student research day - Case Western Reserve University School of ...

Candice A. Bookwalter
Multiple Overlapping k-space Junctions for Investigating Translating Objects
Candice A. Bookwalter and Mark A. Griswold and Jeffrey L. Duerk
Department of Biomedical Engineering and Department of Radiology, Case Western Reserve University
INTRODUCTION: Magnetic Resonance Imaging (MRI) is a useful clinical imaging tool in both diagnostic and interventional
radiology. However, MR images are susceptible to corruption by motion such as bulk motion from an uncooperative patient or
respiratory motion which may obscure useful clinical information. Traditional methods for motion artifact correction including
respiratory gating and navigator echoes undesirably increase imaging time. We describe a novel method called Multiple
Overlapping k-space Junctions for Investigating Translating Objects (MOJITO) which is a k-space (i.e., MRI raw data) based self-
navigated method without significantly increasing acquisition time. The MOJITO method requires a trajectory (i.e., order of
acquiring raw data in k-space) which has multiple intersections.
METHODS: This study investigates the performance of MOJITO in the presence of confounding factors such as noise and field
inhomogeneities when BOWTIE trajectory intersections are used. Multiple calculated phase differences (Δφ) and known k-
space locations (kx and ky) are used to calculate a time-dependent representation of motion (Δx and Δy) occurring throughout a
BOWTIE acquisition using the equation Δφ = Δxkx + Δyky. Simulations, phantom experiments, and in vivo experiments were
used to determine the effects of signal-to-noise ratio (SNR) and off-resonance.
RESULTS/DISCUSSION: Noise simulations showed that an SNR of 12 was sufficient for 1 mm accuracy in both in-plane
directions. Off-resonance simulations showed a small drift and offset error in Δx and a discontinuity in Δy. Phantom and in
vivo data matched simulations results where Δx is detected with good fidelity, while Δy demonstrated a severe discontinuity.
The phantom and in vivo images corrected with only Δx showed excellent results for motion in the x-direction. Unlike
conventional motion artifact correction techniques, MOJITO provides artifact correction without the loss of efficiency seen in
traditional methods. The MOJITO motion artifact correction method will afford new efficiency in correcting 2D rigid body
translational motion.
Supported by National Institutes of Health; Grant Number: T32 GM-07250 Siemens Medical Solutions
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