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Background Despite the efficacy of novel drug eluting stents (DES) in preventing restenosis, this complication still occurs, as do neo-atherosclerosis development and poor stent strut coverage that are associated with stent thrombosis. Safety and efficacy of novel coronary stents are preclinically being tested using an established porcine coronary model. However, the use of young healthy animal only allow limited conclusions to be drawn on the long-term effects, as the artieries do not reflect human pathology of advanced atherosclerosis. A key unresolved question is whether and how the presence, size and composition of pre-existing atherosclerotic plaque affect neointimal healing. Purpose The objective of this study is to understand the role of atherosclerotic plaque in neointimal response following DES placement in a large animal model of coronary artery disease by using optical coherence tomography (OCT) analysis. Methods The study was approved by the animal ethics committee. Familial hypercholesterolemia (FH) swine (n=6 Bretoncelles-Meishan) were given a high fat diet for 12 months to develop atherosclerosis. Stents (n=14) were implanted in n=14 coronary arteries under guidance of OCT with a stent-artery ratio of 1.1:1 at sites of atherosclerotic plaque, and animals were sacrificed after 28 days. Two types of Sirolimus eluting stents with different release profiles were implanted. Serial OCT pullbacks were taken before and after stent placement and after 28 days (follow-up), quantitatively analyzed and compared using dedicated software. The lumen area, stent area, plaque size (calculated as external elastic lamina (EEL) area - lumen area) and neointima (calculated as stent area – lumen area) were evaluated for each frame and averaged per stent. The plaque burden before stent implantation was evaluated at the same site of stent placement using coronary side branches as reference. Results The graph shows the association between the pre-existing plaque size before stenting and neointima formation after 28 days. Surprisingly, more pre-existing plaque size resulted in less neointima (P Conclusion The novel model of adult FH swine shows long-term vessel response to DES, that is similar to human response. This work shows that pre-existing atherosclerotic plaque affects the neointima after DES implantation. This insight highlights the necessity to use relevant disease models for safety and efficacy testing. Plaque size and neointima relation Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): The Netherlands Organisation for Health Research and Development (ZonMw)

Background Intracoronary polarimetry with polarization-sensitive (PS-) optical frequency domain imaging (OFDI) measures polarization properties, including birefringence and depolarization, in parallel with structural features of conventional OFDI (Figure 1A). Collagen, which imparts mechanical integrity to fibrous caps, and collagen-synthesizing smooth muscle cells exhibit elevated birefringence. Depolarization is increased by the presence of macrophages and lipid/necrotic cores. Purpose This study aimed to compare conventional OFDI and polarimetric signatures of coronary lesions between patients with acute coronary syndrome (ACS) and chronic coronary syndrome (CCS). Furthermore, we aimed to determine a birefringence cut-off value for identifying which fibrous caps belong to ACS culprit lesions. Methods This study consisted of 37 patients with ACS (n=23) or CCS (n=14). ACS culprit lesions (ACS-lesions) and CCS stenotic lesions (CCS-lesions) were included in the analysis (820 mm). Qualitative and quantitative conventional OFDI analysis included the presence of plaque rupture, macrophage infiltration, micro-vessels, thrombus, stenosis severity, fibrous cap thickness (FCT), lipid arc, lipid-burden and calcium-burden index. Birefringence and depolarization of the coronary lesions and fibrous caps were measured in the cross-sectional images showing the minimum FCT or minimum luminal area. Predictors of ACS-lesions were investigated by multivariate regression analysis. Receiver operating characteristic (ROC) analysis was used to determine the birefringence cut-off value identifying ACS fibrous caps (ACS-caps). Results There were no significant differences in clinical characteristics between the two groups, except for previous history of coronary artery disease. Compared to CCS-lesions, ACS-lesions featured higher lipid-burden index and maximum lipid arc (both p Conclusions Intracoronary polarimetry provides quantitative assessment of coronary lesions related to their composition. Birefringence was an independent robust predictor of ACS-lesions. Decreased birefringence and pronounced depolarization within the ACS-caps may indicate increased collagenolytic activity and macrophage infiltration, respectively. These results suggest that polarization properties may serve as quantitative imaging markers for assessing plaque vulnerability. Figure 1 Funding Acknowledgement Type of funding source: Other. Main funding source(s): This work was supported by the National Institutes of Health and by Terumo Corporation.

