[en] The issue of The Journal of Nuclear Medicine contains three articles representing advances in emission tomography instrumentation. Common to all three designs is the goal of acquiring volumetric data with good sampling in three dimensions. There are two motivations leading to the volumetric data acquisition. First there is a physiologic and clinical need to take into account the complex nature of the organ such as the brain in x, y, and z directions. Secondly, there is an argument that improved sensitivity will come from systems whose detectors can acquire data from a larger solid angle than provided by positron emission tomography (PET) instrument design with single crystal detector units and septal shields between layers. This editorial is written to serve three purposes: (1) to highlight the distinguishing features of these three instrumentation papers (2) to present quantitative comparisons between the single-photon emission computed tomography (SPECT) and PET instruments (3) to forecast some ideas for the future developments in both SPECT and PET