JPH04288139A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PURPOSE:To provide a magnetic resonance imaging apparatus which allows highly accurate diagnosis by facilitating the adjustment of a high frequency magnetic field distribution without adjusting a hardware and a software of the apparatus. CONSTITUTION:A member which contains a high polymer material such as a mold sheet 10, a PVA gel sheet 20 or a PAR gel sheet 30 using nonconducting fiber, rubber or the like between at least one object to be inspected among transmitting and receiving coils.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to magnetic resonance (MR: ma.
The present invention relates to a magnetic resonance imaging apparatus that obtains morphological information of a subject (living body) and functional information such as spectroscopy using the phenomenon of magnetic resonance.

0002

[Prior Art] Magnetic resonance is a phenomenon in which an atomic nucleus with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs and emits only electromagnetic waves of a specific frequency. The angular frequency ωo (ωo =
2πνo, νo ; Larmor frequency). ωo = γHo Here, γo is the gyromagnetic ratio specific to the type of atomic nucleus, and Ho is the static magnetic field strength.

[0003] An apparatus that performs biological diagnosis using the above-mentioned principle processes the electromagnetic waves of the same frequency as above that are induced after the above-mentioned resonance absorption, and calculates the nuclear density and longitudinal relaxation time T1.
, transverse relaxation time T2, flow, chemical shift, etc., such as slice images of the subject, etc., can be obtained non-invasively.

[0004] Collection of diagnostic information by magnetic resonance can excite all parts of a subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical In response to the above requirements, actual devices excite a specific region and collect its signals.

In this case, the specific region to be imaged is generally a slice region with a certain thickness, and echo signals and FI
A magnetic resonance signal (MR signal) of the D signal is collected by performing a data encoding process many times, and this data group is subjected to image reconstruction processing using, for example, a two-dimensional Fourier transform method to obtain an image of the specific slice region. I am trying to generate . In such magnetic resonance imaging devices, excitation of a specific region is generally performed using a high-frequency magnetic field (
RF pulse) and a gradient magnetic field generated by a gradient magnetic field coil.

[0006]

[Problems to be Solved by the Invention] With such a device, when photographing the abdomen, for example, in order to apply a high-frequency magnetic field to a relatively wide area, a high-frequency magnetic field generating coil for the whole body built into the device is used. It is designed to generate a high frequency magnetic field.

[0007] The subject is placed in a saddle-shaped whole-body coil, and the tomographic plane is exposed to a high-frequency magnetic field (RF pulse) generated by the coil and a gradient magnetic field Gx generated by a gradient magnetic field coil.
, Gy, and Gz.

[0008] In this case, the high-frequency magnetic field distribution is determined by the shape of the coil pattern, the distribution of the divided capacitors, the coil characteristics such as capacitance value, and the current distribution determined by the conductivity, dielectric constant, etc. of the test object. When such a large coil (whole-body coil) is used, the high-frequency magnetic field distribution becomes uneven due to the influence of the coil characteristics, and furthermore, the boundary condition of the high-frequency magnetic field created by the coil due to the surface shape of the object causes When the high-frequency magnetic field distribution inside the specimen becomes distorted (becomes non-uniform), uneven sensitivity may appear in the image. In particular, in a high magnetic field type magnetic resonance imaging device such as 1.5T, the phase of the magnetization spin is likely to vary due to the movement of the heart, etc., and the so-called so-called “Successibility artifact” becomes noticeable. For example, when the abdomen is imaged by cardiac cinegraphy, as shown in FIG. 16, which is an axial cross-sectional view of the abdomen, the left ventricular myocardial region shown by the hatched area becomes black, making it impossible to perform a highly accurate diagnosis.

[0009] In order to eliminate the above-mentioned problems, it is necessary to partially control the high-frequency magnetic field distribution in the coil internal space. For example, it is necessary to adjust the coil characteristics for each imaging condition or to Although a method such as adjusting the transmission signal may be considered, it is practically impossible because the hardware and software must be adjusted for each imaging condition, which causes problems such as being complicated.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic resonance imaging apparatus in which the high-frequency magnetic field distribution can be easily adjusted without adjusting the hardware or software of the apparatus, thereby enabling highly accurate diagnosis. .

