JP2019150418A - Dielectric pad - Google Patents

Abstract

To reduce artifact that arises with B1 inhomogeneity while reducing artifact generated by a dielectric pad.SOLUTION: A dielectric pad includes: a first substance having an acoustic impedance that is substantially same as the acoustic impedance of a biological tissue; and a second substance having at least one of T1-reducing effect and T2-reducing effect.SELECTED DRAWING: Figure 3

Description

  Embodiments of the invention relate to a dielectric pad.

  When magnetic resonance imaging is performed by applying an RF (Radio Frequency) pulse in a high magnetic field such as 3T, dielectric artifacts, which are artifacts due to non-uniformity of the B1 magnetic field, appear. Dielectric artifacts are considered to be caused, for example, by a decrease in RF wavelength in a high magnetic field, generation of eddy currents, reflection / refraction of electromagnetic waves at the interface, or a combination of these effects. Further, artifacts due to the non-uniformity of the B1 magnetic field increase when the shape of the subject deviates from a spherically symmetric shape.

  In order to prevent image quality deterioration due to artifacts due to non-uniformity of the B1 magnetic field, it is conceivable to use a dielectric pad using a dielectric. Specifically, by performing imaging with a pulse sequence executed in a state where the imaging region is covered with a dielectric pad, artifacts due to non-uniformity of the B1 magnetic field are reduced.

  However, in some cases, the dielectric pad itself can cause new artifacts. For example, when the T2 value of the material constituting the dielectric pad is large, high signal artifacts due to the dielectric pad may occur in the final image. For example, even in the case of a differential processing method such as the FBI (Fresh Blood Imaging) method, these high signal artifacts are not canceled in the final image due to the influence of slight body movement during imaging. It may remain.

Marc DL, Daniel K, et al, “High-Permittivity Thin Dielectric Padding Improves Fresh Blood Imaging of Femoral Arteries at 3T”, Invest Radiology, February 2015, 50, 2, p101-107 Kataoka M, et al, “MR imaging of the female pelvis at 3 Tesla: evaluation of image homogeneity using different dielectric pads”, Journal of Magnetic Resonance Imaging, December 2007, 26, 6, p1572-1577

  The problem to be solved by the present invention is to reduce artifacts associated with B1 non-uniformity while reducing artifacts caused by dielectric pads.

  The dielectric pad according to the embodiment includes a first substance having substantially the same acoustic impedance as that of the biological tissue, and a second substance having at least one of the T1 shortening effect and the T2 shortening effect.

FIG. 1 is a diagram illustrating an example of a magnetic resonance imaging apparatus in which the dielectric pad according to the embodiment is used. FIG. 2 is a diagram illustrating the arrangement of dielectric pads according to the embodiment. FIG. 3 is a diagram illustrating experimental data related to the dielectric pad according to the embodiment. FIG. 4 is a diagram illustrating the arrangement of the dielectric pads according to the embodiment. FIG. 5 is a diagram for explaining the effect of the dielectric pad according to the embodiment. FIG. 6 is a diagram for explaining the effect of the dielectric pad according to the comparative example. FIG. 7 is a diagram illustrating an example of an image when a dielectric pad is not used. FIG. 8 is a diagram illustrating an example of an image when the dielectric pad according to the embodiment is used. FIG. 9 is a diagram illustrating the shape of the dielectric pad according to the embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the same code | symbol is attached | subjected to the mutually same structure, and the overlapping description is abbreviate | omitted.

(Embodiment)
First, an example of a magnetic resonance imaging apparatus using the dielectric pad according to the embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram illustrating an example of a magnetic resonance imaging apparatus 100 in which the dielectric pad 1 according to the embodiment is used. FIG. 2 is a diagram for explaining the arrangement of the dielectric pad 1 according to the embodiment. As shown in FIG. 1, the magnetic resonance imaging apparatus 100 includes a static magnetic field magnet 101, a static magnetic field power source (not shown), a gradient magnetic field coil 103, a gradient magnetic field power source 104, a bed 105, and a bed control circuit 106. , A transmission coil 107, a transmission circuit 108, a reception coil 109, a reception circuit 110, a sequence control circuit 120, and a computer 130 (also referred to as “image processing apparatus”). The magnetic resonance imaging apparatus 100 does not include the subject P (for example, a human body). Moreover, the structure shown in FIG. 1 is only an example. For example, each unit in the sequence control circuit 120 and the computer 130 may be appropriately integrated or separated.

