English to Japanese Tech/Engineering Automotive / Cars & Trucks

Using pre-exposed filmstrips. The pre-exposed filmstrips are produced by exposing sections of a conveniently sized film to different quantities of radiation in a progressive manner. On processing this will result in strips of varying density levels down the radiograph. This effect can be achieved using a suitable metal step wedge or by progressively moving the edge of a lead sheet down the film cassette a controlled distance between each exposure.

上記文中にある｢strips of varying density levels down the radiograph｣の日本語訳についてです。様々な 濃度レベルのストリップと放射線写真がどのように関係するのか、いろいろ調べてみたんですが、どのような訳にすればよいかわかりません。　よろしくお願いします。