Programs and Procedures
Testing for electromagnetic compatibility (EMC) in the clinical environment introduces a host of complex conditions not normally encountered in laboratory situations. In the clinical environment, various RF sources of EMI may be present anywhere. Isolating and analyzing the impact from the sources of interference involves a multidisciplined approach based on training in and knowledge of the following:
● Operation of medical devices and their susceptibility to EMI
● RF propagation modalities and interaction theory
● Spectrum-analysis systems and technique (preferably with signature analysis capabilities) and calibrated antennas
● Established methodology of investigating suspected EMI problems, which includes testing protocols and standards
Both standard test procedures adapted for the clinical environment and personnel trained in RF behavior increase the odds of proactively controlling EMI in the clinical environment, thus providing a safer and more effective patient care environment. The methods employed in the following procedures are variations of the OATS (Open Antenna Test Site) technique (ECRI, 1992; ECRI, 1988), a standard for open site testing (Southwick, 1992; Bennett, 1993; ANSI, 1991) and ANSI C63.4-1991 (ANSI, 1991) and ANSI C63.18-1997. The selection of the spectrum analyzer and the options installed in it were influenced by several factors. A spectrum analyzer of the communications system test type was deemed desirable because there is no better way to characterize devices that emit RF— intentional or incidental—and the environment in which those devices operate. Broadband devices indicate relative RF activity but do not indicate the operating frequencies or modulation types. Both characteristics, independently and together, affect the susceptibility of clinical devices. Table 63.1 shows the test equipment used for EMI testing by Texas Children’s Hospital’s Biomedical Engineering Department. A digitally based communications analyzer was needed to archive the results of the EMI tests; both fingerprints and footprints. The flexibility of performance requirements of the device was important, and as a cost-saving benefit, Texas Children’s Hospital also uses it to maintain of the hospital radio communications systems. Since no two modified OATS environments are identical, no two results obtained under the same testing parameters will be identical. Many factors affect the detailed test results, including complex absorption and reflection variables that are totally site-dependant