A method for scan preparation and real-time monitoring implemented on a computing device having one or more processors and one or more storage devices, the method comprising: before a scan to be performed on a target subject by a medical imaging device, obtaining image data of the target subject, wherein the image data is acquired by a first image capturing device for each of one or more components of the medical imaging device, obtaining a planned trajectory of the component during a scan to be performed on the target subject; and determining whether a collision is likely to occur between the target subject and the one or more components of the medical imaging device by performing a virtual scan on the target subject based on the image data of the target subject and the planned trajectories of the one or more components of the medical imaging device; during the scan, obtaining second image data of a plurality of subjects in an examination room where the scan is performed, the plurality of subjects at least including the target subject, the second image data of the plurality of subjects being captured by a second image capturing device mounted in the examination room, the target subject being irradiated by a radiation source of the medical imaging device; obtaining one or more parameter values of one or more radiation parameters of the radiation source; and estimating a dose distribution in the examination room based on the second image data of the plurality of subjects and the one or more parameter values. before a scan to be performed on a target subject by a medical imaging device, obtaining image data of the target subject, wherein the image data is acquired by a first image capturing device for each of one or more components of the medical imaging device, obtaining a planned trajectory of the component during a scan to be performed on the target subject; and determining whether a collision is likely to occur between the target subject and the one or more components of the medical imaging device by performing a virtual scan on the target subject based on the image data of the target subject and the planned trajectories of the one or more components of the medical imaging device; obtaining image data of the target subject, wherein the image data is acquired by a first image capturing device for each of one or more components of the medical imaging device, obtaining a planned trajectory of the component during a scan to be performed on the target subject; and determining whether a collision is likely to occur between the target subject and the one or more components of the medical imaging device by performing a virtual scan on the target subject based on the image data of the target subject and the planned trajectories of the one or more components of the medical imaging device; during the scan, obtaining second image data of a plurality of subjects in an examination room where the scan is performed, the plurality of subjects at least including the target subject, the second image data of the plurality of subjects being captured by a second image capturing device mounted in the examination room, the target subject being irradiated by a radiation source of the medical imaging device; obtaining one or more parameter values of one or more radiation parameters of the radiation source; and estimating a dose distribution in the examination room based on the second image data of the plurality of subjects and the one or more parameter values. obtaining second image data of a plurality of subjects in an examination room where the scan is performed, the plurality of subjects at least including the target subject, the second image data of the plurality of subjects being captured by a second image capturing device mounted in the examination room, the target subject being irradiated by a radiation source of the medical imaging device; obtaining one or more parameter values of one or more radiation parameters of the radiation source; and estimating a dose distribution in the examination room based on the second image data of the plurality of subjects and the one or more parameter values.