Computational requirements for Electrical Impedance Tomography of brain function
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Transcript of Computational requirements for Electrical Impedance Tomography of brain function
Computational requirements for Electrical Impedance Tomography of brain function
David HolderMedical Physics, UCLClinical Neurophysiology, UCH
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Research ClinicalMedical Physics, UCL
David Holder
Kirill AristovichJames AveryTugba DoruHwan KooMarkus JehlMohamed KoronfelElliott MageeEmma MaloneBrett PackhamGustavo SantosAnna Vongerichten
Collaborators
Simon Arridge, CS, UCLTimo Betcke, Maths, UCLBen Hanson, ME, UCLPaul Shearing, Chem Eng, UCL
Eung-Je Woo, BME, S Korea
GE Global Research, Schenectady, USA 221/04/23
Clinical Neurophysiology, UCH
Principal research :Electrical Impedance Tomography of brain function
• A new medical imaging method• Ring(s) of electrodes are placed around the subject• A tiny current is passed at ~50 kHz between various combinations of electrodes • Images of impedance are produced ~10 times per second
• Neuro applications :– Fast neural activity– Acute stroke– Epileptic seizures
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Plane 3
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Plane 1
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xiphoid process
axilla
electrodes
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Frequency in binary steps
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0 Frequency 1 MHz
Current development
Perspex rod
Images :
actual EITEIT of brain function works in :
-Tanks
-Animal studies-Stroke-Epilepsy-Fast neural-Evoked responses
-Does not yet work in patients
Long term goal – fast neural activity, 1 ms, 1 mm
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Every millisecond
Recording protocol (illustrated for square wave)
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Square wave
Evoked potential
Impedance change
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500 ms
EP
Oh, T., Gilad, O., Ghosh, A., Schuettler, M., Holder, D. S. (2011). A novel method for recording neuronal depolarization with recording at 125-825 Hz: implications for imaging fast neural activity in the brain with electrical impedance tomography. Med Biol Eng Comput 49(5), 593-604
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Imaging
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~40 min
1min(120 av)
1min(120 av)
1min(120 av)
1M element rat brain FEM mesh Image ~300um, τ 8 ms reconstruction
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0.2mm, 662,788 elements
Adaptive, 359,797 elements
0.8mm, 49,973 elements
Forward Modelling• Forward solution:
• Computational complexity:
• O(N); O(NlogN);
• 2.106 - 100.106 FEM mesh→ ~ 10-100 Gb Memory ~ 1-30 Gigaflops ~ 10min - 4 hours
Computational considerations
Image reconstruction
• Validation on saline tank phantom using 75k-element cylindrical mesh
• Total variation (TV) regularization:
Projection for future
• Before optimization :– Practical
• ? 10.106 FEM mesh
→ ~ 100 Gb Memory~ 100 Gigaflops~ 2 days per image
– Ideal• ? 100.106 FEM mesh
→ ~ 2 Tb Memory~ 1 Teraflop ~ 20 days per image
• Optimized• ? 106 FEM mesh
→ ~ 10 Gb Memory~ 1 Gigaflop~ 10s per image
150ms
1mm
1.6m
m2.
2mm
2.8m
m3.
4mm
4mm
155ms 160ms 165ms 170ms
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