A magnetic resonance temperature measurement method to reduce motion errors

Abstract

The present application discloses a magnetic resonance temperature measurement method for reducing motion errors, which comprises: acquiring magnetic resonance imaging data of a target part using a gradient echo sequence containing i different echo times, where i is a positive integer greater than or equal to 2, the magnetic resonance imaging data comprising a phase map corresponding to the echo time, selecting at least two groups of phase maps corresponding to different echo times at different moments to obtain phase difference maps or temperature difference maps corresponding to the different moments; using the at least two groups of phase difference maps or temperature difference maps corresponding to different echo times to perform linear least squares fitting at each pixel to remove phase errors caused by motion; and obtaining temperature maps corresponding to different moments based on the temperature difference map.

Description

Technical Field

[0001] The present application relates to the field of medical imaging, and more specifically, to a magnetic resonance temperature measurement method for reducing motion errors. Background Art

[0002] Magnetic resonance thermometry can monitor temperature during ablation therapy. However, heartbeat and cerebrospinal fluid (CSF) movement in the brain can cause errors. Interscan motion is a cause of error in temperature maps measured using proton resonance frequency shift-based thermometry. The size and phase signals of CSF are often altered by normal dynamic CSF movement in pulsed gradient echo sequences, confounding temperature estimates. CSF movement can also cause pixel shifts around the ventricles, leading to errors in phase contrast images. To eliminate temperature image errors caused by motion near the cavity, the present invention provides a method for eliminating motion errors. Summary of the Invention

[0003] To solve the above technical problems, the present application provides a magnetic resonance temperature measurement method that reduces motion errors.

[0004] A magnetic resonance temperature measurement method and related device are used to reduce the error of a target temperature image finally obtained and improve the accuracy of the temperature image.

[0005] In a first aspect, the present invention provides a magnetic resonance temperature measurement method for reducing motion errors, comprising:

[0006] A gradient echo sequence with i different echo times is used to acquire magnetic resonance imaging data of a target part, where i is a positive integer greater than or equal to 2. The magnetic resonance imaging data includes a phase map (TE i ),

[0007] Selecting at least two groups of phase images corresponding to different echo times at different moments to obtain phase difference images or temperature difference images corresponding to the different moments;

[0008] Using at least two sets of phase difference maps or temperature difference maps corresponding to different echo times to perform linear least square fitting at each pixel to remove phase errors caused by motion;

[0009] A temperature map corresponding to different moments is obtained according to the temperature difference map.

[0010] Among them, the error value of the phase difference map or the temperature difference map is obtained by linear least square fitting.

[0011] In the present invention, the temperature difference of the pixel is calculated based on the fact that the temperature difference is proportional to the phase difference, that is, the temperature difference and the phase difference can be converted into each other.

[0012] Optionally, the method of the present invention further comprises performing weighted processing on the temperature maps corresponding to different echo times to obtain a weighted temperature map.

[0013] Optionally, the method of the present invention further includes the step of eliminating systematic errors of the magnetic resonance imaging system, which is performed on a phase difference image or a temperature change image. Furthermore, the step of eliminating systematic errors of the magnetic resonance imaging system selects several regions with stable physical temperatures and uniform tissue as thermal reference points, and performs phase drift correction by subtracting the average phase difference of the thermal reference points from each phase difference image or subtracting the average temperature change of the thermal reference points from the temperature change image.

[0014] In a second aspect, the present invention provides a storage medium having program code stored thereon, which implements the magnetic resonance temperature measurement method of the present invention when the program code is executed.

[0015] In a third aspect, the present invention provides a thermometer, characterized in that it includes: a host, the host includes a processor and is capable of receiving magnetic resonance imaging data, the processor is loaded with program code, and the program code is used to execute the magnetic resonance temperature measurement method of the present invention.

[0016] In a fourth aspect, the present invention provides a laser interstitial thermal therapy device, characterized in that it includes the thermometer described in the third aspect.

[0017] In a fourth aspect, the present invention provides a magnetic resonance temperature measurement system, comprising:

[0018] Phase map module, using a gradient echo sequence with i different echo times to acquire magnetic resonance imaging data of the target part, i is a positive integer greater than or equal to 2, and the magnetic resonance imaging data includes a phase map (TE corresponding to the echo time) i ),

[0019] A phase difference or temperature difference generating module, configured to select at least two groups of phase images corresponding to different echo times at different moments to obtain phase difference images or temperature difference images corresponding to the different moments;

[0020] An image correction module, configured to remove phase errors caused by motion by performing a linear least squares fit at each pixel using at least two sets of phase difference maps or temperature difference maps corresponding to different echo times;

[0021] The temperature image module obtains temperature images corresponding to different moments according to the calibrated temperature difference image. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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 drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0023] Figure 1 Amplitude, phase and temperature maps obtained in the body environment;

