Background: In the last decade, sodium mag-netic resonance imaging was investigated for its potential as a functional cardiac imaging tool for ischemia. Later interest was developed in contrast enhancement for intracellular sodium. Little success was reported to suppress extracellular sodium resulting in the intracellular sodium MRI image acquisition using quantum filters or sodium transition states as contrast properties. Now its clinical application is ex-panding as a new challenge in brain and other cancer tumors. Contrast enhancement: We highlight the physical principles of sodium MRI in three different pulse sequences using filters (single quantum, multiple quantum, and triple quantum) meant for sodium contrast enhancement. The optimization of scan parameters, i.e. times of echo delay (TE), inversion recovery (TI) periods, and utility of Dysprosium (DyPPP) shift contrast agents, enhances contrast in sodium MRI images. Inversion recovery pulse sequence without any shift reagent measures the intracellular sodium concentration to evaluate ischemia, apoptosis and membrane integrity. Membrane integrity loss, apoptosis and malignancy are results of growth factor loss and poor epithelial capability related with MRI visible intracellular sodium concentration. Applications and limitations: The sodium MR imaging technical advances reduced scan time to distinguish intracellular and extracellular sodium signals in malignant tumors by use of quantum filter techniques to generate 3D sodium images without shift regents. We observed the association of malignancy with increased TSC, and reduced apoptosis and epithelial growth factor in breast cancer cells. The validity is still in question. Conclusion: Different modified sodium MRI pulse sequences are research tools of sodium contrast enhancement in brain, cardiac and tumor imaging. The optimized MRI scan pa-rameters in quantum filter techniques generate contrast in intracellular sodium MR images without using invasive contrast shift agents. Still, validity and clinical utility are in
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