Population excess is exaggerated ~100,000× for visibility. Real Boltzmann excess at 1.5T: ~3 per million protons. The tiny population difference is sufficient because MRI detects the sum of ~10¹⁸ protons per voxel.
Physics Note: Individual protons do not "point" up or down — they precess on cones around B₀. The arrows here represent the statistical population excess that creates the net M vector.
Sandbox Controls
Experiment with settings to see how physics principles manifest in different cardiac scenarios. Use Board Hard Mode in the sidebar to test your ability to diagnose artifacts without assistance.
