A terminal structure includes an electrical cable that includes an inner conductor, an insulator provided around the inner conductor, a shield layer made of a metal foil around the insulator, and a sheath layer made of a resin tape around the shield layer, a shielded connector that is connected to a terminal of the electrical cable. The particles are composed of a noble metal or metal alloy core at least partially encapsulated by an atomically thin surface layer of platinum atoms. The microsphere have walls of 40-500 nm thick and are useful in ultrasonic imaging.