A method of gas magnetic resonance imaging for quantitative measurement of oxygen concentration in the lungs

Abstract

The application discloses a gas magnetic resonance imaging method for lung oxygen concentration quantitative measurement, which utilizes hyperpolarized 129 Xe gas to perform magnetic resonance imaging, acquires image data sets corresponding to different breathing times, extracts phase information from the image data sets and corrects the phase information to obtain phase data sets, acquires B0 field images through the phase data sets, and finally acquires oxygen concentration distribution maps in the lungs corresponding to different breathing times according to the B0 field images; the application significantly shortens data acquisition time through B0 field image acquisition; the method of the application allows a larger excitation angle to be used, and compared with the method based on longitudinal relaxation rate in the prior art, a higher signal-to-noise ratio can be obtained, thereby improving evaluation accuracy; the application is based on phase images instead of amplitude images, and the influence of gas molecule diffusion can be reduced between different echoes.

Description

Technical Field

[0001] This invention belongs to the field of magnetic resonance imaging technology, specifically relating to a gas magnetic resonance imaging method for quantitative measurement of lung oxygen concentration, which is suitable for achieving rapid quantitative measurement of lung oxygen concentration. Background Technology

[0002] The lungs are a crucial organ for gas exchange between the body and the external environment, playing a vital role in metabolism. Current methods for measuring intrapulmonary oxygen concentration have several limitations. For example, while repeated-breath nitrogen elution can assess global oxygen concentration, it lacks sensitivity to local lesions. Furthermore, although invasive oxygen probes provide information on local oxygen concentration and blood oxygen saturation, their clinical feasibility is limited due to their invasiveness and susceptibility to variations in probe location.

[0003] In the field of hyperpolarized gas magnetic resonance imaging (HMI) of the lungs, existing research utilizes hyperpolarization... 3 He's longitudinal relaxation rate and oxygen partial pressure are used to quantitatively assess intrapulmonary oxygen concentration. However, this technique has many limitations: (1) due to 3 He is extremely rare in nature and expensive, which limits its clinical application; (2) Due to the irreversible polarization of hyperpolarized gas, radio frequency pulses and longitudinal relaxation during imaging will cause gas depolarization, thereby reducing the image signal-to-noise ratio (Magn Reson Med. 2001 Mar; 45(3): 421-30.); (3) Due to the long scanning time required for longitudinal relaxation rate measurement, this is a challenge for subjects who need to hold their breath for a long time (especially patients with lung diseases) (Magn Reson Med. 2014 Mar; 71(3): 1172-8.); (4) Gas molecules will diffuse to the adjacent area during long-term breath-holding, affecting the measurement of longitudinal relaxation rate, thereby reducing the accuracy of oxygen concentration measurement (Tomography. 2022 Sep 13; 8(5): 2268-2284).

[0004] In recent years, hyperpolarization 129 Xe technology has seen significant development, and its cost has decreased compared to... 3 It is cheaper. Although 129 The high solubility of Xe means that its longitudinal relaxation rate in the lungs is affected by the rate of gas-blood exchange, limiting its application in measuring intrapulmonary oxygen concentration. 129 The high sensitivity of Xe's large electron cloud structure to the external environment offers new possibilities for measuring intrapulmonary oxygen concentration. The concentrations of both oxygen and xenon are related to the probability of collisions between them, and consequently... 129 The frequency change of Xe is related (J. Chem. Phys. 1970 Apr; 53(6); 2310-2321). Theoretically, using129 Xe frequency has the potential to measure intrapulmonary oxygen concentration, but the specific implementation methods and effects still need further research to reveal. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems in the prior art by providing a gas magnetic resonance imaging method for quantitative measurement of lung oxygen concentration.

