Abstract

Complex biological systems often require measurements of multiple parameters with high temporal and spatial resolution. Multimodal approaches and the combination of methods are therefore a powerful tool to address such scientific questions. Laser speckle imaging (LSI) is an optical method that monitors dynamic changes in cortical blood flow (CBF) with high temporal resolution. Positron emission tomography (PET) allows for quantitative imaging of physiological processes and is a gold standard method to determine absolute cerebral blood flow. We developed a setup that allows simultaneous measurement with both modalities. Here, we simultaneously measured CBF with PET and LSI in rats and analyzed how the correlation of PET and LSI is modified when (1) different methods are used for the calculation of speckle inverse correlation time (ICT), (2) speckle data is acquired through thinned or craniectomized skull, (3) influence of surface vessels is removed from the speckle data. For the latter, a method for automated vessel segmentation from LSI data was developed. We obtained the best correlation (R² = 0.890, p<0.001) when correcting for surface vessel structures taking into account the contribution of static scatterers while keeping the coherence factor constant. However, using the originally published relation¹, which allows a 900 times faster computation of blood flow maps, still provided a good correlation (R² = 0.879, p<0.001). Given the good correlation between LSI and PET we used our data to calibrate the speckle ICT. Thus, LSI provides CBF in absolute units at high temporal resolution.

© 2013 SPIE