Mobile C‐Arm with a CMOS detector: Technical assessment of fluoroscopy and Cone‐Beam CT imaging performance

Abstract

Purpose: Indirect-detection CMOS flat-panel detectors (FPDs) offer fine pixel pitch, fast readout, and low electronic noise in comparison to current a-Si:H FPDs. This work investigates the extent to which these potential advantages affect imaging performance in mobile C-arm fluoroscopy and cone-beam CT (CBCT). Methods: FPDs based on CMOS (Xineos 3030HS, 0.151 mm pixel pitch) or a-Si:H (PaxScan 3030X, 0.194 mm pixel pitch) sensors were outfitted on equivalent mobile C-arms for fluoroscopy and CBCT. Technical assessment of 2D and 3D imaging performance included measurement of electronic noise, gain, lag, modulation transfer function (MTF), noise-power spectrum (NPS), detective quantum efficiency (DQE), and noise-equivalent quanta (NEQ) in fluoroscopy (with entrance air kerma ranging 5 - 800 nGy per frame) and cone-beam CT (with weighted CT dose index, CTDIw, ranging 0.08 – 1 mGy). Image quality was evaluated by clinicians in vascular, orthopaedic, and neurological surgery in realistic interventional scenarios with cadaver subjects emulating a variety of 2D and 3D imaging tasks. Results: The CMOS FPD exhibited ~2-3× lower electronic noise and ~7× lower image lag than the a-Si:H FPD. The 2D (projection) DQE was superior for CMOS at ≤50 nGy per frame, especially at high spatial frequencies (~2% improvement at 0.5 mm−1 and ≥50% improvement at 2.3 mm−1) and was somewhat inferior at moderate-high doses (up to 18% lower DQE for CMOS at 0.5 mm−1). For smooth CBCT reconstructions (low-frequency imaging tasks), CMOS exhibited ~10-20% higher NEQ (at 0.1-0.5 mm−1) at the lowest dose levels (CTDIw ≤0.1 mGy), while the a-Si:H system yielded slightly (~5%) improved NEQ (at 0.1-0.5 lp/mm) at higher dose levels (CTDIw ≥ 0.6 mGy). For sharp CBCT reconstructions (high-frequency imaging tasks), NEQ was ~32% higher above 1 mm−1 for the CMOS system at mid-high dose levels and ≥75% higher at the lowest dose levels (CTDIw ≤0.1 mGy). Observer assessment of 2D and 3D cadaver images corroborated the objective metrics with respect to a variety of pertinent interventional imaging tasks. Conclusion: Measurements of image noise, spatial resolution, DQE, and NEQ indicate improved low-dose performance for the CMOS-based system, particularly at lower doses and higher spatial frequencies. Assessment in realistic imaging scenarios confirmed improved visibility of fine details in low-dose fluoroscopy and CBCT. The results quantify the extent to which CMOS detectors improve mobile C-arm imaging performance, especially in 2D and 3D imaging scenarios involving high-resolution tasks and low-dose conditions.

A mobile isocentric C‐arm for intraoperative cone‐beam CT: Technical assessment of dose and 3D imaging performance

“…Reference point air kerma is measured for each protocol and dose level as detailed in Section 2.B.1 to provide an assessment of dose for the system as deployed in 2D imaging applications. The 2D radiographic/fluoroscopic imaging performance characteristics for a system employing a CMOS detector were reported in previous work 29 and were not included in the results below. Table II summarizes the 3D imaging protocols used in this work, including manufacturer-specified protocols and custom protocols.…”

Dental cone beam CT: An updated review

“…FPD technology provides benefits for imaging, including high spatial resolution, large dynamic range of signal levels, slim structure, and more streamlined imaging chain when compared with traditional image intensifier (II) or charge-coupled device (CCD) based image detectors, which have become obsolete in CBCT equipment [3,22,23]. CMOS technology provides even higher resolution, faster image readout, and lower electronic noise in comparison to current amorphous silicon detector models, which have potential for more optimised scans and improved clinical image quality [24]. Acquired raw data in the form of projection x-ray images go through various pre-processing steps before they can be used for image reconstruction.…”

Comparison of CsI:Tl and Gd2O2S:Tb indirect flat panel detector x‐ray imaging performance in front‐ and back‐irradiation geometries

“…), which respectively consist of 600 and 1000 µm of columnar CsI:Tl deposited onto a reflective aluminum substrate. Commercial I‐FPDs for radiography, fluoroscopy and CBCT commonly feature ~600 µm CsI:Tl layers, and thicker CsI:Tl layers (e.g., 1 mm) are of interest for imaging with higher x‐ray energies. The final scintillator was the FSS 1000 HR (Hamamatsu Photonics, K.K.…”