[0006] The above-mentioned objectives of the present invention are achieved by the following technical means:

[0007] A gas magnetic resonance imaging method for quantitative measurement of lung oxygen concentration includes the following steps:

[0008] Step 1: Subject's respiratory hyperpolarization 129 Xe gas was emitted n times and hyperpolarized with each breath of the subject. 129 Data was collected during the Xe gas process to obtain image datasets S1-S corresponding to different respiration rates. n ;

[0009] Step 2: From the image dataset S1-S n Phase information was extracted from the data, and then phases exceeding 360° were corrected to obtain the phase dataset P1-P corresponding to different respiratory rates. n Then, through the phase dataset P1-P n Obtain the B0 field image σ1-σ corresponding to different breathing rates. n ; Construct a formula for calculating intrapulmonary oxygen concentration and hyperpolarization of the i-th respiration. 129 The field strength σ of B0 after Xe gas i The formula, σ1-σ, corresponds to the B0 field image for different breathing numbers. n The field intensity σ of each pixel at the corresponding pixel position in the middle i Substitute the hyperpolarization of the i-th respiration 129 The field strength σ of B0 after Xe gas i The formula is used to obtain the parameter distribution plots of parameters A, B, and r. Finally, the parameters A, B, and σ are... i Substituting into the formula for calculating intrapulmonary oxygen concentration, we obtain the intrapulmonary oxygen concentration distribution map O1-O corresponding to different respiratory rates. n .

[0010] As described above, step 1 includes the following steps:

[0011] Step 1.1: The subject wears a lung tube. 129 Xe imaging coil and enters the scanning magnet;

[0012] Step 1.2: The subject breathes high-purity oxygen to wash out residual nitrogen in the lungs;

[0013] Step 1.3: The subject inhales hyperpolarized air at the end of expiration. 129 Xe gas was used, and the breath was held at the end of inspiration. Data was acquired using a multi-echo gradient echo sequence. This process was repeated n times to obtain image datasets S1-S1 corresponding to different number of breaths. n ;

[0014] Step 1.4: After the collection is completed, the subject inhales high-purity oxygen to restore blood oxygen saturation, and the subject's vital signs are monitored.

[0015] As described above, the i-th respiration hyperpolarization in step 2 129 The field strength σ of B0 after Xe gas i The formula:

[0016] σ i =Ar i +B

[0017] In the formula, i is the number of breaths, and the value of i ranges from 1 to n;

[0018] The formula for calculating intrapulmonary oxygen concentration in step 2 is as follows:

[0019] O i =(B-σ i ) / A

[0020] O i Hyperpolarization of the i-th respiration 129 The oxygen concentration in the lungs after Xe gas.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) Cost reduction: The method of the present invention is applicable to hyperpolarization with lower cost. 129 Xe gas.

[0023] (2) By acquiring B0 field images instead of longitudinal relaxation rate images to measure intrapulmonary oxygen concentration, the data acquisition time is significantly shortened and the subjects' breath-holding compliance is improved. The sampling time of this invention is only 0.4s.

[0024] (3) Since it does not require long-term longitudinal relaxation rate measurement and fewer RF excitations, the method of the present invention allows the use of a larger excitation angle, which can achieve a higher signal-to-noise ratio compared with the longitudinal relaxation rate-based method in the prior art, thereby improving the accuracy of the evaluation.

[0025] (4) The present invention is based on phase images rather than amplitude images, which can reduce the influence of gas molecule diffusion between different echoes. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process of the present invention;

[0027] Figure 2 Respiratory hyperpolarization in Embodiment 1 of the present invention 129 A schematic diagram of Xe gas undergoing n-fold oxidation;

[0028] Figure 3 The diagram O1-O shows the distribution of intrapulmonary oxygen concentration corresponding to different respiratory rates in Example 1 of the present invention. n . Detailed Implementation

[0029] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to embodiments. The embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0030] Example 1:

[0031] A gas magnetic resonance imaging method for quantitative measurement of lung oxygen concentration includes the following steps:

[0032] This embodiment describes the situation of experimental animals (such as rats, mice, and rabbits) whose breathing can be controlled by a ventilator. In this embodiment, SD rats were selected as experimental subjects, and MRI scanners were used to measure the intrapulmonary oxygen concentration of SD rats.

