Inclusion Criteria:

          -  Histologically proven intracranial glioblastoma or gliosarcoma at initial surgery

               -  Patients will be eligible if the original histology was low-grade glioma and a
                  subsequent diagnosis of glioblastoma or gliosarcoma is made (high-grade
                  transformation)

          -  Karnofsky performance status >= 70

          -  Women must not be pregnant or breast-feeding

          -  Progression of disease assessed by local site using Revised Assessment in
             Neuro-Oncology (RANO) criteria, with plan to give whole-dose bevacizumab
             therapeutically, either as single therapy or in conjunction with other
             chemotherapeutic regimens; patients getting bevacizumab to support additional
             radiation therapy or immunotherapy, or primarily for reduction of edema rather than
             for tumor treatment, are excluded; this must be the patient?s initial recurrence

          -  Patient must not have been treated previously with immunotherapies (vaccines,
             checkpoint inhibitors, T-cells)

          -  Intratumoral hemorrhage (acute, subacute, or chronic) as seen on hemosiderin-sensitive
             (gradient-echo) MRI may preclude patient inclusion because of anticipated limited
             evaluation due to magnetic susceptibility artifact on the heavily T2-weighted DSC-MRI
             images; if the region of enhancing tumor not affected by blooming artifact on the
             hemosiderin-sensitive images does not meet the 10 x 10 x 10 mm ?measurable
             enhancement? threshold specified elsewhere, the patient is ineligible

          -  Progressive enhancement (> 25% increase in contrast enhancing volume compared to
             nadir) on MRI within 14 days of registration, >= 42 days since completion of
             radiation/temozolomide therapy, and >= 28 days since surgical resection or cytotoxic
             chemotherapy; measurable enhancement is defined as two perpendicular in-plane
             diameters of at least 10 mm and at least 10 mm in the 3rd orthogonal direction

          -  Patients must be able to tolerate brain MRI scans with dynamic intravenous
             gadolinium-based contrast agent injections

               -  Ability to withstand 22 gauge intravenous (IV) placement

               -  No history of untreatable claustrophobia

               -  No magnetic resonance (MR) incompatible implants/devices or metallic foreign
                  bodies

               -  No contraindication to intravenous contrast administration

                    -  Adequate organ function, including adequate renal function defined as
                       estimated glomerular filtration rate (eGFR) >= 40 mL/min/1.73 m^2 as
                       calculated per institution standard of care, and meeting local site
                       requirements for intravenous administration of gadolinium-based MRI contrast
                       agents

               -  No known allergy-like reaction to gadolinium or moderate or severe allergic
                  reactions to one or more allergens as defined by the American College of
                  Radiology (ACR); patient may be eligible if willing to undergo pre-treatment as
                  defined by the institution's policy and/or ACR guidance

               -  Weight compatible with limits imposed by the MRI scanner table

          -  Patient must be scheduled to receive treatment with a standard dose regimen of
             bevacizumab (bevacizumab infusion on days 1 and 15 of a 28-day treatment cycle);
             patient can be treated with bevacizumab alone or in combination with other
             chemotherapies Exclusion Criteria: (see Inclusion Criteria)