Enlarging the longitudinal coverage of a prototype C-arm photon counting CT system for image-guided interventions

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Existing clinical C-arm interventional x-ray systems equipped with flat panel detectors (FPDs) can generate fluoroscopic, angiographic, and cone-beam CT (CBCT) images with sufficient volumetric coverage for interventional imaging tasks. However, FPD-CBCT does not provide sufficient low-contrast detectability, resolution, or spectral imaging capability desired for certain interventional procedures. To overcome these limitations, a C-arm photon counting detector (PCD) CT prototype was developed by installing an interchangeable strip PCD on the C-arm gantry. The narrow <i>z</i> width of the PCD reduces detector cost and reduces scatter when paired with a narrow beam collimation. However, it does not provide sufficient volumetric coverage compared to the standard FPD. The purpose of this work was to develop a step-and-shoot data acquisition method to enlarge the effective <i>z</i>-coverage of the C-arm strip PCD-CT system. A total of 10 back-and-forth short-scan C-arm gantry rotations were used with image object translation. By using an Arduino board to process the x-ray-on pulse signals in real-time, a motorized patient table prototype was synchronized with the C-arm system such that it translates the object by the PCD width during the rest time in between gantry rotations. To evaluate whether this multisweep step-and-shoot acquisition mode can generate high-quality and volumetric PCD-CT images, experiments were performed using an anthropomorphic head phantom, and a stent. The multi-sweep step-and-shoot C-arm protocol resulted in volumetric PCD-CT images with lower image noise and improved low-contrast visualization over the FPD-CBCT in the head phantom, as well as improved visibility of small iodinated blood vessels using maximum intensity projections. Under an ultra-high-resolution PCD mode, the fine structures of the stent were visualized more clearly by the PCD-CT than the highest-available resolution provided by the FPD-CBCT. The multi-sweep step-and-shoot acquisition can therefore extend the <i>z</i>-coverage of the C-arm PCD-CT prototype by a factor of 10 to enable high-quality and volumetric C-arm PCD-CT images acquired with a narrow beam-narrow detector setup for image-guided interventions.