A gas MRI method for evaluating pulmonary gas-blood exchange function

Abstract

This invention discloses a gas MRI method for assessing pulmonary gas-blood exchange function. It involves acquiring hyperpolarized inert gas magnetic resonance spectra of the subject's lungs and calculating the chemical shift differences between signals. Based on these chemical shift differences, parameters are set and scanned using a k-space radially filled ultrashort echo pulse sequence to obtain raw data simultaneously containing dissolved and gaseous signals. Fourier transform, cyclic shifting, inverse Fourier transform, and gridded reconstruction are performed on the raw data to obtain dissolved and gaseous images. These images are then segmented and divided to obtain a gas-blood exchange ratio distribution map of the lungs. This invention can be used for direct, high signal-to-noise ratio, simultaneous imaging of multiple hyperpolarized inert gas magnetic resonance signals in the lungs.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic resonance imaging, and in particular to a gas MRI method for evaluating pulmonary gas-blood exchange function. Background Art

[0002] At present, the main method for visually evaluating the pulmonary gas-blood exchange function in clinical practice is single photon emission computed tomography (SPECT) (European journal of nuclear medicine and molecular imaging, 2019, 46(12): 2429-2451.). SPECT uses 99mTc-DTPA aerosol to perform ventilation and perfusion imaging on subjects, and indirectly obtains information on the pulmonary gas-blood exchange function of subjects by analyzing the matching of ventilation and perfusion. However, SPECT is radioactive and can damage the lungs of subjects.

[0003] Compared with SPECT, hyperpolarized inert gas magnetic resonance imaging (MRI) technology can evaluate the pulmonary gas-blood exchange function without invasion, ionizing radiation and radioactivity, and has made rapid progress in clinical research in recent years. 129 Xe, 131 Xe, 83 Kr, etc., have good solubility and chemical shift sensitivity. In addition to gaseous signals (Gas, 0ppm), multiple magnetic resonance signals of lung tissue and plasma (Tissue and Plasma, TP, 197ppm) and red blood cells (Red Blood Cell, RBC, 212ppm) can be observed in the human lung. Among them, TP and RBC signals are collectively referred to as dissolved signals. By measuring these three signals, the gas-blood exchange function information of the lung can be obtained. Thanks to the above advantages and the characteristics of MRI itself without ionizing radiation and radioactivity, hyperpolarized inert gas MRI has been widely used in the evaluation of pulmonary gas-blood exchange function. Summary of the invention

[0004] In response to the problems existing in the above-mentioned prior art, the present invention provides a gas MRI method for evaluating the gas-blood exchange function of the lungs, which can directly, with a high signal-to-noise ratio, and simultaneously image multiple hyperpolarized inert gas magnetic resonance signals of the lungs, and ultimately obtain a visual evaluation of the gas-blood exchange function of the lungs.

[0005] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0006] A gas MRI method for evaluating pulmonary gas-blood exchange function comprises the following steps:

[0007] Step 1: The subject inhales a hyperpolarized inert gas in a magnetic resonance imaging apparatus, and uses a high-frequency selective radio frequency pulse to excite the hyperpolarized inert gas magnetic resonance signal in the lungs. The subject's lung magnetic resonance spectrum is collected to obtain dissolved state signals and gaseous state signals, and the chemical shift ind of the dissolved state signal relative to the relative gaseous state signal is calculated. The flip angle α of the radio frequency excited dissolved state signal is calculated. d (ind), and the off-resonance angle α for the gaseous signal g (ind),

[0008] Step 2: Perform a k-space radial filling ultrashort echo pulse sequence scan on the subject's lungs, and set the total number of sampling spokes N proj , the number of sampling points on each spoke is N point , repeat the time TR and sampling trajectory to obtain the raw data Rawdata(ind) containing gaseous signal and dissolved signal,

[0009] Step 3: Reconstruct the image based on the raw data Rawdata(ind) collected in step 2 and the sampling trajectory to obtain the lung ventilation image I g (ind) and lung dissolved image I d (ind),

[0010] Step 4: The lung ventilation image I obtained in step 3 g (ind) and lung dissolved image I d (ind) segmentation to obtain the segmented lung ventilation image I Segment,g (ind) and lung dissolved image I Segment,d (ind);

[0011] The segmented lung dissolved image I Segment,d (ind) and lung ventilation image I Segment,g (ind) Make point-to-point ratios, perform flip angle correction, and calculate the gas-blood exchange ratio distribution map from gaseous signals to dissolved signals d / g (ind).

