What is the abbreviation for the radiographic procedure that produces a series of cross-sectional images?

The answer is MRI. The abbreviation stands for Magnetic Imaging Resonance.  The technique involves the use of powerful magnetic and radiowaves to induce nuclear spins in certain atoms of the object under study (mostly hydrogen in humans). As the nuclear spin decays (following the withdrawal of the powerful magnetic field), the atoms release radio waves hence their locations are read and interpreted by a computer into an image. This is done in cross-sections of the object until the whole image is rendered

Hydrosphere is the correct answer