[0024] Figure 2 A schematic flow chart of a magnetic resonance temperature measurement method provided in one embodiment of the present application;

[0025] Figure 3 The motion error correction result of a single pixel in an in vivo experiment provided in one embodiment of the present application;

[0026] Figure 4 Representative temperature diagram of a dog in an in vivo experiment provided as one example of the present application; DETAILED DESCRIPTION

[0027] Magnetic resonance thermometry can be used to guide various energy-delivery treatments, such as laser interstitial thermal therapy, focused ultrasound therapy, and radiofrequency ablation, monitoring target tissue temperature and therapeutic efficacy. The inventors discovered through research that one of the primary sources of error in MRI thermometry is phase error caused by motion.

[0028] Thermometry based on proton resonance frequency shift is based on the following principle: the resonance frequency of hydrogen protons changes with the temperature of water molecules. For water-containing tissues, the change of the local magnetic field with temperature can be described as:

[0029]

[0030] Wherein, α is the proton resonance frequency coefficient that changes with temperature, which is 0.008-0.015ppm / °C in the present invention. The corresponding resonance frequency change of water protons affected by temperature can be expressed as:

[0031] Δf=αγB0·ΔT; (2)

[0032] Where ΔT represents the temperature change, Δf represents the resonant frequency change, γ represents the gyromagnetic ratio, and B0 represents the static magnetic field strength.

[0033] The change in resonant frequency due to temperature change can be observed in the phase of complex magnetic resonance imaging. For a given gradient echo sequence interval TE, the relative temperature change ΔT can be calculated based on the phase difference Δφ, which can be expressed as:

[0034]

[0035] A gradient echo sequence is a sequence used in temperature measurement methods based on proton resonance frequency shift, and includes sequences corresponding to different echo times. For example, it may include an echo sequence corresponding to i echo times, where i is a positive integer not less than 2. According to formula (3), the longer the echo time in a gradient echo sequence, the greater the phase difference may be due to the same temperature change, and higher temperature sensitivity can be achieved.

[0036] refer to Figure 1 , showing various common problems existing in the prior art with temperature images obtained using an echo sequence with a single echo time, the phases of the first to fourth echoes obtained in vivo using a gradient echo sequence with 4 different echo times used in an embodiment of the present application (first row), and the temperature map calculated according to each TE (echo time) setting using a traditional PRF algorithm (second row). Specifically, due to the movement of cerebrospinal fluid (CSF) in the brain, inter-scan motion is a problem in temperature maps measured by thermometry based on proton resonance frequency shift. The amplitude and phase signals of the cerebrospinal fluid are often changed on a pulse gradient echo sequence by the normal dynamic movement of the cerebrospinal fluid, which may confuse temperature estimates. Cerebrospinal fluid movement may also cause pixels in and around the ventricles to move, resulting in errors in the phase difference map. As Figure 1 As shown in Figure 3, the in vivo temperature map shows false hyperthermia within the third ventricle due to CSF ​​movement. The temperature error is more pronounced on pulsed gradient echo sequences with shorter echo times because, according to Equation (3), they are less tolerant to the magnitude of the phase shift introduced by CSF flow.

[0037] In order to eliminate the error caused by cerebrospinal fluid movement, an embodiment of the present application provides a magnetic resonance temperature measurement method, including:

[0038] A gradient echo sequence with i different echo times is used to acquire magnetic resonance imaging data of a target part, where i is a positive integer greater than or equal to 2. The magnetic resonance imaging data includes a phase map (TE i ),

[0039] Selecting at least two groups of phase images corresponding to different echo times at different moments to obtain phase difference images or temperature difference images corresponding to the different moments;

[0040] Using at least two sets of phase difference maps or temperature difference maps corresponding to different echo times to perform linear least square fitting at each pixel to remove phase errors caused by motion;

[0041] A temperature map corresponding to different moments is obtained according to the temperature difference map.

[0042] Specifically, refer to Figure 2 To explain:

[0043] S101: Acquire magnetic resonance imaging data of a target part using a gradient echo sequence with i different echo times, where i is a positive integer greater than or equal to 2, and the magnetic resonance imaging data includes a phase map (TE i )

[0044] In step S101 , the minimum and maximum values ​​of the echo time in the gradient echo sequence can be determined according to actual needs. For example, for head imaging, the optional echo time range of the gradient time sequence is 3 to 30 ms.

[0045] The i different echo times in the gradient echo sequence may be obtained by reading or receiving from a server or other storage device, or by obtaining them in real time according to the settings of the staff. This application does not limit the specific method of obtaining multiple gradient echo sequences, which depends on the actual situation.