Background Polarization-sensitive (PS-) optical frequency domain imaging (OFDI) measures polarization properties of tissue together with conventional cross-sectional OFDI images of subsurface microstructure. PS-OFDI offers refined insight into plaque morphology and composition, which are implicated in the pathogenesis of acute coronary syndromes (ACS). Purpose This first-in-human pilot study of intravascular polarimetry aimed to investigate birefringence and depolarization features of coronary plaques in patients and to examine the relationship of these features with established structural characteristics available to conventional OFDI and with clinical presentation. Methods 30 patients undergoing PS-OFDI (acute coronary syndrome; ACS, n=12 and stable angina pectoris; SAP, n=18) participated in this study. 342 cross-sectional images evenly distributed along all imaged coronary arteries were classified into one of seven plaque categories according to conventional OFDI. Polarization features averaged over the entire intimal area of each cross-section were compared between plaque types and with structural parameters. Further, we assessed the polarization properties in the fibrous caps of ACS and SAP culprit lesions and compared them with structural features using a generalized linear model. Results The median birefringence and depolarization showed statistically significant differences among plaque types (both p Intravascular polarimetry Conclusions Intravascular polarimetry provides quantitative metrics that help to characterize coronary arterial tissues and may offer refined insight into coronary arterial atherosclerotic lesions in patients (Figure). Quantitative assessment of plaque polarization properties by intravascular polarimetry may open new avenues for studying plaque progression and detecting high-risk patients. Acknowledgement/Funding The JSPS Overseas Research Fellowship, the Uehara Memorial Foundation, and the Japan Heart Foundation and Bayer Yakuhin

We have performed enhanced backscattering experiments in a high gain random laser, under circumstances where a stationary theory predicts the laser intensity to diverge. Above the laser threshold the observed backscatter cone changes only gradually, not showing any signs of the divergence. We present measurements and theory-generalized laser equations with a diffusive transport term for pump and laser light-to explain the observed behavior. The population dynamics prevent an indefinite growth of the intensity. Time dependence is essential for a theory of random lasers above the laser threshold.

Starch plastic sheets were prepared by compression molding of starch-based plastic granulates. The granulates were prepared by extrusion processing of mixtures of granular potato starch and several maltodextrins (5% w/w) in the presence of glycerol and water as plasticizers and lecithin as melt flow accelerator. The materials were semicrystalline, containing B-type, Vh-type, and Eh-type crystallinity. The properties were dependent on water content. For the materials, a brittle-to-ductile transition occurred at a water content in the range of 11-12%, which was in accordance with the observed glass transition temperature. The structural and mechanical properties were a function of starch composition and maltodextrin source as well as molding temperature. The amount of granular remnants and residual B-type crystallinity decreased with increasing processing temperature. The amount of recrystallized single-helical amylose increased with increasing temperature. At molding temperatures in the range of 180-200°C, a sharp decrease in starch molecular mass occurred. The influence of molding temperature was reflected in a sharp increase in elongation at molding temperature above 160°C and a gradual decrease in elastic modulus. The tensile strength showed an initial small increase up to 160°C and a sharp decrease at higher molding temperatures.

Starch plastic sheets were prepared by extrusion processing of mixtures of granular high-amylopectin and high-amylose starches in the presence of glycerol and water as plasticizers. Amylose content varied between 0 and 70% (w/w). Structural characterization and determination of the mechanical properties of the sheets were performed after aging the materials between 40–65% relative humidity for 2 and 35 weeks and at 90% relative humidity for two weeks. The materials were semicrystalline and viscoelastic. The materials were described as complex heterogeneous multiphase materials. They consisted of amorphous and crystalline phases of amylose and amylopectin as well as granular structures and domains of amylose, amylopectin and amylose-amylopectin helices. Single-helical type crystallinity was formed solely by amylose directly after processing while B-type crystallinity was rapidly formed in amylose-rich materials and slowly during aging of amylopectin-rich materials. The stress-strain and stress-rel...