[0033] Step 1: Controlling respiratory hyperpolarization in SD rats 129 Xe gas undergoes n times and respiration hyperpolarization. 129 Data acquisition was performed during the Xe gas process, utilizing hyperpolarization. 129 Xe gas was used for magnetic resonance imaging to obtain image datasets S1-S corresponding to different respiratory rates. n The specific steps are as follows:

[0034] Step 1.1: Anesthetize the SD rats and fix them in place. Insert the rats into an MRI scanner for scanning and positioning, ensuring that the lungs of the SD rats are centered on the magnets and coils of the MRI scanner.

[0035] Step 1.2: Control the SD rats to breathe high-purity oxygen using a ventilator to wash away residual nitrogen in the lungs.

[0036] Step 1.3: At the end of expiration in SD rats, hyperpolarization was introduced via a ventilator. 129 Xe gas (hyperpolarized xenon) was used to collect data from SD rats after they held their breath under mechanical ventilation at the end of inspiration using a multi-echo gradient echo sequence. After data acquisition, the SD rats were induced to exhale under mechanical ventilation. This process was repeated n times to obtain image datasets S1-S1 corresponding to different respiratory counts. n .

[0037] The specific parameters of the multi-echo gradient echo sequence were set as follows: field of view = 32×48mm, matrix = 32×48, slice thickness = 8mm, repetition time TR = 7.85ms, number of echoes = 8, echo time TE = 1.60 / 2.24 / 2.88 / 3.52 / 4.16 / 4.80 / 5.44 / 6.08ms, flip angle = 5°, and the sampling time for each data acquisition using the multi-echo gradient echo sequence was 0.4 seconds, which significantly shortened the data acquisition time and improved the subjects' breath-holding compliance.

[0038] Step 1.4: After the collection is completed, the SD rats are controlled to breathe high-purity oxygen via a ventilator to restore blood oxygen saturation, and the vital signs of the SD rats are monitored.

[0039] Step 2: From the image dataset S1-S n Phase information was extracted from the data, and then phases exceeding 360° were corrected to obtain the phase dataset P1-P corresponding to different respiratory rates. n Then, through the phase dataset P1-P n Obtain the B0 field image σ1-σ corresponding to different breathing rates. n ; Construct a formula for calculating intrapulmonary oxygen concentration and hyperpolarization of the i-th respiration. 129 The field strength σ of B0 after Xe gas i The formula, σ1-σ, corresponds to the B0 field image for different breathing numbers. n The field intensity σ of each pixel at the corresponding pixel position in the middle i Substitute the hyperpolarization of the i-th respiration 129 The field strength σ of B0 after Xe gas i The formula is used to obtain the parameter distribution plots of parameters A, B, and r. Finally, the parameters A, B, and σ are... i Substituting into the formula for calculating intrapulmonary oxygen concentration, we obtain the intrapulmonary oxygen concentration distribution map O1-O corresponding to different respiratory rates. n Specifically, it includes the following steps:

[0040] Step 2.1: From the image dataset S1-S n Phase information was extracted, and a phase unwrapping algorithm was used to correct phases exceeding 360°. The corrected phase dataset P1-P corresponding to different respiratory rates was obtained. n .

[0041] This invention is based on phase images rather than amplitude images, which can reduce the influence of gas molecule diffusion between different echoes.

[0042] Step 2.2: Analyze the phase dataset P1-P corresponding to the different respiratory rates obtained. nThe data was processed to calculate the B0 field image σ1-σ corresponding to different breathing rates. n .

