Characterization of the 3D field response of an MRI gradient system is important for proper system calibration. A powerful approach to 3D characterization is the acquisition of the gradient impulse response function (GIRF) using a set of distributed MRI probes. An alternative approach is the phantom-based measurement of the GIRF using a thin slice method. However, this method currently only delivers 0th order information (ΔB0) and 1st order direct terms (Gxx, Gyy, Gzz), but no cross terms (e.g. Gxy) or higher order information. We present an extension of the thin slice method by adding phase encoding for characterization of 1st order cross terms as well as higher order spatial components. Experimental results on the respective gradient modulation transfer functions (GMTFs) of a clinical system are presented.