Assessment of ultra-high resolution optical coherence tomography for monitoring tissue effects caused by laser photocoagulation of ex-vivo porcine retina

Retinal laser photocoagulation is an established and successful treatment for a variety of retinal diseases. While being a valuable treatment modality, laser photocoagulation shows the drawback of employing high energy lasers which are capable of physically destroying the neural retina. For reliable therapy, it is therefore crucial to closely monitor the therapy effects caused in the retinal tissue. A depth resolved representation of optical tissue properties as provided by optical coherence tomography may provide valuable information about the treatment effects in the retinal layers if recorded simultaneously to laser coagulation. Therefore, in this work, the use of ultra-high resolution optical coherence tomography to represent tissue changes caused by conventional and selective retinal photocoagulation is investigated. Laser lesions were placed on porcine retina ex-vivo using a 577 nm laser as well as a pulsed laser at 527 nm built for selective treatment of the retinal pigment epithelium. Applied energies were varied to generate lesions best representing the span from under- to overtreatment. The lesions were examined using a custom-designed optical coherence tomography system with an axial resolution of 1.78 μm and 70 kHz Ascan rate. Optical coherence tomography scans included volume scans before and after irradiation, as well as time lapse scans (Mscan) of the lesions. Results show OCT lesion visibility thresholds to be below the thresholds of ophthalmoscopic inspection. With the ultra-high resolution OCT, 42% - 44% of ophthalmoscopically invisible lesions could be detected and lesions that were under- or overexposed could be distinguished using the OCT data.

Measurement and stability of the pointing of the BepiColombo Laser Altimeter under thermal load

The BepiColombo Laser Altimeter (BELA) has been selected to fly on ESA׳s BepiColombo mission to Mercury. The instrument will be the first European laser altimeter designed for interplanetary flight. This paper describes the setup used to characterize the angular movements of BELA under the simulated environmental conditions that the instrument will encounter when orbiting Mercury. The system comprises a laser transmitter and a receiving telescope, which can move with respect to each other under thermal load. Tests performed using the Engineering Qualification Model show that the setup is accurate enough to characterize angular movements of the instrument components to an accuracy of ≈10 μrad. The qualification instrument is thermally stable to operate during all mission phases around Mercury proving that the transmitter and receiver sections will remain within the alignment requirements during its mission.

Lutetia׳s lineaments

The European Space Agency׳s Rosetta spacecraft flew by asteroid (21) Lutetia on July 10, 2010. Observations through the OSIRIS camera have revealed many geological features. Lineaments are identified on the entire observed surface of the asteroid. Many of these features are concentric around the North Pole Crater Cluster (NPCC). As observed on (433) Eros and (4) Vesta, this analysis of Lutetia assesses whether or not some of the lineaments could be created orthogonally to observed impact craters. The results indicate that the orientation of lineaments on Lutetia׳s surface could be explained by three impact craters: the Massilia and the NPCC craters observed in the northern hemisphere, and candidate crater Suspicio inferred to be in the southern hemisphere. The latter has not been observed during the Rosetta flyby. Of note, is that the inferred location of the Suspicio impact crater derived from lineaments matches locations where hydrated minerals have been detected from Earth-based observations in the southern hemisphere of Lutetia. Although the presence of these minerals has to be confirmed, this analysis shows that the topography may also have a significant contribution in the modification of the spectral shape and its interpretation. The cross-cutting relationships of craters with lineaments, or between lineaments themselves show that Massilia is the oldest of the three impact feature, the NPCC the youngest, and that the Suspicio impact crater is of intermediate age that is likely occurred closer in time to the Massilia event.

