[1] Quant. Sci. and Energy Engineering, Tohoku University, Sendai 980-8579, Japan
[2] CYRIC Tohoku University, Sendai 980-8578, Japan
[3] PET Centre, Univ. School Med., Debrecen, Hungary
[4] National Cancer Institute, V. Venezian 1, 20133 Milan, Italy
[5] School of Medicine, Tohoku University, Sendai 980-8575, Japan
[6] ATOMKI, P. O. Box 51, H-4001 Debrecen, Hungary