Fig. 3.

The in vivo measurement results for the investigation of optical measurement artifacts induced by scattered x rays. (a) Three autocorrelation curves (g₂) were collected at the time points of 417 (contaminated), 99 (slow flow), and 724 (fast flow) (sec), respectively. Similar to the phantom test results (see Fig. 2a), scattered x rays contaminated the measured autocorrelation curves (empty circles). For the data without contaminations (solid circles), the decay rate of autocorrelation curves depended on the level of blood flow; g₂ decayed faster when blood flow was faster (black solid circles). As expected, β (can be estimated using the measured g₂ data at earliest τ) was independent of blood flow changes when there were no x-ray induced artifacts. (b) Scattered x rays created abnormal increases in β (>0.5, empty circles) depending on the direction/angle of radiation beam. (c) The x-ray beam introduced abnormal increases in blood flow (empty circles) derived from the autocorrelation curves. (d) The x-ray beam induced minor variations in detected photon count rate ( × 10³ photons/s) (empty circles).