[0046] i different echo times refers to at least two different echo times, for example, a gradient echo sequence with (6ms, 18ms), (6ms, 24ms), (12ms, 18ms), (6ms, 12ms, 24ms), (6ms, 18ms, 24ms), (6ms, 12ms, 18ms, 24ms), (6ms, 12ms, 12ms, 24ms), (6ms, 18ms, 18ms, 24ms), etc. as echo times.

[0047] S102: Select at least two groups of phase images corresponding to different echo times at different moments to obtain phase difference images or temperature difference images corresponding to the different moments;

[0048] The phase difference image at the reference time is obtained by subtracting the phase image at any of the different time points from the phase image at the reference time point, wherein the reference time point is any time point before energy (e.g., thermal energy, light energy, radiofrequency ablation, cryoablation) is transmitted to the target tissue, preferably a time point shortly before energy transmission, e.g., a time point immediately before energy transmission;

[0049] Calculating the temperature difference of the pixel based on the temperature difference being proportional to the phase difference;

[0050] S103: using at least two sets of phase difference maps or temperature difference maps corresponding to different echo times to perform linear least square fitting at each pixel to remove phase errors caused by motion;

[0051] The error value of the phase difference map or the temperature difference map is obtained by linear least squares fitting.

[0052] S104: obtaining temperature maps corresponding to different moments according to the temperature difference map, wherein the temperature map is obtained by adding the temperature difference to the temperature of the thermal reference point at the reference moment.

[0053] Optionally, between step S102 and step S103, or between step S103 and step S104, a step of eliminating systematic errors of the magnetic resonance imaging system may be included, and this step is performed on the phase difference image or the temperature change image. Furthermore, the step of eliminating systematic errors of the magnetic resonance imaging system selects several regions with stable physical temperatures and uniform tissue as thermal reference points, and performs phase drift correction by subtracting the average phase difference of the thermal reference points from each phase difference image or subtracting the average temperature change of the thermal reference points from the temperature change image.

[0054] Optionally, the method of the present invention may further include step S105: performing weighted processing on the temperature maps corresponding to the echo sequences at different echo times to obtain a weighted temperature map. The weighting may be performed using various weighting methods, such as average weighting, or the temperature map corresponding to a single echo time may be weighted, i.e., the weighting coefficient of the temperature map is 1, while the weighting coefficients of the temperature maps at other phases are 0.

[0055] After step S104, the following steps may also be included:

[0056] S1041: Perform multiple interpolation processes on the target temperature image, and calculate the ablation area boundary using the target temperature image after the interpolation process.

[0057] The purpose of performing multiple interpolation processes on the target temperature image is to obtain a smoother ablation area boundary. The specific number of interpolation processes can be 2 or 3 times.

[0058] The magnetic resonance temperature measurement method provided in the embodiment of the present application is verified by combining specific experiments below.

[0059] Adult Doberman Pinschers received laser interstitial thermal therapy. Heating was monitored on a 3T MR scanner (Ingenia, Philips Healthcare, Best, The Netherlands) using a 32-line receive head coil using a multi-echo time-of-flight gradient echo sequence (multi-echo rapid gradient echo), flip angle = 30°, TE = 6 / 12 / 18 / 24 ms, TR = 22 ms, matrix = 176 × 176, and field of view = 200 × 200 mm. 2 , slice thickness = 5 mm, 3 s / image.

[0060] refer to Figure 3The phase difference (first row) and temperature (second row) in one pixel are shown as a function of time without (left) and with (right) the motion error correction of the present invention. For an echo time of 6 ms, the phase error Δφ(x,y) bias A large temperature deviation will be introduced, but after linear least squares fitting, the errors of each echo time can be correctly eliminated.

[0061] Figure 4 Representative temperature maps of dogs in in vivo experiments are shown. It should be noted that the ablation area is located close to the third ventricle and lateral ventricle. 100 frames (3s / frame) of images acquired during laser ablation were selected and superimposed on the T2w magnetic resonance thermography after ablation. From top to bottom are temperature images calculated by the prior art algorithm based on single echo time (TE) data (TE=6ms and TE=24ms), and temperature images calculated using the algorithm proposed in the present invention based on the joint TE echo sequence. The first row (TE=6ms) shows pseudo-high temperatures in the third lateral ventricle and lateral ventricle, indicating that the short TE calculated temperature is severely affected by CSF flow artifacts. The CSF-induced artifacts in the third ventricle (indicated by white arrows) are still present in the second row (TE=24ms), but are well suppressed by the magnetic resonance thermometry method proposed in the present invention (third row).

[0062] The proposed method has been shown to exhibit excellent cerebrospinal fluid (CSF) motion error suppression and can provide accurate temperature measurements within and around the ventricles. Compensating for errors caused by CSF motion is clinically important for laser interstitial thermotherapy of periventricular brain lesions. Furthermore, the proposed algorithm is online-compatible and does not require iterative computation, making it well-suited for magnetic resonance thermography, where near-real-time temperature maps are required.

