[Assessment of cerebral ischemia by oxygen pulse-based near-infrared optical topography]

SPECT and angiography are used to assess the cerebral blood flow dynamics; however, they have several drawbacks such as physical stress on the patients and considerable invasiveness. In order to overcome these drawbacks, we proposed and verified an alternative method of involving optical topography (OT).

We used a 48-channel OT system with the 2 faces of 3 x 5 probe-holders on the patient's head, covering the bilateral fronto-temporal areas. The study was conducted with 11 normal volunteers and 30 patients with cerebral ischemia (ICA or MCA stenosis). All measurements were performed at a constant frequency of 10 Hz. In a block fashion, the subjects inhaled room air followed by oxygen for 2 minutes and then room air again, and SpO2 were monitored at the subjects' finger tips. In some cases, IMP-SPECT was performed.

The level of oxyhemoglobin measured by OT in the normal brain regions showed a trapezoid increase in accordance with oxygen inhalation, and similar results were obtained for SpO2. In the ischemic regions, the oxyhemoglobin increase was delayed and/or its height was lower. These observations suggest that the transmission of the systemic SpO2 wave pattern was delayed and its extent was lower in the ischemic region; this phenomenon can be utilized to detect the tissue ischemia. Principal component analysis was performed based on the SpO2 wave pattern. No lateralities were observed in 81.8% of the normal cases. However, in the ischemic cases, the weights of the principal components in the ischemic regions were reduced, and these findings agreed with the SPECT findings regarding of ischemia in 76.2% of the cases.

Our results suggested that the regional attenuation of the oxhemoglobin wave demonstrated by principal component analysis reflects the ischemic state of cerebral blood flow. This novel method uses oxyhemoglobin as an OT. It can be clinically utilized as a real-time noninvasive method for the assessment of cerebral ischemia.