1 Department of Applied Medical Imaging, Gunma University Graduate School of Medicine, 3-39-22 Showa, Maebashi, Gunma 371-8511 Japan. Electronic address: yasuhiro.fukushima@gmail.com.
2 Department of Diagnostic Radiology and Nuclear Medicine, Gunma University Graduate School of Medicine, 3-39-22 Showa, Maebashi, Gunma 371-8511 Japan. Electronic address: yoshitotsushima@gunma-u.ac.jp.