WO2020207159A1 - 一种高质量磁共振图像合成方法 - Google Patents

一种高质量磁共振图像合成方法 Download PDF

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WO2020207159A1
WO2020207159A1 PCT/CN2020/077916 CN2020077916W WO2020207159A1 WO 2020207159 A1 WO2020207159 A1 WO 2020207159A1 CN 2020077916 W CN2020077916 W CN 2020077916W WO 2020207159 A1 WO2020207159 A1 WO 2020207159A1
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magnetic resonance
tissue
signal
negative
resonance image
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何宏建
李军
曹笑之
丁秋萍
钟健晖
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浙江大学
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/5608—Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/50—NMR imaging systems based on the determination of relaxation times, e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/5602—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse

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  • the invention relates to the field of magnetic resonance imaging technology and image processing, in particular to a high-quality magnetic resonance image synthesis method.
  • Synthetic magnetic resonance imaging refers to a method that uses quantitative magnetic resonance scanning analysis to obtain the T1, T2, and PD quantitative tissue parameters of each voxel, and then uses magnetic resonance signal formulas to generate various common magnetic resonance images with different contrasts.
  • the formula (1) represents the signal formula of a spin echo (Spin Echo, SE) sequence.
  • S represents magnetic resonance signal
  • PD Proton Density
  • T1 represents longitudinal relaxation time
  • T2 represents transverse relaxation time
  • TR (Repetition Time) represents scan repetition time
  • TE (Echo Time) represents Echo time.
  • PD, T1, T2 are MRI quantitative tissue parameters, which can be obtained by quantitative MRI scanning analysis.
  • the PD, T1, T2 of each voxel can be obtained by quantitative magnetic resonance scanning analysis.
  • the T1 value can be obtained using multiple inversion time (Inversion Time, TI) inversion recovery (Inversion Recovery, IR) sequences. Fit the signal intensity of multiple TI values to find the T1 value of each voxel in the imaging area.
  • the T2 value can be calculated by using multi-echo SE sequence signal fitting.
  • the new quantitative magnetic resonance sequence can obtain the PD, T1, and T2 of each voxel at the same time in one scan, and they include QRAPMASTER (Quantification of Relaxation Times and Proton Density by Multiecho acquisition of a saturation recovery using Turbo spin Echo Readout) [2 ], MDME (Multiple Dynamic Multiple Echo) [3], and MRF (Magnetic Resonance Fingerprinting) [4], etc.
  • QRAPMASTER Quantification of Relaxation Times and Proton Density by Multiecho acquisition of a saturation recovery using Turbo spin Echo Readout
  • MDME Multiple Dynamic Multiple Echo
  • MRF Magnetic Resonance Fingerprinting
  • Synthetic magnetic resonance images can also be applied to the diagnosis of diseases. In some diseases, its diagnostic effect is similar to that of magnetic resonance images obtained from conventional scans [5]. Synthetic magnetic resonance images are also used in children's clinical disease detection applications [6]. At present, the main focus of research and application is focused on obtaining a variety of synthetic MRI images with different contrasts through signal formula fitting, that is, to achieve the purpose of synthesizing MRI images with multiple application values in one quantitative scan.
  • synthetic MRI still has some obvious limitations. Among them, the contrast effect of the tissue or lesion to be detected and the accuracy of contrast information are the main points.
  • the common synthetic T2-FLAIR image cannot achieve complete CSF suppression effect [3] and so on.
  • the main reason is that the existing synthetic magnetic resonance imaging method mainly relies on the calculation of TR, TE and other scanning parameters set to be the same or similar to the scanning parameters of the conventional scan, so that the image contrast of the synthesized magnetic resonance image can be compared with that of the conventional scan.
  • the scanned magnetic resonance images are the same or similar. In this scenario, the synthesized magnetic resonance image can only achieve an effect similar to the magnetic resonance image obtained by conventional scanning.
  • the present invention proposes a high-quality magnetic resonance image synthesis method, which expands the value range of TE and TR to a negative interval, and expands the contribution of PD parameters to Negative power.
  • the invention can effectively reduce the influence of the measurement error of the magnetic resonance quantitative tissue parameter on the tissue contrast result of the synthetic magnetic resonance image, and can significantly improve the tissue contrast of the synthetic magnetic resonance image. This method will significantly improve the imaging quality of synthetic magnetic resonance, and promote its effect in neuroscience and clinical disease detection.
