Stroke differentiation sequence using low-field magnetic resonance imaging, and device with the differentiation sequence

Abstract

The present invention relates to a stroke differentiation sequence using low-field magnetic resonance imaging, and a device with the differentiation sequence. An inversion recovery sequence is used, and a TE uses the minimum or near-minimum TE value achievable by a system, thereby minimizing the impact of T2 effect on a signal S; moreover, a combination of a TR value and a corresponding TI value is selected, such that the signal of intracerebral hemorrhage is hyperintense, and the signals of cerebral infarct tissue and brain parenchyma are isointense or hypointense, thereby quickly and accurately identifying hemorrhagic stroke; and low-field magnetic resonance imaging is used, thereby achieving higher accessibility for patients.

Description

Low-field magnetic resonance stroke differential sequence and device with the differential sequence TECHNICAL FIELD

[0001] The present application relates to the field of magnetic resonance imaging (MRI), and in particular to a low-field magnetic resonance stroke differential sequence and a device with the low-field magnetic resonance stroke differential sequence. BACKGROUND

[0002] Stroke, also known as cerebral apoplexy, is an acute cerebrovascular disease, including hemorrhagic stroke and ischemic stroke. Hemorrhagic stroke is also known as cerebral hemorrhage, and ischemic stroke is also known as cerebral ischemia or cerebral infarction. The rescue time for cerebral infarction is very limited, and it is generally believed that the optimal treatment time for stroke is within 4.5 hours, and more than 6 hours often misses the optimal rescue time. Therefore, in the diagnosis and treatment of stroke, it is crucial for doctors to determine the treatment plan to judge whether the patient is a cerebral hemorrhage or a cerebral infarction, or an infarction with hemorrhage. How to quickly and accurately determine the patient's condition is related to the patient's treatment effect and life.

[0003] In the existing diagnosis assistance technology and process, CT head scan is a first-line diagnostic method for cerebral hemorrhage in hospitals. Computed tomography (CT) is very sensitive to cerebral hemorrhage and is considered the "gold standard" for the diagnosis of cerebral hemorrhage. It is a necessary examination method for patients with initial diagnosis of stroke and an important image basis for the existing stroke diagnosis and treatment process. However, CT is not sensitive to acute ischemic stroke, and the lesion image is not obvious. Generally, it is believed that CT can only see cerebral infarction lesions greater than 24 hours, and it is difficult to detect early cerebral infarction, which can easily lead to misdiagnosis of early cerebral infarction.

[0004] Some hospitals also use special superconducting magnetic resonance equipment to identify and examine stroke, improve the detection rate of acute cerebral infarction, and accurately determine the time window of cerebral infarction. Magnetic resonance imaging can improve the detection rate of cerebral hemorrhage, especially the detection rate of hemorrhage after cerebral infarction and long-term cerebral hemorrhage. However, current superconducting magnetic resonance equipment is a high-field device, and the field strength commonly used at present is 1.5T and 3.0T, which needs to be installed in a special electromagnetic shielding room. It is extremely unfriendly to patients with stroke who are racing against time to save time, and it is easy to delay the rescue opportunity. Patients with metal implants in their bodies or with other medical auxiliary equipment will absorb electromagnetic waves when scanned by magnetic resonance, and the absorbed electromagnetic waves will be converted into heat. The higher the magnetic field strength, the higher the heat generation. Under the action of a strong magnetic field, the heat generation burns the patient, so such patients cannot be scanned by magnetic resonance imaging, reducing accessibility. SUMMARY

[0005] The present application provides a low-field magnetic resonance brain stroke identification sequence with high accessibility, which can quickly and accurately judge the hemorrhagic stroke, and an equipment with the low-field magnetic resonance brain stroke identification sequence.

[0006] To solve the above technical problems, the present application provides the following technical solutions: a low-field magnetic resonance brain stroke identification sequence adopts an inversion recovery sequence, and the relative signal intensity formula thereof is as follows:

[0007] In the formula, S represents the relative signal intensity;

[0008] PD represents the proton density of the tissue;

[0009] TI represents the inversion recovery time of the sequence;

[0010] T1 represents the T1 relaxation time of the tissue;

[0011] TR represents the repetition time of the sequence;

[0012] TE last represents the last echo time of the multi-echo sequence;

[0013] TE represents the effective echo time;

[0014] T2 represents the T2 relaxation time of the tissue;

[0015] i = 1, 2, …, N represents N components, wherein the brain parenchyma and the brain hemorrhage are a single component model N = 1, and the brain infarction tissue adopts a double component model N = 2; the subscript i represents the value of the ith tissue;

[0016] The brain parenchyma and the brain hemorrhage are a single component model N = 1, and the brain infarction tissue adopts a double component model N = 2.

