Patent ID: 12216188

The reference signs in the accompanying drawings are as follows:

Reference signMeaning201-203StepsS1-S5Change curves of a surface temperature of a local coil atdifferent intensities of a B1 field that are obtained whenMR scanning is performed at the different intensities ofthe B1 fieldS1′-S5′Respective fitted curves of S1-S541Change curve of a surface temperature of a local coil thatis obtained when a total MR scanning duration is 35minutes and the surface temperature of the local coilreaches a maximum safety temperature of 41° C. at theend of scanning42Change curve of a surface temperature of a local coil thatis obtained when a total MR scanning duration isunlimited and a thermal equilibrium temperature of thesurface temperature of the local coil is 41° C.90Apparatus for limiting a B1 field in MRI91B1 field first-intensity obtaining module92B1 field second-intensity obtaining module

DETAILED DESCRIPTION OF THE DISCLOSURE

In order to clarify the object, technical solution, and advantages of the present disclosure, the present disclosure is explained in further detail below by way of embodiments.

To ensure patient safety to the greatest extent, it is usually expected to obtain a maximum intensity of a B1 field that allows a surface temperature of a local coil to not exceed a maximum safety temperature (41° C.) when a total MR scanning duration is unlimited.

FIG.1is a schematic diagram of example change curves of a surface temperature of a local coil as a function of a scanning duration at different intensities of a B1 field, in accordance with an embodiment of the present disclosure. It can be seen that when the total MR scanning duration is unlimited, the surface temperature of the local coil gradually increases as the scanning duration increases, but finally reaches a thermal equilibrium state (that is, the temperature remains substantially unchanged). In addition, it is known through experiments that, in the case of the same initial temperature of the surface temperature of the local coil, the greater the intensity of the B1 field, the higher the thermal equilibrium temperature that the surface temperature of the local coil finally reaches.

In addition, experiments show that it usually takes about 100 minutes for the surface temperature of the local coil to reach a thermal equilibrium state of 41° C. when the total MR scanning duration is unlimited. However, in practical applications, the total MR scanning duration is generally about 20 minutes. Therefore, within such total MR scanning duration, it is only necessary to ensure that the surface temperature of the local coil does not exceed the maximum safety temperature at the end of scanning. Therefore, in this case, the intensity of the B1 field may be increased.

FIG.2is a flowchart of an example method for limiting a B1 field in MRI according to an embodiment of the present disclosure, where the method includes the following steps.

In step201, a first intensity of the B1 field that is required for a thermal equilibrium temperature of a surface temperature of a local coil to be a maximum safety temperature when the local coil is placed at a set position in an inspection bore of an MR scanner is obtained.

During operation of the MR scanner, it can be found through analysis of intensity distribution of the B1 field in the inspection bore of the MR scanner that, the intensity of the B1 field is non-uniform along a vertical direction passing through the bore center of the inspection bore (that is, a direction passing through the bore center and perpendicular to the horizontal plane). Specifically, the intensity of the B1 field is the lowest at the bore center, the farther away from the bore center, the higher the intensity of the B1 field, and the intensity of the B1 field at the vertex of the bore wall (that is, the highest point of the bore wall of the inspection bore) is the highest. Therefore, the set position in step201may be the highest point of the inner bore wall of the inspection bore of the MR scanner.

In an optional embodiment, before step201, the method further includes: when the local coil is placed at the set position and the intensity of the B1 field is one μT, obtaining a temperature difference between the thermal equilibrium temperature of the surface temperature of the local coil and an initial temperature of the surface temperature of the local coil, and setting the temperature difference as a first temperature difference.

Step201includes: when the local coil is placed at the set position in the inspection bore of the MR scanner and the thermal equilibrium temperature of the surface temperature of the local coil is the maximum safety temperature, obtaining a temperature difference between the maximum safety temperature and the initial temperature of the surface temperature of the local coil, and setting the temperature difference as a second temperature difference; and dividing the second temperature difference by the first temperature difference, and using an obtained quotient as a squared value of the first intensity of the B1 field.