[0012] As mentioned in step 2, the k-space radial filling ultrashort echo pulse sequence parameters include receiving bandwidth BW, field of view FOV, RF offset offset RF (ind) and the offset of the analog-to-digital converter ADC (ind),

[0013] BW≤-2·γ·B0·ind

[0014] FOV ≥ 2 FOV min

[0015] offset RF(ind) = γ·B0·ind

[0016] offset ADC (ind)=0.5·γ·B0·ind

[0017] Where, γ is the gyromagnetic ratio of the inert gas, B0 is the main magnetic field strength, FOV min It is the smallest field of view that can encompass the subject's lung anatomy.

[0018] As mentioned above in step 2, the sampling trajectory is a random trajectory combining the spherical Fibonacci spiral and the Halton sequence. The three-dimensional coordinates (x(i), y(i), z(i)) of the sampling spoke end point in k-space are calculated as follows:

[0019]

[0020] y(i)=r(i)×cos(θ(i)),

[0021] z(i)=r(i)×sin(θ(i)),

[0022]

[0023]

[0024] Where i is N proj The number of the root sampling spoke, i∈{1, 2, 3, ..., N proj}.

[0025] As mentioned above, the sampling spokes are numbered Porj in the order of actual sampling. Order1 (i) is obtained based on the following steps:

[0026] Step 2.1: Set the number of spokes N set , the number of beam splitting Bin;

[0027] Step 2.2, initialize temporary variables k1, k2, k3, and initialize the serial number i of the sampling spoke, k1 = 0; k2 = 0; k3 = 0; i = 0;

[0028] Step 2.3, k1=k1+1;

[0029] Step 2.4, k2=k2+1;

[0030] Step 2.5, k3=k3+1;

[0031] Step 2.6, i=i+1;

[0032] Step 2.7. Calculate Porj Order1 (i)

[0033] Porj Order1 (i)=k1+(k2-1)·Bin+(k3-1)·N set ,

[0034] Step 2.8: If k3≤floor(N proj / N set ), then repeat steps 2.5-2.7; otherwise, set k3=0 and proceed to step 2.9;

[0035] Step 2.9: If k2≤floor(N set / Bin), then repeat steps 2.4-2.7; otherwise, set k2=0 and proceed to step 2.10;

[0036] Step 2.10: If k1≤floor(Bin), repeat steps 2.3-2.7; otherwise, end the calculation;

[0037] Among them, floor is the rounding down function.

[0038] As mentioned above, step 3 includes the following steps:

[0039] Step 3.1, Fourier transform: perform Fourier transform on each radial sampling spoke of the collected raw data Rawdata(ind) to obtain the spoke spectrum Proj(ind) of the raw data Rawdata(ind);

[0040] Step 3.2, cyclic shift: cyclically shift the spoke spectrum Proj(ind) of the original data Rawdata(ind) backward by the number of points C(ind) to obtain the spoke spectrum Proj of the dissolved state signal at the center of the spectrum. d (ind); the spoke spectrum Proj(ind) of the original data Rawdata(ind) is moved forward by the number of points C(ind) to obtain the spoke spectrum Proj of the gaseous signal at the center of the spectrum g (ind),

[0041]

[0042] Step 3.3, inverse Fourier transform: the spoke spectrum Proj g (ind) and spoke spectrum Proj d (ind) are respectively subjected to inverse Fourier transform resampling to obtain the gaseous signal spoke set k g (ind) and dissolved signal spoke set k d (ind);

[0043] Step 3.4: Grid reconstruction: For the gaseous signal spoke set k g(ind) and dissolved signal spoke set k d (ind) Perform grid reconstruction to obtain lung ventilation image I g (ind) and lung dissolved image I d (ind).

[0044] As mentioned above, the gas-blood exchange ratio distribution map from gaseous signal to dissolved signal d / g (ind) is based on the following formula:

[0045]

[0046] In step 1 above, the dissolved state signal includes the tissue plasma dissolved state signal and the red blood cell dissolved state signal. The chemical shift of the dissolved state signal relative to the gaseous signal is ind∈{δ RBC ,δ TP}, δ TP is the chemical shift of the tissue plasma dissolved signal relative to the gaseous signal, δ RBC is the chemical shift of the red blood cell dissolved state signal relative to the gaseous state signal,

[0047] In step 1, the magnetic resonance spectrum of the lung of the subject is collected to obtain the tissue plasma dissolved state signal of the hyperpolarized inert gas dissolved in the tissue plasma, the red blood cell dissolved state signal of the hyperpolarized inert gas dissolved in the red blood cells, and the gaseous signal in the alveolar cavity.

[0048] The k-space radial filling ultrashort echo pulse sequence in step 2 includes a steady-state establishment pulse sequence and a data acquisition pulse sequence.

