Indirect MRI of ¹⁷o‐labeled water using steady‐state sequences: Signal simulation and preclinical experiment

<jats:sec><jats:title>BACKGROUND</jats:title><jats:p>Few studies have been reported for T<jats:sub>2</jats:sub>‐weighted indirect <jats:sup>17</jats:sup>O imaging.</jats:p></jats:sec><jats:sec><jats:title>PURPOSE/HYPOTHESIS</jats:title><jats:p>To evaluate the feasibility of steady‐state sequences for indirect <jats:sup>17</jats:sup>O brain imaging.</jats:p></jats:sec><jats:sec><jats:title>STUDY TYPE</jats:title><jats:p>Signal simulation, phantom measurements, and prospective animal experiments were performed in accordance with the institutional guidelines for animal experiments.</jats:p></jats:sec><jats:sec><jats:title>POPULATION/SUBJECTS/PHANTOM/SPECIMEN/ANIMAL MODEL</jats:title><jats:p>Signal simulations of balanced steady‐state free precession (bSSFP) were performed for concentrations of <jats:sup>17</jats:sup>O ranging from 0.037–1.600%. Phantom measurements with concentrations of <jats:sup>17</jats:sup>O water ranging from 0.037–1.566% were also conducted. Six healthy beagle dogs were scanned with intravenous administration of 20% <jats:sup>17</jats:sup>O‐labeled water (1 mL/kg).</jats:p></jats:sec><jats:sec><jats:title>FIELD STRENGTH/SEQUENCE</jats:title><jats:p>Dynamic 3D‐bSSFP scans were performed at 3T MRI. <jats:sup>17</jats:sup>O‐labeled water was injected 60 seconds after the scan start, and the total scan duration was 5 minutes.</jats:p></jats:sec><jats:sec><jats:title>ASSESSMENT</jats:title><jats:p>Based on the result of signal simulation and phantom measurement, signal changes in the beagle dogs were measured and converted into <jats:sup>17</jats:sup>O concentrations.</jats:p></jats:sec><jats:sec><jats:title>STATISTICAL TESTS</jats:title><jats:p>The <jats:sup>17</jats:sup>O concentrations were averaged for every 15 seconds, and compared to the baseline (30–45 sec) with Dunnett's multiple comparison tests.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Signal simulation revealed that the relationships between <jats:sup>17</jats:sup>O concentration and the natural logarithm of relative signals were linear. The intraclass correlation coefficient between relative signals in phantom measurement and signal simulations was 0.974. In the animal experiments, significant increases in <jats:sup>17</jats:sup>O concentration (<jats:italic>P</jats:italic> < 0.05) were observed 60 seconds after the injection of <jats:sup>17</jats:sup>O. At the end of scanning, mean respective <jats:sup>17</jats:sup>O concentrations of 0.084 ± 0.026%, 0.117 ± 0.038, 0.082 ± 0.037%, and 0.049 ± 0.004% were noted for the cerebral cortex, cerebellar cortex, cerebral white matter, and ventricle.</jats:p></jats:sec><jats:sec><jats:title>DATA CONCLUSION</jats:title><jats:p>Dynamic steady‐state sequences were feasible for indirect <jats:sup>17</jats:sup>O imaging, and absolute quantification was possible. This method can be applied for the measurement of permeability and blood flow in the brain, and for kinetic analysis of cerebrospinal fluid.</jats:p><jats:p><jats:bold>Level of Evidence</jats:bold>: 2</jats:p><jats:p><jats:bold>Technical Efficacy</jats:bold>: Stage 1</jats:p><jats:p>J. Magn. Reson. Imaging 2018;47:1373–1379.</jats:p></jats:sec>