For the RF cable measure loop and method for safety monitoring of magnetic resonance systemThe application is to submit Patent Office of the People's Republic of China, Application No. 201310553510.7, invention name on November 08th, 2013The referred to as division of the Chinese patent application of " RF cable measure loop, magnetic resonance radio frequency safety monitoring system and its control method "Application.
Technical field
The present invention relates to a kind of magnetic resonance arts, more particularly to a kind of RF cable measure loop for magnetic resonance systemAnd method for safety monitoring.
Background technology
Medical science magnetic system to patient position to be checked under static magnetic field B0, gradient fields and radiofrequency field b1 collective effects by carrying out intoPicture, but under the irradiation of radiofrequency field b1, patient can produce SAR (the special absorptivities of Specific Absorption Rate),Current fast imaging and high-field magnetic resonance require that the radio-frequency power of transmitting is increasing, cause patient to bear more electromagnetism spokesPenetrate, in order to the requirement for following IEC60601 ensures the safety of patient, magnetic resonance system needs to arrange a SAR security monitorings systemSystem, the SAR absorbed with monitor in real time patient, SAR monitors need very high precision, it is ensured that the SAR of system-computedValue is accurate.
Fig. 1 be magnetic resonance radio frequency safety monitoring system circuit theory schematic diagram, shown in Figure 1, magnetic resonance system oneAs between subset, three rooms of scanning room and operation room, wherein operation room is the room of doctor's operating system, and scanning room is to suffering fromThe room that person is scanned, general scanning room the inside is placed with the portions such as magnet system, gradient system, radio-frequency transmissions/receiving coilPart, in order to monitor from transmitting coil 6 radio-frequency power size with patient is irradiated to, and power coupling can be placed with before transmitting coil 6Device 5, sub-fraction is coupled out the radio-frequency power of forward and backward, is transferred to system receiver 3 and is sampled, and calculates patientThe radio-frequency power size of absorption, the size of the power that system absorbs according to patient and the body weight of patient calculate SAR, monitor in real timeSAR is required less than standard, it is ensured that patient safety.High power components, such as radio frequency work(are typically placed with the equipment room of magnetic resonanceRate amplifier 2, receives the receiver of magnetic resonance signal and the control data processing system of correlation etc..Couple from power coupler 5Signal out is transferred to receiver 3 through very long RF cable 8, in order to coordinate the Ground arrangement of each hospital, it is desirable to the lineThe length of cable is variable, the place close for equipment room and sweep span, it is desirable to which the cable is shorter, and equipment room and scanning roomIt is distant when, the cable needs longer.But the RF cable 8 for the radiofrequency signal being coupled to through different length declinesThe value obtained after subtracting is different, and the signal after the decay is calculated through amplifying, and reduces the value of radio-frequency power, if cablePad value is not right, then have a great impact to result of calculation.Conventional way is fixed from power coupler 5 to receiver 3Length of cable is constant, no matter the size and distance in place, all the time using longer RF cable 8, do so can guarantee that power is examinedThe accuracy of survey, but sacrifices the flexibility of Ground arrangement, it is often necessary to long RF cable 8 is coiled fixation in place, and oneTo improve the cost of the cable, two inconvenient Ground arrangements, three is that cable is long may cause electromagnetic compatibility problem.
The content of the invention
The technical problem to be solved is to provide a kind of RF cable measure loop, magnetic resonance radio frequency security monitoringMethod, can simplify place wiring, and improve the accuracy of magnetic resonance radio frequency security monitoring.
The technical scheme that the present invention is adopted to solve above-mentioned technical problem is to provide a kind of penetrating for magnetic resonance systemFrequency cable measure loop, including receiver, signal source S for correction signal, switching switch and short-circuit direct-connected line, it is described to connectReceipts machine is connected with RF cable, and the RF cable is connected by switching switch with described short-circuit direct-connected line one end, the signalSource S is connected with the other end of short-circuit direct-connected line, and signal source S, RF cable and receiver form occlusion detection loop.
In above-mentioned RF cable measure loop, it is internal that signal source S is arranged at the receiver (3).
