Understanding the MRI scanner's environment and the behavior of hydrogen protons in the body.
Need-to-know for clinical practice
Proton Alignment
Adjust B₀ to see alignment
B₀ Field Strength1.5T
Larmor Freq
63.9 MHz
Net M
0%
Precession
6.39 rev/s
Population Split
↑ 8
↓ 8
ParallelAnti-parallel
Larmor Equation
f = γ × B₀
63.87 = 42.58 × 1.5
Clinical Reference
Earth's field:~0.00005 T
Fridge magnet:~0.005 T
Clinical MRI:1.5 – 3.0 T
Research MRI:7.0 T
💡 Hint:Use the "Quick Challenges" in the sidebar to explore the physics.
You Are Primarily Hydrogen
The human body is ~60% water. Every water molecule contains two hydrogen atoms. In MRI, we ignore the oxygen and focus on the hydrogen nucleus—a single proton.
Essential Insight
Each hydrogen proton behaves like a tiny, spinning bar magnet. Normally, these trillions of magnets point in random directions, so their fields cancel out completely.
When a patient enters the B0, these protons have only two choices: align parallel (pointing up) or anti-parallel (pointing down) with the field.
The B₀ Field & Safety
The B₀ Field is the main, constant magnetic field. At 1.5 Tesla, it is roughly 30,000 times stronger than the Earth's magnetic field.
Cardiac Clinical Correlation
Magnet Safety: Because the heart is located center-chest, we must be extremely cautious with pacemakers or metallic stents. At 3.0T, the force on metal is higher, but the signal (SNR) is doubled, allowing for clearer views of tiny coronary arteries.
The Larmor Equation
f₀ = γ × B₀
This defines the speed of proton Precession. If we increase the magnet's strength (B₀), the protons wobble faster (f₀). To get an image, we must match our radio waves to this exact frequency.
Review Your Knowledge
Ensure you've grasped the basics before moving to 'The Resonance'.
Knowledge Check1 / 2
If the B₀ field strength is doubled from 1.5T to 3.0T, what happens to the Larmor frequency?
