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Spatial and temporal limits of fMRISpatial and temporal limits of fMRI
• Menon RS, Kim SG. Spatial and temporal limits in cognitive
neuroimaging with fMRI. Trends Cogn Sci. 1999 Jun;3(6):207-216.
With supplementary material from:
• Menon RS, Goodyear BG. Submillimeter functional localization in human
striate cortex using BOLD contrast at 4 Tesla: implications for the vascular
point-spread function. Magn Reson Med. 1999 Feb;41(2):230-5.
• Menon RS, Luknowsky DC, Gati JS. Mental chronometry using latency-
resolved functional MRI. Proc Natl Acad Sci U S A. 1998 Sep 1;95(18):10902-7.
Presentation by Robert PinkertonPresentation by Robert Pinkerton
ResolutionResolution
““The ability to resolve 2 different regions of neural The ability to resolve 2 different regions of neural activation.” activation.”
fMRI System ParametersfMRI System Parameters
TemporalTemporal- Volume Acquisition Time (VAT)- Volume Acquisition Time (VAT)
SpatialSpatial - Voxel size - Voxel size
QuestionsQuestions
A)A) How fast?How fast?
B)B) How small?How small?
What are we measuring?What are we measuring?
The signalThe signal
Will this transceive surface coil array…Will this transceive surface coil array…
……??
i) 2 sii) 13 s
LimitationsLimitations
- TechnologyTechnology- Signal to Noise Ratio (SNR)Signal to Noise Ratio (SNR)
- Physiology Physiology - The ultimate limiting factor!The ultimate limiting factor!
Limitations: NoiseLimitations: Noise
- Signal to Noise Ratio (SNR)Signal to Noise Ratio (SNR)Noise Sources:Noise Sources:
PhysiologicalPhysiologicalrespiration, cardiac, motionrespiration, cardiac, motion
ExtrinsicExtrinsicSystem (RF Coil, Gradients, preamps System (RF Coil, Gradients, preamps
etc.)etc.)IntrinsicIntrinsic
Patient LoadingPatient Loading
Ultimately…Ultimately…
“ “Ultimately, it is the extent of the lateral Ultimately, it is the extent of the lateral connections and their inherent activity that connections and their inherent activity that will determine the cortical vasculature point will determine the cortical vasculature point spread function [spatial resolution] in spread function [spatial resolution] in different areas of the brain.”different areas of the brain.”
Mapping ODC using the initial hyperoxygenated BOLD response
Methods to increase spatial Methods to increase spatial resolution by using information resolution by using information
in the time domain.in the time domain.
DipTR ~ 500 ms
Mental Rotation: Figure 1, Menon & Kim
Mental Rotation: Figure 1, Menon & Kim
Widthcompare width to RT
Mental Mental ChronometryChronometry
Menon et al, Proc. Natl. Acad. Sci. USA 1998
Answers: It all depends!Answers: It all depends!
A)A) How fast?How fast?VAT ~ 50 ms - 3 sVAT ~ 50 ms - 3 s
Resolution:
~ 2s normal for ROI studies~ 500 ms for DIP measurements~ 100 ms for single event trials~ 50 ms for one slice, poor res
Answers: It all depends!Answers: It all depends!
B)B) How small?How small?
x, x, y ~ 0.1 - 3 mmy ~ 0.1 - 3 mm
Resolution:
~ 3.8 mm diameter of PSF for feline cortex due to 1mm2 patch of activation~ 0.6 mm diameter of PSF for human cortex odc~ 0.1 mm capillary separation