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Optimization of a dual echo in the steady state (DESS) free‐precession sequence for imaging cartilage
Author(s) -
Hardy Peter A.,
Recht Michael P.,
Piraino David,
Thomasson David
Publication year - 1996
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.1880060212
Subject(s) - flip angle , contrast (vision) , cartilage , pulse sequence , echo (communications protocol) , nuclear magnetic resonance , gradient echo , waveform , image contrast , materials science , physics , sequence (biology) , magnetic resonance imaging , acoustics , biomedical engineering , computer science , optics , medicine , chemistry , anatomy , radiology , computer network , biochemistry , voltage , quantum mechanics
Three‐dimensional (3D) MR imaging of the knee is useful to detect cartilage abnormalities, although the tissue contrast in 3D gradient‐recalled echo (GRE) sequences such as gradient‐recalled acquisition in the steady state (GRASS) or fast low‐angle shot (FLASH) is poor. T2 contrast can be added to a GRASS sequence by combining the signals from the first and second gradient echoes, which form immediately after and immediately before each radiofrequency (RF) pulse in a 3D GRE sequence. We have optimized a 3D dual echo in the steady state (DESS) sequence, which produces one averaged image from the two echoes, for use in the detection of articular cartilage abnormalities. In the optimization process, we examined the imaging parameters of flip angle (α), repetition time (TR), echo time (TE), and bandwidth to maximize the contrast between cartilage and joint fluid. A theoretical simulation of the sequence was confirmed with experiments conducted on phantoms with known T1 and T2. On the basis of theoretical predictions and experiments using healthy volunteers, we determined that an optimized sequence with a bandwidth of 98 Hz per pixel, a TR of 30 msec, a TE of 7.1 msec, and an α of 60° produced the highest contrast between cartilage and fluid within a defined acquisition time of 6 minutes. Additional contrast was obtained by filtering the second‐echo image to eliminate noise before adding it to the first‐echo image.