1. A method of optimizing the 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 an 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 the distance between the first radiation detector and the object; 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.