CN114820838B - Magnetic resonance temperature imaging method for correcting magnetic susceptibility error - Google Patents
Magnetic resonance temperature imaging method for correcting magnetic susceptibility error Download PDFInfo
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- 238000003384 imaging method Methods 0.000 title claims abstract description 16
- 238000010586 diagram Methods 0.000 claims abstract description 24
- 238000010587 phase diagram Methods 0.000 claims abstract description 24
- 238000000034 method Methods 0.000 claims description 18
- 206010020843 Hyperthermia Diseases 0.000 claims description 3
- 230000036031 hyperthermia Effects 0.000 claims description 3
- 230000035945 sensitivity Effects 0.000 description 5
- 238000012937 correction Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 238000004093 laser heating Methods 0.000 description 3
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 description 3
- 238000011282 treatment Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 238000002679 ablation Methods 0.000 description 2
- 238000009529 body temperature measurement Methods 0.000 description 2
- 238000001727 in vivo Methods 0.000 description 2
- 238000000015 thermotherapy Methods 0.000 description 2
- 238000002604 ultrasonography Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 206010027146 Melanoderma Diseases 0.000 description 1
- 238000011298 ablation treatment Methods 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 210000004556 brain Anatomy 0.000 description 1
- 210000005013 brain tissue Anatomy 0.000 description 1
- 238000002059 diagnostic imaging Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000002592 echocardiography Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 1
- 238000002595 magnetic resonance imaging Methods 0.000 description 1
- 230000005415 magnetization Effects 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 238000007674 radiofrequency ablation Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012552 review Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 230000001225 therapeutic effect Effects 0.000 description 1
- 238000002560 therapeutic procedure Methods 0.000 description 1
- 230000003685 thermal hair damage Effects 0.000 description 1
- 238000001931 thermography Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T11/00—2D [Two Dimensional] image generation
- G06T11/003—Reconstruction from projections, e.g. tomography
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The application discloses a magnetic resonance temperature imaging method for correcting susceptibility errors, which uses a gradient echo sequence containing i different echo times to acquire magnetic resonance image data of a target part, selects at least one phase diagram corresponding to the echo time as a first group of phase diagrams, and selects other phase diagrams corresponding to the echo time as a second group of phase diagrams; calculating a first group of phase difference images or temperature difference images by using the first group of phase images, and calculating a second group of phase difference images or temperature difference images by using the second group of phase images; comparing whether the absolute value of the difference value between the phase difference or the temperature difference in the second group of phase difference diagrams or the temperature difference diagrams in the corresponding pixels and the phase difference or the temperature difference in the first group of phase difference diagrams or the temperature difference diagrams exceeds a preset threshold value, and if the absolute value exceeds the preset threshold value, calibrating the phase difference or the temperature difference in the second group of phase difference diagrams or the temperature difference diagrams.
Description
Technical Field
The present application relates to the field of medical imaging, and more particularly to a magnetic resonance temperature imaging method for correcting susceptibility errors.
Background
The magnetic resonance temperature imaging (Magnetic Resonance Temperature Imaging, MRTI) is used for monitoring the temperature change of the target part, and has very important effect on thermal ablation treatment (such as laser interstitial thermotherapy, confocal ultrasound and other minimally invasive or noninvasive operation), however, in the existing method, along with the rapid temperature rise of the part to be ablated, the magnetic susceptibility of the part can be changed rapidly, and the magnetic susceptibility error is caused, so that the temperature of the central part of ablation cannot be acquired or a larger error occurs, and how to eliminate the magnetic susceptibility error caused by temperature rise is a problem to be solved.
Disclosure of Invention
To solve the above technical problem, in a first aspect, the present application provides a magnetic resonance temperature imaging method for correcting a susceptibility error, which includes:
acquiring magnetic resonance image data of a target region using a gradient echo sequence comprising i different echo times, i being a positive integer greater than or equal to 2, the magnetic resonance image data comprising a phase map corresponding to the echo times,
selecting at least one phase diagram corresponding to echo time as a first group of phase diagrams, and selecting the phase diagrams corresponding to other echo time as a second group of phase diagrams;
calculating a first group of phase difference images or temperature difference images by using the first group of phase images, and calculating a second group of phase difference images or temperature difference images by using the second group of phase images;
comparing whether the absolute value of the difference value between the phase difference or the temperature difference in the second group of phase difference diagrams or the temperature difference diagrams in the corresponding pixels and the phase difference or the temperature difference in the first group of phase difference diagrams or the temperature difference diagrams exceeds a preset threshold value, and if the absolute value exceeds the preset threshold value, calibrating the phase difference or the temperature difference in the second group of phase difference diagrams or the temperature difference diagrams.