[0011]

[Means for Solving the Problems] In order to solve the above-mentioned problems and achieve the objects, the present invention takes the following measures. That is, the invention according to claim 1 causes a magnetic resonance phenomenon to occur in a specific region of the subject by irradiating the subject in a static magnetic field with an excitation high-frequency pulse from a transmitting coil, and A magnetic resonance imaging apparatus that collects generated magnetic resonance signals by a receiving coil to obtain diagnostic information about the specific region,
A magnetic resonance imaging apparatus characterized by comprising a member that is disposed between at least one of the transmitting coil and the receiving coil and the subject and that includes a gel-like polymer material. . Moreover, in the invention according to claim 2, the member includes a non-magnetic conductive material.

0012

[Operation] According to the invention according to claim 1, a molded sheet made of non-conductive fibers or rubber, or a PV
It has been confirmed that when a member containing a polymeric material such as an A gel sheet or a PAR gel sheet is placed, the high frequency magnetic field in at least one of the transmitting coil and the receiving coil is attenuated or refracted. The high-frequency magnetic field distribution around parts containing molecular materials changes,
Therefore, the high frequency magnetic field distribution can be easily adjusted without adjusting the hardware or software of the device. According to the invention according to claim 2, the high-frequency magnetic field distribution can be further flexibly adjusted by the action of the non-magnetic conductive material.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the magnetic resonance imaging apparatus according to the present invention will be described below with reference to FIGS. 1 to 3 showing the main parts thereof.

The high frequency magnetic field adjustment device (molded sheet made of non-conductive fibers or rubber) 10 shown in FIG.
Alternatively, it is constructed by molding a mesh sheet-shaped non-magnetic conductive metal 11 for RF shielding with a molding material 12. Here, the properties required for the molding material 12 include flexibility, electrical insulation, and moisture resistance, and typical examples of materials that meet these requirements include non-conductive fibers or polymeric compounds such as rubber. .

The high frequency magnetic field adjusting device (PVA gel sheet) 20 shown in FIG.
It is made up of filling. Here, the characteristics required for the bag 21 include flexibility, electrical insulation, moisture resistance, etc., and a polymer compound such as rubber is a typical example of a material that satisfies these characteristics. Further, as the non-magnetic conductive gel material 22,
Polyvinyl alcohol (PVA) material, which is also a polymer compound, contains Na+, K+, Ca2+, Cl-.
It is composed of a material impregnated with an aqueous inorganic electrolyte ion solution.

The high frequency magnetic field adjusting device (PAR gel sheet) 30 shown in FIG.
, K+, Ca2+, Cl-, etc. impregnated with an aqueous solution of inorganic electrolyte ions.

[0017] Here, the high frequency magnetic field adjustment devices 10, 20,
As shown in FIG. 4, the device 30 is flexible and can be formed into any shape, and can therefore be applied closely to the abdomen of a subject (not shown). For example, FIG. 5 shows a situation in which a high-frequency magnetic field adjustment device (polymer gel sheet) 10 is applied to the flank of the subject P, and FIG. 6 shows a situation in which a high-frequency magnetic field adjustment device (PVA gel sheet) 20 is applied to the flank of the subject P. It shows the situation in which it is applied. Figure 7 shows the high-frequency magnetic field adjustment device (
This shows a situation in which a PAR gel sheet) 30 is applied to the flank of a subject P.

Next, the operation of the embodiment configured as described above will be explained. That is, as shown in FIGS. 5 to 7, the subject P is placed in a gantry (not shown) and is subjected to the effects of a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field for excitation. It is assumed that the devices 10, 20, and 30 are applied to the lateral abdomen of the subject P. When a high-frequency magnetic field for excitation is emitted from the whole-body coil in this state, the presence of the high-frequency magnetic field adjustment devices 10, 20, and 30 causes a high-frequency magnetic field distribution that is different from the high-frequency magnetic field distribution when the high-frequency magnetic field adjustment devices 10, 20, and 30 are not present. The magnetic field distribution will be obtained.

