Editorial Comment—Cerebral Near-Infrared Spectroscopy: How Far Away From a Routine Diagnostic Tool?

Effect of a mirror-like illusion on activation in the precuneus assessed with functional near-infrared spectroscopy

Mirror therapy is a therapy to treat patients with pain syndromes or hemiparesis after stroke. However, the underlying neurophysiologic mechanisms are not clearly understood. In order to determine the effect of a mirror-like illusion (MIR) on brain activity using functional near-infrared spectroscopy, 20 healthy right-handed subjects were examined. A MIR was induced by a digital horizontal inversion of the subjects' filmed hand. Optodes were placed on the primary motor cortex (M1) and the occipito-parietal cortex (precuneus, PC). Regions of interest (ROI) were defined a priori based on previous results of similar studies and confirmed by the analysis of effect sizes. Analysis of variance of the ROI signal revealed a dissociated pattern: at the PC, the MIR caused a significant inversion of a hemispheric lateralization opposite to the perceived hand, independent of the moving hand. In contrast, activity in M1 showed lateralization opposite to the moving hand, but revealed no mirror effect. These findings extend our understanding on interhemispheric rivalry and indicate that a MIR is integrated into visuomotor coordination similar to normal view, irrespective of the hand that is actually performing the task.

Determination of absorption changes from moments of distributions of times of flight of photons: optimization of measurement conditions for a two-layered tissue model

Time-resolved near-infrared spectroscopy allows for depth-selective determination of absorption changes in the adult human head that facilitates separation between cerebral and extra-cerebral responses to brain activation. The aim of the present work is to analyze which combinations of moments of measured distributions of times of flight (DTOF) of photons and source-detector separations are optimal for the reconstruction of absorption changes in a two-layered tissue model corresponding to extra- and intra-cerebral compartments. To this end we calculated the standard deviations of the derived absorption changes in both layers by considering photon noise and a linear relation between the absorption changes and the DTOF moments. The results show that the standard deviation of the absorption change in the deeper (superficial) layer increases (decreases) with the thickness of the superficial layer. It is confirmed that for the deeper layer the use of higher moments, in particular the variance of the DTOF, leads to an improvement. For example, when measurements at four different source-detector separations between 8 and 35 mm are available and a realistic thickness of the upper layer of 12 mm is assumed, the inclusion of the change in mean time of flight, in addition to the change in attenuation, leads to a reduction of the standard deviation of the absorption change in the deeper tissue layer by a factor of 2.5. A reduction by another 4% can be achieved by additionally including the change in variance.

Near infrared spectroscopy for the detection of desaturations in vulnerable ischemic brain tissue: a pilot study at the stroke unit bedside

BACKGROUND AND PURPOSE

There is uncertainty whether bilateral near infrared spectroscopy (NIRS) can be used for monitoring of patients with acute stroke.

METHODS

The NIRS responsiveness to systemic and stroke-related changes was studied overnight by assessing the effects of brief peripheral arterial oxygenation and mean arterial pressure alterations in the affected versus nonaffected hemisphere in 9 patients with acute stroke.

RESULTS

Significantly more NIRS drops were registered in the affected compared with the nonaffected hemisphere (477 drops versus 184, P<0.001). In the affected hemispheres, nearly all peripheral arterial oxygenation drops (n=128; 96%) were detected by NIRS; in the nonaffected hemispheres only 23% (n=30; P=0.17). Only a few mean arterial pressure drops were followed by a significant NIRS drop. This was however significantly different between both hemispheres (32% versus 13%, P=0.01).

CONCLUSIONS

This pilot study found good responsiveness of NIRS signal to systemic and stroke-related changes at the bedside but requires confirmation in a larger sample.

Near Infrared Spectroscopy during pediatric cardiac surgery: errors and pitfalls

As a result of improvements in early outcomes, long-term neurologicalal outcomes are becoming a major issue in pediatric cardiac surgery. The mechanisms of brain injury are numerous, but a vast majority of injuries are impervious to therapy and only a few are modifiable. The quality of perfusion during cardiac surgery is a modifiable factor and cerebral monitoring during bypass is the way to assess the quality of intra-operative cerebral perfusion. Near infrared spectroscopy (NIRS), as a diagnostic tool, has gained in popularity within the perfusion community. However, NIRS is becoming the standard of care before its scientific validation. This manuscript relates four clinical cases, demonstrating the limitations of NIRS monitoring during pediatric cardiac surgery as well as uncertainties about the interpretation of the recorded values.

