Silicone implant for retinal detachment
on CT silicone is hyperdense
on MR silcone is bright on T1 and T2 and demonstrates "super chemical shift" artifact
Chemical Shift
silicone 0.33 ppm
fat about 1.3 ppm
water 4.7 ppm
Larmor frequency at 1.5 T for H nuclei is 63.87 MHz
The difference of 3.4 ppm =217 or close to the 220 Hz that you often see quoted for the frequency difference for fat and water at 1.5 T
The difference between silcone and water is 4.4 ppm. That is why you see "super chemical shift" with silicone.
Q: Silicone is hyperdense on CT. How do patients see if it is so dense?
A: Radiodensity/physical density has nothing to do with the ability to transmit light. Glass is quite dense, yet can be clear.
Scleral band/buckle
Reference:
Radiographics http://radiographics.rsna.org/content/23/4/983.full