CTPA, or Computed Tomography Pulmonary Angiography, is a medical imaging technique used to visualize the blood vessels in the lungs. It is primarily employed to diagnose pulmonary embolism, a condition where blood clots block pulmonary arteries. The procedure involves the injection of a contrast dye followed by a CT scan, allowing for detailed images of the pulmonary vasculature. CTPA is valued for its speed and accuracy in detecting vascular abnormalities in the lungs.