Transcutaneous fiber optic Raman spectroscopy of bone using annular illumination and a circular array of collection fibers

Transcutaneous bone Raman spectroscopy with an exciting annulus of $785-nm$ laser light surrounding the field of view of a circular array of collection fibers is demonstrated. The configuration provides distributed laser light. The annulus is located $2to3mm$ beyond the edge of the field of view of the collection fibers to reject contributions from skin and other overlying tissues. Data are presented for rat and chicken tissue. For rat tibia, the carbonate/phosphate ratio measured at a depth of $1mm$ below the skin is in error by 2.3% at an integration time of $120s$ and within 10% at a $30-s$ integration time. For chicken tibia $4mm$ below the skin surface, the error is less than 8% with a $120-s$ integration time.