  The static magnetic field magnet 101 is a magnet formed in a hollow, substantially cylindrical shape, and generates a static magnetic field in an internal space. The gradient magnetic field coil 103 is a coil formed in a hollow, substantially cylindrical shape, and is disposed inside the static magnetic field magnet 101. The gradient coil 103 is formed by combining three coils corresponding to the X, Y, and Z axes orthogonal to each other, and these three coils individually supply current from the gradient magnetic field power supply 104. In response, a gradient magnetic field is generated in which the magnetic field strength varies along the X, Y, and Z axes. The gradient magnetic field power supply 104 supplies a current to the gradient magnetic field coil 103.

  The couch 105 includes a couchtop 105a on which the subject P is placed. Under the control of the couch control circuit 106, the couchtop 105a is placed in the cavity (with the subject P placed) on the cavity ( Insert it into the imaging port. The couch control circuit 106 drives the couch 105 under the control of the computer 130 to move the couchtop 105a in the longitudinal direction and the vertical direction.

  The transmission coil 107 is disposed inside the gradient magnetic field coil 103 and receives a supply of RF pulses from the transmission circuit 108 to generate a high-frequency magnetic field. The transmission circuit 108 supplies an RF pulse corresponding to a Larmor frequency determined by the type of the target atom and the magnetic field strength to the transmission coil 107.

  The reception coil 109 is disposed inside the gradient magnetic field coil 103 and receives a magnetic resonance signal (hereinafter referred to as “MR signal” as necessary) emitted from the subject P due to the influence of the high-frequency magnetic field. When receiving the magnetic resonance signal, the reception coil 109 outputs the received magnetic resonance signal to the reception circuit 110.

  The receiving circuit 110 detects a magnetic resonance signal output from the receiving coil 109 or the array coil, and generates magnetic resonance image data based on the detected magnetic resonance signal. Specifically, the receiving circuit 110 generates magnetic resonance image data by digitally converting magnetic resonance signals output from the receiving coil 109 and the array coil. The receiving circuit 110 transmits the generated magnetic resonance image data to the sequence control circuit 120. The receiving circuit 110 may be provided on the gantry device side including the static magnetic field magnet 101, the gradient magnetic field coil 103, and the like.

  The sequence control circuit 120 performs imaging of the subject P by driving the gradient magnetic field power source 104, the transmission circuit 108, and the reception circuit 110 based on the sequence information transmitted from the computer 130. Here, the sequence information is information defining a procedure for performing imaging. The sequence information includes the strength of the current supplied from the gradient magnetic field power source 104 to the gradient magnetic field coil 103, the timing of supplying the current, the strength of the RF pulse supplied from the transmission circuit 108 to the transmission coil 107, the timing of applying the RF pulse, and reception. The timing at which the circuit 110 detects the magnetic resonance signal is defined. For example, the sequence control circuit 120 is an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), or an electronic circuit such as a CPU (Central Processing Unit) or MPU (Micro Processing Unit).

  Further, when the sequence control circuit 120 receives the magnetic resonance data from the reception circuit 110 as a result of driving the gradient magnetic field power source 104, the transmission circuit 108, and the reception circuit 110 and imaging the subject P, the sequence control circuit 120 converts the received magnetic resonance data into a computer. Forward to 130.

  An example of a pulse sequence executed by the sequence control circuit 120 is, for example, a Fresh Blood Imaging (FBI) method. In the FBI method, a flow at a low flow rate such as a blood flow in the lower limb can be depicted without administering a contrast medium. In the FBI method, the sequence control circuit 120 executes a pulse sequence at two different cardiac phases, for example, systole and diastole, and collects two data (two original images). Thereafter, the processing circuit 150 to be described later performs a difference process between the two pieces of collected data (two original images) by the image generation function 136 to generate a difference image such as a difference Maximum Intensity Projection (MIP) image, for example. Generate.

