Tierärztliche Hochschule Hannover

Manuskript I
144 msec., TR 2000 msec., 19 1024 samples, spectral bandwidth of 2000 Hz, water
suppression (automated prescan, excitation pulse, followed by frequency selective
second pulse with bandwidth of 140 Hz and a second pulse angle of 300), 20 pencil
beam shimming and the number of signal averages (NSA) 240 or 448. A regional
saturation technique (REST)-slabs was not used. With a NSA of 240, one PRESS
sequence lasted 8.36 minutes (min), while it took 15.32 min. for 448 NSA. MRS was
performed subsequently to the standard MRI protocol including T1- and T2-weighted
sequences, a Fluid-Attenuated-Inversion-Recovery (FLAIR)-sequence and a HEMOsequence.
Small voxel were defined to contain less than one milliliter (mL) tissue
(predominantly voxel around 5x5x5 mm 3 ), the large voxel as a volume of interest
(VOI) containing more than 1mL tissue (mainly 5x5x60 mm 3 ). All voxels were placed
in CNS regions unaffected by any structural abnormality detected by conventional
MRI. Since all examined dogs were patients with medical indication for MRI, one
PRESS sequence was performed either in the brain or spinal cord region. Two runs
for each voxel size were performed at body temperature and at room temperature,
respectively to measure the metabolites in the phantom. The analysis of the data
received was conducted on an Extended MR workspace with the special application
tool SpectroView (R 2.3.6.1, Philips Medical Systems, Eindhoven, the Netherlands).
All metabolite peaks, which were beyond the normal range (Cho = 3.17-3.20 ppm, Cr
= 3.02-3.03 ppm, Glx = 2.35 and 3.7 ppm, 21 lactate = 1.32 ppm, mI = 3.5-3.6 ppm,
NAA = 2.00-2.02 ppm), 5, 7, 10, 18, 22, 23 were excluded. Finally, 21 measurements in the
brain and 22 examinations of the spinal cord could be evaluated. The 21
measurements in the brain were divided into 15 measurements with small voxel and
six with large voxel. In the 22 examinations of the spinal cord 15 measurements were
performed setting a small voxel and seven with large voxel. The metabolite
concentration estimates were calculated by comparison of the areas under the curve
in the CNS and the defined concentrations of the phantom.
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