IR Microscopic Imaging of Pathological States and Fracture Healing of Bone

Abstract

The application of IR microscopic imaging to the study of bone disease and fracture healing is demonstrated. Samples of normal and osteoporotic human iliac crest biopsies were prepared and examined at ∼6–10 μm spatial resolution and 8 cm⁻¹ spectral resolution with a 64 × 64 MCT focal plane array detector coupled to a Fourier transform infrared (FT-IR) microscope and a step-scanning interferometer. Two spectral parameters, one that monitors the extent of mineral (hydroxyapatite) formation in the tissue and another that monitors the size/perfection of the crystals, were compared in the samples generated from normal and pathological tissues. The average mineral levels in the osteoporotic sample were reduced by ∼ 40% from the normal. In addition, the crystal size/perfection was substantially enhanced in the disease state. The applicability of IR imaging techniques to the study of therapeutic intervention was also investigated in a study of the effects of estrogen therapy on fracture healing in rat femurs. Femurs were examined by IR microscopic imaging 4 weeks after fracture. IR imaging showed that the mineral level was enhanced in estrogen-treated samples. In addition, the crystals were larger/more perfect in the treated specimens. These data demonstrate the utility of IR spectroscopic imaging for the study of pathological states of hard tissue.