In above-mentioned RF cable measure loop, the receiver (3) includes multiple signals input, and signal source S is led toCross switching switch (S1) and wherein all the way signal input part is commonly connected to same RF cable (8).
The technical scheme that the present invention is adopted to solve above-mentioned technical problem is to provide a kind of above-mentioned magnetic resonance radio frequency safetyThe control method of monitoring system, comprises the steps：A) by control switching switch so that signal source S, RF cable and receptionThe signal input part of machine forms occlusion detection loop；B) the active loss Loss of every RF cable is calculated；C) cut by controlSwitch is changed, makes the signal input part of the receiver, the signal output part of power coupler be connected, and to coupled power before obtainingPF and reverse coupled power P R；D) active loss Loss, forward direction coupled power PF according to RF cable and reverse coupled powerPR, calculates in real time the radio-frequency power Power that patient absorbs.
The control method of above-mentioned magnetic resonance radio frequency safety monitoring system, wherein, the radio-frequency power Power is calculated such asUnder：
Power=0.001*10^ ((PF+Loss+X)/10) -0.001*10^ ((PR+Loss+X)/10)-CoilPowerloss；
Special absorptivity SAR of the patient is calculated as follows：SAR=Power/mass；
Wherein, X is the degree of coupling of power coupler, and CoilPowerloss is transmitting coil loss, and mass is patient's bodyWeight.
The control method of above-mentioned magnetic resonance radio frequency safety monitoring system, wherein, signal source S is arranged on receiverInterior, the receiver is provided with multiple signals input, per road signal input part by a RF cable and power couplerSignal output part is connected, and signal source S switchs S1 by switching and wherein all the way signal input part is commonly connected to one and penetratesOn frequency cable, the active loss Loss of every RF cable is calculated as follows：
Loss=(REF-PS-3*SwLoss)/2, wherein, when REF is correction signal, the receiver and switching switch S1The power level that connected signal input part is received, PS is the power level of signal source S, and SwLoss is the damage of switching switchConsumption.
The control method of above-mentioned magnetic resonance radio frequency safety monitoring system, wherein, signal source S is arranged on power couplingIt is connected with short-circuit direct-connected line in device and by short cable or PCB trace, the active loss Loss of every RF cable is calculated such asUnder：
Loss=(REF-PS-SwLoss), wherein, when REF is correction signal, the receiver is connected with switching switchThe power level that signal input part is received, PS is the power level of signal source S, and SwLoss is the loss of switching switch.
The control method of above-mentioned magnetic resonance radio frequency safety monitoring system, wherein, signal source S is low-frequency oscillation source,Gate circuit amplitude limiter circuit is provided with before the low-frequency oscillation source, active loss Loss of the every RF cable in security monitoring is schoolThe 1/K for obtaining being lost just is being measured, K is the pad value ratio measured under two different frequencies w0 and w_cal, wherein, w0 is useThe frequency of the radiofrequency signal calculated in SAR, w_cal is the frequency of signal source S for calibration.
The control method of above-mentioned magnetic resonance radio frequency safety monitoring system, wherein, signal source S is DC voltage constant currentSource, the active loss Loss of every RF cable is calculated as follows：Loss=Loss0* (U/ (I*R)), wherein, I is current strength,U is voltage drop of the DC voltage constant-current source after RF cable, and R is that unit of the RF cable under DC voltage constant-current source is damagedConsumption, Loss0 is specific loss of the RF cable under the frequency of the radiofrequency signal calculated for SAR.
Present invention contrast prior art has following beneficial effect：The RF cable measure loop of present invention offer, magnetic are commonShake radio frequency safety monitoring system and its control method, occlusion detection is formed by signal source S, switching switch and short-circuit direct-connected lineLoop, according to place actual conditions RF cable loss is measured in real time, and the RF cable loss calculation control using actual measurement is suffered fromRadio-frequency power and special absorptivity that person absorbs, so as to greatly simplify place wiring, and improve magnetic resonance radio frequency security monitoring calculationThe accuracy of method.
