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Flat Maps
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3.2 Terms
3.2.1 Inplanes, Scans, Sessions, Studies
An inplane is a T1-weighted anatomical image taken in the same plane as functional data. A
scan results in an inplane image or a functional image for a certain visual stimulus. A session
is a contiguous series of scans with one subject. Each session contains only one inplane data
set. It can include more than one functional data set. The functional data sets within one ses-
sion are intrinsically aligned with the inplane data set. Information about each session is
stored in a file called mrSESSION.mat. A study can contain more than one session. The ses-
sions in a study are somehow related to each other.
3.2.2 Magnetic Susceptibility
Magnetic susceptibility is a dimensionless quantity that measures “the extent to which a mate-
rial may be magnetized in relation to a given applied magnetic field”: cm= M/H, where cm is
the (volume) magnetic susceptibility of a material, M the magnetization within the material,
and H the applied magnetic field strength [-, 2001 #22]. The different susceptibilities of de-
oxygenated and oxygenated blood can be used to infer neural activity.
3.3 Magnetic Resonance Imaging (MRI)
When a human body is placed in a strong magnetic field (often called B0), the protons can be
modeled as bar magnets that align with the external magnetic field (equilibrium state). A radio
frequency pulse (RF-pulse) with the right frequency (Larmor frequency = resonance fre-
quency) can be used to disturb the alignment. This induces a voltage in a receiver coil, which
can be measured. After the RF-pulse has been switched off, the protons relax (longitudinal
relaxation time T1; transverse relaxation times T2, T2*) to the equilibrium state. During this
relaxation process, the induced signal is measured. Since the relaxation process and the meas-
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