Table 1.
T1 CONTRAST AGENTS | |||
---|---|---|---|
Contrast Agent | Size | Extractable Vascular Parameters | Modeling Assumptions/Caveats |
GdDTPA | ≈550-600 Da | Ktrans, kep, ve [41, 131] | In general Ktrans=FE=F(1-e-PS/F) |
If PS»F, extraction is complete i.e. E=1 ⇒ Ktrans≈ F |
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If PS«F, E ≈ PS/F ⇒ Ktrans≈ PS | |||
vb, F | If E and mean transit time (MTT) can be estimated. | ||
λ | If tissue density (ρ) is known. | ||
Gadomer-17 | ≈17kDa | vb, Ktrans [132] | PS-limited regime and the larger molecular weight of the CA must be taken into account, i.e. PS«F and Ktrans ≈ PS |
Albumin-GdDTPA | ≈80 kDa | Same as above [56] | Primarily an intravascular tracer and Ktrans ≈ ps as above |
Antibody-conjugated Gd Liposomes | ≈MDa | Receptor density on the luminal surface and turnover [11] | Requires high local concentration of the CA at target sites and high labeling efficiency of CA. Delivery to extravascular targets is challenging. |
T2 CONTRAST AGENTS | |||
Contrast Agent | Size | Extractable Vascular Parameters | Modeling Caveats/Remarks |
Gd-DTPA | ≈500-600 Da | rCBV, rCBF, Time-to-peak, FWHM[133] | Using first-pass tracer kinetics and elimination of recirculation effects. |
≈MTT[134] | This is not the true first moment of the MRI concentration-time curve. | ||
Permeability or leakage [50] | Requires leakage correction for T1 enhancement due to extravasated CA. | ||
F[135] | Requires knowledge of the arterial input function to deconvolve the measured concentration-time curve. | ||
Vessel size index [50] | Requires simultaneous gradient- and spin-echo MRI. | ||
MION/SPIO | ≈0.775-1 MDa | rCBV, rCBF, time-to-peak, FWHM, F, Vessel size index [48] | Same as above. |