CN106667487B - A kind of method and magnetic resonance imaging system monitoring active implantation material surrounding tissue temperature - Google Patents
A kind of method and magnetic resonance imaging system monitoring active implantation material surrounding tissue temperature Download PDFInfo
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Abstract
The present invention relates to a kind of method for monitoring active implantation material surrounding tissue temperature, this method is based on magnetic resonance temperature measurement technology and uses a magnetic resonance imaging system；The magnetic resonance imaging system is used at least generate a kind of sequence 2 for clinical examination or scientific research or other mesh purposes and a kind of for measuring the sequence 3 of Temperature Distribution；This approach includes the following steps：Step S11 is scanned using sequence 2, and interts the scanning for carrying out thermometric sequence 3 in sequence 2；And step S12, security evaluation is carried out according to the scanning result of thermometric sequence 3.The patient that this method can have implantable medical devices with effective monitoring carries out radio frequency temperature rise when MRI scan, excludes security risk.
Description
Technical field
The present invention relates to medical instrument correlative technology fields, in particular, being related to a kind of based on magnetic resonance ((Magnetic
Resonance, MR) thermometry real-time monitoring MR under active implantation material surrounding tissue temperature method and using this method
Magnetic resonance imaging system.
Background technique
Mr imaging technique (Magnetic Resonance Imaging, MRI) and other imaging techniques (such as X-ray,
CT etc.) it compares, have and compares significant advantage：Magnetic resonance imaging is relatively sharp, has very high resolving power to soft tissue, and right
Human body is without ionization radiation injury.So mr imaging technique is widely used among the clinical diagnosis of modern medicine.According to
Estimation, nowadays annual at least 60,000,000 cases in the whole world are checked using nmr imaging technique.
MRI can play a role when working there are three magnetic field.One high-intensitive homogeneous static magnetic field B0, a gradient fields G with
And magnetic field radio frequency (RF) for exciting NMR signal.Specific imaging process is summarized as follows：Firstly, in magnetostatic field B0Work
Under, along magnetostatic field direction precession occurs for the intracorporal hydrogen nuclei of people, according to Larmor theorem, proton precession frequency be ω=
γ B, wherein ω is precession frequency, and γ is gyromagnetic ratio, and B is magnetic field strength；That is the frequency of precession is directly proportional to magnetic field strength.In order to
The signal in specific level is excited, applies gradient fields G on magnetostatic field directionz, so that having not on the spatial position of different layers
Same magnetic field strength；Apply the frequency of radiofrequency field RF, the RF signal of the certain bandwidth of certain frequency simultaneously and bandwidth and selects sheaf space
Interior Larmor frequency is corresponding, therefore only selects the proton in the tissue on layer direction in certain layer that can just be excited, and generates
Signal.Signal starts constantly decaying after being excited, by the combination of RF magnetic field and gradient magnetic, can make the nuclear-magnetism letter of excitation
Number there is local peaking, referred to as echo；Signal acquisition is usually carried out around time what echo occurred.In the layer being excited,
In order to distinguish the signal of different location, spatial position coding is carried out to signal using phase code and frequency encoding gradient field.?
Before signal is read, gradient magnetic (magnetic field gradient is usually along y-axis) is encoded along magnetostatic field direction superposition phase, after certain time
It closes, different location signal has different phases on phase-encoding direction at this time.And then frequency coding is carried out, is similarly existed
Apply gradient magnetic (frequency encoding gradient direction is usually along x-axis) on frequency coding direction, so that on frequency coding direction, it is different
The signal of position has different frequencies.By above-mentioned spatial encoding process, the phase and frequency of signal just contains signal
Spatial positional information, and the intensity of signal reflects the anatomical structure or physiological status of tissue in this position.It is compiled in frequency
While code, commencing signal acquisition：Magnetic resonance signal is read in N number of equidistant time step, there are k-spaces by obtained data
A line.Then it repeats the above process, it is only necessary to different gradient fields G is chosen in the phase code stageyIntensity, by the number of reading
According to another row as k-space, there are corresponding positions, until k-space is filled.In this way, being always obtained one has N × N number of
The character matrix of data point therefrom can construct piece image by two-dimensional Fourier transform in image space.
If patient's body is equipped with implantable medical devices (Implantable Medical Device, IMD), example
Such as：If pacemaker, defibrillator, vagus nerve stimulator, spinal stimulator, lesions located in deep brain device etc., when MRI works
Required three used magnetic field may bring very big security risk to patient.One hidden danger of most important one is implanted
Induction fever of the medical instrument in radiofrequency field has elongated conductive structures especially for those, typical such as brain deep electricity
Stimulator extension lead and electrode cable, cardiac lead.The patient equipped with these implantable medical devices exists in vivo
When carrying out MRI scan, elongated conductive structures tip with organize the position that contacts it is possible that serious temperature rise, in this way
Temperature rise patient may be caused serious injury.However, the patient of most of implantation IMD needs within the instrument life period
MRI inspection is carried out, and RF magnetic field induction bring security risk causes this some patients to be rejected to check.
The heated reason of the induction of elongated conductive structures is between elongated conductive structures and RF magnetic field under RF magnetic field
Coupling.Being coupled in elongated conductive structures between elongated conductive structures and RF magnetic field generates induced current, induced current master
It to be transported in tissue by the part that conductive structure tip is contacted with tissue, form induced electric field integrated distribution.Human body
Tissue resistance rate is higher, can generate more Joule heat.
Tissue fever caused by radio frequency induced electric field can be portrayed with bioheat formula, and heat transfer formula is：
Wherein T is tissue temperature, and Q is the energy of radio frequency induction deposition, and S is the heat that metabolism generates, and ρ is density, C
For specific heat capacity, ω is the filling rate of blood, and subscript b indicates the property of blood, such as TbFor local blood temperature.RF magnetic field is inducted
Electric field cause tissue to heat, and with bioheat rule variation.
Since the place of radio frequency temperature rise most serious usually occurs at implantable medical devices slender conductor structure tip, simultaneously
Also the factors such as electromagnetic interference are influenced under by Biocompatibility, size sensor, MRI, traditional temperature sensor such as heat
Galvanic couple, thermal resistance etc. are difficult to integrate.Allow to integrate, because to apply at MRI, it is real-time with the external world that there is also measurement data
Interactive problem.Therefore after these implantable medical devices are implanted into the patient at present, the radio frequency induction temperature rise of MRI scan is carried out
It there is no effective monitoring means.