  For example, in the case of imaging the lower limb by performing non-contrast MRA (Magnetic Resonance Angiography) with a high magnetic field such as 3T, the image may be deteriorated due to nonuniformity of the B1 magnetic field. For this reason, the processing circuit 150 can obtain an image with improved image quality when the sequence control circuit 120 executes the pulse sequence while the dielectric pad 1 according to the embodiment is placed on the subject P. The dielectric pad 1 is configured by filling a predetermined container with a predetermined substance described later.

  The imaging procedure using the dielectric pad 1 will be described in the case of imaging the lower limbs. For example, as shown in FIG. 2, the top plate 105 a of the bed 105 is outside the bore of the static magnetic field magnet 101. The doctor / engineer who is the user of the magnetic resonance imaging apparatus 100 arranges the dielectric pad 1 so as to cover the imaging region of the subject P. For example, the user arranges the dielectric pad 1 so as to cover the lower limb that is the imaging region of the subject P placed on the top plate 105 a of the bed 105. Subsequently, the bed control circuit 106 moves the top plate 105a on which the subject P is placed into the bore. Thereafter, the sequence control circuit 120 executes a pulse sequence such as the FBI method.

  Returning to FIG. 1, the computer 130 performs overall control of the magnetic resonance imaging apparatus 100, generation of an image, and the like. The computer 130 includes a memory 132, an input interface 134, a display 135, and a processing circuit 150. The processing circuit 150 includes an interface function 131, a control function 133, and an image generation function 136.

  In the embodiment, each processing function performed by the interface function 131, the control function 133, and the image generation function 136 is stored in the memory 132 in the form of a program that can be executed by a computer. The processing circuit 150 is a processor that implements a function corresponding to each program by reading the program from the memory 132 and executing the program.

  The term “processor” used in the above description is, for example, a CPU (Central Processing Unit), a GPU (Graphical Processing Unit), an application specific integrated circuit (ASIC), a programmable logic device (for example, Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (Complex Programmable Logic Device: CPLD), Field Programmable Gate Array (Field Programmable Gate Array: FPGA), etc. It means the road. The processor implements a function by reading and executing a program stored in the memory 132.

  The processing circuit 150 transmits sequence information to the sequence control circuit 120 by the interface function 131 and receives magnetic resonance data from the sequence control circuit 120. When receiving magnetic resonance data, the processing circuit 150 having the interface function 131 stores the received magnetic resonance data in the memory 132.

  The magnetic resonance data stored in the memory 132 is arranged in the k space by the control function 133. As a result, the memory 132 stores k-space data.

  The memory 132 is received by the magnetic resonance data received by the processing circuit 150 having the interface function 131, the k-space data arranged in the k space by the processing circuit 150 having the control function 133, and the processing circuit 150 having the image generation function 136. The generated image data and the like are stored. For example, the memory 132 is a RAM (Random Access Memory), a semiconductor memory device such as a flash memory, a hard disk, an optical disk, or the like.

  The input interface 134 receives various instructions and information input from the operator. The input interface 134 is, for example, a pointing device such as a mouse or a trackball, a selection device such as a mode change switch, or an input device such as a keyboard. The display 135 displays a GUI (Graphical User Interface) for receiving imaging condition input, an image generated by the processing circuit 150 having the image generation function 136, and the like under the control of the processing circuit 150 having the control function 133. To do. The display 135 is a display device such as a liquid crystal display.

  The processing circuit 150 performs overall control of the magnetic resonance imaging apparatus 100 by the control function 133, and controls imaging, image generation, image display, and the like. The processing circuit 150 uses the image generation function 136 to read k-space data from the memory 132, and performs reconstruction processing such as Fourier transform on the read k-space data to generate an image.

  Next, the background according to the embodiment will be briefly described.

