DYNOT / fNIRS

Dynamic Optical Tomography (DYNOT) is an enhanced form of the functional imaging technique often referred to as Functional Near-Infrared Spectroscopy (fNIRS).  DYNOT is the use of optical tomography (OT) to produce 3D images revealing the brain dynamics of the vascular response to neuroactivation. DYNOT provides information like that derived from fMRI, but richer.  DYNOT costs far less than fMRI, has none of the complicated and expensive siting requirements, is inherently compatible with EEG, is portable and allows experiments involving patient movement.

The ability of near infrared light to penetrate through the cranium and interact with the cerebral cortex has prompted investigators for many years to explore the utility of near infrared methods for measuring brain activity. DYNOT extends NIR spectroscopic studies to provide for collection of 3-D tomographic images that detail the dynamics of the vascular response to various forms of neuroactivation. Unlike in functional Magnetic Resonance Imaging (fMRI) the optical method can distinguish between changes in deoxyhemoglobin levels caused by a variation in blood volume or blood oxygenation. In addition, optical methods allow for experimental paradigms that are highly impractical or infeasible with other functional imaging modalities due to restricted patient access and limited freedom of patient movement. While studies using DYNOT for brain imaging applications are just beginning in a serious way, the application domain to the clinical, investigative and other communities is vast.

An example of the image quality obtained using the DYNOT imager is shown at right. Here we imaged the oxyhemoglobin response to activation of the motor cortex in response to finger tapping. The image shown is a result of an GLM computation using a boxcar model function applied to a time series of unconstrained reconstructed 3D images overlaid on a representative brain map obtained by MR. The inset shows an orthogonal view of the image revealing that the region of activation is truly subsurface.

Value/Advantages

• High temporal resolution.
• Excellent intrinsic sensitivity to hemoglobin.
• 3D imaging capability.
• Measurements possible with a variety of tasks.
• Easily adapted to incorporate other measurement techniques (EEG, fMRI).
• Economical, portable, scalable.

Utility for Brain Imaging

Disturbances in brain function can have immediate, severe and lifelong consequences. Monitoring activity of the brain holds considerable significance to a broad range of clinical fields (e.g., neonatology, psychiatry, gerontology, emergency care medicine, neurology) and to a variety of practical problems that range from the study of learning disorders to issues of Homeland Security. Underscoring the expected utility of fNIRS to this area is the well-founded idea that accompanying neural activation is a vascular response that to serves replenish activated tissue with improved blood flow. Functional studies have shown that the brain activation produces a spatially distributed and temporally varying response. Techniques such as electroencephalography (EEG) and its magnetic equivalent, magnetoencephalography (MEG), provide a high degree of temporal resolution but have markedly reduced spatial resolution, especially for EEG, compared to anatomic imaging techniques (e.g., MR, CT). An imaging modality that is proving to have significant impact in investigative studies is functional MRI (fMRI). This technique is sensitive to the vascular response resulting from neuroactivation, specifically to the level of deoxyhemoglobin. While the utility of fMRI continues to expand, it is also clear that the technique has a number of limitations that are not encountered using near infrared techniques.

Specific Applications	Physiological Relevance	Advantages	Complementary Modalities
Study of motor sensory functions Cognitive neuroscience Learning/attention disorders Pharmaceutical applications Drug dependency Psychiatric disorders Epilepsy Stroke Trauma/Intensive Care Senile dementia Parkinson's disease	Cortical vascular response to neuroactivation	Non-invasive, real-time High temporal resolution High sensitivity to hemodynamics Long term monitoring feasible	fMRI/BOLD EEG MEG PET/SPECT