The influence of skin on the bias and reproducibility of regional cerebral oxygenation measurements is investigated using cw near-infrared spectroscopy (NIRS). Receiving optodes are placed over the left and right hemispheres of a piglet (C3, C4 EEG placement code) and one transmitting optode centrally (Cz position). Optical densities (OD) are measured during stable normo, mild, and deep hypoxemia. This is done for skin condition 1: all optodes on the skin; skin condition 2: transmitting optode on the skin and one receiving optode on the skull; and skin condition 3: all optodes on the skull. Absolute changes of oxy- (cO2Hb), deoxyhemoglobin (cHHb), and total hemoglobin (ctHb) concentrations [micromolL] are calculated from the ODs. These absolute changes are calculated for each skin condition with respect to normoxic condition. Additionally, for skin condition 2, the difference of concentration changes between receiver 1 (skull) and receiver 2 (skin) is calculated. The effect of skin removal is an average increase of attenuation changes by a factor of 1.66 (=0.51 OD) and of the concentration changes due to the arterial oxygen saturation steps by 23%. We conclude that skin significantly influences regional oxygenation measurements. Nevertheless, it is hypothesized that the estimated concentration changes are dominated by changes of the oxygenation in the brain.
"Measurements therefore not only contain confounding signals from systemic sources, but also from hemodynamics localized to the superficial tissue layers. Even when combined into sparse (∼3 cm) grids for topographic imaging, NIRS continuous-wave measurement systems have poor spatial sampling and are ill-equipped to discriminate these noise sources (Klaessens et al., 2005; Davis et al., 2006). "
[Show abstract][Hide abstract] ABSTRACT: Functional near infrared spectroscopy (fNIRS) is a portable monitor of cerebral hemodynamics with wide clinical potential. However, in fNIRS, the vascular signal from the brain is often obscured by vascular signals present in the scalp and skull. In this paper, we evaluate two methods for improving in vivo data from adult human subjects through the use of high-density diffuse optical tomography (DOT). First, we test whether we can extend superficial regression methods (which utilize the multiple source-detector pair separations) from sparse optode arrays to application with DOT imaging arrays. In order to accomplish this goal, we modify the method to remove physiological artifacts from deeper sampling channels using an average of shallow measurements. Second, DOT provides three-dimensional image reconstructions and should explicitly separate different tissue layers. We test whether DOT's depth-sectioning can completely remove superficial physiological artifacts. Herein, we assess improvements in signal quality and reproducibility due to these methods using a well-characterized visual paradigm and our high-density DOT system. Both approaches remove noise from the data, resulting in cleaner imaging and more consistent hemodynamic responses. Additionally, the two methods act synergistically, with greater improvements when the approaches are used together.
Frontiers in Neuroenergetics 07/2010; 2. DOI:10.3389/fnene.2010.00014
"As the regions immediately beneath optodes have extremely high sensitivity, blood circulation change beneath or near an optode strongly degrades the reliability of the topograph. NIRS devices cannot distinguish blood circulation change of the cerebral cortex from that of skin with autonomic nerve activity (Klaessens et al., 2005; Scott L. Davis, 2006). Numerous studies have been conducted in the field of 3D diffuse optical tomography (DOT) in order to realize quantitative and accurate imaging of heterogeneity in tissue, through the use of intensive systems such as time-domain or frequency-domain system (Schweiger et al., 1993; O'Leary et al., 1995; Arridge and Schweiger, 1997; Boas et al., 2001; Gao et al., 2002; Kilmer et al., 2003; Stott et al., 2003; Graber et al., 2007; Kim et al., 2008). "
[Show abstract][Hide abstract] ABSTRACT: A compact filtered backprojection algorithm that suppresses the undesirable effects of skin circulation for near-infrared diffuse optical topography is proposed. Our approach centers around a depth-selective filtering algorithm that uses an inverse problem technique and extracts target signals from observation data contaminated by noise from a shallow region. The filtering algorithm is reduced to a compact matrix and is therefore easily incorporated into a real-time system. To demonstrate the validity of this method, we developed a demonstration prototype for depth-selective diffuse optical topography and performed both computer simulations and phantom experiments. The results show that the proposed method significantly suppresses the noise from the shallow region with a minimal degradation of the target signal.
Physics in Medicine and Biology 03/2009; 54(6):1419-33. DOI:10.1088/0031-9155/54/6/003 · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reflectance spectroscopy and thermography are used as non-invasive, non-contact imaging method to study the physiology of skin processes or pathophysiology of skin diseases. In this proceeding the development of a multispectral imaging system based on a tunable LED light source is described. The system is validated under laboratory conditions on volunteers. Different algorithms to calculate the O2Hb and HHb changes in the tissue are being developed and the results are presented for different sets of selected wavelengths. Simultaneously thermal images were recorded to image the temperature changes caused by perfusion changes. The first clinical studies have been started.
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