[0043] Step 2.3: Construct the hyperpolarization of the i-th respiration. 129 The field strength σ of B0 after Xe gas i The formulas for calculating intrapulmonary oxygen concentration are as follows:

[0044] Experiments using in vitro samples showed that, under constant pressure and temperature within the lungs, the field strength σ of B0 is related to... 129 Xe concentration ρ Xe And O2 concentration (oxygen concentration) ρ O The following relationship exists:

[0045] σ=δ0+δ (Xe-Xe) ρ Xe +δ (Xe-O) ρ O (1)

[0046] In the formula, δ0 represents the change in the B0 field caused by the inhomogeneity of the external magnetic field and the magnetic susceptibility effect; δ (Xe-Xe) yes 129 The collision-induced frequency coefficient between Xe molecules, δ (Xe-O) yes 129 Collision-induced frequency coefficient between Xe molecules and oxygen molecules.

[0047] Ignoring the content of gases other than oxygen and xenon in the lungs, formula (1) simplifies to:

[0048] σ=Aρ O +B (2)

[0049] In the formula, A is the difference in collision-induced frequency coefficients (A = δ). (Xe-O) -δ (Xe-Xe) B represents the gaseous state when the oxygen concentration in the lungs is 0. 129 The field intensity of Xe at B0 (B=δ0+δ (Xe-Xe) ).

[0050] An oxygen concentration gradient was established to extract parameters A and B, assuming respiratory hyperpolarization in SD rats. 129 During the Xe gas process, the residual gas coefficient r is:

[0051]

[0052] In the formula, V out V is the amount of residual gas in the alveoli at the end of expiration in SD rats. in This refers to the amount of gas in the alveoli of SD rats at the end of inspiration.

[0053] Then the i-th respiration hyperpolarization 129The oxygen concentration in the lungs after Xe gas is released (i.e., hyperpolarization during the i-th respiration). 129 ρ after Xe gas O )for:

[0054] O i =r i (4)

[0055] In the formula, i is the number of breaths, and the value of i ranges from 1 to n. In this embodiment, the value of i ranges from 1 to 5.

[0056] Substituting equation (4) into equation (2), we obtain the hyperpolarization of the i-th respiration. 129 The field strength σ of B0 after Xe gas i The formula is:

[0057] σ i =Ar i +B (5)

[0058] Step 2.4: Calculate the B0 field image σ1-σ corresponding to different breathing rates. n The field intensity σ of each pixel at the corresponding pixel position in the middle i (i.e., hyperpolarization of the i-th respiration) 129 Substituting the field intensity of B0 after Xe gas into formula (5), we obtain the parameter distribution diagrams of parameters A, B, and r. Then, we input the parameters A, B, and σ... i Substituting the oxygen concentration (O2) of each pixel into the formula for calculating intrapulmonary oxygen concentration... i (i.e., hyperpolarization of the i-th respiration) 129 (Oxygen concentration in the lungs after Xe gas is released), thereby obtaining a lung oxygen concentration distribution map corresponding to different respiratory rates O1-O n ,like Figure 3 As shown;

[0059] The formula for calculating intrapulmonary oxygen concentration is:

[0060] O i =(B-σ i ) / A (6).

[0061] A gas magnetic resonance imaging device for quantitative measurement of lung oxygen concentration includes:

[0062] The lung oxygen concentration distribution calculation module is used to perform step 2 above: from the image dataset S1-S n Phase information was extracted from the data, and then phases exceeding 360° were corrected to obtain the phase dataset P1-P corresponding to different respiratory rates. n Then, through the phase dataset P1-P n Obtain the B0 field image σ1-σ corresponding to different breathing rates. n; Construct a formula for calculating intrapulmonary oxygen concentration and hyperpolarization of the i-th respiration. 129 The field strength σ of B0 after Xe gas i The formula, σ1-σ, corresponds to the B0 field image for different breathing numbers. n The B0 field intensity σ corresponding to each pixel in the image i Substitute the hyperpolarization of the i-th respiration 129 The field strength σ of B0 after Xe gas i The formula is used to obtain the parameter distribution plots of parameters A, B, and r. Finally, the parameters A, B, and σ are... i Substituting into the formula for calculating intrapulmonary oxygen concentration, we obtain the intrapulmonary oxygen concentration distribution map O1-O corresponding to different respiratory rates. n .