In practical applications, the local coil is placed at the set position of the MR scanner, scanning is performed at different intensities of the B1 field to obtain change curves of the surface temperature of the local coil at the different intensities of the B1 field, and these change curves are fitted so as to obtain a relationship between the surface temperature of the local coil and a scanning duration and an intensity of the B1 field during an MR scanning process, which is as follows:

T⁡(t)=T⁢0+B⁢12*Δ⁢T*(1-e-tτ)(1)where t represents a current scanned duration, i.e. a duration between a current moment and a starting moment of MR scanning, T(t) represents a current temperature of the surface temperature of the local coil, T0 represents an initial temperature of the surface temperature of the local coil, B1 represents the intensity of the B1 field, ΔT represents a temperature difference between the thermal equilibrium temperature of the surface temperature of the local coil and the initial temperature of the surface temperature of the local coil when the local coil is placed at the set position in the inspection bore of the MR scanner and the intensity of the B1 field is one μT, and τ represents a scanning duration required for the surface temperature of the local coil to reach 0.632ΔT when the local coil is placed at the set position in the inspection bore of the MR scanner and the intensity of the B1 field is one μT.

Herein, assuming that an increasing degree of the surface temperature of the local coil has a linear relationship with a squared value of the intensity of the B1 field that is applied to the local coil, and a thermal resistance of the local coil remains unchanged during a heating process, a temperature increasing range obtained when the surface temperature of the local coil reaches a thermal equilibrium depends only on the power applied on the local coil or the squared value of the intensity of the B1 field. In addition, it is assumed that different powers applied to the local coil or the squared value of the intensity of the B1 field does not change a time constant, but depends only on a cooling condition.

FIG.3is a schematic diagram of example change curves S1-S5of a surface temperature of a local coil at different intensities of a B1 field that are obtained when MR scanning is performed at the different intensities of the B1 field and respective fitted curves S1′-S5′ of the change curves. InFIG.3, the horizontal coordinate represents a scanning duration, in hours (h), and the vertical coordinate represents the surface temperature of the local coil, in ° C. Since an actual total scanning duration for MR scanning is always limited in practical applications, only a limited total scanning duration needs to be considered for curve fitting. Therefore, inFIG.3, only curves within one hour are fitted, and those beyond one hour are not considered.

When the total MR scanning duration is unlimited, the local coil is placed at the set position in the inspection bore of the MR scanner, and the thermal equilibrium temperature of the surface temperature of the local coil is the maximum safety temperature Tsafety(for example, 41° C.), the following is obtained according to formula (1):

T⁡(∞)=T⁢0+(B⁢1infinite)2*Δ⁢T*(1-e-t⁡(∞)τ)=Ts⁢a⁢f⁢e⁢t⁢y(2)where B1infiniterepresents the corresponding intensity of the B1 field for the thermal equilibrium temperature of the surface temperature of the local coil to be the maximum safety temperature Tsafetywhen the local coil is placed at the set position in the inspection bore of the MR scanner, i.e. the first intensity of the B1 field in step201.

The following is obtained according to formula (2):

(B⁢1infinite)2=Ts⁢a⁢f⁢e⁢t⁢y-T⁢0Δ⁢T(3)

In step202, a second intensity of the B1 field that is required for the surface temperature of the local coil to increase by heating to the maximum safety temperature within a set total MR scanning duration when the local coil is placed at the set position is obtained based on the first intensity of the B1 field and a relationship between the surface temperature of the local coil and a scanning duration and an intensity of the B1 field during an MR scanning process.

When the set total MR scanning duration is tscan, to ensure patient safety, the condition that the surface temperature of the local coil does not exceed the maximum safety temperature Tsafetyat the end of the scanning needs to be met, and the following is obtained according to formula (1):

T⁡(ts⁢c⁢a⁢n)=T⁢0+(B⁢1s⁢h⁢o⁢r⁢t)2*Δ⁢T*(1-e-ts⁢c⁢a⁢nτ)=Tsafety(4)

Where tscanrepresents the set total MR scanning duration, that is, a maximum scanning duration for which the scanning can be performed by using B1shortas the intensity of the B1 field, and B1shortrepresents the corresponding intensity of the B1 field for the surface temperature of the local coil to reach the maximum safety temperature Tsafetyat the end of the scanning when the total MR scanning duration is tscanand the local coil is placed at the set position, i.e. the second intensity of the B1 field in step202.

