Figure 4.

Excitation ratiometry. (a) Time-interlaced fluorescence signal obtained from a single marker tracked through frames of CCD video. Signal is from marker number 5 in Fig. 3b during 700 ms bipolar pacing. (b) De-interlaced signals, corresponding to alternating frames of cyan and royal blue excitation. (c) Common artifacts in the two fluorescence signals (primarily motion) are attenuated in the ratio signal. Fluorescence units are analog-to-digital conversion counts. No temporal filtering was applied to these signals.