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WO2021196866A1 - 利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法及装置 - Google Patents

利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法及装置 Download PDF

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WO2021196866A1
WO2021196866A1 PCT/CN2021/074844 CN2021074844W WO2021196866A1 WO 2021196866 A1 WO2021196866 A1 WO 2021196866A1 CN 2021074844 W CN2021074844 W CN 2021074844W WO 2021196866 A1 WO2021196866 A1 WO 2021196866A1
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diffusion
flow
gradient
bipolar
sequence
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吴丹
蒋玲
孙陶陶
钱朝霞
孙毅
张祎
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Zhejiang University ZJU
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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
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/026—Measuring blood flow
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/43—Detecting, measuring or recording for evaluating the reproductive systems
    • A61B5/4306—Detecting, measuring or recording for evaluating the reproductive systems for evaluating the female reproductive systems, e.g. gynaecological evaluations
    • A61B5/4318—Evaluation of the lower reproductive system

Definitions

  • This application relates to the field of magnetic resonance technology, in particular to the field of diffusion magnetic resonance imaging sequences and modeling.
  • Incoherent intra-voxel imaging (IVIM) technology based on diffusion magnetic resonance can non-invasively reveal information about microcirculation blood flow in capillaries and small vessels in biological tissues, and provide quantitative evaluation indicators, such as the relative blood in microcirculation.
  • IVIM technology has been widely used to evaluate the microcirculation perfusion status of human tissues and organs, including brain, liver, kidney, breast, placenta, etc.
  • the diffusion magnetic resonance imaging sequence with flow rate compensation (FC) gradient has a first-order momentum of 0, which is insensitive to ballistic microcirculation flow, and can be used to separate the influence of blood flow and tissue water diffusion.
  • the present invention uses FC and NC diffusion gradient waveforms to specifically measure the proportion and velocity of ballistic blood flow in the placenta.
  • f ⁇ D* in the traditional IVIM model has been proposed as an approximation of cerebral blood flow, which is derived based on the concept of diffuse blood flow. Therefore, it is necessary to make a systematic comparison between these two flow rate measurement methods and compare them with Doppler ultrasound measurement results to study their role in fetal-placental blood circulation.
  • the present invention proposes a method for measuring the placental blood flow by using velocity compensation and non-compensated diffusion magnetic resonance to obtain the ratio and flow velocity of the ballistic microcirculation flow, and refine the IVIM model Estimated microcirculation parameters.
  • the present invention provides a method for measuring placental blood flow using flow-rate compensated and uncompensated diffuse magnetic resonance, which includes the following steps:
  • FC flow compensation
  • NC non-flow compensation
  • S and S 0 are the diffusion-weighted signal and non-diffusion-weighted signal under the value of b
  • f is the ratio of ballistic microcirculation flow
  • D t is the diffusion coefficient of water molecules in the tissue
  • D b is the diffusion of water molecules in the blood
  • v b is a measure of the velocity of the ballistic microcirculation flow
  • ⁇ is the first moment of the diffusion-encoded gradient field.
  • each step can further provide the following preferred implementation manners. It should be noted that the technical features in each preferred manner can be combined with each other without conflict. Of course, these preferred manners can also be implemented in other manners that can achieve the same technical effect, and do not constitute a limitation.
  • the method of constructing the diffusion weighting sequence of flow compensation is: applying a first bipolar diffusion between the 90° excitation pulse and the 180° refocusing pulse of the spin echo diffusion weighting sequence At the same time, after the 180° refocusing pulse, a second bipolar diffusion gradient that is the same as the first bipolar diffusion gradient is applied to realize the flow rate compensation gradient; the first moment of the first bipolar diffusion gradient and the second bipolar diffusion gradient Zero; apply a single spin echo planar imaging sequence after the second bipolar diffusion gradient for data acquisition.
  • the method for constructing the non-flow-rate compensation (NC) diffusion weighting sequence in the S2 is: between the 90° excitation pulse and the 180° refocusing pulse of the other spin echo diffusion weighting sequence, applying one and all The third bipolar diffusion gradient with the same first bipolar diffusion gradient, and a fourth bipolar diffusion gradient mirror-symmetric to the third bipolar diffusion gradient is applied after the 180° refocusing pulse to realize the non-flow velocity compensation gradient;
  • the first moments of the three bipolar diffusion gradient and the fourth bipolar diffusion gradient are non-zero; a single spin echo planar imaging sequence is applied after the fourth bipolar diffusion gradient for data acquisition.
  • the b value selects multiple numerical points covering the range of 10-600 s/mm 2 , and the IVIM signals of flow velocity compensation and non-flow velocity compensation are collected in 6 diffusion directions at each b value.
  • the diffusion coefficient D b of water molecules in the blood can be set to 1.5 ⁇ m 2 /ms.
  • the S4 before fitting, it is necessary to perform multiple iterations of linear registration on the diffusion-weighted images collected under different b values to correct the motion artifacts caused by the movement of the mother or the fetus, and then The registration is performed between the flow rate compensated and non-flow rate compensated IVIM signals.
  • the joint model of FC-NC signal can adopt least squares nonlinear curve fitting.
  • the present invention provides a device for measuring placental blood flow using flow-rate compensated and uncompensated diffuse magnetic resonance, which includes:
  • FC sequence building module used to apply the same bipolar gradient field on both sides of the 180° refocusing echo of the spin echo diffusion weighting sequence to construct a flow compensation (FC) diffusion weighting sequence;
  • NC sequence building module used to apply mirror-symmetric bipolar gradient fields on both sides of the 180° refocusing echo of the spin echo diffusion weighting sequence to construct a non-flow-rate compensation (NC) diffusion weighting sequence;
  • NC non-flow-rate compensation
  • IVIM signal acquisition module for a number of different diffusion sensitivity coefficient b values, under each b value, the flow compensation (FC) diffusion weighting sequence and the non-flow compensation (NC) diffusion weighting sequence are used to obtain the pregnant woman to be tested IVIM signal of the placenta;
  • FC flow compensation
  • NC non-flow compensation
  • the joint model parameter estimation module used to use the IVIM signal data under the two sequences obtained under different b values to fit the joint model of the FC-NC signal to estimate the ratio f and the flow velocity v of the ballistic microcirculation flow b .
  • the diffusion coefficient D t of water molecules in the tissue; the FC-NC signal joint model is formed by the combination of the NC signal model and the FC signal model, in the form:
  • S and S 0 are the diffusion-weighted signal and non-diffusion-weighted signal under the value of b
  • f is the ratio of ballistic microcirculation flow
  • D t is the diffusion coefficient of water molecules in the tissue
  • D b is the diffusion of water molecules in the blood
  • v b is a measure of the velocity of the ballistic microcirculation flow
  • ⁇ is the first moment of the diffusion-encoded gradient field.
