Reflected QPLI

Transmitted QPLI, as our lab has used extensively in the past, is capable of real time imaging of collagen alignment with adequate temporal and spatial resolution to quantify dynamic structure-function relationships. However, since this QPLI mode is transmission-based, it requires excision and thinning of tissues to allow for light penetration, thereby limiting physiological relevance. By modifying the technique to be reflected light based (rQPLI: reflectance quantitative polarized light imaging), we intend to enable a similar analysis with in situ tissues under more complex loading regimes and environmental conditions. rQPLI can enable nuanced, real time analysis of collagen fiber architecture in scenarios where information about the ECM response is currently not well understood: prior to acute failure or immediately after repair.

Development

Using a custom built wooden arch we are able to position our polarization camera and light source at specific angles. Light is reflected off our tissue of interest and changes are detected by the polarization camera.

rQPLI Setup Optimization

Preliminary experiments have been performed to optimize the rQPLI setup (i.e. light source angle, camera location, polarization state of incident light) for optimal signal-to-noise ratio and to ensure robust data acquisition.

Reflectance vs. Transmission QPLI

We have created engineered tissue analogs  of varying anisotropies to experimentally evaluate signal differences between transmission and reflectance QPLI.

We also are developing Monte Carlo photon transport simulations to computationally evaluate differences.

Current Application

rQPLI is currently being used to evaluate region-specific damage accumulation in the ulnar collateral ligament of the elbow during fatigue valgus loading. This mimics the repetitive overhand throwing motion seen in baseball pitchers that can eventually lead to the need for Tommy John surgery.

Biologically-mediated Tendon Damage

rQPLI is currently being used to evaluate temporal progression of damage accumulation in the rotator cuff during enzymatic digestion. This mimics the onset of degenerative processes associated with disease or aging in the rotator cuff tendons of the shoulder that are not well understood.

In Review

1. King NO, Bhimani R, Castile RM, Garcia M, Gruev V, Lake SP: A non-invasive reflectance-based polarization method for tracking dynamic changes to collagen organization in mechanically loaded connective tissues, In review.