Radiation imaging apparatus and radiation imaging system

A radiation imaging apparatus, comprising:

• an imaging region comprising a plurality of conversion elements configured to perform an imaging operation of obtaining a radiation image corresponding to incident radiation;
• a plurality of detecting portions, each detecting portion comprising a detecting element configured to detect a radiation dose entering the imaging region;
• and
• a controller, wherein the controller is configured to
• perform, before the imaging operation, an offset readout operation of reading out offset signals of the detecting elements from the plurality of detecting portions in a state in which irradiation with radiation is not performed,
• detect, in the imaging operation, the radiation dose entering the imaging region using signals output from the detecting elements during irradiation with radiation and the offset signals, and
• be capable of changing, during a period of the offset readout operation, an order of reading out the offset signals from the plurality of detecting portions.