Method and apparatus for limiting radio frequency alternating magnetic fields in magnetic resonance imaging

Abstract

The embodiment of the present application discloses a method and device for limiting radio frequency alternating magnetic field in magnetic resonance imaging. The method comprises: measuring the vertical distance between a local coil placed on the scanned part of a patient and the center of the detection hole of a magnetic resonance (MR) scanner; determining the deviation between the field strength of the B1 field at the position of the local coil and the field strength of the B1 field at the center of the detection hole according to the vertical distance; calculating the conversion coefficient between the field strength of the B1 field at the position of the local coil and the field strength of the B1 field at the center of the detection hole according to the deviation; and calculating the maximum allowable field strength of the B1 field at the center of the detection hole according to the field strength of the B1 field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature and the conversion coefficient. The embodiment of the present application can limit the B1 field in a smaller but still effective field strength range, thereby reducing the waste of the performance of the B1 field while ensuring the safety of the patient and the quality of the MR imaging.

Description

Technical Field

[0001] This invention relates to the field of MR (Magnetic Resonance) technology, and in particular to a method, apparatus and magnetic resonance scanner for confining radio frequency alternating magnetic fields in MRI (Magnetic Resonance Imaging). Background Technology

[0002] The IEC (Electrical Equipment for Medical Devices) standard stipulates that during MR scanning, the surface temperature of the local coil placed on the scanned human body part must meet the following requirement: maintain below 41°C at radio frequency power to avoid harm to the human body. However, the standard does not specify the method to meet this requirement.

[0003] NEMA (National Electrical Manufacturers Association) MS-14 is a new standard that details radio frequency (RF) heating test instructions for evaluating the safety of MR local coils. The new MS-14 test standard requires measuring the surface temperature of the local coil when thermal equilibrium is reached. Therefore, the RF alternating magnetic field generated by the transmitting coil, i.e., the B1 field, must be more strictly limited and monitored to ensure that older RF coils still comply with the new standard.

[0004] Currently, most MR scanners limit the B1 field based on the patient's SAR (Specific Absorption Rate) or the heating angle of the RF coil surface. In this approach, the B1 field strength is typically limited to a very low value so that even if the local coil contacts the wall of the MR scanner's detection aperture, the local coil surface temperature can be maintained below 41°C. However, most patients are not obese, so the local coil placed on the scanned area is still a considerable distance from the aperture wall. Therefore, setting the B1 field strength too low would result in wasted B1 field performance. Summary of the Invention

[0005] In view of this, embodiments of the present invention propose a B1 field confinement method and apparatus in magnetic resonance imaging, so as to reduce the waste of B1 field performance while ensuring patient safety and MR imaging quality.

[0006] This invention also proposes a magnetic resonance scanner to reduce the waste of B1 field performance while ensuring patient safety and MR imaging quality.

[0007] The technical solution of this invention is implemented as follows:

[0008] A method for confining a radio frequency alternating magnetic field in magnetic resonance imaging, the method comprising:

[0009] Measure the vertical distance between the local coil placed on the patient's scanned area and the center of the detection aperture of the magnetic resonance MR scanner;

[0010] Based on the vertical distance between the local coil and the center of the detection aperture, the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture during MR scanning is determined.

[0011] The conversion coefficient between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole is calculated based on the deviation.

[0012] The maximum permissible field strength of the radio frequency alternating magnetic field at the center of the detection hole is calculated based on the field strength of the radio frequency alternating magnetic field required when the surface temperature of the local coil equals the upper limit of the safe temperature and the conversion coefficient.

[0013] In the above embodiments, by measuring the vertical distance between the local coil and the center of the detection aperture of the MR scanner, since there is a corresponding relationship between the vertical distance between the local coil and the center of the detection aperture of the MR scanner and the field strength deviation between them, and there is a fixed conversion relationship between the field strength deviation between them and the field strength between them, the maximum allowable field strength of the B1 field at the center of the detection aperture can be calculated based on the field strength of the B1 field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature and the conversion relationship. This allows the B1 field to be limited to a smaller but still effective field strength range, reducing the waste of B1 field performance while ensuring patient safety and MR imaging quality.

[0014] The conversion coefficient between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture, calculated based on the deviation, includes:

[0015] α = 10 S / 20

[0016] Wherein, α is the conversion coefficient, and S is the deviation;

[0017] The calculation of the maximum permissible field strength of the radio frequency alternating magnetic field at the center of the detection aperture, based on the field strength of the radio frequency alternating magnetic field required when the local coil surface temperature equals the upper limit of the safe temperature and the conversion coefficient, includes:

[0018] B1_c=B1_rf*α

[0019] Where B1_c is the field strength of the radio frequency alternating magnetic field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature, and B1_rf is the maximum allowable field strength of the radio frequency alternating magnetic field at the center of the detection hole.

[0020] The step of determining the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture during MR scanning, based on the vertical distance between the local coil and the center of the detection aperture, includes:

[0021] In the pre-established vertical distance-deviation correspondence table, find the deviation corresponding to the vertical distance between the local coil and the center of the detection hole, and use the found deviation as the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole during MR scanning.

