WO2017175498A1 - Dispositif d'imagerie par résonance magnétique et procédé de prédiction de sar dans une imagerie en respiration retenue divisée - Google Patents

Dispositif d'imagerie par résonance magnétique et procédé de prédiction de sar dans une imagerie en respiration retenue divisée Download PDF

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WO2017175498A1
WO2017175498A1 PCT/JP2017/006365 JP2017006365W WO2017175498A1 WO 2017175498 A1 WO2017175498 A1 WO 2017175498A1 JP 2017006365 W JP2017006365 W JP 2017006365W WO 2017175498 A1 WO2017175498 A1 WO 2017175498A1
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imaging
sar
breath
prohibition period
magnetic resonance
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PCT/JP2017/006365
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English (en)
Japanese (ja)
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義隆 本間
隆史 常木
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株式会社日立製作所
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging

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  • the present invention measures nuclear magnetic resonance (hereinafter referred to as ⁇ NMR '') signals from hydrogen, phosphorus, etc. in a subject and images nuclear density distribution, relaxation time distribution, etc.
  • ⁇ NMR '' nuclear magnetic resonance
  • the present invention relates to an MRI apparatus that accurately predicts SAR even when performing divided breath-hold imaging.
  • MRI that measures the NMR signals generated by the nuclear spins that make up the tissue of the subject, especially the human body, and visualizes the shape and function of the head, abdomen, limbs, etc. in two or three dimensions
  • the device is known.
  • a gradient magnetic field is generated, a high frequency pulse (hereinafter referred to as an “RF pulse”) is irradiated to the subject, and an NMR signal obtained from the subject is measured by magnetic resonance. Get an image.
  • RF pulse high frequency pulse
  • the MRI system suppresses the temperature rise or SAR (Specific Absorption Ratio) derived from the RF pulse in the subject below the threshold defined by IEC (International Electrotechnical Commission) regulations. Management (SAR management).
  • SAR Specific Absorption Ratio
  • Patent Document 1 discloses that the SAR of a predetermined pulse sequence is calculated as a predicted value based on the amount of RF absorption obtained for each subject. .
  • divided breath-hold imaging that divides into multiple imaging with a short imaging time. May be performed. More specifically, one relatively long time of imaging is divided into 10 to 30 seconds of short-time imaging that can be held by the subject (breath-holding imaging section), and imaging is performed for each division. Pause (free breathing interval) and finally complete one image. The subject can prepare for the next breath-holding imaging by arranging the breathing in the free breathing section.
  • the predicted value of SAR is higher than in actual imaging, and there is a high possibility that the upper limit of the 10-second average and 6-minute average specified by regulations will be exceeded.
  • the degree of freedom in setting the imaging conditions is reduced, such as a restriction.
  • a waiting time is generated due to the limitation of the accumulated SAR, and the imaging time is prolonged.
  • the present invention has been made in view of the above circumstances, and accurately predicts SAR even in divided breath-hold imaging, and improves the degree of freedom in setting imaging conditions without extending imaging time or reducing image quality. With the goal.
  • the present invention provides the following means.
  • One aspect of the present invention receives an input of imaging conditions including divided breath-holding imaging including a breath-holding imaging section and a free-breathing section, receives an imaging start instruction and a stop instruction by an operator, and is based on the imaging conditions. Then, a predicted value of SAR is calculated, and imaging is controlled according to an imaging sequence based on the imaging conditions. Then, a predetermined time in the free breathing interval is set as an imaging prohibition period in which imaging restart is prohibited, reception of an imaging restart instruction in the imaging prohibition period is prohibited, and calculation of the predicted value of the SAR is prohibited in the imaging The period is not included in the calculation target period.
  • the present invention it is possible to accurately predict SAR even in divided breath-hold imaging, and to improve the degree of freedom in setting imaging conditions without extending imaging time and reducing image quality.
  • FIG. 1 is a block diagram showing a schematic configuration of an MRI apparatus according to a first embodiment of the present invention.
  • Flowchart of imaging processing in the MRI apparatus according to the first embodiment of the present invention Flowchart of SAR predicted value calculation processing in the MRI apparatus according to the first embodiment of the present invention
  • Reference diagram for explaining an imaging prohibition period in the MRI apparatus according to the first embodiment of the present invention Explanatory drawing which concerns on the example of a screen which displayed the imaging prohibition period with the respiration waveform on the display in the MRI apparatus which concerns on the 1st Embodiment of this invention.
