Noncontact Respiratory Motion Detection in Anesthetized Rodents

Small animal physiology studies are often complicated, but the level of complexity is greatly increased when performinglive-animal X-ray imaging studies at synchrotron radiation facilities. This is because these facilities are typically not designedspecifically for biomedical research, and the animals and image detectors are located away from the researchers in a radiationenclosure. In respiratory X-ray imaging studies one challenge is the detection of respiration in free-breathing anaesthetisedrodents, to enable images to be acquired at specific phases of the breath and for detecting changes in respiratory rate. Wehave previously used a Philtec RC60 sensor interfaced to a PowerLab data acquisition system and custom-designed timinghub to perform this task. Here we evaluated the Panasonic HL-G108 for respiratory sensing. The performance of the twosensors for accurate and reliable breath detection was directly compared using a single anesthetized rat. We also assessedhow an infrared heat lamp used to maintain body temperature affected sensor performance. Based on positive results fromthese comparisons, the HL-G108 sensor was then used for respiratory motion detection in tracheal X-ray imaging studies of21 rats at the SPring-8 Synchrotron, including its use for gated image acquisition. The results of that test were compared toa similar imaging study that used the RC60 for respiratory detection in 19 rats. Finally, the HL-G108 sensor was tested on 5mice to determine its effectiveness on smaller species. The results showed that the HL-G108 is much more robust and easierto configure than the RC60 sensor and produces an analog signal that is amenable to stable peak detection. Furthermore,gated image acquisition produced sequences with substantially reduced motion artefacts, enabling the additional benefit ofreduced radiation dose through the application of shuttering. Finally, the mouse experiments showed that the HL-G108 isequally capable of detecting respiration in this smaller species.