[0017] In the formula, TE adopts a TE value that can reach or approach the minimum value of the system, so that the value is as close to 1 as possible, and the influence of the T2 effect on the signal S is minimized;

[0018] The TR value and the corresponding TI value combination are selected so that the brain hemorrhage signal is a high signal, and the brain infarction tissue and the brain parenchyma are equal signals or low signals.

[0019] As an improvement of the above technical solution, the selection of the TR value and the corresponding TI value combination conforms to the principle of the fastest clinical scanning speed.

[0020] As an improvement of the above technical solution, the corresponding relationship between the TR and TI conforms to the following fitting result:

[0021] TR = 0.0006925 * TI 2+ 0.7426*TI + 67.78.

[0022] As an improvement of the above technical solution, the TI is fixed, and the TR value is up and down floating 10%; or the TR is fixed, and the TI is up and down floating 10%.

[0023] As an improvement of the above technical solution, the low field is 0.23T, the TE is 24 milliseconds, the TR is 900 milliseconds, and the TI is 685 milliseconds.

[0024] As an improvement of the above technical solution, the low field is 0.23T, the TE is 24 milliseconds, the TR is 1100 milliseconds, and the TI is 800 milliseconds.

[0025] As an improvement of the above technical solution, the low field is 0.23T, the TE is 24 milliseconds, the TR is 1500 milliseconds, and the TI is 1000 milliseconds.

[0026] As an improvement of the above technical solution, the PD is obtained by the signal intensity of the proton weighted image.

[0027] As an improvement of the above technical solution, before the fast spin echo sequence, a series of inversion recovery pulses with different TI values are applied, at this time the signal size of the region of interest is related to the T1 value, and the T1 measurement value is obtained by fitting the following formula:

[0028] Wherein S(τ) is the signal intensity of the tissue;

[0029] α is a weight coefficient;

[0030] τ is the TI value of the scanning sequence;

[0031] TR is the repetition time;

[0032] TE last is the last echo time;

[0033] T1 is the T1 relaxation time of the tissue.

[0034] As an improvement of the above technical solution, the fast spin echo sequence is used, other parameters are kept unchanged except the TE time, the correlation between TE and T2 is used, and the T2 measurement value is obtained by fitting the following formula.

[0035] Wherein S(β) is the signal intensity of the tissue;

[0036] α is a weight coefficient;

[0037] β is a series of echo times;

[0038] T2 is the T2 relaxation time of the tissue.

[0039] To solve the above technical problems, the application further provides the following technical solutions: a low-field magnetic resonance stroke identification device, comprising a magnetic resonance scanner; the magnetic resonance scanner performs the low-field magnetic resonance stroke identification sequence according to any one of the above.

[0040] Compared with the prior art, the application adopts an inversion recovery sequence, the TE value of the system can reach or be close to the minimum TE value, the influence of the T2 effect on the signal S is minimum, the TR value and the corresponding TI value combination are selected, the brain hemorrhage signal is high, the brain infarction and the brain parenchyma are equal or low signals, so that the hemorrhagic stroke can be quickly and accurately judged, and the low-field magnetic resonance is adopted, so that the accessibility of the patient is high. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to make the purpose, technical scheme and beneficial effects of the application more clear, the application provides the following drawings for description:

[0042] Figure 1a: T2 image of pig brain hemorrhage test start (0h);

[0043] Figure 1b: FLAIR image of pig brain hemorrhage test start (0h);

[0044] Figure 1c: DWI image of pig brain hemorrhage test start (0h);

[0045] Figure 1d: T1 image of pig brain hemorrhage test start (0h);

[0046] Figure 2a: T2 image of pig brain hemorrhage test end (17h);

[0047] Figure 2b: FLAIR image of pig brain hemorrhage test end (17h);

[0048] Figure 2c: DWI image of pig brain hemorrhage test end (17h);

[0049] Figure 2d: T1 image of pig brain hemorrhage test end (17h);

[0050] Figure 3a: T1 relaxation time curve of pig brain hemorrhage test;

[0051] Figure 3b: T2 relaxation time curve of pig brain hemorrhage test;

[0052] Figure 3c: PD normalization curve of pig brain hemorrhage test;

[0053] Figure 3d: T1 weighted curve of pig brain hemorrhage test;

[0054] Figure 3e: T2 weighted plot of pig brain hemorrhage experiment;

[0055] Figure 3f: FLAIR plot of pig brain hemorrhage experiment;

[0056] Figure 4a: T2 image at start (Oh) of pig brain ischemia experiment;