Hereinafter, the effect of adjusting the high frequency magnetic field distribution by the apparatus of this embodiment and other effects accompanying this effect will be explained. First, magnetic field characteristics will be explained with reference to FIGS. 8 and 9. That is, FIG. 8 shows a case where a ferromagnetic material X is placed in a static magnetic field B, and FIG. 9 shows a case in which a completely diamagnetic material Y is placed in a static magnetic field B. There are parts where the magnetic flux density increases and parts where it decreases, that is, magnetic field distortion occurs. The present invention applies and utilizes this principle of magnetic field distortion to a high frequency magnetic field. Here, the high-frequency magnetic field adjustment device 10 has a foil shape,
Or it has a mesh sheet-like nonmagnetic conductive metal 11 for RF shielding, and also has high frequency magnetic field adjustment devices 20, 30.
contains an electrolyte substance, so eddy currents are generated, resulting in a state similar to that shown in FIG. It is considered that there is a region where the magnetic flux density increases, or depending on the concentration of the electrolyte solution, the dielectric properties of the gel sheet (PVA gel sheet 20, PAR gel sheet 30) become dominant, and a kind of " It is also possible that the magnetic flux density of the high-frequency magnetic field near the sheet increases due to the effect of refraction, acting like a lens.

The above-mentioned magnetic field distortion affects the magnetization spin, which is an element of the magnetic resonance phenomenon. Therefore,
The strong and weak parts of the magnetic field caused by the influence of magnetic field distortion are
Since the parameters such as the flip angle are different, the signal strength and contrast are also locally different.

According to the above, even if the distribution of the high-frequency magnetic field for excitation by the whole-body coil is distorted, the high-frequency magnetic field adjusting devices 10, 20, and 30 can be adjusted without adjusting the hardware or software of the device. By appropriately arranging it on the subject P, the influence of this magnetic field distortion can be offset by the magnetic field distortion effect of the high-frequency magnetic field adjustment devices 10, 20, and 30, and parameters such as the flip angle can be adjusted under the correct magnetic field distribution. Therefore, accurate diagnostic images can be obtained. For example, even when the abdomen is imaged by cardiac cine imaging, the left ventricular myocardium does not appear dark, allowing highly accurate diagnosis.

Furthermore, especially in a region where the magnetic flux density increases, the signal sensitivity at the time of reception also increases, so high frequency magnetic field adjusting devices 10, 20, etc. are installed in the transmitting coil or receiving coil.
30, it is possible to control the transmission high frequency magnetic field and spatially control the reception sensitivity.

[0023] Also, the high frequency magnetic field adjusting device 10 of this embodiment
, 20, and 30 have flexibility, so they can be appropriately placed on the subject P, and can exert the magnetic field adjustment function in a desired region. Furthermore, high frequency magnetic field adjustment devices 10, 2
0 is moisture-proof, so it is stain resistant and hygienic.
Preferable as a medical device.

Next, gel sheets using the polymer compound of the present invention (PVA gel sheet 20, PAR gel sheet 3)
0) describes in detail the matters studied by the inventors regarding factors that improve the image quality of MR images. (A) Introduction

In general, in a magnetic resonance imaging system with a static magnetic field strength of about 1.5 T, the diagnostic ability of internal organs appears to be improved for subjects with thick fat layers compared to subjects with thin fat layers. It is sometimes said that Therefore,
By placing a sheet-like member in place of the fat layer on a part of the subject, it was expected that diagnostic performance would improve, similar to the way images of people with thick fat layers were obtained. In fact, when taking pictures of the heart, by placing a gel sheet containing an electrolyte solution in a part of the chest, the soft tissue of the heart wall and chest wall can now be clearly depicted.

On the other hand, also in phantom experiments, it has been confirmed with good reproducibility that the signal value near the gel sheet containing electrolyte solution increases. Although it is unclear whether these two phenomena are caused by the same factor,
It seems that there is some kind of relationship. These phenomena are
Initially (at the time of filing the basic application for claiming internal priority for this application), P
This was achieved with a VA gel sheet, but later (before this application was filed) it was confirmed that it could also be achieved with an electrolyte solution. This method is particularly effective for cardiac diagnosis using a magnetic resonance imaging device, and is expected to be applied to controlling the transmission/reception efficiency of a transmitting/receiving RF coil in a magnetic resonance imaging device in the future.

[0027] So-called modalities for diagnosing the chest and abdomen include X-ray imaging devices, X-ray CT scanner devices, magnetic resonance imaging devices, etc. Conventionally, diagnoses were often made using X-ray imaging devices using contrast agents. . However, recent advances in hardware and software for magnetic resonance imaging devices have significantly improved diagnostic performance even without the use of contrast agents. However, magnetic resonance imaging devices currently generally require relatively long imaging times, making them weak for imaging moving organs, etc., and this is said to become especially noticeable as the magnetic field strength increases; for example, when the static magnetic field strength With a 1.5T magnetic resonance imaging device, the cardiac wall was rarely visualized even when electrocardiographic gating was used to image the heart.