[0022] Among them, when the vertical distance between the local coil and the center of the detection hole is measured in advance with different values, the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole during MR scanning is measured. Based on the measurement results, a vertical distance-deviation correspondence table is established.

[0023] After calculating the maximum permissible field strength of the radio frequency alternating magnetic field at the center of the detection aperture, the method further includes:

[0024] During the pre-scanning stage of the MR scanner, the MR scanner is controlled to transmit radio frequency signals using the default radio frequency voltage, and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture is measured. Based on the default radio frequency voltage and the measured field strength, the proportionality coefficient between the radio frequency voltage and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture is calculated.

[0025] Select a field strength that is not greater than the maximum allowable field strength as the reference field strength of the radio frequency alternating magnetic field at the center of the detection hole, and calculate the radio frequency operating voltage based on the reference field strength and the proportional coefficient.

[0026] During the actual scanning phase of the MR scanner, the MR scanner is controlled to use this radio frequency operating voltage to transmit radio frequency signals.

[0027] The measurement of the vertical distance between the local coil placed on the patient's scanned area and the center of the detection aperture of the MR scanner includes:

[0028] When the patient lies on the MR scanner bed, and the local coil has been placed on the patient's scanned area but before the patient is pushed into the detection aperture, the 3D camera mounted above the bed is activated. The positions of the local coil and the bed are detected in the image captured by the camera. The vertical distance between the local coil and the bed is calculated based on their positions. Combined with the vertical distance between the bed and the center of the detection aperture, the vertical distance between the local coil and the center of the detection aperture is calculated. Alternatively...

[0029] Calculate the vertical distance between the local coil and the center of the detection hole based on the three-dimensional spatial coordinates of the detection hole center and the three-dimensional spatial coordinates of the local coil measured by the three-dimensional Hall sensor placed on the local coil; or,

[0030] When the patient is pushed into the detection hole, the laser emitter located at the apex of the detection hole wall emits a laser signal. The vertical distance between the local coil and the apex of the detection hole wall is calculated based on the reflected signal received by the laser reflector. Combined with the radius of the detection hole, the vertical distance between the local coil and the center of the detection hole is calculated.

[0031] A method for confining a radio frequency alternating magnetic field in magnetic resonance scanning, characterized in that the method includes:

[0032] Measure the vertical distance between the local coil placed on the patient's scanned area and the apex of the detection aperture wall of the magnetic resonance MR scanner;

[0033] To obtain the maximum permissible field strength of the radio frequency alternating magnetic field required when the local coil surface temperature equals the upper limit of the safe temperature;

[0034] The radio frequency operating voltage of the MR scanner is determined based on the vertical distance and the maximum permissible field strength.

[0035] In the above embodiments, by measuring the vertical distance between the local coil and the vertex of the detection hole wall of the MR scanner, and obtaining the maximum allowable field strength of the radio frequency alternating magnetic field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature, the radio frequency operating voltage of the MR scanner is determined based on the vertical distance and the maximum allowable field strength. This allows the radio frequency alternating magnetic field to be limited to a smaller but still effective field strength range, ensuring patient safety and MR imaging quality while reducing the waste of radio frequency alternating magnetic field performance.

[0036] The step of determining the radio frequency operating voltage of the MR scanner based on the vertical distance and the maximum permissible field strength includes:

[0037] During the pre-scanning stage of the MR scanner, the MR scanner is controlled to transmit radio frequency signals using the default radio frequency voltage. The location of the local coil is determined based on the vertical distance between the local coil and the vertex of the detection hole wall of the MR scanner. The field strength of the radio frequency alternating magnetic field at the location of the local coil is measured. Based on the default radio frequency voltage and the measured field strength, the proportionality coefficient between the radio frequency voltage and the field strength of the radio frequency alternating magnetic field at the location of the local coil is calculated.

[0038] Select a field strength that is no greater than the maximum allowable field strength as the reference field strength of the radio frequency alternating magnetic field at the location of the local coil, and calculate the radio frequency operating voltage based on the reference field strength and the proportional coefficient.

[0039] During the actual scanning phase of the MR scanner, the MR scanner is controlled to use this radio frequency operating voltage to transmit radio frequency signals.

[0040] The measurement of the vertical distance between the local coil placed on the patient's scanned area and the apex of the detection aperture wall of the MR scanner includes:

[0041] When the patient lies on the MR scanner bed, and the local coil has been placed on the patient's scanned area but before the patient is pushed into the detection aperture, the 3D camera mounted above the bed is activated. The positions of the local coil and the bed are detected in the image captured by the camera. The vertical distance between the local coil and the bed is calculated based on their positions. Combined with the vertical distance between the bed and the vertex of the detection aperture wall, the vertical distance between the local coil and the vertex of the detection aperture wall is calculated. Alternatively...

[0042] Based on the three-dimensional spatial coordinates of the apex of the detection hole wall and the three-dimensional spatial coordinates of the local coil measured by the three-dimensional Hall sensor placed on the local coil, calculate the vertical distance between the local coil and the apex of the detection hole wall; or,

[0043] When the patient is pushed into the detection hole, the laser emitter located at the apex of the detection hole wall emits a laser signal, and the vertical distance between the local coil and the apex of the detection hole wall is calculated based on the reflected signal received by the laser reflector.