Obtaining a first temperature map by using the first group of phase difference maps or the temperature difference maps, obtaining a second temperature map by using the second group of phase difference maps or the temperature difference maps, and then calculating the temperature map.
The threshold value can be freely selected, for example, the threshold value used can be 1, 2, 3, 4, 5, 6, 7, 8 or 9, etc.; there are various ways of correcting, for example, the temperature value of the first temperature map may be used instead of the temperature value of the second temperature map, or the temperature value of an adjacent pixel in the second temperature map may be used instead of the temperature value of the pixel in the second temperature map, or an approximate temperature may be fitted based on the temperature values of the adjacent pixels and the temperature value of the first temperature map instead of the temperature value of the second temperature map.
Optionally, in the method of the present invention, calculating the temperature map includes the step of weighting at least one first temperature map and at least one second temperature map by weighting values on different temperature maps on pixels to form a new temperature map; further, the weighting may be a weighting of various weights, such as an average weighting, or may be a temperature map corresponding to a single echo time, that is, the weighting coefficient of the temperature map is 1, and the weighting coefficients of other phase temperature maps are 0.
Optionally, in the method of the present invention, at least one corresponding echo time in the first set of phase diagrams does not exceed 18ms,17ms,16ms,15ms,14ms,13ms,12ms,11ms,10ms,9ms, 8ms,7ms,6ms,5ms or 4ms. .
Optionally, in the method of the present invention, the echo time corresponding to the first set of phase diagrams is smaller than the echo time corresponding to the second set of phase diagrams compared with the first set of phase diagrams. Further, the first set of phase maps only comprises the phase map corresponding to the minimum echo time.
Optionally, the method of the present invention further comprises the step of correcting the motion induced phase error by removing the motion induced phase error by using a linear least squares fit of at least two sets of phase difference maps or temperature difference maps corresponding to different echo times at each pixel.
In a second aspect, the present invention also provides a storage medium, wherein the storage medium has stored thereon program code, which when executed, implements the magnetic resonance temperature imaging method of the present invention.
In a third aspect, the present invention also provides a temperature imager, including: a host computer comprising a processor and being capable of receiving magnetic resonance image data, the processor being loaded with program code for performing the method of the invention.
In a fourth aspect, the present invention also provides a laser hyperthermia system comprising the temperature imager of the third aspect, capable of performing the method of the present invention.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present application, and that other drawings may be obtained according to the provided drawings without inventive effort to a person skilled in the art.
FIG. 1 is an amplitude and phase image obtained in an ex vivo environment;
FIG. 2 is a temperature plot after providing susceptibility correction according to one embodiment of the present application;
fig. 3 is a comparison of susceptibility correction before and after correction for the same pixel position according to another embodiment of the present application.
Fig. 4 provides a comparison of temperature maps for different frames for yet another embodiment of the present application, showing temperature maps for different processing methods and stages.
Detailed Description
The magnetic resonance temperature imaging can guide various energy delivery type treatment means, such as laser interstitial thermotherapy, focused ultrasound therapy, radio frequency ablation and the like, to monitor the temperature of target tissues and the treatment effect. The inventor finds that the main sources of errors in the acquired temperature map are phase errors caused by phase unwrapping dislocation, magnetic susceptibility errors and phase errors caused by motion through research. As the input energy dose changes, the susceptibility distortion can lead to a decrease in image amplitude and corresponding errors in image phase, thereby destroying the heating center and its surrounding reconstructed temperature map. Errors in reconstructing the temperature map may lead to erroneous estimates of the ablation region, which may lead to variations in the therapeutic effect and thermal damage to critical tissue. Thus, accurate temperature imaging is critical to the effectiveness and safety of the treatment, especially when applied to the ablated region of brain tissue.
The temperature measurement method based on proton resonance frequency shift is based on the following principle: the resonant frequency of hydrogen protons varies with the temperature in water molecules. For aqueous tissue, the local magnetic field variation with temperature can be described as:
where α is the proton resonance frequency coefficient as a function of temperature. The corresponding resonance frequency change of the temperature-affected water protons can be expressed as:
Δf＝αγB 0 ·ΔT； (2)
wherein DeltaT represents temperature change, deltaf represents resonance frequency change, gamma represents gyromagnetic ratio, and B 0 Representing the static magnetic field strength.
