What are the different categories of medical devices and their respective functions? How do diagnostic devices, such as MRI machines and ultrasound scanners, differ from therapeutic devices like pacemakers and insulin pumps? Can you elaborate on the classification of medical devices based on risk, ranging from low-risk items like bandages to high-risk implants and life-supporting equipment? Additionally, what role do wearable medical devices, such as continuous glucose monitors and activity trackers, play in remote patient monitoring and personalized healthcare?