  • each module can further provide the following preferred implementation manners. It should be noted that the technical features in each preferred manner can be combined with each other without conflict. Of course, these preferred manners can also be implemented in other manners that can achieve the same technical effect, and do not constitute a limitation.
  • the method for constructing the flow compensation (FC) diffusion weighting sequence is: applying a first pulse between the 90° excitation pulse and the 180° refocusing pulse of the spin echo diffusion weighting sequence Bipolar diffusion gradient, while applying a second bipolar diffusion gradient that is the same as the first bipolar diffusion gradient after the 180° refocusing pulse to realize the flow rate compensation gradient; the first bipolar diffusion gradient and the second bipolar diffusion gradient The first-order moment is zero; a single spin echo planar imaging sequence is applied after the second bipolar diffusion gradient for data acquisition.
  • the non-flow-rate compensation (NC) diffusion weighting sequence construction method is: applying between the 90° excitation pulse and the 180° refocusing pulse of another spin echo diffusion weighting sequence A third bipolar diffusion gradient that is the same as the first bipolar diffusion gradient, and a fourth bipolar diffusion gradient mirror-symmetric to the third bipolar diffusion gradient is applied after the 180° refocusing pulse to realize non-flow velocity compensation Gradient; the first moments of the third bipolar diffusion gradient and the fourth bipolar diffusion gradient are non-zero; apply a single spin echo planar imaging sequence after the fourth bipolar diffusion gradient for data acquisition.
  • the b value selects multiple numerical points covering the range of 10-600s/mm 2 , and each b value collects flow-rate compensation and non-flow-rate compensation IVIM in 6 diffusion directions. Signal.
  • the diffusion coefficient D b of water molecules in the blood can be set to 1.5 ⁇ m 2 /ms.
  • the joint model parameter estimation module before fitting, it is necessary to perform multiple iterations of linear registration on the diffusion-weighted images collected under different b values to correct the motion artifacts caused by the movement of the mother or fetus. And the registration between the IVIM signal of flow rate compensation and non-flow rate compensation.
  • the joint model of FC-NC signal can adopt least squares nonlinear curve fitting.
  • the present invention provides a device for measuring placental blood flow using flow-rate compensated and uncompensated diffuse magnetic resonance, which includes a memory and a processor;
  • the memory is used to store a computer program
  • the processor is configured to, when the computer program is executed, implement the method for measuring placental blood flow using flow-rate compensated and uncompensated diffuse magnetic resonance as described in any one of the above-mentioned first aspects.
  • the present invention provides a computer-readable storage medium with a computer program stored on the storage medium, and when the computer program is executed by a processor, the utilization of any one of the solutions in the first aspect is realized.
  • the present invention has the following characteristics: a method for measuring placental blood flow using velocity compensation and non-compensated diffusion magnetic resonance is proposed, the diffusion weighting sequence of FC and NC gradient is designed, and the combination of FC-NC signals is established
  • the model for the first time, obtains the velocity information of the ballistic blood in the blood microcirculation.
  • the model proposed by this method refines the ballistic components and diffusion components in the microcirculation blood flow, and uses FC and NC sequences to collect signals to specifically obtain the ballistic type.
  • the ratio and flow rate of the microcirculation flow The ballistic microcirculation flow velocity has a good linear correlation with the umbilical artery flow measured by Doppler ultrasound, and may become a useful indicator for quantitative measurement of placental blood perfusion.
  • Figure 1 is a timing diagram of flow rate compensation (FC) and non-compensation (NC) gradient encoding sequences.
  • Figure 2 shows the performance patterns of IVIM signal curves in the two placentas with low and high umbilical arterial flow measured by FC and NC diffusion weighted sequences, as well as the f diagram and v b diagram obtained by the FC-NC joint model fitting.
  • Figure 3 shows the correlation between the ballistic microcirculation velocity v b , and the f ⁇ D* parameters fitted from FC and NC data respectively, and the systolic/diastolic ratio and pulsatility index obtained by Doppler ultrasound of the umbilical artery.
  • Figure 4 shows the correlation between the ballistic microcirculation velocity v b and the f ⁇ D* parameters fitted from the FC and NC data and the gestational age.
  • the method for measuring placental blood flow by using velocity compensation and non-compensated diffuse magnetic resonance includes the following steps:
  • Step 1 Construct a diffusion weighted sequence for flow rate compensation, and record it as the FC sequence.
  • Figure (A) shows the FC sequence timing diagram of the present invention.
  • the specific construction method is: between the 90° excitation pulse and the 180° refocusing pulse of the spin echo diffusion weighted sequence , Apply a bipolar diffusion gradient (bipolar, denoted as the first bipolar diffusion gradient).
  • the length of a single diffusion gradient in the first bipolar diffusion gradient, that is, the diffusion time is set to 15ms.
  • a bipolar diffusion gradient that is the same as the first bipolar diffusion gradient (denoted as the second bipolar diffusion gradient) is applied to achieve flow velocity compensation.
  • the two bipolar diffusion gradients are center-symmetrical, and their timing polarity is the same, that is, the first moment (the sum of the first-order momentum) of a pair of bipolar gradients before and after the 180° pulse is zero. Then, after the second bipolar diffusion gradient, a single spin echo planar imaging sequence is applied for data acquisition to realize image readout.
  • Step 2 Construct a non-flow-rate compensated diffusion weighted sequence, which is recorded as the NC sequence.
  • FIG. B shows the timing diagram of the NC sequence of the present invention.
  • the specific construction method is: 90° excitation pulse and 180° refocusing pulse in a spin echo diffusion weighted sequence
  • a bipolar diffusion gradient (denoted as the third bipolar diffusion gradient) is applied, and another bipolar diffusion gradient (denoted as the fourth bipolar diffusion gradient) is applied after the 180° refocusing pulse.
  • the third bipolar diffusion gradient should be the same as the first bipolar diffusion gradient in the FC sequence, and the fourth bipolar diffusion gradient should be mirror-symmetrical to the third bipolar diffusion gradient.
  • the polarities of the third bipolar diffusion gradient and the fourth bipolar diffusion gradient are different, and the two are mirror-symmetrical with the 180° refocusing pulse position as the center, so the first moment of the gradient encoding method is non-zero.
  • a single spin echo planar imaging sequence is applied after the fourth bipolar diffusion gradient for data acquisition to achieve image readout.
  • Step 3 Under different b values (diffusion sensitivity coefficient), the FC sequence and NC sequence are used to obtain the IVIM signal of the placenta of the pregnant woman to be tested.
  • This step can be performed on a 1.5T magnetic resonance imager to perform a sagittal scan of the placenta of pregnant women.
