Stimulated echo induced misestimates on diffusion tensor indices and its remedy.
OBJECTIVE
To report possible erroneous estimates of diffusion parameters in the twice-refocused spin-echo (TRSE) technique, proposed to eliminate eddy-current-induced geometric distortions in diffusion-weighted echo-planar imaging, when stimulated echo signals are inappropriately included.


METHODS
Eleven subjects were included for imaging experiments on two 1.5 Tesla systems using the TRSE sequence. Three versions, two with unbalanced crusher gradients inserted to dephase the stimulated echo from the b = 0 images and one with balanced crusher gradients, were implemented. The apparent diffusion coefficients (ADC) and fractional anisotropy (FA) were derived and compared.


RESULTS
The ADCs obtained with unbalanced crusher gradients were closer to values reported in the literature. Stimulated echo led to ADC over-estimations by 34.2%, 50.4%, 54.0%, 51.5%, 24.0%, and 41.9% in the genu of corpus callosum, splenium of corpus callosum, bilateral corona radiata, internal capsule, mediofrontal gyrus, and the cuneus, respectively (P < 0.01), with concomitant reduction in FA in highly anisotropic regions. Over-estimations of diffusion coefficients were found to be roughly equal along all directions.


CONCLUSIONS
Formation of stimulated echo in the TRSE technique can lead to erroneous estimations of the diffusion parameters, even if no prominent morphological artifacts are seen.
Chuang
Tzu-Chao
TC
Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan 804. chuang@ee.nsysu.edu.tw
Wu
Ming-Ting
MT
Huang
Teng-Yi
TY
Lin
Yi-Ru
YR
Tsai
Shang-Yueh
SY
Chang
Hing-Chiu
HC
Chung
Hsiao-Wen
HW
D000328:Adult; D016880:Anisotropy; D001921:Brain / Q000473:pathology; D003198:Computer Simulation; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D015233:Models, Statistical; D012984:Software