We propose an original method for the determination of the physical properties of nanometer sized helium bubbles using spectrum imaging in an energy-filtered transmission electron microscope. Helium bubbles synthesized by high fluence implantation and thermal annealing in silicon are investigated. The acquisition parameters are determined to optimize both signal/noise ratio and time. The limitations to the extent of observable areas on a typical sample are explained. The necessary data correction and helium Kedge position measurement procedures are detailed and the accuracy of the method is discussed. Finally helium density maps are obtained and discussed. (C) 2015 Elsevier Ltd. All rights reserved.