[0057] Figure 4b: FLAIR image at start (Oh) of pig brain ischemia experiment;

[0058] Figure 4c: DWI image at start (Oh) of pig brain ischemia experiment;

[0059] Figure 4d: Tl image at start (Oh) of pig brain ischemia experiment;

[0060] Figure 5a: T2 image at end (24h) of pig brain ischemia experiment;

[0061] Figure 5b: FLAIR image at end (24h) of pig brain ischemia experiment;

[0062] Figure 5c: DWI image at end (24h) of pig brain ischemia experiment;

[0063] Figure 5d: Tl image at end (24h) of pig brain ischemia experiment;

[0064] Figure 6a: Tl relaxation time plot of pig brain ischemia experiment;

[0065] Figure 6b: T2 relaxation time plot of pig brain ischemia experiment;

[0066] Figure 6c: PD normalized plot of pig brain ischemia experiment;

[0067] Figure 6d: Tl weighted plot of pig brain ischemia experiment;

[0068] Figure 6e: T2 weighted plot of pig brain ischemia experiment;

[0069] Figure 6f: FLAIR plot of pig brain ischemia experiment;

[0070] Figure 7a: TE 24ms, TR 900ms fit plot;

[0071] Figure 7b: TE 24ms, TR 1100ms fit plot;

[0072] Figure 7c: TE 24ms, TR 1500ms fit plot;

[0073] Figure 8: TR / TI relationship plot in ms;

[0074] [Rule 91 Correction 10.04.2025] Figure 9a: Bleeding image with TR / TI = 900 / 685 ms, where the thick coil represents the bleeding area and the thin coil represents the brain parenchyma area;

[0075] [Rule 91 Correction 10.04.2025] Figure 9b: Bleeding image with TR / TI = 1100 / 800 ms, where the thick coil represents the bleeding area and the thin coil represents the brain parenchyma area;

[0076] [Rule 91 Correction 10.04.2025] Figure 9c: Bleeding image with TR / TI = 1500 / 1000 ms, where the thick coil represents the bleeding area and the thin coil represents the brain parenchyma area;

[0077] Figure 10a: DWI image of the brain of case one,

[0078] Figure 10b: ADC image of the brain of case one;

[0079] Figure 10c: FLAIR image of the brain of case one;

[0080] Figure 10d: PD image of the brain of case one;

[0081] Figure 11a: DWI image of the brain of case two,

[0082] Figure 11b: ADC image of the brain of case two;

[0083] Figure 11c: FLAIR image of the brain of case two;

[0084] Figure 11d: PD image of the brain of case two;

[0085] Figure 11e: Typical image mosaic of the DWI image, ADC image, FLAIR image, PD image of the brain of case two;

[0086] Figure 12a: DWI image of the brain of case three,

[0087] Figure 12b: ADC image of the brain of case three;

[0088] Figure 12c: FLAIR image of the brain of case three;

[0089] Figure 12d: PD image of the brain of case three;

[0090] Figure 13a: DWI image of the brain of case four,

[0091] Figure 13b: ADC image of the brain of case four;

[0092] Figure 13c: FLAIR image of the brain of case four;

[0093] Figure 13d: PD image of the brain of case four;

[0094] Figure 14a: DWI image of the brain of case five,

[0095] Figure 14b: ADC image of the brain of case five;

[0096] Figure 14c: FLAIR image of the brain of case five;

[0097] Figure 14d: PD image of the brain of case five;

[0098] Figure 15a: DWI image of the brain of case six,

[0099] Figure 15b: ADC image of the brain of case six;

[0100] Figure 15c: FLAIR image of the brain of case six;

[0101] Figure 15d: PD image of the brain of case six;

[0102] [Corrected according to Rule 91 10.04.2025] In the above case images, the thick coil represents the high-light signal area as the lesion area;

[0103] DWI image: a magnetic resonance sequence in clinical image diagnostics, the high signal marked on the image is generally considered to be caused by abnormal lesions;

[0104] ADC image: a magnetic resonance sequence in clinical image diagnostics, it is a calculated value image of DWI, and the signal of the corresponding lesion area of the DWI image is comprehensively diagnosed to determine whether the lesion is acute cerebral stroke;

[0105] FLAIR image: a magnetic resonance sequence image in clinical image diagnostics, the image keeps T2 image of other tissues at the same time, and water is low signal, and the high-light part is generally considered to be caused by lesions;

[0106] PD image: a magnetic resonance sequence in clinical image diagnostics, this image is mainly used to determine whether the suspected cerebral stroke lesion is cerebral ischemia or cerebral hemorrhage lesion. DETAILED DESCRIPTION

[0107] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0108] I. About field strength B0

