Fadda A
Laboratorio di Ingegneria Biomedica, Istituto Superiore di Sanità, Roma.
Ann Ist Super Sanita. 1994;30(1):45-50.
The exposure to radiofrequency (RF) electromagnetic fields is one of the main aspects to be controlled in order to ensure the safety of patients in an NMR environment. Starting from the description of the main physical characteristics of RF fields active in imaging instrumentation, a simple model is obtained which accounts for the experimental interdependence between the parameters of the stimulus and SAR values deposited on the patients. This model can yield a preliminary/approximate prediction of exposure levels for a given test. Some NMR equipment admit the estimation of the actual SAR values during the test on the basis of electrical measurements. The paper illustrates the basic principles of these measurements. The biological effects associated with the absorption of RF energy are discussed with particular attention to the physical and biological factors which may result in local heating on the body, a danger which may not be prevented by simply observing the prescribed thresholds of mean exposure.
为确保核磁共振（NMR）环境中患者的安全，射频（RF）电磁场暴露是需要控制的主要方面之一。从描述成像仪器中活跃的射频场的主要物理特性入手，得到了一个简单模型，该模型说明了刺激参数与沉积在患者身上的比吸收率（SAR）值之间的实验相互依存关系。对于给定的测试，该模型可以给出暴露水平的初步/近似预测。一些NMR设备允许在测试期间根据电学测量估算实际的SAR值。本文阐述了这些测量的基本原理。讨论了与射频能量吸收相关的生物效应，特别关注了可能导致身体局部发热的物理和生物因素，而仅仅遵守规定的平均暴露阈值可能无法预防这种危险。
