How do you handle a situation when a relative or family member is worrying about a possible serious illness?

My mother is experiencing some unusual physical symptoms, so she’s going to have an MRI done on Thursday. I’m just as worried as she is. I want to express how much I love her and appreciate her, but I’m afraid that’ll send the message that I think it might be serious. I don’t want to worry her even more. Have you ever been in this situation?