Biomedical subjects

Dirk J Faber

Publications and source records attributed to Dirk J Faber.

8 recordsLinked to original sources

PubMed2006

Recent developments in optical coherence tomography for imaging the retina.

Optical coherence tomography (OCT) was introduced in ophthalmology a decade ago. Within a few years in vivo imaging of the healthy retina and optic nerve head and of retinal diseases was a fact. In particular the ease with which these images can be acquired considerably changed the diagnostic strategy used by ophthalmologists. The OCT technique currently available in clinical practice is referred to as time-domain OCT, because the depth information of the retina is acquired as a sequence of samples, over time. This can be done either in longitudinal cross-sections perpendicular to, or in the coronal plane parallel to the retinal surface. Only recently, major advances have been made as to image resolution with the introduction of ultrahigh resolution OCT and in imaging speed, signal-to-noise ratio and sensitivity with the introduction of spectral-domain OCT. Functional OCT is the next frontier in OCT imaging. For example, polarization-sensitive OCT uses the birefringent characteristics of the retinal nerve fibre layer to better assess its thickness. Blood flow information from retinal vessels as well as the oxygenation state of retinal tissue can be extracted from the OCT signal. Very promising are the developments in contrast-enhanced molecular optical imaging, for example with the use of scattering tuneable nanoparticles targeted at specific tissue or cell structures. This review will provide an overview of these most recent developments in the field of OCT imaging focussing on applications for the retina.

Humans↗

PubMed2006

Abnormal arterial flows by a distributed model of the fetal circulation.

Modeling the propagation of blood pressure and flow along the fetoplacental arterial tree may improve interpretation of abnormal flow velocity waveforms in fetuses. The current models, however, either do not include a wide range of gestational ages or do not account for variation in anatomical, vascular, or rheological parameters. We developed a mathematical model of the pulsating fetoumbilical arterial circulation using Womersley's oscillatory flow theory and viscoelastic arterial wall properties. Arterial flow waves are calculated at different arterial locations from which the pulsatility index (PI) can be determined. We varied blood viscosity, placental and brain resistances, placental compliance, heart rate, stiffness of the arterial wall, and length of the umbilical arteries. The PI increases in the umbilical artery and decreases in the cerebral arteries, as a result of increasing placental resistance or decreasing brain resistance. Both changes in resistance decrease the flow through the placenta. An increased arterial stiffness increases the PIs in the entire fetoplacental circulation. Blood viscosity and peripheral bed compliance have limited influence on the flow profiles. Bradycardia and tachycardia increase and decrease the PI in all arteries, respectively. Umbilical arterial length has limited influence on the PI but affects the mean arterial pressure at the placental cord insertion. The model may improve the interpretation of arterial flow pulsations and thus may advance both the understanding of pathophysiological processes and clinical management.

Arteries↗

PubMed2005

Toward assessment of blood oxygen saturation by spectroscopic optical coherence tomography.

The use of spectroscopic optical coherence tomography to assess hemoglobin oxygen saturation of whole blood is investigated. We propose to use the differential attenuation coefficient to determine the degree of saturation. Our data show qualitative agreement between the measured differential attenuation coefficients as a function of saturation and predictions based on the oxygen-saturation-dependent absorption and scattering properties of blood.

Algorithms↗

PubMed2005

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.

Algorithms↗

PubMed2004

Oxygen saturation-dependent absorption and scattering of blood.

We report on the scattering properties of oxygenated and deoxygenated whole blood from 250 to 1000 nm. We determine the complex refractive index of oxygenated and deoxygenated hemoglobin using a Kramers-Kronig analysis and optical coherence tomography measurements. Combining these data with Mie theory, the scattering properties are calculated. The strong oxygen saturation dependent scattering effects should be taken into account in the data analysis of optical oxymetry.

Absorption↗

PubMed2003

Light absorption of (oxy-)hemoglobin assessed by spectroscopic optical coherence tomography.

The combination of optical coherence tomography and spectroscopy may allow for highly localized, quantitative measurements of tissue spectral properties. We present, for the first time to our knowledge, quantitative measurements of the absorption coefficients of phantoms and of hemoglobin and oxygenated hemoglobin with spectroscopic optical coherence tomography (SOCT). Our results suggest that SOCT will be able to provide localized, quantitative oxygenation measurements.

Absorption↗

PubMedDate not supplied

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.

Body Temperature↗

PubMedDate not supplied

Doppler optical coherence tomography to monitor the effect of photodynamic therapy on tissue morphology and perfusion.

We investigated the feasibility of using optical coherence tomography (OCT) for noninvasive real-time visualization of the vascular effects of photodynamic therapy (PDT) in normal and tumor tissue in mice. Perfusion control measurements were initially performed after administrating vaso-active drugs or clamping of the subcutaneous tumors. Subsequent measurements were made on tumor-bearing mice before and after PDT using the photosensitizer meta-tetrahydroxyphenylchlorin (mTHPC). Tumors were illuminated using either a short drug light interval (D-L, 3 h), when mTHPC is primarily located in the tumor vasculature or a long D-L interval (48 h), when the drug is distributed throughout the whole tumor. OCT enabled visualization of the different layers of tumor, and overlying skin with a maximal penetration of < or =0.5-1 mm. PDT with a short D-L interval resulted in a significant decrease of perfusion in the tumor periphery, to 20% of pre-treatment values at 160 min, whereas perfusion in the skin initially increased by 10% (at 25 min) and subsequently decreased to 60% of pre-treatment values (at 200 min). PDT with a long D-L interval did not induce significant changes in perfusion. The concept of using noninvasive OCT measurements for monitoring early, treatment-related changes in morphology and perfusion may have applications in evaluating effects of anti-angiogenic or antivascular (cancer) therapy.

Animals↗