And the data that MRI itself is scanned are possible to that a kind of real-time, noninvasive monitoring temperature approach can be provided.A variety of MR ginsengs
Number shows temperature sensitivity, and the temperature change of tissue can be obtained using these temperature sensitive parameters.For example, proton resonance
Frequency can change with the variation of temperature, can also be changed using the phase diagram that gtadient echo (GRE) sequence obtains, phase
Variation meets following relationship with temperature change：
Wherein, Δ φ is the phase difference of two amplitude phase diagram of front and back, the temperature difference at Δ T is front and back Image Acquisition moment twice, α
It is the relevant hydrone chemical bond transfer ratio of temperature, B0It is static magnetic field strength, γ is gyromagnetic ratio, and TE is the echo time.
MR thermometric has been successfully applied to RF ablation damage, focused ultrasound therapy tumour etc. at present.At these
In, heating source both is from external treatment equipment.MR thermometry is only used as a monitoring method.And it is directed to implantable medical device
Radio frequency generated heat of the tool under nuclear-magnetism, heating comes from MRI scan itself, and scanning sequence respectively has purposes, and parameter is different, with MR
The scan difference of thermometry is very big, can not obtain temperature information from the scanning sequence of other purposes.
In addition, the metallic conductor in implantable medical devices can also cause because of magnetizing under the magnetic field of MRI around magnetic
Field distortion, so as to cause image artifacts, so that the MRI signal near conductor loses or serious distortion.And radio frequency induction fever exists
Conductor is nearby most serious, this is also the problems in current MR thermometry application.
Therefore, the present invention proposes the method and device thereof of a kind of MR thermometric sequence and the interspersed progress of general service scanning, with
Patient of the monitoring with implantable medical devices carries out radio frequency temperature rise when MRI scan.Further, it proposes to use MRI image
Valid data other than upper instrument artifact, utilize the method and device thereof of its surface temperature of HEAT TRANSFER LAW reverse.
Summary of the invention
Based on this, the invention proposes metal implant surrounding tissue temperature under a kind of real-time monitoring MR based on MR thermometric
And provide the method and magnetic resonance imaging system of security evaluation.
A method of active implantation material surrounding tissue temperature being monitored, this method is based on magnetic resonance temperature measurement technology and uses one
Magnetic resonance imaging system；The magnetic resonance imaging system is a kind of for clinical examination or scientific research or other mesh at least generating
The sequence 2 of purposes and a kind of for measuring the sequence 3 of Temperature Distribution；This approach includes the following steps：Step S11, using sequence 2
It is scanned, and interts the scanning for carrying out thermometric sequence 3 in sequence 2；And step S12, according to the scanning knot of thermometric sequence 3
Fruit carries out security evaluation.
According to the method for the active implantation material surrounding tissue temperature of above-mentioned monitoring, wherein it is described to be scanned using sequence 2,
And the method for interting the scanning for carrying out thermometric sequence 3 in sequence 2 includes：Sequence 2 is divided into i part, and every part point
N is not contained1, n2..., niA TR unit, wherein TR is the interval time in sequence 2 between two excitation pulses；In the head of sequence 2
Intert the scanning for carrying out sequence 3, and 2 each section of sequence and previous between the latter sequence 3 between tail and each section
Time interval be respectively Δ t1a、Δt1b、Δt2a、Δt2b、…、Δtia、Δtib。
According to the method for the active implantation material surrounding tissue temperature of above-mentioned monitoring, wherein the time interval Δ t1a、Δt1b、
Δt2a、Δt2b、…、Δtia、ΔtibIt is zero.
According to the method for the active implantation material surrounding tissue temperature of above-mentioned monitoring, wherein the step S11 further includes：In sequence
Before column 2 scan, first selects layer to carry out a thermometric scanning thermometric using thermometric sequence 3, obtain initial temperature or temperature is related
Information.
According to the method for the active implantation material surrounding tissue temperature of above-mentioned monitoring, wherein the step S12 includes following step
Suddenly：Step S121, determines assessment area；Step S122 determines the Distribution of temperature rise of assessment area；Step S123, calculating refer to safely
Mark；And step S124, which is compared with secure threshold.
According to the method for the active implantation material surrounding tissue temperature of above-mentioned monitoring, wherein the step S121 includes：Utilize side
Edge detection algorithm determines artifact edge, using outside edge as assessment area.
According to the method for the active implantation material surrounding tissue temperature of above-mentioned monitoring, wherein in the step S122, determine assessment
Region Distribution of temperature rise includes：Sequence 3 is scanned through every time, and the data processing unit of the magnetic resonance imaging system receives one group of number
According to since scanning the 2nd sequence 3, the result that each sequence 3 scans all carries out difference with result before and obtains Distribution of temperature rise.
According to the method for the active implantation material surrounding tissue temperature of above-mentioned monitoring, wherein the step S124 includes：It will calculate
Heat history amount CEM43With the threshold value threshold_CEM being previously set43Compare, or by the maximum temperaturerise Δ T of calculatingmaxWith thing
The maximum temperaturerise threshold value threshold_ Δ T first setmaxBoth compare, or compare simultaneously；Any one is more than threshold value, institute
The data processing unit for stating magnetic resonance imaging system issues danger early warning to MR control unit in time, is automatically stopped MR scanning device
Scanning.
According to the method for the active implantation material surrounding tissue temperature of above-mentioned monitoring, wherein the magnetic resonance imaging system also wraps
Include it is a kind of for position or other and scan purposes sequence 1；It further comprise step S10 before step S11, using sequence 1
Positioning scanning is carried out, determines that thermometric selects layer and imaging to select layer.
A kind of magnetic resonance imaging system comprising：One MR scanning device, the MR scanning device is at least generating a kind of use
In the sequence 2 of clinical examination or scientific research or other mesh purposes and a kind of for measuring the sequence 3 of Temperature Distribution；One MR control
Unit, the MR control unit are scanned for controlling the MR scanning device using sequence 2 and sequence 3；An and data processing
Unit, the data processing unit are used to handle the scanning result of the thermometric sequence 3, wherein the magnetic resonance imaging system has prison
The function of active implantation material surrounding tissue temperature is surveyed, and the magnetic resonance imaging system monitors active implantation material surrounding tissue temperature
Method is any one in the above method.