The clinical relevance of cerebral oxymetry is needed before the use of NIRS as a decision making tool. Multimodal brain monitoring with NIRS, trans-cranial Doppler and electroencephalogram are currently under way in several pediatric centers. The benefit of this time-consuming and expensive monitoring system has yet to be demonstrated.

Cerebrovascular reacivity assessment in patients with carotid artery disease: a combined TCD and NIRS study

BACKGROUND AND PURPOSE

Transcranial Doppler (TCD) and near-infrared spectroscopy (NIRS) are two noninvasive diagnostic tools that have been shown to evaluate cerebral vasomotor reactivity by measuring changes in mean cerebral blood flow velocities (MCBFV) of proximal intracranial arteries and absolute brain-tissue oxygen-saturation (TOS) in microcirculation, respectively, during hemodynamic challenge. We evaluated the potential correlation between TCD and NIRS measurements of vasomotor reactivity (VMR) in patients with carotid artery disease (CARAD).

METHODS

Consecutive patients (n = 24) with CARAD underwent simultaneously TCD and NIRS examinations during voluntary breath-holding (BH). MCBFV and TOS values were recorded at baseline (BAS) and at the end of BH, while BH duration (DBH) was documented. VMR was quantified by means of TCD-BHI (Breath-holding Index: [MCBFV(BH) - MCBFV(BAS)]× 100/MCBFV(BAS)/DBH) and NIRS-BHI ([TOS(BH) - TOS(BAS)]× 100/ TOS(BAS)/DBH).

RESULTS

TCD-BHI correlated positively with NIRS-BHI in the affected side (r = .538, P = .007). A stronger correlation between TCD-BHI and NIRS-BHI was documented in the nonaffected side (r = .768, P< .001). After adjusting for demographic characteristics, stroke risk factors and symptomatic status NIRS-BHI was linearly and independently associated with TCD-BHI both in the affected (β:+ .813, P = .001) and unaffected (β:+ .823, P < .001) side.

CONCLUSIONS

Circulatory assessment of VMR in proximal cerebral vessels by TCD correlates positively to functional measurements of VMR in microcirculation by NIRS in CARAD patients.

Is there a role of near-infrared spectroscopy in predicting the outcome of patients with carotid artery occlusion?

BACKGROUND

Transcranial Doppler (TCD) studies demonstrated that cerebral vasomotor reactivity (VMR) can predict the outcome of carotid artery occlusion (CAO). Near-infrared spectroscopy (NIRS) is a non-invasive optical method for assessing hemoglobin (Hb) oxygenation parameters. The purpose of this study was to evaluate the role of NIRS parameters as prognostic markers of stroke occurrence in patients with CAO.

METHODS

Sixty-five patients (46 men, mean age 68.8 years) with CAO were enrolled. Forty-two patients had previous cerebrovascular events (15 TIA, 27 minor stroke), the remaining 23 were asymptomatic. All subjects underwent simultaneous TCD and NIRS examination at rest and after hypercapnia. All patients completed follow-up (median, 36 months).

RESULTS

During follow-up, 11 strokes occurred. Cerebral VMR measured by TCD had a prognostic role in stroke occurrence (p=0.042). The increase in Hb oxygen saturation detected by NIRS during hypercapnia predicted the occurrence of new cerebrovascular events, although without an overt significance (p=0.058). Hb oxygen saturation at rest, however, failed to be of prognostic value (p=0.65).

CONCLUSIONS

NIRS is potentially useful in monitoring cerebral oxygenation; however, at present NIRS does not effectively predict the outcomes of stroke or vascular death in patients with CAO. This study does confirm the primary role of TCD VMR in the outcome of carotid disease.