The following is obtained according to formula (4):

(B⁢1s⁢h⁢o⁢r⁢t)2=Tsafety-T⁢0Δ⁢T*(1-e-ts⁢c⁢a⁢nτ)(5)

The following is obtained according to formula (3) and formula (5):

(B⁢1short)2(B⁢1infinite)2=11-e-ts⁢c⁢a⁢nτ(6)

Then:

(B⁢1s⁢h⁢o⁢r⁢t)2=(B⁢1infinite)2*11-e-ts⁢c⁢a⁢nτ(7)

In step203, a third intensity of the B1 field that is required when MR scanning is performed for the set total MR scanning duration is determined based on the second intensity of the B1 field, where the third intensity of the B1 field is not greater than the second intensity of the B1 field.

In the above embodiment, the first intensity of the B1 field that is required for the thermal equilibrium temperature of the surface temperature of the local coil to be the maximum safety temperature when the local coil is placed at the set position in the inspection bore of the MR scanner is first obtained, the second intensity of the B1 field that is required for the surface temperature of the local coil to increase by heating to the maximum safety temperature within the set total MR scanning duration when the local coil is placed at the set position is then obtained based on the first intensity of the B1 field and the relationship between the surface temperature of the local coil and the scanning duration and the intensity of the B1 field during the MR scanning process, and the third intensity of the B1 field that is required when MR scanning is performed for the set total MR scanning duration is determined based on the second intensity of the B1 field, where the third intensity of the B1 field is not greater than the second intensity of the B1 field. Therefore, the MR imaging quality is improved and waste of performance of the B1 field is reduced while ensuring patient safety under the condition that the total MR scanning duration is limited.

FIG.4shows example change curves41and42of a surface temperature of a local coil in the case of τ=1454 seconds, where the first curve is obtained when a set total MR scanning duration is 35 minutes, and the surface temperature of the local coil reaches the maximum safety temperature of 41° C. at the end of the scanning, where it can be seen that when the scanning is performed for 2121 seconds (about 35 minutes), the surface temperature of the local coil reaches the maximum safety temperature of 41° C.; and the second curve is obtained when the total MR scanning duration is unlimited and the thermal equilibrium temperature of the surface temperature of the local coil is 41° C., where it can be seen that when the scanning is performed for 11300 seconds (about 188 minutes), the surface temperature of the local coil reaches the thermal equilibrium temperature of 41° C. In the figure, the horizontal coordinate represents the scanning duration, in seconds, and the vertical coordinate represents the surface temperature of the local coil, in ° C. The intensity of the B1 field that corresponds to the first curve41is greater than the intensity of the B1 field that corresponds to the second curve42. Therefore, obviously, the quality of an MR image corresponding to the first curve41is higher.

FIG.5is a schematic diagram of a ratio r of (B1short)2to (B1infinite)2that enables the surface temperature of the local coil to not exceed 41° C. within different limited total MR scanning durations when τ=1454 seconds. In the figure, the horizontal coordinate represents a scanning duration, in minutes, and the vertical coordinate represents the ratio r of (B1short)2to (B1infinite)2.

Table 1 shows specific values of the ratio of (B1short)2to (B1infinite)2that enables the surface temperature of the local coil to not exceed 41° C. within different limited total MR scanning durations when τ=1454 seconds.

TABLE 1Total MR scanningRatio of (B1short)2toτ (seconds)duration (minutes)(B1infinite)21454124.73677203212.6235434738.58809151246.57208224955.36384842764.55950057673.9859428883.55662714493.223470785102.957624028112.740727723122.560542253132.40859387142.278829744152.166810992162.069208321171.983475684181.907632709191.840115842201.779674147211.725294869221.67614931231.631552815241.59093477251.553815789

As shown inFIG.5and Table 1, when the total MR scanning duration is five minutes, and if the surface temperature of the local coil is required to reach 41° C. at the end of the five-minute scanning, (B1short)2=5.363848427*(B1infinite)2used in this case is calculated.

