Influence of Imaging Parameters on High-Intensity Cerebrospinal Fluid Artifacts in Fast-FLAIR MR Imaging
Hsiu-Mei Wua,c,
David M. Yousema,
Hsiao-Wen Chungd,e,
Wan-Yuo Guob,c,
Cheng-Yen Changb,c and
Cheng-Yu Chene
a Department of Radiology, Johns Hopkins University, Baltimore, MD
b the Department of Radiology, Veterans General Hospital-Taipei, Taiwan, ROC
c the Department of Radiology, School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC
d the Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, ROC
e the Department of Radiology, Tri-Service General Hospital, Nei-Hu, Taipei, Taiwan, ROC
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FIG 1. Comparison of images parameters in terms of high-intensity CSF artifacts on fast-FLAIR images obtained in a 37-year-old healthy male volunteer (volunteer 5).
A, Image obtained with section FC, TRF, and interleaving acquisition factor of 3 shows better CSF nulling at prepontine cistern (arrow) than the images in B or C. Notably, in pulse sequences with better CSF nulling at prepontine cistern, fewer high-intensity CSF artifacts are present at the aqueduct (arrowhead).
B, Image obtained with FC, TRF, and an interleaving acquisition factor of 2.
C, Image obtained with only TRF.
D, Additional superior and inferior presaturation does not decrease the high-intensity CSF artifacts (see image in B).
E and F, Images obtained with FC alone without TRF (E) or with superior and inferior presaturations (saturation bands of 80 mm) without TRF (F) demonstrate substantial high-intensity CSF artifacts at the prepontine cistern.
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FIG 2. Schematic diagrams of the fast spin-echo sequence show the effects of section selection gradients on the formation of spin echoes and stimulated echoes.
A, Diagram shows the spin echoes produced with RF excitation by the 90° pulse and refocusing by the ß pulses. At even echoes, the section selection gradient shows a 1-(-2)-1 waveform (dotted-dashed-dotted areas, respectively). Hence, the spin echoes are have inherent motion compensation at even echoes.
B, Diagram shows stimulated echo formation from RF excitation by the 90° pulse and refocusing by the composite of two successive ß pulses. For stimulated echoes, the magnetization vector is stored in the longitudinal direction in between the two ß pulses and, thus, the gradient has no effect on the phase distribution. The resultant 1-(-1) waveform (dotted-dashed areas, respectively) shows no inherent motion compensation. Note that, with flip angle reduction of the ß pulses, as with the selection of the TRF pulse, the signals have a decreased contribution from the spin echo and increases the stimulated echo portion. Therefore, the noncompensated stimulated echo reduces the high-intensity CSF artifacts due to rapid inflow of CSF in the prepontine cisterns.
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