[0109] The MRI market is overwhelmingly dominated by high-field systems, especially for medical or clinical MRI applications. A general trend in medical imaging is to produce MRI scanners with increasingly large field strengths, with the vast majority of clinical MRI scanners operating at 1.5T or 3T, with higher fields of 7T and 9T being used in research environments. "High field" generally refers to MRI systems currently used in clinical settings, more specifically, MRI systems operating with a main magnetic field (i.e., B0 field) of 1.0T or above, clinical systems operating between 0.5T and 1.0T are also often described as "mid-field". Field strengths between approximately 0.3T and 0.5T are described as "mid-low field". In contrast, "low field" generally refers to MRI systems operating with a B0 field in the range of approximately 0.18T and 0.3T. Low-field MRI systems operating with a B0 field of less than 0.18T are referred to as "very low field".

[0110] II. Magnetic resonance manifestations of cerebral hemorrhage and cerebral ischemia (cerebral infarction)

[0111] Studies have shown that the magnetic resonance characteristics of cerebral hemorrhage and cerebral ischemia are generally complex and variable, and this manifestation is not only related to time, but also has a great relationship with field strength.

[0112] For hyperacute cerebral hemorrhage (within 6 hours), due to the increase of paramagnetic substances such as deoxyhemoglobin in red blood cells, the local T2* effect is shortened, so it usually shows isosignal or low signal characteristics in high-field magnetic resonance. Due to the square positive correlation between magnetic susceptibility effect and field strength, the hyperacute hemorrhage is less affected in low-field magnetic resonance, and shows persistent high signal on DWI and FLAIR.

[0113] For hyperacute cerebral ischemia, magnetic resonance usually shows high signal on DWI (diffusion weighted imaging) and isosignal on FLAIR. With the extension of time, due to the damage of blood brain barrier, the FLAIR of cerebral infarction area will gradually change to high signal.

[0114] Therefore, it can be seen that there is a period in which cerebral hemorrhage and cerebral ischemia will have high signal on DWI and FLAIR at the same time in low-field magnetic resonance images, which cannot be distinguished. Therefore, the following animal experiments are carried out to find a low-field magnetic resonance stroke differential sequence that can quickly and accurately judge hemorrhagic stroke.

[0115] 1. T1 and T2 quantitative analysis method

[0116] T1 value measurement: Before the fast spin echo sequence, a series of inversion recovery pulses with different TI values are applied, at this time the signal size of the region of interest is related to the T1 value, and the T1 measurement value is obtained by fitting the following formula.

[0117] where S(τ) is the tissue signal intensity;

[0118] α is a weight coefficient;

[0119] τ is the TI value of the scanning sequence;

[0120] TR is the repetition time;

[0121] TE last is the last echo time;

[0122] T1 is the T1 value of the tissue.

[0123] The fixed scanning parameters of this sequence: the first round of scanning TR 4000 ms, the last echo time TE 107 ms, and a series of TI values τ are [100 150 200 250 400 600 800 1000] ms respectively; the second round of scanning TR 10000 ms, the last echo time TE 107 ms, and a series of TI values τ are [3500 4000 4500] ms respectively, and a series of S(τ) values are obtained correspondingly. By using the above formula to fit the data τ and the data S(τ), the final T1 measurement value is obtained.

[0124] T2 value measurement: a fast spin echo sequence is used, other parameters are kept unchanged except the TE time, the correlation between TE and T2 is used, and the following formula is used for fitting to obtain the T2 measurement value.

[0125] where S(β) is the tissue signal intensity;

[0126] α is a weight coefficient;

[0127] β is a series of echo times;

[0128] T2 is the T2 value of the tissue;

[0129] The scanning parameters of this sequence: TR 4000 ms, a series of echo times β are [42, 56, 70, 84, 98, 112] ms, and a series of S(β) values are obtained correspondingly. By using the above formula to fit the data β and the data S(β), the final T2 calculation value is obtained.

[0130] PD (proton density) value measurement: according to the principle of magnetic resonance, the present application directly uses the signal intensity of the PD weighted image to measure the relative PD value between tissues, and the value is the signal value of the PD weighted image, not the absolute proton density of the tissue. Because the signal value is huge in magnitude, the present application normalizes the order of magnitude to the individual digit level, which does not affect the expression of the trend in the graph. The scan parameters of this sequence are: TE is the minimum TE of the system, and TR is 10000 ms.

[0131] Selection of the region of interest: the basal ganglia region is selected for T1 and T2 value estimation. The signal in this region is relatively uniform, less affected by cerebrospinal fluid and other signals, and the volume effect is relatively not obvious, which can reflect the signal characteristics of the brain parenchyma.

