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