High-resolution echo-planar spectroscopic imaging of the human calf.
BACKGROUND
This study exploits the speed benefits of echo-planar spectroscopic imaging (EPSI) to acquire lipid spectra of skeletal muscle. The main purpose was to develop a high-resolution EPSI technique for clinical MR scanner, to visualise the bulk magnetic susceptibility (BMS) shifts of extra-myocellular lipid (EMCL) spectral lines, and to investigate the feasibility of this method for the assessment of intra-myocellular (IMCL) lipids.


METHODS
The study group consisted of six healthy volunteers. A two dimensional EPSI sequence with point-resolved spectroscopy (PRESS) spatial localization was implemented on a 3T clinical MR scanner. Measurements were performed by means of 64×64 spatial matrix and nominal voxel size 3×3×15 mm(3). The total net measurement time was 3 min 12 sec for non-water-suppressed (1 acquisition) and 12 min 48 sec for water-suppressed scans (4 acquisitions).


RESULTS
Spectra of the human calf had a very good signal-to-noise ratio and linewidths sufficient to differentiate IMCL resonances from EMCL. The use of a large spatial matrix reduces inter-voxel signal contamination of the strong EMCL signals. Small voxels enabled visualisation of the methylene EMCL spectral line splitting and their BMS shifts up to 0.5 ppm relative to the correspondent IMCL line. The mean soleus muscle IMCL content of our six volunteers was 0.30±0.10 vol% (range 0.18-0.46) or 3.6±1.2 mmol/kg wet weight (range: 2.1-5.4).


CONCLUSIONS
This study demonstrates that high-spatial resolution PRESS EPSI of the muscle lipids is feasible on standard clinical scanners.
Department of Radiology, Uppsala University Hospital, Uppsala, Sweden.
Jan
J
Weis
Philips Healthcare, Best, Netherlands.
Morten
M
Bruvold
Department of Radiology, Uppsala University Hospital, Uppsala, Sweden.
Francisco
F
Ortiz-Nieto
Department of Radiology, Uppsala University Hospital, Uppsala, Sweden.
Håkan
H
Ahlström
D000328:Adult; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D008055:Lipids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism*; D059629:Signal-To-Noise Ratio; D055815:Young Adult
D008055:Lipids