  • the technical solution adopted by the present invention is: a high-quality magnetic resonance image synthesis method, which includes the following steps:
  • ⁇ is a negative number
  • TR represents the scan repetition time, and TR is a negative number
  • TE represents the echo time, and TE is a negative number.
  • the present invention has the beneficial effects that: the present invention expands the value range of TE and TR to a negative interval, expands the contribution of PD parameters to negative powers, and can effectively reduce the measurement of magnetic resonance quantitative tissue parameters
  • the effect of errors on the results of the tissue contrast of the synthesized magnetic resonance image can significantly improve the tissue contrast of the synthesized magnetic resonance image, and unexpected technical effects have been achieved.
  • This method further significantly improves the imaging quality of synthetic magnetic resonance imaging without affecting the original advantages of synthetic magnetic resonance imaging, and promotes its practical application in neuroscience and clinical imaging detection.
  • Figure 1 shows the simulation of the change of the signal value of the two tissues with different T2 with TE in the SE sequence when TR is 600ms, and the quotient of the larger tissue signal value divided by the smaller tissue signal value varies with TE The change situation.
  • Figure 2 is the simulation in the SE sequence, when TE is 0ms, the absolute value of the two tissue signals with different T1 changes with TR, and the absolute value of the larger tissue signal divided by the smaller tissue signal The quotient of the absolute value changes with TR.
  • Figure 3 shows the simulation of the change of the signal values of the two tissues with TE when the TR is 600ms in the SE sequence, and T1 and T2 are different, and T1 and T2 fluctuate in a certain range.
  • Figure 4 shows the simulation of the change of the absolute value of the signals of the two tissues with TE when the TR is -1200ms in the SE sequence, and T1 and T2 are different, and T1 and T2 fluctuate in a certain range.
  • Figure 5 shows the simulation of signal changes when the PD is taken to the power of 1, 0, and -1.
  • Figure 6 shows the PD, T1, T2 obtained by quantitative magnetic resonance scanning analysis, using the signal formula of the SE sequence, TR is set to 600ms, TE is set to 6ms, PD is set to the positive power of 1, and the absolute value of the signal is calculated. The resulting composite magnetic resonance image.
  • Figure 7 shows the PD, T1, T2 obtained by quantitative magnetic resonance scanning analysis, using the signal formula of the SE sequence, TR is set to -1200ms, TE is set to -50ms, PD is set to the positive 1 power, and the signal is taken as the absolute value , The calculated synthetic magnetic resonance image.
  • Figure 8 shows the PD, T1, T2 obtained by quantitative magnetic resonance scanning analysis, using the signal formula of the SE sequence, TR is set to -1200ms, TE is set to -50ms, PD is set to the negative 1 power, and the signal is taken as the absolute value , The calculated synthetic magnetic resonance image.
  • Figure 9 is a T1-weighted mprage image obtained from a routine clinical scan.
  • the present invention expands the value range of TE and TR to a negative interval, and expands the contribution of PD parameters to negative powers, thereby improving the relationship between the various tissues in the synthetic magnetic resonance image.
  • the contrast between PD, T1, T2 increased diseased tissue and normal tissue.
  • T1 and T2 values will also increase. It can be seen from Fig. 1 that when TE is a negative number, the larger T2 is, the lower the signal. From Fig. 2, it can be seen that no matter if TR is positive or negative, the larger T1 is, the lower the tissue signal. Therefore, when TE is set to a negative number and TR is a negative number, the larger the T1 and T2, the lower the signal of the tissue, which improves the contrast between different tissues in the synthesized magnetic resonance image, and the resulting synthesized magnetic resonance image has a high contrast Contrast of synthetic magnetic resonance image obtained when TR is a positive number. Therefore, setting TE and TR to negative numbers can increase the contrast between different tissues in the synthesized magnetic resonance image, and also increase the contrast between normal tissues and diseased tissues with elevated T1 and T2.
  • the PD, T1, T2 obtained by quantitative magnetic resonance scanning analysis, using the signal formula of the SE sequence, set TE to 6ms, TR to 600ms, and take the positive power of 1 to PD to calculate the synthetic magnetic resonance image.
  • the PD, T1, T2 obtained by quantitative magnetic resonance scanning analysis, using the signal formula of the SE sequence, set TE to -50ms, TR to -1200ms, and take the positive power of 1 to PD to calculate the synthesis Magnetic resonance image.
