title: Quantitative amide proton transfer imaging with reduced interferences from magnetization transfer asymmetry for human brain tumors at 3T.
abstract: OBJECTIVE
  To develop a novel analysis method to evaluate quantitative amide proton transfer (qAPT) effects with reduced interference of conventional magnetization transfer effect.
  
  
  METHODS
  A modified Z-spectrum is generated by a fitting procedure that achieves an effectively reduced magnetization transfer asymmetry. A qAPT map is then produced by subtraction of the original Z-spectrum from the modified version. This approach has been tested on both healthy volunteers and patients with brain tumors. Comparisons are made between the maps of qAPT and the commonly-used MTRasym(3.5 ppm) at different saturation powers. The negative background (NB) in MTRasym(3.5 ppm) image is recovered from the difference between the MTRasym(3.5 ppm) and qAPT maps.
  
  
  RESULTS
  Both qAPT and MTRasym(3.5 ppm) are strongly dependent on saturation power. At a saturation power below 2 µT, the MTRasym(3.5 ppm) map is dominated by the NB rather than the APT effects for healthy brain tissue. Similar to the MTRasym(3.5 ppm) image, the qAPT image exhibits strong and robust tumor contrast.
  
  
  CONCLUSIONS
  The newly-developed analysis method of qAPT is able to obtain a quantitative APT effect with less inferences from magnetization transfer asymmetry as compared to the conventional MTRasym(3.5 ppm) and can be used to evaluate human brain tumors at 3T. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc. Magn Reson Med 74:208-216, 2015. © 2014 Wiley Periodicals, Inc.
authors.affiliation: Beijing Key Laboratory of Medical Physics and Engineering, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China.|Center for MRI Research, Peking University, Beijing, China.|IS Clinical Science, Philips Healthcare, China.
authors.forename: Xuna
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Department of Radiology, Zhujiang Hospital, Southern Medical University, Guangzhou, Guangdong, China.
authors.forename: Zhibo
authors.initials: Z
authors.lastname: Wen
authors.affiliation: Department of Radiology, Beijing Hospital, Beijing, China.
authors.forename: Chunmei
authors.initials: C
authors.lastname: Li
authors.affiliation: Department of Radiology, Beijing Hospital, Beijing, China.
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.affiliation: Beijing Key Laboratory of Medical Physics and Engineering, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China.|Center for MRI Research, Peking University, Beijing, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Beijing Key Laboratory of Medical Physics and Engineering, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China.|Center for MRI Research, Peking University, Beijing, China.|McGovern Institute for Brain Research, Peking University, Beijing, China.
authors.forename: Jia-Hong
authors.initials: JH
authors.lastname: Gao
keywords: amide proton transfer; brain tumor; chemical exchange-dependent saturation transfer; magnetization transfer contract