When the total MR scanning duration is ten minutes, and if the surface temperature of the local coil is required to reach 41° C. at the end of the ten-minute scanning, (B1short)2=2.957624028*(B1infinite)2used in this case is calculated.

In practical applications, one or more scanning protocols may be used in an MR scanning process.(1) When only one scanning protocol is used within the set total MR scanning duration, the third intensity of the B1 field is used as an intensity of the B1 field that corresponds to the scanning protocol.(2) When a plurality of scanning protocols are used within the set total MR scanning duration and a scanning duration for each scanning protocol is the same, the third intensity of the B1 field is used as a sum of intensities of the B1 field that correspond to all the scanning protocols, where an intensity of the B1 field that corresponds to the nthscanning protocol is:

(B⁢1p⁢r⁢o⁢t⁢o⁢c⁢o⁢l⁢n)2=(12)n*(B⁢1short′)2where B1protocolnrepresents the intensity of the B1 field that corresponds to the nthscanning protocol, and B1short′ represents the third intensity of the B1 field, where 1≤n≤N, and N represents a total number of scanning protocols used within the set total MR scanning duration.

FIG.6is an example schematic diagram of intensities of the B1 field that respectively correspond to five scanning protocols used within the set total MR scanning duration, where a scanning duration for each scanning protocol is the same (that is, tprotocol1=tprotocol2=tprotocol3=tprotocol4=tprotocol5). In the Figure, the horizontal coordinate represents a scanning duration, and the vertical coordinate represents an intensity of the B1 field, where the intensity B1protocol1of the B1 field that corresponds to a scanning protocol 1 is:

(B⁢1protocol⁢1)2=(12)*(B⁢1short′)2the intensity B1protocol2of the B1 field that corresponds to a scanning protocol2is:

(B⁢1p⁢r⁢o⁢t⁢o⁢c⁢o⁢l⁢2)2=(12)2*(B⁢1short′)2

The rest may be deduced by analogy.(3) When a plurality of scanning protocols are used within the set total MR scanning duration and a scanning duration for each scanning protocol is not completely the same, the third intensity of the B1 field is used as a sum of intensities of the B1 field that correspond to all the scanning protocols, where an intensity of the B1 field that corresponds to the nthscanning protocol is:

(B⁢1protocoln)2=(12)n*(B⁢1short′)2*tsingle⁢_⁢protocoltprotocolnwhere B1protocolnrepresents the intensity of the B1 field that corresponds to the nthscanning protocol, B1short′ represents the third intensity of the B1 field, tsingle_protocolrepresents a set standard scanning duration for a single scanning protocol, and tprotocolnrepresents an actual scanning duration for the nthscanning protocol, where 1≤n≤N, and N represents a total number of scanning protocols used within the set total MR scanning duration.

FIG.7is an example schematic diagram showing a comparison between an intensity (B1protocoln)2of the B1 field that corresponds to the nthscanning protocol and an intensity (B1protocolq)2of the B1 field that corresponds to the qthscanning protocol in a plurality of scanning protocols used within the set total MR scanning duration, where a scanning duration for each scanning protocol is not completely the same, the scanning duration tprotocolnfor the nthscanning protocol is not equal to tsingle_protocol, and the scanning duration tprotocolqfor the qthscanning protocol is equal to tsingle_protocol.(4) When a plurality of different types of scanning sequences are used within the set total MR scanning duration, an intensity of the B1 field that is used for each scanning sequence is obtained through the following steps A and B:A. performing initialization m=1, and calculating:

(B⁢1_limitm)2=min⁢{(12)m*(B⁢1single⁢_⁢protocol)2,(B⁢1SAR⁢_⁢limit)2}where:

