Compensated transillumination

Inspiratory contrast for in vivo optical imaging

We demonstrate the use of inspired oxygen and carbon dioxide as a possible route to increase contrast in optical imaging of cancerous tissue. Differential imaging in human xenograft rodent models of cancer exhibits significant variation in signal between normal and cancerous tissue. This differential cancer-specific contrast is stronger and more consistent than the conventional static contrast. This differential technique exploits the response of abnormal tumor vasculature to inhaled gases and could provide a promising alternative to supplement mainstream cancer imaging modalities such as x-rays and MRI.

Frequency-domain immersion technique for accurate optical property measurements of turbid media

We demonstrate that absorption coefficient micro(a) and reduced scattering coefficient micro(s)(?) of a small turbid object can be measured to high accuracy with a frequency-domain immersion technique. For this technique the sample is immersed in a calibrated scattering medium and the optical properties are obtained from a differential measurement. Compared with conventional approaches, the immersion technique improves accuracy, minimizes variations owing to probe coupling and motion, reduces the effects of boundary conditions, and offers simple and rapid measurement once the immersion medium is calibrated. Accuracy tests of immersion-based measurements of micro(a) and micro(s)(?) agree with reference values to within 3.6% and 2.6%, respectively. These tests are limited by the accuracy of the reference samples rather than by the accuracy of the immersion medium or the precision of the immersion approach. We demonstrate the in vivo capabilities of the technique through time-resolved measurements of micro(a) and micro(s)(?) for a human hand during cuff occlusion on the upper arm.