X-rays shine right through things that are radiolucent ( lucere in latin means to shine). Radiolucent structures appear black on exposed X-ray film. ... (12 Dec 1998) ... 
Type: Term Pronunciation: rā′dē-ō-lū′sĕnt Definitions: 1. Relatively penetrable by x-rays or other forms of radiation.
Radiolucent: Anything that permits the penetration and passage of X-rays or other forms of radiation. Radiolucent is as opposed to radiopaque (which refers to anything that blocks the penetration of X-rays). Plastic is usually radiolucent. If a child swallows a radiolucent plastic paperclip, that paperclip will not be visible on X-ray so it may not...
[adj] - almost complete transparent to X-rays or other forms of radiation
radiolucent Transparent to X-rays.radioluminescence, radiolucent Allowing the passage of radiant energy; such as, X-rays, to a varying extent depending on the nature of the object. Also, roentgenolucent. Etymologically related 'light, shine, glow' word families: ethero-; fulg-; lumen-, lum-; luna, luni-; lustr-; phengo-; pheno-; phosp...
adjective almost complete transparent to X-rays or other forms of radiation; `radiolucent tissues`