Methods and systems for controlled administration of a tracer and quantification of uptake of the tracer by a target organ are described. The method includes administering a tracer to a patient and imaging at least two regions of the patient's body that cannot be imaged simultaneously. An input function for the tracer can be determined by imaging a first region of the patient's body during selected times, and using an injector to administer the tracer in a manner that accurately estimates the input function when this first region is not being imaged. One or more additional regions of the body may then be imaged to create data that may be used to estimate the input function. One or more parameters may then be estimated from each additional region of the body based on the input function and the imaging data gathered from each region.