The effect of brain tumor angiogenesis on the in vivo relationship between the gradient-echo relaxation rate change (δR2*) and contrast agent (MION) dose

Abstract

Purpose: To determine in vivo if the susceptibility calibration factor for gradient-echo imaging (kG), which characterizes the relationship between the tissue T2* relaxation rate change (ΔR2*) and tissue contrast agent concentration, is independent of tissue type and condition: in addition, to assess the consequences of such an assumption on the use of relative cerebral blood volume (rCBV) measurements as a direct index of tumor angiogenesis. Materials and Methods: The ΔR2* was measured as a function of monocrystalline iron oxide nanoparticles (MION) contrast agent dose in a rat brain tumor (9L gliosarcoma) model, the blood volume fraction independently measured, and kG calculated and compared for the normal gray matter, normal white matter, tumor, and contralateral brain. Results: The kG was found to be the same for gray and white matter (P = 0.53), but statistically different for tumor compared to contralateral brain (P = 0.005) with kGTumor