We review our most recent results on near-IR studies of human brain activity, which have been evolving in two directions: detection of neuronal signals and measurements of functional hemodynamics. We discuss results obtained so far, describing in detail the techniques we developed for detecting neuronal activity, and presenting results of a study that, as we believe, confirms the feasibility of neuronal signal detection. We review our results on near-IR measurements of cerebral hemodynamics, which are performed simultaneously with functional magnetic resonance imaging (MRI) These results confirm the cerebral origin of hemodynamic signals measured by optical techniques on the surface of the head. We also show how near-IR methods can be used to study the underlying physiology of functional MRI signals.

In this paper we discuss temporal and spatial patterns of brain hemodynamics under rest and motor stimulation conditions obtained by functional magnetic resonance imaging and simultaneous fast multi-channel near-infrared spectro-imaging in the human motor cortex. Our data indicate that the main difference between the brain hemodynamics under the repetitive stimulation and the rest conditions is not in the appearance of hemoglobin concentration changes during the stimulations (since fluctuations occur at rest as well), but in their more regular, Le. phase-synchronous with the stimulation behavior.

To study the behavior of cerebral physiological parameters and to further the understanding of the functional magnetic resonance imaging (fMRI) blood-oxygen-level-dependent (BOLD) effect, multisource frequency-domain near-infrared and BOLD fMRI signals were recorded simultaneously during motor functional activation in humans. From the near-infrared data information was obtained on the changes in cerebral blood volume and oxygenation. To relate our observations to changes in cerebral blood flow the well-known "balloon" model was employed. Our data showed that the deoxyhemoglobin concentration is the major factor determining the time course of the BOLD signal. The increase in cerebral blood oxygenation during functional activation is due to an increase in the velocity of blood flow, and occurs without significant swelling of the blood vessels.

The aim of our study was to explore the possibility of detecting hemodynamic changes in the brain using the phase of the intensity modulated optical signal. To obtain optical signals with the highest possible signal-to-noise ratio, we performed a series of simultaneous NIRS-fMRI measurements, with subsequent correlation of the time courses of both measurements. The cognitive paradigm used arithmetic calculations, with optical signals acquired with sensors placed on the forehead. Measurements were done on seven healthy subjects. In five subjects we demonstrated correlation between the hemodynamic signals obtained using NIRS and BOLD fMRI. In four subjects correlation was found for the hemodynamic signal obtained using the phase of the intensity modulated signal.

The aim of this study was to compare functional cerebral hemodynamic signals obtained simultaneously by near infrared spectroscopy (NIRS) and by functional magnetic resonance imaging (fMRI). The contribution of superficial layers (skin and skull) to the NIRS signal was also assessed. Both methods were used to generate functional maps of the motor cortex area during a periodic sequence of stimulation by finger motion and rest. In all subjects we found a good collocation of the brain activity centers revealed by both methods. We also found a high temporal correlation between the BOLD signal (fMRI) and the deoxy-hemoglobin concentration (NIRS) in the subjects who exhibited low fluctuations in superficial head tissues.

Frequency-domain near-infrared spectro-imaging offers significant advantages over the continuous-wave method in human brain applications. However, the drawback of existing instruments is a low signal-to-noise ratio for measured phase and modulation depth changes caused by cerebral activation. In this paper we show that in the case of the geometry specific for the activated area in the human brain, the SNR can be significantly improved by increasing the modulation frequency. We present the results of two studies: one performed experimentally using a subnanosecond pulsed light source and a spherical absorbing inhomogeneity immersed in a highly scattering solution, and the other performed numerically using Monte Carlo simulations of light transport in an MRI based digital phantom of the adult human head. We show that changes caused by the absorbing inhomogeneity in both phase and modulation depth increase with frequency and reach maximum values at frequencies between 400 and 1400 MHz, depending on the particular source-detector distance. We also show that for the human head geometry an increase of the modulation frequency from 100 to 500 MHz can increase the phase SNR 2-3 times, and the modulation depth SNR up to 10 times.

Frequency-domain near-infrared spectroscopy and imaging offer significant advantages over the continuous-wave method in human brain applications. However, the drawback of existing instruments is a low signal-to-noise ratio for measured phase and modulation depth changes caused by cerebral activation. In this paper we show that in the case of the geometry specific for the activated area in the human brain, the SNR can be significantly improved by increasing the modulation frequency. We present the results of a study performed experimentally using a sub-nanosecond pulsed light source and a spherical absorbing object immersed in a highly scattering solution. We show that changes caused by the absorbing inhomogeneity in both phase and modulation depth increase with frequency and reach maximum values at frequencies between 400 and 1400 MHz, depending on the particular source-detector distance. We also show that for the semi-infinite geometry an increase of the modulation frequency from 100 to 500 MHz can increase the phase signal-to-noise ratio 2-3 times, and the modulation depth SNR up to 10 times.

Near-infrared spectroscopy is a relatively new imaging method, which can provide important information on concentrations of oxy-and deoxy-hemoglobin in cortical areas of the brain. We discuss the advantages of the integration of magnetic resonance and optical imaging techniques and present the results of our experimental study on the comparison of optical and fMRI signals obtained simultaneously on humans during functional activity and at rest. In all subjects we found a good collocation of the brain activity centers revealed by both methods. We also found a high temporal correlation between the BOLD signal (fMRI) and the deoxy-hemoglobin concentration (near-infrared spectroscopy) in the subjects who exhibited low fluctuations in superficial head tissues. The contamination of optical signals superficial tissue layers urgers applying algorithms of three-dimensional optical tomography.

Purpose

The Anal Cancer HSIL Outcomes Research (ANCHOR) trial aims to determine whether treating precancerous anal high-grade squamous intraepithelial lesions (HSIL), versus active surveillance, is effective in reducing anal cancer incidence in HIV-infected individuals. We evaluated the reliability (i.e., internal consistency, test-retest) and between-group stability of a 25-item ANCHOR Health-Related Symptom Index (A-HRSI).

Methods

ANCHOR participants at least 1-month post-randomization to treatment or active surveillance completed the A-HRSI via telephone. Participants were contacted 7-10 days later to complete the A-HRSI and a participant global impression of change (PGIC) item.

Results

Participants (n = 100) were enrolled (mean age = 51.4, 79% cisgender-male, 73% African American, 9% Hispanic) from five ANCHOR sites. Cronbach's α was good for the physical symptoms (0.82) domain and fair for the physical impacts (0.79) and psychological symptoms (0.73) domains. Intraclass correlation coefficients were good for each of respective domains (i.e., 0.80, 0.85, and 0.82). There were no significant differences in PGIC between the treatment (n = 56) and active surveillance (n = 44) groups (F(1,98) = 2.03, p = 0.16).

Conclusions

The A-HRSI is able to reliably assess participant-reported symptoms and impacts of anal HSIL across a 7-10 days of timeframe. Future work will involve the establishment of construct and discriminant validity prior to inclusion in the full ANCHOR trial.

The aim of our study was to explore the possibility of detecting hemodynamic changes in the brain using frequency-domain near-infrared spectroscopy by exploiting the phase of the intensity modulated optical signal. To obtain optical signals with the highest possible signal-to-noise ratio, we performed simultaneous NIRS-fMRI measurements, with subsequent correlation of the time courses of both measurements. The cognitive paradigm used arithmetic calculations, with optical signals acquired with sensors placed on the forehead. In three subjects we demonstrated correlation between the hemodynamic signals obtained using NIRS and BOLD fMRI.