Compared to the prior art, magnetic resonance imaging system provided by the invention monitors active implantation material surrounding tissue temperature
The patient that method can have implantable medical devices with effective monitoring carries out radio frequency temperature rise when MRI scan, excludes security risk.
Detailed description of the invention
Fig. 1 is the structural schematic diagram of lesions located in deep brain device used in the embodiment of the present invention.
Fig. 2 is the module diagram of magnetic resonance imaging system provided in an embodiment of the present invention.
Fig. 3 is the structural schematic diagram that means for correcting is floated in field used in the embodiment of the present invention.
Fig. 4 alternates in sequence 2 for the embodiment of the present invention and carries out the schematic diagram of the scanning mode of thermometric sequence 3.
Fig. 5 is that the embodiment of the present invention continuously interts the schematic diagram for carrying out the scanning mode of thermometric sequence 3 in sequence 2.
Fig. 6, which is that interlayer used in the embodiment of the present invention is interspersed, to carry out thermometric sequence scanning and in the ranks interts to carry out thermometric sequence
The schematic diagram of scanning.
Fig. 7 is the interspersed method flow diagram for carrying out thermometric sequence scanning of interlayer used in the embodiment of the present invention.
Fig. 8 is the method flow diagram used in the embodiment of the present invention in the ranks interting and carrying out thermometric sequence scanning.
Fig. 9 is the method flow diagram for the artifact region that the embodiment of the present invention determines the active implantation material.
Figure 10 is when the embodiment of the present invention corrects temperature change caused by field is floated in drift on the scene correction container correspondence image
If the schematic diagram done is chosen in heart district domain.
Main element symbol description
Lesions located in deep brain device 10
External program control instrument 11
Impulse generator 12
Extension lead 14
Stimulating electrode 16
Electrode contacts 18
Magnetic resonance imaging system 20
MR scanning device 22
MR control unit 24
Data processing unit 26
Field drift means for correcting 30
Head 32
Container 34
Cord 36
Artifact region 40
Artifact edge 42
Tissue signal 44
Central area 46
Following specific embodiment will further illustrate the present invention in conjunction with above-mentioned attached drawing.
Specific embodiment
The present invention provides active implantation material surrounding tissue temperature under a kind of real-time monitoring MR based on MR thermometric and provide
The method of security evaluation and and using this method magnetic resonance imaging system.Wherein the active implantation material can be cardiac pacing
Device, defibrillator, lesions located in deep brain device, spinal stimulator, vagus nerve stimulator, stomach stimulator or other similar plant
Enter formula medical instrument.The present invention is only illustrated by taking lesions located in deep brain device as an example, and in conjunction with attached drawing, the present invention is further described.
Referring to Figure 1, the lesions located in deep brain device 10 includes：One outside program control instrument 11 and the pulse to implant hair
Raw device 12, extension lead 14 and stimulating electrode 16 form.The external program control instrument 11 controls the impulse generator 12 for generating
The current impulse of certain pattern is passed at the electrode contacts 18 of stimulating electrode 16 by the extension lead 14, is touched by the electrode
18 stimulation particular core group of point can achieve the purpose for the treatment of disease.But it is implanted with the patient of the lesions located in deep brain device 10
When carrying out MR scanning, elongated extension lead 14 electromagnetic wave absorption energy as the meeting image antenna of stimulating electrode 16, in electricity
It generates heat at pole contact 18, there are security risks.In order to guarantee safety when these patient scans MR, offer of the present invention can use
Method and system to the temperature implementing monitoring and security evaluation around the electrode contacts 18 of these patients.
Fig. 2 is referred to, magnetic resonance imaging system 20 provided by the invention includes：One MR scanning device 22, MR control are single
Member 24 and a data processing unit 26.
The MR scanning device 22 mainly includes the coil for generating magnetostatic field, generates the coil of gradient fields, generates radiofrequency field
Coil, suitable for the radio-frequency transmissions receiving coil of different parts, MR is scanning bed and matched automation electrical equipment.
The MR control unit 24 includes MR equipment control software and image reconstruction process software.MR equipment control software
Sweep parameter can be set, scanning sequence is set.Particularly, MR equipment control software be integrated with one kind can real-time monitoring subject
The magnetic resonance imaging scheme of person's particular anatomical region temperature change.Scheme includes at least a kind of for clinical examination or scientific research
Or the sequence 2, a kind of for measuring the sequence 3 of Temperature Distribution of other mesh purposes.Intert when both sequence scannings and carries out.
In general, the program further include it is a kind of for position or other and scan the sequence 1 of purposes, the sequence 1 scans
Purpose be determining area-of-interest, especially determine implantation material region.Whenever subject is in MR scanning device 22
Relative position changes or the centre of location of MR scanning device 22 changes or other may cause area-of-interest position
The case where changing appearance is set, requires to rescan sequence 1, to relocate area-of-interest.In general, the sequence
1 should be each first scanning sequence for carrying out the progress of magnetic resonance examination when, if do not had after first time sequence 1 scans
Appearance may cause the case where area-of-interest position changes, then without repeating sequence in scanning process later
1 scanning.The present invention does not limit the parameter and type of sequence 1.
The purposes of the sequence 2 is subject to be checked or diagnosed or is carried out scientific research, and scanning result, which has, to be faced
Bed meaning or scientific value.The parameter and type of the sequence 2 are generally arranged by medical worker or equipment operator, this
Invention comparison is without limitation.It is appreciated that due to the RF magnetic field of magnetic resonance system and the interaction of implantable medical devices,
In the scanning process of sequence 2, temperature is likely to occur in the particular anatomical region of subject and is risen, when temperature is increased beyond centainly
The heat that threshold value or temperature add up is more than margin of safety, may cause subject's local tissue damage, threatens the life of subject
It orders healthy and safe.It is therefore desirable to the temperature of real-time monitoring subject's particular anatomical region in 2 magnetic resonance scan sequences of sequence
Variation.Sweeping scheme provided by the invention is to intert the scanning for carrying out thermometric sequence 3 among sequence 2.
