The invention involves an active phantom that transmits a waveform based on data reflecting free induction decay signals. Where multiple messages require substantially the same response or action, they are presented in aggregate to the user so that the user can review a single message, prepare a single response, and this response can be distributed to the original message senders, resulting in improved message handling efficiency. A pressure relief valve is to open in response to pressure in the print head reaching or exceeding a predetermined value by the provision of gas to the print head by the source of pressurized gas.