[0049] The steady-state pulse sequence performs saturation processing on the dissolved state signal before sampling, so that the dissolved state signal remains steady during the acquisition process under the repetition time TR. High-frequency selective multi-petal sinc pulses or SLR pulses are used to alternately saturate the tissue plasma dissolved state signal and the red blood cell dissolved state signal, and then the dissolved state signal excited to the horizontal direction by the saturation pulse is quickly destroyed following the gradient. The alternating saturation process of the tissue plasma dissolved state signal and the red blood cell dissolved state signal in the entire steady-state establishment sequence is repeated n times, and the repetition time of each time is equal to the repetition time TR of data acquisition;

[0050] During data acquisition, the tissue plasma lysis state signal and the red blood cell lysis state signal are alternately sampled in FID mode according to the data acquisition pulse sequence. The RF and analog-to-digital converter ADC are turned on twice in each repetition time TR. The first RF bias and analog-to-digital converter bias are offset RF (δ RBC ) and offset ADC (δ RBC ), the second RF bias and analog-to-digital converter bias are offsetRF (δ TP ) and offset ADC (δ TP ), and finally the raw data Rawdata(δ RBC ), and the raw data Rawdata(δ TP ), record the original data Rawdata(δ RBC ) and the original data Rawdata(δ TP ) is the original data Rawdata(ind).

[0051] In step 1 above, the dissolved state signal is a tissue plasma dissolved state signal or a red blood cell dissolved state signal.

[0052] The k-space radial filling ultrashort echo pulse sequence in step 2 includes a steady-state establishment pulse sequence and a data acquisition pulse sequence.

[0053] The steady-state establishment pulse sequence performs saturation processing on the dissolved state signal before sampling, so that the dissolved state signal remains steady during the acquisition process under the repetition time TR. The dissolved state signal is saturated with a high-frequency selective multi-petal sinc pulse or an SLR pulse, and then the dissolved state signal excited to the horizontal direction by the saturation pulse is rapidly destroyed following the gradient. The saturation process of the dissolved state signal in the entire steady-state establishment sequence is repeated n times, and the repetition time of each time is equal to the repetition time TR of data acquisition.

[0054] During data acquisition, the dissolved state signal is sampled in FID mode according to the data acquisition pulse sequence. The RF and analog-to-digital converter ADC are turned on once in each repetition time TR, and the RF bias and analog-to-digital converter bias are offset respectively. RF (ind) and offset ADC (ind), and finally the raw data Rawdata(ind) containing both gaseous signal and dissolved signal is obtained.

[0055] Compared with the prior art, the present invention has the following characteristics:

[0056] 1. By using the k-space radial filling ultrashort echo pulse sequence and the reasonable setting of sampling bandwidth, radio frequency and ADC frequency offset, it is possible to directly obtain lung hyperpolarized inert gas double chemical shift images with high signal-to-noise ratio.

[0057] 2. By using high-frequency selective RF pulses and combining the scheme of interleaved acquisition of TP and RBC signals in dissolved state signals, TP and RBC images at specific exchange times can be obtained simultaneously in one pulse sequence.

[0058] 3. By combining the Fibonacci spiral on the sphere and the improved Halton sequence, the sampling spokes can be evenly distributed in the spherical k-space at any time during the radial acquisition process, thereby achieving high-multiple undersampling of data under 3D radial filling while ensuring image quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is a flow chart of the steps of the method of the present invention;

[0060] Figure 2 It is a schematic diagram of a random sampling trajectory combining the Fibonacci spiral on a sphere and the improved Halton sequence in the method of the present invention.

[0061] Figure 3 is a k-space radial filling ultrashort echo pulse sequence diagram used in step 2 of embodiment 1;

[0062] Figure 4 is the image reconstruction flow chart of step 3 in Example 1;

[0063] Figure 5 The original image obtained by gridding reconstruction in step 3 of Example 1 and the exchange ratio distribution map obtained in step 4;

[0064] Figure 6 is a k-space radial filling ultrashort echo pulse sequence diagram used in step 2 of embodiment 2;

[0065] Figure 7 is the image reconstruction flow chart of step 3 in embodiment 2;

[0066] Figure 8 It is the original image obtained by gridding reconstruction in step 3 of Example 2 and the exchange ratio distribution map obtained in step 4. DETAILED DESCRIPTION

[0067] Reference Figure 1 The gas magnetic resonance imaging method for evaluating the pulmonary gas-blood exchange function described in the present invention can be used to perform direct, high signal-to-noise ratio, and simultaneous imaging of multiple hyperpolarized inert gas magnetic resonance signals in the lungs, and ultimately obtain a visualized evaluation of the pulmonary gas-blood exchange function.

