Optical Phantoms by Scott Prahl


Some of the early attempts at creating optical phantoms used Intralipid or Nutralipid, a suspension of lipid particles. These are used for intraveneous feeding in the hospital and it is pretty easy to get fresh or outdated bottles (if one is in a medical center). Intralipid is also relatively cheap.

Intralipid has a long and glorious history of being measured. Consequently one can find references to its optical properties in the literature. I happen to be associated with some of these.

The problem with intralipid is that it is a food substance and not an optical medium. Consequently no effort has been made to make all bottles of Intralipid optically equal. Moreover, it seems that the optical properties of a bottle change over time.

Latex Microspheres

Now these puppies are nice. You can get a Mie scattering program to calculate the optical properties. The concentration is known and they last for a long time. They are also very expensive. You can get them from Duke Scientific.

Solid Epoxy Phantoms

This recipe follows the methods of other groups. Delphy's group was the first to use these phantoms (to our knowledge). Dave Boas provided this recipe and Martin Ostermeyer and Steve Jacques have actually used this recipe.

This stuff has the advantage that it doesn't change, it is a solid, and it can be made with any optical properties you want (well it might be hard to change the scattering anisotropy reliably). Unfortunately, Titanium dioxide is not a known scattering medium and therefore one makes an unknown optical standard.

Finally, this stuff can be machined if you desire.

250 ml resin
19 drops catalyst
TiO2 suspended in small amount of ethanol
ethanol soluble dye

1 mg TiO2 per milliliter of resin gives a a reduced scattering coefficient µs(1-g)=µs' of about 8-10cm-1 around 800nm.

Suspend the TiO2 with an ultrasound cleaner in the least amount of ethanol feasible. Add dye. Mix thoroughly with resin. Add catalyst, mix thoroughly. Cures in about 24 hours at room temperature.

You can get the polyester resin from Amazon under the trade name "Castin' Craft" a clear liquid plastic casting resin and catalyst. Something similiar should also be available from art supply stores.