  • 9 b-values (10, 20, 50, 100, 150, 200, 300, 500, 800 s/mm 2 ) and 6 diffusion-weighted signal acquisitions for each b value (each b value is The IVIM signals measured by FC and NC sequences should be collected respectively).
  • Step 4 Establish a joint model of FC-NC signal.
  • the IVIM signal data under the NC and FC sequences obtained under different b values can be derived from the NC signal model and the FC signal model Jointly obtain the FC-NC signal joint model, which is expressed as follows:
  • S and S 0 are the diffusion-weighted signal and non-diffusion-weighted signal at a specific b value
  • f is the ratio of ballistic microcirculation flow
  • D t is the diffusion coefficient of water molecules in the tissue
  • D b is the water molecules in the blood Diffusion coefficient (D b is set to 1.5 ⁇ m 2 /ms)
  • v b is a measure of the velocity of the ballistic microcirculation flow
  • the diffuse microcirculation component is not included in the current model, because the diffusion distance of water molecules in the blood is about 9.5m at a diffusion time of 15 milliseconds, which is relatively long compared to the vascular segment in the terminal villi Therefore, the diffuse microcirculation flow that spans multiple vascular segments is ignored.
  • the method of the present invention can measure the placental blood flow information using velocity compensation and non-compensated diffusion magnetic resonance, and separately obtain the proportion and flow rate of ballistic blood in the blood microcirculation, which can be used to refine the microcirculation blood.
  • Ballistic and diffuse components in the flow Since f ⁇ D* has been proposed as an approximation of cerebral blood flow, it is derived based on the concept of diffuse blood flow. Therefore, it is necessary to make a systematic comparison between these two flow rate measurement methods and compare them with Doppler ultrasound measurement results to study their role in fetal-placental blood circulation.
  • the method is as step 5:
  • Step 5 Regarding the IVIM signals obtained from the FC and NC sequences, use the conventional double-exponential IVIM model respectively Perform the fitting. Firstly, the approximate values of f, D, and D* are obtained by the method of piecewise fitting, as the initial and boundary values of the nonlinear fitting, and then the least square nonlinear curve fitting is performed to obtain the microcirculation based on FC and NC sequence respectively.
  • the blood ratio f, the diffusion rate D of microcirculation blood and the diffusion rate D* of tissue water, and the f ⁇ D* parameter obtained under the FC sequence are approximated as the flow velocity measurement of the diffusion microcirculation flow.
  • FC and NC gradients were implemented on a 1.5T MAGNETOM Aera magnetic resonance imaging system (Siemens Healthcare, Er Weg, Germany), using 18-channel body coils. With the patient's consent and approval by the local institutional review board, 40 pregnant women (22.7 to 38 weeks gestation) were included in the study.
  • the IVIM data was collected through FC and NC sequences, the field of view was 350 ⁇ 350mm 2 , the resolution within the slice was 2.73 ⁇ 2.73mm 2 , the slice thickness was 6mm, 10 slices were collected along the sagittal direction, and 9 b values (10- 600s/mm 2 ), 6 diffusion directions, one signal average, GRAPPA with an acceleration factor of 2, and the scan time of the FC and NC sequences are 2.5 minutes each.
  • the IVIM image first performs motion correction between the diffusion-weighted images through multiple iterations of affine registration, and uses mutual information as the cost function. This step is performed by FSL (https://fsl.fmrib.ox.ac.uk). /)accomplish.
  • the IVIM parameters are obtained by using least squares nonlinear curve fitting. Among them, f and D t are first approximated according to the FC data based on the double exponential model using the segmentation method, f and D t are fixed, and the approximate value of v b is obtained according to the signal formula of NC.
  • the initial point and upper and lower limits of the parameters are determined according to the approximate values of f, D t and v b.
  • the traditional double-exponential IVIM model (f, D, and D*) was fitted respectively.
  • the piecewise method was used to obtain the initial approximation, and then the nonlinear curve fitting was used to obtain an accurate estimate.
  • the umbilical blood flow velocity waveform measured by Doppler represents the resistance of the downstream or placental blood vessels to blood flow.
  • the pulsatility index (PI) and the systolic/diastolic ratio (SD) are usually used to measure the resistance.
  • PI is defined as (systolic velocity-diastolic velocity)/average velocity
  • SD is defined as systolic velocity/diastolic velocity.
  • the v b value obtained from the FC-NC combined model and the f ⁇ D* value obtained from a single model were correlated with PI and SD, and at the same time correlated with the gestational age of the fetus.
  • Figure 2 shows the performance patterns of the IVIM signal curve measured by the FC and NC diffusion weighted sequence in the two placentas with low and high umbilical arterial flow, as well as the f graph and v b graph obtained by the FC-NC joint model fitting .
  • A In the placenta with relatively high values of umbilical artery PI and SD, at low b values, the signal difference between FC (solid line) and NC (dashed line) signals is obvious, using the v b fitted by the joint model Relatively high.
  • B In the placenta with relatively low cord blood flow, the difference between FC and NC signals is small, and the fitted v b is relatively low.
  • Figure 3 shows the correlation between IVIM-based placental microcirculation flow rate measurements and umbilical artery-based Doppler ultrasound PI and SD.
  • the ballistic velocity v b in the placental microcirculation is positively correlated with the umbilical cord Doppler measurement, indicating that it is directly related to the pressure entering the placental blood stream.
  • FC gradient is not sensitive to ballistic blood flow, so the f ⁇ D* index based on FC may reflect the speed of diffuse blood flow.
  • the f ⁇ D* index based on FC data is negatively correlated with the umbilical cord Doppler measurement, indicating that different IVIM components may have different responses to changes in placental vascular resistance.
  • Figure 4 shows the correlation between IVIM-based measurement of placental microcirculation flow rate and gestational age.
  • the v b of the combined model is negatively correlated with gestational age, while the f ⁇ D* value fitted by FC data is positively correlated with gestational age, and the f ⁇ D* value fitted by NC data is negatively correlated with gestational age.
  • FC data is positively correlated with gestational age
  • NC data is negatively correlated with gestational age.
  • This example shows that the method provided by the present invention can obtain the information of the ballistic blood flow in the blood microcirculation, so as to refine the ballistic and diffusive components in the microcirculation blood flow, which is used to quantify the two types of components in the placenta.
  • the role of microcirculation in the fetal-placental perfusion system, and new quantitative indicators of ballistic blood flow may provide new information for the measurement of placental microcirculation perfusion.