The sequence 3 is temperature sensitive sequence, when the temperature in subject's particular anatomical region changes, sequence 3
Scanning result will appear corresponding variation.Different according to used temperature sensitive physical parameter, the type of sequence 3 has more
Kind.Such as：In using temp measuring method of the Proton Resonance Frequency as temperature sensitive parameter, the type of thermometric sequence is usually ladder
Spend echo sequence (GRE sequence) or echo planar imaging sequence (EPI sequence).Thermometric sequence is also based on proton density (Proton
Density), i.e., according to ANALOGY OF BOLTZMANN DISTRIBUTION, proton density is inversely proportional in absolute temperature, therefore using proton density weighting
MRI image calculates testee temperature.Thermometric sequence is also based on the T1 relaxation time of hydrone, i.e., in biological tissue
SPIN-LATTICE RELAXATION is as caused by the dipolar interaction between large biological molecule and hydrone, which depends on temperature,
When range of temperature is smaller, T1 relaxation time and temperature T are almost linear, therefore can be surveyed by detecting T1
Temperature.Thermometric sequence is also based on diffusion coefficient (Diffusion Coefficient), i.e., under the strong magnetic field circumstance of MRI, water
Molecule spreads the signal dephasing that can cause Diffusion direction in the tissue, and then nuclear magnetic signal is caused to be decayed, attenuation degree with
Diffusion coefficient is directly proportional, and is affected by temperature, therefore available MRI imaging obtains the diffusion coefficient under condition of different temperatures, in turn
Acquire temperature change.The present invention does not limit the parameter and type of sequence 3.Every run-down thermometric sequence 3, at available one
Between put the Temperature Distribution of upper specific region.It is appreciated that for " real-time " of thermometric, the time interval of the scanning of sequence 3
Should not be too long, and the duration of sequence 3 itself can not be too long.Preferably, the time interval that sequence 3 scans should control
Within 6 minutes, the duration was controlled within 2 minutes.It is further preferred that the time interval that sequence 3 scans should be controlled 3
Within minute, the duration was controlled within 30 seconds.Sequence 3 should not also generate biggish energy deposition.Preferably, sequence 3
Local SAR value should be less than 0.4W/kg.It is further preferred that the local SAR value of sequence 3 should be less than 0.1W/kg.In this way can
Additional energy deposition is not generated, and additional security risk is not caused to patient.In practical application, the scanning of sequence 3 several times
It should be able to verily reflect the temperature change time course of specific region.Thermometric sequence is carried out it is appreciated that interting among sequence 2
The scanning of column 3, and the result of sequence 3 is handled in real time, it can be achieved that in magnetic resonance scan sequences real-time monitoring subject
The temperature change of particular anatomical region.
The present invention is described below by related parameters：
t1：The duration that sequence 1 scans.
t2：Duration when sequence 2 uninterruptedly scans, that is, assuming that sequence 2 scans centre uninterruptedly, since scanning
To the time of the end of scan.
t3：The duration that each sequence 3 scans.
Δt：The thermometric interval time of sequence 3, that is, scanned being scanned since a sequence 3 to sequence 3 next time
Time.The selection of thermometric interval of delta t relies on specific sweep situation, can if the sweep situation temperature being related to increases slowly
To be changed using longer Δ t monitoring temperature；But if the sweep situation temperature rise the being related to time gradient of temperature in other words rapidly
Greatly, then need shorter thermometric time interval Δ t, on the one hand can improve the resolution ratio of thermometric time in this way, on the other hand can and
When feedback temperature information guarantee subject safety.In general, the patient for carrying lesions located in deep brain device 10 sweeps under 3T environment
When retouching, Δ t chooses the value within the scope of 10 seconds~6 minutes, because temperature rise quickly, is tied at electrode contacts 18 in order to improve measurement at this time
The accuracy of fruit generally just measures once in short period of time, such as 10 seconds.
Tslice：Time needed for sequence 2 scans 1 layer.
TR：Repetition time in sequence 2, i.e. interval time in sequence 2 between two excitation pulses.
The data processing unit 26 is equipped with the temperature computation software based on MR image information, and the MR control unit 24 is real-time
Acquisition is rebuild obtained thermometric image and passes to the data processing unit 26 in real time by ground.The data processing unit 26 is according to thermometric figure
As the Temperature Distribution of area-of-interest is calculated, and provide at this time for evaluating the safety index of safety, the safety index
Can be a certain temperature rise value or heat history dose value, commonly use 43 degrees Celsius accumulation equivalent the number of minutes characterization (CEM43,
43 DEG C of Cumulative Equivalent Minutes@), the safety index can be at this time the maximum value of area-of-interest, this
When calculate implantation material (such as electrode) surface maximum value, reckoning a certain moment after area-of-interest maximum value, calculate
Implantation material (such as electrode) surface maximum value after a certain moment.Magnetic resonance imaging at this time is judged according to the secure threshold of program setting
Safety, timely feedback to MR control unit 24.If safety index is more than threshold value, the MR control unit 24 stops institute
The MR scanning for stating MR scanning device 22, otherwise, continues to scan on.
It is introduced below that head is carried out to the patient with active implantation material using magnetic resonance imaging system 20 provided by the invention
When portion MR is scanned, metal implant surrounding tissue temperature and the method for providing security evaluation under real-time monitoring MR.This method includes
Following steps：
Step S10 carries out positioning scanning using sequence 1, determines that thermometric selects layer and imaging to select layer；
Step S11 is scanned using sequence 2, and interts the scanning for carrying out thermometric sequence 3 in sequence 2；And
Step S12 carries out security evaluation according to the scanning result of thermometric sequence 3.
In the step S10, it is preferred that a drift means for correcting is first mounted on scanning before carrying out MR scanning by patient
Appropriate area around position, such as head surrounding.This drift means for correcting around scanned position for providing magnetic resonance signal
Reference, when analyzing temperature rise remove magnetic field drift bring influence.As shown in Figure 3.This drift means for correcting 30 includes：
One group of container 34.One group of container 34 is prepared using non-magnetic material.The non-magnetic material can be nylon, polypropylene,
Organic glass etc..One group of container 34 is provided with uniform dielectric, such as physiological saline, agar gel, hydroxyethyl cellulose
(Hydroxy Ethyl Cellulose) gel etc..The dielectric relaxation time is adjusted in general, being also equipped in the uniform dielectric
Substance, such as CuSO4Or other transition metal salts, it is convenient for Magnetic Resonance Imaging.Medium in the container 34 should be kept and MR equipment
The identical temperature of place environment.In the present embodiment, the container 34 is the plastic test tube that four non-magnetic materials are constituted, Mei Geshi
Pipe is provided with agar.During installation, can with two flexible soft cords 36 by the more uniform hoop of four test tubes on head 32
Surrounding makes the orientation of four test tubes be basically parallel to the orientation of stimulating electrode 16, and guarantees that the thermometric at 18 place of electrode contacts selects layer
Include four Tube contents.Selectively, the fixed form of test tube can also pass through the hard shelf with the size that can stretch
It is fixed.