  • Reference diagram for explaining conventional split breath holding imaging Flowchart relating to “scan execution processing” in the flowchart of FIG. Graph showing changes in SAR predicted values over time
  • Graph showing changes in SAR predicted values over time Graph showing changes in SAR predicted values over time
  • the MRI apparatus includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, a reception system 6, a signal processing system 7, a sequencer 4, and a central processing unit (CPU ) 8.
  • a static magnetic field generation system 2 includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, a reception system 6, a signal processing system 7, a sequencer 4, and a central processing unit (CPU ) 8.
  • CPU central processing unit
  • the gradient magnetic field generation system 3 includes a gradient magnetic field coil 9 that applies a gradient magnetic field in three axes of X, Y, and Z, which is a coordinate system (static coordinate system) of the MRI apparatus, and a gradient magnetic field that drives each gradient magnetic field coil 9 Power supply 10 is provided.
  • Gradient magnetic fields Gx, Gy, and Gz are applied in the three axial directions of X, Y, and Z by driving the gradient magnetic field power supply 10 of each coil in accordance with a command from a sequencer 4 to be described later.
  • a slice direction gradient magnetic field pulse is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 1, and the remaining planes orthogonal to the slice plane and orthogonal to each other
  • a phase encoding direction gradient magnetic field pulse (Gp) and a frequency encoding direction gradient magnetic field pulse (Gf) are applied in two directions, and position information in each direction is encoded into an echo signal.
  • the sequencer 4 performs control so that a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) and a gradient magnetic field pulse are repeatedly applied in a predetermined pulse sequence.
  • the sequencer 4 operates under the control of the CPU 8 described later, and transmits various commands necessary for collecting tomographic image data of the subject 1 to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6. Further, the sequencer 4 receives the biological information of the subject 1 detected by the biological signal detection unit 26 via an electrocardiogram electrode, a pulse wave sensor, a respiration sensor, etc., and transmits it to the CPU 8, whereby the CPU 8 Can grasp the ecological information of the elderly.
  • the high-frequency pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 at a timing according to a command from the sequencer 4, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 13 and then placed close to the subject 1.
  • the RF pulse is irradiated to the subject 1.
  • the receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 1, and receives a high-frequency coil (receiving coil) 14b on the receiving side, a signal An amplifier 15, a quadrature detector 16, and an A / D converter 17 are provided.
  • NMR signal nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject
  • the CPU 8 controls the entire MRI apparatus, and when the data from the receiving system 6 is input to the CPU 8, the CPU 8 executes processing such as signal processing and image reconstruction, and the result is a tomographic image of the subject 1 Is displayed on the display 20 and recorded on the magnetic disk 18 of the external storage device.
  • the CPU 8 includes an imaging control unit 30 and controls the sequencer 4 to control imaging according to an imaging sequence based on an imaging condition input by an input unit 23 described later.
  • the CPU 8 generates a respiratory waveform based on the biological information acquired via the sequencer 4 and displays it on the display 20.
  • the imaging control unit 30 sets a predetermined time in the free breathing section. Then, it is determined as an imaging prohibition period in which imaging restart is prohibited, and an input unit 23 (to be described later) is instructed to prohibit acceptance of an imaging restart instruction during the imaging prohibition period.
  • the imaging prohibition period can be stored in advance in the storage device 18 or the like, and can be determined for each imaging according to imaging conditions.
  • the CPU 8 includes a SAR prediction unit 31 and calculates a predicted SAR value based on the imaging conditions. In particular, when divided breath-holding imaging is included in the imaging conditions, the CPU 8 performs SAR prediction without including the imaging prohibition period in the calculation target period when calculating the predicted value of SAR.
  • the operator can interactively control various processes of the MRI apparatus through the operation unit 25 while looking at the display 20.
  • the high-frequency coil 14a and the gradient magnetic field coil 9 on the transmission side are within the static magnetic field space of the static magnetic field generation system 2 into which the subject 1 is inserted. Oppositely, if it is a horizontal magnetic field system, it is installed so as to surround the subject 1. The high-frequency coil 14b on the receiving side is installed so as to face or surround the subject 1.
  • the radionuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton) which is the main constituent of the subject as widely used in clinical practice.
  • proton hydrogen nucleus
  • the form or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.
  • a respiratory sensor is attached to the subject 1 so that the biological signal detection unit 26 can collect a respiratory waveform.
  • step S11 the subject is registered in the MRI apparatus.
  • the input unit 23 receives input of information related to the subject such as the name and age of the subject by the operator.
