CN114910855A - Magnetic resonance temperature imaging method and related device - Google Patents

Abstract

The present application discloses a magnetic resonance temperature imaging method and a related device. The magnetic resonance temperature imaging method obtains i groups of phase maps based on gradient echo sequences containing i different echo times, and selects at least two groups of phases corresponding to different echo times. Figure to obtain a corresponding temperature difference map, and obtain a corresponding temperature map according to the temperature difference map. After research, the inventor found that the temperature map can be obtained based on i groups of phase maps and phase difference maps obtained from gradient echo sequences containing i different echo times, so as to eliminate the influence of magnetic susceptibility changes on the temperature map and reduce the final obtained temperature map. The error of the temperature map, for the purpose of improving the accuracy of the obtained temperature map. Further, the magnetic resonance temperature imaging method is not a retrospective algorithm or an iterative algorithm, and the computational load is small, and an almost real-time temperature map can be provided, which has high reference significance.

Description

Magnetic resonance temperature imaging method and related device

technical field

The present application relates to the technical field of image processing, and more particularly, to a magnetic resonance temperature imaging method and related devices.

Background technique

Magnetic Resonance Temperature Imaging (MRTI) can achieve non-invasive, real-time, in-vivo monitoring of the temperature distribution and changes inside the subject. It has important uses during the monitoring of therapy.

One of the current magnetic resonance temperature imaging methods is the temperature measurement method based on the proton resonance frequency (Proton Resonance Frequency, PRF). The magnetic susceptibility distribution is uneven, and objective environmental factors such as tissue movement caused by respiration/blood flow pulsation have a greater impact, which is likely to cause a large difference between the final temperature map and the actual temperature, which makes the temperature map lose its reference meaning. .

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present application provides a magnetic resonance temperature imaging method and a related device, so as to reduce the error of the finally obtained temperature map and improve the accuracy of the temperature map.

To achieve the above technical purpose, the embodiments of the present application provide the following technical solutions:

A magnetic resonance temperature imaging method, comprising:

Using a gradient echo sequence containing i different echo times to scan the target to be measured, to obtain a phase map corresponding to the echo times, where i is a positive integer greater than or equal to 2;

Select at least two sets of phase maps corresponding to different echo times to obtain corresponding temperature difference maps;

A corresponding temperature map is obtained according to the temperature difference map.

Optionally, the step of obtaining the temperature difference map includes:

Use the phase diagram at any moment to subtract the phase diagram at the reference moment to obtain the phase difference diagram at the moment, select the phase difference diagram corresponding to at least one echo time as the reference phase difference diagram, and compare other echoes based on the reference phase difference diagram. The phase difference map to be calibrated corresponding to the time is calibrated to obtain a calibrated phase difference map, and the echo time corresponding to the reference phase difference map is smaller than the echo time corresponding to the calibrated phase difference map;

The temperature difference map at this moment is calculated using the reference phase difference map and the calibrated phase difference map.

Optionally, the obtaining the calibrated phase difference map includes the following steps:

According to the relationship that the phase difference is proportional to the echo time, based on the echo time and the phase difference of the reference phase difference map, the estimated value of the phase difference of the phase difference map to be calibrated is calculated; then, using the estimated value, according to the phase difference Periodically unwrap the phase difference map to be calibrated to obtain a calibrated phase difference map.

Optionally, the step of eliminating phase drift caused by the magnetic resonance system is also included, and the step of eliminating the phase drift caused by the magnetic resonance system is performed on a phase difference map or a temperature map.

Optionally, the step of eliminating the phase drift caused by the magnetic resonance system on the phase difference map includes:

Selecting a plurality of thermal reference points, by subtracting the average phase difference of the thermal reference points from each phase difference map, an area with stable physical temperature and uniform tissue can be used as a thermal reference point;

The steps to cancel the phase drift caused by the magnetic resonance system on the temperature difference map include:

Correction is made by subtracting the average temperature difference at the thermal reference point from the temperature difference map.

Optionally, it also includes the step of calibrating magnetic susceptibility, and the step of calibrating magnetic susceptibility is performed on the phase difference map or the temperature difference map;

The steps to perform susceptibility correction on the temperature difference map include:

A first temperature map is obtained according to the reference phase difference map, and a corresponding second temperature map is obtained according to the calibrated phase difference map,

Determine whether the absolute value of the difference between the temperature value corresponding to each pixel in the second temperature map and the temperature value corresponding to the corresponding pixel in the first temperature map exceeds a preset temperature threshold; The temperature value corresponding to the corresponding pixel in the second temperature map is corrected;

The steps for performing susceptibility correction on the phase difference map include:

Determine whether the absolute value of the difference between the phase difference value corresponding to each pixel in the calibrated phase difference map and the phase difference value corresponding to the corresponding pixel in the reference phase map exceeds a preset phase difference threshold, and if so, the Correct the phase difference corresponding to the corresponding pixel in the calibration phase difference diagram.

Optionally, it also includes the step of correcting the phase error caused by the motion on the phase difference map or the temperature map;

The steps to correct motion-induced phase errors on the phase difference map include:

A linear least squares fit on the phase difference map at each pixel removes the motion-induced phase error;

The steps to correct motion-induced phase errors on the temperature difference map include:

Motion-induced phase errors were removed with a linear least squares fit at each pixel of the temperature difference map.

