(A) a substrate, and coating at least a portion of (b) the surface of the substrate, when a medical device has been implanted or inserted into a patient, implantation and a hydrogel polymer which visible medical devices in magnetic resonance imaging (MRI) or to provide an insertable medical devices. Also provided is a method of using such implantation or insertable medical devices in medical practitioner, after or during insertion or implantation for inserting or implanting the medical device into the patient, the position of the medical instrument by a magnetic resonance imaging to provide a method used to visually recognize. Further, in the hydrogel polymer of applications for coating at least a portion of the surface of the medical device, the hydrogel polymer, the medical device during or after the insertion or implantation to implantation or insertion into a patient, and visible medical devices in magnetic resonance imaging It provides the use of the hydrogel polymer as is adaptation.