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Identifying tumor vascular permeability heterogeneity with magnetic resonance imaging contrast agents
Michael Aref1, Martin Brechbiel, Erik C Wiener
1Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Champaign, Illinois, USA.
Rationale And Objectives:
Dynamic contrast enhanced (DCE) MR mammography (MRM) uses tumor capillary density differences for prognosis. The heterogeneous response of permeability-surface area products (PS = Kp<-->t) was examined in mammary tumors, as a function of contrast agent size, to determine what effect ROI size might have on PS and prognosis.
Methods:
DCE FLASH signal intensities were converted to gadolinium concentrations by a standard curve, which was fitted by a two-compartment model for the tumor's extravascular extracellular space (EES) volume fraction (ve), and the tumor volume normalized transfer rate between plasma and EES (Kp<-->t/VT).
Results:
For Gd-DTPA ve = 9% to 13% Kp<-->t/VT = 0.01 to 0.06 minutes-1, and the macromolecular agent, PAMAM-TU-DTPA G = 4 ve = 0.8% to 1% Kp<-->t/VT = 0.008 to 0.04 minutes(-1). Significant differences in Kp<-->t/VT for local regions were found for both agents relative to the whole tumor and the macromolecular agent had greater dynamic range.
Conclusions:
Smaller ROI values or pixels should yield more accurate assessment of neovascularization.