By the way, in abdominal magnetic resonance imaging images, images of a subject with a thick fat layer are generally said to have a "good appearance." Therefore, for subjects with a thin fat layer, PVA (Poly-Vin), a material relatively close to the composition of the human body, is
When we expected a similar effect by placing yl Alcohol) on the abdomen of the subject, we found that the effect was particularly noticeable during cine imaging of the heart. (B) Phantom experiment regarding MR signal strength

0
[029] Polymer gel PVA (Poly-Viny
l Alcohol) gel, PAR (Poly-Acr
The following results were obtained from magnetic resonance imaging cardiac cine images using yl Resin) gel. (I) The signal intensity of the human body composition near the polymer gel sheet increases. (II) The extraction ability of the heart wall was improved. Among the above clinical efficacies, we will consider item (I), the effect of increasing signal strength.

In general, the MR signal strength is determined by (a) static magnetic field strength Ho, (b) high frequency magnetic field strength H1, (c) receiver coil sensitivity, (d) relaxation times T1, T2, and (e) temperature T.
, so we investigated the cause of the signal increase effect using the following phantom experiment. (a) Experimental conditions

[0031] As a polymer gel sheet, the length is 340 mm,
A PVA gel sheet with a width of 260 mm and a thickness of about 20 mm was used. The phantom is needed only to measure the change in MR signal intensity caused by the presence or absence of a polymer gel sheet, so the phantom is designed so that shape and size dependence can be ignored.
An oil-filled phantom (oil phantom) was used, which has a low load from the perspective of the RF coil and is less affected by signal strength unevenness caused by the phantom itself due to eddy currents. The RF coil used was a linear type whole-body coil that was used for both transmitting and receiving purposes.Before the start of the experiment, the RF coils were matched under conditions where only the oil phantom was set, and the RF
The 90 degree and 180 degree pulse conditions were adjusted. During the experiment, these conditions were not changed at all, except that RF coil matching was performed for each photograph.

In the case of clinical photography, the change in the Q value of the RF coil due to the presence or absence of a polymer gel sheet is so small that it cannot be measured. In the phantom experiment as well, the setting conditions for the RF coil of the polymer gel sheet were carefully considered so that the change in the Q value of the whole body RF coil was sufficiently small depending on the presence or absence of the polymer gel sheet. Of course, if the RF is shielded by a polymer gel sheet and the Q value of the RF coil is lowered, the MR signal from the oil phantom will drop significantly.

First, non-electrolyte oil was placed in the center of the magnet, and the PVA gel sheet was placed so that the direction of H1 (r) and the wide surface of the sheet were parallel to each other, and the other was placed so that it was perpendicular to it. The changes in the signal value distribution of the oil image near the PVA gel sheet were measured. (b) Confirmation of signal value increase effect

[0034] In order to confirm whether the signal value near the PVA gel sheet increases in the phantom experiment under settings similar to clinical use conditions, an oil-filled phantom 50, which is slightly smaller in size than the human body, was used instead of the human body. For example, a PVA gel sheet 20 is attached to this phantom 50.
When installed under conditions close to actual usage conditions (see Figure 10)
The changes in the signal value of the oil phantom and the changes in the sensitivity distribution were measured from the images. First, 260mm x 260mm x
The effect of increasing the image signal value of the oil phantom in the vicinity of the sheet by a sheet of PVA gel placed so as to cover part of the sides of a 180 mm oil phantom was measured. Figure 11 shows the oil phantom z without the PVA gel sheet.
A tomographic image perpendicular to the axis is taken, and iso-signal lines of the obtained image are shown. Figure 12 shows PVA on the oil phantom.
It can be seen that due to the presence of the gel sheet, the distribution of signal values in the oil phantom in the vicinity changes in the direction of increasing signal values. Moreover, since no geometric distortion was observed in the phantom image due to the presence or absence of the polymer gel sheet, it was not considered that the static magnetic field Ho was locally changing. (c) Quantitative evaluation of signal value increase due to phantom In the phantom experiment described in the previous section (b), the MR signal intensity changes spatially, and the sensitive region (R
OI) is difficult to set.

