Dose and image quality for a cone‐beam C‐arm CT system

TLDR

The relationships between kVp, image noise, dose, and contrast perception are discussed. We assess dose and image quality of a state‑of‑the‑art angiographic C‑arm system for 3D neuro‑imaging at various dose levels and tube voltages, and introduce an associated measurement method. The authors use a small ion chamber to directly measure dose at multiple points, defining a new dose metric comparable to conventional CTDIw, since the C‑arm’s beam covers the entire phantom. The new dose metric aligns with conventional CTDIw, and perception studies show that at 60 mGy the 9 mm inset with 0.5 % contrast is visible across 70–125 kVp, while lower tube voltages improve low‑contrast detectability of small objects at a fixed dose.

Abstract

We assess dose and image quality of a state-of-the-art angiographic C-arm system (Axiom Artis dTA, Siemens Medical Solutions, Forchheim, Germany) for three-dimensional neuro-imaging at various dose levels and tube voltages and an associated measurement method. Unlike conventional CT, the beam length covers the entire phantom, hence, the concept of computed tomography dose index (CTDI) is not the metric of choice, and one can revert to conventional dosimetry methods by directly measuring the dose at various points using a small ion chamber. This method allows us to define and compute a new dose metric that is appropriate for a direct comparison with the familiar CTDIw of conventional CT. A perception study involving the CATPHAN 600 indicates that one can expect to see at least the 9 mm inset with 0.5% nominal contrast at the recommended head-scan dose (60 mGy) when using tube voltages ranging from 70 kVp to 125 kVp. When analyzing the impact of tube voltage on image quality at a fixed dose, we found that lower tube voltages gave improved low contrast detectability for small-diameter objects. The relationships between kVp, image noise, dose, and contrast perception are discussed.