International efforts to standardize emerging biomedical imaging approaches, such as photoacoustic imaging (PAI), require stable physical phantoms to enable routine quality control and robust performance evaluation across devices. Addressing this necessity, the International Photoacoustic Standardization Consortium (IPASC) has undertaken a consensus-finding exercise to establish recommendations for the properties of tissue-mimicking phantom materials and their characterization in the field of PAI. The manufacturing reproducibility of a stable copolymer-in-oil tissue-mimicking material fulfilling these recommendations was tested in an international multi-center study involving n=18 different partner sites. Here, the progress made toward these standardization efforts is outlined, highlighting prospects, challenges, and future trajectories.
Longitudinal characterisation of the tumour vascular response to radiotherapy is essential for understanding the role of oxygenation and microvascular disruption in response to therapy. Using multi-scale in vivo photoacoustic imaging (PAI), we assessed early response to two hypofractionated radiotherapy schemes in two human breast cancer models. Mesoscopic and multispectral tomographic photoacoustic imaging was performed 24h pre-, post-radiotherapy, and at endpoint. PAI biomarkers were validated ex vivo with multiplex immunofluorescence using a 20-plex panel developed specifically for vascular response assessment at sub-cellular resolution. PAI captured radiotherapy response, revealing the differential effect between radiotherapy schemes and models with different hypoxia phenotypes.
Longitudinal mesoscopic photoacoustic imaging of vascular networks requires accurate image co-registration to assess local changes in growing tumours, but remains challenging due to sparsity of data and scan-to-scan variability. Here, we compared a set of 5 curated co-registration methods applied to 49 pairs of vascular images of mouse ears and breast cancer xenografts. Images were segmented using a generative adversarial network and pairs of images and/or segmentations were fed into the 5 tested algorithms. We show the feasibility of co-registering vascular networks accurately using a range of quality metrics, taking a step towards longitudinal characterization of those complex structures.
The International Photoacoustic Standardisation Consortium (IPASC) hereby reports the results of a consensus-finding exercise undertaken to agree recommendations for properties of tissue-mimicking phantom materials and their characterization. Guidelines on material properties are given under defined environmental conditions and include, for example, recommendations on optical and acoustic properties, stability, and structural composition. Multi-center studies involving independent fabrication of phantom material batches are encouraged for reproducibility and verification of properties within acceptable ranges. The recommendations aim to support researchers and manufacturers to develop phantoms that facilitate system performance assessment, inter-device comparisons, and system optimization, ultimately advancing photoacoustic technology.
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