RF connection cable 2 for interconnecting an RF coil and an RF processing apparatus in an RF system of a medical MRI apparatus. The interrogating optical signal is reflected from the oral surface which the spray impacts and detected. The method includes defining a number of main colour values of a received digital colour image, converting the main colour values to converted main colour values such that the converted main colour values are perceived as distinguishable from each other by a colour-blind observer, and rendering the digital colour image with the converted main colour values. The processor can also be operable to initiate issuing a power management request of at least one of the plurality of communication channels in response to comparing the percentage of link utilization to a threshold level. A transform filter may be applied to the image file so that the color data for each undesirable marking is mapped to a non-reproduced color, and the color data for each desirable marking is unchanged. The described methods are applicable to both new calls and existing connected calls.