Authors :
Sami Heymann, MD – Hadassah Medical Center
Netaniel Rein, MD – Hadassah Medical Center
Marco Zurita, MD – Hadassah Medical Center
Revital Shechter, PhD – Hulon Institute of Technology
Zvi Israel, MD PhD – Hadassah Medical Center
Michal Balberg, PhD – Hulon Institute of Technology
Presenting Author: Mordekhay Medvedovsky, MD PhD – Hadassah Medical Center
Guy Rosenthal, MD – Hadassah Medical Center
Rationale:
Rationale – Functional near-infrared spectroscopy (fNIRS) measures brain activity based on neurovascular coupling by detecting the attenuation of near-infrared (NIR) light by oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR). Scalp fNIRS is limited to a depth of 1.5-2 cm, restricting it to superficial brain areas and is also subject to various artifacts. Previous studies have shown fNIRS can detect peri-ictal activity1. To overcome the limitations of scalp fNIRS and the tunnel vision of stereotactic EEG (SEEG), an intracranial fNIRS (ifNIRS) system with optical anchoring bolts (OAB) and depth optodes (Figure 1) was developed and evaluated for its ability to detect HbO2 and HbR fluctuations in an animal model.Methods:
Methods – A previously described swine model of cerebral edema, induced by continuous infusion of hypotonic fluids, was used on 3 female pigs, followed by removal of 2.15-2.5L of blood from each animal via an arterial canula. This procedure was designed to create variations in brain Hb that the ifNIRS system could detect. Despite our end goal of creating a combined ifNIRS and SEEG system for use in patients with DRE and the existence of a swine epilepsy model, this model was chosen for its accessibility at our center and its relative simplicity. Under general anesthesia and fluoroscopy guidance, three OABs and two intracranial depth optodes were implanted per animal. Each depth optode had an emitter, and both detectors and emitters were placed in the OAB. NIR light at wavelengths of 785nm and 830nm was used for HbR and HbO2 level measurements respectively. Total Hb (tHb) was calculated by summation of HbO2 and HbR.
Intracranial pressure, mean arterial pressure and blood gases were measured at baseline, during fluid infusion and bleeding. This terminal experiment was approved by the institutional ethics committee.Results:
Results – In 10 out of 12 ifNIRS channels across all three pigs, tHb levels, as measured by ifNIRS, gradually decreased during bleeding (Figure 2). The two channels that did not show a decrease in tHb were unreliable due to either channel saturation or an unmeasurable signal near the initiation of bleeding. The observed decrease in tHb was consistent in both depth optode-to-OAB channels and OAB-to-OAB channels.
During the infusion of hypotonic saline, two patterns emerged. In 2 animals a steady increase in measured tHb with a greater increase in HbO2 was seen. The third animal had variable tHb patterns with relative increase in HbR. The first pattern could be explained by venous collapse, and the second by arterial vasospasm.Conclusions:
Conclusion – This study demonstrates that ifNIRS, incorporating both OAB and depth optodes, can detect in vivo fluctuations in hemoglobin levels. This method shows potential for depth detection of peri-ictal hemodynamic changes and could be effectively combined with SEEG.Funding:
This work was funded by the Israeli Innovation Authority -grants numbers 77084 and 77092.
1. Seyal, Masud. "Frontal hemodynamic changes precede EEG onset of temporal lobe seizures." Clinical Neurophysiology 125.3 (2014): 442-448.