1. Department of Applied Physics, University of Eastern Finland, POB 1627, Kuopio FI-70211, Finland e-mail:
2. Department of Applied Physics, University of Eastern Finland, POB 1627, Kuopio FI-70211, Finland
3. Department of Applied Physics, University of Eastern Finland, POB 1627, Kuopio FI-70211, Finland;
4. Diagnostic Imaging Centre, Kuopio University Hospital, POB 100, Kuopio FI-70029, Finland
5. Laboratory of Machine Design, Lappeenranta University of Technology, Lappeenranta 53850, Finland
6. Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä 40014, Finland