A method for delineation of bone surfaces in photoacoustic computed tomography of the finger

TL;DR

This paper introduces a novel photoacoustic imaging method that uses epidermal signals as virtual ultrasound sources to accurately delineate bone surfaces and joint spaces in finger imaging, aiding rheumatoid arthritis assessment.

Contribution

The method uniquely treats epidermal photoacoustic signals as virtual transmitters, enabling bone surface and joint space identification without additional ultrasound hardware.

Findings

Successfully tested on phantoms and a human finger

Improves bone surface delineation and artifact removal

Enables joint space localization in photoacoustic imaging

Abstract

Photoacoustic imaging of interphalangeal peripheral joints is of interest in the context of using the synovial membrane as a surrogate marker of rheumatoid arthritis. Previous work has shown that ultrasound produced by absorption of light at the epidermis reflects on the bone surfaces within the finger. When the reflected signals are backprojected in the region of interest, artifacts are produced, confounding interpretation of the images. In this work, we present an approach where the photoacoustic signals known to originate from the epidermis, are treated as virtual ultrasound transmitters, and a separate reconstruction is performed as in ultrasound reflection imaging. This allows us to identify the bone surfaces. Further, the identification of the joint space is important as this provides a landmark to localize a region-of-interest in seeking the inflamed synovial membrane. The ability to delineate bone surfaces allows us not only to identify the artifacts, but also to identify the interphalangeal joint space without recourse to new US hardware or a new measurement. We test the approach on phantoms and on a healthy human finger.