Optionally, the obtaining the temperature map at the corresponding moment according to the temperature difference map includes:

Calculate the temperature difference using the reference phase difference map and the calibrated phase difference map, and perform weighting to obtain a temperature map of the object to be measured;

or

A weighted average of the reference phase difference map and the calibrated phase difference map is used to obtain an average temperature difference, and a temperature map of the object to be measured is calculated according to the average temperature difference.

A magnetic resonance temperature imaging system, comprising:

a data transmission module, which is configured to receive the magnetic resonance sequence image and judge the integrity of the image;

a temperature calculation module, which is configured to select the sequence, calculate the phase difference, calibrate the phase difference, and calculate the temperature;

A temperature display module, which is set to display the temperature in the form of a pseudo-color map or an isotherm;

Wherein, the time for the system to perform a complete calculation does not exceed 1 s.

A magnetic resonance temperature imaging system, comprising: a memory and a processor;

The memory is used to store program codes, and the processor is used to call the program codes, and the program codes are used to execute the magnetic resonance temperature imaging method described in any one of the above.

A storage medium, where program codes are stored on the storage medium, and when the program codes are executed, any one of the magnetic resonance temperature imaging methods described above is implemented.

It can be seen from the above technical solutions that the embodiments of the present application provide a magnetic resonance temperature imaging method and a related device, wherein the magnetic resonance temperature imaging method obtains i groups based on gradient echo sequences containing i different echo times For the phase map, at least two sets of phase maps corresponding to different echo times are selected to obtain a corresponding phase difference map and a temperature difference map, and a temperature map at a corresponding time is obtained according to the temperature difference map. The echo time of the gradient echo sequence is proportional to the size of the susceptibility artifact, so the phase map obtained by the gradient echo sequence corresponding to the smaller echo time is least affected by the susceptibility change due to heating, The image data still maintains the correct phase, so the temperature map can be obtained based on i groups of phase maps and phase difference maps obtained from gradient echo sequences with i different echo times, so as to reduce the error of the final temperature map, The purpose of improving the accuracy of the obtained temperature map.

Further, the magnetic resonance temperature imaging method is not a retrospective algorithm or an iterative algorithm, and the computational load is small, and an almost real-time temperature map can be provided, which has high reference significance.

Description of drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only It is an embodiment of the present application. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without any creative effort.

Figure 1 shows the amplitude and phase images obtained in ex vivo and in vivo environments;

2 is a schematic flowchart of a magnetic resonance temperature imaging method according to an embodiment of the present application;

3 is an acquired phase image and a phase difference diagram provided by an embodiment of the present application;

4 is a schematic flowchart of a magnetic resonance temperature imaging method according to another embodiment of the present application;

5 is a schematic diagram of an experimental device provided by an embodiment of the application;

FIG. 6 is a partial magnification of a temperature map of laser interstitial hyperthermia in an in vitro pork experiment provided by an embodiment of the present application;

Fig. 7 is a schematic diagram of the change of temperature with time during the experiment of tissue mimic (Fig. 7(a)) or in vitro pork (Fig. 7(b)) according to an embodiment of the present application;

FIG. 8 is a representative temperature map of dog O1 in an in vivo experiment provided by an embodiment of the application;

Detailed ways

Magnetic resonance thermography can guide a variety of energy-delivery treatments, such as laser interstitial hyperthermia, focused ultrasound therapy, radiofrequency ablation, etc., to monitor target tissue temperature and treatment effects. The present invention uses magnetic resonance temperature imaging-guided laser interstitial hyperthermia as an example to illustrate the method of the present invention. Magnetic resonance temperature imaging-guided laser interstitial hyperthermia is a minimally invasive treatment method, which is a method for the treatment of surgically challenging patients. Tumors by location (anatomical or functional) create new options. This method can rapidly coagulate tissue and induce tumor cell necrosis through protein denaturation by applying a temperature of 50-80°C or higher for tens of seconds. Compared to open surgery, laser interstitial hyperthermia ablation can target tumors more precisely, reduce discomfort and infection risk, and shorten patient hospital stays. During the hyperthermia process of laser interstitial hyperthermia ablation, concurrent magnetic resonance thermography plays an important role for more efficient ablation of tumor cells and better protection of healthy surrounding cells and key structures. Most laser interstitial hyperthermia ablation procedures rely on thermometry based on proton resonance frequency shift.

However, as described in the background art, the existing magnetic resonance temperature imaging method is greatly affected by factors such as the environment, which is likely to cause a problem that the temperature map finally obtained is greatly different from the actual temperature.

In the treatment process of laser interstitial hyperthermia ablation, the inventor found through research that the main sources of errors in the acquired temperature map are phase errors caused by unpacking errors, magnetic susceptibility errors, and phase errors caused by motion. As the ablation laser dose changes, the magnetic susceptibility causes a reduction in image amplitude and a corresponding error in the image phase, which corrupts the reconstructed temperature map in and around the heating center. Errors in reconstructing the temperature map can lead to erroneous estimation of the ablation area, which can lead to changes in treatment efficacy and thermal damage to critical tissues. Therefore, accurate temperature imaging is critical for the efficacy and safety of laser interstitial hyperthermia ablation, especially when laser interstitial hyperthermia ablation is applied to tighter regions of ablation in brain tissue.

