Concurrent intrinsic optical imaging and fMRI at ultra high field using magnetic field proof optical components.

Intrinsic optical imaging (IOI) is a well-established technique to quantify activation-related hemodynamical changes at the surface of the brain, which can be used to investigate the underlying processes of BOLD signal formation. For being able to directly and quantitatively relate IOI and fMRI, simultaneous measurements with both modalities are necessary. Here, a novel technical solution for a completely in-bore setup is presented, which uses only magnetic field proof components and thus allows concurrent recordings with similar quality as in separate experiments. Measurements of the somatosensory cortex of rats with electrical forepaw stimulation were used to verify this approach. The high spatial and temporal resolution of the fMRI data, which is possible due to the high magnetic field of 14.1 T, the use of a point-spread function based distortion correction and optimized additional anatomical images allowed accurate colocalization of the images of both modalities. Accordingly, detailed investigations of the temporal and spatial relationships of the hemodynamic parameters and the fMRI signal are possible, which demonstrate the linear dependence of the BOLD effect on changes in the concentrations of oxygenated and deoxygenated hemoglobin. Comparisons between the signals emerging from arterial, venous and parenchymal areas are possible and show clearly distinct characteristics. The presented setup allows combining MRI measurements and optical recordings without serious losses in the data quality of either modality. While the proposed combination of fMRI and IOI can help to gain valuable insight into the generation of the BOLD effect, the setup can be easily modified to include different types of optical or MRI measurements.