Chemical-shift artifact reduction in Hadamard-encoded MR spectroscopic imaging at high (3T and 7T) magnetic fields.
Proton MR spectroscopic imaging (MRSI) at higher magnetic fields (B(0)) suffers metabolite localization errors from different chemical-shift displacements (CSDs) if spatially-selective excitation is used. This phenomenon is exacerbated by the decreasing radiofrequency (RF) field strength, B(1), at higher B(0)s, precluding its suppression with stronger gradients. To address this, two new methods are proposed: 1) segmenting the volume-of-interest (VOI) into several slabs, allowing proportionally stronger slice-select gradients; and 2) sequentially cascading rather than superposing the components of the Hadamard selective pulses used for reasons of better point-spread function (PSF) to localize the few slices within each slab. This can reduce the peak B(1) to that of a single slice. Combining these approaches permits us to increase the selective gradient four- to eightfold per given B(1), to 12 or 18mT/m for 4- or 2-cm VOIs. This "brute force" approach reduces the CSD to under 0.05 cm/ppm at 7T, or less than half that at 3T.
Goelman
Gadi
G
Department of Radiology, New York University School of Medicine, New York, New York, USA.|MRI Laboratory, Human Biology Research Center, Department of Medical Biophysics Hadassah Hebrew University Medical Center, Jerusalem, Israel.
Liu
Songtao
S
Department of Radiology, New York University School of Medicine, New York, New York, USA.
Fleysher
Roman
R
Department of Radiology, New York University School of Medicine, New York, New York, USA.
Fleysher
Lazar
L
Department of Radiology, New York University School of Medicine, New York, New York, USA.
Grossman
Robert I
RI
Department of Radiology, New York University School of Medicine, New York, New York, USA.
Gonen
Oded
O
Department of Radiology, New York University School of Medicine, New York, New York, USA.
D016477:Artifacts; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*