  • the signal increases with the increase of PD; when PD is set to the power of 0, the signal does not change with the change of PD; when PD is set to the power of -1, the signal increases with PD The increase and decrease. Therefore, after setting TE and TR to negative numbers, take the negative power of PD to calculate the synthesized magnetic resonance image.
  • the PD, T1, T2 obtained by quantitative magnetic resonance scanning analysis, using the signal formula of the SE sequence, set TE to -50ms, TR to -1200ms, and take the negative 1 power to PD to calculate the synthesis Magnetic resonance image.
  • FIG. 7 is a synthetic magnetic resonance image obtained by taking a positive power of 1 to PD
  • Fig. 8 is a synthetic magnetic resonance image obtained by taking a negative power of 1 to PD. Comparing FIG. 7 and FIG. 8, it can be seen that the image contrast of FIG. 8 is greater than that of FIG. 7. Therefore, on the basis of setting TE and TR to negative numbers, and then taking the negative power to PD, the contrast of the synthesized magnetic resonance image can be further improved.
  • Fig. 8 is a synthetic magnetic resonance image obtained by setting TE to -50ms, TR to -1200ms, and taking the negative power of 1 to the PD
  • Fig. 9 is a T1-weighted mprage image obtained from routine clinical scanning. Comparing Fig. 8 and Fig. 9 it can be seen that the image contrast of Fig. 8 is higher than the image contrast of Fig. 9, and Fig. 8 shows the location and boundary of the lesion more clearly.

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Abstract

本发明公开了一种高质量磁共振图像合成方法，该方法将磁共振信号产生公式中的回波时间TE和扫描重复时间TR的取值范围拓展到负数区间，将质子密度PD参数的贡献拓展为负幂次。本发明可有效减少磁共振定量组织参数的测量误差对合成磁共振图像的组织对比度结果的影响，可显著改善合成磁共振图像的组织对比度。本方法将显著提升合成磁共振的成像质量，促进其在神经科学和临床病变检测效果。本方法最终有望提高合成磁共振的成像质量，促进其在神经科学和临床病变检测效果。

Description

一种高质量磁共振图像合成方法 技术领域
本发明涉及磁共振成像技术及图像处理领域，尤其涉及一种高质量磁共振图像合成方法。
背景技术
合成磁共振成像是指使用定量磁共振扫描分析获得每个体素的T1，T2，PD这些磁共振定量组织参数后，利用磁共振信号公式生成各类常见不同对比度的磁共振图像的方法。如公式(1)表示自旋回波(Spin Echo，SE)序列的信号公式。式(1)中S表示磁共振信号，PD(Proton Density)表示质子密度，T1表示纵向弛豫时间，T2表示横向弛豫时间，TR(Repetition Time)表示扫描重复时间，TE(Echo Time)表示回波时间。PD，T1，T2是磁共振定量组织参数，可通过定量磁共振扫描分析得到。TR，TE是磁共振成像扫描参数，计算时可设定不同的TR，TE来获得不同对比度的合成磁共振图像。传统的合成磁共振图像的计算中，β＝1，TR>TE>0。
