1. A method of reconstructing a tomographic image using a nuclear imaging apparatus having a non-parallel hole collimator comprising: acquiring, by a gamma camera, first incidence information from a radiation field radiating from a subject; reconstructing, by a processor, the first incidence information to generate a first image; identifying, by the processor, one or more regions of interest in the first image; focusing, by the non-parallel hole collimator, on at least one of the regions of interest; acquiring, by the processor, second incidence information from the radiation field; and reconstructing, by the processor, the second incidence information to generate a second image, wherein the second image has a higher number of counts than the first image.