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Hanson Endowed Chair in Radiology"],"award-info":[{"award-number":["Malcolm B. Hanson Endowed Chair in Radiology"]}],"id":[{"id":"10.13039\/100007249","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Magnetic Resonance in Med"],"published-print":{"date-parts":[[2023,5]]},"abstract":"<jats:sec><jats:title>Purpose<\/jats:title><jats:p>To correct image distortions that result from nonlinear spatial variation in the transmit RF field amplitude () when performing spatial encoding with the method called frequency\u2010modulated Rabi encoded echoes (FREE).<\/jats:p><\/jats:sec><jats:sec><jats:title>Theory and Methods<\/jats:title><jats:p>An algorithm developed to correct image distortion resulting from the use of nonlinear static field (<jats:italic>B<\/jats:italic><jats:sub>0<\/jats:sub>) gradients in standard MRI is adapted herein to correct image distortion arising from a nonlinear \u2010gradient field in FREE. From a \u2010map, the algorithm performs linear interpolation and intensity scaling to correct the image. The quality of the distortion correction is evaluated in 1.5T images of a grid phantom and human occipital lobe.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>An expanded theoretical description of FREE revealed the symmetry between this \u2010gradient field spatial\u2010encoding and standard <jats:italic>B<\/jats:italic><jats:sub>0<\/jats:sub>\u2010gradient field spatial\u2010encoding. The adapted distortion\u2010correction algorithm substantially reduced image distortions arising in the spatial dimension that was encoded by the nonlinear  gradient of a circular surface coil.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>Image processing based on straightforward linear interpolation and intensity scaling, as previously applied in conventional MRI, can effectively reduce distortions in FREE images acquired with nonlinear \u2010gradient fields.<\/jats:p><\/jats:sec>","DOI":"10.1002\/mrm.29549","type":"journal-article","created":{"date-parts":[[2022,12,15]],"date-time":"2022-12-15T05:02:53Z","timestamp":1671080573000},"page":"2100-2108","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["Correcting image distortions from a nonlinear B1+$$ {\\boldsymbol{B}}_{\\mathbf{1}}^{+} $$\u2010gradient field in frequency\u2010modulated Rabi\u2010encoded 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