Physical model for the spectroscopic analysis of cortical intrinsic optical signals

Kohl, Matthias; Lindauer, Ute; Royl, Georg; Kühl, Marc; Gold, Lorenz; Villringer, Arno; Dirnagl, Ulrich

doi:10.1088/0031-9155/45/12/317

Cited by 165 publications

(147 citation statements)

References 25 publications

Supporting

Mentioning

141

Contrasting

Unclassified

Order By: Relevance

“…17 and 27). Path length correction, although missing from prior work in monkeys and cats, is necessary to avoid errors in the spectral decomposition and interpretation of ISOI signals (17,27) This quantitative analysis showed that the earliest stimulus-evoked response was driven by a rapid increase in [HbT] with no change in [HbR]. The full multiphasic time course of typical imaging signals, including the initial dip, rebound, and undershoot, could be well explained by a fast increase in [HbT] preceding a more transient decrease in [HbR].…”

Section: Resultsmentioning

confidence: 99%

“…The likely reason for this difference is that we separated our imaging signal into [HbR] and [HbO] by using a model that incorporates changes in optical path length caused by the large changes in absorptivity across wavelengths (27). The earlier results (7,23) were obtained with fixed path lengths, which, as now widely acknowledged (4, 10), can lead to significant errors in spectroscopic analysis (17,27). Our results are robust over a broad range of model parameters when using wavelength-dependent path lengths (Fig.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Spatiotemporal precision and hemodynamic mechanism of optical point spreads in alert primates

Sirotin

Hillman

Bordier

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

116

144

View full text Add to dashboard Cite

In functional brain imaging there is controversy over which hemodynamic signal best represents neural activity. Intrinsic signal optical imaging (ISOI) suggests that the best signal is the early darkening observed at wavelengths absorbed preferentially by deoxyhemoglobin (HbR). It is assumed that this darkening or "initial dip" reports local conversion of oxyhemoglobin (HbO) to HbR, i.e., oxygen consumption caused by local neural activity, thus giving the most specific measure of such activity. The blood volume signal, by contrast, is believed to be more delayed and less specific. Here, we used multiwavelength ISOI to simultaneously map oxygenation and blood volume [i.e., total hemoglobin (HbT)] in primary visual cortex (V1) of the alert macaque. We found that the hemodynamic ''point spread,'' i.e., impulse response to a minimal visual stimulus, was as rapid and retinotopically specific when imaged by using blood volume as when using the initial dip. Quantitative separation of the imaged signal into HbR, HbO, and HbT showed, moreover, that the initial dip was dominated by a fast local increase in HbT, with no increase in HbR. We found only a delayed HbR decrease that was broader in retinotopic spread than HbO or HbT. Further, we show that the multiphasic time course of typical ISOI signals and the strength of the initial dip may reflect the temporal interplay of monophasic HbO, HbR, and HbT signals. Characterizing the hemodynamic response is important for understanding neurovascular coupling and elucidating the physiological basis of imaging techniques such as fMRI.fMRI ͉ imaging ͉ macaque ͉ visual ͉ neurovascular coupling C erebral hemodynamics respond quickly and specifically to local neural activity (1, 2). Hemodynamic signals are thus used extensively as proxies for such activity in functional neuroimaging techniques like fMRI and intrinsic signal optical imaging (ISOI). There has been considerable debate, however, as to which of the possible hemodynamic signals, e.g., changes in local blood oxygenation, volume, or flow, with their distinct response properties, constitutes the ''best'' signal for inferring neural activity (1,(3)(4)(5).The debate regarding the best signal sharpened with reports of initial dips in both ISOI and fMRI signals. ISOI studies consistently found a brief stimulus-evoked darkening followed by a strong brightening at imaging wavelengths preferentially absorbed in deoxyhemoglobin (HbR) [e.g., at 605 nm (6)]. The darkening, later termed the initial dip*, was interpreted as a local conversion of oxyhemoglobin (HbO) to HbR caused by increased oxygen consumption by local neurons before any active vascular response (1, 7) The subsequent brightening was taken to measure the ''rebound'' in [HbO] † caused by a delayed, stimulus-triggered increase in cerebral blood flow (7).In parallel, some fMRI studies reported finding an initial dip before the rise in the blood oxygen level-dependent (BOLD) signal (8). Because the BOLD signal measures changes in [HbR] alone ‡ , the fMRI initial dip was seen a...