Laboratory observations and simulations of phase reddening

The visible reflectance spectrum of many Solar System bodies changes with changing viewing geometry for reasons not fully understood. It is often observed to redden (increasing spectral slope) with increasing solar phase angle, an effect known as phase reddening. Only once, in an observation of the martian surface by the Viking 1 lander, was reddening observed up to a certain phase angle with bluing beyond, making the reflectance ratio as a function of phase angle shaped like an arch. However, in laboratory experiments this arch-shape is frequently encountered. To investigate this, we measured the bidirectional reflectance of particulate samples of several common rock types in the 400–1000 nm wavelength range and performed ray-tracing simulations. We confirm the occurrence of the arch for surfaces that are forward scattering, i.e. are composed of semi-transparent particles and are smooth on the scale of the particles, and for which the reflectance increases from the lower to the higher wavelength in the reflectance ratio. The arch shape is reproduced by the simulations, which assume a smooth surface. However, surface roughness on the scale of the particles, such as the Hapke and van Horn (Hapke, B., van Horn, H. [1963]. J. Geophys. Res. 68, 4545–4570) fairy castles that can spontaneously form when sprinkling a fine powder, leads to monotonic reddening. A further consequence of this form of microscopic roughness (being indistinct without the use of a microscope) is a flattening of the disk function at visible wavelengths, i.e. Lommel–Seeliger-type scattering. The experiments further reveal monotonic reddening for reflectance ratios at near-IR wavelengths. The simulations fail to reproduce this particular reddening, and we suspect that it results from roughness on the surface of the particles. Given that the regolith of atmosphereless Solar System bodies is composed of small particles, our results indicate that the prevalence of monotonic reddening and Lommel–Seeliger-type scattering for these bodies results from microscopic roughness, both in the form of structures built by the particles and roughness on the surface of the particles themselves. It follows from the singular Viking 1 observation that the surface in front of the lander was composed of semi-transparent particles, and was smooth on the scale of the particle size.

Potential desiccation cracks on Mars: A synthesis from modeling, analogue-field studies, and global observations

Potential desiccation polygons (PDPs) are polygonal surface patterns that are a common feature in Noachian-to-Hesperian-aged phyllosilicate- and chloride-bearing terrains and have been observed with size scales that range from cm-wide (by current rovers) to 10s of meters-wide. The global distribution of PDPs shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes. They are mostly associated with sedimentary deposits that display spectral evidence for the presence of Fe/Mg smectites, Al-rich smectites or less commonly kaolinites, carbonates, and sulfates. In addition, PDPs may indicate paleolacustrine environments, which are of high interest for planetary exploration, and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water. A collective synthesis with new data, particularly from the HiRISE camera suggests that desiccation cracks may be more common on the surface of Mars than previously thought. A review of terrestrial research on desiccation processes with emphasis on the theoretical background, field studies, and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on Mars.

CHEOPS: a space telescope for ultra-high precision photometry of exoplanet transits

The CHaracterising ExOPlanet Satellite (CHEOPS) is a joint ESA-Switzerland space mission (expected to launch in 2017) dedicated to search for exoplanet transits by means of ultra-high precision photometry. CHEOPS will provide accurate radii for planets down to Earth size. Targets will mainly come from radial velocity surveys. The CHEOPS instrument is an optical space telescope of 30 cm clear aperture with a single focal plane CCD detector. The tube assembly is passively cooled and thermally controlled to support high precision, low noise photometry. The telescope feeds a re-imaging optic, which supports the straylight suppression concept to achieve the required Signal to Noise. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Radar investigations of Apollinaris Mons on Mars: Exploring the origin of the fan deposits

Apollinaris Mons is an isolated volcano on Mars straddling the boundary between the southern highlands and the northern plains. One of its most distinctive features is its massive fan-shaped deposit that extends from a breach on its summit to distances of more than 150 km and drapes its entire southern flank. The composition and formation mechanism of these deposits remains controversial. We investigate the radar properties of the fan deposits (FD) of Apollinaris Mons using low-frequency sounding radar data in combination with high-resolution images and crater-size frequency analysis to constrain their inner shape and bulk composition. Our analysis indicates that the FD attains an irregular thickness and is gradually thinner towards their lateral margins. The crater-size frequency analysis shows that they may have undergone repeated resurfacing, which is suggestive of long-term evolution. Our analysis of Shallow Radar (SHARAD) radargrams traversing different sections of the FD reveals multiple and different subsurface interfaces among the radargrams crossing the thinnest part, which suggests a layered and complex inner shape. Our estimates for the bulk real part of the dielectric constant of the FD ranges from 3 to 5, which is consistent with an icy-silicate mixture or pyroclastic composition. Therefore, we conclude that lahars or pyroclastic flows are the most likely mechanism that created the FD, yet we cannot rule out additional contributions from lava flows. A combination of multiple processes is also possible since the deposits appear to have been modified by fluvial processes at a later stage of their formation.

