Specific absorption rates

The dB/d/is limited to 6 T/s out of concern that larger values could cause nerve stimulation. The r-f exposure is limited to a specific absorption rate (SAR) of 0.4 W/kg for the whole body, 0.32 W/kg averaged over the head, and less than 8.0 W/kg spatial peakia any one gram of tissue. These numbers are designed to limit the temperature rise to less than 1°C and localized temperature of no greater than 38°C head, 39°C tmnk, and 40°C ia the extremities. 

The specific absorption rate = i (Cj,B ) is a func tion of h and may be computed by combining the rate equation... 

Accordingto Eq. (14-74), when /cl is very large and the ratio ki /mkc is much larger than unity, Xi —x = ykc/k and the specific absorption rate is defined by the equation... 

At the other extreme, when the ratio ki /mkc is much smaller than unity, the interfacial concentration of reactant A may be approximated by the equihbrium relation Xi = y/m, and the specific absorption rate expression is... 

The radiofrequency pulses involved in MRI cause thermal heating of the tissues, and are thus subject to FDA limits on the amount of RF power that is transmitted to a subject during a medical scan. The RF power unit is specified as the specific absorption rate (SAR) and is measured in watts per kilogram of body tissue (W/kg tissue). Powers that exceed this level put the subject at risk of tissue damage incurred as a result of the tissue s inability to remove the heat through blood flow. 

Bioavuilubility is a measure of a substance s availability within the body following external exposure. It is mainly governed and influenced by route-specific absorption rates. It may differ between humans and experimental animals. Consequently, if information is available indicating species-specific differences in bioavailability for the same exposure route, the dose descriptor has to be corrected accordingly. 

Knowing the absorption rate for the heterogeneous- and the homogeneous part of the interface, the specific absorption rate related to the total interface can be expressed as follows ... 

Hyperthermia and thermoablation have been accomplished using capacitive or inductive coupling of rf fields (10-100 MHz), microwaves (> 300 MHz), ultrasound, lasers or external heat [171-177]. Macroscopic metal implants of Cu and other high-conductivity metals have been used to induce eddy-current heating. The absorbed power per mass is called the specific absorption rate (SAR), which can be expressed as... 

The influence of the sulfite concentration on ip is seen in Fig. 10b. As previously shown, the specific absorption rate decreases as the Na2S03 concentration increases (curve a). However, experiments carried out keeping the initial sulfite plus sulfate concentration constant by the addition of Na2S04 show a less marked decrease (curve b). More careful analysis reveals that the specific rate of absorption is independent of sulfite concentration when the experiments are carried out keeping a constant total sulfite plus sulfate concentration. This is demonstrated by recycling a solution partially oxidized into sulfate through the equipment (curve c). This interpretation may explain the different values of n published in the literature. 

SAR specific absorption rate (watts per kg of body-mass or tissue). 

Sacroiliitis - Inflammation in the sacroiliac joint. SAR - Specific Absorption Rate. 

The energy absorbed by the magnetic particles under an applied external AC magnetic field is described by the specific absorption rate [SAR the term specific loss power (SEP) may also be used in some cases]. The SAR can be determined as ... 

Implementation of the Analytical Approximate Solutions Developed in this Section for the Field of Specific Absorption Rate A... 

The specific absorption rate (SAR) of non-ionizing electromagnetic radiation with frequencies <100 GHz is defined (sine waves, W/kg) as ... 

The previous assumptions together with the classical relationships of the different specific absorption rates, depending on the chemical reaction regime used to determine interfacial parameters, lead to the theoretical mean reduced values of the gaseous reactant in the gas exit stream and to absorption efficiency for a gas-liquid dispersion, where a is the geometrical specific interfacial area and Rl is the mean true liquid-side mass transfer coefficient defined for a bubble of diameter dg. ... 

In general, we do not know how the specific rate of absorption varies with p° and B° however we can make the relationship between specific absorption rate and bulk doncentrations in the model the same as that in the industrial plant by using the same values of kg and k (see Figure 18). To get the same inlet and outlet concentrations in both, the integrals on the right hand sides of Eqns. (23) and (24), must be equal. This follows ... 

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. 

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