Method for characterizing degree of edema of brain tissue

Abstract

The invention provides a brain tissue edema degree characterization method which comprises the following steps: controlling a cylindrical pressure head to be pressed into an experimental module at a constant rate, and transmitting a signal to a computer by a sensor to obtain a force-displacement curve. And calculating the relaxation amount of the experiment module according to the force-displacement data. The water content in the brain can be qualitatively represented through the obtained mechanical parameters, so that the edema degree of brain tissues is represented. The method not only can realize the characterization of the edema degree of the brain tissue, but also is beneficial to the precision of the measurement technology, accurate data and reliable performance, and can be used for speculating the cause of the edema of the brain.

Description

Technical Field

[0001] This invention relates to the field of brain tissue detection, specifically a method for characterizing the degree of brain tissue edema. Background Technology

[0002] Cerebral edema is a common pathological change following central nervous system injury (such as traumatic brain injury, stroke, intracranial infection, etc.). Its core characteristic is the abnormal accumulation of fluid within the brain tissue, which can lead to increased intracranial pressure, insufficient cerebral perfusion, and neurological dysfunction. Accurately characterizing the degree and distribution of edema is crucial for clinical diagnosis, treatment planning, and prognostic assessment. Existing methods for characterizing the degree of cerebral edema include: (a) Computed Tomography (CT) CT imaging utilizes the difference in X-ray attenuation between different tissues. Brain edema appears as a low-density shadow (CT value reduced by 5-10 HU compared to normal brain parenchyma), making it particularly suitable for rapid screening of acute brain injuries (such as edema secondary to cerebral hemorrhage). However, it has significant limitations: firstly, its sensitivity is low, making it difficult to identify only early, mild edema; secondly, its quantitative ability is poor, only able to visually assess the extent of edema (e.g., grading by the number of cerebral lobes involved), unable to accurately measure water content; and thirdly, it involves ionizing radiation, making it unsuitable for pregnant patients or patients with chronic edema requiring multiple follow-ups (such as after brain tumor surgery). (ii) Magnetic resonance imaging (MRI) MRI, with its multi-parameter imaging advantages, has become a core technology for characterizing edema. It can differentiate between vasogenic edema (such as edema around brain tumors), cytotoxic edema (such as early edema after ischemic stroke), and interstitial edema (such as hydrocephalus-related edema). Commonly used sequences include the following: T2-weighted imaging (T2WI): The edema area shows high signal and can clearly show the edema boundary. It is the first choice sequence for clinical assessment of the extent of edema. However, it cannot be accurately quantified, and the signal intensity is greatly affected by magnetic field inhomogeneity and scanning parameters. The results of different centers are difficult to standardize. Diffusion-weighted imaging (DWI): This imaging method uses the difference in diffusion motion of water molecules. Cytotoxic edema, due to the disruption of cell membrane integrity and the restriction of water molecule diffusion, appears as a high signal on DWI. It can detect early edema within 30 minutes of the onset of ischemic stroke, with significantly higher sensitivity than CT. However, it has low sensitivity for vasogenic edema and cannot distinguish between edema and inflammatory lesions (such as encephalitis, which can also appear as a high signal on DWI). Dynamic contrast-enhanced MRI (DCE-MRI): This method assesses blood-brain barrier permeability by injecting a contrast agent. Vasogenic edema, due to blood-brain barrier disruption and contrast agent leakage, manifests as enhanced signals. Vascular permeability parameters (such as the volumetric transport constant Ktrans) can be quantitatively calculated. However, it requires the injection of gadolinium-containing contrast agents, is contraindicated in patients with renal insufficiency, and takes a relatively long time (approximately 20-30 minutes). It is not suitable for agitated or critically ill patients who cannot cooperate. (III) Ultrasound Imaging Transcranial Doppler ultrasound (TCD) can indirectly reflect changes in intracranial pressure caused by edema by monitoring intracranial blood flow velocity. Bedside ultrasound can assist in judging intracranial pressure by measuring the optic nerve sheath diameter (ONSD) (ONSD > 5 mm often indicates elevated intracranial pressure, indirectly indicating edema). However, it has obvious limitations: First, it has poor penetration, as the skull severely attenuates ultrasound signals, and imaging can only be obtained through bone windows such as the temporal window and occipital window. About 15%-20% of patients cannot obtain clear images due to special skull structures (such as bone thickening). Second, it is mainly qualitative and cannot directly show the spatial distribution of edema, but can only infer it indirectly. The accuracy depends on the operator's experience.

