Composite tissue markers detectable via multiple detection modalities including radiopaque element

A composite marker, comprising:

• a gel body having an outer surface, wherein the gel body is at least partially cross-linked to persist in a human body for at least 3 weeks;
• a first plurality of sealed ultrasound reflective elements, each sealed ultrasound reflective element respectively comprising a porous particle having a respective outer surface, a respective plurality of cavities and a gas in the plurality of cavities to provide reflectivity of ultrasound imaging signals, wherein each ultrasound reflective element comprises a hydrophobic coating on the respective outer surface thereof that at least temporarily seals respective pores thereof with the gas entrapped therein, the hydrophobic coating comprises a mono-, di-, tri-, or tetra-alkoxysilane;
• and
• at least one radiopaque element carried in or on the gel body, wherein the at least one radiopaque element is not disposed around the outer surface of the gel body,
• wherein the first plurality of sealed ultrasound reflective elements with the hydrophobic coating at least on the respective outer surface thereof are carried in a colloidal dispersion in the at least partially cross-linked gel body.