorbing foam 30 is disposed over an outside diameter of the bore tube 28, that is, between the surface of the bore tube 28 and the surface of the gradient generating means 4.

A gap 32 or other mechanical vibration isolation means separates the sound absorbing foam 30 from the gradient generating means 4 so that the bore tube 28 and the sound absorbing foam 30 are vibrationally isolated from the gradient generating means 4. Optionally, a cooling air flow is driven through the gap 32 to cool the gradient generation means 4. It is also contemplated to mount the sound absorbing foam 30 on the inside surface of the bore tube 28, with a gap remaining between the bore tube 28 and the gradient generation means 4.

In some embodiments, the sound absorbing foam 30 is part no. E-xxxSF open cell sound absorbing foam, available from Aearo E-A-R Specialty™ Composites, Indianapolis, IN, U.S.A. In this part number, the placeholder "xxx" denotes foam thickness in hundredths of an inch, e.g. E-100SF denotes 1-inch thick foam. The foam was applied using a pressure-sensitive adhesive. However, other sound-absorbing foams can also be used. In experiments performed by the inventors, applying the sound absorbing foam directly on the gradient generating means 4 was found to actually increase the sound level, in some cases by as much as 8-10 dB at the isocenter of the magnetic resonance device. Without being limited to any particular theory of operation, it is believed that in these cases the sound absorbing foam disposed on the gradient generating means vibrates along with the gradient generating means, and the open cells of the sound absorbing foam act as noise amplifying resonating cavities.

Additionally, the inventors found that it is advantageous to substantially acoustically seal the gradient generation means 4 from the examination space 12. This was achieved by mounting the sound absorbing foam 30 circumferentially around the whole diameter of the bore tube 28 without gaps for sound to propagate through. Additionally, end covers 36 (only one of which is visible in the partial sectional view of FIGURE 7) of the shell, casing, or housing are lined with additional sound absorbing foam 38 to acoustically seal off the ends of the generally cylindrical gradient generation means 4. In the illustrated embodiment, the end covers 36 with additional sound absorbing foam 38 connect with the bore tube 28 and extend as annular flanges over the gradient generation means 4 and the main magnet vessel 2. An annular end gap 40 between the additional sound absorbing foam 38 and the gradient generation means 4 provides vibrational isolation between the additional sound absorbing foam 38 and the gradient generation means 4. It was found that including the end covers 36 with additional sound absorbing foam 38 provided about 3 dB further noise reduction. With reference to FIGURE 8, a tradeoff is involved between the thickness of the sound absorbing foam 30, on the one hand, and the diameter of the examination space 12, on the other hand. Typical tube-style gradient generation means 4 have a fundamental vibration frequency f₀ of about 500-700 Hz, with a first harmonic ft at about 1 kHz to 1.4 kHz, a second harmonic at about 1.5 kHz to 2.1 kHz, and so forth. In the example FIGURE 8, the fundamental vibration mode fo=55O Hz, and the higher order harmonics are above 1 kHz.

As further shown in FIGURE 8, the gradient amplifiers 4a typically have a low-pass bandwidth of around 1 kHz, such as an example bandwidth of about 1.1 kHz shown in FIGURE 8. Accordingly, the gradient amplifiers 4a can be expected to energize the fundamental vibration resonance fό to a large extent, and the first harmonic vibration resonance ft to a lesser extent. The higher order vibration resonances f₂ and so forth lie beyond the cutoff frequency of the gradient amplifiers 4a and accordingly are much less strongly excited. The sound absorbing foam 30 typically has a low-pass noise absorption characteristic in which sound at frequencies above a cutoff frequency is strongly absorbed but sound below the cutoff frequency is passed with limited attenuation. As shown in FIGURE 8, the cutoff frequency is a function of the thickness of the sound absorbing foam 30, with thicker foam producing lower cutoff frequency. For the Aearo E-A-R Specialty™ Composites open cell sound absorbing foam used by the inventors, the cutoff frequency is: about 1 kHz for foam having a thickness of about 1.3 cm (0.5-inch foam, part no. E-50SF); about 750 Hz for foam having a thickness of about 1.9 cm (0.75-inch foam, part no. E-75SF); and about 500 Hz for foam having a thickness of about 2.5 cm (1-inch foam, part no. E-IOOSF). Thus, good absorption of the fundamental fj> resonance frequency of the gradient generation means 4 is achieved when the sound absorbing foam 30 is about 2 cm or more thick when using open cell sound absorbing foam.

