# Presentation: 349357

## Peter A. Bandettini, Ph.D.

Section on Functional Imaging Methods
http://fim.nimh.nih.gov
Laboratory of Brain and Cognition
&
Functional MRI Facility
http://fmrif.nimh.nih.gov

- Section on Functional Imaging Methods
- http://fim.nimh.nih.gov
- Laboratory of Brain and Cognition
- &
- Functional MRI Facility
- http://fmrif.nimh.nih.gov

**Spatial, Temporal, and Interpretative Limits of fMRI**

**Notes:**
30 minutes

## 1991

**1991**

## What really limits fMRI ?

**Imaging Methodology**
**Hemodynamic Response Function**

**We can typically image faster and at higher resolution than the functional resolution that is determined by the hemodynamic response function.**

## T2* decay

**T2* decay**

**EPI Readout Window**

**≈ ****20 to 40 ms**

- Single Shot Echo Planar Imaging (EPI)

## Multi-shot imaging

**Multi-shot imaging**
**Partial k-space imaging**
**RF coils**
**SENSE imaging**
**Higher field strength**

## Multi-shot imaging

**T2* decay**

**EPI Window 2**

**Multi-shot imaging**

**Requires navigator pulses**
**Temporal resolution and stability tradeoff**

## Multi-shot imaging

**Excitations****	****1****	****        2****	****	****     4****	****	****    8****	**
**Matrix Size  64 x 64    128 x 128****	****256 x 128 ****	****256 x 256**

**Multi-shot imaging**

## Partial k-space imaging

**Partial k-space imaging**

**More warping**
**Lower image SNR**
**Improvement in one dimension**

## Partial k-space imaging

**Partial k-space imaging**

## RF coils

- J. Bodurka, et al, MRM 51 (2004) 165-171.

**RF coils**

## Simulated gains in TNSR with doubling sensitivity

**Simulated gains in TNSR with doubling sensitivity**

## J. Bodurka, F. Ye, N Petridou, P. A. Bandettini, Mapping the MRI voxel volume in which thermal noise matches physiological noise – implications for fMRI. NeuroImage, 34, 542-549 (2007) 

**J. Bodurka, F. Ye, N Petridou, P. A. Bandettini, Mapping the MRI voxel volume in which thermal noise matches physiological noise – implications for fMRI. *****NeuroImage,***** 34, 542-549 (2007) **

## Finding the “Suggested resolution”

## Slide 14

## ≈ 5 to 30 ms

**≈ ****5 to 30 ms**

**Pruessmann, et al. **

**SENSE Imaging**

**Gain in resolution per window width**
**If shorter readout window is used:**
**Small gain in #slices per TR**
**Reduced distortions**
**Reduced Image SNR**

## SENSE Imaging

**SENSE Imaging**

**Bodurka et al.**

## ?

**Hemodynamics**

**?**

**?**

**?**

**Measured Signal**

**Noise**

**The Hemodynamic Response Function**

## Slide 18

## The effect of increasing spatial resolution

**The effect of increasing spatial resolution**

**Large vessel effects tend to be amplified...**

## Hemodynamic Specificity

**Venous inflow**
**(Perf. No VN)**

**Arterial inflow**
**(BOLD TR < 500 ms)**

**Hemodynamic Specificity**

**Some pulse sequence strategies..**

## Spin-echo, %HbO2 = 60

**Spin-echo, %HbO****2**** = 60**

**Gradient-echo, %HbO****2**** = 60**

**Field strength dependence of intravascular effects **

## Slide 22

## Multi-shot with navigator pulse

- Cheng, et al. (2001) Neuron,32:359-374

- 0.47 x 0.47 in plane resolution

- Menon et al, (1999) MRM 41 (2): 230-235

- 0.54 x 0.54 in plane resolution

**Multi-shot with navigator pulse**

**Detailed structure is extractable**

## Slide 24

## Orientation Columns in Human V1as Revealed by fMRI at 7T

- Scalebar = 0.5 mm

- Orientation Columns in Human V1as Revealed by fMRI at 7T

- Phase Map

- Yacoub, Ugurbil & Harel
- University of Minnesota / CMRR
- HBM 2006

**Technology**

## Perfusion (ASL)

## BOLD

**BOLD**

**Perfusion**

**Simultaneous BOLD and Perfusion**

## Is Vascular Space Occupancy Imaging (VASO) more specific?

- Lu et al, MRM 50 (2): 263-274 (2003)

## Temporal resolution

## Temporal Resolution

**How rapidly can one switch on and off?**

- P. A. Bandettini,, Functional MRI using the BOLD approach: dynamic characteristics and data analysis methods, in  "Diffusion and Perfusion: Magnetic Resonance Imaging" (D. L. Bihan, Ed.), p.351-362, Raven Press, New York, 1995.

