Measuring the Concentration of Contrast Agent in Blood for DSC MRI from the Extra-Vascular Phase Shift

Introduction: The large extra-vascular phase shifts associated with venous blood vessels have been exploited in Susceptibility Weighted Imaging (SWI) to enhance vessel contrast [1]. These phase shifts are a direct result of the large vessel/tissue susceptibility difference due to the paramagnetic deoxyhemoglobin content of venous blood. Recently, it has been shown that the susceptibility of a uniform object with an arbitrary geometry can be quantified by least-squares fitting measured phase data to the simulated field-shift for that geometry [2]. The simulated field-shift can be created using a Fourierbased method [3]. It has also been shown that phase data from a single large artery of simple geometry (outside the brain) can yield an accurate measure of the concentration of paramagnetic contrast agent over the course of a Dynamic Susceptibility Contrast (DSC) experiment [4]. Here, we describe the implementation of a least squares fitting method to monitor the susceptibility of blood in the human brain from the extra-vascular field-shifts measured during a DSC experiment, and use this method to calculate the concentration of the contrast agent in the blood as a function of time.