  When an RF pulse is applied in a high magnetic field such as 3T and magnetic resonance imaging is performed, dielectric artifacts, which are artifacts due to non-uniformity of the B1 magnetic field, appear. Dielectric artifacts are considered to be caused, for example, by a decrease in RF wavelength in a high magnetic field, generation of eddy currents, reflection / refraction of electromagnetic waves at the interface, or a combination of these effects.

  In order to prevent image quality deterioration due to artifacts due to non-uniformity of the B1 magnetic field, it is conceivable to use a dielectric pad using a dielectric. Specifically, when the imaging region is covered with a dielectric pad, the sequence control circuit 120 executes imaging by performing a pulse sequence, thereby reducing dielectric artifacts due to non-uniformity of the B1 magnetic field.

  However, in some cases, the dielectric pad itself can cause new artifacts. For example, when the T2 value of the material constituting the dielectric pad is large, high signal artifacts due to the dielectric pad may occur in the final image. Even in the case of a difference processing method such as the FBI method, these high signal artifacts may remain without being canceled in the final image due to the influence of slight body movement during imaging. there were.

  Under such a background, the dielectric pad 1 according to the embodiment has a first substance having substantially the same acoustic impedance as that of the biological tissue, and a second substance having at least one of the T1 shortening effect and the T2 shortening effect. Substances. This can reduce dielectric artifacts associated with B1 non-uniformity while reducing artifacts caused by the dielectric pads.

  This configuration will be described in detail below.

  First, the 1st substance contained in the dielectric pad 1 which concerns on embodiment is demonstrated. The first substance is composed of a substance having a composition similar to that of living tissue. In other words, the dielectric pad 1 according to the embodiment includes a first substance similar to a biological tissue and a second substance having at least one of a T1 shortening effect and a T2 shortening effect. In terms of the weight ratio, in the dielectric pad 1, for example, the first substance is a main component, and the second substance is a component added in a small amount compared to the first substance.

  Here, the reason why the dielectric pad 1 is composed of the first substance, which is a substance having a composition similar to that of a living tissue, as a main component is as follows. Artifacts due to the non-uniformity of the B1 magnetic field become large when the shape of the subject P deviates from a spherically symmetric shape. Therefore, when the shape of the subject P deviates from the spherically symmetric shape, the place corresponding to “air” is replaced with the first substance, which is a substance having a composition similar to the biological tissue, The shape combined with the dielectric pad approaches a spherically symmetric shape. Therefore, artifacts due to the non-uniformity of the B1 magnetic field are reduced. In other words, by selecting, as the first material, a material whose similarity between the living tissue and the first material is at least greater than the similarity between the living tissue and air, artifacts due to the non-uniformity of the B1 magnetic field are reduced. be able to.

  Next, as specific examples of “similar to biological tissue”, various specific examples can be considered. As an example, the acoustic impedance of the substance is substantially the same as the acoustic impedance of biological tissue. Is mentioned. In such a case, the dielectric pad 1 includes a first material having an acoustic impedance substantially the same as the acoustic impedance of the living tissue.

  Here, the gel for ultrasonic diagnostic examination is designed so that its acoustic impedance is substantially the same as the acoustic impedance of the living tissue. Accordingly, the ultrasonic diagnostic gel is an example of the first substance.

  Here, the advantage that the dielectric pad 1 uses as a main component a first substance having substantially the same acoustic impedance as that of the living tissue, for example, a gel for ultrasonic diagnostic examination, is as follows.

  In an ultrasonic diagnostic apparatus, a pulse wave of several MHz band is emitted from an ultrasonic probe, which is an ultrasonic transmission / reception element composed of a piezoelectric body, and a reflected wave from the internal body is received by the same ultrasonic probe. By wave, the image inside the body is visualized. Here, the ultrasonic diagnostic gel acts as an acoustic coupling agent, that is, air is mixed by filling the space between the ultrasonic probe and the living tissue with a jelly having a specific acoustic impedance close to that of the living body. To minimize the loss of ultrasound transmission and reception. In this sense, the ultrasonic diagnostic examination gel improves the response characteristics in the vicinity of the ultrasonic interface.

