<p>To investigate magnetic relaxation properties of the tailored contrast using paramagnetic gadolinium (Gd) chelates and superparamagnetic iron oxide particles (SPIOs) for cellular magnetic resonance imaging. The study included three different exposed environments with two different characteristic contrast agents which used gadodiamide (Omniscan; Gd-DTPA-BMA) and ferumoxide (Feridex; SPIO) in C6 brain cancer cells. Based on the minimal mutual interaction between these two agents in vitro, we examined the possibility of using mixture of cells that are separately labeled with two contrast agents or using concurrently labeled cells with different concentrations of the two contrast agents. In order to characterize the MR relaxation properties, aqueous solutions containing various concentrations of the two contrast agents were prepared as well as Ficoll solution suspensions containing labeled cells by different labeling schemes and subsequently investigated R₁ and R₂ relaxation rates. The tailored contrast can be created by concurrent labeling of the two contrast agents as well as combining separately labeled cells with the two contrast agents. The proposed method would be applied to generate tailored contrast for efficient detection of magnetically-labeled cells in molecular imaging and cell-based therapy.</p>