The test sample, consisting of the cylindrical calibration polyacetal test socket and polycarbonate tube [Figs. 1] is relevant to the proposed application of this technique, as the same sample was also used to calibrate the system used for in vivo fluorescence measurements. Gel samples were prepared by placing small amounts of the gel within the calibration socket containing five wide grooves, each a different depth (50, 106, 192, 277, and ), with bottoms concentric to the tube surface [Fig. 1]. A halved transparent tube was placed within the calibration socket, spreading the gel within the groove and providing a front surface for the gel to adhere to [Fig. 1]. The tube was secured to the calibration socket to prevent lateral movement of the tube within the socket during measurement. In the experiments presented below, KY Jelly (Johnson & Johnson, Inc.) was used as a sample gel. This gel is based on hydroxyl ethyl cellulose, and has been characterized in vaginal imaging studies in women. The calibration socket was translated laterally relative to the beam exiting the fiber, positioning the beam at each groove for data collection. For the experiments with the clinical fluorescence-based system, the gel was deployed within a similar cylindrical test socket, which is routinely used for calibration prior to clinical application. This second socket also has a series of wide grooves, each of a different depth (94, 183, 294, 373, and ). These grooves are filled with gel rendered fluorescent by the addition of 0.1% USP grade injectable fluorescein powder to allow thickness measurement using the fluorescence-based system.