A cooling apparatus includes a container configured to contain a coolant within a space. and in the absence of a solvent. In order to detect the measurable variable in the sensor zone, a measuring hole which allows the medium to advance directly to the sensor zone is provided in the sensor casing. MR images indicative of the degree of mechanical shear connectivity at the tissue interface are reconstructed from the acquired NMR signals in which low-friction shearing motion at the tissue interface is characterized by a loss of magnitude signal due to intravoxel phase dispersion. A well defined jitterless transition in frequency of the arbitrary waveform is provided which coincides with the beginning of the phase cycle of the DDS output signal from the second DDS circuit.