(B⁢1single⁢_⁢protocol)2=(B⁢1infinite)2*11-e-tsingle⁢_⁢protocolτtallowed⁢_⁢duration⁢_⁢m=(B⁢1single⁢_⁢protocol)2(B⁢1_limitm)2*tsingle⁢_⁢protocoland calculating a maximum value that satisfies:

∑pm=1pm=Pmtseq-⁢pm≤tallowed-⁢duration-⁢mwhere the maximum value Pmis the number of scanning sequences for which B1_limitmis used as the intensity of the B1 field;where:B1_limitmrepresents the mthintensity of the B1 field that is used during a current MR scanning process, B1single_protocolrepresents an intensity of the B1 field that is for a single scanning protocol, B1SAR_limitrepresents a preset SAR-based limit value of the intensity of the B1 field, B1infiniterepresents the first intensity of the B1 field, tsingle_protocolrepresents a set standard scanning duration for a single scanning protocol, τ represents a scanning duration required for the surface temperature of the local coil to reach 0.632*(the thermal equilibrium temperature—an initial temperature of the surface temperature of the local coil) when the local coil is placed at the set position in the inspection bore of the MR scanner and the intensity of the B1 field is one μT, tallowed_duration_mrepresents an upper limit of a scanning duration for the mthintensity of the B1 field, pmrepresents a sequence number of the pthscanning sequence in all scanning sequences for which B1_limitmis used as the intensity of the B1 field during the current MR scanning process, Pmrepresents the number of scanning sequences for which B1_limitmis used as the intensity of the B1 field during the current MR scanning process, and tseq_pmrepresents a scanning duration for the pthscanning sequence in all scanning sequences for which B1_limitmis used as the intensity of the B1 field during the current MR scanning process;B. letting m=m+1, and returning to step A until:
ΣPm≥Pwhere P represents a total number of scanning sequences used during the current MR scanning process.

FIG.8is an example schematic diagram of intensities of a B1 field that respectively correspond to a plurality of scanning sequences used within a set total MR scanning duration. As shown inFIG.8, B1_limit1is used as the intensity of the B1 field for the first to fourth scanning sequences, and B1_limit2is used as the intensity of the B1 field for the fifth to seventh scanning sequences, where a sum of scanning durations for the first to fourth scanning sequences is tseq_1+tseq_2+tseq_3+tseq_4≤tallowed_duratton_1, and a sum of scanning durations for the fifth to seventh scanning sequences is tseq_5+tseq_6+tseq_7≤tallowed_duration_2.

FIG.9is an example schematic structural diagram of an apparatus90for limiting a B1 field in MRI according to an embodiment of the present disclosure. The apparatus90mainly includes a B1 field first-intensity obtaining module91and a B1 field second-intensity obtaining module92. Although not shown inFIG.9for purposes of brevity, the apparatus90may additionally comprise any suitable number and/or type of processor, processing circuitry, etc., configured to execute computer-readable instructions stored in the modules91,92. By way of the execution of the computer-readable instructions stored in the respective modules91,92, any of the embodiments as discussed herein may be implemented.

The B1 field first-intensity obtaining module91is configured to obtain a first intensity of the B1 field that is required for a thermal equilibrium temperature of a surface temperature of a local coil to be a maximum safety temperature when the local coil is placed at a set position in an inspection bore of an MR scanner.

The B1 field second-intensity obtaining module92is configured to obtain, based on the first intensity of the B1 field and a relationship between the surface temperature of the local coil and a scanning duration and an intensity of the B1 field during an MR scanning process, a second intensity of the B1 field that is required for the local coil to be heated to the maximum safety temperature within a set total MR scanning duration when the local coil is placed at the set position; and determine, based on the second intensity of the B1 field, a third intensity of the B1 field that is required when MR scanning is performed for the set total MR scanning duration, where the third intensity of the B1 field is not greater than the second intensity of the B1 field.

In an optional embodiment, the set position in each of the B1 field first-intensity obtaining module91and the B1 field second-intensity obtaining module92is the highest point of an inner bore wall of the inspection bore of the MR scanner.