The inventors found through further research that the thermometry method based on the proton resonance frequency shift is based on the fact that the resonance frequency of hydrogen protons varies with the temperature in water molecules. For aqueous tissue, the change in the local magnetic field with temperature can be described as:

Wherein, α is the proton resonance frequency coefficient that changes with temperature, which is taken as 0.008-0.015ppm/°C in the present invention. The corresponding resonant frequency change of water protons affected by temperature can be expressed as:

Δf=αγB ₀ ·ΔT; (2)

Among them, ΔT represents the temperature change, Δf represents the resonant frequency change, γ represents the gyromagnetic ratio, and B ₀ represents the static magnetic field strength.

Changes in resonant frequency due to temperature changes can be observed in the phase of complex magnetic resonance imaging. For a given echo time TE of a gradient echo sequence, the relative temperature change ΔT can be calculated from the phase difference Δφ, and the equation can be expressed as:

Gradient echo sequences are sequences used in thermometry based on proton resonance frequency shifts. According to formula (3), the longer the gradient echo time is, the larger the phase difference may be caused by the same temperature change, indicating that higher temperature sensitivity can be obtained.

Referring to Fig. 1, as the echo time of the gradient echo sequence increases, both phase contrast and phase wrapping increase, indicating that the temperature sensitivity is higher and the phase unwrapping procedure is more at later echo times. In Fig. 1, the first to fourth echoes obtained by gradient echo sequences containing 4 different echo times used in the examples of the present application in (a) (ex vivo, pig brain) and (b) (in vivo) Amplitude (top row) and phase (second row) of waves. The temperature map (lower row) was calculated for each TE (echo time) setting using a conventional PRF algorithm. More phase wrapping occurs with longer echo times because the image contrast increases accordingly. Note that intense laser heating causes signal loss due to changes in magnetic susceptibility and also translates into phase and temperature errors in pixels around the heating center. In the in vivo experiments, note that CSF motion induces inappropriately high temperatures on the MRTI, which is more pronounced in the previous echo, as shorter TEs are less tolerant of the similar phase errors introduced.

For example, scan-to-scan motion can be a big problem in thermograms measured by thermometry based on proton resonance frequency shifts due to the motion of Cerebrospinal Fluid (CSF) in the brain. The magnitude and phase signals of the CSF are often altered on pulsed gradient echo sequences by the normal dynamic motion of the CSF, which can confound temperature estimates. CSF motion may also cause pixels in and around the ventricle to shift, causing errors in phase contrast maps. As shown in Figure 1b, the in vivo temperature map shows pseudo-hyperthermia in the third ventricle due to cerebrospinal fluid movement. Temperature errors are more pronounced on pulsed gradient echo sequences with shorter echo times because they are less tolerant of the intensity of the phase shift introduced by the cerebrospinal fluid flow in (3).

In fact, the local magnetic field of water protons should also consider the magnetic susceptibility x ₀ , and equation (1) becomes:

where _σχ0 represents the local magnetic field change caused by magnetic susceptibility.

Further investigation found that laser heating induced significant magnetization artifacts in GRE imaging around the laser tip. Still referring to Fig. 1, a heated center with a sharp temperature change (shown by the arrow in Fig. 1(a)) shows severe signal loss on the order of longer echo times. The intra-voxel spin phase shift is caused by local magnetic field inhomogeneities caused by temperature and susceptibility changes.

The magnetization artifact caused by laser heating, especially the magnetization artifact in the image corresponding to the gradient echo sequence with longer echo time, is an important cause of the error. Still referring to Figure 1, in ex vivo or in vivo experiments, phase errors around the heating center translate into pseudo-low temperatures on magnetic resonance thermography. Typically, in imaging procedures, it is recommended to use gradient pulse sequences with as short an echo time as possible to minimize susceptibility artifacts. However, gradient pulse sequences with longer echo times can provide better temperature sensitivity and signal-to-noise ratio, which is the current dilemma.

In order to take into account temperature sensitivity, signal-to-noise ratio and low error, an embodiment of the present application provides a magnetic resonance temperature imaging method, including:

Scan the target to be measured using a gradient echo sequence containing i different echo times, and obtain i groups of phase maps corresponding to the echo times, where i is a positive integer greater than or equal to 2;

Select at least two sets of phase maps corresponding to different echo times to obtain corresponding temperature difference maps;

A corresponding temperature map is obtained according to the temperature difference map.

The magnetic resonance temperature imaging method obtains i groups of phase maps based on gradient echo sequences containing i different echo times, selects at least two sets of phase maps corresponding to different echo times to obtain corresponding phase difference maps, and according to the temperature Difference map to obtain the corresponding temperature map. The inventor found through research that the echo time of the gradient echo sequence is proportional to the size of the magnetic susceptibility artifact, so the phase map obtained by the gradient echo sequence corresponding to the smaller echo time is subject to the magnetization caused by heating. The influence of the rate change is minimal, and the image data still maintains the correct phase, so the temperature map can be obtained based on the i groups of phase maps and phase difference maps obtained from gradient echo sequences containing i different echo times to reduce the final The error of the temperature map is for the purpose of improving the accuracy of the obtained temperature map.