Changes in resonance frequency due to temperature changes can be observed in the phases of complex magnetic resonance imaging. For a given interval TE of the gradient echo sequence, the relative temperature change Δt can be calculated from the phase difference ΔΦ, which equation can be expressed as:
the gradient recall echo pulse sequence, which is abbreviated as gradient echo sequence, is the most commonly used sequence in the temperature measurement method based on proton resonance frequency displacement. From equation (3), the longer the gradient echo sequence, the greater the phase difference may be caused by the same temperature change, indicating that a higher temperature sensitivity may be obtained.
In fig. 1, as the echo time of the gradient echo sequence increases, both the phase contrast and the phase wrapping increase, which indicates that the temperature sensitivity is higher and the phase unwrapping procedure is more in the later echo time. The amplitude, phase and temperature of the first to fourth echoes obtained in (ex vivo, pig brain) by the gradient echo sequence containing 4 different echo times used in the examples of the present application. Using conventional algorithms to calculate a temperature map (bottom row) from each TE (echo time) setting, intense laser heating can result in signal loss due to changes in susceptibility, which in turn can lead to phase and temperature anomalies for pixels around the heating center.
The local magnetic field of the water protons should also take into account the magnetic susceptibility x 0 Equation (1) becomes:
wherein,,
indicating the local magnetic field change caused by susceptibility.
The inventors have found that laser heating can cause significant magnetization artifacts in GRE imaging around the laser tip. Referring to fig. 1, a heating center (as indicated by an arrow in fig. 1) in which temperature is abruptly changed shows a serious signal loss on the order of a long echo time.
Susceptibility artifacts caused by laser heating, in particular in images corresponding to gradient echo sequences of longer echo times, are important causes of errors. Referring to fig. 1, in an ex vivo or in vivo experiment, the phase error around the heating center translates into a pseudo low temperature on the magnetic resonance thermal imaging. Theoretically, in the imaging process, gradient pulse sequences with as short echo times as possible are used together to minimize susceptibility artifacts. However, a longer echo time gradient pulse sequence can provide better temperature sensitivity and signal-to-noise ratio, and how to achieve coordination of sensitivity and signal-to-noise ratio is a problem to be solved.
In order to achieve the effects of temperature sensitivity, signal-to-noise ratio and low error, the embodiment of the application provides a magnetic resonance temperature imaging method for correcting magnetic susceptibility error, which comprises the following steps:
acquiring magnetic resonance image data of a target region using a gradient echo sequence comprising i different echo times, i being a positive integer greater than or equal to 2, the magnetic resonance image data comprising a phase map corresponding to the echo times,
selecting at least one phase diagram corresponding to echo time as a first group of phase diagrams, and selecting the phase diagrams corresponding to other echo time as a second group of phase diagrams;
calculating a first group of phase difference images or temperature difference images by using the first group of phase images, and calculating a second group of phase difference images or temperature difference images by using the second group of phase images;
comparing whether the absolute value of the difference value between the phase difference or the temperature difference in the second group of phase difference diagrams or the temperature difference diagrams in the corresponding pixels and the phase difference or the temperature difference in the first group of phase difference diagrams or the temperature difference diagrams exceeds a preset threshold value, and if the absolute value exceeds the preset threshold value, calibrating the phase difference or the temperature difference in the second group of phase difference diagrams or the temperature difference diagrams.
Obtaining a first temperature map by using the first group of phase difference maps or the temperature difference maps, obtaining a second temperature map by using the second group of phase difference maps or the temperature difference maps, and then calculating the temperature map.
The threshold may be selected according to actual needs, for example, in the temperature difference map, the used threshold may be 1, 2, 3, 4, 5, 6, 7, 8, or 9, and the phase difference or the temperature difference in the second group of phase difference maps or temperature difference maps may be calibrated in various manners, for example, the temperature value of the first temperature map may be used to replace the temperature value of the second temperature map, an approximate temperature may be fitted to replace the temperature value of the second temperature map based on the temperature value of the adjacent pixel and the temperature value of the first temperature map, or the temperature value of the adjacent pixel may be used to replace or estimate.
The magnetic resonance temperature imaging method provided in the embodiments of the present application is verified in conjunction with specific experiments.
