MRI physics
,MRI scanner: how does it work?
• MRI scanners use strong magnetic fields and radio waves to generate very
detailed images of the brain.
• Different components
1. Main magnetic field (B0) to align the hydrogen protons with the magnetic fi
2. Radiofrequency pulse (B1) to temporarily disrupt the alignment of the proto
3. Gradient coils to encode spatial information
,Properties of protons
• When a strong magnetic field is applied protons:
1. align themselves with the main magnetic field. This alignment is often rega
as the ‘phase’ of the protons
2. ‘’spin’ or ‘precess’ around the direction of the main magnetic field at a freq
called Larmor frequency
, Static magnetic field (B0) and RF pulse
• A strong static magnetic field is applied to align hydrogen protons. However,
B0 is not responsible for the image formation.
• Following the B0, an RF pulse is applied. This pulse will resonate at the same
frequency as the Larmor Frequency of the hydrogen protons.
This pulse temporarily disrupts the alignment of the protons ‘knocking them out of place’. T
called the excitation phase, as protons absorb the energy from the pulse.
When the RF pulse is turned off, the protons go back to alignment. As they do so, they relea
the energy that was absorbed during the excitation.
The released energy gets detected by the RF coils during a process called reception. This cr
the MRI signal
,MRI scanner: how does it work?
• MRI scanners use strong magnetic fields and radio waves to generate very
detailed images of the brain.
• Different components
1. Main magnetic field (B0) to align the hydrogen protons with the magnetic fi
2. Radiofrequency pulse (B1) to temporarily disrupt the alignment of the proto
3. Gradient coils to encode spatial information
,Properties of protons
• When a strong magnetic field is applied protons:
1. align themselves with the main magnetic field. This alignment is often rega
as the ‘phase’ of the protons
2. ‘’spin’ or ‘precess’ around the direction of the main magnetic field at a freq
called Larmor frequency
, Static magnetic field (B0) and RF pulse
• A strong static magnetic field is applied to align hydrogen protons. However,
B0 is not responsible for the image formation.
• Following the B0, an RF pulse is applied. This pulse will resonate at the same
frequency as the Larmor Frequency of the hydrogen protons.
This pulse temporarily disrupts the alignment of the protons ‘knocking them out of place’. T
called the excitation phase, as protons absorb the energy from the pulse.
When the RF pulse is turned off, the protons go back to alignment. As they do so, they relea
the energy that was absorbed during the excitation.
The released energy gets detected by the RF coils during a process called reception. This cr
the MRI signal