[0044] A radio frequency alternating magnetic field confinement device for magnetic resonance imaging, the device comprising:

[0045] The distance measurement module is used to measure the vertical distance between the local coil placed on the patient's scanned area and the center of the detection aperture of the magnetic resonance MR scanner;

[0046] The field strength deviation detection module is used to determine the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole during MR scanning, based on the vertical distance between the local coil and the center of the detection hole.

[0047] The field strength conversion coefficient calculation module is used to calculate the conversion coefficient between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole, based on the deviation.

[0048] The field strength limiting module is used to calculate the maximum allowable field strength of the radio frequency alternating magnetic field at the center of the detection hole based on the field strength of the radio frequency alternating magnetic field required when the local coil surface temperature equals the upper limit of the safe temperature and the conversion coefficient.

[0049] A radio frequency alternating magnetic field confinement device for magnetic resonance scanning, the device comprising:

[0050] The distance measurement module is used to measure the vertical distance between the local coil placed on the patient's scanned area and the apex of the detection aperture wall of the magnetic resonance MR scanner;

[0051] The field strength limiting module is used to obtain the maximum permissible field strength of the radio frequency alternating magnetic field required when the local coil surface temperature equals the upper limit of the safe temperature.

[0052] The scanning control module is used to determine the radio frequency operating voltage of the MR scanner based on the vertical distance and the maximum allowable field strength.

[0053] A magnetic resonance scanner includes a radio frequency alternating magnetic field confinement device for magnetic resonance scanning as described in any of the above.

[0054] The embodiments of the present invention can limit the B1 field to a smaller but still effective field strength range, thereby reducing the waste of B1 field performance while ensuring patient safety and MR imaging quality. Attached Figure Description

[0055] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which will make the above and other features and advantages of the present invention more apparent to those skilled in the art. In the drawings:

[0056] Figure 1 This is a field strength distribution map of the B1 field on the patient's cross section during an MR scan.

[0057] Figure 2 This is a field strength distribution diagram of the B1 field in the vertical direction through the center of the MR scanner's detection aperture.

[0058] Figure 3 This is a flowchart of the B1 field confinement method in MRI provided in the first embodiment of the present invention;

[0059] Figure 4 This is a schematic diagram illustrating the measurement of the vertical distance between the local coil and the center of the detection hole using Method 1 of the first embodiment of the present invention;

[0060] Figure 5 This is a schematic diagram of the pre-scanning area and FOV (Field of View, imaging area) in the first embodiment of the present invention;

[0061] Figure 6 This is a flowchart of the B1 field confinement method in MRI provided in the second embodiment of the present invention;

[0062] Figure 7 This is a schematic diagram of the pre-scanning area and FOV in the second embodiment of the present invention;

[0063] Figure 8A schematic diagram of the B1 field confinement device in MRI provided in the first embodiment of the present invention;

[0064] Figure 9 This is a schematic diagram of the structure of the B1 field confinement device in MRI provided in the second embodiment of the present invention.

[0065] The reference numerals in the attached figures are as follows:

[0066] label meaning 21 Detect the top of the hole wall 301-305 step 41 3D camera 42 bed board 43 Detection hole 51，71 Pre-scan area 52，72 FOV 601-603 step 80 The B1 field confinement device in MRI provided in the first embodiment of the present invention 81 The distance measurement module provided in the first embodiment of the present invention 82 The field strength deviation detection module provided in the first embodiment of the present invention 83 The field strength conversion coefficient calculation module provided in the first embodiment of the present invention 84 The field strength limiting module provided in the first embodiment of the present invention 85 The scanning control module provided in the first embodiment of the present invention 90 The B1 field confinement device in MRI provided in the second embodiment of the present invention 91 The distance measurement module provided in the second embodiment of the present invention 92 The field strength limiting module provided in the second embodiment of the present invention 93 The scanning control module provided in the second embodiment of the present invention Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of the present invention clearer, the following embodiments are provided to further illustrate the present invention in detail.

[0068] When the MR scanner is working, the field strength distribution of the B1 field in the detection hole of the MR scanner can be analyzed. It can be found that the field strength of the B1 field is not uniform in the direction perpendicular to the center of the detection hole (i.e., the direction that passes through the center of the hole and is perpendicular to the horizontal plane). Specifically, the field strength of the B1 field is the weakest at the center of the hole and the further away from the center of the hole, the stronger the field strength of the B1 field. The field strength of the B1 field is the strongest at the top of the hole wall (i.e., the highest point of the detection hole wall).

[0069] Figure 1 The image shows the field strength distribution of the B1 field on the patient's cross-section during MR scanning. It can be seen that the field strength of the B1 field gradually increases from the center of the detection aperture to the aperture wall.

