Some of our projects are envisioned and put into action in a truly multimodal instrumentation context. This includes research on (large-field-of-view, LFOV) PET-CT and PET-MRI (clinical systems) as well as optical imaging combined with any other modality. The world's first triple modality SPECT-FMI/BLI-CT mouse imager (left figure, top:front view of the trimodality imaging system, bottom: fused MIP view of reconstructed CT, SPECT, and 2-D FMT data (reference)) was build in this research group.

The objective of this instrument was intended for simultaneous detection of radiolabeled pharmaceutical distributions (SPECT), near-infrared fluorescent molecular markers (fluorescence mediated imaging and tomography (FMI/FMT)) and/or bioluminescence imaging (BLI) and high-resolution x-ray tomography (CT) with axially un-shifted (i.e. identical), spatially over-lapping field-of-views (FOV) of all involved sub-modalities. For SPECT imaging a compact gamma detector (Thomas Jefferson National Accelerator Facility, USA) is implemented. It consists of a 2x2 array of Hamamatsu H8500 position sensitive photomultiplier tubes which are attached to a 66x66 array of opto-decoupled 1.3x1.3x6 mm³ NaI(Tl) crystal elements (St. Gobain) yielding a total detector area of 10x10 cm². Various collimators (pinhole, fan beam, parallel beam) can be attached to the camera for specific imaging purposes. A high resolution ORCA AG cooled CCD camera (Hamamatsu) is used for the optical detector sub-system, containing a progressive scan interline CCD chip with a 1344x1024 pixel array and 12 bit digital output. Various laser sources, selected by wavelength and light power requirements, can be mounted on the gantry. The x-ray CT sub-system employs a Series 5000 Apogee x-ray tube (Oxford Instruments) with a maximum power of 50W, at 4 to 50kV, 0 to 1mA. The focal spot size is 35µm and the cone angle is 24 degrees. The x-ray detector is a Shad-o-Box 2048 (Rad-icon Imaging Corp.) containing a 50x100 mm² Gd₂O₂S scintillator screen that is placed in direct contact with a CMOS photodiode array with 48µm sensor pixel size. The integration concept is laid out in a fully modular manner whereby all components are mounted on a common gantry system such that a wide range of applications can be performed. Such design yields highest possible sub- and/or multi-modality performance. The entire assembly is enclosed in a light-tight and gamma-ray shielded compartment which is mounted on a movable trolley containing another compartment holding all necessary camera control, data read-out, laser light, gantry and linear stage motion control electronics as well as high-voltage and power supply, and workstation computers. Unified simultaneous data acquisition, image reconstruction, and fused planar and tomographic image display is possible using our tri-modal imager thus providing intrinsically registered potentially three-dimensional fluorescence and radiopharmaca distribution maps carrying molecular and functional information that is correlated to the anatomy of the imaged object provided by x-ray.

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