[0068] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the following Figures 2 to 8 Two specific implementation modes of the present invention (a case where there are three hyperpolarized inert gas magnetic resonance signals in the lungs and a case where there are two hyperpolarized inert gas magnetic resonance signals in the lungs) are described in detail respectively.

[0069] Example 1

[0070] This example describes the application of the method to hyperpolarized noble gases 129 Xe, 131 Xe or 83 Kr In the case where there are three magnetic resonance signals (gaseous signal, tissue plasma signal and red blood cell signal) in the lungs, such as rats and humans, the purpose is to image the three signals simultaneously and calculate the exchange ratio of the gaseous signal to the two dissolved signals.

[0071] A gas magnetic resonance imaging method for evaluating pulmonary gas-blood exchange function comprises the following steps:

[0072] Step 1. The subject inhales a hyperpolarized inert gas in a magnetic resonance imaging apparatus, and a high-frequency selective radio frequency pulse is used to excite the hyperpolarized inert gas magnetic resonance (MR) signal in the lung, and the subject's lung magnetic resonance spectrum is collected to obtain a tissue plasma dissolved state signal of the hyperpolarized inert gas dissolved in tissue plasma (TP), a red blood cell dissolved state signal dissolved in red blood cells (RBC), and a gaseous (Gas) signal in the alveolar cavity; wherein the tissue plasma dissolved state signal and the red blood cell dissolved state signal are both referred to as dissolved state (d) signals; the gaseous signal is taken as a reference, recorded as 0 ppm, and the chemical shifts of the tissue plasma dissolved state signal and the red blood cell dissolved state signal relative to the gaseous signal are recorded as chemical shift δ TP and chemical shift δ RBC Then, the flip angle α of the RF excited dissolved state signal is calculated d (ind), and the off-resonance angle α for the gaseous signal g (ind), where ind is the chemical shift of the dissolved state signal of the hyperpolarized noble gas in the lung, ind∈{δ RBC ,δ TP}. Wherein, the preferred high frequency selective radio frequency pulse in this step is a multi-lobe sinc pulse or an SLR pulse;

[0073] Step 2: Perform a k-space radial filling ultra-short echo pulse sequence scan on the subject's lungs, where the k-space radial filling ultra-short echo pulse sequence parameters need to be set according to the chemical shift ind calculated in step 1. Specifically, the receiving bandwidth BW (Bandwidth), field of view FOV (Field of View), RF offset offset RF (ind) and the offset of the analog-to-digital converter ADC (ind), satisfies the following formula:

[0074] BW≤-2·γ·B0·ind Formula 1

[0075] FOV ≥ 2 FOV min Formula 2

[0076] offset RF (ind) = γ·B0·ind Formula 3

[0077] offset ADC (ind)=0.5·γ·B0·ind Formula 4

[0078] Where, γ is the gyromagnetic ratio of the inert gas, B0 is the main magnetic field strength, FOV min is the minimum field of view FOV that can envelop the anatomical structure of the subject's lungs, ind is the chemical shift of the dissolved signal of the hyperpolarized inert gas in the lungs described in step 1, ind∈{δ RBC ,δ TP For tissue plasma and red blood cells, different k-space radial filling ultrashort echo pulse sequence parameters are used, that is, the chemical shift δ corresponding to the tissue plasma and red blood cells selected by ind RBC and δ TP , respectively set the BW and offset calculated by formulas 1, 3, and 4 RF and offset ADC ;For the convenience of post-processing, the FOV selected twice is the same;

[0079] In addition to the above parameters, set the total number of sampling spokes N proj , the number of sampling points on each spoke is N point , repetition time TR and sampling trajectory (random trajectory or sequential trajectory), where the sampling trajectory refers to the position of the sampling spoke end point in k space under k space radial filling; preferably, the sampling trajectory is a random trajectory combining the spherical Fibonacci spiral and the optimized Halton sequence. Specifically, the three-dimensional coordinates (x(i), y(i), z(i)) of the sampling spoke end point in k space are first calculated by the spherical Fibonacci spiral, and the calculation formula is as follows:

[0080]

[0081] y(i)=r(i)×cos(θ(i)), Formula 6

[0082] z(i)=r(i)×sin(θ(i)), Formula 7

[0083]

[0084]

[0085] Where i is N proj The number of the root sampling spoke, i∈{1, 2, 3, ..., N proj};

[0086] Then, the order of the sampling spokes corresponding to the sequence number i in the above formula is rearranged according to the optimized Halton sequence. Specifically, the sequence number Porj of the sampling spokes corresponding to the sequence number i in actual sampling is generated by the following steps: Order1 (i)

[0087] Step 2.1: Parameter setting, including the number of spokes N set , the number of beam splitting Bin;

[0088] Step 2.2, initialize the temporary variables k1, k2, k3 and i, k1 = 0; k2 = 0; k3 = 0; i = 0;