[0063] A terminal, comprising a processor and a storage medium;

[0064] The storage medium is used to store instructions;

[0065] The processor is used to perform step 2 according to the instructions.

[0066] A computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements step 2.

[0067] Example 2:

[0068] This embodiment assumes that the subject is able to receive instructions and control their breathing autonomously. In this embodiment, a human imaging device is used to measure the intrapulmonary oxygen concentration of the human subject.

[0069] A gas magnetic resonance imaging method for quantitative measurement of lung oxygen concentration includes the following steps:

[0070] Step 1: Respiratory hyperpolarization in human subjects 129 Xe gas is passed through n times, and data is collected to obtain image datasets S1-S corresponding to different numbers of breaths. n Specifically, it includes the following steps:

[0071] Step 1.1: Human subjects wear lung transfusions. 129 The Xe imaging coil enters the scanning magnet of the human body imaging instrument to scan and locate the image.

[0072] Step 1.2: Human subjects breathe high-purity oxygen to wash out residual nitrogen in their lungs.

[0073] Step 1.3: Give instructions to the human subject to guide the human subject to hyperpolarize respiration. 129 Xe gas is passed n times, and data is collected during each breath (n is 3 in this embodiment to reduce the hypoxic response in human subjects), utilizing hyperpolarization.129 Xe gas was used for magnetic resonance imaging to obtain image datasets S1-S corresponding to different respiratory rates. n .

[0074] Instructions were given to human subjects to guide their breathing hyperpolarization. 129 The process of collecting data from Xe gas n times during each breath is as follows: At the end of expiration, the human subject is given an instruction to inhale hyperpolarized gas. 129 Xe gas was used, and then the human subjects were instructed to hold their breath at the end of their inspiration. Data was collected using a multi-echo gradient echo sequence to obtain image datasets S1-S1 corresponding to different breath counts. n .

[0075] The specific parameters of the multi-echo gradient echo sequence are modified and set according to the experimental conditions.

[0076] Step 1.4: After the collection is completed, the human subjects inhale high-purity oxygen to restore blood oxygen saturation, and the vital signs of the human subjects are monitored and any adverse reactions are inquired about.

[0077] Step 2: From the image dataset S1-S n Phase information was extracted from the data, and then phases exceeding 360° were corrected to obtain the phase dataset P1-P corresponding to different respiratory rates. n Then, through the phase dataset P1-P n Obtain the B0 field image σ1-σ corresponding to different breathing rates. n ; Construct a formula for calculating intrapulmonary oxygen concentration and hyperpolarization of the i-th respiration. 129 The field strength σ of B0 after Xe gas i The formula, σ1-σ, corresponds to the B0 field image for different breathing numbers. n The field intensity σ of each pixel at the corresponding pixel position in the middle i Substitute the hyperpolarization of the i-th respiration 129 The field strength σ of B0 after Xe gas i The formula is used to obtain the parameter distribution plots of parameters A, B, and r. Finally, the parameters A, B, and σ are... i Substituting into the formula for calculating intrapulmonary oxygen concentration, we obtain the intrapulmonary oxygen concentration distribution map O1-O corresponding to different respiratory rates. n Specifically, it includes the following steps:

[0078] Since the lung expansion state of human subjects cannot remain completely consistent across different breathing stages, it is necessary to first process the image dataset S1-S corresponding to different breathing counts obtained in step 1.3. nImage registration was performed, and then the image datasets S1-S corresponding to different registered respiratory counts were analyzed. n Perform phase correction;

[0079] Steps 2.1 to 2.4 are the same as steps 2.1 to 2.4 in Example 1, and will not be repeated here.