Photoacoustic signals originating from weak sources can be hard to discriminate from higher intensity signals resulting from the photoacoustic background. In order to reveal these weaker signals we propose a method where the expected background signal is subtracted from the actual signals. In this method an ultrasound image provides the geometry for the pressure distribution used in a photoacoustic wave field simulation. The simulated photoacoustic signals are subtracted from the actual recordings and the residual is used for image reconstruction. This method was successfully validated experimentally with a vessel phantom containing three optical absorption irregularities within the vessel wall.

We demonstrate the feasibility of intravascular ultrasound (IVUS) chirp imaging as well as chirp reversal ultrasound contrast imaging at intravascular ultrasound frequency. Chirp excitations were emitted with a 34MHz single crystal intravascular transducer and compared to conventional Gaussian-shaped pulses of equal acoustic pressure. The signal to noise ratio of the chirp images was increased by up to 9 dB relative to the conventional images. Imaging of contrast microbubbles was implemented by chirp reversal, achieving a contrast to tissue ratio of 12 dB. The method shows potential for intravascular imaging of structures in and beyond coronary atherosclerotic plaques including vasa vasorum. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3679375]

Optical coherence tomography (OCT) is a novel light-based imaging modality for application in the coronary circulation. Compared to conventional intravascular ultrasound, OCT has a ten-fold higher image resolution. This advantage has seen OCT successfully applied in the assessment of atherosclerotic plaque, stent apposition, and tissue coverage, heralding a new era in intravascular coronary imaging. The present article discusses the diagnostic value of OCT, both in cardiovascular research as well as in potential clinical application. The unparalleled high image resolution and strong contrast between the coronary lumen and the vessel wall structure enable fast and reliable image interpretation. OCT makes it possible to visualize the presence of atherosclerotic plaque in order to characterize the structure and extent of coronary plaque and to quantify lumen dimensions, as well as the extent of lumen narrowing, in unprecedented detail. Based on optical properties, OCT is able to distinguish different tissue types, such as fibrous, lipid-rich, necrotic, or calcified tissue. Furthermore, OCT is able to cover the visualization of a variety of features of atherosclerotic plaques that have been associated with rapid lesion progression and clinical events, such as thin cap fibroatheroma, fibrous cap thickness, dense macrophage infiltration, and thrombus formation. These unique features allow the use of OCT to assess patients with acute coronary syndrome and to study the dynamic nature of coronary atherosclerosis in vivo and over time. This permits new insights into plaque progression, regression, and rupture, as well as the study of effects of therapies aimed at modulating these developments. Today's OCT technology allows high detail resolution as well as fast and safe clinical image acquisition. These unique features have established OCT as the gold standard for the assessment of coronary stents. This technique makes it possible to study stent expansion, peri-procedural vessel trauma, and the interaction of the stent with the vessel wall down to the level of individual stent struts, both acutely as well as in the long term, where it is has proven extremely sensitive to the detection of even minor amounts of tissue coverage. These qualities render OCT indispensable to addressing vexing clinical questions such as the relationship of drug-eluting stent deployment, vascular healing, the true time course of endothelial stent coverage, and late stent thrombosis. This may also better guide the optimal duration of dual anti-platelet therapy that currently remains unclear and relatively empirical. In the future, OCT might emerge, parallel to its undisputed position in research, as the tool of choice in all clinical scenarios where angiography is limited by its nature as a two-dimensional luminogram.

Intravascular ultrasound (IVUS) is a technology that uses an ultrasound element on the tip of a catheter. This catheter is advanced through the groin into the coronary arteries. In this way a tomographic image of the vascular wall and atherosclerotic plaques can be produced.

