Complementary Sensitivity of Fixed‐Time and Fixed‐Oscillation Regimes to Exchange and Structural Disorder in the Human Brain Revealed Using Oscillating‐Gradient Diffusion <scp>MRI</scp> With Ultra‐Strong Gradients

Fixed- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>T</mml:mi></mml:mrow> <mml:annotation>$$ T $$</mml:annotation></mml:semantics> </mml:math> and fixed- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>N</mml:mi></mml:mrow> <mml:annotation>$$ N $$</mml:annotation></mml:semantics> </mml:math> OGSE provide complementary sensitivity to microstructural features. Fixed- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>T</mml:mi></mml:mrow> <mml:annotation>$$ T $$</mml:annotation></mml:semantics> </mml:math> emphasizes structural disorder, while fixed- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>N</mml:mi></mml:mrow> <mml:annotation>$$ N $$</mml:annotation></mml:semantics> </mml:math> highlights membrane permeability and exchange. The extended frequency regimes enabled by ultra-strong gradients advance OGSE as a powerful tool for probing human brain tissue microstructure.