[0089] Step 2.3, temporary variable assignment calculation, k1 = k1 + 1;

[0090] Step 2.4, temporary variable assignment calculation, k2=k2+1;

[0091] Step 2.5, temporary variable assignment calculation, k3=k3+1;

[0092] Step 2.6, temporary variable assignment calculation, i=i+1;

[0093] Step 2.7, calculate the sequence number of the actual sampling,

[0094] Porj Order1 (i)=k1+(k2-1)·Bin+(k3-1)·N set , Formula 10

[0095] Step 2.8: If k3≤floor(N proj / N set ), then repeat steps 2.5-2.7; otherwise, set k3=0 and proceed to step 2.9;

[0096] Step 2.9: If k2≤floor(N set / Bin), then repeat steps 2.4-2.7; otherwise, set k2=0 and proceed to step 2.10;

[0097] Step 2.10: If k1≤floor(Bin), repeat steps 2.3-2.7; otherwise, end the calculation;

[0098] Where i is the number of the sampling spoke in k-space as described above, i∈{1, 2, 3, ..., N proj}; Porj Order1 (i) is the sequence number of the sampling spoke corresponding to serial number i during actual sampling; N set is the number of defined cross spokes; Bin is the number of defined beams, and floor is the floor function;

[0099] In actual sampling, the sampling spoke end point selection order is based on Porj Order1 The value of (i) determines, Figure 2 Shows N proj When it is set to 1000, the distribution of the actually sampled filled spokes in the spherical k-space is obtained when i is 1, 2, 3, 10, 100 and 1000 respectively.

[0100] After completing the parameter setting, the k-space radial filling ultrashort echo pulse sequence is as follows Figure 3 As shown, it mainly includes two parts: steady-state establishment pulse sequence and data acquisition pulse sequence (parameters include receiving bandwidth (Bandwidth, BW), field of view (Field of View, FOV), RF offset (offset RF ) and the offset of the analog-to-digital converter ADC )):

[0101] The steady-state pulse sequence performs saturation processing on the dissolved state signal before sampling, so that the dissolved state signal remains steady during the acquisition process under the repetition time TR. High-frequency selective multi-petal sinc pulses or SLR pulses are used to alternately saturate the tissue plasma dissolved state signal and the red blood cell dissolved state signal, and then the dissolved state signal excited to the horizontal direction by the saturation pulse is quickly destroyed following the gradient. The alternating saturation process of the tissue plasma dissolved state signal and the red blood cell dissolved state signal in the entire steady-state establishment sequence is repeated n times, and the repetition time of each time is equal to the repetition time TR of data acquisition;

[0102] During data acquisition, the tissue plasma lysis state signal and the red blood cell lysis state signal are alternately sampled in FID mode according to the data acquisition pulse sequence. The RF and analog-to-digital converter ADC are turned on twice in each repetition time TR. The first RF bias and analog-to-digital converter bias are offset RF (δ RBC ) and offset ADC (δ RBC ), the second RF bias and analog-to-digital converter bias are offset RF (δ TP ) and offset ADC (δ TP Finally, the raw data Rawdata (δ RBC ), and the raw data Rawdata(δ TP ), for the convenience of expression, the original data is recorded as Rawdata(δ RBC ) and the original data Rawdata(δ TP) is the raw data Rawdata(ind); ind is the chemical shift of the dissolved state signal of the hyperpolarized inert gas in the lung described in step 1, ind∈{δ RBC ,δ TP}.

[0103] Step 3: Reconstruct the image based on the raw data (ind) collected in step 2 and the sampling trajectory. This step mainly includes four parts: Fourier transform, cyclic shift, inverse Fourier transform and grid reconstruction. Figure 4 As shown:

[0104] Step 3.1, Fourier transform includes the following steps: performing Fourier transform on each radial sampling spoke of the collected raw data Rawdata(ind) to obtain the spoke spectrum Proj(ind) of the raw data Rawdata(ind);

[0105] Step 3.2, cyclic point shifting includes the following steps: cyclically shifting the spoke spectrum Proj(ind) forward (or backward) by C(ind) points according to formula 11;

[0106]

[0107] Where γ is the gyromagnetic ratio of the inert gas, B0 is the main magnetic field strength, BW is the receiving bandwidth, ind is the chemical shift of the dissolved state signal of the hyperpolarized inert gas in the lung described in step 1, and ind∈{δ RBC ,δ TP}.

