System development for high frequency ultrasound-guided fluorescence quantification of skin layers

A high frequency ultrasound-coupled fluores- cence tomography system, primarily designed for imaging of protoporphyrin IX production in skin tumors in vivo ,i s demonstrated for the first time. The design couples fiber- based spectral sampling of the protoporphyrin IX fluores- cence emission with high frequency ultrasound imaging, allowing thin-layer fluorescence intensities to be quanti- fied. The system measurements are obtained by serial illu- mination of four linear source locations, with parallel de- tection at each of five interspersed detection locations, providing 20 overlapping measures of subsurface fluores- cence from both superficial and deep locations in the ul- trasound field. Tissue layers are defined from the seg- mented ultrasound images and diffusion theory used to estimate the fluorescence in these layers. The system cali- bration is presented with simulation and phantom valida- tion of the system in multilayer regions. Pilot in-vivo data are also presented, showing recovery of subcutaneous tu- mor tissue values of protoporphyrin IX in a subcutaneous U251 tumor, which has less fluorescence than the skin.