  On the other hand, in magnetic resonance imaging, an RF pulse is applied. Here, as the reason for the occurrence of artifacts due to B1 inhomogeneity due to the application of RF pulses, reflection and refraction of RF pulses at the interface between air and living tissue, skin effects such as eddy currents, etc. are candidates. ing. That is, if the response characteristics near the interface of the RF pulse are improved, artifacts due to B1 nonuniformity are also improved. Here, the transmission characteristics of ultrasonic waves and the transmission characteristics of RF pulses are different from each other, but both are common in the sense that they are greatly affected by the response near the interface. Thus, by using an ultrasound diagnostic gel that reduces the discontinuity of the response to ultrasound near the interface, the discontinuity of the response to the RF pulse near the interface is reduced, resulting in artifacts due to B1 non-uniformity. Is expected to be reduced. This fact has also been confirmed experimentally as described later.

  In addition, using the gel for ultrasonic diagnostic examination as a 1st substance has the following additional advantages. First, gels for ultrasonic diagnostic tests are inexpensive, are premised on being applied to the human body, and are actually used for clinical tests and are highly safe. This is an advantageous feature compared to, for example, a dielectric pad using barium titanate, which is a hazardous substance and is expensive. Secondly, the ultrasonic diagnostic gel does not rot, so there is no problem with hygiene management. This is an advantageous feature compared to a dielectric pad using raw rice or the like that is food and rots.

  Subsequently, the second substance contained in the dielectric pad 1 according to the embodiment will be described. As described above, the second substance has at least one of the T1 shortening effect and the T2 shortening effect. Here, the second substance is a substance that is added in a small weight compared to the first substance for the purpose of reducing artifacts newly generated by the dielectric pad itself composed of the first substance. .

  For example, when a gel for ultrasonic diagnostic examination is used as the first substance, the T1 value and T2 value of the gel for ultrasonic diagnostic examination are long, so that the first substance itself causes high signal artifacts during imaging. May occur. Therefore, in the embodiment, a substance having at least one of the T1 shortening effect and the T2 shortening effect is used as the second substance. Thereby, the high signal artifacts caused by the first material are canceled out, and the artifacts newly generated by the dielectric pad 1 are reduced.

  For example, a contrast agent is selected as the second substance. Here, advantages of using the contrast agent are as follows. In general, the T1 relaxation time and T2 relaxation time of a substance contained in a contrast agent have values different from the T1 relaxation time and T2 relaxation time of a biological tissue. It can be drawn separately from the part. In other words, the contrast agent is a substance whose T1 relaxation time or T2 relaxation time per unit weight tends to be largely different from the T1 relaxation time or T2 relaxation time of the living tissue. Therefore, by using a contrast agent as the second substance, signal artifacts caused by the first substance can be canceled with the addition of the second substance having a small weight.

  As an example of such a contrast agent, for example, GBCA (Gadolinium Based Contrast Agent) is selected.

  In addition, as a 2nd substance, copper sulfate, manganese sulfate, manganese chloride etc. may be selected, for example.

  As for the content of the second substance, the second substance has at least one of the T1 shortening effect and the T2 shortening effect as compared with the case where the dielectric pad 1 is not added with the second substance. More than the weight, for example, 4% or more of the weight of the first substance is added. This is because the content of the second substance requires a predetermined weight in order to cancel the signal artifact caused by the first substance.

  In addition, the second substance is added in an amount not more than the weight of the dielectric pad 1 having dielectric characteristics (the dielectric pad 1 does not lose the dielectric characteristics), for example, not more than 20% of the weight of the first substance. This is because if the ratio of the first material is too small, the performance as a dielectric pad is reduced.

  FIG. 3 shows experimental data related to the dielectric pad according to the embodiment. Fig. 3 shows the use of Zono Jelly M manufactured by Toshiba Medical Supplies Co., Ltd. as a gel for ultrasonic diagnostic testing used as the first substance, and the injection of dimeglumine gadopentetate (generic name: meglumine gadopentetate) manufactured by Bayer Yakuhin. , Used as a contrast agent used as the second substance, and the weight ratio (dilution ratio) of the second substance to the first substance is 0.5%, 1.0%, 2.0%, and 3.0, respectively. %, 4.0%, 5.0%, and 10%, FBI imaging was performed on the dielectric pad 1 composed of the first material and the second material, and magnetic resonance imaging was performed. is there. The horizontal axis represents the weight ratio of the second substance to the first substance, and the signal intensity 13 represents the signal intensity of the dielectric pad 1 when the addition amount (dilution rate) of the second substance is changed.