[0108] The spoke spectrum Proj(ind) of the original data Rawdata(ind) is moved backward by the number of points C(ind) to obtain the spoke spectrum Proj of the dissolved state signal at the center of the spectrum. d (ind); the spoke spectrum Proj(ind) of the original data Rawdata(ind) is moved forward by the number of points C(ind) to obtain the spoke spectrum Proj of the gaseous signal at the center of the spectrum g (ind);

[0109] Step 3.3, inverse Fourier transform includes the following steps: g (ind) and spoke spectrum Proj d (ind) are respectively subjected to inverse Fourier transform resampling to obtain the gaseous signal spoke set k g (ind) and dissolved signal spoke set k d (ind);

[0110] Step 3.4: Grid reconstruction: For the above gaseous signal spoke set k g(ind) and dissolved signal spoke set k d (ind) Perform grid reconstruction to obtain lung ventilation image I g (ind) and lung dissolved image I d (ind); ind is the chemical shift of the dissolved state signal of the hyperpolarized inert gas in the lung described in step 1, ind∈{δ RBC ,δ TP}.

[0111] Step 4: The lung ventilation image I obtained in step 3.4 g (ind) and lung dissolved image I d (ind) segmentation to obtain the segmented lung ventilation image I Segment,g (ind) and lung dissolved image I Segment,d (ind);

[0112] The segmented lung dissolved image I Segment,d (ind) and lung ventilation image I Segment,g (ind) Make a point-to-point ratio and perform flip angle correction. According to formula 12, the gas-blood exchange ratio distribution map of the gaseous signal to the dissolved signal is obtained. d / g The calculation formula of (ind) is,

[0113]

[0114] Figure 5 Shows α d Lung ventilation image I when (ind) is 90° g (ind), dissolved image I d (ind) and dissolved image to ventilation image ratio Map d / g (ind), ind∈{δ RBC ,δ TP}.

[0115] As an implementable embodiment, step 1, step 2, step 3, and step 4 in this embodiment are respectively implemented by module 1, module 2, module 3, and module 4 in a gas magnetic resonance imaging device for evaluating pulmonary gas-blood exchange function.

[0116] Example 2

[0117] In this embodiment, the method is applicable to hyperpolarized noble gas 129 Xe, 131 Xe or 83In the case where there are two magnetic resonance signals (one gaseous signal and one dissolved signal) in the lungs of Kr, such as mice, rabbits and other animals, the purpose is to image the two signals simultaneously and calculate the exchange ratio of the gaseous signal to the dissolved signal. This embodiment will focus on the differences between the steps and embodiment 1.

[0118] A gas magnetic resonance imaging method for evaluating pulmonary gas-blood exchange function comprises the following steps:

[0119] Step 1 is basically the same as step 1 in Example 1, collecting the magnetic resonance spectrum of the lung of the subject. The difference is that only one dissolved state (d) signal of hyperpolarized inert gas (tissue plasma dissolved state signal or red blood cell dissolved state signal) is obtained, and the gaseous (Gas) signal in the alveoli is used as a reference, and the chemical shift of the dissolved state signal is recorded as δ d At the same time, the flip angle α of the RF pulse on the dissolved state signal is calculated d (ind), and the off-resonance angle α for the gaseous signal g (ind); that is, in this embodiment, the chemical shift ind of the dissolved state signal of the hyperpolarized inert gas in the lung has only one value, ind∈{δ d};

[0120] Step 2 is basically the same as step 2 in embodiment 1, except that the k-space radial filling ultrashort echo pulse sequence includes a steady-state establishment pulse sequence and a data acquisition pulse sequence. Figure 6 As shown,

[0121] The k-space radial filling ultrashort echo pulse sequence includes a steady-state establishment pulse sequence and a data acquisition pulse sequence.

[0122] The steady-state establishment pulse sequence performs saturation processing on the dissolved state signal before sampling, so that the dissolved state signal remains steady during the acquisition process under the repetition time TR. The dissolved state signal is saturated with a high-frequency selective multi-petal sinc pulse or an SLR pulse, and then the dissolved state signal excited to the horizontal direction by the saturation pulse is rapidly destroyed following the gradient. The saturation process of the dissolved state signal in the entire steady-state establishment sequence is repeated n times, and the repetition time of each time is equal to the repetition time TR of data acquisition.

[0123] During data acquisition, the dissolved state signal is sampled in FID mode according to the data acquisition pulse sequence. The RF and analog-to-digital converter ADC are turned on once in each repetition time TR, and the RF bias and analog-to-digital converter bias are offset respectively. RF (ind) and offset ADC (ind), and finally the raw data Rawdata(ind) containing both gaseous signal and dissolved signal is obtained.

[0124] Step 3 is the same as step 3 in Example 1. Figure 7 As shown, the final lung ventilation image I g (ind) and dissolved image I d (ind), ind∈{δ d};

[0125] Step 4 is the same as step 4 in Example 1. Figure 8 Shows α d Lung ventilation image I when it is 90° g (ind), dissolved image I d (ind), and the ratio of the two d / g (ind) result, ind∈{δ d}.

