fMRI 101 , Part 1!
Geoffrey K Aguirre, MD, PhD! functional neural activity! MRI image! raw data over time! processed result! lying!
processed result! inference!
GK Aguirre! processed result! influence!
GK Aguirre! neural activity!
GK Aguirre! GK Aguirre! x-ray human head!
GK Aguirre! pneumoencephalography!
GK Aguirre! CT scanner!
Griff Wason! axial CT scan of the brain!
GK Aguirre! Allan M. Cormack! Godfrey Hounsfield!
1979 Nobel Prize in Physiology or Medicine !
Griff Wason! quantify radioactive decay!
radioactive Xenon gas isotope!
Glass and Harper (1963) measure global cerebral blood flow!
GK Aguirre! inject radio-labeled sugar or water!
GK Aguirre! co-incidence detection for positron emission tomography!
GK Aguirre! PET scan of the brain!
GK Aguirre! GK Aguirre! GK Aguirre!
H2O! H2O! B0!
M0! B0! H2O! 90° radio- Z! frequency pulse!
X! B0!
Y!
high energy state T1 signal! RF energy released! Z! Z! Z!
X! X! X! B0!
Y! Y! Y!
high energy state protons relax low energy state
T1 time constant of decay! RF energyRF ! time! T2 signal!
Z! Z! Z!
X! X! X! B0!
Y! Y! Y!
high energy state protons de-phase protons fully de-phased
T2 time constant of decay! RF energyRF ! time! a room-sized Faraday cage!
GK Aguirre! a head coil!
GK Aguirre! T1 weighted! T2 weighted!
GK Aguirre! FLAIR pulse sequence! GK Aguirre! Paul Lauterbur! Sir Peter Mansfield!
2003 Nobel Prize in Physiology or Medicine !
Griff Wason! diffusion weighted (DWI)! gradient echo!
FLAIR! MRA!
GK Aguirre! sagittal! axial! coronal!
GK Aguirre! GK Aguirre! 63.9 MHz at 1.5 Tesla! 127.6 MHz at 3 Tesla! Z!
X! X!
Y! Y! weaker magnetic field STRONGER magnetic field
The Larmor frequency is determined! by the strength of the local magnetic field!
GK Aguirre! Create a gradient of magnetic field strength across space,! allowing the excitation of protons at a given location!
GK Aguirre! GK Aguirre! GK Aguirre! Create a gradient of magnetic field strength across space,! allowing the excitation of protons at a given location!
GK Aguirre! susceptibility artifact from metallic face paint!
GK Aguirre! susceptibility artifact from iron oxide particles! suspended in beeswax in hair!
GK Aguirre! susceptibility from air-tissue interface!
GK Aguirre! air-tissue interfaces concentrate magnetic field lines!
GK Aguirre! 63.9 MHz at 1.5 Tesla! 127.6 MHz at 3 Tesla! Z!
X! X!
Y! Y! weaker magnetic field STRONGER magnetic field
The Larmor frequency is determined! by the strength of the local magnetic field!
GK Aguirre! T2* signal!
180° re- Z! focusing Z! Z! pulse!
X! X! X! B0!
Y! Y! Y!
protons de-phase phases invert protons re-focus
The component that does not refocus is T2*! RF energyRF ! time! susceptibility effects from bleeding in! amyloid angiopathy!
GK Aguirre! hemoglobin contains iron atoms!
GK Aguirre! Linus Pauling! paramagnetic! diamagnetic!
GK Aguirre! Deoxyhemoglobin creates magnetic field inhomo- geneities, causing spin dephasing!
Z!
X!
Y!
protons de-phase gradient echoplanar image!
GK Aguirre! Courtesy, Dr. Arthur W. Toga, Laboratory of Neuro Imaging at UCLA! Neuro-vascular coupling!
↑ blood flow!
physiologic delay! ↑ blood volume! ↓ [deoxy-Hgb]! neuro-imaging!
coupling! imagingsignal !
time(secs)!
GK Aguirre!