[0132] 2. Test equipment

[0133] The equipment used in the present application is a mobile head and neck magnetic resonance system ACUTA Elfin manufactured by Foshan Ruiga Graph Medical Technology Co., Ltd. The basic parameters are as follows:

[0134] Nominal B0 value: 0.23T ± 0.01T

[0135] Maximum spatial encoding gradient: 25mT / m

[0136] Maximum gradient switching rate: 60T / m / s

[0137] 3. Hemorrhage experiment results

[0138] In this test, pig venous blood was collected and injected into the basal ganglia of the pig brain, and the magnetic resonance showed that the hemorrhagic focus was clearly visible. Starting from the blood injection, a round of magnetic resonance sequence scanning was completed every hour, and the signal change of the hemorrhagic focus was continuously evaluated within 17 hours.

[0139] Referring to FIGS. 1a-3f, the measurement value of each hour is continuously calculated using the above measurement method, and it is found that the change within 17 hours is not obvious, so the average value of the 17-hour data is obtained to facilitate subsequent calculation. By directly measuring the signal intensity of the T1 weighted, T2 weighted, FLAIR image, it can be found that under 0.23T magnetic resonance, the T1WI of the hemorrhagic focus within 17 hours is slightly low signal, and the T2WI, FLAIR and DWI are high signal, and the signal intensity does not change obviously with time.

[0140] According to the above measurement method, the average value of the T1, T2 and proton density PD of the brain parenchyma and the hemorrhage is as follows:

[0141] Table 1

[0142] 4. Ischemia experiment results

[0143] The brain ischemia region analyzed in this test is located in the medulla oblongata. The brain ischemia model is also started from the formation of cerebral infarction, and the signal changes within 24 hours after the formation of the hemorrhagic lesion are continuously evaluated.

[0144] As shown in FIGS. 4a-6f, through 24 hours of monitoring, it is found that the T2WI, FLAIR, DWI signals of brain ischemia continuously increase, and the T1 weighted signal continuously decreases under 0.23T magnetic resonance.

[0145] According to the above measurement method, the T1, T2, PD normalized values measured hour by hour are shown by the red lines in FIGS. 6a-6c. Since the data changes with time are not stable, the present application considers that the cerebral infarction phenomenon at different onset times cannot be explained by a single component model. Sean C. L. Deoni et al. also proposed in the literature that there is a multi-component analysis model for the T1 characteristics of tissues in magnetic resonance scanning. According to the results of this test and the physiological process of cerebral infarction, the present application considers that after the occurrence of cerebral infarction, there are magnetic resonance visible water molecules in the lesion, which gradually change from the characteristics of brain parenchyma to the characteristics similar to edema (long T1, long T2), and the proportion of this change increases with time. Part of this water molecule is transformed from the water molecules in the brain parenchyma, and part of it may be water entering from outside the lesion, and it continuously increases with time. Therefore, the present application considers that the physiological process of cerebral infarction tissue can be simulated by two components of brain parenchyma and edema-like, and the proportion of these two components changes with time. In addition, since the slice thickness of this test is 7mm, and the pig brain is relatively small, the brain tissue slice thickness at the medulla oblongata is less than 7mm, and the cerebrospinal fluid signal is mixed in the scanning slice at this position. Therefore, the simulation calculation model of this test is three different components, namely brain parenchyma, cerebrospinal fluid and edema-like. Due to the entry of external water, the content of brain parenchyma decreases with time, its PD value decreases, the content of edema-like increases with time, and its PD value increases, and the content of cerebrospinal fluid does not change because it is a real existing tissue in the slice.

[0146] Therefore, the simulation formula described in measurement method 1 is changed to multi-component in the cerebral infarction test, and the formula is as follows:

[0147] The multi-component T1 acquisition sequence signal fitting formula is:

[0148] The multi-component T2 acquisition sequence signal fitting formula is:

[0149] The multi-component T1 weighted imaging and FLAIR imaging signal fitting formula is:

[0150] The multi-component PD weighted imaging and T2 weighted imaging signal fitting formula is:

[0151] Where i = 1, 2, …, N represents N kinds of components, according to the above description, N of the brain infarction test is 3. The meanings of T1, T2 and PD are the same as above, and the subscript i represents the value of the ith tissue.

[0152] Wherein the expression of the PD value of the three tissues changes with time as follows:

[0153] The expression of the brain parenchymal content decreasing with time t (unit: hour) is PD 脑实质 = 1.15 - b 脑实质 t

[0154] The expression of the cerebrospinal fluid content is PD 脑脊液 = PD 0脑脊液

[0155] The expression of the Cystoid Edema content increasing with time t (unit: hour) is PD 类水肿 = 0 + b 类水肿 t

[0156] The PD formula of the three tissues is brought into the above formula for calculation.

