Quantitative amide proton transfer imaging with reduced interferences from magnetization transfer asymmetry for human brain tumors at 3T

Xuna Zhao; Zhibo Wen; Chunmei Li; Min Chen; Yi Wang; Jia-Hong Gao

doi:10.1002/mrm.25411

Quantitative amide proton transfer imaging with reduced interferences from magnetization transfer asymmetry for human brain tumors at 3T

Magn Reson Med. 2015 Jul;74(1):208-216. doi: 10.1002/mrm.25411. Epub 2014 Aug 7.

Authors

Xuna Zhao^{1

2

3}, Zhibo Wen⁴, Chunmei Li⁵, Min Chen⁵, Yi Wang^{1

2}, Jia-Hong Gao^{1

2

6}

Affiliations

¹ Beijing Key Laboratory of Medical Physics and Engineering, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China.
² Center for MRI Research, Peking University, Beijing, China.
³ IS Clinical Science, Philips Healthcare, China.
⁴ Department of Radiology, Zhujiang Hospital, Southern Medical University, Guangzhou, Guangdong, China.
⁵ Department of Radiology, Beijing Hospital, Beijing, China.
⁶ McGovern Institute for Brain Research, Peking University, Beijing, China.

PMID: 25104296
DOI: 10.1002/mrm.25411

Abstract

Purpose: 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 MTR_asym (3.5 ppm) at different saturation powers. The negative background (NB) in MTR_asym (3.5 ppm) image is recovered from the difference between the MTR_asym (3.5 ppm) and qAPT maps.

Results: Both qAPT and MTR_asym (3.5 ppm) are strongly dependent on saturation power. At a saturation power below 2 µT, the MTR_asym (3.5 ppm) map is dominated by the NB rather than the APT effects for healthy brain tissue. Similar to the MTR_asym (3.5 ppm) image, the qAPT image exhibits strong and robust tumor contrast.

Conclusion: 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 MTR_asym (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.

Keywords: amide proton transfer; brain tumor; chemical exchange-dependent saturation transfer; magnetization transfer contract.