Variable flip angle imaging and fat suppression in combined gradient and spin-echo (GREASE) techniques

Journal Article · Mon Jan 01 00:00:00 EST 1990 · Magnetic Resonance Imaging; (USA)

DOI:https://doi.org/10.1016/0730-725X(90)90246-X· OSTI ID:6743904

Vinitski, S; Mitchell, D G; Szumowski, J; Burk, Jr, D L; Rifkin, M D ^[1]

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1. Thomas Jefferson Univ. Hospital, Philadelphia, PA (USA)

Conventional proton density and T2-weighted spin-echo images are susceptible to motion induced artifact, which is exacerbated by lipid signals. Gradient moment nulling can reduce motion artifact but lengthens the minimum TE, degrading the proton density contrast. We designed a pulse sequence capable of optimizing proton density and T2-weighted contrast while suppressing lipid signals and motion induced artifacts. Proton density weighting was obtained by rapid readout gradient reversal immediately after the excitation RF pulse, within a conventional spin-echo sequence. By analyzing the behavior of the macroscopic magnetization and optimizing excitation flip angle, we suppressed T1 contribution to the image, thereby enhancing proton density and T2-weighted contrast with a two- to four-fold reduction of repetition time. This permitted an increased number of averages to be used, reducing motion induced artifacts. Fat suppression in the presence of motion was investigated in two groups of 8 volunteers each by (i) modified Dixon technique, (ii) selective excitation, and (iii) hybrid of both. Elimination of fat signal by the first technique was relatively uniform across the field of view, but it did not fully suppress the ghosts originating from fat motion. Selective excitation, while sensitive to the main field inhomogeneity, largely eliminated the ghosts (0.21 +/- 0.05 vs. 0.29 +/- 0.06, p less than 0.01). The hybrid of both techniques combined with bandwidth optimization, however, showed the best results (0.17 +/- 0.04, p less than 0.001). Variable flip-angle imaging allows optimization of image contrast which, along with averaging and effective fat suppression, significantly improves gradient- and spin-echo imaging, particularly in the presence of motion.

• OSTI ID: 6743904
• Journal Information: Magnetic Resonance Imaging; (USA), Vol. 8:2; ISSN 0730-725X
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
NMR IMAGING
OPTIMIZATION
ADIPOSE TISSUE
LIPIDS
LIVER
MAN
PROTONS
SPIN ECHO
SPLEEN
ANIMAL TISSUES
ANIMALS
BARYONS
BODY
CONNECTIVE TISSUE
DIAGNOSTIC TECHNIQUES
DIGESTIVE SYSTEM
ELEMENTARY PARTICLES
FERMIONS
GLANDS
HADRONS
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PRIMATES
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550600* - Medicine