Optimising the Edinburgh Pipe Phantom for the assessment of nonlinear imaging techniques

Josephine Hoare¹, Raphaela Baesso², Scott Inglis³, Stephen Pye¹, Carmel M Moran¹, ¹Centre for Cardiovascular Science, University of Edinburgh, ²Ultrasound and Underwater Acoustics, National Physical Laboratory, ³Royal Infirmary of Edinburgh, NHS Lothian

Introduction:

Quality assurance (QA) in medical ultrasound ensures that imaging equipment performs reliably
throughout its clinical lifetime. The Edinburgh Pipe Phantom (EPP) has been previously developed to
measure a single figure of merit, the resolution integral (Pye and Ellis, 2004). This metric assesses
ultrasound scanner performance throughout its clinical lifetime, but can also be used during
research and development, and for supporting scanner procurement and replacement decisions.

Since phantoms must accurately mimic the acoustic properties of soft tissue, characterisation
of key acoustic parameters such as speed of sound (SoS), the attenuation coefficient (α), and the
nonlinearity parameter (B/A) is essential to ensure phantom suitability for QA applications and
advanced imaging techniques like tissue harmonic imaging.

Methods:

An experimental setup implementing the finite-amplitude insertion substitution (FAIS) technique
has been developed based on prior work (Zeqiri et al., 2015), and validated using ethylene glycol — a
well-characterised reference material with established literature values. This validation confirms the
system’s capability for precise B/A measurement.

The previous measurement system has been redesigned to include a 5-axis motorised tank,
improving positioning accuracy and repeatability compared to the original 2015 setup. Using this
enhanced system, initial characterisation of acoustic properties (SoS and α) was performed across
the frequency range of 1 – 20 MHz on two versions of the IEC standard agar tissue-mimicking
material (TMM): one manufactured at the National Physical Laboratory (NPL), and another at the
Royal Infirmary of Edinburgh (RIE).

Results:

Variation in the manufacturing procedure between the RIE and NPL does not produce statistically
significant differences in speed of sound and the attenuation coefficient across the studied
frequency range, supporting the consistency and reliability of the EPP TMM for QA phantoms.

Conclusion:

Ongoing work focuses on comprehensive B/A characterisation to further refine phantom materials,
enabling improved replication of soft tissue acoustic behaviour and enhancing the evaluation of
emerging nonlinear ultrasound imaging.
 

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