  • a device for measuring placental blood flow using flow-rate compensated and non-compensated diffuse magnetic resonance which includes:
  • FC sequence building module used to apply the same bipolar gradient field on both sides of the 180° refocusing echo of the spin echo diffusion weighting sequence to construct a flow compensation (FC) diffusion weighting sequence;
  • NC sequence building module used to apply mirror-symmetric bipolar gradient fields on both sides of the 180° refocusing echo of the spin echo diffusion weighting sequence to construct a non-flow-rate compensation (NC) diffusion weighting sequence;
  • NC non-flow-rate compensation
  • IVIM signal acquisition module for a number of different diffusion sensitivity coefficient b values, under each b value, the flow compensation (FC) diffusion weighting sequence and the non-flow compensation (NC) diffusion weighting sequence are used to obtain the pregnant woman to be tested IVIM signal of the placenta;
  • FC flow compensation
  • NC non-flow compensation
  • the joint model parameter estimation module used to use the IVIM signal data under the two sequences obtained under different b values to fit the joint model of the FC-NC signal to estimate the ratio f and the flow velocity v of the ballistic microcirculation flow b .
  • the diffusion coefficient D t of water molecules in the tissue; the FC-NC signal joint model is formed by the combination of the NC signal model and the FC signal model, in the form:
  • S and S 0 are the diffusion-weighted signal and non-diffusion-weighted signal under the value of b
  • f is the ratio of ballistic microcirculation flow
  • D t is the diffusion coefficient of water molecules in the tissue
  • D b is the diffusion of water molecules in the blood
  • v b is a measure of the velocity of the ballistic microcirculation flow
  • ⁇ is the first moment of the diffusion-encoded gradient field.
  • Each module in the above-mentioned device essentially corresponds to the aforementioned step 1 to step 4, and the specific methods in the aforementioned step 1 to step 4 can also be applied to each module of the device.
  • a device for measuring placental blood flow by using flow-rate compensated and non-compensated diffuse magnetic resonance which includes a memory and a processor;
  • the memory is used to store a computer program
  • the processor is configured to implement the method of measuring placental blood flow by using flow-rate compensated and uncompensated diffuse magnetic resonance as shown in step 1 to step 4 when the computer program is executed.
  • the memory may include random access memory (Random Access Memory, RAM), and may also include non-volatile memory (Non-Volatile Memory, NVM), such as at least one disk storage.
  • the foregoing processor may be a general-purpose processor, including a central processing unit (CPU), a network processor (Network Processor, NP), etc.; it may also be a digital signal processor (Digital Signal Processing, DSP), a dedicated integrated Circuit (Application Specific Integrated Circuit, ASIC), Field-Programmable Gate Array (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components.
  • DSP Digital Signal Processing
  • ASIC Application Specific Integrated Circuit
  • FPGA Field-Programmable Gate Array
  • the device should also have necessary components for program operation, such as a power supply, a communication bus, and so on.
  • the memory and the processor can be further integrated in the data processing equipment of the magnetic resonance imaging system. After the magnetic resonance imaging system obtains the corresponding IVIM signal data of the diagnostic object, it can be stored in the memory and then passed through the processor. It calls the internal program for processing and outputs the result directly.
