advance fmri (fast fmri)

Advanced functional MRI

(Fast fMRI)

Shwan KakaMedical School Department of

Cardiovascular Science

03/05/2023© The University of Sheffield

Outline I • Introduction (CH1)• Fast fMRI vs. BOLD technique• Biological basis• Methodology (CH2)

• Phantom Study (CH3) 1- Axon phantom2- Conductive Gel Phantom3- NaCl Solution phantom


Outline II • Subject studies

1- Rapid functional MRI measurements of the wrist using TENS stimulation of the median nerve (CH4)

2- Visual stimulation – a comparison of direct detection fast fMRI with the BOLD technique (CH5)

3- Rapid functional MRI measurements of the thalamus and motor-sensory cortex using stimulation of the median nerve. In addition, real and imaginary finger tapping (CH6)

• Conclusion and future work (CH7)


What is fast fMRI?

• Fast Functional Magnetic Resonance Imaging (fast fMRI): uses MRI to measure nerve or brain activity directly

• Uses MRI to detect the electromagnetic field that is generated by ionic currents (action potential)


Why use fast fMRI?

• Provide excellent temporal resolution of neuronal population dynamics as well as capabilities for source localization

• To better understand brain and nerve function in animals and humans


Biological basis

Source: fMRIB Introduction to fMRI

Fast fMRI BOLD fMRI

http://www.fmrib.ox.ac.uk/fmri_intro/




Fast fMRI• Dependent on transient

ionic currents• Active-population of firing

action potentials

• Electromagnetic field generated by ionic currents

• Differences in magnitude and phase distribution can be measured (T2*)

• Dependent on the Blood Oxygen Level Dependent signal

• Active-increased in oxyhemoglobin: deoxyhemoglobin

• Diamagnetic vs. Paramagnetic

• Differences in magnetic susceptibility can be measured (T2*)

BOLD fMRI


Volunteer studies - methodologySubject preparation

• All volunteer experiments were performed in accordance with local ethical committee guidelines and approval. (12 volunteers) .

MRI data acquisition• fMRI data were acquired with a 1.5 Tesla MR Scanner using

an 8 channel array wrist and head coil with the following EPI imaging parameters; TR/TE=88/25 ms, flip angle=90o, acquisition matrix=64x64, FOV =240mm, slice thickness=5mm and 3.75 mm in- plane resolution with 500 dynamic scans


• TENS (transcutaneous electrical nerve stimulation) The median nerve and somatosensory cortex were

activated using a voltage ~80V applied to the palm of the hand.

• Strobe light The visual cortex was activated using a flashing light (QTX

20W Mini) located outside the magnet room.

• These areas were stimulated with high frequencies > 2.5 Hz

Stimulation presentation

03/05/2023© The University of Sheffield03/05/2023© The University of Sheffield

Data Analysis• The fMRI data was analysed using MATLAB 6.5

software programs.

03/05/2023

Volunteer studiesReference Control Experiments.• Each subject was tested with a control scan without stimulation

prior to the stimulation experiments.• The control experiments showed spectral peaks due to heart

beat and respiration only. • No specific frequency responses were recorded at the

stimulation frequency from the median nerve, somatosensory cortex or visual cortex in the control experiments.

Figures for fast fMRI Fourier transform of MR time series of the median nerve, the motosensory and the visual cortex at rest state (control experiments)

03/05/2023

• ROI’s were selected in the median nerve and in muscle tissue, Figs 2 and 3.

• Fig 4. shows a typical response at 2.8 Hz recorded from the ROI in the median nerve (blue) but not from muscle tissue (red).

1- Responses in the Median Nerve

Median nerve

1 MR image shows an axial slice position in the sagittal plane scout image

2 Anatomy MR Image 3 GE-EPI magnitude image in axial plane during the ROI stimulated at

2.8Hz, with Z=2.5A.U

f (Hz)

4 FT of MR time series 2.8Hz

Stimulation frequency

03/05/2023

3- Possible fast fMRI responses in the visual cortex


2 Functional overlay on MR Image , with Z=2.5

3 GE-EPI magnitude image in axial plane showing the ROI stimulated at

2.8Hz

4 FTof MR time series 2.8Hz

• Fig. 2 shows a typical response on the overlay image from an acquisition calculated with a Z score = 2.5.

• A typical ROI selected in the visual cortex is shown in Figure 3.

• Fig. 4 shows a Fourier transform of the MR time series illustrating the frequency spectrum from the ROI in the visual cortex during visual stimulation at 2.8Hz which correlates with the task stimulation frequency.

03/05/2023

2- mapping of motor sensory cortex function


2 Function overlay MR Image, with Z=2.5 3 GE-EPI magnitude image in axial plane during the ROI stimulated at

2.7Hz. A.U

f (Hz)

4 FT of MR time series 2.7Hz

• Figure 2 shows a Z map (Z>2.5) overlaid on the EPI image showing response in the motor-sensory area.

• This location was selected in the motor cortex as shown in the ROI in figure 3 using the axial plane for acquisition.

• Figure 4 shows the spectral response from the motor-sensory area at 2.7 Hz with SNR>3:1. and the heartbeat at approximately 1.1 Hz.

Stimulation frequency

03/05/2023

Conclusions

• Evidence of fast fMRI responses in the median nerve, the somatosensory and visual cortices during ROI area stimulation by TENS and strobe light were observed at high stimulation frequencies > 2.5 Hz.

• Similar responses were observed at the applied stimulation frequencies with SNR>3:1 in volunteers for the median nerve, the somatosensory and visual cortices respectively.

• Fast fMRI did appear to detect weak response to the stimulated frequencies and seeks to improve the spatial and temporal accuracy in detecting neuronal function compared to conventional BOLD fMRI.

03/05/2023

Acknowledgements

I gratefully acknowledge the sponsorship of the Human Capacity Development Program in Kurdistan Regional Government.

I take this opportunity to express my gratitude and regards to Professor Martyn Paley/ Academic Radiology/ Department of Cardiovascular Science for his exemplary guidance, monitoring and constant encouragement throughout the course of this study

Prof. Martyn Paley

Thank you very much to the volunteers who participated in the experiments we have carried out under ethical permission from the University.

advance fmri (fast fmri)

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