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Reproducibility of cerebral phenylalanine levels in patients with phenylketonuria determined by 1 H‐MR spectroscopy
Author(s) -
Kreis R.,
Zwygart K.,
Boesch C.,
Nuoffer JM.
Publication year - 2009
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21983
Subject(s) - reproducibility , phenylalanine , nuclear magnetic resonance , metabolite , spectroscopy , nuclear medicine , chemistry , medicine , analytical chemistry (journal) , chromatography , physics , biochemistry , quantum mechanics , amino acid
The reproducibility of metabolite content determined by MR spectroscopy (MRS) is usually at best a few percent for the prominent singlets. When studying low‐concentration metabolites, like phenylalanine (Phe), where tissue content can be <100 μmol/kg, better reproducibility is paramount—particularly in view of using MRS results for potential individual treatment advice. An optimized, targeted spectroscopy method was established at 1.5T and reproducibility was established in 21 patients with phenylketonuria (PKU) where three spectra were recorded in each of three independent sessions, two of which were in immediate succession to minimize physiologic variation. Intersession variation was found to be only 7 μmol/kg Phe for back‐to‐back repetition of sessions, in close agreement with the variation of 16 μmol/kg observed for single spectra within a session. Analysis of variance proved the individuality of the blood/brain Phe ratio—though this ratio seems to be influenced by physiologic factors that are not stable in time. The excellent reproducibility was achieved through optimization of various factors, including signal‐to‐noise ratio, repositioning, and prescan calibrations, but also by enforcing as much prior information as possible (e.g., lineshape and phase from reference scans, constant prior‐knowledge‐locked baseline). While the application of maximum general prior knowledge is a general method to reduce fluctuations, one should remember that it may introduce systematic errors. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.