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Optical Topography: An overview. Nima Kasraie Spring 2007. What When Where. Oxymetric Near Infrared Imaging Images higher order brain functions Developed by Hitachi Advanced Research Laboratory Already in clinical use in Japan. Red Light Transmission . Features. Small Easy to use

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Optical topography an overview

Optical Topography: An overview

Nima Kasraie

Spring 2007


What when where
What When Where

  • Oxymetric Near Infrared Imaging

  • Images higher order brain functions

  • Developed by Hitachi Advanced Research Laboratory

  • Already in clinical use in Japan.



Features
Features

  • Small

  • Easy to use

  • Patient mobility

  • Extended recordings

  • Not noisy

  • Aclaustrophobic

  • “Real time” imaging


Principle of ot system
Principle of OT system

  • 1.5mW NIR laser diode illuminates head from optical fibers attached to headset.

  • dmax≈ 3cm

  • Reflection (0.1%)

  • Detection


3cm ≈ dcortex





Resolution
Resolution produces a better SNR than time-sharing and time-resolved methods.


Physiological noise
Physiological Noise produces a better SNR than time-sharing and time-resolved methods.


  • The presence of low frequency modulation of both vascular (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.

  • The cause of these low frequency oscillations are not exactly known

  • but may be attributed to extra-cerebral activities such as respiration.

  • One method of removing the low frequency artifact is to convolve the response signal with a model of stimulus signal.


Similarities with fMRI (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.



Differences with fmri
Differences with fMRI (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.


In concept

In concept (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.

fMRI measures differences between the Fe content in blood based on the metal’s response to the magnetic field.

OT relies on different light absorption characteristics of the two forms.


In operation

In operation (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.

Lower spatial resolution than fMRI

2mm vs. 20mm

Higher temporal resolution than fMRI

1 Sec vs. 1 mSec


  • fMRI and OT can be complementary (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.

  • Can also be combined with structural imaging


Current applications
Current applications (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.

  • Developmental plasticity

    • Neonatology (only functional imaging method)

  • Neurosurgery

    • Identifying the focus of epileptic seizures i.e. check for dominant hemisphere (e.g. Broca’s area) before removal of eliptogenic tissue


Concluding remark
Concluding remark (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.

OT does not measure exact blood volume concentrations; it measures concentration changes of molecular species, including oxyhemoglobin and deoxyhemoglobin.


References and further reading (Hb, HbO) and metabolic responses to visual stimuli with unknown origin have been observed.

  • Spinney, Laura. "Optical topography and the color of blood: OT gives neuroscientists a new and faster view of the brain, and an alternative to fMRI." The Scientist 19.2 (Jan 31, 2005): 25(3).

  • Hideaki Koizumi, “Optical topography: practical problems and new applications”. Applied Optics, Vol. 42, No. 16, June 2003

  • Il-Young Son, “Near Infrared Imaging and Spectroscopy for Brain Activity Monitoring”.

  • http://www.medphys.ucl.ac.uk/research/borl/sheddinglight/brain.htm

  • http://www.hitachi-medical.co.jp/info/opt-e/index.html


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