[0157] The T1 measurement acquisition sequence scanning parameters are: the first round of scanning TR 4000 ms, the last echo time TE 107 ms, and a series of TI values τ are [100 150 200 250 400 600 800 1000] ms; the second round of scanning TR 10000 ms, the last echo time TE 107 ms, and a series of TI values τ are [3500 4000 4500] ms, corresponding to a series of S(τ) values, and the final T1 measurement value is obtained by numerically fitting the data τ and the data S(τ) using the above formula.

[0158] The T2 measurement acquisition sequence scanning parameters are: TR 4000 ms, a series of echo times τ are [42, 56, 70, 84, 98, 112] ms, and corresponding to a series of S(β) values, and the final T2 measurement value is obtained by numerically fitting the data β and the data S(β) using the above formula.

[0159] The T1 weighted image scanning parameters are: TR 1420 ms, TE 24.3 ms, and TI 425 ms.

[0160] The FLAIR image scanning parameters are: TR 4380 ms, TE 104 ms, and TI 1600 ms.

[0161] The PD weighted image scanning parameters are: TR 10000 ms, and TE 21 ms.

[0162] T2 weighted image scanning parameters: TR 2800ms, TE 104ms.

[0163] Among the three components of this experiment, the T1 and T2 of the brain parenchyma and cerebrospinal fluid have been measured by the formula in 1 and are fixed. The unknown variable in the above formula is the time change rate b of the PD of the brain parenchyma 脑实质 , the PD value of the cerebrospinal fluid, the T1 and T2 values of the edema-like tissue, and the time change rate b of the PD 类水肿 . The above six groups of data are brought into the respective formulas, and the values in the following table are obtained through numerical fitting:

[0164] Table 2

[0165] Note: 1. The unit of time t is hour (h)

[0166] 2. Due to insufficient anesthesia of the pig at the 6th hour, the experimental data of the first 6 hours were not involved in the fitting calculation, and the subsequent values were highly correlated with the fitting values.

[0167] 5. Parameters of the cerebral hemorrhage identification sequence

[0168] According to the data obtained in sections 3 and 4, the inversion recovery sequence is used to identify cerebral hemorrhage, and the relative signal intensity formula is as follows:

[0169] This formula is used for simulation calculation. In actual scanning, the T2 effect on the signal is minimized by using the minimum TE value of the system in the scanning sequence, so that the T2 effect on the signal is minimized, the contrast of cerebral hemorrhage with cerebral infarction and brain parenchyma is optimal, and the longer the TE, the closer the contrast of cerebral hemorrhage with cerebral infarction and brain parenchyma, which is not conducive to differentiation. However, a TE slightly higher than the minimum TE value can be appropriately selected to distinguish the contrast of cerebral hemorrhage with cerebral infarction and brain parenchyma. Given a certain TR value, the TI and relative signal intensity S are numerically fitted according to the formula. The brain parenchyma and cerebral hemorrhage are single-component models N = 1, and the T1, T2, and PD values are the parameters in Table 1. The brain ischemia model does not have cerebrospinal fluid contamination due to the absence of brain infarction tissue, and the cerebrospinal fluid is removed. A double-component model is used, N = 2. The simulated double components are brain parenchyma and edema-like tissue, and the T1, T2, and PD values are the data in Table 2. The brain ischemia model simulates the signal change every hour within 24 hours, and the PD values within 24 hours are the initial values and the linear change coefficients in Table 2.

[0170] It is found by fitting calculation that for any given TR value, there is a critical point for signal intensity, which makes the brain parenchyma and 1-24 hour cerebral infarction tissue have equal signal, and the hemorrhage signal is greater than the signal of the brain parenchyma and 1-24 hour cerebral infarction tissue. The signal intensity is shown on the image as bright signal of brain hemorrhage, and equal signal of brain parenchyma and 1-24 hour cerebral infarction tissue. FIGS. 7a-c take TR values of 900 ms, 1100 ms and 1500 ms as examples. The solid lines of three colors in the figure legend correspond to the signals of brain hemorrhage, brain parenchyma and 24 hour cerebral infarction respectively, and the dashed lines correspond to the signals of 1-23 hour cerebral infarction after the start of cerebral infarction. It can be concluded that the critical point is TI 685 ms when TR is 900 ms, TI 800 ms when TR is 1100 ms, and TI 1000 ms when TR is 1500 ms.