Optical coherence tomography (OCT) allows highly accurate diagnosis of atherosclerotic plaques, including measurement of the thickness of fibrous caps, permitting an assessment of the risk of rupture. While the OCT image presents morphological information in highly resolved detail, it relies on interpretation by trained readers for the identification of tissue type. We developed a method for quantitative classification of atherosclerotic plaque constituents. The optical attenuation coefficient μ t distinguishes different tissue types: necrotic core and macrophage infiltration exhibit strong attenuation, μ t ≥10 mm−1, while calcific and fibrous tissue have a lower μ t ≈2–5 mm−1. (Neth Heart J 2009;17:448–50.)

In root canal therapy, complications frequently arise as a result of root fracture or imperfect cleaning of fins and invaginations. To date, there is no imaging method for nondestructive in vivo evaluation of the condition of the root canal, during or after treatment. There is a clinical need for a technique to detect defects before they give rise to complications. In this study we evaluate the ability of optical coherence tomography (OCT) to image root canal walls, and its capacity to identify complicating factors in root canal treatment. While the potential of OCT to identify caries has been explored before, endodontic imaging has not been reported. We imaged extracted lower front teeth after endodontic preparation and correlated these images to histological sections. A 3D OCT pullback scan was made with an endoscopic rotating optical fiber probe inside the root canal. All oval canals, uncleaned fins, risk zones, and one perforation that were detected by histology were also imaged by OCT. As an example of an area where OCT has clinical potential, we present a study of vertical root fracture identification with OCT.

Endoscopic optical coherence tomography (OCT), and other imaging modalities that use a mechanically rotated probe, often suffer from image degradation due to non-uniform rotation distortion (NURD). In this paper we present a new method to align a sequence of images by globally optimizing the match between individual lines in subsequent frames. It uses dynamic programming to find a continuous path through a cost matrix that measures the similarity between regions of two frames being aligned. The path represents the angular mismatch corresponding to the NURD. The prime advantage of this novel approach compared to earlier work is the line-to-line continuity, which accurately captures slow intra-frame variations in rotational velocity of the probe. The algorithm is optimized using data from a clinically available intravascular OCT instrument in a realistic vessel phantom. Sensitivity of the performance to imaging and optimization parameters is investigated using a computational phantom. Finally, the algorithm's efficacy is demonstrated on an in vivo recording inside a human coronary artery, exhibiting strong motion artifact.

We investigate the influence of the excitation spot diameter on the laser threshold of a scattering amplifying medium. Fluorescence spectra are recorded from a suspension of TiO(2) scatterers in Sulforhodamine B dye. The threshold pump intensity becomes larger by a factor of 70 if the excitation beam diameter gets close to the mean free path?. This increase is explained by use of a simple model describing diffusion out of the amplifying volume and is confirmed by a Monte Carlo simulation.

Acoustic radiation force (ARF) has become a common excitation mechanism in elasticity imaging; however, the high acoustic intensities and subsequent generation of harmonics hamper the effectiveness of using conventional radio frequency (RF) tracking to investigate the dynamics of tissues and catheter- based transducers, especially during the excitation. Thus, in trying to gain a better understanding of their response to ARF excitations, a more robust tracking option could prove useful. We propose a combined optical-ultrasound tracking method, where the dynamic response resulting from an ARF-induced excitation in soft tissue and on an unbounded catheter is tracked during and after insoniflcation. Both impulsive and harmonic (i.e. amplitude-modulated) excitations were investigated. The displacement estimates obtained from the optical method were then compared to those obtained from the more conventional ultrasound-based method. For the impulsive excitation case (pulse length >1.3 ms), the mean absolute percent difference between the peak displacements estimated by the two methods was 4.0%. For the harmonic excitation case, the mean absolute percent difference between amplitude estimations obtained from the two techniques was 7.4% at lower frequencies (50-200 Hz) and 29.1% at 500 Hz. The relatively large disparity between the displacement estimates at higher frequencies is thought to be a result of the finite length of the tracking marker, which was assumed to move as an infinitesimal point. Given the good agreement seen for the harmonic case at lower frequencies and the impulsive case at longer pulse lengths, this technique could be insightful in future investigations of tissue/transducer response to ARF- induced excitations in controlled, experimental settings.

