Tungsten Polymers X-ray Absorption for Medical Devices

Tungsten polymers are used to produce catheters and other devices that are inserted into the body for diagnostic or interventional procedures are commonly filled with substances opaque to x-rays, thereby rendering the devices visible under fluoroscopy or x-ray imaging. These fillers, or radiopacifiers—tungsten(typically dense metal powders)—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, could be a suitable material for X-ray absorption for many radioan facilities especially medical devices. 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 provides the contrast needed to accurately position the device in the affected area. Image contrast and sharpness can be varied by the type and amount of radiopacifier used, and can be tailored to the specific application of the device.

For example, a device designed for use near the surface of the skin requires less radiopaque filler to achieve the required level of attenuation compared with one used inside the coronary vasculature. 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 a formulation.

Among the most widely used radiopacifiers 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. This article discusses those radiopaque fillers commonly used with medical-grade thermoplastic polymers and the factors involved in their selection.

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