[0070] Figure 2 This is a graph showing the B1 field intensity distribution in the vertical direction through the center of the MR scanner's detection aperture during MR scanning. The horizontal axis represents the distance from the aperture center in the vertical direction, measured in mm (millimeters), with 0 corresponding to the aperture center. The vertical axis represents the B1 field intensity, measured in μT (microtesla), with 21 corresponding to the apex of the aperture wall and 22 corresponding to the lowest point of the aperture wall. It can be seen that the B1 field intensity gradually increases from the aperture center to the aperture wall. This is because the emitter coil of the MR scanner is not perfectly circular; it is semi-circular in the upper half of the aperture and slightly elliptical in the lower half. Therefore, the field intensity distribution above and below the aperture center (i.e.,...) varies. Figure 2 The electric field distribution on the left and right sides of the curve is not symmetrical. From... Figure 2 It can also be seen that the field strength of the B1 field near the wall of the detection hole is about 1.5 times that of the B1 field at the center of the hole. Therefore, if the local coil is not actually close to the hole wall, the B1 performance of MRI imaging will be sacrificed by about 1 - (1 / 1.5) = 33%.

[0071] Based on the above analysis, it can be seen that if the position of the local coil can be accurately determined, the field strength of field B1 can be accurately set.

[0072] Figure 3 The flowchart of the B1 field confinement method in MRI provided in the first embodiment of the present invention is as follows:

[0073] Step 301: Measure the vertical distance between the local coil placed on the patient's scanned area and the center of the detection aperture of the MR scanner.

[0074] In one optional embodiment, this step can be implemented in one of the following three ways:

[0075] Method 1: When the patient is lying on the bed of the MR scanner, and the local coil has been placed on the patient's scanned area, but the patient has not yet been pushed into the detection hole, the 3D camera installed above the bed is activated. The positions of the local coil and the bed are detected in the image captured by the camera. The vertical distance between the local coil and the bed is calculated based on the positions of the local coil and the bed. Combined with the vertical distance between the bed and the center of the detection hole, the vertical distance between the local coil and the center of the detection hole is calculated.

[0076] Figure 4 This is a schematic diagram illustrating the method for measuring the vertical distance between the local coil and the center of the detection hole using Method 1. In the diagram, 41 represents the 3D camera, 42 represents the bed board, and 43 represents the detection hole.

[0077] Method 2: Calculate the vertical distance between the local coil and the center of the detection hole based on the three-dimensional spatial coordinates of the detection hole center and the three-dimensional spatial coordinates of the local coil measured by the three-dimensional Hall sensor placed on the local coil.

[0078] Method 3: When the patient is pushed into the detection hole, the laser emitter located at the apex of the detection hole wall emits a laser signal. The vertical distance between the local coil and the apex of the detection hole wall is calculated based on the reflected signal received by the laser reflector. Combined with the radius of the detection hole, the vertical distance between the local coil and the center of the detection hole is calculated.

[0079] Detect the apex of the hole wall, that is, detect the highest point of the hole wall.

[0080] Step 302: Based on the vertical distance between the local coil and the center of the detection aperture, determine the deviation between the field strength of the B1 field at the location of the local coil and the field strength of the B1 field at the center of the detection aperture during MR scanning.

[0081] In one optional embodiment, in a pre-established vertical distance-deviation correspondence table, the deviation corresponding to the vertical distance between the local coil and the center of the detection hole is found, and the found deviation is used as the deviation between the field strength of the radio frequency B1 field at the location of the local coil and the field strength of the B1 field at the center of the detection hole during MR scanning; wherein, when the vertical distance between the local coil and the center of the detection hole takes different values, the deviation between the field strength of the B1 field at the location of the local coil and the field strength of the B1 field at the center of the detection hole during MR scanning is measured in advance, and a vertical distance-deviation correspondence table is established based on the measurement results.

[0082] An example of the vertical distance-deviation correspondence table is shown in Table 1:

[0083]

[0084] Table 1

[0085] According to Table 1, once the vertical distance between the local coil and the center of the detection aperture is obtained, the deviation between the field strength of the B1 field at the location of the local coil and the field strength of the B1 field at the center of the detection aperture during MR scanning can be determined by referring to the table.

[0086] Step 303: Calculate the conversion coefficient between the field strength of field B1 at the location of the local coil and the field strength of field B1 at the center of the detection hole based on the deviation.

[0087] In one optional embodiment, this step can be expressed by the following formula:

[0088] α = 10 S / 20

[0089] Where α is the conversion coefficient, and S is the deviation in step 302, with the unit of deviation being dB.

[0090] Step 304: Calculate the maximum allowable field strength of the B1 field at the center of the detection hole based on the field strength of the B1 field required when the local coil surface temperature equals the upper limit of the safe temperature and the conversion coefficient obtained in step 303.

[0091] According to IEC standards, the upper limit for safe temperature is 41°C.

[0092] In one optional embodiment, this step can be expressed by the formula:

[0093] B1_c=B1_rf*α

[0094] Where B1_c is the field strength of the B1 field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature, B1_rf is the maximum allowable field strength of the B1 field at the center of the detection hole, and α is the conversion coefficient.

[0095] Step 305: Determine the radio frequency operating voltage of the MR scanner based on the maximum permissible field strength in step 304.

