Effects of skin on bias and reproducibility of near-infrared spectroscopy measurement of cerebral oxygenation changes in porcine brain.
ABSTRACT 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.
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ABSTRACT: During clinical interventions objective and quantitative information of the tissue perfusion, oxygenation or temperature can be useful for the surgical strategy. Local (point) measurements give limited information and affected areas can easily be missed, therefore imaging large areas is required. In this study a LED based multispectral imaging system (MSI, 17 different wavelengths 370nm-880nm) and a thermo camera were applied during clinical interventions: tissue flap transplantations (ENT), local anesthetic block and during open brain surgery (epileptic seizure). The images covered an area of 20x20 cm, when doing measurements in an (operating) room, they turned out to be more complicated than laboratory experiments due to light fluctuations, movement of the patient and limited angle of view. By constantly measuring the background light and the use of a white reference, light fluctuations and movement were corrected. Oxygenation concentration images could be calculated and combined with the thermal images. The effectively of local anesthesia of a hand could be predicted in an early stage using the thermal camera and the reperfusion of transplanted skin flap could be imaged. During brain surgery, a temporary hyper-perfused area was witnessed which was probably related to an epileptic attack. A LED based multispectral imaging system combined with thermal imaging provide complementary information on perfusion and oxygenation changes and are promising techniques for real-time diagnostics during clinical interventions.SPIE Proceedings Vol. 8572. 03/2013;
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ABSTRACT: Optical spectroscopy for in vivo tissue diagnosis is performed traditionally in a static manner; a snap shot of the tissue biochemical and morphological characteristics is captured through the interaction between light and the tissue. This approach does not capture the dynamic nature of a living organ, which is critical to the studies of brain disorders such as epilepsy. Therefore, a time-dependent diffuse reflectance spectroscopy system with a fiber-optic probe was designed and developed. The system was designed to acquire broadband diffuse reflectance spectra (240 ~ 932 nm) at an acquisition rate of 33 Hz. The broadband spectral acquisition feature allows simultaneous monitoring of various physiological characteristics of tissues. The utility of such a system in guiding pediatric epilepsy surgery was tested in a pilot clinical study including 13 epilepsy patients and seven brain tumor patients. The control patients were children undergoing suregery for brain tumors in which measurements were taken from normal brain exposed during the surgery. Diffuse reflectance spectra were acquired for 12 seconds from various parts of the brain of the patients during surgery. Recorded spectra were processed and analyzed in both spectral and time domains to gain insights into the dynamic changes in, for example, hemodynamics of the investigated brain tissue. One finding from this pilot study is that unsynchronized alterations in local blood oxygenation and local blood volume were observed in epileptogenic cortex. These study results suggest the advantage of using a time-dependent diffuse reflectance spectroscopy system to study epileptogenic brain in vivo.Proceedings of SPIE - The International Society for Optical Engineering 03/2008; · 0.20 Impact Factor
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ABSTRACT: This study describes noninvasive noncontact methods to acquire and analyze functional information from the skin. Multispectral images at several selected wavelengths in the visible and near infrared region are collected and used in mathematical methods to calculate concentrations of different chromophores in the epidermis and dermis of the skin. This is based on the continuous wave Near Infrared Spectroscopy method, which is a well known non-invasive technique for measuring oxygenation changes in the brain and in muscle tissue. Concentration changes of hemoglobin (dO2Hb, dHHb and dtHb) can be calculated from light attenuations using the modified Lambert Beer equation. We applied this technique on multi-spectral images taken from the skin surface using different algorithms for calculating changes in O2Hb, HHb and tHb. In clinical settings, the imaging of local oxygenation variations and/or blood perfusion in the skin can be useful for e.g. detection of skin cancer, detection of early inflammation, checking the level of peripheral nerve block anesthesia, study of wound healing and tissue viability by skin flap transplantations. Images from the skin are obtained with a multi-spectral imaging system consisting of a 12-bit CCD camera in combination with a Liquid Crystal Tunable Filter. The skin is illuminated with either a broad band light source or a tunable multi wavelength LED light source. A polarization filter is used to block the direct reflected light. The collected multi-spectral imaging data are images of the skin surface radiance; each pixel contains either the full spectrum (420 - 730 nm) or a set of selected wavelengths. These images were converted to reflectance spectra. The algorithms were validated during skin oxygen saturation changes induced by temporary arm clamping and applied to some clinical examples. The initial results with the multi-spectral skin imaging system show good results for detecting dynamic changes in oxygen concentration. However, the optimal algorithm needs to be determined. Multi-spectral skin imaging shows to be a promising technique for various clinical applications were the local distribution of oxygenation is of major importance.Proceedings of SPIE - The International Society for Optical Engineering 01/2009; · 0.20 Impact Factor