[0171] A series of TRs [900 1000 1100 1200 1300 1400 1500 1750 2000 3000 ms] are selected for simulation respectively, and the corresponding critical points TI are obtained. A quadratic polynomial fitting is performed, and FIG. 8 can show that the optimal correspondence between TR and TI conforms to the following fitting result: TR = 0.0006925*TI + 0.7426*TI + 67.78. 2 +0.7426*TI + 67.78.

[0172] Generally, the influence of 10% up and down floating of TR value or 10% up and down floating of TI on image quality is not large when TI is fixed or TR is fixed.

[0173] The selection principle of general TR value and corresponding TI value combination is to make the signal of brain hemorrhage be high signal, and the signals of cerebral infarction tissue and brain parenchyma be equal signal or low signal. The selection of TR and TI conforms to the principle of fastest clinical scanning speed. The scanning time requirement can be appropriately relaxed under the condition that the patient can accept, so that the contrast between brain hemorrhage and cerebral infarction tissue and brain parenchyma is stronger, and it is easier to identify.

[0174] Clinical results select TR 900, 1100 and 1500 ms for testing, and the results are shown in FIGS. 9a-c. The gray values of the hemorrhagic lesions (annotated in red) and the normal brain tissue on the contralateral side (annotated in blue) are measured, and the results are compared with the simulation results as follows.

[0175] It can be seen that the test results are highly consistent with the fitting values.

[0176] 5. Stroke cases

[0177] The following clinical trials were conducted using a device with a low-field magnetic resonance stroke differentiation sequence, which verified that the low-field magnetic resonance stroke differentiation sequence can quickly and accurately determine hemorrhagic stroke. The device is a mobile head and neck magnetic resonance system ACUTA Elfin manufactured by Foshan Ruigaotu Medical Technology Co., Ltd. The TR / TI combination used in the following cases is 1100 / 800 ms, and the TE is the minimum value of the system, which is 24 ms.

[0178] Case one: male patient, 47 years old, diagnosed with left limb weakness for 24 hours, CT examination confirmed cerebral infarction after admission, and then scanned by mobile head and neck magnetic resonance system ACUTA Elfin device, obtained images as shown in Figures 10a-10d, DWI image shows multiple high-intensity signals in the right frontal lobe and basal ganglia region, ADC corresponding lesion area is low signal, frontal lobe is equal signal, FLAIR corresponding lesion area is high signal, PD corresponding lesion area is equal signal, according to the image and combined with clinical comprehensive judgment, this case is acute / subacute multiple cerebral infarction.

[0179] Case two: female patient, 64 years old, slurred speech and general weakness for 24.6 hours, admitted to hospital and scanned by mobile head and neck magnetic resonance system ACUTA Elfin device, obtained images as shown in Figures 11a-11e, DWI image shows high-intensity signal in the left basal ganglia, ADC corresponding lesion area is low signal, FLAIR corresponding lesion area is high signal, PD corresponding lesion area is equal signal, according to the image and combined with clinical comprehensive judgment, this case is acute cerebral infarction. CT suggests that cerebral infarction is possible, further examination is recommended, and accurate judgment cannot be made.

[0180] Case three: male patient, 50 years old, dizziness, sudden left limb weakness for 29 hours, admitted to hospital and scanned by mobile head and neck magnetic resonance system ACUTA Elfin device, obtained images as shown in Figures 12a-12d, DWI image shows high-intensity signal in the right brainstem, ADC corresponding lesion area is low signal, FLAIR corresponding lesion area is high signal, preliminary judgment is cerebral stroke, PD corresponding lesion area is high-intensity signal, according to the image and combined with clinical comprehensive judgment, this case is acute cerebral hemorrhage. At the same time, CT report is acute cerebral hemorrhage, which is consistent with the image results of mobile head and neck magnetic resonance system ACUTA Elfin device.

[0181] Case four: male patient, 50 years old, the first diagnosis of right half body numbness, into the mobile head and neck magnetic resonance system ACUTA Elfin device scanning, get the image as shown in Figures 13a-13d, DWI image shows left basal ganglia, corona high signal, ADC corresponding lesion area is low signal, FLAIR corresponding lesion area is high signal, preliminary judgment for stroke, PD corresponding lesion area is high signal, according to the image and combined with clinical comprehensive judgment of this case is acute cerebral hemorrhage. At the same time, CT report for acute cerebral hemorrhage, and mobile head and neck magnetic resonance system ACUTA Elfin device imaging results are consistent.