Further, the magnetic resonance temperature imaging method is not a retrospective algorithm or an iterative algorithm, and the computational load is small, and an almost real-time temperature map can be provided, which has high reference significance.

The embodiment of the present application provides a magnetic resonance temperature imaging method, as shown in FIG. 2 , including:

S101: use a gradient echo sequence containing i different echo times to scan the target to be measured, and obtain i groups of phase maps corresponding to the echo times, where i is a positive integer greater than or equal to 2;

In step S101, the minimum value and the maximum value of the echo time in the gradient echo sequence can be determined according to actual needs. The minimum value of the echo time in the gradient echo sequence can be the minimum value that can be obtained by the magnetic resonance temperature imaging device, and the maximum value of the echo time in the gradient echo sequence generally does not exceed the echo of the object to be measured. The upper limit of the value range of time. For example, in the case of head imaging, the value range of the echo time of the optional gradient time sequence is 3-30ms, and the specific value of the echo time included in the gradient echo sequence must be within the range of the echo time. within the value range.

Referring to FIG. 3 , with specific reference to FIG. 3( a ), the acquired phase diagram is shown in FIG. 3( a ), and the phase diagram shown in FIG. 3( a ) is the image phase during heating. Then, as shown in Fig. 3(b), the phase difference map is calculated by a complex subtraction procedure, and the arrows in Fig. 3(b) point out the phase wrapping in the phase difference map. Complex subtraction avoids problematic phase wrapping.

The acquisition of gradient echo sequence information containing i different echo times can be read or received from a server or other storage device, or it can be acquired in real time according to the settings of the staff. The specific method is not limited, and it depends on the actual situation.

S102: Select at least two sets of phase maps corresponding to different echo times to obtain corresponding temperature difference maps;

Optionally, between step S102 and step S103, a drift correction of the static magnetic field intensity of the phase map and the phase difference map may also be included, so as to eliminate errors caused by the static magnetic field intensity.

S103: Obtain a temperature map at a corresponding time according to the temperature difference map.

The following describes feasible implementation manners of each step of the magnetic resonance temperature imaging method provided by the embodiments of the present application.

On the basis of the above embodiment, in an embodiment of the present application, the specific steps of obtaining the temperature difference map include:

Using the phase map at any time to subtract the phase map at the reference time to obtain the phase difference map at the time, the reference time is any time before the energy (such as thermal energy, light energy, radiofrequency ablation, cryoablation) is transmitted to the target tissue, preferably For the moment shortly before the energy transfer, such as the moment when the energy transfer is about to occur;

The phase difference map corresponding to at least one echo time at this moment is selected as the reference phase difference map, and the phase difference maps corresponding to other echo times are calibrated to obtain a calibrated phase difference map. The reference phase difference map corresponds to The echo time is less than the echo time corresponding to the calibrated phase difference map;

A temperature difference map at this moment is calculated using the reference phase difference map and the calibrated phase difference map.

Optionally, the value of the echo time of the reference phase difference map is less than or equal to 18ms, preferably, the value of the echo time of the reference phase difference map does not exceed 17ms, 16ms, 15ms, 14ms, 13ms, 12ms, 11ms, 10ms, 9ms, 8ms or 7ms, more preferably, the value of the echo time of the reference phase difference map does not exceed 6ms, 5ms or 4ms.

Optionally, the phase map corresponding to the minimum echo time in the gradient echo sequence can be used as the reference phase map, and the reference phase difference map can be obtained based on the reference phase map, so as to minimize the heating caused by the phase map as much as possible. The effect of magnetic susceptibility changes. As mentioned above, the minimum echo time in the gradient echo sequence may be the minimum value that the magnetic resonance temperature imaging device can take.

The phase difference map corresponding to at least one echo time at this moment is selected as the reference phase difference map, and the calibration of the phase difference maps corresponding to other echo times includes the following steps:

Using the reference phase difference map and the phase difference map corresponding to the echo time to be calibrated, according to the proportional relationship between the phase difference and the echo time, and based on the phase difference between the echo time and the reference phase difference map, calculate the The estimated value of the phase difference of the phase difference map corresponding to the calibrated echo time; then, using the estimated value, the phase difference to be calibrated is unwrapped according to the phase periodicity to obtain the calibrated phase difference.

On the basis of the above embodiment, in another embodiment of the present application, the magnetic resonance temperature imaging method further includes:

S104: the step of eliminating the phase drift caused by the magnetic resonance system, the step of eliminating the phase drift caused by the magnetic resonance system is performed on the phase difference map or the temperature map.

The steps to remove phase drift caused by the magnetic resonance system on the phase difference map include:

Selecting a plurality of hot reference points (Region of Interest, ROI), by subtracting the average phase difference of the hot reference points from each phase difference map;

The steps to cancel the phase drift caused by the magnetic resonance system on the temperature difference map include:

Correction is made by subtracting the average temperature difference at any of the thermal reference points from the temperature difference map.

