Explain the main principles behind the use of nuclear magnetic resonance imaging (NMRI) to obtain information about internal body structures.

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

1. [B1] strong (uniform) magnetic field
2. [B1] * nuclei precess/rotate about field (direction)
3. [B1] radio frequency pulse/RF pulse (applied)
4. [B1] * RF or pulse is at Larmor frequency / frequency of precession
5. [B1] causes resonance / excitation (of nuclei)/nuclei to absorb energy
6. [B1] on relaxation/de-excitation, nuclei emit RF/pulse
7. [B1] * (emitted) RF/pulse detected and processed
8. [B1] non-uniform field (superposed on uniform field)
9. [B1] allows positions of (resonating) nuclei to be determined
10. [B1] * allows for position of detection to be changed/different slices to be studied
11. [B2] max. 2 of additional detail points marked *