Quantitative amide proton transfer imaging with reduced interferences from magnetization transfer asymmetry for human...

To develop a novel analysis method to evaluate quantitative amide proton transfer (qAPT) effects with reduced interference of conventional magnetization transfer effect.

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.

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.

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.