Anna-Liisa Satomaa1, Suvi Vänttinen2, Herkko Mattila3. 1. Department of Clinical Neurophysiology, Tampere University Hospital, Medical Imaging Center and Hospital Pharmacy, Pirkanmaa Hospital District, Tampere, Finland. Electronic address: anna-liisa.satomaa@pshp.fi. 2. Department of Clinical Neurophysiology, Tampere University Hospital, Medical Imaging Center and Hospital Pharmacy, Pirkanmaa Hospital District, Tampere, Finland. 3. Department of Clinical Neurophysiology, Tampere University Hospital, Medical Imaging Center and Hospital Pharmacy, Pirkanmaa Hospital District, Tampere, Finland; Department of Medical Physics, Medical Imaging Center, Pirkanmaa Hospital District, Tampere, Finland.