Infographics / MRI Physics

Diffusion-weighted imaging & ADC maps

A two-panel comparison. Paired diffusion-sensitising gradients dephase then rephase spins. Left panel: freely diffusing water moves far, spins end out of phase and cancel, so signal is lost — dark on DWI, bright on the ADC map (high ADC). Right panel: restricted water is confined within a cell, spins stay coherent and keep signal — bright on DWI, dark on the ADC map (low ADC). Higher b-value gives stronger diffusion weighting.

Diffusion-weighted imaging: free versus restricted water and the resulting DWI and ADC signal A two-panel comparison. Paired diffusion-sensitising gradients dephase then rephase spins. Left panel: freely diffusing water moves far, spins end out of phase and cancel, so signal is lost — dark on DWI, bright on the ADC map (high ADC). Right panel: restricted water is confined within a cell, spins stay coherent and keep signal — bright on DWI, dark on the ADC map (low ADC). Higher b-value gives stronger diffusion weighting. Diffusion-weighted imaging: free vs restricted water Paired diffusion-sensitising gradients dephase then rephase spins Freely diffusing water molecules move far (high ADC) spins dephase → signal lost DWI ADC map Restricted diffusion confined by cell (low ADC) spins rephase → signal kept DWI ADC map dark bright bright dark Higher b-value → stronger diffusion weighting; S(b) = S₀·e^(−b·ADC): low ADC keeps DWI bright
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