Apoptosis- and necrosis-induced changes in light attenuation measured by optical coherence tomography.

Optical coherence tomography (OCT) was used to determine optical properties of pelleted human fibroblasts in which necrosis or apoptosis had been induced. We analysed the OCT data, including both the scattering properties of the medium and the axial point spread function of the OCT system. The optical attenuation coefficient in necrotic cells decreased from 2.2 +/- 0.3 mm(1) to 1.3 +/- 0.6 mm(-1), whereas, in the apoptotic cells, an increase to 6.4 +/- 1.7 mm(-1) was observed. The results from cultured cells, as presented in this study, indicate the ability of OCT to detect and differentiate between viable, apoptotic, and necrotic cells, based on their attenuation coefficient. This functional supplement to high-resolution OCT imaging can be of great clinical benefit, enabling on-line monitoring of tissues, e.g. for feedback in cancer treatment.

Temperature-dependent optical properties of individual vascular wall components measured by optical coherence tomography.

Optical properties of tissues and tissue components are important parameters in biomedical optics. We report measurements of tissue refractive index n and the attenuation coefficient mu(t) using optical coherence tomography (OCT) of individual vascular wall layers and plaque components. Moreover, since the temperature dependence of optical properties is widely known, we compare measurements at room and body temperatures. A decrease of n and mu(t) is observed in all samples, with the most profound effect on samples with high lipid content. The sample temperature is of influence on the quantitative measurements within OCT images. For extrapolation of ex-vivo experimental results, especially for structures with high lipid content, this effect should be taken into account.

Localized measurement of optical attenuation coefficients of atherosclerotic plaque constituents by quantitative optical coherence tomography.

Optical coherence tomography (OCT) is a novel, high-resolution diagnostic tool that is capable of imaging the arterial wall and plaques. The differentiation between different types of atherosclerotic plaque is based on qualitative differences in gray levels and structural appearance. We hypothesize that a quantitative data analysis of the OCT signal allows measurement of light attenuation by the local tissue components, which can facilitate quantitative spatial discrimination between plaque constituents. High-resolution OCT images (at 800 nm) of human atherosclerotic arterial segments obtained at autopsy were histologically validated. Using a new, simple analysis algorithm, which incorporates the confocal properties of the OCT system, the light attenuation coefficients for these constituents were determined: for diffuse intimal thickening (5.5 +/- 1.2 mm(-1)) and lipid-rich regions (3.2 +/- 1.1 mm(-1)), the attenuation differed significantly from media (9.9 +/- 1.8 mm(-1)), calcifications (11.1 +/- 4.9 mm(-1) ) and thrombi (11.2 +/- 2.3 mm(-1)) (p < 0.01). These proof of principle studies show that simple quantitative analysis of the OCT signals allows spatial determination of the intrinsic optical attenuation coefficient of atherosclerotic tissue components within regions of interest. Combining morphological imaging by OCT with the observed differences in optical attenuation coefficients of the various regions may enhance discrimination between various plaque types.

Matrix metalloproteinase inhibition reduces adventitial thickening and collagen accumulation following balloon dilation.

OBJECTIVE: Constrictive arterial remodeling following balloon angioplasty has been related to adventitial collagen accumulation and subsequent thickening and can be prevented by matrix metalloproteinase (MMP) inhibition. Following balloon dilation, we examined the effect of MMP inhibition on collagen turnover and the relationship between adventitial area and degree of constrictive remodeling. METHODS: In 12 non-atherosclerotic landrace pigs, balloon dilation was performed in 39 peripheral arteries with and without MMP inhibition. Follow up with intravascular ultrasound was performed at 42 days. Collagen content was quantified using polarized light and digital image microscopy. Procollagen expression was determined using immunochemistry and Western blotting. RESULTS: In the MMP inhibitor group, constrictive remodeling was inhibited at 42 days follow up. In control and MMP inhibitor groups, a positive relation was observed between adventitial thickness and degree of constrictive remodeling (P<0.001). Adventitial thickening and adventitial collagen content were reduced in the MMP inhibitor group (P=0.002 and P=0.001, respectively). Procollagen immunostaining, but not protein analysis on Western blotting, was decreased in the MMP inhibitor group. CONCLUSION: MMP inhibition impaired adventitial thickening by reduction of collagen content 42 days after balloon dilation. This might explain its inhibitory effect on constrictive remodeling.