  • the input unit 23 transmits the input subject information to the CPU 8, and the CPU 8 stores the subject information in the storage device 18 or the like, thereby performing subject registration on the MRI apparatus.
  • step S12 the input unit 23 receives input of imaging conditions by the operator, and the CPU 8 receives imaging conditions from the input unit 23, and sets an imaging sequence based on the imaging conditions or a combination of a plurality of imaging sequences. Select a protocol.
  • step S14 in view of the predicted SAR value calculated in the previous step S13, the operator determines whether to change the imaging condition. If the imaging condition is changed, the process proceeds to step S15. The imaging condition is customized through the input unit 23, and the predicted SAR value is calculated again in step S13. After the calculation of the predicted SAR value, if the imaging condition is not changed in step S14, the process proceeds to step S16, and imaging, that is, scanning is executed according to the set imaging condition. Details of the scan execution process will be described later.
  • step S21 the SAR prediction unit 31 of the CPU 8 determines whether or not the divided breath holding imaging is included in the imaging sequence based on the set imaging condition, and determines that the divided breath holding imaging is not included. In the case, the process proceeds to step S22.
  • the SAR prediction unit 31 calculates a predicted value of a 10-second average SAR and a 6-minute average SAR for each imaging (scan) for a plurality of imaging included in the imaging condition, and the calculated predicted value is Check that the upper limit (hereinafter referred to as “specified value”) specified in the standard is not exceeded.
  • the CPU 8 displays the required waiting time (prediction). To display.
  • the waiting time is an interval between imaging and means a period during which the subject is not irradiated with RF pulses.
  • step S21 when the SAR prediction unit 31 of the CPU 8 determines that the divided breath holding imaging is included, the process proceeds to step S23, and the imaging control unit 30 performs the free breathing interval between the breath holding imaging intervals. Then, an imaging prohibition period of a predetermined fixed value (for example, 10 seconds) is determined, and a predicted SAR value is calculated. Estimate the predicted SAR values for all scans, and if there is a 10-second average or 6-minute average prediction that exceeds the specified value, display the required waiting time (prediction).
  • a predetermined fixed value for example, 10 seconds
  • the imaging condition input by the input unit 23 includes divided breath-hold imaging including two breath-hold imaging sections and one free breath section.
  • divided breath holding imaging divides one scan into two breath holding imaging sections, and between the first breath holding imaging (Scan 1) and the second breath holding imaging (Scan 2). It consists of one free breathing interval.
  • the free breathing interval is started.
  • a certain period of time from the start of the free breathing interval is set as an “imaging prohibition period” by the imaging control unit 30, and the imaging prohibition period can be set even if the operator inputs an imaging restart instruction to the input unit 23. Does not accept an imaging resumption instruction. For this reason, since imaging is not performed during the imaging prohibited period, the subject 1 is not irradiated with the RF pulse.
  • the imaging prohibition period ends, the operator looks at the state of the subject, gives a breath holding instruction to the subject, resumes imaging, and executes the second breath holding imaging (Scan 2).
  • the SAR prediction unit 31 may take into account the time obtained by subtracting the imaging prohibition period in the free breathing section and the time required for Scan1 and Scan2. Further, as shown in FIG. 5, the imaging prohibition period may be presented to the operator by displaying the imaging prohibition period together with the respiratory waveform on the display 20. The example of FIG. 5 shows a case where the imaging prohibition period is highlighted on the respiratory waveform.
  • the SAR prediction unit 31 when calculating the predicted value of SAR, the SAR prediction unit 31 must consider the time required for Scan1, Scan2 and the free breathing section shown in FIG. In other words, in the example of Fig. 6, even if the RF pulse is not irradiated in the free breathing interval, it is treated as the time that must be taken into account when calculating the SAR, so the calculated predicted value is compared with the actual SAR. And it becomes a big value.
  • the time for calculating the predicted value of the SAR is different, and the obtained predicted value is also different.
  • step S16 in FIG. 2 will be described with reference to the flowchart in FIG. In the flowchart of FIG. 7, description will be made assuming that divided breath holding imaging is included in the imaging condition.
  • step S14 in FIG. 2 confirms that the subject's information registration, imaging condition input, SAR predicted value calculation and predicted value are appropriate, the imaging preparation is completed. Then, imaging (scanning) is started. When the imaging is started, the CPU 8 measures the SAR in parallel with the imaging.
  • step S31 for every imaging included in the imaging conditions, it is determined for each imaging (scan) whether or not the imaging is a divided breath holding imaging, and if not, the process proceeds to step S32. If it is divided breath holding imaging, the process proceeds to step S34.
