The Deficiency Coefficient of Diffusing Molecules

Denis LeBihan, M.D., Ph.D., is a clinician and physicist, a relentless innovator in the field of MRI and fMRI since the late 80’s, and—as we hear in this podcast—a broad, deep, and highly creative thinker who remains passionate about his work. Denis is the founding director of NeuroSpin in Orsay, France and spends time in Japan as a guest professor at the University of Kyoto and National Institutes of Physical Sciences in Okazaki.  

Denis Le Bihan has achieved international recognition for his truly fundamental contributions to the development of diffusion MRI, diffusion tensor imaging (DTI), and the concept of IVIM to image perfusion. It is the b in his name from which the ubiquitous b-factor in diffusion comes from. He has more recently demonstrated the ability to image brain activation-related diffusion coefficient changes.

In this podcast, we discuss the intellectual history of Denis’ career. He produced the first diffusion-weighted images, helped establish diffusion tensor imaging, and advanced the concept of imaging perfusion as having an “apparent diffusion coefficient” (ADC) and order of magnitude higher than water diffusion. He has also demonstrated that water diffusion, when imaged with very high b-values, decreases with brain activation. Cell swelling increases the surface area of cells where low diffusion coefficient water resides, thus lowering overall diffusion coefficient. This last result is still debated but generally gaining acceptance with each new paper demonstrating the effect. He also spends some time in the episode talking about his foray into modeling brain function, tapping into inspiration from Einstein and relativity. Overall, it was a fun and inspiring conversation!