A noninvasive technique for simultaneous measurement of the arterial input function (AIF) for
gadodiamide (
Omniscan) and its uptake in
tumor was demonstrated in mice. Implantation of a
tumor at a suitable location enabled its visualization in a cardiac short axis image. Sets of gated, low-resolution saturation recovery images were acquired from each of five
tumor-bearing mice following
intravenous administration of a bolus of
contrast agent (CA). The AIF was extracted from the signal intensity changes in left ventricular blood using literature values of the CA relaxivity and a precontrast T1 map. The time-dependent 1H2O relaxation rate constant (R1 = 1/T1) in the
tumor was modeled using the BOLus Enhanced Relaxation Overview (
BOLERO) method in two modes regarding the equilibrium transcytolemmal water exchange system: 1) constraining it exclusively to the fast exchange limit (FXL) (the conventional assumption), and 2) allowing its transient departure from FXL and access to the fast exchange regime (FXR), thus designated FXL/FXR. The FXL/FXR analysis yielded better fittings than the FXL-constrained analysis for data from the
tumor rims, whereas the results based on the two modes were indistinguishable for data from the
tumor cores. For the
tumor rims, the values of Ktrans (the rate constant for CA transfer from the vasculature to the interstitium) and ve (volume fraction of the tissue extracellular and extravascular space) returned from FXL/FXR analysis are consistently greater than those from the FXL-constrained analysis by
a factor of 1.5 or more corresponding to a CA dose of 0.05 mmole/kg.