  From FIG. 3, regarding the dilution rate of the second substance, the signal intensity 13 of the dielectric pad 1 when FBI imaging is performed decreases monotonously. Further, when the dilution ratio of the second substance is 4% or more, the signal intensity 13 of the dielectric pad 1 reaches a plateau. For this reason, the second substance is added, for example, 4% or more of the weight of the first substance.

  When the amount of the second substance added is too large, for example, when the second substance is added by 20% or more of the weight of the first substance, the dielectric pad loses the dielectric characteristics, and the performance of the dielectric pad 1 is reduced. descend.

  Then, the arrangement | positioning place of the dielectric pad 1 which concerns on embodiment is demonstrated using FIGS. FIG. 4 is a diagram illustrating the arrangement of the dielectric pads according to the embodiment. Hereinafter, on the phantom simulating the thigh, imaging was performed after the dielectric pad 1 was arranged while changing the arrangement, and the signal values were compared.

  The phantom 20 is a cylindrical phantom that simulates the thigh of the right foot, and is a phantom having a concentration of added copper sulfate of 0.32%. FIG. 4 shows the axial direction of the cylinder of the phantom 20 A cross-sectional view in a cross section perpendicular to is shown. The phantom 21 is a cylindrical phantom simulating the thigh of the left foot, and is a phantom having a concentration of added copper sulfate of 0.055%. FIG. A cross-sectional view in a cross section perpendicular to the axial direction is shown. Reflecting the concentration of the added copper sulfate, the signal value of the phantom 21 is lower than the signal value of the phantom 20. This simulates that in actual imaging, the signal value of the thigh of the left foot is lower than the signal value of the thigh of the right foot.

  Here, imaging was performed by changing the arrangement of the dielectric pads 1 to Patterns 1 to 7 described later, and BRI (B1 value ratio index) was calculated for each arrangement of the dielectric pads 1. BRI is a quantity that represents the difference between the left and right signals, where A is the average signal value in the ROI (Region Of Interest) of the signal related to the phantom 20, and A−B) / A × 100 (%). Here, since the difference between the left and right signal values decreases as the BRI value decreases and approaches 0, it is considered that the effect of suppressing B1 nonuniformity increases.

  In FIG. 4, Pattern 1 is a pattern in which the dielectric pad 1 is not disposed, and is a reference pattern. Pattern 2 is a pattern in which one dielectric pad 1 is arranged on the right foot as shown by the dielectric pad 1a. Pattern 3 is a pattern in which two dielectric pads 1 are arranged on the right foot as indicated by the dielectric pad 1b. Pattern 4 is a pattern in which one dielectric pad 1 is arranged on the left foot, as indicated by the dielectric pad 1c. Pattern 5 is a pattern in which two dielectric pads 1 are arranged on the left foot, as indicated by the dielectric pad 1d. Pattern 6 is a pattern in which one dielectric pad 1 is disposed between the left foot and the right foot, as indicated by the dielectric pad 1e. Pattern 7 is a pattern in which two dielectric pads 1 are arranged between the left foot and the right foot, as indicated by the dielectric pad 1f.

  FIG. 5 shows a case where the dielectric pad 1 is a dielectric pad to which an ultrasonic diagnostic test gel is selected as the first substance and a contrast agent is added at a weight of 4.0% as the second substance. 4 is a plot of the BRI value for each of the four patterns of the arrangement of the dielectric pads 1. BRIs 30a, 30b, 30c, 30d, 30e, 30f, and 30g are patterns corresponding to Pattern 1, Pattern 2, Pattern 3, Pattern 4, Pattern 5, Pattern 6, and Pattern 7, respectively, in FIG. FIG. 6 shows a case where the dielectric pad 1 is a dielectric pad for a control experiment that is composed of only an ultrasonic diagnostic examination gel without adding a contrast agent. BRI values are plotted for the arrangement pattern. BRIs 31a, 31b, 31c, 31d, 31e, 31f, and 31g are patterns corresponding to Pattern 1, Pattern 2, Pattern 3, Pattern 4, Pattern 5, Pattern 6, and Pattern 7, respectively.

