A method of radioactive-emission-measurement. The method comprises providing a camera for the detection of single emissions, which defines proximal and distal ends. The camera is configured for enabling a reconstruction of a volumetric image having a line spread function of less than 7 mm Full Width Half Maximum (FWHM) when given a substantially line source of radioactive emission, with an activity of 5 mCi, within a region-of-interest volume, at a distance of at least 100 mm from said distal end, with air being substantially the only operating medium. The method further comprises detecting at least 1 of every 5000 photons, emitted from at least one radioactive-emission source, located within a certain region-of-interest volume, using the camera, and reconstructing a volumetric radioactive-emission image from the detected photons.