Description of the drawings
Fig. 1 is magnetic resonance radio frequency safety monitoring system circuit theory schematic diagram；
Fig. 2 is the magnetic resonance radio frequency safety monitoring system correcting signal source distribution connection diagram of the present invention；
Fig. 3 is another kind of distribution connection diagram in magnetic resonance radio frequency safety monitoring system correcting signal source of the present invention.
In figure：
The receiver of 1 host computer, 2 radio-frequency power amplifier 3
The transmitting coil of 4 power splitter, 5 power coupler 6
The short-circuit direct-connected line of 7 receiving coil array, 8 RF cable 9
Specific embodiment
With reference to the accompanying drawings and examples the invention will be further described.
Fig. 2 is the magnetic resonance radio frequency safety monitoring system correcting signal source distribution connection diagram of the present invention.
Fig. 1 and Fig. 2 is referred to, the RF cable measure loop that the present invention is provided including signal source S for correction, is cutChange switch and short-circuit direct-connected line 9, signal source S is connected with one end of short-circuit direct-connected line 9, the short-circuit direct-connected line 9 it is anotherOne end is connected to form occlusion detection loop by switching switch and RF cable 8.
The magnetic resonance radio frequency safety monitoring system that the present invention is provided includes receiver 3 and transmitting coil 6, the transmitting coilPower coupler 5 is provided with before 6, the receiver 3 is connected by RF cable 8 with power coupler 5, wherein, also including above-mentionedRF cable measure loop, when signal source S is connected by switching switch with short-circuit direct-connected line 9, signal source S, penetratesFrequency cable 8 and receiver 3 form occlusion detection loop.
The magnetic resonance radio frequency safety monitoring system that the present invention is provided, signal source S typically may be provided in receiver 3,The receiver 3 is provided with multiple signals input, per road signal input part by a RF cable 8 and power coupler 5Signal output part is connected, and signal source S switchs S1 by switching and wherein all the way signal input part is commonly connected to one and penetratesOn frequency cable 8.The short-circuit direct-connected line 9 may be provided in power coupler 5, and one end of the short-circuit direct-connected line 9 can be by cuttingChange switch S2 to be connected with RF cable 8, the other end then can be connected by switching switch S3 with RF cable 8.
Existing RF cable active loss value is as follows to the impact for calculating SAR：In magnetic resonance system, radiofrequency signal passes throughDistribute through power splitter 4 after radio-frequency power amplifier 2, respectively through feed-in transmitting coil 6 after power coupler 5, radio-frequency powerSAR is produced with patient by transmitting coil 6, the size of SAR is relevant with power P ower that patient absorbs, SAR=Power/Mass, wherein mass are the body weight of patient.Watt level is typically detected by power coupler 5 and receiver 3, for two passagesSystem, general power coupler is coupled out 4 road signals, respectively the first forward path, the first backward channel, the second forward pathWith the second backward channel.As shown in Fig. 2 F_1, F_2, R_1, R_2 are respectively the first forward path, and the second forward path, firstBackward channel, the power that the second backward channel is coupled to, it is assumed that the degree of coupling of power coupler is X (dB), RF cable declinesLoss (dB) is kept to, the first forward path voltage that receiver is detected is U_F_1 (V), and the first backward channel voltage is U_R_1(V), the second forward path voltage U_F_2 (V), the second backward channel voltage U_R_2 (V), then in the forward power of receiver endFor PF=10log ((U_F_1^2/Z0)+(U_F_2^2/Z0)/0.001) (dBm), backward power is PR=10log ((U_R_1^2/Z0)+(U_R_2^2/Z0)/0.001) (dBm), wherein Z0 is the characteristic impedance of system.According to forward power PF and reverse work(Rate PR, it is considered to which the decay Loss (dB) of RF cable and degree of coupling X (dB) of power coupler can calculate power couplerThe forward power at end is PF+Loss+X and backward power PR+Loss+X, further according to the loss CoilPowerloss of transmitting coilPower P ower=0.001*10^ ((PF+Loss+X)/10)-the 0.001*10^ ((PR+Loss+ of patient's absorption can be calculatedX)/10)-CoilPowerloss and SAR=Power/mass.It can be seen that in this patient's absorbed power monitoring system, radio frequencyThe loss of cable influences whether the SAR value of final calculating.