In some magnetic resonance devices, 2 cm thick foam is problematic. Thick sound absorbing foam can adversely impact the diameter of the examination space 12, availability of bore space for the whole-body radio frequency coil 6, or so forth. Substantial decrease in foam thickness can be achieved by reducing the amplitude of lowest the fundamental resonance fό, or by reducing the amplitudes of the lowest and first order fundamental resonances fo and ft. In one actually constructed embodiment, the inventors reduced the lowest and first order fundamental resonances fό and fi by increasing the stiffness of the generally tubular gradient generation means. The stiffening was achieved using known techniques such as placing an annular stiffening glass wrap around the outer diameter of the gradient generation means, increasing thicknesses of the dielectric formers, and so forth.

FIGURE 9 diagrammatically shows the effect of the stiffening of the gradient generating means on the resonances of the gradient generating means. The stiffening substantially reduced the fundamental and first order resonances f₀ and fi, but had lesser effect on the higher order resonances such as f₂. However, the higher order resonances are effectively blocked by the low-pass sound absorbing foam 30, even when the sound-absorbing foam is less than 1.3 cm thick. Accordingly, by combining stiffening of the tubular gradient generating means 4 with sound absorbing foam 30, the obtained noise reduction is substantially greater than the sum of the noise reduction achieved by each technique (stiffening and sound-proofing) separately. The invention has been described with reference to the preferred embodiments.

Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMSHaving described the preferred embodiments, the invention is now claimed to be:

1. A magnetic resonance device comprising: a main magnet (2, 2a) for generating a static magnetic field in an examination space (12) into which an associated object of interest can be inserted, the main magnet being supported on an associated floor by support means (3); gradient generation means (4) for generating a magnetic field gradient in the examination space; and means (8, 9, 30, 38) for suppressing an effect of vibration generated by the gradient generation means (4) at least at one of the main magnet (2, 2a) and the examination space (12).

2. The magnetic resonance device as set forth in claim 1, wherein the suppressing means (8, 9, 30, 38) includes: a framework (8, 9) supporting the gradient generation means, the framework (8, 9) being connected to the support means (3) or to the main magnet near the support means (3).

3. The magnetic resonance device as set forth in claim 2, wherein the framework (8, 9) is connected with the support means (3) but not with the main magnet (2, 2a).

4. The magnetic resonance device as set forth in claim 3, wherein the support means (3) includes base members disposed on the associated floor.

5. The magnetic resonance device as set forth in claim 1, wherein the framework (8, 9) includes flexible elements near the locations (15) where it is connected to said support means (3) or said main magnet (2, 2a).

6. The magnetic resonance device as set forth in claim 1, wherein the framework (8, 9) includes a supporting structure (8) connected to said gradient generation means (4) near each axial end of the gradient generation means.

7. The magnet resonance device as set forth in claim 6, characterized in that the supporting structures (8) at the axial ends of the gradient generation means (4) are connected by axially oriented connecting members (9).

8. The magnetic resonance device as set forth in claim 1, further including: a radio-frequency coil (6) for at least one of transmitting radio-frequency signals and receiving magnetic resonance signals, the radio-frequency coil being supported by the main magnet (2, 2a) and not by the gradient generation means (4).

9. The magnet resonance device as claimed in claim 8, wherein at least a substantial part of the main magnet (2, 2a) and the framework (8, 9) are enclosed in a cover (19), and the radio-frequency coil (6) is supported by the cover.