Possible open-system (hydraulic) pingos in and around the Argyre impact region of Mars

We report the observation of possible (hydraulic) open-system pingos (OSPs ) at the mid latitudes (∼37°S) in and around the Argyre impact-basin. OSPs are perennial (water)–ice cored mounds; they originate and evolve in periglacial and pro-glacial landscapes on Earth where intra- or sub-permafrost water under hydraulic/artesian pressure uplifts localised sections of surface or near-surface permafrost that then freezes in-situ. We invoke three lines of evidence in support of our analogue-based interpretation: (1) similarities of shape, size and summit traits between terrestrial OSPs and the Martian mounds; (2) clustered distribution and the slope-side location of the mounds, consistent with terrestrial permafrost-environments where OSPs are found; and, (3) spatially-associated landforms putatively indicative of periglacial and glacial processes on Mars that characterise OSP landscapes on Earth. This article presents five OSP candidate-locations and nests these mound locations within a new geological map of the Argyre impact-basin and margins. It also presents three periglacial hypotheses about the possible origin of the water required to develop the mounds. Alternative (non-periglacial) formation-hypotheses also are considered; however, we show that their robustness is not equal to that of the periglacial ones.

Three-dimensional printing for perioperative planning of complex aortic arch surgery

Purpose In this study, we show the use of three-dimensional printing models for preoperative planning of surgery for patients with complex aortic arch anomalies. Description A 70-year-old man with an extensively arteriosclerotic aneurysm reaching from the ascending aorta to the descending aorta was referred to our center for complete aortic arch replacement. We visualized and reconstructed computed tomography data of the patient and fabricated a flexible three-dimensional model of the aortic arch including the aneurysm. Evaluation This model was very helpful for the preoperative decision making and planning of the frozen elephant trunk procedure owing to the exact and lifelike illustration of the native aortic arch. Conclusions Three-dimensional models are helpful in preoperative planning and postoperative evaluation of frozen elephant trunk procedures in patients with complex aortic anatomy.

Snow shielding factors for cosmogenic nuclide dating inferred from long-term neutron detector monitoring

The depth-dependent attenuation of the secondary cosmic-ray particle flux due to snow cover and its effects on production rates of cosmogenic nuclides constitutes a potential source of uncertainty for studies conducted in regions characterized by frequent seasonal snow burial. Recent experimental and numerical modelling studies have yielded new constraints on the effect of hydrogen-rich media on the production rates of cosmogenic nuclides by low- and high-energy neutrons (<10(-3) MeV and >10(2) MeV, respectively). Here we present long-term neutron-detector monitoring data from a natural setting that we use to quantify the effect of snow cover on the attenuation of fast neutrons (0.1-10 MeV), which are responsible for the production of Ne-21 from Mg and Cl-36 from K. We use data measured between July 2001 and May 2008 at seven stations located throughout the Ecrins-Pelvoux massif (French Western Alps) and its surroundings, at elevations ranging from 200 to 2500 m a.s.l. From the cosmic-ray fluxes recorded during summer, when snow is absent, we infer an apparent attenuation length of 148 g cm(-2) in the atmosphere at a latitude of similar to 45 degrees N and for altitudes ranging from similar to 200 to 2500 m a.s.l. Using snow water-equivalent (SWE) values obtained through snow-coring campaigns that overlap in time the neutron monitoring for five stations, we show that fast neutrons are much more strongly attenuated in snow than predicted by a conventional mass-shielding formulation and the attenuation length estimated in the atmosphere. We suggest that such strong attenuation results from boundary effects at the atmosphere/snow interface induced by the high efficiency of water as a neutron moderator. Finally, we propose an empirical model that allows calculating snow-shielding correction factors as a function of SWE for studies using Ne-21 and Cl-36 analyses in Mg- and K-rich minerals, respectively. This empirical model is of interest for studies with a focus on cosmic-ray exposure dating, particularly if the target rocks are made up of mafic to ultramafic units where seasonal snow-cover is a common phenomenon.