In general, first carrying out positioning scanning sequence 1, substantially observation area-of-interest and the implantation material that need to be monitored when scanning
Position.Sequence 1 can be multiple sequences, for further determining that the subsequent region to be scanned.The knot scanned by sequence 1
Fruit determines the region that the area-of-interest of sequence 2 and sequence 3 need to monitor.To be implanted into sweeping for lesions located in deep brain device system
For retouching, usual electrode contacts surface temperature rise most serious needs key monitoring, therefore chooses the region work where electrode contacts 18
For the scanning area of sequence 3, determine that thermometric selects layer.It is true that the imaging of sequence 2 selects layer then to carry out according to practical diagnosis or Research Requirements
It is fixed, here with no restrictions.Sequence 2 and the scanning area of sequence 3 are mutually indepedent with parameter setting, do not interfere with each other.It is appreciated that such as
Fruit implantation material position it is known in advance that, step S10 can be omitted.
Table 1, which is illustrated, lists some possible sequence major parameters used, and when application is not limited in table listed.
The citing of 1 sequence major parameter of table
In the step S11, before the scanning of sequence 2, first selects layer to carry out a thermometric thermometric using thermometric sequence 3 and sweep
It retouches, obtains initial temperature or temperature relevant information.In general, gradin-echo (GRE) or Echo-plane imaging can be used
(EPI) sequence selects layer to be scanned thermometric as thermometric sequence, using obtained phase diagram as initial fixed phase figure
The scanning mode for interting progress thermometric sequence 3 in the scanning of sequence 2 is as shown in Figure 4.Sequence 2 is divided into more
A part, every part are made of several units, and it includes a series of specific RF pulse-to-pulses that each unit, which is within a TR time,
The timing variations of punching and gradient magnetic, and one group of data can be acquired, constitute a part of 2 image k-space of sequence.Then exist
Intert the scanning for carrying out sequence 3 between the head and the tail and each section of sequence 2, forms temperature rise monitoring.As shown in Figure 4, sequence 2 by
The part i forms, and n is contained in every part respectively1, n2..., niA TR unit.It is appreciated that n1TR+n2TR+…+niTR=t2.Sequence
2 each section of column and the previous time interval between the latter sequence 3 are respectively Δ t1a、Δt1b、Δt2a、Δt2b、…、
Δtia、Δtib.Particularly, as shown in figure 5, in another embodiment, can not have between each section and sequence 3 of sequence 2
Having time interval, continuous scanning.More particularly, the interval between sequence 3 is equal, i.e. Δ t1=Δ t2=...=Δ ti=Δ t.
The unit number contained in each section that sequence 2 is divided into is also equal, i.e. n1=n2=...=ni.Because the initial segment of sequence 2 can
Can containing the shimming pulse different from further part, overturning pulse etc., it includes unit number be also not necessarily the integral multiple of i,
Therefore n1, n2..., niCan be different, Δ t1, Δ t2..., Δ tiIt can also be different.
One group of data can be obtained by scanning through sequence 3 every time, be transmitted to data processing unit 26 and handled, obtain sequence
The temperature relevant information of 3 scanning area of column.Since scanning the 2nd sequence 3, the result that each sequence 3 scans can be with the 1st
The result that secondary sequence 3 scans is compared, and obtains the Distribution of temperature rise of 3 scanning area of sequence by data processing.In turn, it provides
At this time for evaluating the safety index of safety, which can be temperature rise value or heat history dose value, and it is Celsius to commonly use 43
The equivalent the number of minutes characterization (43 DEG C of CEM43, Cumulative Equivalent Minutes@) of the accumulation of degree, which can
Be 3 scanning area of sequence maximum value, at this time calculate implantation material (such as electrode) surface maximum value, reckoning a certain moment after
The maximum value of 3 scanning area of sequence, implantation material (such as electrode) surface maximum value after a certain moment of reckoning.It is set according to program
Fixed secure threshold judges the safety of magnetic resonance imaging at this time, timely feedbacks to MR control unit 24.If safety index is super
Threshold value is crossed, then the MR control unit 24 stops the MR scanning of the MR scanning device 22, otherwise, continues to scan on.
Fig. 6, which illustrates, indicates the partitioning scheme of sequence 2.Sequence 2 may need to scan multi-layer image, each tomographic image by
The data reconstruction of one group of k-space obtains, and each group of k-space data is generated by the scanning of multiple TR units, each TR unit scan
Generate a line or a few row data in k-space.Sequence 3 can be interspersed in interlayer, i.e., each layer or every several layers of interspersed sequence 3
Scanning.More generally, the multi-layer image scanning of sequence 2 is all made of several TR units.Therefore, sequence 3 can also be interspersed in
One tomographic image k-space data is in the ranks.The interspersed mode of sequence 3 can be according to niTR and TsliceRelationship be adjusted and set
It sets.Work as n by taking the scanning of the shaft-like figure on entire head as an example referring to Fig. 7iTR>TsliceWhen, the k that imaging sequence obtains can be chosen at
The interspersed mode for carrying out thermometric and the thermometric sequence 3 of layer being selected to scan of spatial data interlayer.Assuming that niTR=nTslice, n is natural number.
The image scanning that n-layer image just stops sequence 2 is often obtained, selects layer to carry out the scanning of a thermometric sequence 3 thermometric, works as survey
After warm 3 end of scan of sequence, continue to stop after the scanning of sequence 2 obtains next n-layer image from the position that last time stops
Only, it then selects layer to carry out the scanning of a thermometric sequence 3 thermometric, successively continues.
