Rpm system

Three healthy volunteers were tested in the current study. All were male in their 20’s or 30’s with BMI < 25. Subjects did not receive training or instruction prior to respiratory signal measurements. Subjects were placed on a CT simulator equipped with a Varian RPM system. Subjects were simultaneously outfitted with a CBD imprinted shirt from Nyx Devices (capacitors located over the right costal margin) and an RPM infrared reflector box on the upper abdomen. Respiratory information from both devices was simultaneously recorded for approximately 5 minutes at a rate of 30 Hz for the RPM trace and 5 Hz for the CBD. Subjects were instructed to breathe normally except at an arbitrary time point during each recording where they were asked to take a series of short rapid breaths, hold their breath, and then take several more short rapid breaths before resuming normal breathing. For one subject respiratory data was also measured with a small adhesive CBD placed sequentially at each of 3 locations: the mid abdomen at the level of the navel, costal margin and mid thorax adjacent to the right nipple.

In contrast to the breathing signal tracking approaches using external sources such as the real-time position management (RPM) system (Varian Medical Systems, Palo Alto, CA) or the fluoroscopic tracking where both the patient and the imaging devices remain still, CBCT projections are acquired at various gantry angles. As briefly mentioned in the Introduction, varying gantry angles incur anisotropic attenuation on the projection images. Thus, the contrast of structures of interest deteriorates, which compromises the breathing signal extraction. To quantitatively assess the effect of the gantry rotation on the breathing signal extraction, we scanned a Quasar phantom (Modus Medical Devices Inc., London, Canada) with programmed SI moving amplitude of 2.0 cm and a cycle of 4.0 s. The AS obtained from the phantom data and the extracted signal is shown in figure 8. The regular wavy pattern is conspicuously present on the AS image (figure 8(a)). As depicted in figure 8(b), the extracted signal (blue curve) faithfully reproduced the programmed sine wave (green curve). The relative error of the bpm is as small as 0.0049. This experiment demonstrates that the impact of gantry rotation is minimal on the extracted breathing signal cycle/frequency, in spite of the harmful signal diminishment from attenuation variations, which the first part of our effort is devoted to reestablish.