1. A method for image reconstruction, the method comprising: acquiring emission data at a plurality of energy windows for a person having administered thereto a radiopharmaceutical comprising at least one radioactive isotope, wherein the energy windows comprise (i) at least a peak energy window centered around a peak emission of the isotope and (ii) at least one scatter energy window at an energy range lower than the peak energy window; performing a preliminary reconstruction of the acquired emission data to create one or more preliminary images of the peak energy window and the scatter energy window; determining a body outline of the person from at least one of the reconstructed preliminary image of the peak energy window or the reconstructed preliminary image of the scatter energy window; identifying a heart contour of the person from the reconstructed preliminary image of the peak energy window; segmenting at least the left lung of the person from the reconstructed preliminary image of the scatter energy window using the identified heart contour as a landmark; defining an attenuation map based on at least the determined body outline and the segmented left lung; and reconstructing an image of a region of interest of the person using an iterative joint estimation reconstruction including updating the attenuation map and the image of the peak energy window, wherein the joint estimation reconstruction comprises using data acquired in the plurality of energy windows.