Effects of Substituents on the Properties of Metal-Free MRI Contrast Agents oleh Ryoma Shiraishi, Tomoyo Kaneko, Kazuteru Usui, Tatsuya Naganuma, Naoko Iizuka, Kosuke Morishita, Shigeki Kobayashi, Yasufumi Fuchi, Yuta Matsuoka, Go Hirai, Ken-ichi Yamada, Satoru Karasawa