Unformatted text preview: nce of an externally
generated static magnetic ﬁeld.” (DeYoe, 1994).!
Must have person in a high mag. ﬁeld. When in the mag ﬁeld the
hydrogen protons will align with mag. ﬁeld and spin around, and
eventually come back around... After the RF pulse, the spinning proton returns to a state of
low-energy, parallel to the magnetic ﬁeld. This releases
electromagnetic energy that can be detected by a RF coil.! Anatomical MRI!
T1 weighted images!
Different tissues have different relaxation rates.!
Thus some tissues will appear
brighter than others Functional MRI (fMRI)!
T2* weighted images!
Oxygenated and deoxygenated hemoglobin also have different
relaxation rates (BOLD).! magnetic ﬁeld! Physics of fMRI! Physics of fMRI! VOXEL
e.g., 6 mm In-plane resolution
e.g., 192 mm / 64
= 3 mm 3 mm IN-PLANE SLICE SAGITTAL SLICE
Number of Slices
e.g., 10 Matrix Size
e.g., 64 x 64
Field of View (FOV)
e.g., 19.2 cm Collect many different slices (x25) and within each slice of data collecting data in small VOXELs of
space. Typically 64 X 64 6 mm
3 mm Physics of fMRI!
64 radio frequencies (RF) are sent with a repetition
time (RT) of 50 milliseconds. One slice takes 3.2
seconds, 25 sli...
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- Fall '11
- Magnetic resonance imaging, Functional magnetic resonance, neural activity, BOLD Signal, Functional magnetic resonance imaging