[0003] The disadvantages of existing technologies are as follows: 1. Existing CT and conventional MRI rely heavily on visual judgment, which has a large subjective error. This method directly correlates brain tissue water content with mechanical parameters, and the results are repeatable and highly accurate. 2. CT scans involve ionizing radiation, and MRI scans involve gadolinium-containing contrast agents, both of which are highly destructive to tissues. 3. Limited applicability; it can only be used for biomimetic tissues in laboratories and is easily affected by interference.

[0004] 4. Low sensitivity; current CT scans require a 3%-5% increase in water content to detect it. Summary of the Invention

[0005] To address the problems of existing technologies, this invention provides a method for characterizing the degree of brain tissue edema. This method has small errors, a wide range of applications, a safe and reliable measurement method, low measurement sensitivity, and can detect edema early and accurately calculate water content.

[0006] This invention provides a method for characterizing the degree of brain tissue edema, comprising the following steps: 1) Place the culture dish of brain tissue on the sensor; 2) Control the cylindrical indenter to be pressed into the brain tissue at a constant rate, and obtain the maximum pressure F0 measured under instantaneous loading and the residual force F measured when time approaches positive infinity. n Where F0 is the initial stress response of brain tissue under instantaneous loading, F n The residual stress is the stress under steady-state mechanical conditions after complete stress relaxation. 3) The sensor transmits the signal to the computer to obtain the force-displacement curve, defining the maximum pressure F0 measured by the sensor at the beginning of the experiment and the residual force F measured when time approaches positive infinity. n The ratio is the relaxation amount X, where X = F0 / F n， The relaxation amount of brain tissue was calculated based on force-displacement data; 4) Calculate the water content in brain tissue based on the relaxation amount X: f(x) = a0 + a1cos(ω) x )+b1sin(ω x )+a2cos(2ω x )+b2sin(2ω x ), where a0, a1, b1, a2, b2, and ω are characteristic parameters related to water content calculation, obtained by fitting experimental data.

[0007] In a further improvement, the tip diameter of the cylindrical indenter in contact with the brain tissue is 2 mm.

[0008] In a further improvement, in step 4), a0=-1.581, a1=-0.2308, b1=10.99, a2=7.317, b2=9.917, ω=3.483.

[0009] The beneficial effects of this invention are as follows: 1. It can accurately quantify the water content of brain tissue by directly linking mechanical parameters, and the results are repeatable and highly accurate.

[0010] 2. High safety, no ionizing radiation like CT, no need for gadolinium-containing contrast agents like MRI, and avoids the invasive risks of ICP monitoring. 3. It has a wide range of applications and is not limited by skull structure or internal metal implants. It can measure mild, moderate and severe edema.

[0011] 4. High sensitivity: Existing CT scans require a 3%-5% increase in water content to detect edema, while this method can identify it with an increase of only 0.5%-1%, enabling early detection of edema and accurate calculation of water content. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the experimental setup.

[0014] Figure 2 This is a schematic diagram of the force-time curve for an indentation relaxation experiment.

[0015] Figure 3 Fitting curves for characteristic parameters related to water content calculation.

[0016] Figure 4 Force-time curve for indentation relaxation experiment.

[0017] Figure 5 The force-time curve is shown on logarithmic coordinates.

[0018] Figure 6 This is the relaxation amount-moisture content experimental curve. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a method for characterizing the degree of cerebral edema. This method utilizes a dynamic magnetic fatigue testing machine, sensors, a cylindrical indenter, and a computer. A specific implementation is as follows: Figure 1 As shown, a brain tissue experimental module is also included. A cylindrical indenter is pressed into the experimental module at a constant rate, and sensors transmit signals to a computer to obtain a force-displacement curve. The relaxation amount of the experimental module is calculated based on the force-displacement data. The amount of water content in the brain can be qualitatively represented by the obtained mechanical parameters, thereby characterizing the degree of brain tissue edema. This invention not only characterizes the degree of brain tissue edema but also benefits from the precision of the measurement technology, resulting in accurate and reliable data, which can be used to infer the causes of brain edema.

[0021] In studies on the correlation between brain tissue biomechanical properties and water content (degree of edema), it is necessary to clarify the definitions and physical meanings of core parameters: f(x) represents the water content index of brain tissue, a key physical quantity for quantifying the degree of edema; while a0, a1, b1, a2, b2, and ω are characteristic parameters related to water content calculation. These parameters are obtained by fitting experimental data, and the fitting curve is shown in the figure. Figure 3 As shown, a0=-1.581, a1=-0.2308, b1=10.99, a2=7.317, b2=9.917, ω=3.483, and their values ​​directly reflect the correlation coefficient between water content and relaxation amount. Furthermore, relaxation amount x, as an important mechanical indicator describing the viscoelastic behavior of brain tissue, is a core parameter for measuring the stress decay characteristics of materials under constant deformation over time.

