Exogenous Absorbers

ICG can be used to detect blood-flow dynamics. In the brain the absorption ehange after an ICG bolus shows differenees in superfieial and deeper blood vessels [327, 328, 329], and may be useful to indieate oeelusion of vessels and areas of inereased sboke risk. ICG dynamics have also been used for breast tumor iden-tifieation. Tumors usually have increased blood eontent, an inereased number of blood vessels, and inereased leakage of dye from the vessels into the tissue. Even with ICG injeetion, however, the contrast between tumour tissue and healthy tissue remains low. Moreover, the dwell time of ICG in the tissue is only about 10 minutes so that short aequisition times are required. 

For a given number of recorded photons, fluoreseenee deteetion in general yields a better intrinsie SNR than an absorption measurement. However, compared to the diffusely transmitted or reflected intensity the fluoreseenee intensity is much lower. The SNR actually obtained depends on the effieieney of the optics and the detection system, the tissue thickness, the fluorophore concentration and quantum yield, and the acceptable acquisition time. 

The change of the lifetime can be estimated from the differences in the first moment of the curves. Referred to pH 7 the change for pH 10 and pH 4 is -60 ps and +80 ps, respectively. The variation of the recorded signal shape with the depth of the beads in the phantom are shown in Fig. 5.56. 

The extraction of pH-induced fluorescence lifetime variations from time-of-flight curves has been studied in [175]. The authors use a fluorescent inclusion in a homogeneous medium. They show that the fluorescence decay can be separated from the instrument response function and the time-of-flight distribution of the bulk medium. 

Certainly in human patients the condition of a well-localised inclusion in a homogeneous, nonfluorescent bulk medium is not fulfilled. The condition is better, yet not perfectly, met in small animals where the tissue depth does not exceed a few millimeters. The contribution of the bulk medium and its inhomogeneity is correspondingly smaller. Therefore DOT fluorescence is currently used mainly for small-animal imaging (see section below). 

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Near infrared laser-tissue welding using nanoshells as an exogenous absorber, A. M. Gobin, D. P. 0 Neal, D. M. Watkins, N. J. Halas, R. A. Drezek, and J. L. West, Lasers Surg. Med., 2005, 37, 123. 

Rgure 2.3 The antioxidant activity of butyiated hydroxytoluene in the presence of exogenous iipid hydroperoxides. The oxidation of LDL was monitored by measuring the increase in absorbance at 234 nm as described in Fig. 2.2 and the lag phase (time before the phase of maximum rate of oxidation) estimated as described by Esterbauer et at. (1989). Samples of LDL were supplemented with the cortcentrations of 13-hydroperoxyoctadecanoic acid (13-HPODE) indicated and in the presence of 3 fM BHT. The lag phase in the absence of BHT for this preparation of LDL was 48 min. 

High-molecular-weight hyaluronic acid is a constituent of normal cartilage that provides lubrication with motion and shock absorbency during rapid movements. Because the concentration and molecular size of endogenous hyaluronic acid decrease in OA, exogenous administration has been studied in an attempt to reconstitute synovial fluid and reduce symptoms. 

Most of any exogenous chemical absorbed from the GI tract must pass through the liver via the hepatic-portal system (leading to the so-called first-pass effect) and, as mixing of the venous blood with arterial blood from the liver occurs, considera-... 

The basis of this assay was first used to measure the activity of superoxide dismutase (SOD) using a xanthine/xanthine oxidase 02"-generating system. O2 generated via this enzyme will reduce feni (oxidised)-cytochrome c, but SOD (which has a much higher affinity for O2" than cytochrome c) will prevent this reduction. Babior, Kipnes and Cumutte (1973) modified this technique to provide a specific assay to measure O2 production by activated neutrophils. Thus, 02" reduces cytochrome c (measured by an absorbance increase at 550 nm), but this reduction will be blocked by the addition of exogenous SOD (Fig. 5.10). 

Chylomicron 99 80-95 2-6 3-9 1 Transport of fat absorbed in the intestine to the liver and adipose tissues (exogenous triacylglycerol)... 

The absorbability and subsequent bioavailability of Ca salts in humans and animals is simultaneously influenced by a number of exogenous and endogenous factors. In summary, these factors include, although are not limited to ... 

Little is known about the function of gangliosides. Gangliosides may serve as cell surface receptors (45) and as biotransducers of membrane-mediated information ). The ganglioside GM1 has been implicated as the receptor for choleragen. Our studies clearly indicate that butyrate induces toxin receptors and GM1 in parallel. In addition, the toxin receptors induced by butyrate are functionally indistinguishable from exogenous GM1 that has been absorbed by the cells. We believe that these observations are the quintessential evidence that GM1 alone is the receptor for choleragen. 

Yoshikawa, H., K. Takada, and S. Muranishi. 1984. Molecular weight dependence of permselectivity to rat small intestinal blood-lymph barrier for exogenous macromolecules absorbed from lumen. J Pharmacobiodyn 7 1. 

At harvest, the grapes must be transferred with caution into a tank, previously filled up with C02. The gas may come from a carbon dioxide cylinder or from another tank containing fermenting must. After vatting, an exogenous supply of C02 must be provided until berry and yeast fermentation produces this gas in sufficient quantities. Initially, the berries absorb variable amounts of C02, depending on the harvest temperature, for example, 50% of the tank volume at 35 °C. This results in an infusion of outside air, delaying the onset of AM. 

Interest has focussed on four main areas (a) the nature of exogenous carbohydrates utilised by cestodes, (b) the mechanisms by which these carbohydrates are absorbed, (c) the pathways of carbohydrate catabolism and (d) the regulatory control of these pathways. 

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