[0096] In one optional embodiment, step 305 specifically includes:

[0097] Step 3051: In the pre-scanning stage of the MR scanner, control the MR scanner to transmit RF signals using the default RF voltage and measure the field strength of the B1 field at the center of the detection aperture. Calculate the proportionality coefficient between the RF voltage and the field strength of the B1 field at the center of the detection aperture based on the default RF voltage and the measured field strength.

[0098] There is a fixed direct proportional relationship between the radio frequency voltage and the field strength of the B1 field at the center of the detection aperture.

[0099] Step 3052: Select a field strength that is no greater than the maximum allowable field strength in step 304 as the reference field strength of field B1 at the center of the detection hole. Calculate the radio frequency operating voltage based on the reference field strength and the scaling factor in step 3051.

[0100] Step 3053: During the formal scanning phase of the MR scanner, control the MR scanner to transmit radio frequency signals using the radio frequency operating voltage.

[0101] In the above embodiments, by measuring the vertical distance between the local coil and the center of the detection aperture of the MR scanner, since there is a corresponding relationship between the vertical distance between the local coil and the center of the detection aperture of the MR scanner and the field strength deviation between them, and there is a fixed conversion relationship between the field strength deviation between them and the field strength between them, the maximum allowable field strength of the B1 field at the center of the detection aperture can be calculated based on the field strength of the B1 field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature and the conversion relationship. This allows the B1 field to be limited to a smaller but still effective field strength range, reducing the waste of B1 field performance while ensuring patient safety and MR imaging quality.

[0102] Figure 5 A schematic diagram of the pre-scanning region 51 and the FOV (Field of View, imaging region) 52 in the first embodiment of the present invention is provided. Figure 5 As shown, the pre-scanning area 51 is at the center of the detection hole 43, and the FOV 52 is at the local coil position, where 42 is the bed plate.

[0103] Figure 6 The flowchart of the B1 field confinement method in MRI provided in the second embodiment of the present invention is as follows:

[0104] Step 601: Measure the vertical distance between the local coil placed on the patient's scanned area and the apex of the detection aperture wall of the magnetic resonance MR scanner.

[0105] In one optional embodiment, this step can be implemented in one of the following three ways:

[0106] Method 1: When the patient is lying on the bed of the MR scanner, and the local coil has been placed on the patient's scanned area, but the patient has not yet been pushed into the detection hole, the 3D camera installed above the bed is activated. The positions of the local coil and the bed are detected in the image captured by the camera. The vertical distance between the local coil and the bed is calculated based on the positions of the local coil and the bed. Combined with the vertical distance between the bed and the vertex of the detection hole wall, the vertical distance between the local coil and the vertex of the detection hole wall is calculated.

[0107] Method 2: Calculate the vertical distance between the local coil and the vertex of the detection hole wall based on the three-dimensional spatial coordinates of the detection hole wall and the three-dimensional spatial coordinates of the local coil measured by the three-dimensional Hall sensor placed on the local coil.

[0108] Method 3: When the patient is pushed into the detection hole, the laser emitter located at the apex of the detection hole wall emits a laser signal, and the vertical distance between the local coil and the apex of the detection hole wall is calculated based on the reflected signal received by the laser reflector.

[0109] Step 602: Obtain the maximum permissible field strength of the radio frequency B1 field required when the local coil surface temperature equals the upper limit of the safe temperature.

[0110] Step 603: Determine the radio frequency operating voltage of the MR scanner based on the vertical distance in step 601 and the maximum allowable field strength in step 602.

[0111] In one optional embodiment, step 603 specifically includes:

[0112] Step 6031: In the pre-scanning stage of the MR scanner, the MR scanner is controlled to transmit radio frequency signals using the default radio frequency voltage. Based on the vertical distance between the local coil and the vertex of the detection hole wall of the MR scanner determined in step 601, the location of the local coil is determined, the field strength of the B1 field at the location of the local coil is measured, and the proportionality coefficient between the radio frequency voltage and the field strength of the B1 field at the location of the local coil is calculated.

[0113] Step 6032: Select a field strength that is no greater than the maximum allowable field strength in step 602 as the reference field strength of field B1 at the location of the local coil. Calculate the RF operating voltage based on the reference field strength and the scaling factor in step 6031.

[0114] Step 6033: During the formal scanning phase of the MR scanner, control the MR scanner to transmit radio frequency signals using the radio frequency operating voltage.

[0115] In the above embodiments, by measuring the vertical distance between the local coil and the vertex of the detection hole wall of the MR scanner, and obtaining the maximum allowable field strength of the B1 field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature, and determining the radio frequency operating voltage of the MR scanner based on the vertical distance and the maximum allowable field strength, the B1 field can be limited to a smaller but still effective field strength range, thereby reducing the waste of B1 field performance while ensuring patient safety and MR imaging quality.

[0116] Figure 7 A schematic diagram of the pre-scanning region 71 and FOV 72 in the second embodiment of the present invention is provided. Figure 7 As shown, the pre-scanning area 71 and FOV 72 are both located at the local coil position, where 42 is the bed plate and 43 is the detection hole.

