Pyramid approach for the reduction of parallax-related artefacts in optical recordings of moving translucent volumes.

Functional optical imaging (OI) of intrinsic signals (like blood oxygenation coupled reflection changes) and of extrinsic properties of voltage sensitive probes (like voltage-sensitive dyes (VSD)) forms a group of invasive neuroimaging techniques, that possess up to date the highest temporal and spatial resolution on a meso- to macroscopic scale. There are different sources that contribute to the OI signal of which many are noise. In our previous works, we have used dense optical flow for the reduction of movement artefacts. The translucent surface of the cortex allows contributions from multiple depths. Due to the depth offield (DOF) effect, we get an implicit relation of depth and 2D frequency components. In this work, we introduce registration on the levels of a Laplacian pyramid to remove movement artefacts which have different motion components in different spatial frequency bands. This aims to resolve artefacts that remain after normal registration and are caused e.g. by parallax motion, dead pixels or dust on the sensor and other high frequent, moving particles on the cortex surface without the compromise of using high smoothness weights.

Motion invariant contrast enhancement of optical imaging data in the gradient domain.

Functional optical imaging (OI) of intrinsic signals (like blood oxygenation coupled reflection changes) and of extrinsic properties of voltage sensitive probes (like voltage-sensitive dyes (VSD)) forms a group of neuroimaging techniques that possess up to date highest temporal and spatial resolution on a meso-to macroscopic scale. An inherent problem of OI is a very low signal to noise ratio (SNR), which restricts the recordings to be completely motionless and requires detailed knowledge of the properties of the different noise sources. In our experiments we performed a durectomy and did not use an imaging chamber to allow us future joint electroencephalography-optical imaging (EEG-OI) measures, which resulted in movement artifacts. With the goal of motion compensation in OI recordings and magnification of signal changes, we present a novel processing pipeline, which is based on optic flow guided denoising and gradient domain tone mapping for spatiotemporal contrast enhancement.

Compensation of pulsation artifacts during optical imaging with and without cranial chamber.

Functional Optical Imaging (OI) through the opened skull forms a group of Neuroimaging techniques characterized by a high temporal and spatial resolution on a meso-to macroscopic scale. State of the art OI experiments are generally difficult to execute, with a very timely surgical preparation preceding the experiment, that requires a skilled surgeon to mount a sealed imaging chamber onto the skull. The chamber reduces brain pulsation artifacts and swelling of the brain through movement restriction. In this work, we present preliminary results of a novel approach that does not rely on the usage of an imaging chamber with the goal to facilitate heavily the surgical animal preparation and to allow straightforward joint Electroencephalography - Optical Imaging recordings in the future. We carried out experiments to compare the movement restricting properties of the imaging chamber with the movement in a recording of an unconstrained and periodically irrigated brain. We used high-level image processing techniques to reduce brain pulsation artifacts and did a quantitative movement analysis of the recordings. Our results suggest that while recordings with imaging chamber show less sagittal movement, both with and without imaging chamber comprise the same lateral movements.