Background:
Near-infrared Spectroscopy (NIRS) may provide continuous, multiregional parenchymal bedside perfusion monitoring without the risks of patient transport, contrast, or radiation. Time-domain NIRS (TD-NIRS) uses pulsed light attenuation at multiple wavelengths (600-950 nm) to discretely quantify oxyhemoglobin and deoxyhemoglobin and determine total hemoglobin, oxygen saturation (OS) and cerebral blood volume (BV) in the region between each light source and detector. This study aimed to assess the feasibility of employing a novel TD-NIRS technology to assess absolute levels of cerebral BV and OS with broad spatial coverage in order to detect regions of ischemia.
Methods:
Ischemic stroke (IS) and subarachnoid hemorrhage (SAH) patients underwent TD-NIRS measurements. IS patients were fitted with a rectangular probe over the region of ischemia (2 rows of 4 sources between 3 rows of 5 detectors), using CT as a guide (external acoustic meatus as reference). SAH patients were fitted with a linear “anterior crown” probe with light sources and detectors arranged alternating in a single row (7 sources, 6 detectors). Clearance above the frontal sinus was guided by CT imaging (nasion as reference). 1.8 cm separated all source-detector pairs. Time-correlated single photon-counting photomultiplier tubes detected photons to measure absorption of pulsed light emitted at 3 wavelengths (690, 805, and 835 nm). Maximal OS (OSmax) and BV (BVmax) were calculated for the entire region measured by the probe to enable multiple comparisons.
Results:
In IS patients, ischemic regions (n=4) had an OSmax of 65.8 SD 13.1; contralateral normal tissue had an OSmax of 85.3 SD 27.1 (paired t-test; p 0.14). Ischemic regions had a BVmax of 76.25 SD 24.17 compared with 104.0 SD 42.5 in contralateral normal tissue (p 0.18). Regional inspection showed good visual correlation with infarcts (
Figure
). Of SAH patients with serial measures (n=2), one developed heparin-induced thrombocytopenia and bilateral infarcts, coincident with decreased BVmax on the right (72, day 1; 48, day 12) and left (153, day 1; 56, day 12); OS did not change.
Conclusion:
We were able to calculate multiregional BV and OS for patients with cerebral ischemia. Despite small sample size, we demonstrated a trend between contralateral (ischemic stroke) and historical (subarachnoid hemorrhage) controls. Leakage of light and absorption by hair produced artifacts that will require improvement in future applications. This system requires validation and further ergonomic refinement but has potential to enable continuous multiregional parenchymal monitoring.
Time-domain near-infrared spectroscopy in acute ischemic stroke patients
