(a) The experimental setup is shown, with the array transducer (A) scanning through a water bath (W) and gel membrane (G) mounted over the shaved abdomen of an anesthetized pregnant mouse. Labels: H, heating pad; P, respiratory pillow; RT, rectal temperature probe. (b) A typical measured respiratory signal (inspiration + expiration), with a period close to 1.5s. (c) The digital waveform, derived from the respiratory signal, and used to trigger respiratory-gated acquisition. The vertical lines between triggers represent the acquisition of data, during the “quiet” (expiration) phase of the respiratory cycle, for each of the 5 scans of the transducer.