High‐resolution dynamic oxygen‐17 MR imaging of mouse brain with golden‐ratio–based radial sampling and k‐space–weighted image reconstruction
17O‐MRI has been used extensively to evaluate cerebral metabolic activity in rats 6, healthy cats 7, and mice 8. Quantification of the cerebral metabolic rate of oxygen consumption (CMRO2) was accomplished by calculating the rate of JOURNAL/mrim/04.02/01445475-201801000-00025/math_25MM2/v/2017-12-21T175206Z/r/image-png generation from inhaled 17O‐labeled oxygen gas (17O2). Water dynamics and CBF can also be assessed with 17O‐MRI by observing the kinetics of JOURNAL/mrim/04.02/01445475-201801000-00025/math_25MM3/v/2017-12-21T175206Z/r/image-png signal either from a bolus injection of 17O‐labeled water or from metabolically produced JOURNAL/mrim/04.02/01445475-201801000-00025/math_25MM4/v/2017-12-21T175206Z/r/image-png from inhaled 17O28. Most of these studies used spectroscopic imaging methods with Cartesian encoding 10, but alternative 17O‐MRI methods have used ultra‐short echo time sequences with non‐Cartesian encoding 12, including the density‐adapted three‐dimensional (3D) radial pulse sequence 12 and the flexible twisted projection imaging acquisition 14. These methods have achieved a spatial resolution of 8 to 8.5 mm and a temporal resolution of 40 to 50 s in humans at high field. However, such spatial and temporal resolution is not sufficient for imaging small rodents.
The aim of this study was to develop a 3D dynamic 17O‐MRI method to delineate the kinetics of 17O water uptake and washout in the mouse brain. A stack‐of‐stars radial sampling method was implemented based on the golden‐angle acquisition scheme 15. A k‐space–weighted image contrast (KWIC) reconstruction was applied to the acquired data to improve the temporal rate with preserved spatial resolution 16. Simulation studies were performed to validate the method. Using this method, the kinetics of JOURNAL/mrim/04.02/01445475-201801000-00025/math_25MM5/v/2017-12-21T175206Z/r/image-png uptake and washout in the brains of mice with glioblastoma (GBM) were delineated after an intravenous bolus injection of JOURNAL/mrim/04.02/01445475-201801000-00025/math_25MM6/v/2017-12-21T175206Z/r/image-png . A temporal resolution of 7.56 s with a nominal voxel size of 5.625 μL was achieved in this study.