Magnetic Resonance Spectroscopic Imaging (MRSI) has proven to provide unique information for the diagnosis and management of brain tumors, epilepsy, multiple sclerosis and traumatic brain injury. Despite the obvious advantage of imaging approaches over single volume measurements, clinically, most MRS studies are still performed as single voxel studies. The reluctance to include MRSI in clinical evaluations arises primarily from four factors: 1) increased acquisition times; 2) limitations in spectral quality when data is acquired over larger brain regions; 3) limitations in SNR and 4) challenges in sampling the cortical periphery. To overcome these limitations we will develop a fast MRSI method (5-10min.) which uses: 1) two dimensional rosette encoding trajectories to rapidly sample the brain in two dimensions while minimizing gradient demands and improve spectral quality; 2) Hadamard encoding in the third dimension to minimize localization artifacts and provide excellent slice profiles for smaller numbers of partitions (4-8) covering the most relevant brain region; 3) a high degree shim insert to maximize magnetic field homogeneity and improve spectral quality and 4) dynamic spatially selective dephasing to maximize SNR and sample the cortical periphery. Consistent with what is the most widely accepted MRS clinical application currently, we will evaluate the methods in patients with high-grade brain tumors receiving immunotherapy. Although immunotherapy is a highly promising new therapeutic approach for brain tumors, treatment effects can mimic tumor progression on conventional MRI, compromising our ability to effectively monitor and manage these patients. MRSI offers an alternative means to monitor progression, based on tumor metabolism and physiology as opposed to relaxation properties of tissue water (conventional MRI). Thus we believe that MRSI may provide additive values and significantly aid in the management of these patients. This work will be performed at 3T and 7T.