  • the CPU 8 controls the sequencer 4 to perform imaging based on the predicted SAR value and taking into account the measured SAR value (step S32). Step S33). When the imaging is completed, the process proceeds to step S37.
  • the imaging control unit 30 sets an imaging prohibition period in the free breathing interval based on the predicted value of the SAR, and prohibits reception of an imaging resumption instruction to the input unit 23 (step S34). .
  • a screen that allows the breath-holding imaging section, the free breathing section, and the imaging-prohibited period to be visually recognized may be displayed on the display 20 together with the respiratory waveform.
  • the CPU 8 After the elapse of the imaging prohibition period, the CPU 8 permits input reception to the input unit 23, and the operator gives a breath holding instruction to the subject.
  • the instruction to hold the breath can be transmitted to the subject through the intercom by the operator, or can be transmitted by automatic voice using the instruction to resume imaging as a trigger.
  • the operator refers to the respiratory waveform monitor displayed on the display 20 (see FIG. 5), and after confirming the subject's breath hold, inputs an instruction to resume imaging to the input unit 23.
  • the CPU 8 controls the sequencer 4 to perform breath-hold imaging (step S35).
  • step S36 it is determined whether or not the divided breath holding imaging has been completed. If not, the process returns to step S34 and the above-described processing is repeated. On the other hand, if it is determined in step S36 that the divided breath-holding imaging has been completed, the process proceeds to step S37, where it is determined whether or not all the imaging included in the imaging conditions have been completed.
  • step S37 If it is determined in step S37 that all the imaging included in the imaging conditions have not been completed, the process returns to step S31 to determine whether or not the next imaging is a divided breath holding imaging, and the above Repeat the process. When all the imaging included in the imaging conditions is completed, the scan execution process is terminated.
  • the CPU 8 actually measures the SAR, and for example, as shown in FIG. 8, the SAR (6-minute average) that changes with the progress of imaging is graphed and displayed on the display 20, so that the SAR has a specified value. You may show to an operator so that it may not exceed.
  • the SAR increases during the breath-holding imaging section Thold, and decreases during the free breathing section Trest. In the breath holding divided scan execution, an imaging prohibition period is included in the free breathing section Trest.
  • the MRI apparatus can be set in advance so that the imaging is automatically stopped.
  • an “imaging prohibition period” is set in the free breathing interval between breath-hold imaging, and an imaging resumption instruction is input during this imaging prohibition period. Is not accepted, so no image is taken.
  • the subject since the subject is not irradiated with an RF pulse during the imaging prohibition period, when calculating the predicted value of the SAR, the time required for breath-hold imaging and the time obtained by subtracting the imaging prohibition period from the free breathing interval should be considered. Good.
  • the time to be taken into account can be kept to the minimum necessary, so that it is possible to accurately predict the SAR by avoiding overestimation of the SAR, thereby extending the imaging time and It is possible to improve the degree of freedom in setting the imaging conditions without degrading the image quality.
  • the determination of the imaging prohibition period in the present embodiment is performed in the SAR predicted value calculation process.
  • the following describes the SAR predicted value calculation processing in the present embodiment with reference to the flowchart of FIG.
  • step S41 the SAR prediction unit 31 of the CPU 8 determines whether or not the divided breath holding imaging is included in the imaging sequence based on the set imaging condition, and the divided breath holding imaging is performed. If it is determined that it is not included, the process proceeds to step S42.
  • step S42 the SAR prediction unit 31 calculates a predicted value of a 10-second average SAR and a 6-minute average SAR for each imaging (scan) for all imaging included in the imaging conditions, and the calculated predicted value is Check that the upper limit (hereinafter referred to as “specified value”) specified in the standard is not exceeded.
  • the CPU 8 After estimating the predicted SAR values for all imaging by the SAR prediction unit 31, the CPU 8 waits when there is a 10-second average or 6-minute average predicted value that exceeds the specified value. (Prediction) is displayed on the display 20.
  • the waiting time is an interval between imaging and means a period during which the subject is not irradiated with RF pulses.
  • step S41 when the SAR prediction unit 31 of the CPU 8 determines that the divided breath-holding imaging is included, the process proceeds to step S43, and the SAR prediction unit 31 calculates a predicted value of the SAR.
  • the predicted value here is calculated based on the predicted value of the SAR in the imaging before the divided breath-hold imaging and the predicted value of the SAR in the divided breath-hold imaging among all the imaging included in the imaging conditions.
  • the required waiting time is displayed on the display 20.