[0117] Figure 8 This is a schematic diagram of the structure of the B1 field confinement device 80 in MRI provided in the first embodiment of the present invention. The device 80 mainly includes:

[0118] The distance measurement module 81 is used to measure the vertical distance between the local coil placed on the patient's scanned area and the center of the detection aperture of the MR scanner.

[0119] The field strength deviation detection module 82 is used to determine the deviation between the field strength of the B1 field at the location of the local coil and the field strength of the B1 field at the center of the detection hole during MR scanning, based on the vertical distance between the local coil and the center of the detection hole measured by the distance measurement module 81.

[0120] The field strength conversion coefficient calculation module 83 is used to calculate the conversion coefficient between the field strength of field B1 at the location of the local coil and the field strength of field B1 at the center of the detection hole, based on the deviation determined by the field strength deviation detection module 82.

[0121] The field strength limiting module 84 is used to calculate the maximum allowable field strength of the B1 field at the center of the detection hole based on the field strength of the B1 field required when the local coil surface temperature is equal to the upper limit of the safe temperature and the conversion coefficient calculated by the field strength conversion coefficient calculation module 83.

[0122] In one optional embodiment, the field strength conversion coefficient calculation module 83 is specifically used to calculate α = 10 S / 20 , where α is the conversion coefficient between the field strength of field B1 at the location of the local coil and the field strength of field B1 at the center of the detection hole, and S is the deviation determined by the field strength deviation detection module 82, where the unit of deviation is dB.

[0123] The field strength limiting module 84 is specifically used to calculate B1_c = B1_rf * α, where B1_c is the field strength of the B1 field required when the local coil surface temperature is equal to the upper limit of the safe temperature, and B1_rf is the maximum allowable field strength of the B1 field at the center of the detection hole.

[0124] In one optional embodiment, the field strength deviation detection module 82 is specifically used to find the deviation corresponding to the vertical distance between the local coil and the center of the detection hole measured by the distance measurement module 81 in a pre-established vertical distance-deviation correspondence table, and use the found deviation as the deviation between the field strength of the radio frequency B1 field at the location of the local coil and the field strength of the B1 field at the center of the detection hole during MR scanning; wherein, when the vertical distance between the local coil and the center of the detection hole takes different values, the deviation between the field strength of the B1 field at the location of the local coil and the field strength of the B1 field at the center of the detection hole during MR scanning is measured in advance, and a vertical distance-deviation correspondence table is established based on the measurement results.

[0125] In an optional embodiment, the above-mentioned device 80 further includes a scanning control module 85, configured to: control the MR scanner to transmit radio frequency signals using a default radio frequency voltage during the pre-scanning stage of the MR scanner, and measure the field strength of the B1 field at the center of the detection aperture; calculate the proportionality coefficient between the radio frequency voltage and the field strength of the B1 field at the center of the detection aperture based on the default radio frequency voltage and the measured field strength; select a field strength not greater than the maximum allowable field strength calculated by the field strength limiting module 84 as a reference field strength of the B1 field at the center of the detection aperture, and calculate the radio frequency operating voltage based on the reference field strength and the proportionality coefficient; and control the MR scanner to transmit radio frequency signals using the radio frequency operating voltage during the formal scanning stage of the MR scanner.

[0126] In one optional embodiment, the distance measurement module 81 is specifically used for:

[0127] When the patient lies on the MR scanner bed, and the local coil has been placed on the patient's scanned area but before the patient is pushed into the detection aperture, the 3D camera mounted above the bed is activated. The positions of the local coil and the bed are detected in the image captured by the camera. The vertical distance between the local coil and the bed is calculated based on their positions. Combined with the vertical distance between the bed and the center of the detection aperture, the vertical distance between the local coil and the center of the detection aperture is calculated. Alternatively...

[0128] Calculate the vertical distance between the local coil and the center of the detection hole based on the three-dimensional spatial coordinates of the detection hole center and the three-dimensional spatial coordinates of the local coil measured by the three-dimensional Hall sensor placed on the local coil; or,

[0129] When the patient is pushed into the detection hole, the laser emitter located at the apex of the detection hole wall emits a laser signal. The vertical distance between the local coil and the apex of the detection hole wall is calculated based on the reflected signal received by the laser reflector. Combined with the radius of the detection hole, the vertical distance between the local coil and the center of the detection hole is calculated.

[0130] Figure 9 This is a schematic diagram of the structure of a B1 field confinement device 90 in MRI provided in the second embodiment of the present invention. The device 90 mainly includes:

[0131] The distance measurement module 91 is used to measure the vertical distance between the local coil placed on the patient's scanned area and the apex of the detection aperture wall of the MR scanner.

[0132] The field strength limiting module 92 is used to obtain the maximum permissible field strength of the B1 field required when the local coil surface temperature is equal to the upper limit of the safe temperature.

[0133] The scanning control module 93 is used to determine the radio frequency operating voltage of the MR scanner based on the vertical distance measured by the distance measurement module 91 and the maximum allowable field strength obtained by the field strength limiting module 92.