[0126] As an implementable embodiment, step 1, step 2, step 3, and step 4 in this embodiment are respectively implemented by module 1, module 2, module 3, and module 4 in a gas magnetic resonance imaging device for evaluating pulmonary gas-blood exchange function.

[0127] The above are some specific implementation methods of the present invention, and the protection scope of the present invention is not limited thereto. Any changes and substitutions that can be easily conceived by any person familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A gas MRI method for evaluating pulmonary gas-blood exchange function, characterized in that: The following steps are included: Step 1: The subject inhales a hyperpolarized inert gas in a magnetic resonance imaging apparatus, and uses a high-frequency selective radio frequency pulse to excite the hyperpolarized inert gas magnetic resonance signal in the lungs. The subject's lung magnetic resonance spectrum is collected to obtain dissolved state signals and gaseous state signals, and the chemical shift ind of the dissolved state signal relative to the relative gaseous state signal is calculated. The flip angle α of the radio frequency excited dissolved state signal is calculated. d (ind), and the off-resonance angle α for the gaseous signal g (ind), Step 2: Perform a k-space radial filling ultrashort echo pulse sequence scan on the subject's lungs, and set the total number of sampling spokes N proj , the number of sampling points on each spoke is N point , repeat the time TR and sampling trajectory to obtain the raw data Rawdata(ind) containing gaseous signal and dissolved signal, Step 3: Reconstruct the image based on the raw data Rawdata(ind) collected in step 2 and the sampling trajectory to obtain the lung ventilation image I g (ind) and lung dissolved image I d (ind), Step 4: The lung ventilation image I obtained in step 3 g (ind) and lung dissolved image I d (ind) segmentation to obtain the segmented lung ventilation image I Segment,g (ind) and lung dissolved image I Segment,d (ind); The segmented lung dissolved image I Segment,d (ind) and lung ventilation image I Segment,g (ind) Make point-to-point ratios, perform flip angle correction, and calculate the gas-blood exchange ratio distribution map from gaseous signals to dissolved signals d / g (ind), The step 3 comprises the following steps: Step 3.1, Fourier transform: perform Fourier transform on each radial sampling spoke of the collected raw data Rawdata(ind) to obtain the spoke spectrum Proj(ind) of the raw data Rawdata(ind); Step 3.2, cyclic shift: cyclically shift the spoke spectrum Proj(ind) of the original data Rawdata(ind) backward by the number of points C(ind) to obtain the spoke spectrum Proj of the dissolved state signal at the center of the spectrum. d (ind); the spoke spectrum Proj(ind) of the original data Rawdata(ind) is moved forward by the number of points C(ind) to obtain the spoke spectrum Proj of the gaseous signal at the center of the spectrum g (ind), Step 3.3, inverse Fourier transform: the spoke spectrum Proj g (ind) and spoke spectrum Proj d (ind) are respectively subjected to inverse Fourier transform resampling to obtain the gaseous signal spoke set k g (ind) and dissolved signal spoke set k d (ind); Step 3.4: Grid reconstruction: For the gaseous signal spoke set k d (ind) and dissolved signal spoke set k d (ind) Perform grid reconstruction to obtain lung ventilation image I g (ind) and lung dissolved image I d (ind), The gas-blood exchange ratio distribution map of the gaseous signal to the dissolved signal d / g (ind) is based on the following formula:

2. A gas MRI method for evaluating pulmonary gas-blood exchange function according to claim 1, characterized in that: In step 2, the k-space radial filling ultrashort echo pulse sequence parameters include receiving bandwidth BW, field of view FOV, radio frequency offset offset RF (ind) and the offset of the analog-to-digital converter ADC (ind), BW≤-2·γ·B0·ind FOV≥2·FOV min offset RF (in)=γ·B0·in offset ADC (in)=0.5·γ·B0·in Where, γ is the gyromagnetic ratio of the inert gas, B0 is the main magnetic field strength, FOV min It is the smallest field of view that can encompass the subject's lung anatomy.

3. A gas MRI method for evaluating pulmonary gas-blood exchange function according to claim 1, characterized in that: In step 2, the sampling trajectory is a random trajectory combining the spherical Fibonacci spiral and the Halton sequence, and the three-dimensional coordinates (x(i), y(i), z(i)) of the sampling spoke end point in k-space are calculated as follows: y(i)=r(i)×cos(θ(i)), z(i)=r(i)×sin(θ(i)), Where i is N proj The number of the root sampling spoke, i∈{1, 2, 3, ..., N proj }.