The present invention measures the actual attenuation value of the RF cable for using, as shown in Fig. 2 the course of work of the present invention and controlMethod processed is as follows：S1 is connected to ADC1 ends when being normally carried out security monitoring, and S2 and S3 is connected respectively to F_1 and F_2, leads to during calibration(signal source calibrates the power of good transmitting before dispatching from the factory to signal source S being placed on inside receiver to cross switching switch S1Level, for as the reference of measurement actual attenuation, it is assumed that S=0dBm in the present embodiment), S2 and S3 is to short-circuit direct-connected line for switching9, the radio-frequency power of such signal source S transmitting returns to the signal input part ADC2 of receiver by two isometric RF cables 8,It is Loss by being calculated the pad value of every RF cable 8 if the power level that now ADC2 is received is REF (dBm)=(REF-PS-3*Sw)/2, PS is the power level of signal source S, and Sw is the loss of switching switch, by the calibration steps, canTo measure the active loss of the RF cable 8 for radio frequency monitoring, there is provided use to the calculating of SAR, it is ensured that security monitoringPrecision, the calibration steps can once complete and record in systems Loss after system installation, it is also possible to every time moreRecalibrate when changing RF cable, even if the length or loss value of circuit change, also can guarantee that and change penetrating after cableFrequency monitoring precision.By this calibration steps, according to different place configuring conditions, security monitoring software for calculation can call differentRF cable loss value, correctly calculates SAR, so as to ensure the safety of patient.
The magnetic resonance radio frequency safety monitoring system that the present invention is provided, signal source S for calibration can be placed on elsewhere,Can not such as be integrated in inside magnetic resonance emitter in receiver 3, calibration signal is switched to by switch by emitter, orPerson is integrated in inside other electronic units, as long as known its is transferred to the decay in power coupler path (such as the line of regular lengthCable), such as the RF cable in the length of cable and Fig. 2 of signal source S to power coupler uses identical length, or shifts to an earlier dateThe signal amplitude that signal source is transferred to power coupler end is calibrated before dispatching from the factory, you can calculate accurate according to above-mentioned computational methodsPerformance number, be not limited to the hardware connection figure of Fig. 2.
Fig. 3 is another kind of distribution connection diagram in magnetic resonance radio frequency safety monitoring system correcting signal source of the present invention.Fig. 3 is referred to, signal source S is arranged in power coupler 5 and by short cable or PCB trace and short-circuit direct-connected line 9It is connected, it is advantageous in that can be integrated in calibration signal source S and power coupler 5 in same circuit module, strengthens reliableProperty.Now, the pad value of the every RF cable for measuring is Loss=(REF-PS-Sw).
Calibration signal source S is not necessarily used and system identical rf frequency, in order to realize that conveniently, calibration signal can beLow frequency signal, in general low frequency signal easily realization, increases low-frequency oscillation source such as in the circuit of power coupler 5, passes throughGate circuit amplitude limit ensures calibration level, if using low frequency signal, the cable decay of low frequency signal and the cable of high-frequency signalThere is conversion relation in decay, if the frequency of the radiofrequency signal calculated for SAR is w0, the frequency of calibration signal source is w_cal, andWhat measurement obtained RF cable under w_cal frequencies decays to its k times under w0 frequencies, then can be according under calibration frequencyMeasurement decay be multiplied by the decay Loss that k obtains for calculating SAR value.K is RF cable in two different frequencies w0 and w_The ratio of the decay measured under cal.
Additionally, calibration signal source S can use DC voltage (constant-current source, it is assumed that electric current is I), by voltage drop U (V) andKnow that specific loss Loss0s of specific loss R (ohm/m) and RF cable of the RF cable in direct current under the frequency can also be countedCalculate radio frequency complete attenuation Loss of the RF cable for monitoring：
Loss=Loss0* (U/ (I*R)).
Although the present invention is disclosed as above with preferred embodiment, so it is not limited to the present invention, any this area skillArt personnel, without departing from the spirit and scope of the present invention, when a little modification and perfect, therefore the protection model of the present invention can be madeEnclose when by being defined that claims are defined.