Amide proton transfer (APT) imaging can detect pH-related changes in ischemic stroke lesions. However, the widely-used magnetization transfer ratio asymmetry (MTRasym) analysis method is susceptible to various contamination sources. Here we improved the previous extrapolated semisolid magnetization transfer reference (EMR) method by numerical fitting of the EMR signal (NEMR) in the modified Bloch-McConnel equation. The proposed NEMR method was compared with the previous EMR method in Monte Carlo simulations, demonstrating superior accuracy. Furthermore, the NEMR maps were compared with EMR and MTRasym maps in nine ischemic stroke patients, yielding a better depiction of the ischemic lesions.