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Background
Dynamic susceptibility contrast (DSC) MR perfusion is a specialized imaging technique that provides hemodynamic information on brain tumors and aids both diagnostic and therapeutic decision-making. Standard combined-treatment approaches for high-grade gliomas include surgical resection, radiotherapy, chemotherapeutics, and antiangiogenic agents. Follow-up conventional MRI can be limited in differentiating treatment-related changes from tumor progression, which can both demonstrate perilesional edema, contrast enhancement, and mass effect (pseudoprogression/radiation necrosis). In addition, treatment with antiangiogenic therapeutics can result in an imaging appearance suggesting treatment response, despite persistence of viable neoplasm (pseudoresponse). In these settings, MR perfusion reveals important perfusion parameters that help distinguish these entities, on the basis of viable tumors demonstrating hyperperfusion and treatment-related changes leading to hypoperfusion.

Educational Goals / Teaching Points
The main goal is to review the basic principles and interpretation of DSC MR perfusion specifically in the context of glioma follow-up imaging. The technical pitfalls and limitations will also be covered with the aim of outlining the current state and future direction of this technique for the trainee to consider in his/her future practice.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The DSC MR perfusion technique takes advantage of primarily gadolinium-based paramagnetic contrast agents that produce susceptibility-induced signal loss. To achieve first-pass bolus tracking through the brain vasculature, rapid imaging must be performed with T2*-sensitive sequences such as the gradient-echo echoplanar sequence. The conversion of T2*-related signal loss to a tissue contrast concentration-time curve then yields useful hemodynamic information, particularly in the form of cerebral blood volume maps. This data sheds light on pathophysiologic changes in tumor angiogenesis/microvascularity and blood-brain barrier permeability, thereby granting better insight into the evolution of disease through stages of pseudoprogression, pseudoresponse, and true progression.

Conclusion
As a complement to traditional structural imaging, DSC MR perfusion has become an increasingly utilized technique at academic institutions to diagnose and manage brain tumors. Understanding the basic principles and relevant treatment-related phenomena is an important step to ensure optimal utilization, proper interpretation, and clear communication with referring providers, in a multidisciplinary effort to deliver individualized patient care.