Quantitative MR imaging R2 relaxometry in elderly participants reporting memory loss.
OBJECTIVE
In Alzheimer disease (AD), elevated brain iron concentrations in gray matter suggest a disruption in iron homeostasis, while demyelination processes in white matter increase the water content. Our aim was to assess whether the transverse proton relaxation rate, or R2, an MR imaging parameter affected by changes in brain iron concentration and water content, was different in elderly participants with mild to severe levels of cognitive impairment compared with healthy controls.


METHODS
Twelve elderly participants reporting memory problems and 11 healthy volunteers underwent single-spin-echo MR imaging in a 1.5T scanner, with subsequent neuropsychological testing. R2 data were collected from 14 brain regions in cortical and subcortical gray and white matter. Those with memory complaints were separated into 2 further subgroups: MC1 (no objective cognitive impairment) and MC2 (mild to severe objective cognitive impairment).


RESULTS
Mean brain R2 values from the 11 controls correlated strongly (r = 0.94, P < .0001) with reference brain iron concentrations for healthy adults. R2 values in the MC1 and MC2 subgroups were significantly higher in the right temporal cortex and significantly lower in the left internal capsule, compared with healthy controls. R2 values in the MC2 subgroup were significantly lower in the left temporal and frontal white matter, compared with healthy controls.


CONCLUSIONS
R2 differences between both subgroups and the healthy controls suggest iron has increased in the temporal cortex, and myelin has been lost from several white matter regions in those with memory complaints, consistent with incipient AD pathogenesis and biochemical data.
School of Physics, University of Western Australia.
M J
MJ
House
T G
TG
St Pierre
J K
JK
Foster
R N
RN
Martins
R
R
Clarnette
D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000175:diagnosis* / Q000503:physiopathology; D000647:Amnesia / Q000175:diagnosis* / Q000503:physiopathology; D001921:Brain / Q000473:pathology; D003711:Demyelinating Diseases / Q000175:diagnosis*; D005260:Female; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007501:Iron / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009484:Neuropsychology; D012016:Reference Values; D013223:Statistics as Topic; D014882:Water-Electrolyte Balance / Q000502:physiology*
D007501:Iron