Functional imaging with laser speckle contrast analysis: vascular compartment analysis and correlation with laser Doppler flowmetry and somatosensory evoked potentials.

Laser Speckle Contrast Analysis (LASCA), a novel, high-resolution blood flow imaging method, was performed on rat somatosensory cortex during functional activation. In the same animals, cerebral blood flow (CBF) was measured with Laser Doppler Flowmetry. To obtain a quantitative estimate of the underlying neuronal activity, somatosensory evoked potentials were recorded simultaneously with an epidural EEG. Our results show that: 1. CBF changes measured by LASCA or LDF are nonlinearly dependent on the magnitude of electrical neural activity revealed by somatosensory evoked potentials. 2. The magnitude of relative CBF changes measured by LASCA and LDF shows a strong correlation. 3. LASCA imaging localizes the highest relative changes of CBF in microcirculatory areas, with a smaller contribution by larger vessels. This study demonstrates that LASCA is a reliable method that provides 2D-imaging of CBF changes that are comparable to LDF measurements. It further suggests that functional neuroimaging methods based on CBF enhance areas of microcirculation and thus might prove more accurate in localizing neural activity than oxygenation related methods like BOLD-fMRI.