CT: Computed Tomography (CT) is an electronic computerized tomography device that uses an X-ray beam to scan a certain layer of the head, and a detector that receives the transmitted X-rays to produce visible light, which is converted into photocurrent by a converter, and then into digital by an analog/digital converter and sent to an electronic computer for processing. Finally, the digital information is reconstructed into CT images by the analog/digital converter. Therefore, CT has the features of high tissue density resolution, no overlap, safety and rapidity, which are of great value in showing various structures of brain tissue. the application of CT enables many cerebrovascular diseases, such as cerebral infarction and cerebral hemorrhage, to be diagnosed timely and accurately. CT has great diagnostic value for cerebral infarction, cerebral hemorrhage intracranial aneurysm or subarachnoid hemorrhage due to cerebrovascular malformation rupture, etc., and should be preferred. DSA: digital subtraction angiography (DSA) is a subtraction technique that uses an electronic computer to process the digital information of angiography, so as to display only the “pure blood vessels” themselves and eliminate the interference of surrounding soft tissues and bones. In the current general time subtraction method, the image data of the area to be examined is entered into two memories of an electronic computer before and after the rapid injection of organic iodine contrast into the blood vessel through the catheter. Then, the subtraction command is given immediately, and the electronic computer will subtract the pre-imaging data from the post-imaging data. The result is then passed through the conversion system to obtain a display of only the contrasted vessels. The rest of the soft tissue and bone images are eliminated. Depending on the route of contrast injection into the artery or vein, there are two types of DSA: arterial DSA and venous DSA. Currently, arterial DSA is commonly used. Cerebrovascular DSA: It is of great value for the diagnosis of intracranial aneurysm and cerebrovascular malformation. MRI: short for Magnetic Resonance Imaging, is an imaging technique that uses signals generated by the phenomenon of magnetic resonance to reconstruct images. The nucleus of any material has the property of motion, and the nucleus of hydrogen atom is no exception. The hydrogen nucleus, which is most abundant in the human body, has a spin-like motion, is positively charged, and has a magnetic moment. When the human body is examined in a uniform static magnetic field, the hydrogen proton spin axes are aligned in the direction of the magnetic lines of force of the magnetic field. If you give a specific frequency of radio frequency pulse, excitation of hydrogen protons, after absorbing energy, the magnetic resonance phenomenon will occur. When the RF pulse is discontinued, the energy absorbed by the hydrogen protons is released to restore the original state. This recovery process is called the relaxation process. The time required to complete the relaxation process is called the relaxation time. There are two types of relaxation times, one is the spin-lattice relaxation time, expressed as T1, which is the time required for the hydrogen proton to transfer the absorbed energy to the surrounding nucleus. The other is the spin-spin relaxation time, denoted by T2, which is the time it takes for the hydrogen proton to recover from the high energy level to the low energy level state. Different tissues and pathological tissues in the human body have relatively fixed T1 or T2 due to the different states of the hydrogen protons they contain, and there are differences between them, and this difference is the basic of magnetic resonance imaging. It must be noted that CT has only one absorption coefficient difference imaging, while MRI has a rich variety of parameters such as T1, T2 and proton density imaging. Thus, MRI reflects the state of MR signal intensity or T1, T2, etc. If it mainly reflects T1 between tissues, it is a T1-weighted image, which is best for showing anatomical details; if it mainly reflects T2 between tissues, it is a T2-weighted image, which is best for determining the characteristics of diseased tissues; and if it mainly reflects proton density differences between tissues, it is a proton-weighted image. Therefore, the same MRI scan level can have the above three different images at the same time, which is richer than what CT shows. In addition, MRI has higher tissue resolution than CT, and can directly image in multiple directions without cranial artifacts, and has the characteristics of vascular flow-void effect, so that the display rate of cerebrovascular diseases is sharply more accurate than that of CT. MRI is more sensitive than CT for cerebrovascular malformations and smog that are more difficult to determine with CT. Ultrasound: TAD: transcranial doppler is the use of ultrasound Doppler effect, using a combination of low emission frequency and pulse emission technology, so that ultrasound penetrates the thinner part of the skull, non-invasively obtain the cerebral base artery blood flow velocity, in order to reflect the functional state of the cerebral circulation. Doppler ultrasonography: The most basic parameters are blood flow velocity and frequency pattern. Flow velocity includes peak systolic flow velocity (Vs), maximum end-diastolic flow velocity (Vd) and mean flow velocity (Vm), with Vm being the most representative. An increase in flow velocity can indicate high blood flow, arterial spasm or arterial stenosis; a slowing of flow velocity can be the result of proximal arterial stenosis or increased resistance at the distal end of the circulation. The Fourier coefficient (FPI) is a new set of frequency domain resistance indicators. Based on a fast Fourier transformation of the Doppler flow waveform envelope, the proportion of each frequency component in the original wave, or FPI.