Increased cerebral vasomotor reactivity in migraine with aura: an autoregulation disorder? A transcranial Doppler and near-infrared spectroscopy study

Migraine with aura (MA) is associated with changes in cerebral blood flow (CBF), whereas the role of cerebral autoregulation is uncertain. This study aimed to evaluate basal CBF, cerebral blood volume (CBV) and vasomotor reactivity (VMR) in MA patients. Twenty-one controls and 16 MA patients (eight with side predominance) underwent simultaneous examination of flow velocity in the middle cerebral arteries by transcranial Doppler (TCD) and of near-infrared spectroscopy (NIRS) parameters [oxygen haemoglobin saturation: oxygen%, and total haemoglobin content (THC)] at rest and after hypercapnia. Cerebral VMR, THC and oxygen% increases were significantly greater on the predominant compared with the non-predominant migraine side, with both sides of patients without side predominance and with controls. These findings suggest altered autoregulation in MA patients, possibly secondary to impaired cerebrovascular autonomic control. Simultaneous TCD and NIRS investigation could represent a non-invasive approach to evaluate cerebral haemodynamics at the cortical and subcortical level.

Neuromonitoring in the intensive care unit. II. Cerebral oxygenation monitoring and microdialysis

BACKGROUND

Monitoring the injured brain is an integral part of the management of severely brain injured patients in intensive care. There is increasing interest in methods to monitor global and regional cerebral oxygenation. There have been significant advances in analysing tissue oxygenation and local metabolites in the injured brain over the past decade.

DISCUSSION

Cerebral oxygenation can be assessed on a global or regional basis by jugular venous oximetry and near infra-red spectroscopy respectively. Techniques of brain tissue oxygenation monitoring and microdialysis are also covered in this review.

CONCLUSIONS

Various modalities are available to monitor oxygenation and the local milieu in the injured brain in the intensive care unit. Use of these modalities helps to optimise brain oxygen delivery and metabolism in patients with acute brain injury.

A quantitative near-infrared spectroscopy study: A decrease in cerebral hemoglobin oxygenation in Alzheimer’s disease and mild cognitive impairment

A newly developed quantitative near-infrared spectroscopy (NIRS) system was used to measure changes in cortical hemoglobin oxygenation during the Verbal Fluency Task in 32 healthy controls, 15 subjects with mild cognitive impairment (MCI), and 15 patients with Alzheimer's disease (AD). The amplitude of changes in the waveform, which was quantitatively calculated by a signal processing method, was significantly lower in the frontal, and the bilateral parietal areas in the AD group, whereas that in the MCI group was significantly lower only in the right parietal area. The NIRS system may be a potential tool for the primary screening of AD.

Hemoglobin oxygen saturation as a marker of cerebral hemodynamics in carotid artery occlusion

Cerebral hemodynamics play a pivotal role in stroke pathogenesis. Transcranial Doppler (TCD) studies demonstrated the importance of cerebral vasomotor reactivity (VMR) on the outcome of carotid artery occlusion (CAO). So far, positron emission tomography represents the best technique for detecting both hemodynamic and metabolic aspects of cerebral perfusion adaptive processes in cerebrovascular patients. Near-infrared spectroscopy (NIRS) is a new method allowing for a non-invasive assessment of cerebral blood flow and hemoglobin (Hb) oxygenation parameters.A recent TCD and NIRS study demonstrated that patients with symptomatic CAO had lower VMR values measured by TCD and lower oxygen saturation (oxygen%) increases detected by NIRS than asymptomatic ones. The parameters were obtained simultaneously after CO(2) inhalation. The present study aims to investigate if Hb oxygen % could represent also at rest a marker of hemodynamic status in carotid disease.Thirty-five symptomatic and 17 asymptomatic patients with CAO underwent a simultaneous examination by means of TCD and NIRS at rest condition and during CO(2) reactivity test. Symptomatic patients presented with oxygen% values at rest higher (p = 0.001) and VMR values lower (p < 0.001) than asymptomatic subjects. According to a logistic model, for each unitary VMR increase, the odds of being symptomatic decreases of about 10% (OR = 0.9, p = 0.001); for each unitary increase of oxygen% at baseline, this odd increases of about 23% (OR = 1.23, p = 0.031). In addition to TCD VMR values, oxygen hemoglobin saturation at rest detected by NIRS can discriminate symptomatic from asymptomatic patients with CAO. NIRS can add an important contribution to explain pathophysiological mechanisms of stroke occurrence.