In an optional embodiment, before the obtaining, by the B1 field first-intensity obtaining module91, of a first intensity of the B1 field that is required for a thermal equilibrium temperature of a surface temperature of a local coil to be a maximum safety temperature when the local coil is placed at a set position in an inspection bore of an MR scanner, the following step is further included: when the local coil is placed at the set position and the intensity of the B1 field is one μT, obtaining a temperature difference between the thermal equilibrium temperature of the surface temperature of the local coil and an initial temperature of the surface temperature of the local coil, and setting the temperature difference as a first temperature difference.

The obtaining, by the B1 field first-intensity obtaining module91, of a first intensity of the B1 field that is required for a thermal equilibrium temperature of a surface temperature of a local coil to be a maximum safety temperature when the local coil is placed at a set position in an inspection bore of an MR scanner includes: when the local coil is placed at the set position in the inspection bore of the MR scanner and the thermal equilibrium temperature of the surface temperature of the local coil is the maximum safety temperature, obtaining a temperature difference between the maximum safety temperature and the initial temperature of the surface temperature of the local coil, and setting the temperature difference as a second temperature difference; and dividing the second temperature difference by the first temperature difference, and using an obtained quotient as a squared value of the first intensity of the B1 field.

In an optional embodiment, the relationship, on which the B1 field second-intensity obtaining module92is based, between the surface temperature of the local coil and a scanning duration and an intensity of the B1 field during an MR scanning process is:

T⁡(t)=T⁢0+B⁢12*Δ⁢T*(1-e-tτ)where t represents a current scanned duration, T(t) represents a current temperature of the surface temperature of the local coil, T0 represents an initial temperature of the surface temperature of the local coil, B1 represents the intensity of the B1 field, ΔT represents a temperature difference between the thermal equilibrium temperature of the surface temperature of the local coil and the initial temperature of the surface temperature of the local coil when the local coil is placed at the set position in the inspection bore of the MR scanner and the intensity of the B1 field is one μT, and τ represents a scanning duration required for the surface temperature of the local coil to reach 0.632ΔT when the local coil is placed at the set position in the inspection bore of the MR scanner and the intensity of the B1 field is one μT.

In an optional embodiment, the obtaining, by the B1 field second-intensity obtaining module92, of a second intensity of the B1 field that is required for the surface temperature of the local coil to increase by heating to the maximum safety temperature within a set total MR scanning duration when the local coil is placed at the set position includes:

(B⁢1short)2=(B⁢1infinite)2*11-e-tscanτwhere B1shortrepresents the second intensity of the B1 field, B1infiniterepresents the first intensity of the B1 field, and tscanrepresents the set total MR scanning duration.

In an optional embodiment, the determining, by the B1 field second-intensity obtaining module92based on the second intensity of the B1 field, of a third intensity of the B1 field that is required when MR scanning is performed for the set total MR scanning duration includes: when only one scanning protocol is used within the set total MR scanning duration, using the third intensity of the B1 field as an intensity of the B1 field that corresponds to the scanning protocol.

In an optional embodiment, the determining, by the B1 field second-intensity obtaining module92based on the second intensity of the B1 field, of a third intensity of the B1 field that is required when MR scanning is performed for the set total MR scanning duration includes: when a plurality of scanning protocols are used within the set total MR scanning duration and a scanning duration for each scanning protocol is the same, using the third intensity of the B1 field as a sum of intensities of the B1 field that correspond to all the scanning protocols, where an intensity of the B1 field that corresponds to the nthscanning protocol is:

(B⁢1protocoln)2=(12)n*(B⁢1short′)2,where B1protocolnrepresents the intensity of the B1 field that corresponds to the nthscanning protocol, and B1short′ represents the third intensity of the B1 field, where 1≤n≤N, and N represents a total number of scanning protocols used within the set total MR scanning duration.