  • the imaging control unit 30 sets the imaging prohibition time to an arbitrary time of 0 or more in accordance with an instruction to the input unit 23 by the operator (Step S46).
  • the imaging prohibition period between breath-holding imaging is not necessarily a fixed time.
  • the second imaging prohibition period and the second imaging prohibition period can be set to different times.
  • the time to be considered in calculating the SAR can be kept to the minimum necessary.
  • the time for one breath-holding imaging can be set to a predetermined constant value or can be determined according to the subject.
  • the time for breath-hold imaging according to the subject for example, depending on the subject, enter the upper limit time for one breath-hold imaging, and calculate the number of images that can be captured during this upper-limit time. Based on these, the predicted value of SAR is calculated.
  • the CPU 8 can graph the predicted value of SAR (6-minute average) on the display 20 and display it on the display 20.
  • the operator can refer to the graph and use the input unit 23 to hold the breath-hold imaging time or free breathing period.
  • the imaging prohibition period can be adjusted.
  • the free-breath section Trest802 was initially set, but you want to adjust the free-breath section based on the margin with the SAR regulation value or the expected breathing state of the subject
  • the scan start time is changed from 807 to 808 with the input unit 23 such as a mouse cursor.
  • the SAR prediction unit 31 recalculates the predicted SAR value so that Trest802 becomes Trest'803 and Thold804 becomes Thold'05, and the graph is updated. Even during the execution of imaging, Thold and Trest may be changed on this graph to be linked with the imaging being executed.
  • breath-holding imaging is scheduled to be executed twice in the breath-holding imaging section Thold 901, but a breath-hold failure is detected in the second breath-holding imaging.
  • the detection of the failure to hold the breath is performed as follows. That is, for example, the CPU 8 monitors the differentiation of the respiratory waveform, and detects that the breath holding has ended, that is, the breath holding has failed when a change of a certain amount or more is detected.
  • the image captured until the breath holding failure detection 905 in FIG. 11 is adopted, and the imaging schedule is changed so that an image that could not be captured is captured at the next breath holding imaging. .
  • Trest 902 in FIG. 11 is changed to Trest'904 and the Thold901 is changed to Thold'903 by the input unit 23, the SAR prediction value is recalculated by the SAR prediction unit 31, and the graph is automatically corrected.
  • 2 static magnetic field generation system 3 gradient magnetic field generation system, 4 sequencer, 5 transmission system, 6 reception system, 7 signal processing system, 8 central processing unit (CPU), 9 gradient magnetic field coil, 10 gradient magnetic field power supply, 11 high frequency oscillator, 12 modulator, 13 high frequency amplifier, 14a, 14b high frequency coil, 15 signal amplifier, 16 quadrature phase detector, 17 A / D converter, 18 storage device, 19 external storage device, 20 display, 23 input unit, 25 operation unit , 30 Imaging control unit, 31 SAR prediction unit

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Abstract

L'invention vise à prédire avec précision un SAR même dans une imagerie en respiration retenue divisée et à améliorer le degré de liberté dans le réglage d'une condition d'imagerie sans augmenter le temps d'imagerie ou réduire la qualité d'image. Ce dispositif d'IRM comporte : une unité d'entrée pour recevoir une entrée d'une condition d'imagerie comprenant une imagerie en respiration retenue divisée comprenant un intervalle d'imagerie en respiration retenue et un intervalle de respiration libre, et recevoir une instruction pour reprendre l'imagerie par un opérateur ; une unité de prédiction de SAR pour calculer une valeur prédite de SAR sur la base de la condition d'imagerie ; et une unité de commande d'imagerie pour commander l'imagerie selon une séquence d'imagerie sur la base de la condition d'imagerie ; l'unité de commande d'imagerie établissant un temps prédéterminé dans l'intervalle de respiration libre en tant que période d'imagerie interdite pour laquelle la reprise de l'imagerie est interdite, l'unité d'entrée interdisant la réception d'une instruction de reprise d'imagerie dans la période d'imagerie interdite, et l'unité de prédiction de SAR calculant la valeur prédite du SAR dans une période objet de calcul qui ne comprend pas la période d'imagerie interdite.
PCT/JP2017/006365 2016-04-04 2017-02-21 Dispositif d'imagerie par résonance magnétique et procédé de prédiction de sar dans une imagerie en respiration retenue divisée WO2017175498A1 (fr)

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WO2014080781A1 (fr) * 2012-11-20 2014-05-30 株式会社 日立メディコ Dispositif d'imagerie par résonance magnétique et procédé de prédiction de taux d'absorption spécifique (sar)
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