  In FIG. 5, comparing the BRIs 30b and 30c corresponding to Patterns 2 and 3 with the BRIs 30d and 30e corresponding to Patterns 4 and 5, the BRIs of Patterns 4 and 5 are lower than the BRIs of Patterns 2 and 3 in FIG. It has become. Therefore, it is considered that the effect of suppressing the nonuniformity of B1 becomes higher when the dielectric pad 1 is arranged on the phantom 21 side where the signal value becomes lower. Moreover, since the BRI in Pattern 4 and Pattern 5 is significantly lower than the BRI in Pattern 1, the effect of suppressing the B1 nonuniformity by arranging the dielectric pad 1 is recognized. In addition, since Pattern 5 with two dielectric pads 1 arranged has a smaller BRI value than Pattern 4 with one dielectric pad 1 arranged, the number of dielectric pads 1 arranged is larger. , BRI is lowered, and therefore, the effect of suppressing B1 non-uniformity is considered to be increased. In Patterns 6 and 7, the value of BRI remained at the same level as in Pattern 1. As one of the causes, it is considered that a gap between the phantoms 20 and 21 and the dielectric pad 1 is formed, so that the effect of suppressing the B1 nonuniformity of the dielectric pad 1 is not sufficient.

  In addition, as shown in FIG. 6, the dielectric pad 1 according to the embodiment is used even when the first substance is composed of only an ultrasonic diagnostic examination gel and no contrast agent is added as the second substance. As in the case of the pattern 4, in Patterns 4 and 5, a decrease in BRI is recognized as compared with Pattern 1 in which no dielectric pad is arranged. Here, comparing FIG. 5 with FIG. 6, the ratio of BRI 30d in Pattern 4 and 5 in FIG. 5 and BRI 30a in Pattern 1 of BRI 30e as a reference is based on BRI 31d in Pattern 4 and 5 in FIG. 6 and BRI 31a in Pattern 1 of BRI 31e in FIG. It can be seen that the ratio is comparable or less than the ratio. Therefore, it can be seen that even when the contrast agent is added as the second substance, the effect of the dielectric pad 1 to reduce the B1 nonuniformity is not impaired. On the other hand, as shown in FIG. 3, by adding the second substance, artifacts newly caused by the dielectric pad 1 itself can be reduced. Therefore, it can be seen from FIGS. 3 to 6 that according to the dielectric pad 1 according to the embodiment, artifacts caused by B1 non-uniformity can be reduced while reducing artifacts caused by the dielectric pads.

  An image obtained using the dielectric pad 1 according to the embodiment will be described with reference to FIGS. 7 and 8. FIG. 7 is a diagram illustrating an example of an image when the dielectric pad 1 according to the embodiment is not used. On the other hand, FIG. 8 is a diagram illustrating an example of an image when the dielectric pad 1 according to the embodiment is used. Specifically, imaging was performed after two dielectric pads 1 according to the embodiment were stacked on the left thigh. 7 and 8 are images of volunteers, and FBI was used as the pulse sequence.

  In FIG. 7, the signal of the blood vessel 41a, which is the thigh portion of the left foot, is lower than the signal of the blood vessel 40a, which is the thigh portion of the right foot. On the other hand, in FIG. 8 which is an image when the dielectric pad 1 according to the embodiment is used, the signal value of the blood vessel 41b which is the thigh portion of the left foot is increased particularly in the region 42, and the thigh portion of the right foot is increased. It is almost equal to the signal value of a certain blood vessel 41a. Therefore, artifacts associated with B1 nonuniformity could be reduced. On the other hand, in the dielectric pad 1 according to the embodiment, the dielectric pad 1 did not cause an artifact. Actually, even in the image before the FBI difference, the artifacts due to the dielectric pad 1 could not be confirmed.