Referring to Fig. 8, work as niTR<TsliceWhen or niTR is not TsliceIntegral multiple when, need select in k-space data
In the ranks intert the mode that thermometric selects the thermometric sequence 3 of layer to scan that carries out.Assuming that the space K of imaging sequence shares P row, each phase
The corresponding a line for filling out the space K of the data acquired after coding, i.e. TR time acquire a line K space data.In certain of imaging sequence
After one layer of K space acquisition j row, suspend the scanning of imaging sequence 2, by the acquired data conversion storage in the space K to storage unit,
Then start the scanning for selecting thermometric layer to carry out thermometric sequence 3, the real-time data transmission of acquisition is obtained to data processing unit 26
Temperature Distribution.After 3 end of scan of thermometric sequence, continue the scanning of imaging sequence 2 since+1 row of jth, the data of acquisition after
Continuation of insurance is stored to storage unit, and follow up scan process is similar.In above-mentioned scanning process, the MR control unit 24 will adopt in real time
The data collected pass to the data processing unit 26.
In the step S12, the data processing unit 26 is according to the thermometric picture number from the MR control unit 24
According to profiling temperatures at this time are calculated, in turn, provide at this time for evaluating the safety index of safety, with the threshold being previously set
Value compares, and provides feedback in time and is transmitted to the MR control unit 24.
Specifically, in the step S12, it is described according to the scanning result of thermometric sequence 3 carry out security evaluation include following
Step：
Step S121, determines assessment area；
Step S122 determines the Distribution of temperature rise of assessment area；
Step S123 calculates safety index；And
The safety index is compared by step S124 with secure threshold.
In the step S121, the data processing unit 26 determines security evaluation according to sequence 1 or the data of sequence 3
Region.In general, the selection of assessment area should be touched close to the serious implant surface that generates heat, such as lesions located in deep brain electrode as far as possible
Point surface.Since implantation material is different from the physical property of biological tissue, the susceptibility of especially metal part is different, can be in magnetic
Led to the distortion of field of surrounding by static magnetic field under resonance environment, so that implantation material peripheral image signal is caused to be distorted, performance
For image artifacts.The signal of this usual partial region is difficult to extract useful information.Therefore, this will usually be determined by choosing assessment area
The artifact region of active implantation material.In general, the RF magnetic field of active implantation material and magnetic resonance interaction and generate induct
Electric field is most strong at the tip end surface of slender conductor structure, thus generate temperature rise highest, and with to heat transfer around and by
Gradually reduce.Such as at lesions located in deep brain electrode contacts, more it is also easy to produce temperature rise.Therefore assessment safety is it needs to be determined that implantation material is pseudo-
Assessment area around shadow as close to implant surface temperature rise highest point, and can be believed Extracting temperature from the data of sequence 3
Breath.
Preferably, assessment area chooses the region from artifact edge a certain distance outward.Preferably, this distance for 1~
6mm.Artifact edge 42 can be detected by threshold method, and artifact internal signal intensity is I0, and peripheral region signal strength is I1,
Some value I2 between I0 and I1 is set as threshold value, is considered assessment area other than artifact higher than this threshold value.Preferably,
(I2-I0)/(I1-I0) is 0.3~0.5.Artifact edge 42 can also be determined using edge detection algorithm, determination process is as schemed
Shown in 9, it is preferred that can use canny algorithm, sober algorithm, Roberts algorithm determines artifact edge 42.Choose artifact side
Region other than edge 42 is as assessment area.It is further preferred that the artifact edge 42 belongs to metal artifacts region 40 to group
The transition region for knitting signal 44 determines the affiliated type of 42 pixel of artifact edge with sorting algorithm, if belonging to tissue signal 44,
It covers in assessment area.Preferably, it can use Bayesian Classification Arithmetic to classify to artifact edge 42, determine artifact side
The pixel generic that edge 42 is covered, tissue signal 44 or artifact region 40, in this way, just artifact region from image
40 determine.
In the step S122, determine that assessment area Distribution of temperature rise includes the following steps：Sequence 3, data are scanned through every time
Processing unit 26 receives one group of data, by the temperature relevant information for handling available assessment area.It is swept from the 2nd sequence 3
Beginning is retouched, the result that each sequence 3 scans can carry out difference with result before, obtain Distribution of temperature rise.Particularly, it sweeps every time
It retouches and carries out difference with the scanning result of the 1st sequence 3, obtain the Distribution of temperature rise of state before scanning relative to sequence 2.
The temperature relevant information relies on different magnetic resonance temperature measurement methods, it is preferable that can be using based on proton resonance
The MR temp measuring method of frequency shift (FS) obtains temperature profile.Thermometric process includes, and before sequence scanning of imaging, first carries out one
The scanning of secondary thermometric sequence 3, using obtained phase diagram as fixed phase figureThe phase diagram that kth time collects is denoted asTemperature change profile Δ T when kth time acquisitionmapIt can be acquired according to formula (3),
Wherein phase difference
Since in practical MRI image, the value range of phase is usually [- π, π], and at edge, phase can be jumped, produce
Raw so-called phase-wrapping.Therefore the above-mentioned method for seeking phase difference of directly subtracting each other is likely to occur large error.To avoid phase-wrapping,
Phase difference can be calculated such as following formula (4)
WhereinIt is the complex exponential form of twice sweep phase signal, Im (), Re (), which is respectively indicated, seeks plural number
Imaginary part and real part.Above-mentioned calculating formula is unfolded, following formula (5) are obtained
It substitutes into temperature change calculation formula, temperature variation when kth scanning can be calculated.
The magnetostatic field that MRI scanner generates is it is possible that drift, leads to phase change, so as to cause asking in above-mentioned steps
The Temperature Distribution inaccuracy obtained.It is preferred, therefore, that needing to correct temperature change caused by field is floated.Magnetostatic field drifts about in space
There are distribution, this distribution can be fitted with polynomial approximation.General correction needs to choose at least three position and does 1 rank plane
Correction.Particularly, smaller relative to distribution of static magnetic field for measured zone, 1 rank influences little situation, can directly pass through
The mode for subtracting mean value c does the correction of 0 rank, at least chooses 1 point at this time.As shown in Figure 10, in temperature profile, each drift
It is done if the central area 46 of correction 34 correspondence image of container is chosen.The method of another kind correction field drift does not depend on field drift correction and holds
Device.(MRI image includes map of magnitudes, phase diagram and temperature profile) chooses at least one reference from tissue signal MRI image
Region, reference zone should contain at least one pixel.The present invention does not limit the shape, size and selection method of reference zone.
It is readily appreciated that, the reference zone used in the bearing calibration of field drift herein also may include the corresponding image-region of field drift correction container.