[0080] A gas magnetic resonance imaging device for quantitative measurement of lung oxygen concentration includes:

[0081] The lung oxygen concentration distribution calculation module is used to perform step 2 above: from the image dataset S1-S n Phase information was extracted from the data, and then phases exceeding 360° were corrected to obtain the phase dataset P1-P corresponding to different respiratory rates. n Then, through the phase dataset P1-P n Obtain the B0 field image σ1-σ corresponding to different breathing rates. n ; Construct a formula for calculating intrapulmonary oxygen concentration and hyperpolarization of the i-th respiration. 129 The field strength σ of B0 after Xe gas i The formula, σ1-σ, corresponds to the B0 field image for different breathing numbers. n The B0 field intensity σ corresponding to each pixel in the image i Substitute the hyperpolarization of the i-th respiration 129 The field strength σ of B0 after Xe gas i The formula is used to obtain the parameter distribution plots of parameters A, B, and r. Finally, the parameters A, B, and σ are... i Substituting into the formula for calculating intrapulmonary oxygen concentration, we obtain the intrapulmonary oxygen concentration distribution map O1-O corresponding to different respiratory rates. n .

[0082] A terminal, comprising a processor and a storage medium;

[0083] The storage medium is used to store instructions;

[0084] The processor is used to perform step 2 according to the instructions.

[0085] A computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements step 2.

[0086] It should be noted that the embodiments described in this invention are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains can make various modifications or additions to the described embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A gas magnetic resonance imaging method for quantitative measurement of lung oxygen concentration, characterized in that, Includes the following steps: Step 1: Subject's respiratory hyperpolarization 129 Xe gas Each time, the subject experienced respiratory hyperpolarization. 129 Data is collected during the Xe gas process to obtain image datasets corresponding to different respiration rates. ; Step 2: From the image dataset Phase information is extracted from the data, and then phases exceeding 360° are corrected to obtain phase datasets corresponding to different respiratory rates. Then through the phase dataset Obtain the corresponding number of breaths Field image ; Construct a formula for calculating intrapulmonary oxygen concentration and the first Secondary respiratory hyperpolarization 129 Xe gas after Field strength The formula corresponds to different numbers of breaths. Field image Each pixel at the corresponding pixel position Field strength Substitute the first Secondary respiratory hyperpolarization 129 Xe gas after Field strength The formula is used to obtain the parameters. , and The parameter distribution plot, and finally the parameters , and Substituting into the formula for calculating intrapulmonary oxygen concentration, we obtain the intrapulmonary oxygen concentration distribution map corresponding to different respiratory rates. , In step 2 Secondary respiratory hyperpolarization 129 Xe gas after Field strength The formula: In the formula, It's the number of breaths. The range of values ​​is ; The formula for calculating intrapulmonary oxygen concentration in step 2 is as follows: For the first Secondary respiratory hyperpolarization 129 The oxygen concentration in the lungs after Xe gas is emitted. in, The difference in collision-induced frequency coefficients. The gaseous state when the oxygen concentration in the lungs is 0 129 Xe Field strength, This represents the residual gas coefficient.

2. The gas magnetic resonance imaging method for quantitative measurement of lung oxygen concentration according to claim 1, characterized in that, Step 1 includes the following steps: Step 1.1: The subject wears a lung tube. 129 Xe imaging coil and enters the scanning magnet; Step 1.2: The subject breathes high-purity oxygen to wash out residual nitrogen in the lungs; Step 1.3: The subject inhales hyperpolarized air at the end of expiration. 129 Xe gas was used, and the breath was held at the end of inspiration. Data was then collected using a multi-echo gradient echo sequence. The above process was repeated. Next, obtain image datasets corresponding to different breathing counts. ; Step 1.4: After the collection is completed, the subject inhales high-purity oxygen to restore blood oxygen saturation, and the subject's vital signs are monitored.

Images