Du Bingou in vivo experiments have been approved by the institutional review board of the Qinghai university. Adult Du Bingou received laser interstitial hyperthermia. The heating process was monitored on a 3T MR scanner (Ingenia, philips Healthcare, best, netherlands) with 32 receiver head coils using a multi-echo time gradient echo sequence, flip angle = 30 °, TE = 6/12/18/24ms, tr = 22ms, matrix = 176 x 176, fov = 200 x200mm 2 Slice thickness = 5mm,3 s/image. And using a sequence corresponding to 6ms as a first group of sequences, using sequences corresponding to the rest echo time as a second group of sequences, and using the numerical value of the first group of temperature maps to replace the numerical value of the second group of temperature maps in the pixel when the absolute value of the difference value between the phase difference in the second group of temperature maps and the temperature difference of the first group of temperature maps exceeds 5 ℃.
The experimental results are shown in fig. 2 to 4.
Fig. 2 shows a temperature map of one section of the whole, eliminating the abnormal temperature of the heating center (black spot occurrence) caused by the abrupt change of magnetic susceptibility.
Fig. 3 is a graph of temperature versus time for one pixel, where the susceptibility errors in the sequence of 12, 18, 24ms echo times are corrected using the sequence of 6ms echo times.
A comparison of the results of the different methods is shown in fig. 4, the first row of results shows a conventional unwrapped temperature map, the different frames represent different positions, the second row is the unwrapped corrected temperature result, and the third row is the remembered after the susceptibility correction of the present invention, it can be seen that the temperature distortion for the center has been corrected; the fourth line is the result of weighted averaging of temperature maps obtained using a sequence of different echo times, with the transition of the temperature maps being smoother.
Features described in the embodiments in this specification may be replaced or combined with each other, and each embodiment is mainly described in the differences from the other embodiments, and identical and similar parts between the embodiments are all enough to be referred to each other.
The previous description of the disclosed embodiments is provided to enable 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 applied to other embodiments without departing from the spirit or scope of the application. Thus, the present 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 (8)
1. A magnetic resonance temperature imaging method for correcting susceptibility errors, comprising:
acquiring magnetic resonance image data of a target region using a gradient echo sequence comprising i different echo times, i being a positive integer greater than or equal to 2, the magnetic resonance image data comprising a phase map corresponding to the echo times,
selecting at least one phase diagram corresponding to echo time as a first group of phase diagrams, wherein phase diagrams corresponding to other echo time are second group of phase diagrams, the echo time corresponding to at least one of the first group of phase diagrams is not more than 18ms, and the echo time corresponding to the first group of phase diagrams is smaller than the echo time corresponding to the second group of phase diagrams compared with the first group of phase diagrams;
calculating a first group of phase difference images or temperature difference images by using the first group of phase images, and calculating a second group of phase difference images or temperature difference images by using the second group of phase images;
comparing whether the absolute value of the difference value between the phase difference or the temperature difference in the second group of phase difference diagrams or the temperature difference diagrams in the corresponding pixels and the phase difference or the temperature difference in the first group of phase difference diagrams or the temperature difference diagrams exceeds a preset threshold value, and if the absolute value exceeds the preset threshold value, calibrating the phase difference or the temperature difference in the second group of phase difference diagrams or the temperature difference diagrams;
obtaining a first temperature map by using the first group of phase difference maps or the temperature difference maps, obtaining a second temperature map by using the second group of phase difference maps or the temperature difference maps, and then calculating the temperature map.
2. The method of claim 1, wherein calculating the temperature map includes the step of weighting at least one first temperature map and at least one second temperature map by weighting values on different temperature maps on pixels to form a new temperature map.
3. The method of claim 2, wherein the weighting is an average weighting.
4. The method of claim 1, wherein the first set of phase maps comprises only the phase map corresponding to the minimum echo time.
5. The method according to any one of claims 1 to 4, further comprising the step of correcting the motion induced phase error by removing the motion induced phase error using a linear least squares fit of at least two sets of phase difference maps or temperature difference maps corresponding to different echo times at each pixel.
6. A storage medium having stored thereon program code which when executed implements the magnetic resonance temperature imaging method of any one of claims 1 to 5.
7. A temperature imager, comprising: a host computer comprising a processor and being capable of receiving magnetic resonance image data, the processor being loaded with program code for performing the method of any one of claims 1 to 5.
8. A laser hyperthermia system comprising the temperature imager of claim 7, capable of performing the method of any of claims 1-5.
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