  The shape of the dielectric pad 1 will be described with reference to FIG. FIG. 9 is a diagram illustrating the shape of the dielectric pad 1 according to the embodiment.

  The dielectric pad 1 according to the embodiment is configured by filling a predetermined container with the above-described first substance and second substance, but the container may be deformable. In this case, as shown in FIG. 9A, the dielectric pad 1 is in close contact with the dielectric pad 1 between the phantom 20 and the phantom 21, and the clearance area between them is reduced. In other words, the dielectric pad 1 according to the embodiment is configured to be deformable so that a clearance region between the pelvis or the thigh and the dielectric pad 1 becomes small when performing imaging by the magnetic resonance imaging apparatus. It may be.

  In addition, the container of the dielectric pad 1 according to the embodiment may have a shape that fits into the clearance region of the imaging region. For example, as shown in FIG. 9B, the dielectric pad 1 has a gap region formed between the phantom 20 and the phantom 21 due to a part of the cross section having a triangular shape, and the dielectric pad 1. Will fit. In other words, the dielectric pad 1 according to the embodiment is configured to have a shape that fits into a gap region formed between the left thigh and the right thigh when imaging is performed by the magnetic resonance imaging apparatus. It may be.

  The embodiment is not limited to the above-described example. In the embodiment, the case where the first substance included in the dielectric pad 1 is selected by paying attention to the acoustic impedance has been described. However, the embodiment is not limited to this, and is similar to a living tissue in terms of other physical properties. The substance may be selected as the first substance. For example, the dielectric pad 1 may include, as the first substance, a substance having a dielectric property similar to that of living tissue, for example, a substance having a dielectric constant similar to that of living tissue. In addition, the dielectric pad 1 may include, as the first substance, a substance having a magnetic property similar to that of a living tissue, for example, a substance having a permeability similar to that of the living tissue. In addition, the dielectric pad 1 may include a substance having a density similar to that of a living tissue as the first substance. Further, the dielectric pad 1 may include a substance having a proton density similar to that of a living tissue as the first substance.

  In the embodiment, the case where GBCA is used as the second substance has been described, but the embodiment is not limited thereto. For example, a transition metal complex may be selected as the second substance. For example, a metal complex having gadolinium, copper, manganese, or the like may be selected as the second substance. Further, a metal chelate compound, for example, a chelate compound containing gadolinium may be selected as the second substance.

  The dielectric pad according to at least one embodiment described above can reduce artifacts associated with B1 non-uniformity while reducing artifacts caused by the dielectric pads.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

1 Dielectric pad

Claims (10)

A first substance having substantially the same acoustic impedance as that of the biological tissue;
A dielectric pad comprising: a second material having at least one of a T1 shortening effect and a T2 shortening effect.   The dielectric pad according to claim 1, wherein the first substance is an ultrasonic diagnostic examination gel.   The dielectric pad according to claim 1, wherein the second substance is a contrast agent.   The dielectric pad according to claim 3, wherein the contrast agent is GBCA (Gadolinium Based Contrast Agent).   The dielectric pad according to claim 1, wherein the second material includes at least one of copper sulfate, manganese sulfate, and manganese chloride.   The dielectric pad according to claim 1, wherein the content of the second substance is 4% or more of the weight of the first substance.   2. The dielectric pad according to claim 1, wherein the content of the second substance is 20% or less of the weight of the first substance.   2. The dielectric pad according to claim 1, wherein the weight of the second substance has at least one of the T1 shortening effect and the T2 shortening effect, and the dielectric pad has a dielectric property.   The dielectric pad according to claim 1, wherein the shape can be deformed so that a clearance area between a pelvis or a thigh and the dielectric pad is small when imaging is performed by a magnetic resonance imaging apparatus.   The dielectric pad according to claim 1, wherein the dielectric pad has a shape that fits into a clearance region formed between the left thigh and the right thigh when imaging is performed by the magnetic resonance imaging apparatus.