  • a computer-readable storage medium may also be provided, the storage medium stores a computer program, and when the computer program is executed by the processor, the utilization as shown in step 1 to step 4 is realized.

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Abstract

一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法，包括以下步骤：首先，基于自旋回波扩散加权序列，通过极性相同的双极性梯度场，构建流速补偿(FC)的扩散加权序列；其次，使用极性镜像对称的双极性梯度场构建非流速补偿(NC)的扩散加权序列；然后，分别采用FC和NC序列对孕妇胎盘测量多b值的体素内非相关运动(IVIM)信号；最后，建立FC-NC联合模型，拟合估计弹道型血液微循环流的比例和流速，以及组织水的扩散率。还公开了一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置。与临床上常规使用的IVIM成像方式相比，该方法细化了微循环血流中的弹道型成分和扩散型成分，提出了新的IVIM量化指标，能够定量说明胎盘中两种微循环在胎儿-胎盘灌注系统中的作用。

Description

利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法及装置 技术领域
本申请涉及磁共振技术领域，尤其涉及弥散磁共振成像序列和建模领域。
背景技术
基于弥散磁共振的体素内非相干成像(IVIM)技术可以无创地揭示生物组织中关于毛细血管和小血管中微循环血流的信息，并提供了定量的评估指标，例如微循环中血液相对于组织水的比例(f)、微循环的扩散率(D*)以及组织水的扩散率(D)。IVIM技术已被广泛应用于人体组织器官的微循环灌注状态评估，包括大脑、肝脏、肾脏、乳腺、胎盘等。其中，IVIM在胎盘成像中的应用越来越受到关注，因为胎盘的灌注情况不能通过常规的动态增强磁共振(DCE)得到，而多普勒超声也仅能测量脐带或子宫动静脉的血流。前期研究已经证明通过胎盘IVIM技术可有效检测宫内发育受限、子痫、小于胎龄儿、先天性心脏病等产前疾病。
然而常规的IVIM仅能对微循环血液的比例和扩散率做笼统的计算且对血流速度未有精确的测量方法。已知IVIM模型由三个部分组成，即组织水、通过多个血管段的微循环流(扩散极限)和保留在一段或少数几个血管段中的微循环流(弹道极限)。传统的IVIM成像使用单极或双聚焦的扩散敏化梯度，属于非流动补偿(NC)梯度，因此，常规测量的IVIM效应包含扩散型和弹道型微循环血流。具有流速补偿(FC)梯度的扩散磁共振成像序列的一阶动量为0，对弹道型微循环流不敏感，可用于分离血流和组织水扩散的影响。
本发明联合使用FC和NC扩散梯度波形来具体测量胎盘中弹道型血流的比例和速度。另外，传统IVIM模型中的f·D*已经被提出作为脑血流的近似，它是基于扩散型血流的概念推导出来的。因此，有必要将这两种流速测量方法做一系统的比较，并将它们与多普勒超声的测量结果对比，研究它们在胎儿-胎盘血循环中的作用。
发明内容
为了克服现有IVIM方法的存在的不足，本发明提出了一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法，得到弹道型微循环流的比例和流速，细化IVIM模型中的微循环参数估计。
为了达到上述目的，本发明采用以下技术方案予以实现：
第一方面，本发明提供了一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法，其包括以下步骤：
S1：在自旋回波扩散加权序列的180°重聚回波两侧施加相同的双极性梯度场，构建流速补偿(FC)的扩散加权序列；
S2：在自旋回波扩散加权序列的180°重聚回波两侧施加镜像对称的双极性梯度场，构建非流速补偿(NC)的扩散加权序列；
S3：针对若干不同的扩散敏感系数b值，在每个b值下分别采用流速补偿(FC)的扩散加权序列和非流速补偿(NC)的扩散加权序列获取待测的孕妇胎盘的IVIM信号；
S4：利用不同b值下得到的两种序列下的IVIM信号数据，对FC-NC信号的联合模型进行拟合，估计得到弹道型微循环流的比例f和流速v b、和组织中水分子的扩散系数D t；所述FC-NC信号的联合模型由NC信号模型和FC信号模型联合而成，形式为：
Figure PCTCN2021074844-appb-000001
Figure PCTCN2021074844-appb-000002
其中S和S 0分别是b值下的弥散加权信号和非扩散加权信号，f是弹道型微循环流的比例，D t是组织中水分子的扩散系数，D b是血液中水分子的扩散系数，v b是弹道型微循环流流速的量度，α是扩散编码梯度场的一阶矩。
基于上述第一方面的方案，各步骤还可以进一步提供以下优选的实现方式。需要注意的是，各优选方式中的技术特征在没有冲突的情况下均可进行相互组合。当然这些优选方式也可以通过其他能够实现相同技术效果的方式实现，不构成限制。
作为优选，所述的S1中，流速补偿(FC)的扩散加权序列构建方法为：在自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个第一 双极扩散梯度，同时在180°重聚焦脉冲之后施加一个与第一双极扩散梯度相同的第二双极扩散梯度，实现流速补偿梯度；第一双极扩散梯度和第二双极扩散梯度的一阶矩为零；在第二双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集。
作为优选，所述的S2中，非流速补偿(NC)的扩散加权序列构建方法为：在另一条自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个与所述第一双极扩散梯度相同的第三双极扩散梯度，同时在180°重聚焦脉冲之后施加一个与第三双极扩散梯度镜像对称的第四双极扩散梯度，实现非流速补偿梯度；第三双极扩散梯度和第四双极扩散梯度的一阶矩为非零；在第四双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集。
作为优选，所述的S3中，b值选择覆盖10-600s/mm 2范围的多个数值点，且每个b值下分别在6个扩散方向采集流速补偿和非流速补偿的IVIM信号。
作为优选，所述的S4中，血液中水分子的扩散系数D b可以设置为1.5μm 2/ms。
作为优选，所述的S4中，在进行拟合之前，需要首先对不同b值下采集的扩散加权图像进行多次迭代的线性配准，校正由于母体或胎儿运动导致的运动伪影，并将流速补偿和非流速补偿的IVIM信号之间进行配准。
作为优选，FC-NC信号的联合模型可以采用最小二乘非线性曲线拟合。
第二方面，本发明提供了一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其包括：
FC序列构建模块：用于在自旋回波扩散加权序列的180°重聚回波两侧施加相同的双极性梯度场，构建流速补偿(FC)的扩散加权序列；
NC序列构建模块：用于在自旋回波扩散加权序列的180°重聚回波两侧施加镜像对称的双极性梯度场，构建非流速补偿(NC)的扩散加权序列；
IVIM信号获取模块：用于针对若干不同的扩散敏感系数b值，在每个b值下分别采用流速补偿(FC)的扩散加权序列和非流速补偿(NC)的扩散加权序列获取待测的孕妇胎盘的IVIM信号；
以及联合模型参数估计模块：用于利用不同b值下得到的两种序列下的IVIM信号数据，对FC-NC信号的联合模型进行拟合，估计得到弹道型微循环流的比例f和流速v b、和组织中水分子的扩散系数D t；所述FC-NC信号的联合模型由NC信号模型和FC信号模型联合而成，形式为：
Figure PCTCN2021074844-appb-000003
