Hk. Song et Fw. Wehrli, VARIABLE TE GRADIENT AND SPIN-ECHO SEQUENCES FOR IN-VIVO MR MICROSCOPY OF SHORT T-2 SPECIES, Magnetic resonance in medicine, 39(2), 1998, pp. 251-258
Collagen-rich tissues such as skin or fibrous cartilage have very shor
t T-2 ,and thus, in order to be visible, demand a commensurate reducti
on in echo time. Whereas short echo time for imaging of humans is stra
ightforward at large fields of view with currently available whole bod
y gradient hardware, the problem is more challenging in the microscopi
c resolution regime (<100 mu m). In this work a simple approach consis
ting of shortening the echo time dynamically toward the lower spatial
frequencies is described for three-dimensional partial flip-angle grad
ient and spin-echo sequences. Microimages obtained in vivo at 50 mu m
resolution on a 1.5 T whole body scanner are shown to afford a signal-
to-noise gain of over 100% in the dermis of the human skin. A point-sp
read function analysis indicates that the variable echo time gradient-
echo sequence produces a unique not previously reported off-resonance
artifact in the phase-encoding direction. The artifact results from th
e phase modulation occurring during the variable echo time and can man
ifest as both blurring and intensity fluctuations, as well as shifts o
f boundaries in the phase-encoding direction. However, for the on-reso
nance condition, the images are free from these artifacts and exhibit
significantly improved signal-to-noise ratio.