Various encapsulation techniques are available for improving the efficiency of aroma chemicals in fragranced consumer products. Encapsulation techniques are still being optimised in terms of fragrance performance, scaling up and costs. Environmental aspects are becoming more important, putting constraints on the use of non-biodegradable fragrances, which are used in large excess and end up in the environment. Encapsulation could be the tool to make more efficient use of fragrances as slow or controlled delivery systems. Encapsulation opens the way in using biodegradable fragrances which could not be used before because of the too low chemical stability (during processing, storage or usage). A straightforward route to develop microencapsulated fragrance materials is to adapt existing methods developed for pharmacy, foods, agriculture or cosmetics. However, industrial constraints (cost in use) should be taken into account in a cost-competitive market area such as consumer products.

We present a quantitative OCT analysis, and stress measurements, of PVA cryogel atherosclerotic vessel phantom for optical elastography. The optical parameters and elasticity can be tuned to match those of in vivo vascular tissue.

In this paper we present an extensive validation of calibrated SCIAMACHY nadir reflectance in the UV (240–400 nm) by comparison with spectra calculated with a fast radiative transfer model. We use operationally delivered near-real-time level 1 data, processed with 5 standard calibration tools. A total of 9 months of data has been analysed. This is the first reflectance validation study incorporating such a large amount of data. It is shown that this method is a valuable tool for spotting spatial and temporal anomalies. We conclude that SCIAMACHY reflectance data in this wavelength range are stable over the investigated period. In addition, we show an example of an 10 anomaly in the data due to an error in the processing chain that could be detected by our comparison. This validation method could be extremely useful too for validation of other satellite spectrometers, such as OMI and GOME-2.

[1] We present a reflectance validation method, using a polarized radiative transfer model as a reference. The method involves calculating the complete radiative transfer in the ultraviolet for a carefully selected, natural, cloud-free Earth target. An extensive sensitivity study shows that in the ultraviolet, the ozone profile (mainly below 330 nm) and the surface albedo (mainly above 330 nm) are the important parameters that affect the reflectance and are therefore the major sources of error in the modeled reflectances. The accuracy with which the reflectance in the UV range of 240–400 nm can be calculated, because of uncertainty in input parameters, is 2–6%, depending on wavelength. The method is applied to Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), using a cloud-free scene over the Sahara desert. The reflectance measured by SCIAMACHY turns out to show a scan-angle-independent calibration error of 10–25% for this particular Sahara target. The result is confirmed for ocean and vegetation targets.

Progress on the development of retrieval algorithms for tropospheric nitrogen dioxide and ozone from the GOME, SCIAMACHY, OMI and GOME-2 instruments is outlined. New techniques are reported that significantly improve on the existing products. A better insight in the accuracy has been achieved. GOME data has been made available through web access.

The quest for developing ever stronger interacting photonic materials has caused the birth of a widely expanding research field. Successful achievement of very strong elastic interaction between light and matter would allow demonstration of conceptually new physical phenomena, among which Anderson localization [1] and a full photonic bandgap [2, 3] are prime examples. Experimental realization of these phenomena would open new avenues in control and manipulation of light and matter [4], and could lead to fascinating new developments in quantum optics.

