Polyacrylamide hydrogel phantoms for performance evaluation of multispectral photoacoustic imaging systems

Abstract

As photoacoustic imaging (PAI) begins to mature and undergo clinical translation, there is a need for well-validated, standardized performance test methods to support device development, quality control, and regulatory evaluation. Despite recent progress, current PAI phantoms may not adequately replicate tissue light and sound transport over the full range of optical wavelengths and acoustic frequencies employed by reported PAI devices. Here we introduce polyacrylamide (PAA) hydrogel as a candidate material for fabricating stable phantoms with well-characterized optical and acoustic properties that are biologically relevant over a broad range of system design parameters. We evaluated suitability of PAA phantoms for conducting image quality assessment of three PAI systems with substantially different operating parameters including two commercial systems and a custom system. Imaging results indicated that appropriately tuned PAA phantoms are useful tools for assessing and comparing PAI system image quality. These phantoms may also facilitate future standardization of performance test methodology.

Review of consensus test methods in medical imaging and current practices in photoacoustic image quality assessment

“…One self-consistent set of metric definitions capturing both of these effects that we have employed is , , and , which also yields the relationship . 92 One benefit of developing consensus documents is the establishment of standardized terms and definitions to enable reproducible data analysis and comparison of test results between systems.…”

“…2.4 . 86 , 92 Because depth of visualization depends on target absorption coefficient, target absorption values should be relevant to the intended imaging application and should include low-contrast conditions.…”

“…The ideal phantom for testing sensitivity should have targets of various absorption coefficients located at several depths. 92 , 128 It may also be appropriate to perform testing in phantoms with different background optical and/or acoustic properties to characterize how tissue background affects sensitivity and target detectability. 139 , 153 …”

Suite of 3D test objects for performance assessment of hybrid photoacoustic-ultrasound breast imaging systems

“…Wires or channels filled with blood mimicking liquids located at different depths in a tissue-mimicking material have been reported multiple times to measure the imaging depth of PA systems with a linear or planar detector array. 28,[35][36][37][38] As an approach to measure the imaging depth of a system with a 3D imaging aperture, a transparent disk printed with red dots was placed at different heights in an acoustically absorbing medium. 32,39 To assess the ability of a system to resolve an object from the background, targets with different optical absorption coefficients have been embedded in a material with tissue relevant properties.…”

“…27 (ii) The second phase usually consists of a set of measurements where the image quality characteristics (IQCs) of the system are assessed and benchmarked under methodical changes of the measurement sequence and parameters in the reconstruction algorithms. [28][29][30] Measurement settings resulting in optimized IQCs with a minimum required measurement time to minimize motion artefacts and burden to the patient are hereby the target. (iii) In the third phase, measurements on more complex objects, such as breast mimicking phantoms or healthy breasts, are performed to test the system to a higher extent and to train the users.…”