[0134] In one optional embodiment, the scanning control module 93 is specifically used to: control the MR scanner to transmit radio frequency signals using a default radio frequency voltage during the pre-scanning stage of the MR scanner, determine the location of the local coil based on the vertical distance between the local coil and the vertex of the detection hole wall of the MR scanner measured by the distance measurement module 91, measure the field strength of the B1 field at the location of the local coil, calculate the proportionality coefficient between the radio frequency voltage and the field strength of the B1 field at the location of the local coil based on the default radio frequency voltage and the measured field strength; select a field strength not greater than the maximum allowable field strength obtained by the field strength limiting module 92 as the reference field strength of the B1 field at the location of the local coil, calculate the radio frequency operating voltage based on the reference field strength and the proportionality coefficient; and control the MR scanner to transmit radio frequency signals using the radio frequency operating voltage during the formal scanning stage of the MR scanner.

[0135] In one optional embodiment, the distance measurement module 91 is specifically used for:

[0136] When the patient lies on the MR scanner bed, and the local coil has been placed on the patient's scanned area but before the patient is pushed into the detection aperture, the 3D camera mounted above the bed is activated. The positions of the local coil and the bed are detected in the image captured by the camera. The vertical distance between the local coil and the bed is calculated based on their positions. Combined with the vertical distance between the bed and the vertex of the detection aperture wall, the vertical distance between the local coil and the vertex of the detection aperture wall is calculated. Alternatively...

[0137] Based on the three-dimensional spatial coordinates of the apex of the detection hole wall and the three-dimensional spatial coordinates of the local coil measured by the three-dimensional Hall sensor placed on the local coil, calculate the vertical distance between the local coil and the apex of the detection hole wall; or,

[0138] When the patient is pushed into the detection hole, the laser emitter located at the apex of the detection hole wall emits a laser signal, and the vertical distance between the local coil and the apex of the detection hole wall is calculated based on the reflected signal received by the laser reflector.

[0139] This invention also provides an MR scanner, including a B1 field confinement device 80 or 90 as described in any of the above-described MRI methods.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for confining a radio frequency alternating magnetic field in magnetic resonance imaging, characterized in that, The method includes: Measure the vertical distance between the local coil placed on the patient's scanned area and the center of the detection aperture of the magnetic resonance MR scanner; Based on the vertical distance between the local coil and the center of the detection aperture, the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture during MR scanning is determined. The conversion coefficient between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole is calculated based on the deviation. The maximum permissible field strength of the radio frequency alternating magnetic field at the center of the detection hole is calculated based on the field strength of the radio frequency alternating magnetic field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature and the conversion coefficient.

2. The method according to claim 1, characterized in that, The conversion coefficient between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture, calculated based on the deviation, includes: α＝10 S / 20 Wherein, α is the conversion coefficient, S is the deviation, and the unit of deviation is dB; The calculation of the maximum permissible field strength of the radio frequency alternating magnetic field at the center of the detection aperture, based on the field strength of the radio frequency alternating magnetic field required when the local coil surface temperature equals the upper limit of the safe temperature and the conversion coefficient, includes: B1_c=B1_rf*α Where B1_c is the field strength of the radio frequency alternating magnetic field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature, and B1_rf is the maximum allowable field strength of the radio frequency alternating magnetic field at the center of the detection hole.

3. The method according to claim 1, characterized in that, The step of determining the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture during MR scanning, based on the vertical distance between the local coil and the center of the detection aperture, includes: In the pre-established vertical distance-deviation correspondence table, find the deviation corresponding to the vertical distance between the local coil and the center of the detection hole, and use the found deviation as the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole during MR scanning. Among them, when the vertical distance between the local coil and the center of the detection hole is measured in advance with different values, the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole during MR scanning is measured. Based on the measurement results, a vertical distance-deviation correspondence table is established.

4. The method according to claim 1, characterized in that, After calculating the maximum permissible field strength of the radio frequency alternating magnetic field at the center of the detection aperture, the method further includes: During the pre-scanning stage of the MR scanner, the MR scanner is controlled to transmit radio frequency signals using the default radio frequency voltage, and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture is measured. Based on the default radio frequency voltage and the measured field strength, the proportionality coefficient between the radio frequency voltage and the field strength of the radio frequency alternating magnetic field at the center of the detection aperture is calculated. Select a field strength that is not greater than the maximum allowable field strength as the reference field strength of the radio frequency alternating magnetic field at the center of the detection hole, and calculate the radio frequency operating voltage based on the reference field strength and the proportional coefficient. During the actual scanning phase of the MR scanner, the MR scanner is controlled to use this radio frequency operating voltage to transmit radio frequency signals.

