1. A method for at least one of at least partly determining and adapting an attenuation map used for attenuation correction of Positron Emission Tomography image data sets in a combined Magnetic Resonance-Positron Emission Tomography device, the method comprising: recording at least one one-dimensional magnetic resonance data set of a patient along an imaging direction; determining boundaries, of at least one part of a body of the patient intersected by the imaging direction, from the recorded at least one-dimensional magnetic resonance data set; and at least one of at least partly determining and adapting the attenuation map, at least in part, depending on the determined boundaries.