An ultrasound gel isprovided for use with internal ultrasoundimaging and/or therapy. The gel can haveacoustic properties that can closely matcha soft tissue to be imaged/treated and canbe of a high viscosity that is maintained atbody temperature. In some embodiments,the gel can act as a lubricant and, althoughwater based, can be hydrophobic and notdissolve in bodily fluids. In someembodiments, the gel can be sterile, safe foringestion, safe for application over mucousmembranes, and include a preservative. Inorder to achieve sterility while maintaininga desired viscosity range, the gel caninclude a viscosity stabilising agent such as aviscosity protection agent for protectionfrom radiation induced breakdown. Insome embodiments, methods of altering ormaintaining the viscosity of a gel isprovided.
