Single photon emission computed tomograph using focused modular collimators

A single photon emission computed tomograph comprising a detector ring and a rotatable collimator assembly disposed within the detector ring. The rotatable collimator assembly comprises four collimator quadrants, and each of the four collimator quadrants comprises a plurality of collimator modules with their axes assembled in parallel. Each of the modules contains a plurality of inwardly directed channels focused to a single point on its own axis with a long focal length. The focal length of each of the collimator modules is individually and flexibly chosen to suit a particular imaging task. The four collimator quadrants are installed in the rotatable collimator assembly at a slightly different angular offset so as to achieve fine data sampling.