@UNC CS dMRI .pdf

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Fast diffusion imaging using
compressed sensing in q-space
Yogesh Rathi
Assistant Professor
Brigham and Women’s Hospital,
Harvard Medical School, Boston

1

Outline
•  Why fast diffusion imaging ?
•  Approaches to fast diffusion imaging
–  Fast acquisition sequences
–  Smart signal reconstruction

•  Compressed sensing
•  Spherical Ridgelets and extensions
•  Experiments and Results
2

Background – diffusion MRI

Diffusion MRI (dMRI) allows non-invasive investigation of
neural architecture of the brain. It is one of the most widely
used mechanisms to study several brain disorders.
3

dMRI and mental disorders
•  dMRI used to identify location of stroke
•  Used in characterizing edema (Pasternak, 2009)
•  High b-value data was very sensitive to disease load in
MS patients in characterizing normal appearing white
matter (Cohen 2002)
•  Q-space sampling allows to characterize the fast and
slow diffusing components which may belong to different
tissue regions (AxCaliber – Assaf et al)
•  Diffusion Kurtosis Imaging (DKI) has been shown to be
more sensitive to tissue changes (neurodevelopmental
and in mild TBI)
4

Background - dMRI

•  Typically, diffusion tensor imaging is used
in clinical settings (requires only 7 gradient
directions).
5

Diffusion Tensor Imaging

• At each location, the diffusion behavior of water is modeled as
an ellipsoid.
• In medical imaging this ellipsoid is called a diffusion tensor.
Slide 6

Advantages of HARDI
Aim of Tractography : In-vivo tracing of neural pathways of the brain.

[Campbell et al.]

(Rathi et al.)
Slide 7

Advanced- dMRI
To address this problem, Tuch et al (2004), proposed High
Angular Resolution Diffusion Imaging (HARDI), which involves
acquiring several gradient directions uniformly spread over a
sphere.
"  With HARDI, multiple fiber
crossings can be detected.
"  Acquisition time (10-20
minutes) increases
significantly, since many
measurements are
required.

Picture from Kaden et al, Neuroimage,
2008
8

Time Considerations

Need at-least 6 gradient
directions and at-most 5
minutes of scan time.
1-Tensor

?
Need more than 45 gradient
directions and about 15-20
minutes of scan time.
2-Tensor
Kalman Filter

9


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