[0035] Therefore, in order to quantitatively evaluate the increment in signal intensity from a relatively uniform image with good reproducibility, a sufficiently small (oil) phantom compared to the transmitting/receiving coil (whole body coil) was surrounded by this sheet. do an experiment. (Of course, the change in the Q value of the whole body coil due to the installation of the sheet is below the measurement limit).

[0036] The phantom actually used had a diameter of 60 mm.
, a bottle with a length of 100 mm (the container is made of plastic and has a wall thickness of about 1 mm) is filled with oil. When collecting images, the center of the magnetic resonance imaging device is set so that the axis of the static magnetic field (z-axis) and the axis of the cylindrical phantom coincide. In addition, when investigating the effect of the PVA gel sheet, wrap the PVA gel sheet around this bottle-shaped oil phantom so that it is completely wrapped around it, and wrap it in the same way so that the central axis of the bottle-shaped oil phantom also coincides with the central axis of the static magnetic field. Set to . In this state, a tomographic image perpendicular to the z-axis was taken, and changes in signal values of the obtained images were examined. Here, the oil phantom is sufficiently small compared to the whole body coil for transmitting and receiving, and is set at the center of the coil, so the H1 of transmitting and receiving under no load in that area
(r) The distribution is assumed to be uniform. (c-1) Regarding changes in relaxation time

[0037]
In order to confirm that the relaxation time of the phantom solution (oil) did not change depending on the presence or absence of the polymer gel sheet, the relaxation times T1 and T2 were measured. Here, in order to eliminate the influence of the 180 degree pulse, the measurement was performed using a field echo method (gradient echo method, hereinafter abbreviated as FE method). As a result, no significant change was observed in the relaxation time of oil placed near the PVA gel sheet depending on the presence or absence of the PVA gel sheet. In other words, without PVA sheet, T
1 is 149 (msec), and T2* is 42.
5 (msec). T1 with PVA sheet
is 150 (msec) and T2* is 42.3
(msec). (c-2) Measuring changes in local high-frequency magnetic field distribution

Polymer gel sheet and high frequency magnetic field H1 (r
) can be understood by determining whether the degree of the effect of increasing the signal value actually changes depending on the arrangement of the sheet in the direction of H1 (r). Due to the relationship between the oil phantom, gel sheet, and high-frequency magnetic field, compared to when the PVA gel sheet is set parallel to H1 (r),
It was confirmed that when the setting is perpendicular to H1(r), the signal value increases even in the area near the sheet and exactly in the shadow of the sheet. These phenomena suggest that H1 (r) is involved in the increase in signal value.

In the FE method, changing the flip angle in software settings is equivalent to changing the RF input power to the transmitting coil. Also, FE
If we sweep the RF input power to the transmitter coil using the method,
This changes the strength of the high-frequency magnetic field created by the coil, which is reflected in the flip angle θ. Generally, the MR signal strength S obtained by the FE method is given by the following equation 1.

[0040]

[Equation 1] Here, T1 is longitudinal relaxation time, T2 is transverse relaxation time, T
2 * is the apparent transverse relaxation time due to magnetic field inhomogeneity, T
R represents repetition time and TE represents echo time. This equation has a peak value at a certain angle θ when graphed with the horizontal axis representing the transmission power to the RF coil and the vertical axis representing the signal strength.

[0041] Now, images are collected using the bottle-shaped oil phantom described above and changing the flip angle set in the software each time the image is taken. Next, the oil phantom is completely wrapped in a PVA gel sheet, and images are collected by changing the flip angle in the software settings each time the image is taken. At this time, changing the "software-set flip angle" corresponds to changing the high-frequency power input to the transmitting coil. Here, if the PVA gel sheet acts to increase the strength of the high-frequency magnetic field around it, the graph will shift in the direction of arrow a in Figure 13 compared to the graph when there is no PVA gel sheet, and conversely it will decrease. When working in the direction, arrow b in Figure 13
The graph shifts in the direction of .

