Using GRE sequences the decrease of the liver signal is specific to
iron excess, if we avoid "out-of-phase" TE. If not, a decrease
of liver signal can be due to steatosis (29-30).
The use of a body coil is mandatory to get a homogeneous signal
in the whole MR slice, and to be able to compare the liver signal
intensity to that of the paraspinous muscles.
The MR protocol is based on GRE sequences with a TR of 120 ms and
with differents TE « in phase » (4-30 ms) and two pulse
angles (20°-90°) in order to get T1, proton density (PD)
and T2 images. The selected TE must be "in-phase" (ie
a multiple of 6.8 ms/Bo, Bo is corresponding to the magnetic field
in Tesla). For this reason the MR protocol was adapted to the magnetic
field of the MR unit.
Selected sequences :
|GRE "T1" sequence
|GRE "PD" sequence
|GRE "T2" sequence
|GRE "T2+" sequence
|GRE "T2++" sequence
The field of view must be adapted to the patient abdominal diameter
(30-45 cm). Using a single excitation and a 128x256 matrix, the
acquisition time is 15 seconds. Slice thickness is usually 10 mm
(15 mm could be usefull at .5 T to increase signal to noise ratio).
Presaturations are not needed.