On the effects of spatial filtering--a comparative fMRI study of episodic memory encoding at high and low resolution.
The effects of spatial filtering in functional magnetic resonance imaging were investigated by reevaluating the data of a previous study of episodic memory encoding at 2 x 2 x 4-mm(3) resolution with use of a SPM99 analysis involving a Gaussian kernel of 8-mm full width at half maximum. In addition, a multisubject analysis of activated regions was performed by normalizing the functional images to an approximate Talairach brain atlas. In individual subjects, spatial filtering merged activations in anatomically separated brain regions. Moreover, small foci of activated pixels which originated from veins became blurred and hence indistinguishable from parenchymal responses. The multisubject analysis resulted in activation of the hippocampus proper, a finding which could not be confirmed by the activation maps obtained at high resolution. It is concluded that the validity of multisubject fMRI analyses can be considerably improved by first analyzing individual data sets at optimum resolution to assess the effects of spatial filtering and minimize the risk of signal contamination by macroscopically visible vessels.
MR Research Center, Department of Clinical Neuroscience, Karolinska Institutet/Karolinska Hospital, Stockholm, Sweden. Peter.Fransson@cns.ki.se
Peter
P
Fransson
Klaus-Dietmar
KD
Merboldt
Karl Magnus
KM
Petersson
Martin
M
Ingvar
Jens
J
Frahm
D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D002560:Cerebrovascular Circulation; D006624:Hippocampus / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008568:Memory / Q000502:physiology*; D010100:Oxygen / Q000097:blood
D010100:Oxygen