Quantification of SPIO nanoparticles using phase gradient mapping.

A new method is developed to quantify the concentration of super-paramagnetic iron oxide (SPIO) contrast agent using magnetic resonance imaging (MRI). The proposed method utilizes a positive contrast method, known as phase gradient mapping (PGM), to find the gradient of the field map. Then the concentration is calculated by fitting the gradient of the field map to the gradient of an ideal geometric model. The proposed method was compared to relaxivity-based SPIO quantification method and was applied to calculate the concentration of SPIO contrast agent for MRI experiments performed on a phantom with known concentrations. The results obtained from the proposed method accord well with the true concentrations.