Optical Camera for Simultaneous Optical and MR Imaging
Widefield optical imaging is an important tool for neuroscientific research, either for directly observing changes in the oxygenation and blood volume during activation with intrinsic optical imaging, or for using dyes or genetically encoded indicators to look at calcium inflow or electrical cellular events.
While concurrent optical imaging and MRI has a large potential for examining neuronal processes during brain activity, the high magnetic field and restricted space make it difficult to implement the necessary instrumentation for this kind of experiments. While previous approaches have used endoscopes to transfer the light out of the magnet, our approach is to try to move the full optical imaging setup into the magnet with the aim of preserve the full quality of both optical and MR images as obtained in separate experiments. For this, a magnetic field proof high sensitivity scientific CMOS camera was combined with two professional objectives, with all metallic parts carefully removed, to form a tandem lens system as often used in optical imaging experiments. To fit into the 12 cm gradient, the lenses are positioned above the animal and the light is deflected from the brain surface into the optics by a prism. Optical fibers are used to transfer the light to illuminate the brain from LEDs positioned outside the scanner room. A surface coil on top of the rat head is used to acquire MRI data.
Optical data acquisition, stimulation and illumination is controlled by self-written software and three Arduino microcontrollers and triggered by the pulse sequence running on the scanner. Twenty images per second are acquired, with illumination wavelength changing between images due to in-house built, high speed LED drivers. Additional filters can be inserted into the light paths of both illumination and image recording, which allows to use the setup for fluorescence imaging.