Single and Triple Quantum Sodium MRI of Primary Human Brain Tumors

We demonstrate the use of triple quantum (TQ) filtered sodium MRI in a group of patients undergoing clinical evaluation for primary brain tumors. The TQ images were acquired using a twisted-projection readout in tandem with a three-pulse triple quantum filter. Our results demonstrate that TQ sodium MRI provides a source of contrast that it is not biased by the large sodium content of the extracellular pool and is, therefore, better suited for monitoring the changes in intracellular sodium content associated with the development of neoplastic changes. Introduction Brain tumors account for about 60% of all intracranial neoplasms diagnosed each year in the United States. Because of their heterogeneous behavior and poor prognosis, the treatment regime for malignant brain tumors is usually designed considering a number of prognostic factors such as cell density, neuronal displacement, mitotic activity and vascular proliferation. Sodium MRI techniques have the potential to provide information about proliferative activity in a non-invasive fashion as the intracellular sodium concentration has been previously found to have a positive correlation with mitotic activity in various types of human neoplasms [1]. These changes in intracellular sodium content, however, are difficult to detect through measurement of the total tissue sodium concentration (TSC) due to the large sodium content of the extracellular pool. Triple quantum (TQ) sodium imaging has been proposed as a means for monitoring the changes in intracellular sodium content during the course of disease. The weak nature of the TQ sodium signal, however, has previously hindered TQ sodium imaging using conventional spatial encoding schemes. Recently, the use of efficient spatial encoding schemes [2] has allowed the demonstration of in vivo TQ sodium MRI in normal human brain [3] and articular cartilage [4]. In this work we demonstrate the use of TQ sodium MRI in a group of subjects diagnosed with primary brain tumors.