IIIT Hyderabad Publications
Development of Point of Care Testing Device for NIRS Based Online Imaging During Electric Brain Stimulation
Author: Utkarsh Jindal
Report no: IIIT/TH/2016/69
Advisor:Shubhajit Roy Chowdhury,Rahul Shrestha
In this thesis we present the development of a low cost point of care testing(POCT) device for mon- itoring cerebral oxygenation using near infrared spectroscopy (NIRS). The changes in optical measurements of tissue oxy-(HbO2) and deoxy-(Hb) hemoglobin concentration can be monitored using NIRS and these changes can be coupled with anodal transcranial direct current stimulation (tDCS) to find impairments in the cerebral micro-vessels functionality, where impairments in cerebral microvessels functionality may lead to impairments in the cerebrovascular reactivity (CVR). In fact severely reduced CVR predicts the chances of transient ischemic attack and ipsilateral stroke. The feasibility studies on healthy subjects and stroke survivors showed detectable changes in the NIRS responses to anodal tDCS of current density 0.526 A/m 2 . A clinical studyhas been conducted on 14 stroke survivors using our NIRS data acquisition (DAQ) device and our anodal tDCS device. This study revealed that the lesioned hemisphere with impaired circulation showed significantly (p <0.01) less change in HbO2 concentration than the non-lesioned side in response to anodal tDCS. The NIRS sensors used in the study are not disposable as opposed to the present state of the art technology. Our low cost NIRS-DAQ device has been further integrated with the commercially used CE-approved SomaSensor (Covidien, USA). This was done under a ”clinical study in human subjects of a CE-marked device (being used within indication) to evaluate additional parameters.” Here, Medical Devices Directive covers a diverse range of devices that are classified into one of four risk-based Classifications. Our SomaSensor based low-cost NIRS data acquisition device to monitor hemodynamics during non-invasive brain stimulation (NIBS) should be classified as Class IIa - Medium risk, often short-termnon-invasive device. The reusability of the SomaSensor was also tested as the commercially used SomaSensors are labelled as disposable. A large chunk of the complete cost of the NIRS setup comes from the procurement of the CE-approved SomaSensors. By proving the reusability of the SomaSensors the complete cost of the NIRS setup was also reduced. The performance of the SomaSensor interfaced with our low cost NIRS-DAQ device was also tested with the help of a dual layer dynamic phantom filled human blood and intralipid. NIRS and anodal tDCS have been further combined with electroencephalography (EEG) to develop a NIRS-EEG/tDCS joint-imaging method. This was done to investigate local post-tDCS alterations from baseline at the site of anodal tDCS using NIRS-EEG/tDCS joint-imaging. In a separate study the changes in local post-tDCS alterations in motor evoked potentials (MEP)-measure of corticospinal excitability were investigated. We found that post-tDCS changes in the mean regional cerebral oxygen saturation (rSO 2 ) from baseline mostly correlated with the corresponding post-tDCS change in log-transformed mean-power of EEG within 0.5Hz - 11.25Hz frequency band. Moreover, a decrease in log-transformed mean power of EEG within 0.5Hz - 11.25Hz frequency band corresponded with an increase in the MEP-measure of corticospinal excitability found in the second study. Therefore, we propose to combine NIRS-EEG/tDCS joint-imaging with corticospinal excitability investigation in a single study to confirm these findings.
Full thesis: pdf
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