A PET-MRI system for imaging an object is provided. The PET-MRI system includes a magnetic resonance imaging sub-system, a positron emission tomography sub-system, an optical sensor, and a data processing controller. The magnetic resonance imaging sub-system includes a surface coil that acquires magnetic resonance signals from the object. The positron emission tomography sub-system acquires PET emissions from the object. The optical sensor detects at least one of a spatial location and a shape of the surface coil. The data processing controller communicates with the magnetic resonance imaging sub-system, the positron emission tomography sub-system, and the optical sensor, and utilizes at least one of the detected spatial location and the detected shape of the surface coil to correct the acquired PET emissions for attenuation.