On the basis of the above embodiment, in another embodiment of the present application, the magnetic resonance temperature imaging method further includes:

S105: the step of magnetic susceptibility correction, the step of magnetic susceptibility correction is performed on the phase difference map or the temperature map;

The steps to perform susceptibility correction on a temperature map include:

Obtain a first temperature map according to the reference phase difference map, and obtain a corresponding second temperature map according to the calibrated phase difference map;

Optionally, determining a preset area in the first temperature map and each of the second temperature maps;

Determine whether the absolute value of the difference between the temperature value corresponding to each pixel in the second temperature map and the temperature value corresponding to the corresponding pixel in the preset area of the first temperature map exceeds the preset temperature threshold, and if so , the temperature value corresponding to the corresponding pixel in the second temperature map is corrected; there are various methods for correction, for example, the temperature value of the first temperature map can be used to replace the temperature value of the second temperature map, or the temperature value of the second temperature map can be replaced by the temperature value of the second temperature map. The temperature value of the adjacent pixel in the figure replaces the temperature value of the pixel in the second temperature map, or an approximate temperature is fitted based on the temperature value of the adjacent pixel and the temperature value of the first temperature map to replace the temperature value of the second temperature map;

The steps for performing susceptibility correction on the phase difference map include:

determining a preset region in the reference phase difference map and the calibrated phase difference map;

judging whether the absolute value of the difference between the phase difference value corresponding to each pixel in the calibrated phase difference map and the phase difference value corresponding to the corresponding pixel in the preset area in the reference phase map exceeds a preset phase difference threshold, If yes, correct the phase difference in the calibrated phase difference map, the correction method is similar to the previous one, and will not be repeated.

On the basis of the above embodiment, in another embodiment of the present application, the magnetic resonance temperature imaging method further includes:

S106: the step of correcting the phase error caused by the motion on the phase difference map or the temperature map;

The steps to correct motion-induced phase errors on the phase difference map include:

Motion-induced phase error is removed by a linear least squares fit at each pixel using the reference phase difference map and the calibrated phase difference map;

The steps to correct motion-induced phase errors on the temperature map include:

Obtain a first temperature map according to the reference phase difference map, and obtain a corresponding second temperature map according to the calibrated phase difference map;

Motion-induced phase errors are removed by a linear least squares fit at each pixel using the first temperature map and the second temperature map.

Still referring to Figure 4(c), Figure 4(c) shows the phase difference (first row) and relative temperature change ( second line). For short echo times, the phase error Δφ(x,y) _bias introduces a large temperature bias, but is correctly eliminated after a linear least squares fit.

As mentioned above, steps S104, S105 and S106 can be performed on the phase difference layer surface or on the temperature map. That is, the step of eliminating the phase drift caused by the magnetic resonance system is performed on the phase difference map and/or the temperature map, the step of susceptibility correction is performed on the phase difference map and/or the temperature map, and the correction motion caused by The step of phase error is performed on a phase difference map and/or a temperature map.

In addition, steps S104, S105 and S106 are all optional steps. In the actual application process, steps S104, S105 and S106 can be selected and executed according to the actual situation. It is also possible to not select all of them, and the sequence of execution of steps S104, S105 and S106 is not limited, and the execution sequence can be arbitrarily arranged according to the actual situation.

Still referring to Fig. 3, Fig. 3(c) shows the phase difference map for unwrapping and drift correction, Fig. 3(d) shows the temperature map, the arrows in Fig. 3(d) point out the error caused by the magnetic susceptibility in the temperature map, Fig. 3(e) shows the image after susceptibility error correction, and FIG. 3(f) shows the image after motion error correction.

On the basis of the above embodiment, in another embodiment of the present application, the obtaining a temperature map at a corresponding time according to the temperature difference map includes:

S1031: Calculate the temperature using the reference phase difference map and the calibrated phase difference map, and weight the calculated temperature to obtain a temperature map of the target to be measured;

or

A weighted average of the reference phase difference map and the calibrated phase difference map is used to obtain an average temperature difference, and a temperature map of the object to be measured is calculated according to the average temperature difference.

In step S1031, the weighting may be various weighting methods, such as average weighting, or may be a temperature map corresponding to a single echo time, that is, the weighting coefficient of the temperature map corresponding to this echo time is 1, and other echo times The corresponding temperature map has a weighting factor of 0.

After step S1031, it may further include:

S107: Perform multiple interpolation processing on the temperature map of the object to be measured, and calculate the boundary of the ablation area by using the temperature map of the object to be measured after the interpolation processing.

The purpose of performing multiple interpolation processing on the temperature map of the target to be measured is to obtain a smoother ablation region boundary, and the specific number of difference processing may be 2 or 3 times.

In the process of calculating the boundary of the ablation region, the following formula is specifically used:

where E _a is the activation energy, A is the frequency factor, R is the universal gas constant, T(τ) is a function of temperature (°C) and time τ, and t is the current time. Pixels whose Ω value exceeds a set threshold (eg, 1) are considered ablated.

The magnetic resonance temperature imaging method provided by the embodiments of the present application is verified below with reference to specific experiments.

