SPION MRI Contrast & T2* Darkening (2D)

SPION Injection

Nanoparticle concentration 60

Core size 14 nm

MRI Readout

Echo time TE 40 ms

Tissue baseline Grey matter

Particles in ROI

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Mean ROI signal

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Signal drop

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Dephasing radius

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How it works

Superparamagnetic iron-oxide nanoparticles (SPIONs) don't emit an MRI signal themselves — they distort the local magnetic field around them. Water protons diffusing through that distorted field dephase faster, shortening the effective T2* relaxation time and darkening any voxel near the particles once enough echo time has passed. This 2D companion draws the T2*-weighted slice directly, top-down, the way a radiologist actually reads it.

S(TE) = S0 · exp(-TE · R2*local)
R2*local = R2_tissue + Σᵢ A(size) / (1 + (d / r_dephase)²)

Concentration — more particles accumulated in the region (e.g. uptake by a lesion) sum their field distortions, darkening a wider patch of the slice.
Core size — a bigger iron-oxide core carries a larger magnetic moment, so each particle darkens a disproportionately large "blooming" halo well beyond its physical size.
Echo time — dephasing accumulates with time; a longer TE lets even a faint field distortion sink the local signal toward black.
Tissue baseline — the surrounding tissue's own T2 sets the starting brightness before any SPION effect is added; oedema and CSF-adjacent tissue are already dimmer at a given TE.

Click anywhere on the slice to re-seed the nanoparticle cluster at that spot.

ROI: Cortical lesion

click slice to re-seed dose

Signal vs. echo time (ROI mean)