1. A method for generating images from time of flight (TOF) data associated with a scan of at least one object using a positron emission tomography system, comprising: providing initial values for an activity image to yield a current activity image; estimating initial values for an attenuation map (μ-map) image based on the TOF data to yield a current μ-map image; repeating, until at least one termination condition is met, the steps of: updating the current activity image based on at least the current μ-map and a first update algorithm, and updating the current μ-map image based on at least on the updated activity image and a second update algorithm, outputting an image of the at least one object based on the current μ-map and the current activity image.