# Intraoperative Imaging of Cortical Blood Flow by Camera-Based Photoplethysmography at Green Light
## Results  
### Patient with Pathological Formation of the Lateral Right Brain Ventricle  
Parameters of cerebral blood-flow pulsations evaluated in the case of pathological formation of the brain right lateral ventricle are shown in Figure 1, where images of the upper and lower rows were obtained before and after surgery, respectively. Photographs of the open brain before and after tumor resection are shown in Figure 1A,D, respectively. The tumor was situated about three cm below the cortex in the brain right ventricle, near the region of the yellow dashed line (Figure 1A,D) marking the cortex dissection to access the tumor. Maps of APC (panels B and E) and PAT (panels C and F) in Figure 1 overlay respective images of the brain. Figure 1: Mapping the blood pulsations parameters in the brain cortex in the case of a patient with a tumor: The upper and lower rows of images of the open brain were obtained before and after tumor resection, respectively. Panels (**A**) and (**D**) show photographs of the open brain with the dissection area indicated by a yellow line and three selected regions of interest (ROIs) marked as P1, P2, and P3. Spatial distributions of amplitude of the pulsatile component (APC) and pulse arrival time (PAT) overlaid with still images of the open brain cortex are shown in (**B**), (**E**) and (**C**), (**F**), respectively. The color scales on the right side of images (**B**) and (**E**) show APC in percent, whereas that of images (**C**) and (**F**) is PAT in milliseconds. Before surgery, the amplitude of blood pulsations is distributed rather evenly over the cerebral cortex with the exception of the lower left part of the APC map with a reduced APC indicated in blue in Figure 1B. The mean APC in the lower left quarter of the map in Figure 1B is \(1.12\pm 0.51\%\) whereas it is \(2.74\pm 0.68\%\) in the rest of the APC map. Probably, these changes are explained by the mechanical effect of the volumetric process on the local hemodynamics of the cortex, leading to compression of the vessels by the tumor. Lack of uniformity in the spatial distribution of PAT (Figure 1C) was observed as well. The blue area in the same quarter of the PAT map means that the pulse wave reached this area with a greater delay than the rest of the cortex: \(188\pm 65\) ms vs. \(82\pm 54\) ms, respectively. After tumor removal, a significant decrease in the amplitude of pulsations was observed in the area around the dissection of the pia matter (dark blue area in Figure 1E) that might be caused by drawing apart the pia matter to reach the tumor. While before surgery the APC average within this region was \(2.14\pm 0.67\%\), it became \(1.21\pm 1.02\%\) after intervention. Notably, the mean PAT in the same area increased from \(98\pm 70\) ms (Figure 1C) to \(237\pm 114\) ms (Figure 1F). It is worth noting that significant increase in the average APC outside the dissection area was observed: \(2.38\pm 1.01\%\) before surgery vs. \(3.48\pm 1.05\%\) after it. The average PAT value outside the dissection region decreased moderately from \(109\pm 61\) to \(81\pm 36\) ms.  
To estimate changes in the pulse shape and its spatial stability, we selected three representative ROIs marked as P1, P2, and P3 in Figure 1. In addition, to illustrate temporal variability of the PPG-pulse shape, we calculated the PPG waveform in the central pixel of each ROI and showed PPG pulses for every cardiac cycle during 40-s of recording by thin colored lines in Figure 2 (graphs A, B, and C in both the lower and upper rows). While in a single pixel we observed the pulse-shape variability in time, the spatial variability was assessed in a ROI of size \(7\times 7\) pixels. The data are shown in Figure 2, where together with instability of the pulse shape before operation, we found that the shape of the PPG waveforms is also different in different cortex areas. Note that instability of PPG pulses both in time and in space was observed before surgery especially in the area with diminished APC (lower left quarter of the map in Figure 1B).