Preferably, selected reference zone inner tissue should not be heated or cool down during the scanning process, and letter in reference zone
Number should relatively uniform (tissue signal includes range signal, phase signal and temperature signal), guarantee reference zone have represent
Property.1 rank is corrected, >=3 points are chosen, the location information of each point and temperature information are stored in matrix A (i, j, Δ
T in), pseudo- temperature change distribution map caused by finding out field drift with the method for linear interpolation.Calculating process can be asked by solving
Topic：
Wherein, [i j 1]n×3First be classified as A (:, 1), second be classified as A (:, 2), third column are 1 entirely.Solution obtains most
Small two multiply fit Plane z (i, j)=ai+bj+c under meaning, and original temperature change profile figure is subtracted z, is just obtained
Actual temperature profile Δ T after correctioncorrection, i.e. formula (7),
ΔTcorrection(i, j)=Δ Tmap(i,j)-z(i,j) (7)。
0 rank is corrected, is done if being chosen in all reference zones, the temperature information of each point is stored in
In vector B (i), the average value of the temperature information of selected point is calculated, finds out puppet temperature change z caused by the drift of field, meter
Calculation process such as following formula (8)：
Wherein n is the number of point selected in all reference zones, i.e. element number in amount B (i).Original temperature is become
Change in distribution map and subtracts z, the Temperature Distribution formula (9) after just being corrected：
ΔTcorrection(i, j)=Δ Tmap(i,j)-z (9)
In the step S123, safety index can be temperature rise value or heat history dose value, commonly use 43 degrees Celsius of accumulation
Equivalent the number of minutes characterizes (43 DEG C of CEM43, Cumulative Equivalent Minutes@).The safety index can be assessment
The maximum value in region, i.e. maximum value in selecting step S122.Can also be but not limited to this when calculate implantation material (as electricity
Pole) surface maximum value, reckoning a certain moment after the maximum value of assessment area, implantation material after a certain moment of reckoning is (such as electricity
Pole) surface maximum value etc..
The projectional technique of safety index includes the empirical table obtained according to experiment or empirical equation, or according to temperature rise
HEAT TRANSFER LAW is obtained with the method for the method of approximate fits or numerical analysis.
Since the signal-to-noise ratio in artifact region 40 is very low, 40 temperature data is unreliable in pseudo- shadow zone, needs by artifact
The temperature of 40 outside of region calculates the temperature change acquired in artifact region 40.Generally, 42 certain models outside artifact edge are chosen
The location information of each pixel and temperature information are stored in by the pixel temperature information in enclosing respectively as boundary condition
Matrix r=(r1,r2,...rm) and pk=(Tk1,Tk2,...,Tkm), wherein rmIndicate the location information of m-th of pixel, TkmTable
Show the temperature change that m-th of pixel kth time measurement obtains.Kth time measurement is combined first k-1 times and measures obtained temperature data
It is stored in a matrix P,
Consider the bio-heat transfer method as shown in formula (1), disregards metabolic heat production, it is assumed that uniform dielectric simultaneously chooses blood
Temperature TbOn the basis of, the available distribution relation formula (11) about temperature rise：
The formula has homogeneous characteristic, i.e., a certain spatial point, the temperature rise Δ T sometime put are directly proportional to heat source Q.And at this
Invent in the nuclear-magnetism radio frequency generated heat problem that is related to, heat source Q and induced electric field E's is square directly proportional, electric field E and current density, J at
Direct ratio.It is recognised that temperature rise Δ T is also square directly proportional with current density, J.Using this feature, in conjunction with heat transfer space and
Time Distribution can calculate the temperature rise at other moment, other regions according to a certain moment, some region of temperature rise.
Specifically, electromagnetic field and heat transfer numerical model are established, it is close with electric current at active implantation material current-carrying part-organizational interface
J is spent as the field distribution under the available different heating mode of parameter, and then available heat transfer Diffusion Law.The present embodiment
In, with current density, J0, such as 1000A/m2, as standard thermal diffusion model, out position is calculated in r=(r1,r2,...rm), it is right
The temperature change matrix st_P at moment should be scanned in k times,
It is appreciated that st_P (i, j) represents in standard diffusion model position in rjThe temperature at corresponding i-th scanning moment becomes
Change value.According to formula Δ T=aJ2It is available,
Herein, Δ T1=P, Δ T0=st_P can acquire λ under least square meaning, that is, ask formula (14)
Minimum value, enabling above formula derivation be equal to zero can acquire extreme pointValue,
It willIt is brought into thermal diffusion simulation model st_P (i, j) and has just obtained the corresponding thermal diffusion model of experiment,
The temperature variation curve of temperature rise highest point can be extracted from model.Temperature variation curve, that is, tissue of the temperature rise highest point
Interface temperature change curve.
Further, referred to according to corresponding safety in the available sweep time range of organizational interface's temperature variation curve
Mark, such as maximum temperaturerise Δ TmaxWith heat history amount.It is appreciated that thermal damage depends not only on the height of temperature, temperature is also depended on
Duration, i.e., so-called heat history amount.More commonly used heat history amount model is CEM43, calculation formula (16) is,
Wherein, as T (t)>At 43 DEG C, R=0.5；As T (t)<At 43 DEG C, R=0.25.
In the step S124, the safety index being calculated is compared with the secure threshold being previously set.Such as
By the heat history amount CEM of calculating43With the threshold value threshold_CEM being previously set43Compare, or compares maximum temperaturerise Δ Tmax
With the maximum temperaturerise threshold value threshold_ Δ T being previously setmaxBoth, or compare simultaneously, any one is more than threshold value, institute
It states data processing unit 26 and issues danger early warning to the MR control unit 24 in time, be automatically stopped sweeping for MR scanning device 22
It retouches.
Multiple embodiments of the invention are given above, it is to be understood that without departing from present disclosure essence
In the case where mind and range, it can make a variety of changes, replace and change, these embodiments are also in guarantor of the invention
It protects in range.
Claims (10)
1. a kind of method for monitoring active implantation material surrounding tissue temperature, this method is based on magnetic resonance temperature measurement technology and uses a magnetic
Resonance imaging system；The magnetic resonance imaging system is used at least generating one kind for clinical examination or scientific research or other mesh
The sequence 2 on way and a kind of for measuring the sequence 3 of Temperature Distribution；This approach includes the following steps：
Step S11 is scanned using sequence 2, and interts the scanning for carrying out thermometric sequence 3 in sequence 2, thus by sequence 2
Multiple portions are divided into, every part is made of several units, and each unit is within a TR time, comprising a series of specific
Radio-frequency pulse and gradient magnetic timing variations, and one group of data can be acquired, constitute one of 2 image k-space of sequence
Point；And
Step S12 carries out security evaluation according to the scanning result of thermometric sequence 3, judges the active implantation material surrounding tissue temperature
Safety index whether more than a secure threshold.
