Multimodal embryonic imaging using optical coherence tomography, selective plane illumination microscopy, and optical projection tomography.

The murine model is commonly utilized for studying developmental diseases. Different optical techniques have been developed to image mouse embryos, but each has its own set of limitations and restrictions. In this study, we compare the performance of the well-established technique of optical coherence tomography (OCT) to the relatively new methods of selective plane illumination microscopy (SPIM) and optical projection tomography (OPT) to assess murine embryonic development. OCT can provide label free high resolution images of the mouse embryo, but suffers from light attenuation that limits visualization of deeper structures. SPIM is able to image shallow regions with great detail utilizing fluorescent contrast. OPT can provide superior imaging depth, and can also use fluorescence labels but, it requires samples to be fixed and cleared before imaging. OCT requires no modification of the embryo, and thus, can be used in vivo and in utero. In this study, we compare the efficacy of OCT, SPIM, and OPT for imaging murine embryonic development. The data demonstrate the superior capability of SPIM and OPT for imaging fine structures with high resolution while only OCT can provide structural and functional imaging of live embryos with micrometer scale resolution.

A focused air-pulse system for optical-coherence-tomography-based measurements of tissue elasticity.

Accurate non-invasive assessment of tissue elasticity in vivo is required for early diagnostics of many tissue abnormalities. We have developed a focused air-pulse system that produces a low-pressure and short-duration air stream, which can be used to excite transient surface waves (SWs) in soft tissues. System characteristics were studied using a high-resolution analog pressure transducer to describe the excitation pressure. Results indicate that the excitation pressure provided by the air-pulse system can be easily controlled by the air source pressure, the angle of delivery, and the distance between the tissue surface and the port of the air-pulse system. Furthermore, we integrated this focused air-pulse system with phase-sensitive optical coherence tomography (PhS-OCT) to make non-contact measurements of tissue elasticity. The PhS-OCT system is used to assess the group velocity of SW propagation, which can be used to determine Young's modulus. Pilot experiments were performed on gelatin phantoms with different concentrations (10%, 12% and 14% w/w). The results demonstrate the feasibility of using this focused air-pulse system combined with PhS-OCT to estimate tissue elasticity. This easily controlled non-contact technique is potentially useful to study the biomechanical properties of ocular and other tissues in vivo.

Permeation of human plasma lipoproteins in human carotid endarterectomy tissues: measurement by optical coherence tomography.

Atherosclerosis is an inflammatory process occurring in arterial tissue, involving the subintimal accumulation of LDL. Measurement of the rate at which LDL and other lipoproteins, such as HDL and VLDL, enter and exit the tissue can provide insight into the mechanisms involved in the development of atherosclerotic lesions. Permeation of VLDL, LDL, HDL, and glucose was measured for both normal and atherosclerotic human carotid endarterectomy tissues (CEA) at 20°C and 37°C using optical coherence tomography (OCT). The rates for LDL permeation through normal CEA tissue were (3.16 ± 0.37) × 10(-5) cm/s at 20°C and (4.77 ± 0.48) × 10(-5) cm/s at 37°C, significantly greater (P < 0.05) than the rates for atherosclerotic CEA tissue at these temperatures [(1.97 ± 0.34) × 10(-5) cm/s at 20°C and (2.01 ± 0.23) × 10(-5) cm/s at 37°C]. This study effectively used OCT to measure the rates at which naturally occurring lipoproteins enter both normal and diseased carotid intimal tissue.

Time dependent changes in aortic tissue during cold storage in physiological solution.

BACKGROUND: Stored vascular tissues are employed in biomedical research for studies in imaging, in biomechanics, and/or in assessing vessel diseases. In the present study, the stability of aortic tissue in phosphate buffer saline (PBS) at 4°C was monitored over a course of 10 days as determined by the rate of glucose permeation measured by optical coherence tomography (OCT) and validated by histology. METHODS AND RESULTS: The initial mean permeability through fresh porcine aorta was (2.32 ± 0.46)× 10(-5)cm/s (n=5); after maintaining the tissue at 4°C for 10 days, the mean rate was (7.37 ± 0.41)× 10(-5)cm/s (n=4), an increase of nearly 300%. A z-test verified that a significant change in the permeability rate (p<0.05) had occurred after 4 days of 4°C storage. Histology was used to quantify changes in tissue pore area. The increase in average pore area paralleled the increase in permeability rate over 10 days. CONCLUSIONS: These results suggest that (1) the structural integrity of aortic tissue at 4°C is retained for at least the first three days after resection and (2) OCT is a powerful technology well suited for evaluating tissue structural integrity over time. GENERAL SIGNIFICANCE: Functional OCT imaging provides for a noninvasive and quantitative technique in determining the structural integrity of aortic tissue stored at 4°C. This modality may be used for assessing the efficacy of other preservation techniques.

Noninvasive monitoring of glucose concentration with optical coherence tomography.

We have proposed a tested in tissue phantoms and in vivo a novel sensor based on optical coherence tomography (OCT) for noninvasive and continuous monitoring of blood glucose concentration. OCT images were obtained from pig and rabbit skin before and after glucose administration. Slopes of OCT signals decreased substantially (~40% in tissues in vivo) and linearly with the increase of blood glucose concentration from 4 to 30 mM, typical for normal and diabetic subjects. Phantom studies demonstrated 1% accuracy of scattering-coefficient measurement. Our theoretical and experimental studies suggest that glucose concentration can potentially be measured noninvasively with high sensitivity and accuracy with OCT systems.