Actually, the FE method (TR=45 msec, TE
Fig. 14 shows a plot of the signal values of the oil phantom each time an image is taken while changing the high frequency power input to the transmitting coil (=9 msec). This graph agrees well with the graph in FIG. 13 when the high frequency magnetic field H1 (r) in the vicinity increases due to the PVA gel sheet. Actually, T1 = 150 msec, TR = 45
msec, T2 * = 42 msec, TE = 9 msec
At c. Assuming that H1 (r) increases by 7% due to the PVA gel sheet, the graph calculated from Equation 1 is as shown in Figure 1.
5, which agrees well with the graph of FIG. 14, which is the experimental value. From this, it is expected that the signal value near the sheet increases due to a change in the local high-frequency magnetic field distribution due to the installation of the PVA gel sheet. (C) Discussion First, from the experimental results,

(C-1) From FIG. 12, no geometric distortion of the image is observed in the vicinity of the polymer gel sheet, so it seems that there is no change in the static magnetic field Ho in the vicinity due to the installation of the sheet. . Therefore, it seems that the phantom signal value is not changing due to a change in the static magnetic field.

(C-2) From the measurement of the relaxation time in term c, the installation of the polymer gel sheet does not cause any change in the relaxation time of the phantom in the vicinity, so the signal value of the phantom changes due to the change in relaxation time. It seems that it is not rising.

(C-3) There is a large difference between the temperature of the gel sheet and the temperature of the patient, and the effect of increasing the signal value is observed even in a phantom where there is almost no temperature difference even if the patient's body temperature changes locally. Moreover, it is impossible for the temperature to change rapidly deep within the body during a short photo shoot. Therefore, it seems that the signal value is not increasing due to a change in the temperature of the phantom.

(C-4) Experiments in which the high-frequency power input to the transmitter coil was changed each time an image was taken using the FE method revealed that the transmission and reception efficiency increased due to changes in the high-frequency magnetic field distribution of the transmitter and receiver coils, and the polymer gel sheet It is thought that the signal value of the phantom is increasing because the strength of the high-frequency magnetic field in the vicinity of is increasing.

As described above, the cause of the image quality improvement effect of the PVA gel sheet and PAR gel sheet is currently not clear, but it is thought that the high frequency magnetic field is somehow involved in these phenomena. Furthermore, by optimizing the concentration of the electrolyte solution with which the gel sheet is impregnated, it is expected that there will be conditions under which these effects will be noticeable. This may depend on whether the dielectric or conductive properties of the gel sheet containing the electrolyte solution are predominant. In general, the following reports have been made in magnetic resonance imaging.

(C-5) Whole body RF coil and RF
When the space between the shields is filled with a dielectric material, the wave number of the RF wave in the z direction increases and the wave number in the x (or y) direction relatively decreases, so that the wavelength of the RF wave incident on the human body becomes longer. (C-6) When the resonance mode of a dielectric resonator changes due to the dielectric properties of the human body, the intensity distribution of signal values changes.

(C-7) RF waves incident on an electrolyte material placed in a static magnetic field are transmitted through the sheet after undergoing disturbances such as phase due to eddy currents.Conversely, MR signals are also affected by the static magnetic field and eddy currents. The influence will similarly change the intensity, direction, and phase.

We currently believe that some of these reports may be able to explain the cause of the present image quality improvement effect. Furthermore, due to the anisotropy of a polymer gel sheet, the RF wave may have two types of refractive index within the substance, so that the state of polarization may change. (D) Conclusion

Clinically, PVA gel sheet or PA
By setting the R gel sheet on the patient's chest and performing cardiac cine imaging, the signal value of the chest wall near the sheet increases and the myocardium on the rear wall side becomes clearly visualized. Regarding the effect of increasing the signal value in the vicinity of the sheet, the increase in the signal value of about 6 to 7% was measured with good reproducibility in the phantom experiment as well.

Regarding the increase in signal value, assuming that the high-frequency magnetic field strength locally increases by 6 to 7% near the sheet, the increase in the phantom when the high-frequency power input to the transmitting coil is swept using the FE method. From the graph of changes in signal strength, it was observed that the rate of improvement in the transmission efficiency and reception efficiency of the high-frequency magnetic field to the region near the sheet was 6 to 7%, which is in relatively good agreement with the results expected from calculations.

From these results, it is clear that PVA gel sheets and P
The image quality improvement effect of the AR gel sheet is thought to be due to an increase in local high-frequency magnetic field strength due to a change in the distribution of the transmitted and received high-frequency magnetic field H1 (r). The present invention is not limited to the above embodiments, but can be implemented with various modifications without departing from the gist of the present invention.

