Nowadays, silicone based biocompatible polymers are used to produce catheters and other devices that are inserted into the body for interventional procedures.
The inserted parts are commonly filled with substances opaque to x-rays, thereby rendering the devices visible under fluoroscopy or x-ray imaging. These fillers or radiopacifiers are based on typically dense metal or metallic salt powders that affect the energy attenuation of photons in an x-ray beam as it passes through matter, reducing the intensity of the photons by absorbing or deflecting them. Because these materials exhibit a higher attenuation coefficient than soft tissue or bone, they appear lighter on a fluoroscope or x-ray film. This visibility helps to accurately position the device in the affected area. Image contrast and sharpness can be varied by the type and amount of radiopacifier used. Device design is also a factor; a higher loading of radiopaque material, for instance, is needed for thin-wall catheter tubing than for products with thicker walls. Generally, compounds should contain only the amount of additives absolutely required for the application, since overloading can result in the loss of the polymer’s mechanical properties. Blending together several radiopaque materials can produce better results than using only one type in the solution. Among the most widely used radio pacifiers for medical devices are barium sulfate, bismuth compounds, and tungsten - metals that are excellent absorbers of x-rays. Selection of the correct fillers in the proper amount requires a thorough understanding of attenuation and how it is affected by various radiopaque compounds.
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