Download - 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
03/05/2023© The University of Sheffield
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)
03/05/2023© The University of Sheffield
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)
03/05/2023© The University of Sheffield
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
03/05/2023© The University of Sheffield
Biological basis
Source: fMRIB Introduction to fMRI
Fast fMRI BOLD fMRI
03/05/2023© The University of Sheffield
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
03/05/2023© The University of Sheffield
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
03/05/2023© The University of Sheffield
• 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.
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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
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3- Possible fast fMRI responses in the visual cortex
1 MR image shows an axial slice position in the sagittal plane scout image
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.
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2- mapping of motor sensory cortex function
1 MR image shows an axial slice position in the sagittal plane scout image
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
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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.
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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.