The tissue simulant (gel phantom) was heated using a laser ablation system including a 10W, 980nm diode laser and a cooled laser applicator system. Phase images were acquired on a 3T MR scanner (Ingenia, Philips Healthcare, Best, The Netherlands) using 16 receiver coils using a multi-echo temporal gradient echo sequence: flip angle=30°, TE=6/12/18/24ms, TR=22ms, matrix=176×176, FOV=200×200mm ² , slice thickness=5mm, 3s/image.

As shown in Figure 5, two MR-compatible fiber-optic temperature probes were also inserted into the tissue simulant, with the probe tips positioned close to the ablation fiber, to obtain the gel temperature at each point. Since the fiber optic probe is affected by the ablating fiber during heating, the thermometer only monitors the cooling phase. Figure 5. Specifically, Figure 5 shows the insertion of an ablation fiber and two fiber-optic temperature probes into the tissue simulant, with a gel-filled reference tube fixed around as an insulating reference.

The ex vivo experiments of pork and porcine brain were performed using the same scanning parameters as the tissue mock experiments. Two experiments were performed on each type of tissue (gel, pork, pig brain), one with several laser cycles and the other with continuous heating and cooling. The root mean square error between the MR measurement temperature and the fiber measurement temperature was calculated as a measure of temperature accuracy.

The in vivo experiments in Doberman dogs have been approved by the Ethics Review Committee of Tsinghua University. Nine adult Doberman pinschers received laser interstitial hyperthermia. The heating process was monitored on a 3T MR scanner (Ingenia, Philips Healthcare, Best, The Netherlands) with 32 receiver head coils using a multi-echo temporal gradient echo sequence.

Still referring to FIG. 3 and FIG. 4 , FIG. 3 and FIG. 4 illustrate an example of the magnetic resonance temperature imaging method provided by the embodiment of the present application. Figure 3 shows a specific example step of magnetic resonance thermography. Fig. 3(a), one time obtained during laser hyperthermia, the coil combined phase image is first obtained by a multi-TE echo sequence; Fig. 3(b), the phase difference map is then obtained, the white arrows indicate the phase around the heating center The phase wrapping occurs on the graph; Figure 3(c) shows the phase difference map after phase unwrapping and B0 drift correction. Fig. 3(d) The temperature map calculated from Fig. 3(c) according to the PRF migration method. White arrows highlight susceptibility-induced errors. Figure 3(e) Temperature map after susceptibility correction. White arrows show errors caused by residual cerebrospinal fluid movement. Figure 3(f) Motion-corrected temperature map.

In FIG. 4, an exemplary method flow for a representative pixel includes: Step 1, obtaining a phase difference map and a phase map obtained by unwrapping the reference phase difference map (TE1), as shown by black arrows, in the case of rapid temperature changes Below, the phase difference maps corresponding to some echo times are wrapped. Step 2, obtain phase unwrapping map, Step 3, static magnetic field strength (B ₀ ) drift correction (B ₀ Drift Correction), B0 drift correction is to reduce system fluctuations, Step 4, phase error correction caused by magnetic susceptibility, use the shortest The echo time (TE) of , corrects for temperature errors caused by susceptibility changes (black arrows) over longer echo times. Step 5 Motion-induced phase error correction. The graphs in the first row and the second row are the phase difference versus time and the corresponding temperature versus time, respectively. The motion-induced phase errors (black arrows) are nearly the same for multiple echo times, thus leading to more pronounced temperature errors on shorter TEs. The result of correcting the motion error shows a smoother phase and temperature curve.

Tissue mimics and in vitro results:

Figure 6 shows a representative temperature map of an ex vivo pork experiment during laser interstitial hyperthermia. Six representative images (#50 for the 50th frame, #146 for the 146th frame, and so on) were selected from the 300 frames (3s/frame) acquired during the thermal cycle. The first row and the second row respectively use the traditional phase unwrapping method and the multi-echo time-based phase unwrapping method (multi-TE unwrapping) proposed in the embodiments of the present application. Using state-of-the-art phase unwrapping methods, the pixels on the temperature map can be severely damaged due to the change in susceptibility caused by laser heat, and cannot be recovered even if the laser is no longer used. The technical principle is as follows: The phase unwrapping method of the prior art is applied to the time dimension for phase jump detection. If the phase difference map of the current frame is wrongly unwrapped, all subsequent frames will be affected. On the other hand, the magnetic resonance temperature imaging method proposed by the present invention is performed on the basis of multiple echo dimensions, thus avoiding interference from previous frames. The third row is a phase-unwrapped and susceptibility-corrected single echo time-temperature map with damaged pixels around the heating center recovered correctly. The last row is the result of combining multi-echo time data using the magnetic resonance temperature imaging method provided in the embodiment of the present application. The final magnetic resonance thermography was shown to be more uniform in temperature at the hot spot.

Figure 7 shows temperature as a function of time during experiments with tissue mimics (Fig. 7(a)) or ex vivo pork (Fig. 7(b)), measured by two thermometric fibers (red lines) and the present application, respectively. Calculated by the method provided in the examples (dashed black line). In the case of multiple heating (Fig. 7(a)) or single heating (Fig. 7(b)), the temperature-time behavior of the proton resonance frequency (PRF) calculation in the cooling stage is comparable to that of the fiber-optic temperature probe (also known as the The measured temperature-time measured by the temperature fiber) is very well matched. Table 1 lists the root mean square error (RMSE) values between the MR calculated values and the thermometric fiber measurements, which represent the temperature accuracy of the proposed algorithm. Experiment 1 performed several laser cycles of heating, while Experiment 2 had successive heating and cooling stages. The results showed that the RMSE error of gel, pork or pig brain tissue was less than 0.5°C in most cases. In Figure 7, the probe (left) represents the left temperature measuring fiber, and the probe (right) represents the right temperature measuring fiber.

