SAR distribution

Huber R, Schruder J, Graf T, et al. Radio frequency electromagnetic Held exposure in humans Estimation of SAR distribution in the brain, effects on sleep and heart rate. Bioelectromagnetics 2003 24(4) 262-76. 

Ideal Treatment Volume and Temperature Distribution. Heating pattern or specific absorption rate (SAR) induced by external devices is defined as the heat energy deposited in the tissue or tumor per second per unit mass or volume of tissue. In optimal treatment planning, it is the temperature rather than the SAR distribution that is optimized in the treatment plan. The maximum temperature generally occurs in the tissue region with heat deposition. However, one should note that SAR and temperature distribution may not have the same profile, since temperature distribution can also be affected by the environment or imposed boundary conditions. 

Determination of SAR. Several methods are used to determine the SAR distribution induced by various heating applicators. The SAR distribution can be directly derived from the Maxwell equation of the electromagnetic field (Camart et al., 2000 Gentili et al., 1995 Ling et al., 1999 Stauffer et al., 1998 Strohbehn, 1984). The electrical field E and magnetic field B are first determined analytically or numerically from the Maxwell equation. The SAR (W/kg) is then calculated by the following equation (Sapozink et al, 1998) ... 

The simplest experimental approach to determining the SAR distribution is from the temperature transient at the instant of power on (Wong et al., 1993 Zhu et al., 1996b). In this approach, temperature sensors are placed at different spatial locations within the gel. Before the experiment, the gel is allowed to establish a uniform temperature distribution within itself. As soon as the initial heating power level is applied, the gel temperature is elevated and the temperatures at all sensor locations are measured and recorded by a computer. The transient temperature field in the gel can be described by the heat conduction equation ... 

It is simple to determine the SAR distribution from the initial temperature transient. This method is fairly accurate as long as the temperature is uniform before the power is turned on. However, to obtain an accurate expression for the SAR distribution, enough temperature sensors should be placed in the region where the energy is absorbed. In the situation when the SAR decays rapidly in the radial direction because of the superficial penetration of the energy, and it is difficult to place many... 

In the experimental study by Zhu et al. (1998), the heating pattern induced by a microwave antenna was quantified by solving the inverse problem of heat conduction in a tissue equivalent gel. In this approach, detailed temperature distribution in the gel is required and predicted by solving a two- or three-dimensional heat conduction equation in the gel. In the experimental study, all the temperature probes were not required to be placed in the near field of the catheter. Experiments were first performed in the gel to measure the temperature elevation induced by the applicator. An expression with several unknown parameters was proposed for the SAR distribution. Then, a theoretical heat transfer model was developed with appropriate boundary conditions and initial condition of the experiment to study the temperature distribution in the gel. The values of those unknown parameters in the proposed SAR expression were initially assumed and the temperatiue field in the gel was calculated by the model. The parameters were then adjusted to minimize the square error of the deviations theoretically predict from the experimentally measured temperatures at all temperature sensor locations. 

Ling, J. X., Hand, J. W., and Young, I. R., 1999, Effect of the SAR Distribution of a Radio Frequency (RF) Coil on the Temperature Field Within a Human Leg Numerical Studies, ASME HTD—Vol. 363, Advances in Heat and Mass Transfer in Biotechnology, pp. 1-7. 

In TOF-SARS [9], a low-keV, monoenergetic, mass-selected, pulsed noble gas ion beam is focused onto a sample surface. The velocity distributions of scattered and recoiled particles are measured by standard TOF methods. A chaimel electron multiplier is used to detect fast (>800 eV) neutrals and ions. This type of detector has a small acceptance solid angle. A fixed angle is used between the pulsed ion beam and detector directions with respect to the sample as shown in figure Bl.23.4. The sample has to be rotated to measure ion scattering... 

Thiolactomycin (16) is another natural product that reversibly inhibits E. coli FabF, FabB, and FabH with respective ICso s of 6, 25 and 110 (iM. Unlike cerulenin, it binds the malonyl-ACP site of the enzyme [27]. Despite modest double-digit MICs on . coli, S. aureus, Serratia marces-cens, and Mycobacterium tuberculosis, 16 has generated quite some interest due to its good in vivo protection against an oral or intramuscular S. marcescens urinary tract infection model where it displayed rapid tissue distribution [28]. Despite several medicinal chemistry efforts, thiolactomycin has proven difficult to optimize due to some strict functional group requirements for its SAR [29]. 

The classic endogenous opioid peptides are derived from one of three families of precursors proopiomelanocortin (POMC), pro-dynorphin, and pro-enkephalin. Many active opioid peptides are derived from these three, but the best known are )S-endorphin, enkephalin, and dynorphin. POMC is produced by nuclei in the hypothalamus and medulla (Khachaturian et al. 1985 Watson et al. 1978 Bloom et al. 1978). Enkephalin and dynorphin neurons are distributed to all levels of the central nervous system (Hokfelt et al. 1977 Khachaturian et al. 1983 Sar et al. 1978 Khachaturian et al. 1985). 

Building predictive QSAR and QSPR models is a cost-effective way to estimate biological activities, physicochemical properties such as partition coefficients and solubility, and more complicated pharmaceutical endpoints such as metabolic stability and volume of distribution. It seems to be reasonable to assume that structurally similar molecules should behave similarly. That is, similar molecules should have similar biological activities and physicochemical properties. This is the (Q)SAR/(Q)SPR hypothesis. Qualitatively, both molecular interactions and molecular properties are determined by, and therefore are functions of, molecular structures. Or... 

In this workflow, chemists want to draw or import a set of molecules, profile their molecular properties, such as computed ADME T (absorption, distribution, metabolism, excretion, and toxicity) properties, estimated activities against specific protein targets based on existing SAR models, and make selections based on the analysis of structural features and computed molecular properties of those singleton molecules. 

Key words PGVL Hub, combinatorial chemistry, library design, reaction, synthesis protocol, reactant, product, enumeration, filtering, Chkl, kinase, inhibitor, SAR, ADME T (Adsorption, Distribution, Metabolism, Excretion, and Toxicity), selectivity, solubility, protein-ligand complex. 

Integrating concentration- and effect-addition principles with (Q)SAR opens the door for (Q)SAR-based mixture assessments. As discussed above, linking interspecies correlations (Asfaw et al. 2004) with the USEPA s ECOSAR program allowed for the generation of species sensitivity distributions, hence a probabilistic estimate for aquatic community effects. Estimated HC5s for 4 chemicals were within a factor of 2 of published values, suggesting that current uncertainty factors overestimate NOECs established via data-based SSDs even SSDs derived... 

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