[0182] Case five: female patient, 59 years old, admitted to hospital for visual abnormalities, headache for 24 hours, then into the mobile head and neck magnetic resonance system ACUTA Elfin device scanning, get the image as shown in Figures 14a-14d, DWI image shows left posterior fossa high signal, ADC corresponding lesion area is low signal, FLAIR corresponding lesion area is high signal, preliminary judgment for stroke, PD corresponding lesion area is high signal, according to the image and combined with clinical comprehensive judgment of this case is subacute cerebral hemorrhage. At the same time, CT report is not defined, after clinical verification, this case is subacute cerebral hemorrhage.

[0183] Case six: male patient, 43 years old, admitted to hospital for sudden left limb weakness without obvious inducement 5.5 hours ago, then into the mobile head and neck magnetic resonance system ACUTA Elfin device scanning, get the image as shown in Figures 15a-15d, DWI image shows right basal ganglia, insular and corona region large area high signal, ADC corresponding lesion area is low signal, FLAIR corresponding lesion area is high signal, preliminary judgment for stroke, PD corresponding lesion area is high signal, according to the image and combined with clinical comprehensive judgment of this case is acute cerebral hemorrhage. At the same time, CT report for acute cerebral hemorrhage, and mobile head and neck magnetic resonance system ACUTA Elfin device imaging results are consistent.

Claims

1. A low-field magnetic resonance stroke differential sequence, characterized by: The relative signal strength formula of the inversion recovery sequence is as follows: In the formula, S represents relative signal intensity; PD represents proton density of the tissue; TI represents inversion recovery time of the sequence; T1 represents T1 relaxation time of the tissue; TR represents repetition time of the sequence; TE last representing the last echo time of the multi-echo sequence; TE represents effective echo time; T2 represents T2 relaxation time of the tissue; i = 1, 2, …, N represents N kinds of components, wherein the brain parenchyma and the brain hemorrhage are a single component model N = 1, and the cerebral infarction tissue adopts a double component model N = 2; the subscript i represents the value of the i-th tissue; In the formula, S represents relative signal intensity; wherein the TE is adopted by the system to reach a minimum or near-minimum TE value, such that The T2 effect has the least influence on the signal S as close as possible to 1. The TR value and the corresponding TI value combination are selected so that the brain hemorrhage signal is high, and the cerebral infarction tissue and the brain parenchyma are equal or low.

2. The low-field magnetic resonance stroke differentiation sequence of claim 1, wherein: The selection of the TR value and the corresponding TI value combination conforms to the principle of the fastest clinical scanning speed.

3. The low-field magnetic resonance stroke differentiation sequence of claim 1, wherein: The correspondence of the TR and TI conforms to the following fitting result: TR = 0.0006925*TI 2 + 0.7426*TI + 67.

78.

4. The low-field magnetic resonance stroke differentiation sequence of claim 3, wherein: The TI is fixed, and the TR value floats up and down by 10%; or the TR is fixed, and the TI floats up and down by 10%.

5. The low-field magnetic resonance stroke differentiation sequence of claim 1, wherein: When the low field is 0.23T, the TE is 24 milliseconds, and the TR is 900 milliseconds, the TI is 685 milliseconds.

6. The low-field magnetic resonance stroke differentiation sequence of claim 1, wherein: When the low field is 0.23T, the TE is 24 milliseconds, and the TR is 1100 milliseconds, the TI is 800 milliseconds.

7. The low-field magnetic resonance stroke differentiation sequence of claim 1, wherein: When the low field is 0.23T, the TE is 24 milliseconds, and the TR is 1500 milliseconds, the TI is 1000 milliseconds.

8. The low-field magnetic resonance stroke differentiation sequence of claim 1, wherein: The PD is obtained through the signal intensity of the proton weighted image.

9. The low-field magnetic resonance stroke differentiation sequence of claim 1, wherein: Prior to the fast spin echo sequence, a series of inversion recovery pulses of different TI values are applied, at which time the signal size of the region of interest is related to the Tl value, which is fitted using the following equation to obtain the Tl measurement: In the formula, S(τ) is the signal intensity of the tissue; α is a weight coefficient; τ is the TI value of the scanning sequence; TR is the repetition time; TE last is the last echo time; T1 is the T1 relaxation time of the tissue.

10. The low-field magnetic resonance stroke differentiation sequence of claim 1, wherein: Using the fast spin echo sequence, keeping other parameters unchanged except TE time, using the correlation between TE and T2, using the following formula for fitting, the T2 measurement value is obtained. In the formula, S(β) is the signal intensity of the tissue; α is a weight coefficient; β is a series of echo times; T2 is the T2 relaxation time of the tissue.

11. A low-field magnetic resonance stroke differentiation apparatus comprising a magnetic resonance scanner; characterized by: The magnetic resonance scanner performs the low-field magnetic resonance stroke identification sequence according to any one of claims 1-8.

Images