The invention provides for a magnetic resonance imaging system (100, 300). The magnetic resonance imaging system comprises: a subject support (120) configured for moving a subject between a loading position (121) and an imaging position (200)； a receive magnetic resonance imaging coil (114) configured for being placed on the subject； and a light detection system (115) comprising at least one ambient light sensor for measuring light data (144). The light detection system is any one of the following: mounted to the main magnet such that the light data is measured from the imaging zone and mounted to the receive magnetic resonance imaging coil. The execution of the machine executable (140) instructions by a processor (130) cause the processor to: move (500) the subject support from the loading position to the imaging position； acquire (502) the light data using the at least one ambient light sensor when the subject support is in the imaging position； determine (504) if the receive magnetic resonance imaging coil is positioned for acquiring magnetic resonance imaging data using the light data； and provide (506) a signal (146) if the receive magnetic resonance imaging coil is positioned for acquiring the magnetic resonance imaging data.
