Question:  How to diagnose Pulmonary Embolism ?
Answer: Pulmonary embolism (PE) is diagnosed based on your medical history, a physical exam, and test results.
                
Doctors who treat patients in the emergency room often are the ones to diagnose PE with the help of a radiologist. A radiologist is a doctor who deals with x rays and other similar tests.
                
Medical History and Physical Exam
                
To diagnose PE, the doctor will ask about your medical history. He or she will want to: 
                
Find out your deep vein thrombosis (DVT) and PE risk factors
                
See how likely it is that you could have PE
                
Rule out other possible causes for your symptoms
                
Your doctor also will do a physical exam. During the exam, he or she will check your legs for signs of DVT. He or she also will check your blood pressure and your heart and lungs.
                
Diagnostic Tests
                
Many tests can help diagnose PE. Which tests you have will depend on how you feel when you get to the hospital, your risk factors, available testing options, and other conditions you could possibly have. You may have one or more of the following tests.
                
Ultrasound
                
Doctors can use ultrasound to look for blood clots in your legs. Ultrasound uses sound waves to check blood flow in your veins.
                
For this test, gel is put on the skin of your legs. A hand-held device called a transducer is moved back and forth over the affected areas. The transducer gives off ultrasound waves and detects their echoes as they bounce off the vein walls and blood cells.
                
A computer turns the echoes into a picture on a computer screen, allowing the doctor to see blood flow in your legs. If the doctor finds blood clots in the deep veins of your legs, he or she will recommend treatment.
                
DVT and PE both are treated with the same medicines.
                
Computed Tomography Scans
                
Doctors can use computed tomography (to-MOG-rah-fee) scans, or CT scans, to look for blood clots in the lungs and legs.
                
For this test, dye is injected into a vein in your arm. The dye makes the blood vessels in your lungs and legs show up on x-ray images. You'll lie on a table, and an x-ray tube will rotate around you. The tube will take pictures from many angles.
                
This test allows doctors to detect most cases of PE. The test only takes a few minutes. Results are available shortly after the scan is done.
                
Lung Ventilation/Perfusion Scan
                
A lung ventilation/perfusion scan, or VQ scan, uses a radioactive substance to show how well oxygen and blood are flowing to all areas of your lungs. This test can help detect PE.
                
Pulmonary Angiography
                
Pulmonary angiography (an-jee-OG-rah-fee) is another test used to diagnose PE. This test isn't available at all hospitals, and a trained specialist must do the test.
                
For this test, a flexible tube called a catheter is threaded through the groin (upper thigh) or arm to the blood vessels in the lungs. Dye is injected into the blood vessels through the catheter.
                
X-ray pictures are taken to show blood flowing through the blood vessels in the lungs. If a blood clot is found, your doctor may use the catheter to remove it or deliver medicine to dissolve it.
                
Blood Tests
                
Certain blood tests may help your doctor find out whether you're likely to have PE.
                
A D-dimer test measures a substance in the blood that's released when a blood clot breaks down. High levels of the substance may mean a clot is present. If your test is normal and you have few risk factors, PE isn't likely.
                
Other blood tests check for inherited disorders that cause blood clots. Blood tests also can measure the amount of oxygen and carbon dioxide in your blood. A clot in a blood vessel in your lungs may lower the level of oxygen in your blood.
                
Other Tests
                
To rule out other possible causes of your symptoms, your doctor may use one or more of the following tests.
                
Echocardiography (echo). This test uses sound waves to create a moving picture of your heart. Doctors use echo to check heart function and detect blood clots inside the heart.
                
EKG (electrocardiogram). An EKG is a simple, painless test that detects and records the heart's electrical activity.
                
Chest x ray. This test creates pictures of your lungs, heart, large arteries, ribs, and diaphragm (the muscle below your lungs).
                
Chest MRI (magnetic resonance imaging). This test uses radio waves and magnetic fields to create pictures of organs and structures inside the body. MRI often can provide more information than an x ray.