S∝PD β(1-e -TR/T1)e -TE/T2     (1)
通过定量磁共振扫描分析可以获得每个体素的PD，T1，T2。如T1值可采用多个反转时间(Inversion Time,TI)的反转恢复(Inversion Recovery,IR)序列获得。拟合多个TI值的信号强度，求出成像区域各体素的T1值。T2值可采用多回波的SE序列的信号拟合计算得到。新型定量磁共振序列可以在一次扫描内同时获得每个体素的PD、T1和T2，它们包括QRAPMASTER(Quantification of Relaxation Times and Proton Density by Multiecho acquisition of a saturation‐recovery using Turbo spin‐Echo Readout)[2]，MDME(Multiple Dynamic Multiple Echo)[3]，和MRF(Magnetic Resonance Fingerprinting)[4]等。
定量磁共振序列的发展也促进了合成磁共振成像的发展。现已有对于合成磁共振成像广泛的研究，并且合成磁共振图像的图像效果也得到研究人员的认可。在合成磁共振图像的计算中，将TR，TE等扫描参数设置成与常规扫描的扫描参数相同时，合成磁共振图像的图像效果已经接近于常规扫描得到的磁共振图像的图像效果错误！未找到引用源。。合成磁共振图像也可以应用于疾病的诊断，在某些疾病上，其诊断效果与常规扫描得到的磁共振图像的诊断效果类似[5]。合成磁共振图像也见用于儿童的临床疾病检测应用中[6]。目前研究和应用的主要热点集中在通过信号公式拟合得到多种不同对比度的合成磁共振图像，即达到一次定量 扫描合成多种应用价值的磁共振图像的目的。
然而，合成磁共振成像还存在一些明显的局限性。其中待检测组织或病变的对比度效果及其对比度信息准确性是主要要点。如常见合成T2-FLAIR图像无法达到完全的CSF抑制效果[3]等。主要原因在于，现有的合成磁共振成像方法主要依赖在计算中，将TR，TE等扫描参数设定成与常规扫描的扫描参数相同或相近，从而使得合成磁共振图像的图像对比度可以与常规扫描得到的磁共振图像相同或相近。在该场景下，合成磁共振图像只能达到与常规扫描得到的磁共振图像相近的效果。此外，由于磁共振定量组织参数的测量存在误差。若不同组织的定量参数差值不能显著大于测量误差，其合成磁共振图像的准确度将受到置疑。因此，现有合成磁共振图像在对比度效果和准确度等方面都无法显著优于常规临床扫描的图像，极大地限制了该技术在临床的进一步实际应用。
[1]Bernstein M,King K,Zhou K.Handbook of MRI Pulse Sequences.Elsevier Science,2004.ISBN:9780080533124.
[2]Warntjes JBM,Leinhard OD,West J,Lundberg P.Rapid magnetic resonance quantification on the brain:optimization for clinical usage.Magn Reson Med,2008；60:320–329.
[3]Tanenbaum LN,Tsiouris AJ,Johnson AN,Naidich TP,DeLano MC,Melhem ER.Quarterman P,Parameswaran SX.,Shankaranarayanan A,Goyen M,AS.Synthetic MRI for clinical neuroimaging:results of the Magnetic Resonance Image Compilation(MAGiC)prospective，multicenter，multireader trial.AJNR Am J Neuroradiol,2017；38:1103–10
[4]Ma D,Gulani V,Seiberlich N,Liu K,Sunshine JL,Duerk JL,Griswold MA.Magnetic resonance fingerprinting.Nature,2013；495:187–192.
[5]Blystad I,Warntjes JB,Smedby O,Landtblom AM,Lundberg P,Larsson EM.Synthetic MRI of the brain in a clinical setting.Acta Radiol,2012；53:1158–1163.
[6]Betts AM,Leach JL,Jones BV,Bin Zhang,Suraj Serai.Brain imaging with synthetic MR in children:clinical quality assessment.Neuroradiology,2016；58:1017–1026.
