Use of an imaging system to acquire image data of a subject, said imaging system comprising: an annular gantry housing configured to encircle a region of the subject and adapted by the provision of moving means so that it is possible to move the gantry to a position relative to the subject; an x-ray source movable within the annular gantry housing and configured to emit x-rays; an image detector movable within the annular gantry housing, such that the image detector is substantially diametrically opposed to the x-ray source, and configured to detect the x-rays from the x-ray source; control means for controlling the image detector movement relative to a patient and for controlling the possible movements of the gantry, wherein the control means is further adapted to move automatically at least one of the gantry housing, the x-ray source, or the image detector to acquire initial image data of a region of the subject; processing means adapted to construct a three-dimensional model of the region of the subject with the initial image data, selection means adapted to permit discriminatory image data to be acquired of selected spaced apart locations of the patient after a period of time, said control means being adapted allow movement of the image detector and source, and/or adapted to allow the control of the position of the gantry, to acquire the discriminatory discrete location image data of at least a portion of the region of the subject, said discriminatory discrete location image data being discrete images that are acquired of selected spaced apart locations of the patient; processing means adapted to compare the acquired discriminatory discrete location image data to at least a portion of the constructed three-dimensional model of the region of the subject, and adapted to identify specific regions of change between the acquired discriminatory discrete location image data and the constructed three-dimensional model of the region of the subject, in which method of use said discriminatory discrete location image data comprises fewer images than the initial image data, and wherein the processing means is adapted to determine, after the period of time, and based upon the determined regions of change, one or more comparative paths along which the image detector within the gantry shall move to acquire comparative image data and adapted to form a comparative model based upon the comparative image data and the three-dimensional model. an annular gantry housing configured to encircle a region of the subject and adapted by the provision of moving means so that it is possible to move the gantry to a position relative to the subject; an x-ray source movable within the annular gantry housing and configured to emit x-rays; an image detector movable within the annular gantry housing, such that the image detector is substantially diametrically opposed to the x-ray source, and configured to detect the x-rays from the x-ray source; control means for controlling the image detector movement relative to a patient and for controlling the possible movements of the gantry, wherein the control means is further adapted to move automatically at least one of the gantry housing, the x-ray source, or the image detector to acquire initial image data of a region of the subject; processing means adapted to construct a three-dimensional model of the region of the subject with the initial image data, selection means adapted to permit discriminatory image data to be acquired of selected spaced apart locations of the patient after a period of time, said control means being adapted allow movement of the image detector and source, and/or adapted to allow the control of the position of the gantry, to acquire the discriminatory discrete location image data of at least a portion of the region of the subject, said discriminatory discrete location image data being discrete images that are acquired of selected spaced apart locations of the patient; processing means adapted to compare the acquired discriminatory discrete location image data to at least a portion of the constructed three-dimensional model of the region of the subject, and adapted to identify specific regions of change between the acquired discriminatory discrete location image data and the constructed three-dimensional model of the region of the subject, in which method of use said discriminatory discrete location image data comprises fewer images than the initial image data, and wherein the processing means is adapted to determine, after the period of time, and based upon the determined regions of change, one or more comparative paths along which the image detector within the gantry shall move to acquire comparative image data and adapted to form a comparative model based upon the comparative image data and the three-dimensional model.