5. The method according to claim 1, characterized in that, The measurement of the vertical distance between the local coil placed on the patient's scanned area and the center of the detection aperture of the MR scanner includes: When the patient lies on the MR scanner bed, and the local coil has been placed on the patient's scanned area but before the patient is pushed into the detection aperture, the 3D camera mounted above the bed is activated. The positions of the local coil and the bed are detected in the image captured by the camera. The vertical distance between the local coil and the bed is calculated based on their positions. Combined with the vertical distance between the bed and the center of the detection aperture, the vertical distance between the local coil and the center of the detection aperture is calculated. Alternatively... Calculate the vertical distance between the local coil and the center of the detection hole based on the three-dimensional spatial coordinates of the detection hole center and the three-dimensional spatial coordinates of the local coil measured by the three-dimensional Hall sensor placed on the local coil; or, When the patient is pushed into the detection hole, the laser emitter located at the apex of the detection hole wall emits a laser signal. The vertical distance between the local coil and the apex of the detection hole wall is calculated based on the reflected signal received by the laser reflector. Combined with the radius of the detection hole, the vertical distance between the local coil and the center of the detection hole is calculated.

6. A method for confining a radio frequency alternating magnetic field in magnetic resonance scanning, characterized in that, The method includes: Measure the vertical distance between the local coil placed on the patient's scanned area and the apex of the detection aperture wall of the magnetic resonance MR scanner; To obtain the maximum permissible field strength of the radio frequency alternating magnetic field required when the local coil surface temperature equals the upper limit of the safe temperature; The radio frequency operating voltage of the MR scanner is determined based on the vertical distance and the maximum permissible field strength.

7. The method according to claim 6, characterized in that, The step of determining the radio frequency operating voltage of the MR scanner based on the vertical distance and the maximum permissible field strength includes: During the pre-scanning stage of the MR scanner, the MR scanner is controlled to transmit radio frequency signals using the default radio frequency voltage. The location of the local coil is determined based on the vertical distance between the local coil and the vertex of the detection hole wall of the MR scanner. The field strength of the radio frequency alternating magnetic field at the location of the local coil is measured. Based on the default radio frequency voltage and the measured field strength, the proportionality coefficient between the radio frequency voltage and the field strength of the radio frequency alternating magnetic field at the location of the local coil is calculated. Select a field strength that is no greater than the maximum allowable field strength as the reference field strength of the radio frequency alternating magnetic field at the location of the local coil, and calculate the radio frequency operating voltage based on the reference field strength and the proportional coefficient. During the actual scanning phase of the MR scanner, the MR scanner is controlled to use this radio frequency operating voltage to transmit radio frequency signals.

8. The method according to claim 6, characterized in that, The measurement of the vertical distance between the local coil placed on the patient's scanned area and the apex of the detection aperture wall of the MR scanner includes: When the patient lies on the MR scanner bed, and the local coil has been placed on the patient's scanned area but before the patient is pushed into the detection aperture, the 3D camera mounted above the bed is activated. The positions of the local coil and the bed are detected in the image captured by the camera. The vertical distance between the local coil and the bed is calculated based on their positions. Combined with the vertical distance between the bed and the vertex of the detection aperture wall, the vertical distance between the local coil and the vertex of the detection aperture wall is calculated. Alternatively... Based on the three-dimensional spatial coordinates of the apex of the detection hole wall and the three-dimensional spatial coordinates of the local coil measured by the three-dimensional Hall sensor placed on the local coil, calculate the vertical distance between the local coil and the apex of the detection hole wall; or, When the patient is pushed into the detection hole, the laser emitter located at the apex of the detection hole wall emits a laser signal, and the vertical distance between the local coil and the apex of the detection hole wall is calculated based on the reflected signal received by the laser reflector.

9. A radio frequency alternating magnetic field confinement device (80) for magnetic resonance imaging, characterized in that, The device (80) includes: The distance measurement module (81) is used to measure the vertical distance between the local coil placed on the patient's scanned area and the center of the detection aperture of the magnetic resonance MR scanner; The field strength deviation detection module (82) is used to determine the deviation between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole during MR scanning, based on the vertical distance between the local coil and the center of the detection hole. The field strength conversion coefficient calculation module (83) is used to calculate the conversion coefficient between the field strength of the radio frequency alternating magnetic field at the location of the local coil and the field strength of the radio frequency alternating magnetic field at the center of the detection hole based on the deviation. The field strength limiting module (84) is used to calculate the maximum allowable field strength of the radio frequency alternating magnetic field at the center of the detection hole based on the field strength of the radio frequency alternating magnetic field required when the surface temperature of the local coil is equal to the upper limit of the safe temperature and the conversion coefficient.

10. A radio frequency alternating magnetic field confinement device (90) for magnetic resonance scanning, characterized in that, The device (90) includes: The distance measurement module (91) is used to measure the vertical distance between the local coil placed on the patient's scanned area and the apex of the detection aperture wall of the magnetic resonance MR scanner; The field strength limiting module (92) is used to obtain the maximum permissible field strength of the radio frequency alternating magnetic field required when the local coil surface temperature is equal to the upper limit of the safe temperature. The scanning control module (93) is used to determine the radio frequency operating voltage of the MR scanner based on the vertical distance and the maximum allowable field strength.

11. A magnetic resonance scanner, characterized in that, Includes the radio frequency alternating magnetic field limiting device in magnetic resonance imaging as described in claim 9 or the radio frequency alternating magnetic field limiting device in magnetic resonance scanning as described in claim 10 (80, 90).

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