Figure PCTCN2021074844-appb-000004
其中S和S 0分别是b值下的弥散加权信号和非扩散加权信号，f是弹道型微循环流的比例，D t是组织中水分子的扩散系数，D b是血液中水分子的扩散系数，v b是弹道型微循环流流速的量度，α是扩散编码梯度场的一阶矩。
基于上述第二方面的方案，各模块还可以进一步提供以下优选的实现方式。需要注意的是，各优选方式中的技术特征在没有冲突的情况下均可进行相互组合。当然这些优选方式也可以通过其他能够实现相同技术效果的方式实现，不构成限制。
作为优选，所述的FC序列构建模块中，流速补偿(FC)的扩散加权序列构建方法为：在自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个第一双极扩散梯度，同时在180°重聚焦脉冲之后施加一个与第一双极扩散梯度相同的第二双极扩散梯度，实现流速补偿梯度；第一双极扩散梯度和第二双极扩散梯度的一阶矩为零；在第二双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集。
作为优选，所述的NC序列构建模块中，非流速补偿(NC)的扩散加权序列构建方法为：在另一条自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个与所述第一双极扩散梯度相同的第三双极扩散梯度，同时在180°重聚焦脉冲之后施加一个与第三双极扩散梯度镜像对称的第四双极扩散梯度，实现非流速补偿梯度；第三双极扩散梯度和第四双极扩散梯度的一阶矩为非零；在第四双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集。
作为优选，所述的IVIM信号获取模块中，b值选择覆盖10-600s/mm 2范围的多个数值点，且每个b值下分别在6个扩散方向采集流速补偿和非流速补偿的IVIM信号。
作为优选，所述的IVIM信号获取模块中，血液中水分子的扩散系数D b可以设置为1.5μm 2/ms。
。
作为优选，所述的联合模型参数估计模块中，在进行拟合之前，需要首先对不同b值下采集的扩散加权图像进行多次迭代的线性配准，校正由于母体或胎儿运动导致的运动伪影，并将流速补偿和非流速补偿的IVIM信号之间进行配准。
作为优选，FC-NC信号的联合模型可以采用最小二乘非线性曲线拟合。
第三方面，本发明提供了一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其包括存储器和处理器；
所述存储器，用于存储计算机程序；
所述处理器，用于当执行所述计算机程序时，实现如上述第一方面中任一项方案所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法。
第四方面，本发明提供了一种计算机可读存储介质，所述存储介质上存储有计算机程序，当所述计算机程序被处理器执行时，实现第一方面中任一项方案所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法。
相对于现有技术，本发明具有以下特点：提出了一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法，设计FC和NC梯度的扩散加权序列，建立FC-NC信号的联合模型，首次得到血液微循环中弹道型血液的流速信息。与临床上常规使用的IVIM成像方式相比，本方法提出的模型细化了微循环血流中的弹道型成分和扩散型成分，并联合使用FC和NC序列采集信号，特定性地获取弹道型微循环流的比例和流速。弹道型微循环流流速与与多普勒超声测量的脐带动脉流存在较好的线性相关性，可能成为胎盘血液灌注定量测量的有用指标。
附图说明
图1是流速补偿(FC)和非补偿(NC)梯度编码序列的时序图。
图2是采用FC和NC扩散加权序列测得的IVIM信号曲线在脐带动脉流低和高的两个胎盘中的表现模式，以及通过FC-NC联合模型拟合得到的f图和v b图。
图3是弹道型微循环流速v b，以及从FC和NC数据中分别拟合得到的f·D*参量与脐带动脉多普勒超声得到的收缩/舒张比和搏动指数之间的相关性。
图4是弹道型微循环流速v b，以及从FC和NC数据中分别拟合得到的f·D*参量与胎龄之间的相关性。
具体实施方式
下面基于本发明提出的方法结合实施例展示其具体的技术效果，以便本领域 技术人员更好地理解本发明的实质。
在本发明的一种较优实现方式中，利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法包括以下步骤：
步骤一：构建流速补偿的扩散加权序列，记为FC序列。
本步骤具体参见图1，图中(A)所示即为本发明的FC序列时序图，其具体构建方法为：在自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个双极扩散梯度(bipolar，记为第一双极扩散梯度)。第一双极扩散梯度中单个扩散梯度的长度，即扩散时间设置为15ms。接着在180°重聚焦脉冲后，施加一个与第一双极扩散梯度相同的双极扩散梯度(记为第二双极扩散梯度)，来实现流速补偿。两个双极扩散梯度呈中心对称，其时序极性相同，即180°脉冲前后一对双极梯度的一阶矩(一阶动量总和)为零。然后，在第二双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集，实现图像的读出。
步骤二：构建非流速补偿的扩散加权序列，记为NC序列。
本步骤具体参见参见图1，图中(B)所示即为本发明的NC序列时序图，其具体构建方法为：在一条自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个双极扩散梯度(记为第三双极扩散梯度)，同时在180°重聚焦脉冲之后施加另一个双极扩散梯度(记为第四双极扩散梯度)。第三双极扩散梯度应当与FC序列中的第一双极扩散梯度相同，而第四双极扩散梯度则与第三双极扩散梯度镜像对称。第三双极扩散梯度和第四双极扩散梯度的极性是不同的，两者以180°重聚焦脉冲位置为中心呈镜像对称，因此该梯度编码方式的一阶矩为非零。同样的，在第四双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集，实现图像的读出。
步骤三：在不同的b值下(扩散敏感系数)，分别采用FC序列和NC序列获取待测的孕妇胎盘的IVIM信号。
本步骤具体可在1.5T磁共振成像仪上，对孕妇胎盘进行矢状位扫描。分别基于FC和NC梯度的扩散加权序列，采集9个b值(10,20,50,100,150,200,300,500,800s/mm 2)和每个b值下分别6个扩散方向的扩散加权信号采集(每个b值下都应采集FC和NC序列分别测得的IVIM信号)。
步骤四：建立FC-NC信号的联合模型。
假设血管中流速的分布遵循高斯分布，考虑弹道型微循环流成分和组织水成分，利用不同b值下得到的NC和FC两种序列下的IVIM信号数据，可以由NC信号模型和FC信号模型联合得到FC-NC信号联合模型，表示如下：
Figure PCTCN2021074844-appb-000005
(NC信号模型)
Figure PCTCN2021074844-appb-000006
(FC信号模型)
其中S和S 0分别是特定b值下的弥散加权信号和非扩散加权信号，f是弹道型微循环流的比例，D t是组织中水分子的扩散系数，D b是血液中水分子的扩散系数(D b设置为1.5μm 2/ms)，v b是弹道型微循环流流速的量度，α是扩散编码梯度场的一阶矩(FC序列中，α＝0)。通过FC-NC的联合模型，可对未知参量f、D t和v b进行拟合。注意，扩散型的微循环成分不包括在当前模型中，因为在15毫秒的扩散时间下，血液中水分子的扩散距离约为9.5m，这与末端绒毛中的血管段相比是相对较长的距离，故忽略跨越多个血管段的扩散型微循环流。
在进行上述拟合之前，需要首先对不同b值下采集的扩散加权图像进行多次迭代的(6～10次)线性配准，校正由于母体或胎儿运动导致的运动伪影，并将FC与NC两组数据之间进行配准。然后基于上述公式，对FC和NC数据进行最小二乘非线性曲线拟合，得到FC-NC信号联合模型的模型参数f、D t和v b，此步骤在MATLAB中通过信赖域的优化算法实现。人工在胎盘图像上刻画感兴趣区域，排除拟合的异常值，得到ROI的均值做为个体的f、D t和v b测量。
