Optimising image quality in intravenous cerebral cone beam computed tomography

Abstract

Introduction: The efficacy of intravenous cerebral Cone Beam Computed Tomography (IV CBCT) is well established; however, image quality has only ever been authenticated by subjective evaluation. The aim of this study was to quantify the factors pertinent to achieving consistent and optimal image quality when performing IV CBCT.

Methods: Between 1 March 2021 and 30 October 2022, 79 patients received IV CBCT. These candidates were divided into three main acquisition field size categories (22/32, 42 and 48 cm) according to the clinical indication. The images were analysed using both a quantitative assessment and a subjective evaluation. Here, a comparison of Hounsfield units (HUs), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and noise index was conducted for each study and compared relative to the acquisition field size. The subjective analysis was performed in a non-blinded fashion where the diagnostic value (DV) of the exam was determined according to a graded scale. A phantom analysis for each of the acquisition field sizes was conducted and modulation transfer function (MTF) graphed.

Results: Significantly higher HU, SNR, CNR and lower noise indices were achieved with the 42-cm protocol than the 22/32 and 48-cm protocols. Here a greater DV was also reported. The MTF demonstrates marginally improved spatial resolution for the 22-cm protocol, but this is near equivocal for the 32-, 42 and 48-cm protocols.

Conclusion: The use of larger acquisition field sizes provides improved image quality when performing IV CBCT as an alternative to intra-arterial (IA) CBCT.

Keywords: angiography; head and neck; vascular interventional.

Figure 1

Measured and fitted modulation transfer function for 22, 32, 42, 48‐cm fields of view, using the small focus.

Figure 2

Identical patient – a comparison of 22‐cm versus 42‐cm FOV with regard to acquisition KV, spatial resolution and image noise. (A) A significant increase in in image noise when compared to (B) obscuring visualisation of the orbitofrontal and anterior temporal arteries.

Figure 3

‘Refined volume’ reconstruction combined with standard and sharp algorithms. (A) Full skull, 10mm MIP. (B) Full skull, digital zoom, 10mm MIP. (C) 'Refined volume', 10mm MIP. (D) 'Refined volume', sharp algorithm, 10mm MIP.