Low power method for estimating the magnetization transfer bound-pool macromolecular fraction

Abstract

We present a practical method to estimate the magnetization transfer (MT) bound-pool fraction (M(o)/(b)). The method is based on a first-order approximation of the saturation equation and allows an in vivo estimate of M(o)/(b), previously estimated only in vitro and requiring multiple (on the order of 102) measurements. This method requires one saturation measurement, a T1 estimate, an accurate value for input power, and uses to advantage the low power limitations of clinical scanners. The approximation is shown to be feasible in expected tissue parameter ranges using simulations. Unlike the phenomenologic magnetization transfer ratio (MTR), M(o)/(b) is a true tissue parameter representing the semisolid proton concentration involved in saturation transfer, allowing comparability of MT effect independent of input power, off-resonance frequency, or equipment.