通过上述步骤一～步骤四，本发明的方法可以利用流速补偿和非补偿的弥散磁共振测量胎盘血流信息，单独得到血液微循环中弹道型血液的比例、流速，用于细化微循环血流中的弹道型成分和扩散型成分。由于f·D*已经被提出作为脑血流的近似，它是基于扩散型血流的概念推导出来的。因此，有必要将这两种流速测量方法做一系统的比较，并将它们与多普勒超声的测量结果对比，研究它们在胎儿-胎盘血循环中的作用。其做法如步骤五：
步骤五：针对FC和NC序列得到的IVIM信号，分别采用常规的双指数IVIM模型
Figure PCTCN2021074844-appb-000007
进行拟合。首先采用分段拟合的方法得到f、D、D*的近似值，作为非线性拟合的初始值和边界值，然后进行最小二乘非线性曲线拟合，分别得到基于FC和NC序列微循环血比例f，微循环血的扩散率D和 组织水的扩散率D*，并将FC序列下得到的f·D*参量近似作为扩散型微循环流的流速量度。
下面基于上述方法的步骤一到五，结合实施例对其技术效果进行展示，以便本领域技术人员更好地理解本发明的实质。
实施例
本实验在1.5T MAGNETOM Aera磁共振成像系统(Siemens Healthcare,Erlangen,Germany)上实现了FC和NC梯度的扩散加权序列，采用18通道体线圈进行。经患者同意并经当地机构审查委员会批准，40名孕妇(孕22.7至38周)被纳入研究。通过FC和NC序列采集IVIM数据，其采集视场为350×350mm 2，层面内分辨率为2.73×2.73mm 2，层厚6mm，沿矢状方向采10层，使用9个b值(10-600s/mm 2)，6个扩散方向，一个信号平均值，加速因子为2的GRAPPA，FC和NC序列的扫描时间各为2.5分钟。
IVIM图像首先通过多次迭代仿射配准的方法在各个扩散加权图像之间的进行运动校正，将互信息作为代价函数，该步骤通过FSL(https://fsl.fmrib.ox.ac.uk/)实现。基于步骤三中的FC-NC联合模型，利用最小二乘非线性曲线拟合，得到IVIM参数。其中f和D t首先根据基于双指数模型的FC数据，使用分段方法进行近似，将将f和D t固定，根据NC的信号公式得到v b近似值。然后，根据f、D t、v b的近似值确定参数的初始点和上下限。对FC和NC数据，分别进行传统双指数的IVIM模型的(f、D和D*)拟合，先使用分段方法获得初始近似，然后使用非线性曲线拟合获得精确估计。对整个胎盘手动描绘感兴趣区域，获取感兴趣区域的参数均值，排除异常值。
同时在这40名受试者中，有25名接受了脐血动脉多普勒超声测量。多普勒测量的脐血流速度波形代表下游或胎盘血管对血流的阻力，在临床实践中通常使用搏动指数(PI)和收缩/舒张比(SD)来测量该阻力。PI定义为(收缩速度-舒张速度)/平均速度，SD定义为收缩速度/舒张速度。将FC-NC联合模型得到的v b值和单个模型得到的f·D*值与PI和SD进行相关分析，同时与胎儿胎龄进行相关分析。
附图2显示采用FC和NC扩散加权序列测得的IVIM信号曲线在脐带动脉流低和高的两个胎盘中的表现模式，以及通过FC-NC联合模型拟合得到的f图和v b图。(A)在脐血动脉PI和SD值相对较高的胎盘中，在低b值下，FC(实 线)和NC(虚线)信号之间的信号差异明显，使用联合模型拟合的v b相对较高。(B)在脐血流相对较低的胎盘中，FC和NC信号之间差异较小，拟合的v b相对较低。
附图3显示基于IVIM的胎盘微循环流速测量值与基于脐带动脉的多普勒超声PI和SD之间的相关性。(A-B)胎盘内弹道型微循环流速与SD(r＝0.61)和PI(r＝0.50)呈强正相关。用双指数模型拟合FC数据得到的f·D*值与SD呈负相关(r＝-0.48)，但与PI无显著相关。从NC数据拟合的f·D*值与SD(r＝0.49)和PI(r＝0.47)呈正相关。胎盘微循环中的弹道型流速v b与脐带多普勒测量值正相关，表明它与进入胎盘血流的压力直接相关。FC梯度对弹道型血流不敏感，因而基于FC的f·D*指数可能反映扩散型血流的速度。基于FC数据的f·D*指数与脐带多普勒测量值呈负相关，表明不同的IVIM成分对胎盘血管阻力的变化可能有不同的反应。
附图4显示基于IVIM的胎盘微循环流速测量值与胎龄的相关性。(A)联合模型的v b与胎龄呈负相关，而FC数据拟合的f·D*值与胎龄呈正相关，NC数据拟合的f·D*值与胎龄呈负相关。已知在正常妊娠中，由于绒毛血管形成的增加和扩张，胎盘血管阻力在整个妊娠过程中逐渐降低，PI和SD值也随之胎龄的增长而降低。因此，鉴于上述IVIM参数与SD和PI之间的关系，v b和f·D*与胎龄的关系符合预期。
通过本实施例表明，本发明提供的方法可以得到血液微循环中弹道型血流的信息，以便于细化微循环血流中的弹道型成分和扩散型成分，用于定量说明胎盘中两种微循环在胎儿-胎盘灌注系统中的作用，弹道型血流的新型定量指标可能对胎盘微循环灌注的测量提供新的信息。
另外，在上述步骤一～步骤四的基础上，还可以进一步提供一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其包括：
FC序列构建模块：用于在自旋回波扩散加权序列的180°重聚回波两侧施加相同的双极性梯度场，构建流速补偿(FC)的扩散加权序列；
NC序列构建模块：用于在自旋回波扩散加权序列的180°重聚回波两侧施加镜像对称的双极性梯度场，构建非流速补偿(NC)的扩散加权序列；
IVIM信号获取模块：用于针对若干不同的扩散敏感系数b值，在每个b值下分别采用流速补偿(FC)的扩散加权序列和非流速补偿(NC)的扩散加权序列获取待测的孕妇胎盘的IVIM信号；
以及联合模型参数估计模块：用于利用不同b值下得到的两种序列下的IVIM信号数据，对FC-NC信号的联合模型进行拟合，估计得到弹道型微循环流的比例f和流速v b、和组织中水分子的扩散系数D t；所述FC-NC信号的联合模型由NC信号模型和FC信号模型联合而成，形式为：
Figure PCTCN2021074844-appb-000008
Figure PCTCN2021074844-appb-000009
其中S和S 0分别是b值下的弥散加权信号和非扩散加权信号，f是弹道型微循环流的比例，D t是组织中水分子的扩散系数，D b是血液中水分子的扩散系数，v b是弹道型微循环流流速的量度，α是扩散编码梯度场的一阶矩。
上述装置中的各模块，本质上对应于前述的步骤一～步骤四，前述步骤一～步骤四中的具体做法也都可以应用于该装置的各模块中。
本领域的技术人员应当知道，本发明中所涉及的各模块、功能可以通过电路、其他硬件或者可执行的程序代码来完成，只要能够实现相应功能即可。若采用代码，则代码可存储于存储装置中，并有计算装置中的相应元件执行。本发明的实现更不限制于任何特定的硬件和软件结合。本发明中的各硬件型号均可采用市售产品，可根据实际用户需求进行选择。当然，在上述装置中，必要时也需要配合其他必要硬件或软件、系统，本领域技术人员可根据实际进行设计，此处不再赘述。
另外，在其他实施例中，还可以提供一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其包括存储器和处理器；
所述存储器，用于存储计算机程序；
所述处理器，用于当执行所述计算机程序时，实现如步骤一～步骤四所展示的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法。
需要注意的是，存储器可以包括随机存取存储器(Random Access Memory，RAM)，也可以包括非易失性存储器(Non-Volatile Memory，NVM)，例如至少一个磁盘存储器。上述的处理器可以是通用处理器，包括中央处理器(Central  Processing Unit，CPU)、网络处理器(Network Processor，NP)等；还可以是数字信号处理器(Digital Signal Processing，DSP)、专用集成电路(Application Specific Integrated Circuit，ASIC)、现场可编程门阵列(Field-Programmable Gate Array，FPGA)或者其他可编程逻辑器件、分立门或者晶体管逻辑器件、分立硬件组件。当然，还装置中还应当具有实现程序运行的必要组件，例如电源、通信总线等等。
另外，在上述装置中，存储器和处理器还可以进一步集成在磁共振成像系统的数据处理设备中，磁共振成像系统获取诊断对象的相应IVIM信号数据后，可以存储在存储器中，然后通过处理器对其调用内部程序进行处理，直接输出结果。
