Phantoms for use in optical coherence elastography

Optical coherence elastography (OCE) is an emerging biomedical imaging technique for mapping the micro-scale mechanical properties of tissue. Phantoms are vital for assessing OCE imaging performance in a controlled and systematic manner. Although the use of phantoms in OCE has been widely demonstrated, there is no consensus on suitable phantom materials or fabrication methods, limiting reproducibility and inter-laboratory comparison of OCE techniques.

Our aim is to establish a unified framework for selecting, fabricating, and characterizing OCE phantoms by systematically evaluating the mechanical, optical, and structural properties of silicone, agar, and gelatin, the three most widely used OCE phantom materials.

We conducted a literature review of phantom fabrication methods reported in OCE studies published between 1998 and 2025, comprising 223 papers, and identified silicone, agar, and gelatin as the most widely used OCE phantom materials. We experimentally characterized the elasticity, viscoelasticity, and attenuation coefficient of homogeneous phantoms fabricated from each material and investigated the effects of shelf life and optical scatterer concentration on mechanical properties. We further fabricated inclusion phantoms and tissue-mimicking surface roughness phantoms derived from optical coherence tomography (OCT) scans of human breast tissue using all three materials and evaluated their imaging performance using a compression OCE technique, quantitative micro-elastography (QME).

The elastic (tangent) modulus ranged from 7.2 to 175.9 kPa for silicone, 9.7 to 229.1 kPa for agar, and 3.5 to 29.4 kPa for gelatin, while OCT attenuation coefficients ranged from 0.2 to $13.1{\mathrm{mm}}^{-1}$ across the three materials. Stress relaxation testing revealed distinct viscoelastic signatures, with relaxation time constants ranging from $\sim 2s$ in silicone to over 1600 s in gelatin. We demonstrated that optical attenuation in these materials can be varied independently of mechanical properties. Inclusion and surface roughness phantoms were successfully fabricated from all three materials, with QME measurements revealing material-specific fabrication artifacts and demonstrating that surface topography can produce erroneous mechanical contrast in mechanically uniform materials.

This study provides a framework to guide phantom material selection, fabrication, and characterization in OCE, identifying silicone as best suited for durable, predominantly elastic phantoms; agar for viscoelastic phantoms across a broad elasticity range; and gelatin for soft, highly viscoelastic phantoms. We believe that the results presented here will support standardization in OCE phantom development and will enable more detailed analysis, validation, and comparison of OCE techniques.