A method of tracking immune cells to detect immune response. The method including steps of identifying a patient having a disease associated with an organ； administering biocompatible magnetic nanoparticles into the blood stream of the patient； and obtaining a magnetic resonance image of the organ. The presence of hyperintense or hypointense spots in the magnetic resonance image indicates immune response in the patient.一種追蹤免疫細胞以檢測免疫反應的方法。該方法包括下列步驟：鑑別一具有一與一器官相關之疾病的病患；投予生物相容性磁性奈米粒子至該病患的血流；以及取得一該器官的磁振影像。在該磁振影像中高信號區或低信號區的存在表示在該病患中的免疫反應。
