Chemical Exchange Saturation Transfer MRI for Differentiating Radiation Necrosis From Tumor Progression in Brain Metastasis—Application in a Clinical Setting

Abstract

(a) MTRrNOE,0.52μT map for low power chemical exchange saturation transfer (CEST) for a patient along with (b) the histogram of this metric value in the lesion. The lesion includes a large number of voxels with high magnetization transfer ratio (MTR) values (in the tumor range) as well as a large number of voxels with low chemical exchange saturation transfer (CEST) values (in the radiation necrosis range). The clinical outcome of this lesion is progressive tumor. However, the presence of a large number of voxels with low MTR values lead to the incorrect diagnosis of radiation necrosis when using MTRrNOE,0.52μT. (c) Using MTR of Amide at high power (MTRAmide,2.0μT) on the other hand, suggests that the lesion is tumor, which highlights the need for considering multiple metrics. There are also two distinct metric value clusters in MTRAmide,2.0μT histogram suggesting presence of large areas of both tumor and radiation necrosis. A detailed analysis of the histogram also suggests the presence of a large region with viable tumor even at the low power CEST. By Mehrabian H. et al. (1713–1725).