A C-arm photon counting CT prototype with volumetric coverage using multi-sweep step-and-shoot acquisitions

Abstract

Objective: Existing clinical C-arm interventional systems use scintillator-based energy-integrating flat panel detectors (FPDs) to generate cone-beam CT (CBCT) images. Despite its volumetric coverage, FPD-CBCT does not provide sufficient low-contrast detectability desired for certain interventional procedures. The purpose of this work was to develop a C-arm photon counting detector (PCD) CT system with a step-and-shoot data acquisition method to further improve the tomographic imaging performance of interventional systems. Approach: As a proof-of-concept, a cadmium telluride-based 51 cm × 0.6 cm PCD was mounted in front of a FPD in an Artis Zee biplane system. A total of 10 C-arm sweeps (5 forward and 5 backward) were prescribed. A motorized patient table prototype was synchronized with the C-arm system such that it translates the object by a designated distance during the sub-second rest time in between gantry sweeps. To evaluate whether this multi-sweep step-and-shoot acquisition strategy can generate high-quality and volumetric PCD-CT images without geometric distortion artifacts, experiments were performed using physical phantoms, a human cadaver head, and an in vivo swine subject. Comparison with FPD-CT was made under matched narrow beam collimation and radiation dose conditions. Main Results: Compared with FPD-CT images, PCD-CT images had lower noise and improved visualization of low-contrast lesion models, as well as improved visibility of small iodinated blood vessels. Fine structures were visualized more clearly by the PCD-CT than the highest-available resolution provided by FPD-CBCT and MDCT. No perceivable geometric distortion artifacts were observed in the multi-planar PCD-CT images. Significance: This work is the first demonstration of the feasibility of high-quality and multi-planar (volumetric) PCD-CT imaging with a rotating C-arm gantry.

Photon counting-energy integrating hybrid flat panel detector systems for image-guided interventions: an experimental proof-of-concept

“…Again, note that the unbinned (1 × 1) EID-CBCT was acquired under a longer 20 s rotation rather than a 7 s rotation due to detector readout speed limitations when the pixels are unbinned. These images are similar to those obtained with a more narrow PCD-CT in previous work (Treb et al 2022 ) but can be obtained with a single gantry rotation rather than with the multiple rotations needed to obtain sufficient z-coverage in the previous work. For the in vivo animal study, figure 6 shows PCD-CBCT and EID-CBCT MIPs of the brain region of two swine subjects covering the entire axial cross-section.…”

“…These previous results are directly applicable to the PCD module of the hybrid detector design. Subsequent works upgraded the same narrow-width PCD-CT C-arm system with step-and-shoot capabilities to enable volumetric imaging even with narrow beam collimation to avoid scatter and cone-beam artifacts (Treb et al 2022 ), and explored the high-resolution potential of the PCD for UHR PCD-CT. The hybrid PCD-EID design reported in this work represents the next step in developing this prototype PCD C-arm system, and introduces a wider PCD with 2.5 cm z-coverage to enable 2D PCD imaging and reduce the number of step-and-shoot gantry rotations for PCD-CBCT with a given z-coverage.…”

“…Additionally, PCDs weight all individual detected photons equally regardless of their energy since each photon is recorded as a single count, which is a more optimal weighting for image contrast than that of energy integrating detectors (EIDs). PCDs also have negligible detector lag and ghosting which can enable the use of very high frame rates compared to EIDs, and can remove lag artifacts in CT images compared to EID-CBCT (Treb et al 2022 ). Lastly, PCDs offer the additional benefit of superior spatial resolution potential and a much more relaxed tradeoff between spatial resolution and sensor thickness through the use of a semiconductor sensor rather than a scintillator, which reduces the problem of spatial spreading of secondary light quanta in the sensor and opens up possibilities for ultra-high-resolution (UHR) x-ray imaging without sacrificing dose efficiency.…”

“…Another approach is to use an inverse geometry system with a smaller detector and a narrow-beam collimation (Slagowski 2017 ), although inverse geometry C-arms are not commercially available. Alternatively, a PCD strip was mounted on a C-arm to demonstrate the benefits of PCD-CT in improving the low-contrast detectability and spatial resolution (Ji et al 2021 , Treb et al 2021 , 2022 ). To preserve the functionality of the existing FPD, the PCD and the FPD are interchangeable.…”