The invention describes a method that provides a practical means of accurately estimating the electromagnetic fields and therefore the SAR (specific absorption rate) distributions of a subject in magnetic resonance imaging (MRI) scan. The disclosed method consists of several steps. If the coil information is unavailable during the patent imaging, the first step, generally performed before patient (or target) imaging, estimates the geometry of the radiofrequency (RF) coils. The second step estimates the patient-specific tissue volumes by deforming an appropriate reference with known tissue distribution from a database to the said target. Finally, the electromagnetic fields and the SAR distributions are calculated using numerical methods performed on the accurately estimated RF coils and patient-specific tissue volumes. The proposed method can be used for safe, accurate MR imaging at any magnetic field strengths, particular suitable for high-field applications.