In many custom tubing applications, it is desirable to manufacture the components such that they can be seen with fluoroscopy or x-ray imaging. Typically this is done by blending the polymer with another material, the radiopacifier, which is chosen because it has a higher radiopacity. With many different radiopacifiers available, it is useful to understand the strengths and weaknesses of each before making a selection.
Barium Sulfate(BaSO4) – Barium Sulfate is the most commonly used radiopacifier for almost all medical applications where imaging is an issue, including catheters and other types of tubing. While BaSO4 does not have the highest level of radiopacity, it remains moderately priced compared to the alternatives. Because it is not as dense as other radiopacifiers, a high volume of barium is needed to achieve a high level of radiopacity and typically the barium begins to affect the strength of the polymer after it exceeds 20% by volume. BaS04 also tends to mix more easily with elastomers than the other alternatives.
Bismuth(Bi) – Several different bismuth salts are commonly used as radiopacifiers, all of which have a higher density than Barium Sulfate. The high density creates a higher weight-to-volume ratio, which means that the resulting polymer can be more radiopaque with a lower volume percentage of the bismuth salt. While bismuth fillers have been growing in popularity, the fact that they are much more expensive than Barium Sulfate still precludes their use for certain applications.
Tungsten(W) – Tungsten is considerably more dense than the other alternatives, providing the highest weight-to-volume ratio of any commonly used radiopacifier. Because of this, polymers made with tungsten can be extremely radiopaque without a significant change in mechanical properties. Though raw tungsten is also relatively inexpensive, its other properties ultimately make it a more expensive choice for many applications:
- 1. Tungsten is highly flammable
- 2. Tungsten is black and extremely difficult to change the color of
- 3. Tungsten is abrasive, causing accelerated wear on processing equipment and surface roughness in the end result.