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Spatiotemporal precision and hemodynamic mechanism of optical point spreads in alert primates

Sirotin

Hillman

Bordier

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

116

144

View full text Add to dashboard Cite

show abstract

“…These systematic errors can create cross-talk in the estimates of the changes in the hemoglobin concentrations such that a change in oxyhemoglobin may appear as a change in deoxyhemoglobin and vice versa. This issue has been discussed in Boas et al (2001), Matcher et al (1995), Mayhew et al (1999), Kohl et al (2000) and Uludag et al (2002).…”

Section: Optimum Wavelengths and Cross-talk In Estimating Hemoglobin mentioning

confidence: 99%

Diffuse optical imaging of brain activation: approaches to optimizing image sensitivity, resolution, and accuracy

2004

View full text Add to dashboard Cite

Near-infrared spectroscopy (NIRS) and diffuse optical imaging (DOI) are finding widespread application in the study of human brain activation, motivating further application-specific development of the technology. NIRS and DOI offer the potential to quantify changes in deoxyhemoglobin (HbR) and total hemoglobin (HbT) concentration, thus enabling distinction of oxygen consumption and blood flow changes during brain activation. While the techniques implemented presently provide important results for cognition and the neurosciences through their relative measures of HbR and HbT concentrations, there is much to be done to improve sensitivity, accuracy, and resolution. In this paper, we review the advances currently being made and issues to consider for improving optical image quality. These include the optimal selection of wavelengths to minimize random and systematic error propagation in the calculation of the hemoglobin concentrations, the filtering of systemic physiological signal clutter to improve sensitivity to the hemodynamic response to brain activation, the implementation of overlapping measurements to improve image spatial resolution and uniformity, and the utilization of spatial prior information from structural and functional MRI to reduce DOI partial volume error and improve image quantitative accuracy. D 2004 Elsevier Inc. All rights reserved.

show abstract

“…Indeed, Orbach (1988) and Orbach et al (1985) estimated the "smearing" of a local optical signal to be of ϳ200 m. This explains why in the present measurements the recorded response was found to begin approximately simultaneously in all microvascular compartments; however, we could rule out the possibility that the obtained intercompartmental differences in the recorded CBV dynamics were confounded by those nonlocality effects. Indeed, although light scattering itself is nearly constant in the wavelength range used, its effects on the recorded signals are tightly linked to absorption (Kohl et al, 2000), which was estimated to vary by at least one order of magnitude between the wavelengths used in the reflection and fluorescence measurements. Nonlocality effects are thus very different at the two performed measurements and so is the cross-talk among compartments.…”

Section: Effects Of Light Scatteringmentioning

confidence: 99%

“…In light of these small amplitudes, the need encountered by Malonek and Grinvald (1996) to invoke light-scattering changes to explain their imaging spectroscopy data (range, 500 -650 nm) is likely to be the result of simplifications in the spectroscopic decomposition that they used. Indeed, more recent studies using an improved spectroscopic model concluded that the intrinsic signal can be explained by the effects of changes in [Hbr] and [HbO2] alone (Kohl et al, 2000;Lindauer et al, 2001). In these studies, the wavelength dependence of the optical-path length in tissue was taken into account; indeed, with their model, the fit of the spectroscopic data (up to 805 nm) was more accurate.…”

Section: Effects Of Light Scatteringmentioning

confidence: 99%

Compartment-Resolved Imaging of Activity-Dependent Dynamics of Cortical Blood Volume and Oximetry

Vanzetta¹,

Hildesheim²,

Grinvald³

2005

J. Neurosci.

115

View full text Add to dashboard Cite

Optical imaging, positron emission tomography, and functional magnetic resonance imaging (fMRI) all rely on vascular responses to image neuronal activity. Although these imaging techniques are used successfully for functional brain mapping, the detailed spatiotemporal dynamics of hemodynamic events in the various microvascular compartments have remained unknown. Here we used highresolution optical imaging in area 18 of anesthetized cats to selectively explore sensory-evoked cerebral blood-volume (CBV) changes in the various cortical microvascular compartments. To avoid the confounding effects of hematocrit and oximetry changes, we developed and used a new fluorescent blood plasma tracer and combined these measurements with optical imaging of intrinsic signals at a near-isosbestic wavelength for hemoglobin (565 nm). The vascular response began at the arteriolar level, rapidly spreading toward capillaries and venules. Larger veins lagged behind. Capillaries exhibited clear blood-volume changes. Arterioles and arteries had the largest response, whereas the venous response was smallest. Information about compartment-specific oxygen tension dynamics was obtained in imaging sessions using 605 nm illumination, a wavelength known to reflect primarily oximetric changes, thus being more directly related to electrical activity than CBV changes. Those images were radically different: the response began at the parenchyma level, followed only later by the other microvascular compartments. These results have implications for the modeling of fMRI responses (e.g., the balloon model). Furthermore, functional maps obtained by imaging the capillary CBV response were similar but not identical to those obtained using the early oximetric signal, suggesting the presence of different regulatory mechanisms underlying these two hemodynamic processes.

show abstract

Physical model for the spectroscopic analysis of cortical intrinsic optical signals

Cited by 165 publications

References 25 publications

Spatiotemporal precision and hemodynamic mechanism of optical point spreads in alert primates

Spatiotemporal precision and hemodynamic mechanism of optical point spreads in alert primates

Diffuse optical imaging of brain activation: approaches to optimizing image sensitivity, resolution, and accuracy

Compartment-Resolved Imaging of Activity-Dependent Dynamics of Cortical Blood Volume and Oximetry

Contact Info

Product

Resources

About