X-Ray Imaging Physics for Nuclear Medicine Technologists. Part 2: X-Ray Interactions and Image Formation

Image formation process from point source (A) and distributed source (B) and associated geometry terms are illustrated. By comparing similar triangles, it can be shown that M = SID/SOD. In B, blurring of object is caused by focal spot distribution incident on detector. Amount of blur, known as penumbra, increases with magnification for given focal spot size and also increases apparent magnification of object (compare I_b with I). SID = source image distance; SOD = source object distance; OID = object image distance; O = object; I = image; F = focal spot distribution; f = focal spot projection. Magnification is equal to ratio of image size to object size, M = I/O, for point source.