The ring vortex complex flow phantom: characterisation, optimisation and expansion

The field of cardiovascular diagnostic imaging is rapidly evolving, with emerging state-of-the-art medical flow visualisation technologies demonstrating superior quantitative abilities. These techniques require rigorous QA through flow phantoms which generate well-characterised and challenging flows, a requirement not met by current flow test objects. The ring vortex complex flow phantom is a prototype device designed and manufactured in previous work, intended to challenge and assess these next-generation technologies and enable comparison between modalities. The ultrasound-compatible phantom generates
ring vortices over a range of Reynolds numbers. These vortices were previously visualised using Laser-PIV and noted for their reproducibility at the macro-scale.
This work strove to continue the development of this device, by optimising the device, characterising its functionality (both in device and flow) and expanding its modality compatibility. Achieving these objectives would produce a pre-commercial device compatible with both US and MRI, where high confidence is held in its capabilities.
Firstly, the phantom vortices were characterised at the micro-scale, with stability of 80% and reproducibility of 10% found for a range of generating conditions. These thresholds established the levels to which this device and its flows can perform. A QA tool was manufactured to ensure these behaviours were met, with device and flow behaviour tracked in real-time to heighten confidence in correct functionality. The device was optimised to ensure efficient and consistent behaviour, through refinement of the device components and flow generating conditions.
Phantom vortices were then further characterised in the context of analytical models, with vortices found to behave according to the Kaplanski-Rudi viscous vortex ring model. Updated experimental visualisation was performed on the optimised phantom version, with the vortices found to retain their high stability and reproducibility, and low stroke-ratio rings acting according to Kaplanski-Rudi. This consistent agreement established Kaplanski-Rudi model as a useful tool for analytical ground-truth datasets for flow characterisation.
With the ultrasound-compatible phantom suitable for more widespread use, its restriction to US modalities was addressed, and an MRI-compatible version was manufactured. High stability and reproducibility were observed at the macro-scale, and micro-scale analysis revealed Kaplanski-Rudi behaviour despite the significant design change. This proved the consistency of vortex behaviour over a wide range of generating conditions, and its robustness to design changes.
This project significantly improved confidence in the ring vortex phantom, through characterising its vortices’ behaviour (experimentally and analytically), demonstrating device functionality in real-time, and retaining its abilities through a significant re-design for MRI application. The ring vortex phantom is now equipped for the final pre-commercial stage, where widespread imaging through clinical and pre-clinical technologies will demonstrate its usefulness and potential.