另外，在其他实施例中，还可以提供一种计算机可读存储介质，该存储介质上存储有计算机程序，当所述计算机程序被处理器执行时，实现如步骤一～步骤四所展示的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法。
需要指出的是，以上所述的实施例只是本发明的一种较佳的方案，然其并非用以限制本发明。有关技术领域的普通技术人员，在不脱离本发明的精神和范围的情况下，还可以做出各种变化和变型。因此凡采取等同替换或等效变换的方式所获得的技术方案，均落在本发明的保护范围内。

Claims (10)

  1. 一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法，其特征在于，包括以下步骤：
    S1：在自旋回波扩散加权序列的180°重聚回波两侧施加相同的双极性梯度场，构建流速补偿(FC)的扩散加权序列；
    S2：在自旋回波扩散加权序列的180°重聚回波两侧施加镜像对称的双极性梯度场，构建非流速补偿(NC)的扩散加权序列；
    S3：针对若干不同的扩散敏感系数b值，在每个b值下分别采用流速补偿(FC)的扩散加权序列和非流速补偿(NC)的扩散加权序列获取待测的孕妇胎盘的IVIM信号；
    S4：利用不同b值下得到的两种序列下的IVIM信号数据，对FC-NC信号的联合模型进行拟合，估计得到弹道型微循环流的比例f和流速v b、和组织中水分子的扩散系数D t；所述FC-NC信号的联合模型由NC信号模型和FC信号模型联合而成，形式为：
    Figure PCTCN2021074844-appb-100001
    Figure PCTCN2021074844-appb-100002
    其中S和S 0分别是b值下的弥散加权信号和非扩散加权信号，f是弹道型微循环流的比例，D t是组织中水分子的扩散系数，D b是血液中水分子的扩散系数，v b是弹道型微循环流流速的量度，α是扩散编码梯度场的一阶矩。
  2. 如权利要求1所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法，其特征在于，所述的S1中，流速补偿(FC)的扩散加权序列构建方法为：在自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个第一双极扩散梯度，同时在180°重聚焦脉冲之后施加一个与第一双极扩散梯度相同的第二双极扩散梯度，实现流速补偿梯度；第一双极扩散梯度和第二双极扩散梯度的一阶矩为零；在第二双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集；
    所述的S2中，非流速补偿(NC)的扩散加权序列构建方法为：在另一条自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个与所述 第一双极扩散梯度相同的第三双极扩散梯度，同时在180°重聚焦脉冲之后施加一个与第三双极扩散梯度镜像对称的第四双极扩散梯度，实现非流速补偿梯度；第三双极扩散梯度和第四双极扩散梯度的一阶矩为非零；在第四双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集。
  3. 如权利要求1所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法，其特征在于，所述的S3中，b值选择覆盖10-600s/mm 2范围的多个数值点，且每个b值下分别在6个扩散方向采集流速补偿和非流速补偿的IVIM信号。
  4. 如权利要求1所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法，其特征在于，所述的S4中，在进行拟合之前，需要首先对不同b值下采集的扩散加权图像进行多次迭代的线性配准，校正由于母体或胎儿运动导致的运动伪影，并将流速补偿和非流速补偿的IVIM信号之间进行配准；所述的S4中，血液中水分子的扩散系数D b可以设置为1.5μm 2/ms，在流速补偿(FC)的扩散加权序列中，扩散编码梯度场的一阶矩α可以设置为0；FC-NC信号的联合模型可以采用最小二乘非线性曲线拟合。
  5. 一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其特征在于，包括：
    FC序列构建模块：用于在自旋回波扩散加权序列的180°重聚回波两侧施加相同的双极性梯度场，构建流速补偿(FC)的扩散加权序列；
    NC序列构建模块：用于在自旋回波扩散加权序列的180°重聚回波两侧施加镜像对称的双极性梯度场，构建非流速补偿(NC)的扩散加权序列；
    IVIM信号获取模块：用于针对若干不同的扩散敏感系数b值，在每个b值下分别采用流速补偿(FC)的扩散加权序列和非流速补偿(NC)的扩散加权序列获取待测的孕妇胎盘的IVIM信号；
    以及联合模型参数估计模块：用于利用不同b值下得到的两种序列下的IVIM信号数据，对FC-NC信号的联合模型进行拟合，估计得到弹道型微循环流的比例f和流速v b、和组织中水分子的扩散系数D t；所述FC-NC信号的联合模型由NC信号模型和FC信号模型联合而成，形式为：
    Figure PCTCN2021074844-appb-100003
    Figure PCTCN2021074844-appb-100004
    其中S和S 0分别是b值下的弥散加权信号和非扩散加权信号，f是弹道型微循环流的比例，D t是组织中水分子的扩散系数，D b是血液中水分子的扩散系数，v b是弹道型微循环流流速的量度，α是扩散编码梯度场的一阶矩。
  6. 如权利要求5所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其特征在于，所述的FC序列构建模块中，流速补偿(FC)的扩散加权序列构建方法为：在自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个第一双极扩散梯度，同时在180°重聚焦脉冲之后施加一个与第一双极扩散梯度相同的第二双极扩散梯度，实现流速补偿梯度；第一双极扩散梯度和第二双极扩散梯度的一阶矩为零；在第二双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集；
    所述的NC序列构建模块中，非流速补偿(NC)的扩散加权序列构建方法为：在另一条自旋回波扩散加权序列的90°激发脉冲与180°重聚焦脉冲之间，施加一个与所述第一双极扩散梯度相同的第三双极扩散梯度，同时在180°重聚焦脉冲之后施加一个与第三双极扩散梯度镜像对称的第四双极扩散梯度，实现非流速补偿梯度；第三双极扩散梯度和第四双极扩散梯度的一阶矩为非零；在第四双极扩散梯度之后施加单次自旋回波平面成像序列，用于数据采集。
  7. 如权利要求5所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其特征在于，所述的IVIM信号获取模块中，b值选择覆盖10-600s/mm 2范围的多个数值点，且每个b值下分别在6个扩散方向采集流速补偿和非流速补偿的IVIM信号。
  8. 如权利要求5所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其特征在于，所述的联合模型参数估计模块中，在进行拟合之前，需要首先对不同b值下采集的扩散加权图像进行多次迭代的线性配准，校正由于母体或胎儿运动导致的运动伪影，并将流速补偿和非流速补偿的IVIM信号之间进行配准；所述的S4中，血液中水分子的扩散系数D b可以设置为1.5μm 2/ms，在流速补偿(FC)的扩散加权序列中，扩散编码梯度场的一阶矩α为0；FC-NC信号的联合模型可以采用最小二乘非线性曲线拟合。
  9. 一种利用流速补偿和非补偿的弥散磁共振测量胎盘血流的装置，其特征在于，包括存储器和处理器；
    所述存储器，用于存储计算机程序；
    所述处理器，用于当执行所述计算机程序时，实现如权利要求1～4任一项所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法。
  10. 一种计算机可读存储介质，其特征在于，所述存储介质上存储有计算机程序，当所述计算机程序被处理器执行时，实现如权利要求1～4任一项所述的利用流速补偿和非补偿的弥散磁共振测量胎盘血流的方法。
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