Automatic estimation of noise parameters in Fourier-domain optical coherence tomography cross sectional images using statistical information

We present an application and sample independent method for the automatic discrimination of noise and signal in optical coherence tomography Bscans. The proposed algorithm models the observed noise probabilistically and allows for a dynamic determination of image noise parameters and the choice of appropriate image rendering parameters. This overcomes the observer variability and the need for a priori information about the content of sample images, both of which are challenging to estimate systematically with current systems. As such, our approach has the advantage of automatically determining crucial parameters for evaluating rendered image quality in a systematic and task independent way. We tested our algorithm on data from four different biological and nonbiological samples (index finger, lemon slices, sticky tape, and detector cards) acquired with three different experimental spectral domain optical coherence tomography (OCT) measurement systems including a swept source OCT. The results are compared to parameters determined manually by four experienced OCT users. Overall, our algorithm works reliably regardless of which system and sample are used and estimates noise parameters in all cases within the confidence interval of those found by observers.

Reconstruction of 3D Vertebral Models from a Single 2D Lateral Fluoroscopic Image

Accurate three-dimensional (3D) models of lumbar vertebrae are required for image-based 3D kinematics analysis. MRI or CT datasets are frequently used to derive 3D models but have the disadvantages that they are expensive, time-consuming or involving ionizing radiation (e.g., CT acquisition). In this chapter, we present an alternative technique that can reconstruct a scaled 3D lumbar vertebral model from a single two-dimensional (2D) lateral fluoroscopic image and a statistical shape model. Cadaveric studies are conducted to verify the reconstruction accuracy by comparing the surface models reconstructed from a single lateral fluoroscopic image to the ground truth data from 3D CT segmentation. A mean reconstruction error between 0.7 and 1.4 mm was found.

Graphical Model-Based Vertebra Identification from X-Ray Image(s)

Automated identification of vertebrae from X-ray image(s) is an important step for various medical image computing tasks such as 2D/3D rigid and non-rigid registration. In this chapter we present a graphical model-based solution for automated vertebra identification from X-ray image(s). Our solution does not ask for a training process using training data and has the capability to automatically determine the number of vertebrae visible in the image(s). This is achieved by combining a graphical model-based maximum a posterior probability (MAP) estimate with a mean-shift based clustering. Experiments conducted on simulated X-ray images as well as on a low-dose low quality X-ray spinal image of a scoliotic patient verified its performance.

Fully Automatic CT Segmentation for Computer-Assisted Pre-operative Planning of Hip Arthroscopy

Extraction of both pelvic and femoral surface models of a hip joint from CT data for computer-assisted pre-operative planning of hip arthroscopy is addressed. We present a method for a fully automatic image segmentation of a hip joint. Our method works by combining fast random forest (RF) regression based landmark detection, atlas-based segmentation, with articulated statistical shape model (aSSM) based hip joint reconstruction. The two fundamental contributions of our method are: (1) An improved fast Gaussian transform (IFGT) is used within the RF regression framework for a fast and accurate landmark detection, which then allows for a fully automatic initialization of the atlas-based segmentation; and (2) aSSM based fitting is used to preserve hip joint structure and to avoid penetration between the pelvic and femoral models. Validation on 30 hip CT images show that our method achieves high performance in segmenting pelvis, left proximal femur, and right proximal femur surfaces with an average accuracy of 0.59 mm, 0.62 mm, and 0.58 mm, respectively.