Digital subtraction angiography




Digital subtraction angiography (DSA) is a fluoroscopy technique used in interventional radiology.



It aims  to clearly visualize blood vessels in a bony or dense soft tissue environment. 



DSA images are produced using contrast medium by subtracting a pre-contrast image from subsequent images, once the contrast medium has been introduced into a structure. 



In traditional angiography, images are acquired by exposing an area of interest with x-rays while injecting contrast medium into the blood vessels. 



The resultant images  includes blood vessels, together with all overlying and underlying structures.



The images are useful for determining the anatomical position and variations of blood vessels but not for visualizing blood vessels accurately.



To remove the distracting structures to see the vessels better, a mask image is acquired. 



The mask image refers to an image of the same area before the contrast is administered. 



An X-ray image intensifier, keeps producing images of the same area at a  rate of 1 to 7.5 frames per second.



Each subsequent image gets the original baseline image subtracted out. 



Images produced have a pale grey background, allowing  a high contrast to the blood vessels, which appear a very dark grey., 



IV-DSA is used to study the vessels of the brain and heart and has helped detect carotid artery obstruction and to map patterns of cerebral blood flow. 



IV-DSA helps detect and diagnose lesions in the carotid arteries, a potential cause of strokes.



IV-DSA has also been useful in assessing patients prior to surgery and after coronary artery bypass surgery.



DSA is useful in the diagnosis and treatment of arterial and venous occlusions,  carotid artery stenosis, pulmonary embolism, and acute limb ischemia; arterial stenosis, which is particularly useful for potential kidney donors in detecting renal artery stenosis, cerebral aneurysms and arteriovenous malformations (AVM).



DSA is being replaced by computed tomography angiography (CTA), which can produce 3D images, is less invasive and magnetic resonance angiography (MRA), which avoids X-rays and nephrotoxic contrast agents.


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