[0022] Relaxation can be expressed as the ratio of the maximum pressure measured at the beginning of the experiment by the dynamic magnetic fatigue testing machine (corresponding to the initial stress response of brain tissue under instantaneous loading) to the residual force measured when time approaches positive infinity (corresponding to the steady-state mechanical state of brain tissue after complete stress relaxation). The physical significance of this calculation method lies in its elimination of the influence of instantaneous elastic deformation during loading, more accurately reflecting the relaxation characteristics dominated by viscous deformation of brain tissue. These relaxation characteristics are closely related to the water distribution within the brain tissue—when brain tissue experiences edema (increased water content), the ratio of extracellular fluid to intracellular fluid changes, directly affecting the viscoelasticity of the tissue and consequently leading to corresponding changes in relaxation. Water content can be expressed as the difference between the wet weight and the dry weight after drying, expressed as a percentage of the wet weight.

[0023] Figure 4 This is the force-time curve for the indentation relaxation experiment. The black curve represents the original experimental data, and the gray curve represents the smoothed result (moving average method). In the initial loading stage, the maximum force corresponds to the instantaneous stress response (F0), and the curve gradually decays and tends to stabilize at the residual force (Fn). The relaxation amount X = F0 / Fn eliminates the influence of instantaneous elastic deformation and better reflects the viscoelastic properties under long-term loading. As the water content increases, the curve decays faster, the residual force decreases, and the relaxation amount changes significantly, which can serve as a sensitive indicator of the degree of brain tissue edema.

[0024] Figure 5 This is a force-time curve on logarithmic coordinates. At smaller time scales (left), the force value rises sharply at the initial loading instant; a distinct peak appears in the middle region, reflecting the main stage of tissue viscoelastic relaxation; at larger time scales (right), the force gradually decays and tends to plateau, representing the stress relaxation to steady state process. This logarithmic representation reveals the mechanical response characteristics in different time domains, providing a basis for establishing a quantitative relationship between relaxation amount and water content.

[0025] Through fitting analysis of a large amount of experimental data, we obtained a quantitative relationship between relaxation amount and water content. This relationship has been verified multiple times, and its goodness of fit (e.g., R² value) meets the requirements for high-precision research. This indicates that there is an accurate and stable functional relationship between relaxation amount and water content. Figure 6 As shown, when the moisture content changes slightly, the relaxation amount will exhibit a predictable and regular change.

[0026] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. In particular, for the device embodiments, the above descriptions are merely preferred embodiments of the present invention. Since they are fundamentally similar to the method embodiments, the descriptions are relatively simple, and relevant parts can be referred to the descriptions of the method embodiments. The above descriptions are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention, without departing from the principle of the present invention, should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for characterizing the degree of brain edema, characterized in that... Includes the following steps: 1) Place the culture dish of brain tissue on the sensor; 2) Control the cylindrical indenter to be pressed into the brain tissue at a constant rate, and obtain the maximum pressure F0 measured under instantaneous loading and the residual force F measured when time approaches positive infinity. n Where F0 is the initial stress response of brain tissue under instantaneous loading, F n The residual stress is the stress under steady-state mechanical conditions after complete stress relaxation. 3) The sensor transmits the signal to the computer to obtain the force-displacement curve, defining the maximum pressure F0 measured by the sensor at the beginning of the experiment and the residual force F measured when time approaches positive infinity. n The ratio is the relaxation amount X, where X = F0 / F n， The relaxation amount of brain tissue was calculated based on force-displacement data; 4) Calculate the water content in brain tissue based on the relaxation amount X: f(x) = a0 + a1cos(ω) x )+b1sin(ω x )+a2cos(2ω x )+b2sin(2ω x ), where a0, a1, b1, a2, b2, and ω are all characteristic parameters related to water content calculation, obtained by fitting experimental data.

2. The method for characterizing the degree of brain tissue edema according to claim 1, characterized in that: The tip diameter of the cylindrical indenter in contact with the brain tissue is 2 mm.

3. The method for characterizing the degree of brain edema according to claim 1, characterized in that: In step 4), a0=-1.581, a1=-0.2308, b1=10.99, a2=7.317, b2=9.917, ω=3.483.

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