Different scans

I am not sure where to ask these types of questions. I am starting medical school next semester and I know what the different scans look like but I get confused when you would use a CT scan vs an MRI vs ultrasound. I am just curious if someone could direct me to a website or tell me. For example, you would use this type of scan for cancer, this type of scan for crohns disease. I just see all these diseases and they each have their own way of Diagnosing it with scans but is there a way to... Different scans
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums