  We present a photoacoustic computed tomography investigation on a healthy
human finger, to image blood vessels with a focus on vascularity across the
interphalangeal joints. The cross-sectional images were acquired using an
imager specifically developed for this purpose. The images show rich detail of
the digital blood vessels with diameters between 100 $\mu$m and 1.5 mm in
various orientations and at various depths. Different vascular layers in the
skin including the subpapillary plexus could also be visualized. Acoustic
reflections on the finger bone of photoacoustic signals from skin were visible
in sequential slice images along the finger except at the location of the joint
gaps. Not unexpectedly, the healthy synovial membrane at the joint gaps was not
detected due to its small size and normal vascularization. Future research will
concentrate on studying digits afflicted with rheumatoid arthritis to detect
the inflamed synovium with its heightened vascularization, whose
characteristics are potential markers for disease activity.
