Abstract:
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Purpose: To develop and evaluate a new radial MRI pulse sequence which
acquires a set of perfectly co-registered T1, proton density (PD) and T2
weighted images in less time than a conventional PD/T2 weighted double echo
sequence.
Methods and Materials: Our method is based on the k-Space Weighted Image
Contrast (KWIC) technique. Each radial k-space line is acquired as a spin echo
with the echo occurring at the center of k-space. To achieve adequate sampling
density at the outer edge of k-space, a radial scan generally takes 60% longer
than a conventional Cartesian scan. Our sequence introduces a turbo factor of 3
to reduce imaging time while acquiring a fully-sampled radial data set. We
perform three interleaved radial scans, each at different tissue contrast: T1,
PD and T2 weighted. Each individual scan undersamples outer k-space, but the
combined data set is fully sampled. We create three new data sets: each
includes all data from outer k-space but near the center contains only data
corresponding to one contrast. Since the center of k-space is highly
oversampled in radial imaging, adequate sampling density is maintained. An
image is reconstructed from each data set by direct application of the discrete
Fourier transform. Since the overall image contrast is dominated by the center
of k-space, the reconstructed images have distinct contrasts. The result is
three perfectly co-registered images with different contrast properties. Axial
PD, T2 and T1 weighted images of a preserved human brain were obtained using both
our radial sequence and a Cartesian spin echo sequence with identical
repetition and echo times. A radiologist blinded to the image acquisition
method evaluated the two sets of images for the presence of image artifacts and
compared the image quality.
Results: We successfully obtained multicontrast radial images in a time 30%
less than a PD/T2 weighted Cartesian double spin echo acquisition. Artifacts
that did not degrade image interpretation were seen in both the radial and
Cartesian images. The quality of images from the conventional spin echo scans
was deemed slightly better than the radial images but the degree of tissue
contrast was the same.
Conclusion: Using multicontrast radial imaging, nearly artifact free T1, PD and
T2 weighted images of the brain can be acquired in less time than a
conventional T2 weighted spin echo image. These images are perfectly
co-registered, and are of similar quality as equivalent images acquired using
conventional Cartesian k-space trajectories. (Research supported in part by a
general research grant from Siemens Medical Solutions.)
Questions about this event email: wilson.miller@virginia.edu
Miller PhD, W,
Multi-Contrast Radial Spin-Echo MR Imaging for the Simultaneous Acquisition of T1, Proton Density and T2-weighted Images. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3101869.html
