Variations due to analysis technique in intracellular pH measurements in simulated and in vivo 31P MR spectra of the human brain.
OBJECTIVE
To investigate variation in pH generated by different analysis techniques and to find the most robust method, 31P MR brain spectra were acquired in vivo. Three different methods were used to measure the chemical shift of inorganic phosphate (Pi) relative to phosphocreatine (PCr).


METHODS
Eight healthy volunteers were scanned four times, and manual measurement of the chemical shift in a frequency domain spectrum using the manufacturer's software was compared with values produced by a frequency-domain analysis method (NMR1) and a prior-knowledge-based time-domain technique (MRUI). To explain the in vivo data, simulations of brain spectra, modified in ways typical of real variations in vivo, were produced and the pH was measured using manual measurement and MRUI.


RESULTS
Different measurement techniques produced systematically different pH values, with manual measurement producing the lowest variability (manual measurement: pH = 6.999, CoV = 0.297; NMR1: pH = 7.042, CoV = 0.501; MRUI: pH = 7.036, CoV = 0.606). While MRUI more accurately measured the pH of unaltered simulations, it was systematically affected by altering the simulated spectra. Manual measurement was unaffected.


CONCLUSIONS
Manual measurement produces the most consistent pH value, and there is no benefit in using more complex automated spectral fitting methods to measure the pH.
Hamilton
Gavin
G
Robert Steiner MR Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Faculty of Medicine, Imperial College London, London, United Kingdom. dr_g_hamilton@yahoo.co.uk
Allsop
Joanna M
JM
Patel
Nayna
N
Forton
Daniel M
DM
Thomas
Howard C
HC
O'Sullivan
Catherine P A
CP
Hajnal
Joseph V
JV
Taylor-Robinson
Simon D
SD
D000328:Adult; D001921:Brain / Q000378:metabolism*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism*; D010759:Phosphorus Isotopes
D010710:Phosphates; D010759:Phosphorus Isotopes; D010725:Phosphocreatine