1. A magnetic resonance imaging (MRI) system configured to perform non-contrast magnetic resonance imaging, said system comprising: an MRI gantry including a static magnet, gradient magnet coils and at least one radio frequency (RF) coil defining a patient imaging region into which a patient's anatomical region of interest can be located; RF receiver and transmitter circuits coupled to said at least one RF coil; and control circuits connected to said gantry and to said RF receiver and transmitter circuits, said control circuits having an operator display and an operator control input port for configuring and operating said MRI system to acquire and process MRI data from said patient, said control circuits being configured to control said MRI gantry and said RF receiver and transmitter circuits to perform non-contrast MR imaging by acquiring a representation of MR signal versus position of patient anatomy and automatically determining a spatially selective tag pulse region based on the acquired representation of MR signal versus position of patient anatomy and preset signal level threshold.