Signal intensity measured on T1-weighted image is not proportional to the gadolinium concentration in vivo after administration of contrast agent. Thus, some calculations are required to estimate gadolinium concentration using quantitative values before and after gadolinium administration. We created gadolinium concentration maps that directly show the amount of contrast agent using quantitative maps calculated using synthetic MRI. The gadolinium concentration map we created using phantoms showed high accuracy and precision. The gadolinium concentration map could reliably measure the concentration of gadolinium in metastatic brain tumors.