A medical imaging system has a radiation source, a radiation sensor, a data-collection unit, and an imaging system. The radiation source has an opening to direct a collimated radiation beam in a direction towards a patient. The radiation sensor is disposed proximate the opening and within the collimated radiation beam to measure a fluence of the collimated radiation beam. The data-collection unit is disposed to collect radiation from the collimated beam after interaction with the patient. The imaging system is in communication with the data-collection unit and configured to generate an image of a portion of the patient from the collected radiation.