Quantification of the in vivo brain ultrashort-T2* component in healthy volunteers

Abstract

Purpose: Recent work has shown MRI is able to measure and quantify signals of phospholipid membrane-bound protons associated with myelin in the human brain. This work seeks to develop an improved technique for characterizing this brain ultrashort- $T_2\ast$ component in vivo accounting for $T_1$ weighting.

Methods: Data from ultrashort echo time scans from 16 healthy volunteers with variable flip angles (VFA) were collected and fitted into an advanced regression model to quantify signal fraction, relaxation time, and frequency shift of the ultrashort- $T_2\ast$ component.

Results: The fitted components show intra-subject differences of different white matter structures and significantly elevated ultrashort- $T_2\ast$ signal fraction in the corticospinal tracts measured at 0.09 versus 0.06 in other white matter structures and significantly elevated ultrashort- $T_2\ast$ frequency shift in the body of the corpus callosum at $-$ 1.5 versus $-$ 2.0 ppm in other white matter structures.

Conclusion: The significantly different measured components and measured $T_1$ relaxation time of the ultrashort- $T_2\ast$ component suggest that this method is picking up novel signals from phospholipid membrane-bound protons.

Keywords: T 2 ∗ $$ {\mathrm{T}}_2\ast $$ ; UTE; brain imaging; multicomponent fit model; myelin; ultrashort echo time.