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二氧化钍(Thorotrast)为1928年第一次采用的造影剂,其低浓度亦具有不透X线的性能,已广泛应用于肝、脾、肾、鼻窦及血管的造影。早在1932年对其特性及放射性即有了报道。为一种自然存在的放射活性物质,可放射出α,β及γ射线。其中以α射线最为重要,虽其穿透力低(约为1毫米),但其毒性比值较之γ射线高10,000倍。β及γ射线对生理方面的作用,微不足道。二氧化钍的半衰期据估计为1.4×10~(10)年。放射性的测定并非固定不变,因其分解物放射性钍及新钍的继续放射及其积蓄作用,可在多少年之后,仍增加其放射性。
Thorotrast is a contrast agent used for the first time in 1928. Its low concentration also has radiopaque properties. It has been widely used in liver, spleen, kidney, paranasal sinuses, and blood vessels. As early as 1932, its characteristics and radioactivity were reported. It is a naturally occurring radioactive material that emits alpha, beta, and gamma rays. Among them, α rays are the most important. Although their penetrating power is low (about 1 mm), their toxicity ratio is 10,000 times higher than that of γ rays. The physiological effects of β and γ rays are negligible. The half-life of ceria is estimated to be 1.4×10 10 years. The determination of radioactivity is not constant, but because of its radioactive decomposition and the continued emission of new nevus and its accumulation, it can still increase its radioactivity after many years.