MRI is a non-invasive, non-radiographic imaging technology, with the ability to directly cut layers in any direction, combined with different orientations of the layers, can comprehensively display the structure of the examined tissues and organs, with no observation dead ends. The application of volumetric scanning allows real-time reconstruction of various planes, curved surfaces or irregular layers, which facilitates three-dimensional tracking of anatomical structures or lesions. Among all the medical imaging means, MRI has the highest soft-tissue contrast resolution, which can clearly separate various soft tissues, differentiate between higher-signal endocardium, medium-signal myocardium, and epicardium and low-signal pericardium under the high-signal fat lining. MRI has many imaging parameters, contains a large amount of information, and has high spatial resolution, which is effective in the diagnosis of cardiac macrovascular diseases, including PTE. Tang Xiaofeng, Department of Radiology, Yantai Mountain Hospital I. Main imaging sequences of MR examination 1.3PL localization slice: with 2D gradient echo sequence. TR15-50ms, TE6-15ms, flip angle 25-30°, matrix 128X256, layer thickness 10mm, spacing 2mm, FOV38-45CM, 1 time acquisition. 2. Transverse Axis Bit SE T1WI: using cardiac gating, TR/TE=500ms/15ms, layer thickness 5-8mm, interval 1-2mm, FOV 35cmX35cm, matrix 192X256, 1 acquisition. 3. 3D contrast-enhanced magnetic resonance pulmonary artery imaging (3D CE MRPA): FSPGR sequence was used, TR/TE=100ms/3.2ms, flip angle 80°, layer thickness 5mm, interval 1mm, FOV 35.0cmX35.0cm, matrix 192X256, coronal plane imaging, scanning time about 20 seconds. Patients were trained to breathe and hold their breath before examination. Plain scanning was routinely performed first, followed by enhancement scanning. Gd-DTPA contrast agent was used, with a dosage of 0.2 mmol/kg and an injection rate of 2-3 ml/s. It was injected from the anterior elbow vein by hand-push or high-pressure syringe. Scanning was initiated according to the cyclic determination time or delayed by 5 seconds, and the scanning was repeated 2 times after a 10-second interval. The images obtained from each scan were reconstructed by maximum intensity projection method. II. MR manifestations of pulmonary embolism: 1. Acute pulmonary embolism: The embolus of acute pulmonary embolism is located in the lumen of the blood vessel, which is characterized by an abnormal signal in the lumen of the blood vessel in the form of a strip, while the vessel contour is mostly without abnormality. Early cardiac gated SE sequence scanning, in the flow of empty low or no signal in the lumen of the vessel, the thrombus was moderate or moderately high signal, in the multi-echo sequence of the signal does not change. GRE sequence is sensitive to blood flow, flowing blood was high signal, while the embolus was typical low signal. the sensitivity of MRI for pulmonary thrombus is 80%, specificity is 92%, accuracy is 88%. 2. Chronic pulmonary embolism: It is characterized by irregular vessel contour, narrowed or interrupted lumen, etc. It often shows lateralized appendage thrombus, with moderately high signal in T1WI. On GRE or MRA images, compared with the high signal blood flow, the vessels within the pulmonary artery show luminal signal-free filling defects or obstruction and truncation of the pulmonary artery branches. Chronic pulmonary artery thrombosis is a less common sequela of acute pulmonary embolism, in which the thrombus becomes mechanized and adheres to the pulmonary artery wall, forming a chronic mechanized thrombus, which further develops into pulmonary hypertension if the lesion is extensive. 3. Enhanced scanning: with the progress of MR technology, its diagnostic value for pulmonary embolism is getting bigger and bigger, especially fast enhanced MRA. enhanced by contrast, only the image of the pulmonary artery that has been head of contrast is captured, avoiding the interference of the pulmonary vein and the heart and the aorta, and it is able to show the image of the whole pulmonary artery tree. CE-MRA of pulmonary embolism shows signs of limited dilatation of the pulmonary arteries, filling defects within the pulmonary arteries and absence of branches within the pulmonary arteries. It clearly shows the localized filling defect caused by the embolus in the pulmonary artery, clarifies the site, morphology, size and length of the embolus, and observes the relationship between the embolized artery and the embolus from all angles. According to different pulmonary embolism, the embolus can be located in the center of the artery, forming a more complete embolus; can also be located on the side of the artery, forming eccentric stenosis; contrast agent can more or less pass through the narrowed segment of the embolus, so that the distal segment of the artery to varying degrees of visualization.CE-MRA can also be used as a follow-up tool after the treatment of pulmonary arterial embolism, to understand the situation of the embolus after the treatment, in order to determine the effectiveness of its treatment. Data show that: CE-MRA for the diagnosis of pulmonary artery embolism, its sensitivity and specificity in 75%-100%, for the center type pulmonary artery embolism sensitivity and specificity is slightly higher than the subsegmental pulmonary artery embolism. MRI can also be examined through the lower extremity veins, clear lower extremity veins with or without thrombosis. MR diagnosis of PTE in a variety of imaging methods in the status and role of the past diagnosis of PTE imaging methods are mainly chest X-ray film, radionuclide pulmonary ventilation / perfusion imaging and X-ray pulmonary arteriography. Chest X-ray has been widely used as the first choice and screening test. Experienced radiologists analyzing the findings on chest X-ray can make a qualitative diagnosis of most patients with PTE. Radionuclide pulmonary ventilation/perfusion imaging combined with lower extremity venography has a sensitivity of up to 95% for the diagnosis of PTE, and can also be used for screening and for the diagnosis of distal pulmonary artery embolism.X-ray pulmonary arteriography was once considered to be the gold standard for the diagnosis of PTE, but it is invasive and complicated to perform, with complications occurring in about 6% of the patients, and is not currently used as a preferred method. Non-traumatic CTA and MRA have become comprehensive and reliable diagnostic methods for this disease, and have been gradually popularized and applied in the clinic, and have become the preferred and confirmatory diagnostic methods for diagnosing PTE in hospitals with the condition.