the resistor 20 are both then fed to a computing means 64 the respiratory signal data passing via an analogue to digital converter 66 the respiratory signal data can then be used to select samples from the imaging data that correspond to like phase points in the respiratory cycle these selected images can be used to construct a three dimensional tomography via known computing methods in another example in which the siemens sensation open ct scanner is used employing the anzai sensor port system the signal entering the connection unit 56 via 54 is duplicated within unit 56 the signal is directed via 62 to sensor port 60 and can also be received by 66 the sensor port provides the respiration signal to the ct scanner computer where it is stored together with the imaging data in other words in this example unit 56 is a simple rewiring device without any active components and could simply be replaced by two separate cables for ct applications the computer 64 is only used for monitoring the signal to adjust the right offset and gain on the amplifier unit 52 in a kv fluoroscopy application the computer 64 is used to store the respiration signal together with kv images provided to this computer alternatively the respiratory signal data can be analysed in real time and used to gate the ct scanner 58 thereby creating images that.