发明内容
为了提高合成磁共振成像的组织对比度和对抗测量误差的能力，本发明提出了一种高质量磁共振图像合成方法，将TE和TR的取值范围拓展到负数区间，将PD参数的贡献拓展为负幂次。本发明可有效减少磁共振定量组织参数的测量误差对合成磁共振图像的组织对比度 结果的影响，可显著改善合成磁共振图像的组织对比度。本方法将显著提升合成磁共振的成像质量，促进其在神经科学和临床病变检测效果。
本发明所采用的技术方案是：一种高质量磁共振图像合成方法，该方法包括如下步骤：
(1)通过磁共振仪对被试进行扫描，并通过进一步重建计算获取质子密度PD、纵向弛豫时间T1和横向弛豫时间T2；
(2)将步骤(1)获得的PD、T1和T2代入公式(1)中，获得磁共振信号S：
S∝PD β(1-e -TR/T1)e -TE/T2    (1)
其中，β为负数；TR表示扫描重复时间，TR为负数；TE表示回波时间，TE为负数。
本发明与背景技术相比，具有的有益效果是：本发明将TE和TR的取值范围拓展到负数区间，将PD参数的贡献拓展为负幂次，可有效减少磁共振定量组织参数的测量误差对合成磁共振图像的组织对比度结果的影响，可显著改善合成磁共振图像的组织对比度，取得了意想不到的技术效果。本方法在不影响合成磁共振成像原有优势的基础上，进一步显著提升合成磁共振的成像质量，促进其在神经科学和临床影像检测中的实际推广应用。
附图说明
为了更清楚地说明本发明的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍。显而易见的是，下面描述中的附图仅仅是本申请中记载的特定实施例，其不是对本发明的保护范围的限制。对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，当然还可以根据本发明的如下实施例及其附图获得一些其它的实施例和附图
图1为模拟在SE序列中，当TR为600ms时，仅T2不同的两种组织的信号值随TE的变化情况，以及较大的组织信号值除以较小的组织信号值的商随TE的变化情况。
图2为模拟在SE序列中，当TE为0ms时，仅T1不同的两种组织的信号的绝对值随TR的变化情况,以及较大的组织信号的绝对值除以较小的组织信号的绝对值的商随TR的变化情况。
图3为模拟在SE序列中，当TR为600ms时，T1，T2都不同，且T1，T2在某一个范围波动的两种组织的信号值随TE的变化情况。
图4为模拟在SE序列中，当TR为-1200ms时，T1，T2都不同，且T1，T2在某一个范围波动的两种组织的信号的绝对值随TE的变化情况。
图5为模拟在PD分别取1次幂，0次幂，-1次幂时，信号的变化情况。
图6为使用定量磁共振扫描分析得到的PD，T1，T2，利用SE序列的信号公式，TR设置 成600ms，TE设置成6ms，对PD取正1次幂，并对信号取绝对值，计算得到的合成磁共振图像。
图7为使用定量磁共振扫描分析得到的PD，T1，T2，利用SE序列的信号公式，TR设置为-1200ms，TE设置成-50ms，对PD取正1次幂，并对信号取绝对值，计算得到的合成磁共振图像。
图8为使用定量磁共振扫描分析得到的PD，T1，T2，利用SE序列的信号公式，TR设置为-1200ms，TE设置成-50ms，对PD取负1次幂，并对信号取绝对值，计算得到的合成磁共振图像。
图9为常规临床扫描得到的T1加权mprage图像。
具体实施方式
为了使本领域的人员更好地理解本申请中的技术方案，下面将结合附图对本发明作进一步的说明。以SE序列的合成磁共振图像的计算作为实施例。但这仅仅是本申请的一部分实施例，而不是全部的实施例。基于本申请所述的具体实施例，本领域的其他人员在没有做出创造性劳动的前提下所获得的其他实施例，都应当落在本发明的构思范围之内。
以下参考附图描述本发明的优选实施例。
总体而言，本发明在合成磁共振图像的计算中，将TE和TR的取值范围拓展到负数区间，将PD参数的贡献拓展为负幂次，从而提高合成磁共振图像中各组织之间的对比度以及PD，T1，T2增大的病变组织与正常组织之间的对比度。
在合成磁共振信号的计算中，按照磁共振信号公式，当TR为负数时，得到的信号值为负数。故当TR为负数时，其信号值为利用磁共振信号公式计算得到的信号值的绝对值。
如图1所示，当其他条件相同时，利用SE序列的信号公式，模拟当TR为600ms时，TE对于仅有T2不同的两种组织的信号的影响，以及TE对于两种组织信号的商的影响。假设T2较小的组织为正常组织，T2较大的组织为病变组织。当TE为正数时，T2值较大的病变组织的信号较高，T2值较小的正常组织的信号较低。当TE为负数时，T2值较大的病变组织的信号较低，T2值较小的正常组织的信号较高。当TE的绝对值相同时，较大的组织信号值除以较小的组织信号值的商相等，且TE的绝对值越大，商越大。