[0054]

Effects of the Invention The invention according to claim 1 produces a magnetic resonance phenomenon in a specific region of the subject by irradiating the subject in a static magnetic field with an excitation high-frequency pulse from a transmitting coil, and In a magnetic resonance imaging apparatus that obtains diagnostic information about the specific region by collecting magnetic resonance signals generated by a receiving coil using a receiving coil, a 1. A magnetic resonance imaging apparatus characterized by comprising a member containing a polymeric material.

According to the invention according to claim 1, it has been confirmed that the high frequency magnetic field in at least one of the transmitting coil and the receiving coil is attenuated or refracted, and as a result, the high frequency magnetic field in the vicinity of the member containing the polymer material is The radio frequency magnetic field distribution changes, and therefore the radio frequency magnetic field distribution can be easily adjusted without adjusting the hardware or software of the device. According to a second aspect of the invention, the member includes at least one of a nonmagnetic conductive material and a magnetic material. According to the invention according to claim 2, the high frequency magnetic field distribution can be further flexibly adjusted by the action of the nonmagnetic conductive material and the magnetic material.

Therefore, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus in which the high-frequency magnetic field distribution can be easily adjusted without adjusting the hardware or software of the apparatus, thereby enabling highly accurate diagnosis. .

[Brief explanation of the drawing]

FIG. 1: The first part of the high-frequency magnetic field adjustment device, which is the main part of the present invention.
FIG. 2 is a cross-sectional view of an example (molded sheet made of non-conductive fibers or rubber).

[Fig. 2] The second part of the high frequency magnetic field adjusting device which is the main part of the present invention.
FIG. 3 is a cross-sectional view of Example (PVA gel sheet).

[Fig. 3] The third part of the high-frequency magnetic field adjusting device which is the main part of the present invention.
FIG. 3 is a cross-sectional view of Example (PAR gel sheet).

FIG. 4 is a perspective view of the high frequency magnetic field adjustment device shown in FIG. 1, FIG. 2, or FIG. 3.

FIG. 5 is a diagram showing how the high-frequency magnetic field adjusting device of the first embodiment is used.

FIG. 6 is a diagram showing how the high-frequency magnetic field adjusting device of the second embodiment is used.

FIG. 7 is a diagram showing how the high-frequency magnetic field adjusting device of the third embodiment is used.

FIG. 8 is a diagram showing one characteristic of a magnetic field and a specific substance.

FIG. 9 is a diagram showing other characteristics of a magnetic field and a specific substance.

FIG. 10 is a perspective view showing a state in which a PVA gel sheet is attached to an oil phantom.

FIG. 11 is a diagram showing the signal intensity distribution within an oil phantom without a PVA gel sheet.

FIG. 12 is a diagram showing signal intensity distribution within an oil phantom covered with a PVA gel sheet.

[Figure 13] Input RF with and without PVA gel sheet
A characteristic diagram showing the relationship between power and signal strength.

FIG. 14 is a characteristic diagram showing the relationship between input RF power and signal strength in the presence of a PVA gel sheet based on experimental results.

FIG. 15 is a calculated characteristic diagram of the relationship between input RF power and signal strength in the presence of a PVA gel sheet.

FIG. 16 is a diagram showing an axial tomographic image showing problems in the prior art.

[Explanation of symbols]

1...Saddle type whole body coil (transmission coil), 10, 20, 3
0... High frequency magnetic field adjustment device, 11... Non-magnetic conductive metal in the form of foil or mesh sheet for RF shielding, 12... Mold material, 21, 31... Bag, 22, 32... Non-magnetic conductive gel material.

Claims (2)

[Claims] Claim 1: A magnetic resonance phenomenon is caused in a specific region of the subject by irradiating a high-frequency excitation pulse from a transmitting coil to the subject in a static magnetic field, and a magnetic resonance signal generated due to the phenomenon is generated. A magnetic resonance imaging apparatus that obtains diagnostic information about the specific region by collecting information using a receiving coil, the magnetic resonance imaging apparatus being arranged between at least one of the transmitting coil and the receiving coil and the subject, A magnetic resonance imaging apparatus comprising a member containing a material. 2. The magnetic resonance imaging apparatus of claim 1, wherein the member includes a nonmagnetic conductive material.