Background Intravascular imaging modalities are used clinically to investigate ambiguous angiographic coronary lesions, guide and optimise stent deployment, and assess stent-related complications. Both intravascular ultrasound (IVUS) and optical coherence tomography (OCT) facilitate characterisation of plaque components, although a lack of adequate spatial resolution and depth of penetration, respectively, limit their clinical application. Adaptation of the existing technologies and novel techniques are in development but require further validation. We have developed an ex-vivo whole heart cadaveric model that facilitates multi-modality imaging and accurate comparison with histology. Methods We have developed a model for fluoroscopic and invasive assessment of coronary arteries within “whole heart” cadaveric specimens. Hearts are provided by the West of England heart valve bio-bank, following harvesting of valves for homograft production. The coronary ostium is dissected and mobilised to allow cannulation with a modified 6F coronary guiding catheter (Abstract 023 figure 1A), secured with sutures. The cadaveric specimen is held within a purpose-built perspex container, with adaptors on both sides of the container9s lid allowing connection of the guide catheter internally, and a Y-connector and pressure/injector manifold externally, see Abstract 023 figure 1 panel B. Cadaveric specimens undergo angiography (see Abstract 023 figure 1C,D), placement of a 0.014″ guide wire and imaging catheter manipulation with the artery held at physiological temperature and pressure. In collaboration with the Department of Bioengineering, Erasmus MC, Rotterdam, we are using this model for assessment and validation of optical attenuation analysis as a tool to accurately delineate areas of macrophage infiltration, a major marker of plaque vulnerability. Optical attenuation governs the signal drop-off associated with tissue penetration. It is derived by fitting the following functional relation to the OCT data, I (z) = I 0 exp(- μ t z), where μ t (z) is the local optical attenuation, the parameter of interest. The local signal intensity, I 0 , is also a free parameter in the fit, but is currently not analysed. The data are fitted in windows of 200 μm length, after appropriate processing to reduce speckle noise. Results Comparison of OCT, IVUS, and VH-IVUS against histology confirm the challenges in characterising plaque (Abstract 023 figure 2A–D: arrows indicate calcium). Analysis of optical attenuation appears to correlate with areas of macrophage infiltration (arrows in Abstract 023 figure 2E–H). Conclusions Our ex-vivo whole heart cadaveric model facilitates accurate comparison of imaging modalities against histology. Developments in the imaging technologies are necessary to facilitate plaque characterisation as a clinical application. Optical attenuation may offer additional information regarding the macrophage content and “vulnerability” of plaque, validation work using our cadaveric model is ongoing.

A random laser is a disordered medium that both scatters and amplifies light. Important parameters in this system are the transport mean free path l, the size of the amplifying volume and the amplification length l amp. Properties of light that is propagating through such a medium are modified by the presence of gain, giving rise to a range of surprising phenomena. One of these is the occurrence of a lasing threshold in the output power, pulse duration and spectral width of the emission [1]. These experiments have raised a large number of questions regarding the mechanism that gives rise to these phenomena. One of the most intriguing is how to connect the multiple scattering picture with the laser picture.

ROELEVELD, K.,R.V. BARATTA, M. SOLOMONOW, A.G. VAN SOEST, AND P. A. HUIJING.RC& ~ftendonp~~~perties on thedynamic performance of different isometric muscles. J. Appl. Physiol. 74(3): 1348-1355, 1993.-The effect of the tendon’s viscoelastic stiffness on the dynamic performance of muscles with different architecture was determined using the cat's medial gastrocnemius and extensor digitorum longus. Dynamic response models were derived under sinusoidal contraction-relaxation in the range of 0.4-6.0 Hz and between 20 and 80% of the muscles’ maximal isometric tension, manipulated by orderly recruitment-derecruitment of motor units together with firing rate increase-decrease. It was shown that, for isometric contractions at the muscle’s optimum length, the dynamic response of the muscles was not significantly different before and after dissection of the tendon. Therefore the conclusion that under these conditions the tendon acts like a stiff force transmitter without significantly modifying the muscle’s performance was confirmed and extended to muscles with different architecture.

The equilibrium between the solid and gas phases has been studied, using the flow method. The pressure varied from 1.3 atm up to 50 atm. The composition of the gas phase has been determined by means of the solidification of N2 (or CO) with the aid of liquid hydrogen. The most favourable conditions for the purification of hydrogen were deduced from the experimental results with respect to the binary mixtures H2−N2 and H2−CO. The agreement between theory and experiments proved to be satisfactory. The behaviour of the ternary mixture H2−N2−CO is shown in the corresponding diagrams.