如图2所示，当其他条件相同时，利用SE序列的信号公式，模拟当TE为0ms时，TR对于仅有T1不同的两种组织的信号的影响，以及TR对于两种组织的信号的商值的影响。假设T1较小的组织为正常组织，T1较大的组织为病变组织。无论TR为正数或为负数，T1较小的正常组织的信号大于T1较大的病变组织的信号。当TR为负数时，正常组织的信号除以病变 组织的信号的商较大，并且TR的绝对值越大，正常组织的信号除以病变组织的信号的商越大。
如图3所示，当其他条件相同时，利用SE序列的信号公式，模拟当TR为600ms时，TE对于T1，T2都不同，且T1，T2在一定范围内波动的两种组织的信号的影响。当TE为正数时，两种组织的信号可能会出现重叠现象。当TE为负数时，两种组织的信号不会出现重叠现象，并且随着TE绝对值的增大，两种组织的信号之差越来越大。
如图4所示，当其他条件相同时，利用SE序列的信号公式，模拟当TR为-1200ms时，TE对于T1，T2都不同，且T1，T2在一定范围内波动的两种组织的信号的影响。当TE为正数时，两种组织的信号可能会出现重叠现象。当TE为负数时，两种组织的信号不会出现重叠现象，并且随着TE绝对值的增大，两种组织的信号之差越来越大。
对比图3和图4，图3中的TR为600ms，图4中的TR为-1200ms。对比图3与图4可知，当TE小于0时，相同TE下，图4中两种组织信号的差值大于图3中两种组织信号的差值。由此可知，当TE，TR为负数时，可以增大不同组织之间的对比度，并且当磁共振定量组织参数有测量误差时，将TE，TR设置成负数可以有效减少磁共振定量组织参数测量误差对合成图像组织对比度结果的影响。
大部分脑组织的T1和T2存在正相关关系，并且许多病变组织伴随游离水的增加，T1，T2值也会升高。由图1可知，当TE为负数时，T2越大，信号越低，由图2可知，无论TR是正数还是负数，T1越大，组织信号也越低。所以当设定TE为负数,TR为负数时，T1，T2越大的组织的信号越低，从而提高了合成磁共振图像中不同组织之间的对比度,且得到的合成磁共振图像的对比度高于TR为正数时得到的合成磁共振图像的对比度。故将TE，TR设置成负数，可以提高合成磁共振图像中不同组织之间的对比度，也可以提高正常组织和T1，T2升高的病变组织之间的对比度。
如图6所示，使用定量磁共振扫描分析得到的PD，T1，T2，利用SE序列的信号公式，设定TE为6ms，TR为600ms，对PD取正1次幂，计算得到合成磁共振图像。
如图7所示，使用定量磁共振扫描分析得到的PD，T1，T2，利用SE序列的信号公式，设定TE为-50ms，TR为-1200ms，对PD取正1次幂，计算得到合成磁共振图像。
对比图6和图7，其他条件相同,图6中TE，TR为正数，图7中TE，TR为负数。对比图6和图7可知，图7的图像对比度大于图6的图像对比度，故设定TE，TR为负数可以有效提高合成磁共振图像的对比度。
T1，T2越大的组织PD往往也越大。将TE，TR设置成负数，T1，T2大的组织信号为低信号。如图5所示，对PD取正1次幂时，信号随PD的增大而增大；PD取0次幂时，信号不随 PD变化而变化；PD取-1次幂时，信号随PD的增大而减小。故将TE，TR设置成负数后，再对PD取负次幂进行合成磁共振图像的计算，PD，T1，T2越大的组织，信号越低，可以进一步提高不同组织之间的对比度，也可以提高正常组织与PD，T1，T2升高的病变组织之间的对比度。
如图8所示，使用定量磁共振扫描分析得到的PD，T1，T2，利用SE序列的信号公式，设定TE为-50ms，TR为-1200ms，对PD取负1次幂，计算得到合成磁共振图像。
对比图7和图8，其他条件相同,图7为对PD取正1次幂得到的合成磁共振图像，图8为对PD取负1次幂得到的合成磁共振图像。对比图7和图8可知，图8的图像对比度大于图7的图像对比度。故在将TE，TR设成负数的基础上，再对PD取负次幂，可以进一步提高合成磁共振图像的对比度。
对比图8和图9，图8为设定TE为-50ms，TR为-1200ms，并对PD取负1次幂得到的合成磁共振图像，图9为常规临床扫描得到的T1加权mprage图像。对比图8和图9可知，图8的图像对比度高于图9的图像对比度，图8更加清楚地显示了病灶的位置和边界。
以上所述仅是本申请的优选实施方式。本申请不会被限制与本文所述的这些具体实施例，而是可以覆盖与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (1)

  1. 一种高质量磁共振图像合成方法，其特征在于，该方法包括如下步骤：
    (1)通过磁共振扫描仪对被试进行扫描，并通过进一步的重建计算获取质子密度PD、纵向弛豫时间T1和横向弛豫时间T2；
    (2)将步骤(1)获得的PD、T1和T2代入公式(1)中，获得磁共振信号S：
    S∝PD β(1-e -TR/T1)e -TE/T2    (1)
    其中，β为负数；TR表示模拟扫描重复时间，TR为负数；TE表示模拟回波时间，TE为负数。
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