Abstract: A medical imaging device for use in imaging a subject using both gamma rays and light rays emanating from the subject, the device comprising: separation means to separate gamma rays and light rays emanating from the subject into a gamma ray channel comprising gamma rays and a light ray channel comprising light rays; first sensor means arranged to receive and detect gamma rays from the gamma ray channel and to generate first signals for use in forming a first image of the subject; second sensor means arranged to receive and detect light rays from the light ray channel and to generate second signals for use in forming a second image of the subject; wherein the first sensor means and the second sensor means are arranged to receive gamma rays and light rays, respectively, which propagate from the subject upon substantially coincident paths.