Question

9 across: which imaging technique is procedure in which high resolution images are constructed from the measurement of radio - frequency waves that hydrogen atoms emit as they align with a powerful magnetic field? (abbreviation only)

Explanation:

This description matches the principle of Magnetic - Resonance Imaging (MRI), which uses the alignment of hydrogen atoms in a magnetic field and the measurement of radio - frequency waves they emit to create high - resolution images.

Answer:

MRI