  Quantitative measurement of functional and anatomical traits of 4D tongue
motion in the course of speech or other lingual behaviors remains a major
challenge in scientific research and clinical applications. Here, we introduce
a statistical multimodal atlas of 4D tongue motion using healthy subjects,
which enables a combined quantitative characterization of tongue motion in a
reference anatomical configuration. This atlas framework, termed Speech Map,
combines cine- and tagged-MRI in order to provide both the anatomic reference
and motion information during speech. Our approach involves a series of steps
including (1) construction of a common reference anatomical configuration from
cine-MRI, (2) motion estimation from tagged-MRI, (3) transformation of the
motion estimations to the reference anatomical configuration, and (4)
computation of motion quantities such as Lagrangian strain. Using this
framework, the anatomic configuration of the tongue appears motionless, while
the motion fields and associated strain measurements change over the time
course of speech. In addition, to form a succinct representation of the
high-dimensional and complex motion fields, principal component analysis is
carried out to characterize the central tendencies and variations of motion
fields of our speech tasks. Our proposed method provides a platform to
quantitatively and objectively explain the differences and variability of
tongue motion by illuminating internal motion and strain that have so far been
intractable. The findings are used to understand how tongue function for speech
is limited by abnormal internal motion and strain in glossectomy patients.