[0063] The following describes a magnetic resonance temperature measurement system provided in an embodiment of the present application. The magnetic resonance temperature measurement system described below can be referenced in correspondence with the magnetic resonance temperature measurement method described above.

[0064] Accordingly, an embodiment of the present application further provides a magnetic resonance temperature measurement system, comprising:

[0065] Phase map module, using a gradient echo sequence with i different echo times to acquire magnetic resonance imaging data of the target part, i is a positive integer greater than or equal to 2, and the magnetic resonance imaging data includes a phase map (TE corresponding to the echo time) i ),

[0066] A phase difference or temperature difference generating module, configured to select at least two groups of phase images corresponding to different echo times at different moments to obtain phase difference images or temperature difference images corresponding to the different moments;

[0067] An image correction module, configured to remove phase errors caused by motion by performing a linear least squares fit at each pixel using at least two sets of phase difference maps or temperature difference maps corresponding to different echo times;

[0068] The temperature image module obtains temperature images corresponding to different moments according to the calibrated temperature difference image.

[0069] Accordingly, an embodiment of the present application provides a storage medium having program code stored thereon, and when the program code is executed, the magnetic resonance temperature measurement method of the present invention is implemented.

[0070] The present invention provides a thermometer, which comprises: a host, the host including a processor and capable of receiving magnetic resonance imaging data, the processor being loaded with program code, and the program code being used to execute the magnetic resonance temperature measurement method of the present invention.

[0071] The present invention also provides a laser interstitial thermal therapy device, characterized in that it comprises the temperature measuring device of the present invention.

[0072] Furthermore, the magnetic resonance temperature measurement method of the present invention is not a retrospective algorithm or an iterative algorithm, has a small amount of computation, can provide an almost real-time target temperature image, and has a high reference value.

[0073] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0074] The features described in the embodiments of this specification can be replaced or combined with each other. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referenced to each other.

[0075] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A magnetic resonance temperature measurement method for reducing motion errors, characterized in that: include: A gradient echo sequence with i different echo times is used to acquire magnetic resonance imaging data of a target portion, where i is a positive integer greater than or equal to 2, and the magnetic resonance imaging data includes a phase map (TE) corresponding to the echo time. i ), Selecting at least two groups of phase images corresponding to different echo times at different moments to obtain phase difference images or temperature difference images corresponding to the different moments; Using a linear least squares fit at each pixel of at least two sets of phase difference maps or temperature difference maps corresponding to different echo times to remove the phase error caused by motion, the linear least squares fit obtaining an error value of the phase difference map or the temperature difference map; The temperature maps corresponding to different moments are obtained according to the calibrated temperature difference map.

2. The method according to claim 1, characterized in that The temperature difference of the pixels is calculated based on the fact that the temperature difference is proportional to the phase difference.

3. The method according to claim 1, characterized in that The method further includes performing weighted processing on the temperature maps corresponding to different echo times to obtain a weighted temperature map.

4. The method according to claim 1, wherein The method further includes a step of eliminating a systematic error of the magnetic resonance system, which is performed on a phase difference map or a temperature change map.

5. The method according to claim 4, characterized in that The step of eliminating the systematic error of the magnetic resonance system selects several areas with stable physical temperature and uniform tissue as thermal reference points, and performs phase drift correction by subtracting the average phase difference of the thermal reference points from each phase difference image or subtracting the average temperature change of the thermal reference points from the temperature change map.

6. A storage medium, characterized in that The storage medium stores program code, and when the program code is executed, the magnetic resonance temperature measurement method according to any one of claims 1 to 5 is implemented.

7. A thermometer, characterized in that: include: A host, comprising a processor and capable of receiving magnetic resonance imaging data, wherein the processor is loaded with a program code, and the program code is used to execute the method according to any one of claims 1 to 5.

8. A magnetic resonance temperature measurement system comprising: The phase map module acquires magnetic resonance imaging data of the target part using a gradient echo sequence with i different echo times, where i is a positive integer greater than or equal to 2, and the magnetic resonance imaging data includes a phase map (TEi) corresponding to the echo time. A phase difference or temperature difference generating module, configured to select at least two groups of phase images corresponding to different echo times at different moments to obtain phase difference images or temperature difference images corresponding to the different moments; An image correction module, configured to remove phase errors caused by motion by performing a linear least squares fit at each pixel using at least two sets of phase difference maps or temperature difference maps corresponding to different echo times; The temperature image module obtains temperature images corresponding to different moments according to the calibrated temperature difference image.

9. A laser interstitial thermal therapy device, characterized in that: It comprises the thermometer according to claim 7 or the magnetic resonance temperature measurement system according to claim 8.

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