A diagnostic system for articular cartilage using non-destructive pulsed laser irradiation

Osteoarthritis involves dysfunction caused by cartilage degeneration, but objective evaluation methodologies based on the original function of the articular cartilage remain unavailable. Evaluations for osteoarthritis are mostly based simply on patient symptoms or the degree of joint space narrowing on X-ray images. Accurate measurement and quantitative evaluation of the mechanical characteristics of the cartilage is important, and the tissue properties of the original articular cartilage must be clarified to understand the pathological condition in detail and to correctly judge the efficacy of treatment. We have developed new methods to measure some essential properties of cartilage: a photoacoustic measurement method; and time-resolved fluorescence spectroscopy.

A nanosecond-pulsed laser, which is completely non-destructive, is focused onto the target cartilage and induces a photoacoustic wave that will propagate with attenuation and is affected by the viscoelasticity of the surrounding cartilage. We also investigated whether pulsed laser irradiation and the measurement of excited autofluorescence allow real-time, non-invasive evaluation of tissue characteristics.

The decay time, during which the amplitude of the photoacoustic wave is reduced by a factor of 1/e, represents the key numerical value used to characterize and evaluate the viscoelasticity and rheological behavior of the cartilage. Our findings show that time-resolved laser-induced autofluorescence spectroscopy (TR-LIFS) is useful for evaluating tissue-engineered cartilage.

Photoacoustic measurement and TR-LIFS, predicated on the interactions between optics and living organs, is a suitable methodology for diagnosis during arthroscopy, allowing quantitative and multidirectional evaluation of the original function of the cartilage based on a variety of parameters.