Fig. 1. A blood-exchange method for direct CTC kinetics studies.

a Schematic demonstrating the blood exchange method in which the circulatory systems of two mice (one tumor-bearing mouse (TBM) and one healthy mouse (HM)) are connected in a closed-loop through two CTC counters. Two peristaltic pumps set to identical flow rates push the blood around the system and through the CTC counters. For each CTC counter, a series of two laser lines is used to excite the flowing genetically-fluorescent CTCs (see Supplementary Figs. 1−3 for more details). The emitted signal is directed through a dichroic filter toward a photomultiplier tube (PMT) for detection. b PMT raw and lowpass-filtered (LPF) spectra demonstrate a series of detected CTCs by each of the two CTC counters’ PMTs (PMT 1 = CTC counter 1 (blue), PMT 2 = CTC counter 2 (orange)). The inset demonstrates the LPF dual-peak configuration created when each CTC passes under the two laser lines projected across the flow channel. c Cumulative CTC counts over time from the two CTC counters demonstrate a higher injection rate (blue trajectory with left Y-axis) compared to return rate (orange trajectory with the right Y-axis). Gray-shaded regions represent the assumed steady-state time interval over which the exchange rates were estimated.