Shallow breast lesions less than 1.0 cm deep are frequently seen in patients when they are
scanned in a supine position by a hand-held combined ultrasound and optical probe.
Reflection boundary condition is suitable for imaging shallow lesions, but it is not
sensitive enough for imaging lesions deeper than 1.0 cm. The absorption boundary
condition is more desirable for imaging deeper lesions. However, it is less sensitive to
shallower lesions unless the optical sources are positioned right on top of the lesion
which is unknown in general. To solve this problem, we have designed a new probe
which incorporates three angled sources to improve the illumination of the shallow region
underneath the co-registered ultrasound probe. Monte Carlo method is extended to
include an absorber in the medium and used to evaluate the analytical results.
Simulations have shown that the combination of tilted and peripherally located sources
can improve reconstruction compared with the probe with no tilted sources. Phantom
experiments agree with simulation results.