4. A gas MRI method for evaluating pulmonary gas-blood exchange function according to claim 3, characterized in that: The sampling spokes are numbered Porj in order during actual sampling. Order1 (i) is obtained based on the following steps: Step 2.1: Set the number of spokes N set , the number of beam splitting Bin; Step 2.2, initialize temporary variables k1, k2, k3, and initialize the serial number i of the sampling spoke, k1 = 0; k2 = 0; k3 = 0; i = 0; Step 2.3, k1=k1+1; Step 2.4, k2=k2+1; Step 2.5, k3=k3+1; Step 2.6, i=i+1; Step 2.

7. Calculate Porj Order1 (i) Porj Order1 (i)=k1+(k2-1)·Bin+(k3-1)·N set , Step 2.8: If k3≤floor(N proj / N set ), then repeat steps 2.5-2.7; otherwise, set k3=0 and proceed to step 2.9; Step 2.9: If k2≤floor(N set / Bin), then repeat steps 2.4-2.7; otherwise, set k2=0 and proceed to step 2.10; Step 2.10: If k1≤floor(Bin), repeat steps 2.3-2.7; otherwise, end the calculation; Among them, floor is the rounding down function.

5. A gas MRI method for evaluating pulmonary gas-blood exchange function according to claim 1, characterized in that: In step 1, the dissolved state signal includes the tissue plasma dissolved state signal and the red blood cell dissolved state signal, and the chemical shift of the dissolved state signal relative to the gaseous signal is ind∈{δ RBC ,δ TP }, δ TP is the chemical shift of the tissue plasma dissolved signal relative to the gaseous signal, δ RBC is the chemical shift of the red blood cell dissolved state signal relative to the gaseous state signal, In step 1, the magnetic resonance spectrum of the lung of the subject is collected to obtain the tissue plasma dissolved state signal of the hyperpolarized inert gas dissolved in the tissue plasma, the red blood cell dissolved state signal of the hyperpolarized inert gas dissolved in the red blood cells, and the gaseous signal in the alveolar cavity. In step 2, the k-space radial filling ultrashort echo pulse sequence includes a steady-state establishment pulse sequence and a data acquisition pulse sequence. The steady-state pulse sequence performs saturation processing on the dissolved state signal before sampling, so that the dissolved state signal remains steady during the acquisition process under the repetition time TR. High-frequency selective multi-petal sinc pulses or SLR pulses are used to alternately saturate the tissue plasma dissolved state signal and the red blood cell dissolved state signal, and then the dissolved state signal excited to the horizontal direction by the saturation pulse is quickly destroyed following the gradient. The alternating saturation process of the tissue plasma dissolved state signal and the red blood cell dissolved state signal in the entire steady-state establishment sequence is repeated n times, and the repetition time of each time is equal to the repetition time TR of data acquisition; During data acquisition, the tissue plasma lysis state signal and the red blood cell lysis state signal are alternately sampled in FID mode according to the data acquisition pulse sequence. The RF and analog-to-digital converter ADC are turned on twice in each repetition time TR. The first RF bias and analog-to-digital converter bias are offset RF (δ RBC ) and offset ADC (δ RBC ), the second RF bias and analog-to-digital converter bias are offset RF (δ TP ) and offset ADC (δ TP ), and finally the raw data Rawdata(δ RBC ), and the raw data Rawdata(δ TP ), record the original data Rawdata(δ RBC ) and the original data Rawdata(δ TP ) is the original data Rawdata(ind).

6. A gas MRI method for evaluating pulmonary gas-blood exchange function according to claim 1, characterized in that: In step 1, the dissolved state signal is a tissue plasma dissolved state signal or a red blood cell dissolved state signal, In step 2, the k-space radial filling ultrashort echo pulse sequence includes a steady-state establishment pulse sequence and a data acquisition pulse sequence. The steady-state establishment pulse sequence performs saturation processing on the dissolved state signal before sampling, so that the dissolved state signal remains steady during the acquisition process under the repetition time TR. The dissolved state signal is saturated with a high-frequency selective multi-petal sinc pulse or an SLR pulse, and then the dissolved state signal excited to the horizontal direction by the saturation pulse is rapidly destroyed following the gradient. The saturation process of the dissolved state signal in the entire steady-state establishment sequence is repeated n times, and the repetition time of each time is equal to the repetition time TR of data acquisition. During data acquisition, the dissolved state signal is sampled in FID mode according to the data acquisition pulse sequence. The RF and analog-to-digital converter ADC are turned on once in each repetition time TR, and the RF bias and analog-to-digital converter bias are offset respectively. RF (ind) and offset ADC (ind), and finally the raw data Rawdata(ind) containing both gaseous signal and dissolved signal is obtained.

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