DSA is an acronym for Digital Subtraction Angiography, the basic principle of which is to digitize two frames of X-ray images taken before and after the injection of contrast medium into an image computer, and then eliminate the bone and soft tissue images from the angiographic image through the process of subtraction, enhancement and re-imaging to obtain a clear and pure vascular image. It is an examination method that combines computerized and conventional X-ray angiography. Generally speaking, the contrast agent is injected into the blood vessel to be examined, so that the blood vessel is revealed in its original form. Then the system processes the blood vessels to make them appear more clearly, making it easier for the doctor to diagnose or perform surgery.
DSA is mainly used for observation of vascular lesions, localization and measurement of vascular stenosis, as well as providing real three-dimensional images for interventional therapy, and is essential for various interventional treatments. It is suitable for cardiovascular and cerebrovascular, peripheral vascular, tumor examination and interventional minimally invasive treatment.
Characteristics of DSA
DSA has the advantages of high contrast resolution, short examination time, low contrast dosage, low concentration, significantly reduced patient X-ray absorption, and film saving, etc., which is of great significance in clinical diagnosis of vascular diseases.
Classification of DSA
Based on whether the contrast agent is injected into an artery or a vein, it is classified into arterial DSA (intraarterial DSA, IADSA) and intravenous DSA (intravenous DSA, IVDSA). IADSA is more often used because of its clear vascular imaging and low contrast agent dosage.
The imaging procedure of DSA
The operation of IADSA is to insert the catheter into the artery, and then inject 3,000 to 5,000 u of heparin through the catheter to perform systemic hypo-heparinization, in order to prevent the catheter from clotting. The catheter tip was inserted into the opening of the artery to be investigated, and the end of the catheter was connected to a pressure syringe for rapid injection of contrast medium. Before injecting the contrast agent, the flat panel detector was aligned with the screen to the examination site. Before and during the entire contrast procedure, the camera is operated for 7 to 10 seconds at a frame rate of 1 to 3 frames per second or more. A subtracted vascular image is processed on the operating table.
IVDSA can be performed by injecting a contrast agent into a vein through a catheter or needle and then subtracting the image.
Advantages of DSA
At present, the display of arteries by IADSA has reached or exceeded the level of conventional selective arteriography, and by applying selective or super-selective cannulae, small vessels and small lesions with diameters of less than 200 μ can be well displayed by IADSA. The observation of larger arteries can no longer be performed without selective cannulation. The concentration of contrast agent used is low and the dose is small. It is also possible to observe the dynamic image of blood flow in real time, as a means of functional checking.DSA can be used to store digital information.
IVDSA through the peripheral vein injection of contrast medium, you can get arteriography, easy to operate, but the examination area of the large vessels at the same time, overlap each other, the dosage of contrast medium is more, so the clinical application of less, but in the arterial seeding difficult or not suitable for IADSA can be used.
Clinical application of DSA
I. DSA is helpful in the examination of heart and large vessels. DSA can be used for aortic coarctation, aortic aneurysm, aortic constriction or anomalous development of the aorta, and for examination of the pulmonary artery.
II. DSA is the gold standard for the display of coronary arteries.
Three, IADSA is clearer to show the carotid and intracranial arteries, and can be used to diagnose carotid artery stenosis or occlusion, intracranial aneurysm, vascular developmental anomalies and arterial occlusion, as well as intracranial and intracranial tumors of the blood-supplying arteries and tumor staining and so on.
Fourth, the abdominal aorta and its large branches and limb vascular examination, DSA can be very good display. DSA technology is developing rapidly, has now reached three-dimensional real-time imaging, more conducive to the display of lesions.
New technology and outlookIn recent years, the development trend of DSA macro is to specialization, that is, unidirectional C-arm system is used for systemic angiography and interventional radiology, bidirectional C-arm system is used for cardiac and cerebrovascular examination. At present, rotary DSA imaging equipment has been applied to the clinic, which can make the X-ray tube make rotary motion or multi-track motion, and can realize the subtraction image display of three-dimensional angiography, and at the same time, the method of storing montages in the computer or the realization of programmed step-by-step DSA improves the deficiencies of the conventional DSA in the past. Effectively improve the spatial and temporal resolution of DSA images, reduce X-ray dose, further enhance the system's examination efficiency, improve the quantitative analysis of images, the main development trend of the DSA system, but also the key to medical imaging diagnosis and treatment.