Table 1. Comparison between the temperature measured by the optical fiber and the temperature calculated by the MR of the method provided in the embodiment of the present application.

Abbreviations: RMSE, root mean square error; experimental, experimental L(R), fiber optic temperature probe on the left (right).

Figure 8 shows a representative temperature profile of Dog 01 in an in vivo experiment. It is important to note that the ablation area is located close to the third and lateral ventricles. 100 frames (3s/frame) of images acquired during laser ablation were selected to be superimposed on the post-ablation T2w magnetic resonance thermography. From top to bottom are the temperature maps calculated from single echo time (TE) data (TE=6ms and TE=24ms) by prior art algorithms, and calculated from multiple TE echo sequences using the algorithm proposed in the present invention out the temperature map (joint TE). The first row (TE = 6 ms) shows pseudo-hyperthermia in the third and lateral ventricles, indicating that the short TE calculated temperature is severely affected by CSF flow artifacts. CSF-induced third intraventricular artifacts (indicated by white arrows) were still present in the second row (TE = 24 ms), but were well suppressed by the proposed multiple (joint) TE echo sequence algorithm. The second row shows that longer TE (TE=24ms) can provide smoother boundaries and better temperature signal-to-noise ratio compared to shorter TE (TE=6ms), but as mentioned above, due to the magnetic susceptibility changes, the pixels around the heating center will be damaged. On the other hand, our proposed method integrates the information of multiple echoes, so the obtained temperature map removes both CSF-induced errors and magnetic susceptibility-induced errors, showing a more uniform and symmetrical heating area.

The above experimental results show that the magnetic resonance temperature imaging method provided by the embodiments of the present application can be used to correct the error caused by the magnetic susceptibility in the proton resonance frequency temperature map caused by the heating laser itself. We first propose the application of multi-echo temporal gradient echo pulse sequences to magnetic resonance thermography by the proton resonance frequency shift method. Instead of single-echo sequences, multi-gradient echo sequences provide more information without additional scan time and provide new methods for phase unwrapping and artifact removal.

Shorter echo times can tolerate susceptibility artifacts but are sensitive to noise, while longer echo times have better temperature sensitivity and signal-to-noise ratio, but are greatly affected by susceptibility artifacts. The magnetic resonance temperature imaging method proposed in the present invention combines the advantages of different echoes to obtain better temperature map measurement results. Moreover, the magnetic resonance thermography method of the present invention can significantly improve the robustness and signal-to-noise ratio of magnetic resonance thermography, thereby avoiding damage to healthy tissue due to misestimation of low temperature.

The method of the present invention also has excellent cerebrospinal fluid flow error suppression and can provide accurate temperature measurements in or around the ventricle. Compensation for errors caused by cerebrospinal fluid motion is clinically important for laser interstitial hyperthermia in the treatment of periventricular brain lesions. Furthermore, the proposed algorithm is online compatible and does not require iterative computations, making it well suited for magnetic resonance thermography as very close to real-time temperature maps are required.

The magnetic resonance temperature imaging system provided by the embodiments of the present application is described below, and the magnetic resonance temperature imaging system described below can be referred to each other correspondingly with the magnetic resonance temperature imaging method described above.

Correspondingly, the embodiments of the present application also provide a magnetic resonance temperature imaging system, including:

a data transmission module, which is configured to receive the magnetic resonance sequence image and judge the integrity of the image;

a temperature calculation module, which is configured to select the sequence, calculate the phase difference, calibrate the phase difference, and calculate the temperature;

A temperature display module, which is set to display the temperature in the form of a pseudo-color map or an isotherm;

Wherein, the time for the system to perform a complete calculation does not exceed 1 s.

In some embodiments of the present application, the time for the system to perform a complete calculation is preferably no more than 0.5s, most preferably no more than 0.1s.

Correspondingly, an embodiment of the present application further provides a magnetic resonance temperature imaging system, including: a memory and a processor;

The memory is used to store program codes, and the processor is used to call the program codes, and the program codes are used to execute the magnetic resonance temperature imaging method described in any one of the above embodiments.

Correspondingly, an embodiment of the present application further provides a storage medium, where a program code is stored on the storage medium, and when the program code is executed, the magnetic resonance temperature imaging method described in any of the foregoing embodiments is implemented.

To sum up, the embodiments of the present application provide a magnetic resonance temperature imaging method and a related device, wherein the magnetic resonance temperature imaging method obtains i groups of phase maps based on gradient echo sequences containing i different echo times, At least two sets of phase maps corresponding to different echo times are selected to obtain corresponding phase difference maps, and temperature maps at corresponding times are obtained according to the temperature difference maps. The inventor found through research that the echo time of the gradient echo sequence is proportional to the size of the magnetic susceptibility artifact, so the phase map obtained by the gradient echo sequence corresponding to the smaller echo time is subject to the magnetization caused by heating. The influence of the rate change is minimal, and the image data still maintains the correct phase, so the temperature map can be obtained based on the i groups of phase maps and phase difference maps obtained from gradient echo sequences containing i different echo times to reduce the final The error of the temperature map is for the purpose of improving the accuracy of the obtained temperature map.