## Temporal Resolution

**How brief of a stimulus can one give?**

- R. L. Savoy, et al., Pushing the temporal resolution of fMRI: studies of very brief visual stimuli, onset variability and asynchrony, and stimulus-correlated changes in noise, 3'rd Proc. Soc. Magn. Reson., Nice, p. 450. (1995).

## Temporal Resolution

**Temporal Resolution**

## 0

- 5

- 10

- 15

- 20

- 25

- 30

- 100

- 200

- 300

- 400

- 500

- Number of runs

- 8 sec on/off

- 16 sec on/off

- Smallest latency
- Variation Detectable
- (ms) (p < 0.001)

- t

- 1 run:

- -1000

- -500

- 500

- 1000

- Number

- delay estimate (ms)

- delay = 107ms

**11**

- 1% Noise
- 4% BOLD
- 256 time pts /run
- 1 second TR

## Slide 34

## Hemi-Field Experiment

**Right Hemisphere**

**Left Hemisphere**

## =

**=**

**+ 2.5 s**

**- 2.5 s**

**0 s**

**500 ms**

**500 ms**

**Right**** ****Hemifield**

**Left Hemifield**

**-**

## Task timing modulation

**Task timing modulation**

## No calibration

- Formisano, E. and R. Goebel, *Tracking cognitive processes with functional MRI mental chronometry.* Current Opinion in Neurobiology, 2003. **13**: p. 174-181.

## No calibration

- 11.7 T

## Slide 40

## 11026–11031  PNAS  September 26, 2000 vol. 97  no. 20

## Functional Neuroimaging Techniques

- Log Time (sec)

- Log Size (mm)

- Non-invasive

- Invasive

## Slow Limits...

**Perfusion is better than BOLD for slow “state change” comparisons.. **

**Slow Limits...**

## Perfusion vs. BOLD: Low Task Frequency

- Wang et al., 2002

**Perfusion**

**BOLD**

## Logothetis et al. (2001) “Neurophysiological investigation of the basis of the fMRI signal” Nature, 412, 150-157

**S. M. Rao et al, (1996) “Relationship between finger movement rate and functional magnetic resonance signal change in human primary motor cortex.” *****J. Cereb. Blood Flow and Met.***** 16, 1250-1254.**

## R. M. Birn, et. al, (2001) NeuroImage, 14: 817-826. 

**Logothetis et al. (2001) Nature, 412, 150-157.**

**P. A. Bandettini et al, (2001) Nature Neuroscience, 4:  864-866.**

**R. M. Birn, et. al, (2001**) **NeuroImage, 14: 817-826. **

- Linearity

## Sources of this Nonlinearity

- ∆ Volume

- Flow In

- Flow Out

- Oxygen Extraction

- Neuronal
- Hemodynamic
- Oxygen extraction
- Blood volume dynamics

- Linearity

## Contrast Reversing Checkerboard

- 0

- 1

- 2

- 3

- 4

- 5

- 0

- 5

- 10

- Stimulus Duration (s)

- Amplitude (%)

- 0

- 5

- 10

- 15

- 2000ms

- 1000ms

- 500ms

- 250ms

- time (s)

- Signal

- Estimated Neuronal Activity

*Contrast Reversing Checkerboard*

- Linearity

## Static Grating

- time (s)

- Signal

- time(s)

- Estimated Neuronal Activity

*Static Grating*

- Linearity

## Duty Cycle Effects

- Linearity

**R.M. Birn, et al, NeuroImage, 27, 70-82 (2005) **

## duty cycle effects

**R.M. Birn, et al, NeuroImage, 27, 70-82 (2005) **

- Linearity

## Linearity

## Linearity

**Tuan, Birn et al.**

## Linearity

**Tuan, Birn et al.**

## BOLD post-stimulus undershoot

- A BOLD undershoot without a CBF undershoot could be due to a slow return to baseline of either CBV or CMRO2

**Courtesy Rick Buxton**

**Post Undershoot**

## Simulated BOLD Signal Dynamics

**Post Undershoot**

**Courtesy Rick Buxton**

## Evidence for sustained elevated CMRO2(VASO indicates fast return of CBV despite BOLD undershoot)

- Lu, et al: JCBF+M 24:764, 2004

- All activated voxels

- Overlapped voxels

- VASO (Vascular Space Occupancy)

**Post Undershoot**

## Section on Functional Imaging Methods & Functional MRI Facility Jan 19, 2007

**Section on Functional Imaging Methods**** & ****Functional MRI Facility ****Jan 19, 2007**

**Back row: ****Wenming Luh****, ****Niko Kriegeskorte, Rasmus Birn, Tyler Jones,**** ****Sean Marrett**
**Middle row: ****Jon West,**** Kay Kuhns, ****Anthony Boemio,**** Peter Bandettini, ****Joey Dunsmoor, Doug Ruff, Kevin Murphy**
**Front row: ****Dorian Van Tassel,**** ****Jerzy Bodurka****, ****Adam Thomas****, ****Marieke Mur,**** ****David Knight**** **