Synopsis A method for the determination of the heat capacity of small quantities of isotopic mixtures of liquid helium has been developed and used also for the measurement of the specific heat of 4 He. The scattering of the experimental points within 4% along the smoothed curve given by Kramers, Wasscher and Gorter 1) confirms their results. The same experimental setup has been used for the determination of the specific heat of a mixture of 4 He with 2.50% of 3 He between 1.05 and 2.3°K. With respect to pure 4 He an appreciable increase of the heat capacity of the mixture (about 40% at 1.1°K, the relative increase diminishing with the rise in temperature) and a shift of the λ-temperature of 0.037 degK has been found as a result of three series of measurements.

Synopsis A directed heat current in a reservoir containing a 3He-4He-mixture below the lambda-point drives the 3He towards that part of the reservoir which is artificially kept cold. The quasi-osmotic pressure due to this con- centration gradient must in equilibrium be balanced by a fountain pressure caused by an appropriate temperature gradient. Thus a difference in 3He concentration, X, across the reservoir gives rise to a difference in temper- ature, according to the equation −RTρΔX = f ΔT. This temperature difference is equivalent to a resistance to the heat current, so that He II containing some 3He does not have the virtually infinite heat conductivity of He II containing only 4He. The heat resistances have been measured as a function of the heat current for various concentrations of 3He. It was found to be proportional to the 3He-concentration. By combining the above equation with the diffusion equation D(dX/dz) vnX = 0 one can calculate from the heat resistance and the known 3He-concentration the diffusion constant D. This was found to be independent of 3He-concentration, and, at lower temperatures, in good agreement with the values calculated by applying a gas model to the normal component of He II. The method of this experiment can be used to determine 3He-concentrations down to about 5 × 10−5 with a relative error of less than 5%.

Recently, Fourier domain OCT (FD-OCT) has been introduced for clinical use. This approach allows in vivo, high resolution (15 micron) imaging with very fast data acquisition, however, it requires brief flushing of the lumen during imaging. The reproducibility of such fast data acquisition under intracoronary flush application is poorly understood. To assess the inter-study variability of FD-OCT and to compare lumen morphometry to the established invasive imaging method, IVUS. 18 consecutive patients with coronary artery disease scheduled for PCI were included. In each target vessel a FD-OCT pullback (MGH system, light source 1,310 nm, 105 fps, pullback speed 20 mm/s) was acquired during brief (3 s) injection of X-ray contrast (flow 3 ml/s) through the guiding catheter. A second pullback was repeated under the same conditions after re-introduction of the FD OCT catheter into the coronary artery. IVUS and OCT imaging was performed in random order. FD-OCT and IVUS pullback data were analyzed using a recently developed software employing semi automated lumen contour and stent strut detection algorithms. Corresponding ROI were matched based on anatomical landmarks such as side branches and/or stent edges. Inter-study variability is presented as the absolute difference between the two pullbacks. FD-OCT showed remarkably good reproducibility. Inter-study variability in native vessels (cohort A) was very low for mean and minimal luminal area (0.10 +/- A 0.38, 0.19 +/- A 0.57 mm(2), respectively). Likewise inter-study variability was very low in stented coronary segments (cohort B) for mean lumen, mean stent, minimal luminal and minimal stent area (0.06 +/- A 0.08, 0.07 +/- A 0.10, 0.04 +/- A 0.09, 0.04 +/- A 0.10 mm(2), respectively). Comparison to IVUS morphometry revealed no significant differences. The differences between both imaging methods, OCT and IVUS, were very low for mean lumen, mean stent, minimal luminal and minimal stent area (0.10 +/- A 0.45, 0.10 +/- A 0.36, 0.26 +/- A 0.54, 0.05 +/- A 0.47 mm(2), respectively). FD-OCT shows excellent reproducibility and very low inter-study variability in both, native and stented coronary segments. No significant differences in quantitative lumen morphometry were observed between FD-OCT and IVUS. Evaluating these results suggest that FD-OCT is a reliable imaging tool to apply in longitudinal coronary artery disease studies.