2. the method for the active implantation material surrounding tissue temperature of monitoring according to claim 1, which is characterized in that described to use sequence
2 are scanned, and the method for interting the scanning for carrying out thermometric sequence 3 in sequence 2 includes：Sequence 2 is divided into i part,
And n is contained in every part respectively1, n2...,
niA TR unit, wherein TR is the interval time in sequence 2 between two excitation pulses；Head and the tail and each portion in sequence 2
/ interspersed the scanning for carrying out sequence 3, and 2 each section of sequence and the previous time interval between the latter sequence 3
Respectively Δ t1a、Δt1b、Δt2a、Δt2b、…、Δtia、Δtib。
3. the method for the active implantation material surrounding tissue temperature of monitoring according to claim 2, which is characterized in that the time interval
Δt1a、Δt1b、Δt2a、Δt2b、…、Δtia、ΔtibIt is zero.
4. the method for the active implantation material surrounding tissue temperature of monitoring according to claim 1, which is characterized in that the step S11
Further include：Before the scanning of sequence 2, first selects layer to carry out a thermometric scanning thermometric using thermometric sequence 3, obtain initial temperature
Or temperature relevant information.
5. the method for the active implantation material surrounding tissue temperature of monitoring according to claim 1, which is characterized in that the step S12
Include the following steps：
Step S121, determines assessment area；
Step S122 determines the Distribution of temperature rise of assessment area；
Step S123 calculates the maximum temperaturerise Δ T of the assessment areamaxOr the heat history amount CEM of the assessment area43, thus conduct
The safety index；And
The safety index is compared by step S124 with secure threshold.
6. the method for the active implantation material surrounding tissue temperature of monitoring according to claim 5, which is characterized in that the step S121
Including：Artifact edge is determined using edge detection algorithm, using outside edge as assessment area.
7. the method for the active implantation material surrounding tissue temperature of monitoring according to claim 5, which is characterized in that the step S122
In, determine that assessment area Distribution of temperature rise includes：Sequence 3, the data processing unit of the magnetic resonance imaging system are scanned through every time
One group of data is received, since scanning the 2nd sequence 3, the result that each sequence 3 scans all carries out difference with result before and obtains
Distribution of temperature rise.
8. the method for the active implantation material surrounding tissue temperature of monitoring according to claim 5, which is characterized in that the step S124
Including：By the heat history amount CEM of calculating43With the threshold value threshold_CEM being previously set43Compare, or by the highest temperature of calculating
Rise Δ TmaxWith the maximum temperaturerise threshold value threshold_ Δ T being previously setmaxBoth compare, or compare simultaneously；Any one
More than threshold value, the data processing unit of the magnetic resonance imaging system issues danger early warning to MR control unit in time, stops automatically
The only scanning of MR scanning device.
9. the method for the active implantation material surrounding tissue temperature of monitoring according to claim 1, which is characterized in that the magnetic resonance at
As system further include it is a kind of for position or other and scan purposes sequence 1；
Further comprise step S10 before step S11, positioning scanning is carried out using sequence 1, determines that thermometric selects layer and imaging choosing
Layer.
10. a kind of magnetic resonance imaging system comprising：
One MR scanning device, the MR scanning device are used at least generating one kind for clinical examination or scientific research or other mesh
The sequence 2 on way and a kind of for measuring the sequence 3 of Temperature Distribution；
One MR control unit, the MR control unit are scanned for controlling the MR scanning device using sequence 2 and sequence 3；With
And
One data processing unit, the data processing unit are used to handle the scanning result of the thermometric sequence 3,
It is characterized in that, the magnetic resonance imaging system has the function of the active implantation material surrounding tissue temperature of monitoring, and the magnetic is total
The method that vibration imaging system monitors active implantation material surrounding tissue temperature is square as in one of claimed in any of claims 1 to 9
Method.
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| PCT/CN2017/114799 WO2018113518A1 (en) | 2016-12-23 | 2017-12-06 | Method for monitoring temperature of tissues surrounding active implant, and magnetic resonance imaging system |
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| CN106667487B (en) * | 2016-12-23 | 2018-11-23 | 清华大学 | A kind of method and magnetic resonance imaging system monitoring active implantation material surrounding tissue temperature |
| CN109044355B (en) * | 2018-06-28 | 2022-02-01 | 上海联影医疗科技股份有限公司 | Temperature imaging method, temperature imaging device, computer equipment and storage medium |
| CN109541511B (en) * | 2018-11-26 | 2020-02-14 | 清华大学 | Temperature rise prediction method and device |
| CN111543961B (en) * | 2020-05-11 | 2021-03-09 | 清华大学 | Wireless flexible patch type temperature sensor and preparation method thereof |
| CN111833315B (en) * | 2020-06-23 | 2022-04-19 | 哈尔滨医科大学 | Device for monitoring temperature of focal zone in real time through magnetic resonance |
| CN112156383B (en) * | 2020-08-31 | 2022-10-11 | 上海沈德医疗器械科技有限公司 | Magnetic resonance temperature correction method and system based on k-space energy spectrum analysis |
| CN115458143B (en) * | 2022-09-16 | 2023-05-23 | 兰州大学 | Passive implantable medical device radio-frequency heating evaluation method based on neural network |
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| CN104739382A (en) * | 2013-12-31 | 2015-07-01 | 深圳先进技术研究院 | Reference-temperature-free imaging method and reference-temperature-free imaging device |
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| CN104125802A (en) * | 2012-03-05 | 2014-10-29 | 皇家飞利浦有限公司 | Modification of treatment plan using magnetic resonance data acquired during cooling period |
| CN103829947A (en) * | 2012-11-23 | 2014-06-04 | 西门子公司 | Method and device for quick detection of regions of modified temperature |
| CN104739382A (en) * | 2013-12-31 | 2015-07-01 | 深圳先进技术研究院 | Reference-temperature-free imaging method and reference-temperature-free imaging device |
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