Standard MT and ihMT ratio (ihMTR) measures can be sensitive to B1 and T1, making them less specific to tissue microstructure. Using the inverse signal, i.e. one divided by the signal, and a high flip-angle reference image in calculation of an ihMTR metric has been proposed as a metric with improved insensitivity to T1 and B1 in steady-state gradient-echo sequences. We present a modified method for use in prepared sequences such as magnetization prepared rapid gradient echo (MPRAGE). The sensitivity of ihMT MPRAGE metrics to T1 and B1 was tested using simulations and acquisitions in brains of healthy volunteers.