This study was performed to characterize coronary plaque types by optical coherence tomography (OCT) and intravascular ultrasound (IVUS) radiofrequency (RF) data analysis, and to investigate the possibility of error reduction by combining these techniques. Intracoronary imaging methods have greatly enhanced the diagnostic capabilities for the detection of high-risk atherosclerotic plaques. IVUS RF data analysis and OCT are two techniques focusing on plaque morphology and composition. Regions of interest were selected and imaged with OCT and IVUS in 50 sections, from 14 human coronary arteries, sectioned post-mortem from 14 hearts of patients dying of non-cardiovascular causes. Plaques were classified based on IVUS RF data analysis (VH-IVUS(TM)), OCT and the combination of those. Histology was the benchmark. Imaging with both modalities and coregistered histology was successful in 36 sections. OCT correctly classified 24; VH-IVUS 25, and VH-IVUS/OCT combined, 27 out of 36 cross-sections. Systematic misclassifications in OCT were intimal thickening classified as fibroatheroma in 8 cross-sections. Misclassifications in VH-IVUS were mainly fibroatheroma as intimal thickening in 5 cross-sections. Typical image artifacts were found to affect the interpretation of OCT data, misclassifying intimal thickening as fibroatheroma or thin-cap fibroatheroma. Adding VH-IVUS to OCT reduced the error rate in this study.

Doppler and photoplethysmography studies were compared with invasive venous pressure measurements in ten healthy volunteers and 20 patients with a postthrombotic syndrome to assess the accuracy of noninvasive studies in detecting venous valve incompetence in the lower extremity. Using a refilling time of 20 seconds or less for valve incompetence, photoplethysmography was as accurate as invasive pressure measurements. In the Doppler studies there were two false-positive and three false-negative studies as compared with the invasive method. Photoplethysmography is an accurate and simple method for detecting valve incompetence. The method should be used in patients with suspected chronic venous disease, in evaluation of thrombolytic agents used for acute venous thrombosis, and in evaluation of the results of venous valve reconstruction.

With the intention towards more distal amputation of the lower extremity for peripheral vascular disease, failure of amputation wound healing remains a common clinical problem. Because calf blood flow correlates well with the indirect systolic ankle pressure, this pressure could be a prognostic guide to the outcome of amputation wound healing. To evaluate the clinical role of systolic ankle pressure measurements for selecting the most appropriate level of amputation, data of 93 patients undergoing 100 amputations were studied retrospectively. Of the 54 initial below knee (BK) amputations 83% healed and 17% failed to heal. Of the 46 initial above knee (AK) amputations 88% healed and 12% needed stump correction. Although all extremities with a systolic ankle pressure of more than 70 mm Hg healed in BK amputations there was no clinical predictive value of indirect systolic ankle pressure measurements. There was no difference in wound healing between diabetic and non-diabetic patients.

The calibration of SCIAMACHY was thoroughly checked since the instrument was launched on-board ENVISAT in February 2002. While SCIAMACHY's functional performance is excellent since launch, a number of technical difficulties have appeared, that required adjustments to the calibration. The problems can be separated into three types: (1) Those caused by the instrument and/or platform environment. Among these are the high water content in the satellite structure and/or MLI layer. This results in the deposition of ice on the detectors in channels 7 and 8 which seriously affects the retrievals in the IR, mostly because of the continuous change of the slit function caused by scattering of the light through the ice layer. Additionally a light leak in channel 7 severely hampers any retrieval from this channel. (2) Problems due to errors in the on-ground calibration and/or data processing affecting for example the radiometric calibration. A new approach based on a mixture of on-ground and in-flight data is shortly described here. (3) Problems caused by principal limitations of the calibration concept, e.g. the possible appearance of spectral structures after the polarisation correction due to unavoidable errors in the determination of atmospheric polarisation. In this paper we give a complete overview of the calibration and problems that still have to be solved. We will also give an indication of the effect of calibration problems on retrievals where possible. Since the operational processing chain is currently being updated and no newly processed data are available at this point in time, for some calibration issues only a rough estimate of the effect on Level 2 products can be given. However, it is the intention of this paper to serve as a future reference for detailed studies into specific calibration issues.