What type of silicon dioxide is used increase the viscosity of water soluble ultrasound gel?

Question

(silicon dioxide as thickening agent in ultrasound transmission gel)

Answer 1

This was all I could find when I looked up the brand "Aquasonic" gel" You might have to contact them directly for more answers, they have all kinds of gel, and they are water soluble.

Acoustically correct for the broad range of frequencies used
Completely aqueous, will not stain clothing or damage transducers
Unique hypoallergenic, bacteriostatic, non-sensitizing and non-irritating
No formaldehyde
Not a spermicide
Used and recommended by leading manufacturers of medical ultrasound equipment worldwide

Answer 2

flour?