In an optional embodiment, the determining, by the B1 field second-intensity obtaining module92based on the second intensity of the B1 field, of a third intensity of the B1 field that is required when MR scanning is performed for the set total MR scanning duration includes: when a plurality of scanning protocols are used within the set total MR scanning duration and a scanning duration for each scanning protocol is not completely the same, using the third intensity of the B1 field as a sum of intensities of the B1 field that correspond to all the scanning protocols, where an intensity of the B1 field that corresponds to the nthscanning protocol is:

(B⁢1protocoln)2=(12)n*(B⁢1short′)2*tsingle⁢_⁢protocoltprotocolnwhere B1protocolnrepresents the intensity of the B1 field that corresponds to the nthscanning protocol, B1short′ represents the third intensity of the B1 field, tsingle_protocolrepresents a set standard scanning duration for a single scanning protocol, and tprotocolnrepresents an actual scanning duration for the nthscanning protocol, where 1≤n≤N, and N represents a total number of scanning protocols used within the set total MR scanning duration.

In an optional embodiment, the determining, by the B1 field second-intensity obtaining module92based on the second intensity of the B1 field, of a third intensity of the B1 field that is required when MR scanning is performed for the set total MR scanning duration includes: when a plurality of different types of scanning sequences are used within the set total MR scanning duration, obtaining an intensity of the B1 field that is used for each scanning sequence through the following steps A and B:A. performing initialization m=1, and calculating:

(B⁢1_limitm)2=min⁢{(12)m*(B⁢1single⁢_⁢protocol)2,(B⁢1SAR⁢_⁢limit)2}where:

(B⁢1single⁢_⁢protocol)2=(B⁢1infinite)2*11-e-tsingle⁢_⁢protocolτtallowed⁢_⁢duration⁢_⁢m=(B⁢1single⁢_⁢protocol)2(B⁢1_limitm)2*tsingle⁢_⁢protocoland calculating a maximum value that satisfies:

∑pm=1pm=Pmtseq-⁢pm≤tallowed-⁢duration-⁢mwhere the maximum value Pmis the number of scanning sequences for which B1_limitmis used as the intensity of the B1 field;where:B1_limitmrepresents the mthintensity of the B1 field that is used during a current MR scanning process, B1single_protocolrepresents an intensity of the B1 field that is for a single scanning protocol, B1SAR_limitrepresents a preset SAR-based limit value of the intensity of the B1 field, B1infiniterepresents the first intensity of the B1 field, tsingle_protocolrepresents a set standard scanning duration for a single scanning protocol, τ represents a scanning duration required for the surface temperature of the local coil to reach 0.632*(the thermal equilibrium temperature—an initial temperature of the surface temperature of the local coil) when the local coil is placed at the set position in the inspection bore of the MR scanner and the intensity of the B1 field is one μT, tallowed_duration_mrepresents an upper limit of a scanning duration for the mthintensity of the B1 field, pmrepresents a sequence number of the pthscanning sequence in all scanning sequences for which B1_limitmis used as the intensity of the B1 field during the current MR scanning process, Pmrepresents the number of scanning sequences for which B1_limitmis used as the intensity of the B1 field during the current MR scanning process, and tseq_pmrepresents a scanning duration for the pthscanning sequence in all scanning sequences for which B1_limitmis used as the intensity of the B1 field during the current MR scanning process;B. letting m=m+1, and returning to step A until:
ΣPm≥Pwhere P represents a total number of scanning sequences used during the current MR scanning process.

An embodiment of the present disclosure further provides an MR scanner, including the apparatus90for limiting a B1 field in MRI.

The embodiments above are merely preferred embodiments of the present disclosure, which are not intended to limit it. Any amendments, equivalent substitutions or improvements etc. made within the spirit and principles of the present disclosure shall be included in the scope of protection thereof.

The various components described herein may be referred to as “modules.” Such components may be implemented via any suitable combination of hardware and/or software components as applicable and/or known to achieve their intended respective functionality. This may include mechanical and/or electrical components, processors, processing circuitry, or other suitable hardware components, in addition to or instead of those discussed herein. Such components may be configured to operate independently, or configured to store and/or execute instructions or computer programs that are stored on a suitable computer-readable medium. Alternatively, the modules may themselves be part of a computer-readable medium and store respective computer-executable instructions thereon.