An active, hardware-based retinal tracker is integrated with a clinical optical coherence tomography (OCT) system to investigate the effects of stabilization on acquisition of high-resolution retinal sections. The prototype retinal tracker locks onto common fundus features, detects transverse eye motion via changes in feature reflectance, and positions the OCT diagnostic beam to fixed coordinates on the retina with mirrors driven by a feedback control loop. The system is tested in a full clinical protocol on subjects with normal and glaucomatous eyes. Experimental analysis software is developed to coalign and coadd multiple fundus and OCT images and to extract quantitative information on the location of structures in the images. Tracking is highly accurate and reproducible on all but one subject, resulting in the ability to scan the same retinal location continually over long periods of time. The results show qualitative improvement in 97% of coadded OCT scans and a reduction in the variance of the position of the optic disc cup edge to less than 1 pixel (<60 µm). The tracking system can be easily configured for use in research on ultra-high-resolution OCT systems for advanced image modalities. For example, tracking will enable very high density 3-D scans of the retina, which are susceptible to eye motion artifacts even for new high-speed systems.
An ultrahigh resolution ophthalmic optical coherence tomography (OCT) system has been developed. Using a femtosecond Ti:sapphire laser light source, which generates bandwidths of ~150 nm at 800 nm, real-time, cross-sectional imaging of the retina with ~3 μm axial resolution is possible. Ultrahigh resolution OCT images of retinal morphology were obtained in normal subjects and patients with retinal disease. Intraretinal architectural morphology associated with macular diseases such as macular edema, epiretinal membranes, and macular holes can be visualized with unprecedented resolution. Ultrahigh resolution ophthalmic OCT promises to improve the early diagnosis of retinal diseases as well as enable monitoring of disease progression and the efficacy of therapeutic intervention.
KEYWORDS: Glucose, Blood, Scattering, Near infrared, Absorption, Near infrared spectroscopy, Spectroscopy, Light scattering, In vitro testing, Data acquisition
We study the correlation between (mu) s' and THC obtained in vitro, in a highly scattering medium containing human blood. We used a frequency domain near infrared spectrometer (modulation frequency: 110 MHz, wavelengths: 758 and 830 nm) to measure in real time (acquisition time: 0.64 s) (mu) s' and THC. We used Liposyn suspension and red blood cells in saline buffer solution. After a couple of minutes of baseline acquisition, several consecutive increments of 3-5 ml blood were added to the solution yielding THC equals 15-100 (mu) M and (mu) a equals 0.03-0.3 1/cm. At the last amount of blood added, increments of glucose in the range of 0.5-20 g/L were added. For each step of blood and glucose added, data were acquired for a couple of minutes. This was repeated 6 times. Average of data was calculated for both (mu) s' and THC for each of the red blood cells and glucose increments added. We found a high correlation between (mu) s' and THC (0.018 X THC + 4.51, R2 equals 0.98 at 758 nm and 0.012 X THC + 4.86, R2 equals 0.97 at 830 nm). We studied the effect of glucose on (mu) s' and we found a high correlation between the glucose added to the suspension and the decrease in (mu) s' for the case of high glucose concentrations. The slope of this correlation is -0.011 at both wavelengths and the correlation factors were R2 X 0.96 at 830 nm and R2 equals 0.91 at 758 nm (case shown). The effect of glucose was less significant at 830 nm than at 758 nm in general. This work is a proof of principle for detection of (mu) s' changes with glucose. This approach also establishes limits for glucose detection in physiological conditions.
We present non-invasive measurements of the calf muscle blood flow (BF) and oxygen consumption (OC) by near-infrared spectroscopy. We used a frequency domain tissue oximeter (modulation frequency: 110 MHz, wavelengths: 758 and 830 nm) to measure in real time (acquisition time: 0.64 s) the hemoglobin concentration and saturation. After 1-min of baseline acquisition, we achieved venous occlusion by inflating a pneumatic cuff on the subjectÕs thigh to a pressure of 60 mmHg. The cuff was released after 1 min. The baseline/inflation/release procedure was repeated 3 times to verify reproducibility. We calculated the BF and OC from the initial rate of increase of the total hemoglobin and deoxy-hemoglobin concentration immediately after the onset of venous occlusion. We examined 8 healthy subjects and 18 patients affected by peripheral vascular disease (PVD) in 1 or 2 legs to investigate whether muscle BF and OC at rest can be useful indicators of vascular insufficiency. In healthy legs, we obtained average values of BF=0.73 ml/(100ml)/min and OC=0.10 ml/(100g)/min. The corresponding average values found in legs affected by PVD are BF=1.39 ml/(100ml)/min and OC=0.16 ml/(100g)/min. The ranges of values of BF and OC measured in the healthy legs broadly overlap with the corresponding ranges measured in the PVD legs.
We present a novel technique based on tilting the bed where the subject is lying, to non-invasively measure the tissue blood flow (BF) and oxygen consumption (OC) with near-infrared (NIR) spectroscopy. We used a NIR, frequency domain spectrometer to measure the concentrations of oxy-hemoglobin ([HbO2]), deoxy-hemoglobin ([Hb]) and total hemoglobin (THC) in the calf muscle of human subjects. The subject was lying horizontally, and after a baseline acquisition, the bed was tilted by 10 degrees (feet down, head up). This position was kept for 1 min, then the subject was brought back to the horizontal position. This tilting procedure caused variations in the calf [Hb02], [Hb], and THC similar to those observed during a pneumatic-cuff-induced venous occlusion. The increasing rate of THC and [Hb] caused by tilting allowed the calculation of blood flow and oxygen consumption. We found a quantitative agreement between the values of BF (OC) measured with the tilting table and with the venous occlusion protocols. On the 26 subjects examined with the tilting table protocol, we found population average values of BF = 1.51 ml (100ml)-1-min-1 and OC = 6.10 ?mol( 100ml)-1 min-1.
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