Phase-based Contrast Agent Concentration Measurement for Determination of Mouse Arterial Input Function

Introduction: Dynamic Contrast Enhanced (DCE) MRI and pharmacokinetic modeling have shown promise for imaging tumours based on tissue vascularity [1]. The volume transfer function between the plasma and interstitial space, K, can be determined based on measurements of contrast agent concentration time-courses in these spaces [2]. The results of DCE-MRI are believed to have clinical significance for diagnosing tumours, as well as having value for investigating potential therapies in rodent models of cancer. The current standard method for measuring concentration relies on the linear relationship between contrast agent concentration and the changes in relaxation rate R1 (the reciprocal of T1) of water resulting from the presence of the contrast agent. However, this method is prone to inaccuracy, particularly in measuring the arterial plasma concentration time-course (called the arterial input function, AIF) [3]. T1-based AIF measurements in preclinical rodent tumour models have been reported in the heart [4] and tail vessel [5]. We propose an alternative method for obtaining the AIF in the mouse by performing phase measurements in the artery of the mouse tail. The magnetic susceptibility of the contrast agent introduces additional magnetic fields in the sample, which produce a change in signal phase within the vessel. We present experimental results, from a tail phantom, that demonstrate the feasibility of this technique.