AbstractObjective.Current C-arm x-ray systems equipped with scintillator-based flat panel detectors (FPDs) lack sufficient low-contrast detectability and spectral, high-resolution capabilities much desired for certain interventional procedures. Semiconductor-based direct-conversion photon counting detectors (PCDs) offer these imaging capabilities, although the cost of full field-of-view (FOV) PCD is still too high at the moment. The purpose of this work was to present a hybrid photon counting-energy integrating FPD design as a cost-effective solution to high-quality interventional imaging.Approach.In the proposed hybrid detector design, the central scintillator and thin-film transistor elements in the FPD are replaced with a semiconductor PCD module to upgrade the imaging capabilities of the C-arm system while preserving the full FOV coverage. The central PCD module can be used for high-quality 2D and 3D region-of-interest imaging with improved spatial- and temporal-resolution as well as spectral resolving capability. An experimental proof-of-concept was conducted using a 30 × 2.5 cm2CdTe PCD and a 40 × 30 cm2CsI(Tl)-aSi(H) FPD.Main results.Phantom andin vivoanimal studies show (1) improved visualization of small stent wires in both 2D and 3D images due to the better spatial resolution of the PCD; (2) dual-energy angiography imaging capability by using the spectral PCD; (3) better conspicuity of small peripheral iodinated vessels (contrast-to-noise ratio improvement range: (29%, 151%)); (4) the central PCD outputs can be fused seamlessly with the surrounding scintillator detector outputs to provide full field imaging: A post-processing chain was developed by leveraging the PCD’s spectral information to match the image contrast of the PCD images to the surrounding scintillator detector, followed by spatial filtering of the PCD image to match noise texture and spatial resolution.Significance.The hybrid FPD design provides a cost-effective option to upgrade C-arm systems with spectral and ultra-high resolution capabilities without interfering with the clinical need for full FOV imaging.