Abstract: In a method for assessing ambient conditions of an installation site of a magnetic resonance imaging device, various places in an area surrounding the installation site are examined by means of a detection unit for changes in a test magnetic field and the ambient conditions are determined from the results of the examination. The detection unit includes a magnetic field generator and a magnetic field sensor.

Abstract: A sensing device which includes a sensing element in the form of an optical fiber, a device for coupling light into the fiber and a device for measuring changes in the specific physical parameters of the light passing through the fiber to determine special physical influences applied to the fiber characterized by the fiber being a multicore fiber having at least two adjacently extending cores surrounded by a common cladding and the means for measuring the changes in the parameter of the light measuring the alterations in the light passing through each of the cores. To make the device sensitive to bending and deformation in all directions, the fiber may have two cores and be twisted through 90.degree. or the fiber may have three or more cores which are not disposed in the same plane. The measuring of the amount of change may be by measuring the interference pattern from superimposed beams of the output from the two cores or by measuring the intensity of each of the output beams separately.