1. A method of optimizing a scanning trajectory of a first radiation detector device about an object to be scanned, comprising: obtaining image data corresponding to a plurality of images of the object using a second radiation detector device of a different imaging modality; determining a maximum object boundary based on the image data; calculating an optimal scan trajectory of said first radiation detector device relative to the object based on the maximum object boundary, where the optimal scan trajectory minimizes a distance between the first radiation detector and the object; and scanning the object with the first radiation detector device along the optimal scan trajectory so as to detect radiation photons emanating from the object to acquire projection image data.