10. The magnetic resonance device as set forth in claim 1, further comprising: a support member (7) disposed at least partially in the examination space (12) for supporting the associated object of interest, the support member being supported by the main magnet (2, 2a) and not by the gradient generation means (4).

11. The magnet resonance device as claimed in claim 10, wherein at least a substantial part of the main magnet (2, 2a) and the framework (8, 9) are enclosed in a cover (19), and the support member (7) is supported by the cover.

12. The magnetic resonance device as set forth in claim 2, wherein the suppressing means (8, 9, 30, 38) further includes: sound absorbing foam (30, 38) substantially acoustically sealing the gradient generation means (4) from the examination space (12).

13. The magnetic resonance device as set forth in claim 1, wherein the suppressing means (8, 9, 30, 38) includes: sound absorbing foam (30, 38) acoustically isolating the gradient generation means (4) from the examination space (12), the sound absorbing foam being vibrationally isolated from the gradient generating means (4).

14. The magnetic resonance device as set forth in claim 13, wherein the gradient generation means (4) is generally cylindrical, and the sound absorbing foam (30, 38) includes: generally cylindrical sound absorbing foam (30) disposed coaxially inside the generally cylindrical gradient generation means (4).

15. The magnetic resonance device as set forth in claim 14, wherein the sound absorbing foam (30, 38) further includes: additional sound absorbing foam (38) disposed to acoustically close the ends of the generally cylindrical gradient generation means (4).

16. The magnetic resonance device as set forth in claim 14, further including: a bore tube (28) disposed coaxially inside of and spaced apart from the generally cylindrical gradient generation means (4), the generally cylindrical sound absorbing foam (30) being attached to a surface of the bore tube.

17. The magnetic resonance device as set forth in claim 14, wherein the sound absorbing foam (30, 38) has a low-pass noise absorption characteristic in which noise at frequencies substantially below a cutoff frequency are substantially not absorbed, and the generally cylindrical gradient generation means (4) is stiffened to substantially suppress at least a fundamental vibration resonance frequency.

18. The magnetic resonance device as set forth in claim 13, wherein the sound absorbing foam (30, 38) is vibrationally isolated from the gradient generating means (4) by one or more air gaps (32, 40).

19. The magnetic resonance device as set forth in claim 1, wherein the suppressing means (8, 9, 30, 38) includes: gradient generation means (4) being stiffened to substantially suppress an amplitude of low frequency harmonic vibration of the gradient generation means; and low-pass sound absorbing foam (30, 38) disposed between the gradient generation means (4) and the examination space (12) that substantially absorbs sound at higher frequencies not suppressed by the stiffened gradient generating means.

20. The magnetic resonance device as set forth in claim 19, wherein the sound absorbing foam has a thickness of less than about 1.3 cm.

21. A method for suppressing sound pressure levels in an examination space (12) of a magnetic resonance device, the method comprising: stiffening a gradient generation means (4) to substantially suppresses lower frequency vibration of the gradient generation means; and absorbing higher frequency sound generated by the stiffened gradient generation means (4) using a sound absorbing foam disposed between the stiffened gradient generation means (4) and the examination space (12).

22. A method for suppressing sound pressure levels in an examination space (12) of a magnetic resonance device, the method comprising: supporting a main magnet (2, 2a) for generating a static magnetic field in an examination space (12) into which an associated object of interest can be inserted on a floor by support means (3); and mounting a gradient generation means (4) for generating a magnetic field gradient in the examination space by a framework (8, 9) connected to the support means (3) or to the main magnet near the support means (3).

23. A device that is part of a magnetic resonance imaging system, which device comprises static magnet means (2, 2a) for generating a static magnetic field in an examination region (12) into which an associated object of interest can be inserted, and gradient generation means (4) for generating a magnetic field gradient in the examination region (12), in which the static magnet means (2, 2a) are supported by support means (3) located at the lower side of the static magnet means (2, 2a), and the gradient generation means (4) are supported by a framework (8, 9) connected to the support means (3) or to the static magnet means (2, 2a) near the support means (3).