Schematic drawing of the optical coherence tomography (OCT) system and the imaging probe used. The OCT system (a) includes a light source with a broad wavelength distribution (called a low-coherence light source), an interferometer (for dividing/recombining the light), and detection electronics. A compact, pen-sized, handheld probe was used for lateral scanning of the articular cartilage, in conjunction with an aiming beam. The handheld OCT imaging probe (b) consists of a four-lens relay and a scanning mirror. The outer shell of the probe can be detached for ease of sterilization. A/D, analog-to-digital converter; VCR, video cassette recorder.