What Is a Lung Perfusion Scan?

In the normal image, the outlines of the two lungs are complete, and the radioactive distribution is relatively uniform. At the AP position, the right lung base is usually curved upward. The left lung has aortic arches and heart pressure traces, and is therefore smaller than the right lung. The two lungs in PA position are close in size, the middle blank area is the spine and mediastinum, and the heart shadow is obscured by the lower left lung. The depression of the anterior inferior margin of the LL position is a cardiac impression.

Lung perfusion imaging agents are 99mTc-labeled large aggregate human serum protein particles (99mTc-MAA) or 99mTc-labeled microspheres, which have a diameter of about 10-30 m and a single dose of 0.5-1.5 mg, which is about 100,000-300,000 particles. When the reagent is injected into the vein, it enters the right heart with the blood, and is fully mixed with the blood in the right heart, and then perfused into the vascular bed of the lung with the blood flow through the pulmonary artery. Larger particles can temporarily occlude the pulmonary capillary anterior blood vessels, smaller The embolism of pulmonary capillaries. (99mTc-MAA) The amount of embolized vascular beds in various parts of the lung is directly proportional to the amount of blood perfusion in the local area. Therefore, the (99mTc-MAA) radioactivity distribution image in the lung taken by the scanner or gamma camera, That is the image of blood flow perfusion in the lung. The higher radioactivity indicates that the local blood flow is better, and the lower position indicates that the blood flow is poor. If radioactivity is absent in a certain area, it indicates that there is no blood perfusion in the area, indicating that the blood vessels perfused there have been blocked or occluded. The distribution of radioactivity in the lungs of normal people is basically uniform. Due to the influence of blood flow and (99mTc-MAA) on gravity, the radioactivity of the lung tip is slightly lower when injected in the sitting position, and the radioactivity in the dorsal lung is slightly higher when injected in the supine position. At the time of imaging, the number of blocked blood vessels only accounts for a few tenths of a million and a few millionths of the total number of anterior capillaries and capillaries of the lungs, so it does not cause significant changes in hemodynamics and pulmonary function.

Name: Lung perfusion imaging

category: Radionuclide

Normal lung perfusion imaging

Clinical significance of pulmonary perfusion imaging

Abnormal results: (1) The abnormal lung perfusion imaging manifests as lobes or segmental lungs (wedges, common in pulmonary embolism) or irregular radioactive defects, but the defects in one position, especially the oblique position, must be in other If the body has the same defect, the abnormality can be judged. (2) Images of normal smokers may sometimes have small perfusion defects. (3) Pleural lesions can affect normal graphics, such as thickening of the pleura or a small amount of pleural effusion in the lateral or oblique position can produce "leaf sign" (interstitial fissure widens, forming a linear radiation defect); moderate effusion can A segmental lung-like radiation defect is formed, but the position imaging can disappear; a large amount of fluid can compress the entire lung and reduce the lung shadow. People to be checked: Patients with abnormalities in the lungs who need lung examinations

Precautions for lung perfusion imaging

Not suitable for people: (1) Congenital heart disease, pulmonary arteriovenous fistula, severe pulmonary movement impairment, severe granulocytopenia, thrombocytopenia, aplastic anemia, which are prohibited in right and left shunts. (2) Persons with a history of severe allergies should not do this test in principle. Note before the test: Ask an allergy history before the test, but those who need the condition should first perform a skin test. Observation of non-positive response for 15 minutes after skin test can be used for lung perfusion imaging, but it is necessary to observe closely and provide emergency medicine. Inspection requirements: (1) Inhale oxygen for 10 minutes before intravenous injection to avoid false positives caused by pulmonary vasospasm. (2) The speed of intravenous injection of imaging agents should be slow, and less blood should be drawn back, so as to prevent the returning blood and imaging agents from clotting into large clumps to block the pulmonary arterioles, otherwise it may cause abnormal radioactive hot spots in lung imaging and affect the test results; And excessive obstruction of pulmonary blood vessels can lead to adverse reactions such as radon. For patients with allergies and patients whose pulmonary vascular bed has been significantly damaged, injection should be stopped immediately when symptoms occur during the injection. (3) For patients with one side of the lung absent, lobectomy, or known significant damage to the pulmonary vascular bed, the injection particles should be reduced accordingly. The amount of injection for children during lung perfusion imaging should be calculated with reference to body weight, and it is generally injected at 2-3 MBq per kilogram of body weight. (4) Radiation protection for injection patients and medical staff.

Lung perfusion imaging

First perform a skin test, then inhale oxygen for 10 minutes, then inject the reagent, and finally the machine develops.

Pulmonary perfusion imaging related diseases

Silicosis, acute right heart failure, pulmonary hypoplasia, pulmonary actinomycosis, pulmonary arteriovenous tumor, pulmonary embolism, pulmonary artery stenosis

Symptoms related to pulmonary perfusion imaging

Atelectasis, serum anti-GBM antibody positive, pleural thickening, pulmonary arterial murmur, mediastinal lesions, immune damage, nausea, low pulmonary blood flow, pulmonary consolidation, and children crying ^[1]