ABSTRACT Gliomas, the most common primary brain tumors, are biologically complex and exhibit substantial molecular and phenotypic spatial variation. A major obstacle in both the daily management of patients with gliomas, and in the development of new therapies for these cancers, is the inability of neuroimaging to accurately define the tumor burden. Specifically, gadolinium (Gd) enhancement reveals focal areas of malignant gliomas where the blood-brain barrier (BBB) is disrupted, but it does not show large high-risk areas of infiltrating tumor with a high cellularity. The recent breakthrough in the understanding of genetic features in gliomas, such as isocitrate dehydrogenase (IDH) mutations, has resulted in a prompt reappraisal of the molecular oncogenesis of this group of diseases. Notably, the most recent 2016 WHO classification of CNS tumors uses molecular parameters, in addition to histology, to define tumor entities. The 2016 CNS WHO represents an unmet radiographic need, namely, the identification of genetic biomarkers preoperatively, with non-invasive methods such as MRI. This project has been very successful during the 2nd funding period (9/13- 7/17) in developing an important protein-based molecular MRI technology, called amide proton transfer- weighted (APTw) imaging, into a sensitive, user-friendly, and reproducible approach for routine clinical use. Numerous early clinical data have demonstrated that APTw imaging adds important value to the standard clinical MRI sequences in brain cancer diagnosis. Compared to the contralateral normal-appearing brain tissue, the conspicuous, highly reproducible APTw hyperintensity can always be visualized in high-grade gliomas (including those without Gd enhancement). Thus, APTw imaging allowed accurate identification of high-grade regions within heterogeneous gliomas?a core need during neurosurgical procedures. Notably, we have recently found that the APTw signal could be a valuable imaging biomarker by which to identify IDH mutation status in low-grade gliomas. These early findings are very exciting. However, all currently used imaging protocols are essentially not quantitative, and the images obtained are often called APT-weighted images because of other contributions. The overall goals of this renewal application are to develop highly sensitive, fast, and quantitative APT-MRI methodologies on 3T clinical MRI scanners and to evaluate the potential of these methodologies in brain cancer molecular diagnosis. We have designed the following specific aims: (i) develop quantitative APT-MRI methodologies using compressed sensing at 3T; (ii) determine the capability of APT-MRI for the prediction of IDH mutation status in grade-II gliomas; and (iii) determine the accuracy of APT-MRI for the identification of high-risk regions of tumor outside Gd-enhancing masses in patients with glioblastomas. If successful, our results will significantly push, to a whole new level, the APT-MRI methodology research and clinical applications for brain tumors.