Further, the magnetic resonance temperature imaging method is not a retrospective algorithm or an iterative algorithm, and the computational load is small, and an almost real-time temperature map can be provided, which has high reference significance.

The features described in the various embodiments in this specification can be replaced or combined with each other, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, this application is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. a magnetic resonance temperature imaging method, is characterized in that, comprises: Using a gradient echo sequence containing i different echo times to scan the target to be measured, to obtain a phase map corresponding to the echo times, where i is a positive integer greater than or equal to 2; Select at least two sets of phase maps corresponding to different echo times to obtain corresponding temperature difference maps; A temperature map is obtained from the temperature difference map. 2. The method according to claim 1, wherein the step of obtaining the temperature difference map comprises: Use the phase diagram at any moment to subtract the phase diagram at the reference moment to obtain the phase difference diagram at the moment, select the phase difference diagram corresponding to at least one echo time as the reference phase difference diagram, and compare other echoes based on the reference phase difference diagram. The phase difference map to be calibrated corresponding to the time is calibrated to obtain a calibrated phase difference map, and the echo time corresponding to the reference phase difference map is smaller than the echo time corresponding to the calibrated phase difference map; The temperature difference map at this moment is calculated using the reference phase difference map and the calibrated phase difference map. 3. The method according to claim 2, wherein the obtaining the calibrated phase difference diagram comprises the following steps: According to the relationship that the phase difference is proportional to the echo time, based on the echo time and the phase difference of the reference phase difference map, the estimated value of the phase difference of the phase difference map to be calibrated is calculated; then, using the estimated value, according to the phase difference Periodically unwrap the phase difference map to be calibrated to obtain a calibrated phase difference map. 4. The method according to any one of claims 1 to 3, further comprising the step of eliminating phase drift caused by the magnetic resonance system, wherein the step of eliminating the phase drift caused by the magnetic resonance system is in the phase difference diagram or on a temperature map. 5. The method according to claim 4, wherein the step of eliminating the phase drift caused by the magnetic resonance system on the phase difference map comprises: selecting a plurality of thermal reference points, by subtracting the average phase difference of the thermal reference points from each phase difference map; The steps to cancel the phase drift caused by the magnetic resonance system on the temperature difference map include: Correction is made by subtracting the average temperature difference at the thermal reference point from the temperature difference map. 6. The method according to any one of claims 1 to 5, further comprising a step of magnetic susceptibility correction, wherein the step of magnetic susceptibility correction is performed on a phase difference map or a temperature difference map; The steps to perform susceptibility correction on the temperature difference map include: A first temperature map is obtained according to the reference phase difference map, and a corresponding second temperature map is obtained according to the calibrated phase difference map, Determine whether the absolute value of the difference between the temperature value corresponding to each pixel in the second temperature map and the temperature value corresponding to the corresponding pixel in the first temperature map exceeds a preset temperature threshold; The temperature value corresponding to the corresponding pixel in the second temperature map is corrected; The steps for performing susceptibility correction on the phase difference map include: Determine whether the absolute value of the difference between the phase difference value corresponding to each pixel in the calibrated phase difference map and the phase difference value corresponding to the corresponding pixel in the reference phase map exceeds a preset phase difference threshold, and if so, the Correct the phase difference corresponding to the corresponding pixel in the calibration phase difference diagram. 7. The method according to any one of claims 1 to 6, further comprising the step of correcting the phase error caused by the movement performed on the phase difference map or the temperature difference map; The steps to correct motion-induced phase errors on the phase difference map include: A linear least squares fit at each pixel of the phase difference map removes the motion-induced phase error; The steps to correct motion-induced phase errors on the temperature difference map include: Motion-induced phase errors were removed with a linear least squares fit at each pixel of the temperature difference map. 8. The method according to any one of claims 1 to 7, wherein the obtaining a temperature map at a corresponding moment according to the temperature difference map comprises: Calculate the temperature difference using the reference phase difference map and the calibrated phase difference map, and perform weighting to obtain a temperature map of the object to be measured; or A weighted average of the reference phase difference map and the calibrated phase difference map is used to obtain an average temperature difference, and a temperature map of the object to be measured is calculated according to the average temperature difference. 9. A magnetic resonance temperature imaging system, comprising: a data transmission module, which is configured to receive the magnetic resonance sequence image and judge the integrity of the image; a temperature calculation module, which is configured to select the sequence, calculate the phase difference, calibrate the phase difference, and calculate the temperature; A temperature display module, which is set to display the temperature in the form of a pseudo-color map or an isotherm; Wherein, the time for the system to perform a complete calculation does not exceed 1 s. 10 . A storage medium, wherein a program code is stored on the storage medium, and when the program code is executed, the magnetic resonance temperature imaging method according to any one of claims 1-8 is implemented. 11 .

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