High-resolution three-dimensional 3 T magnetic resonance angiography for the evaluation of experimental aneurysm in the rabbit

OBJECTIVE: The standard technique of two-dimensional intra-arterial digital subtraction angiography (2D-DSA) for the imaging of experimental rabbit aneurysms is invasive and has considerable surgical risks. Therefore, minimally invasive techniques ideally providing three-dimensional imaging for intervention planning and follow-up are needed. This study evaluates the feasibility and quality of three-dimensional 3-T magnetic resonance angiography (3D-3T-MRA) and compares 3D-3T-MRA with 2D-DSA in experimental aneurysms in the rabbit. METHOD: Three microsurgically created aneurysms in three rabbits were evaluated using 2D-DSA and 3D-3T-MRA. Imaging of the aneurysms was performed 2 weeks after creation using 2D-DSA and contrast-enhanced (CE) MRA. Measurements included aneurysm dome (length and width) and aneurysm neck. Aneurysm volumes were determined using CE-MRA. RESULTS: The measurements of the aneurysms' dimensions and the evaluation of vicinity vessels with both techniques showed a good correlation. The mean aneurysm length, aneurysm width and neck width measured with DSA (6.9, 4.1 and 2.8 mm, respectively) correlated with the measurements performed in 3D-3T-MRA (6.9, 4 and 2.5 mm, respectively). The mean aneurysm volumes measured with CE-MRA was 46.7 mm(3). CONCLUSION: 3D-3T CE-MRA is feasible and less invasive and is a safer imaging alternative to DSA for experimental aneurysm. Additionally, aneurysm technique this precise offers the possibility of repetitive 3D aneurysm volumetry for long-term follow-up studies after endovascular aneurysm occlusion.

High-resolution summer temperature reconstruction from Lake Silvaplana based on in-situ reflectance spectroscopy

Annually laminated (varved) sediments of proglacial Lake Silvaplana (46 ̊27’N, 9 ̊48’E, 1791 m a.s.l., Engadine, eastern Swiss Alps) provide an excellent archive for quantitative high-resolution (seasonal – annual) reconstruction of high- and lowfrequency climate signals back to AD 1580. The chronology of the core is based on varve counting, Cs-137, Pb-210 and event stratigraphy. In this study we present a reconstruction based on in-situ reflectance spectroscopy. In situ reflectance spectroscopy is known as a cost- and time-effective non destructtive method for semi-quantitative analysis of pigments (e.g., chlorines and carotenoids) and of lithoclastic sediment fractions. Reflectance-dependent absorption (RDA) was measured with a Gretac Macbeth spectrolino at 2 mm resolution. The spectral coverage ranges from 380 nm to 730 nm at 10 nm band resolution. In proglacial Lake Silvaplana, 99% of the sediment is lithoclastic prior to AD 1950. Therefore, we concentrate on absorption features that are characteristic for lithoclastic sediment fractions. In Lake Silvaplana, two significant correlations that are stable in time were found between RDA typical for lithoclastics and meteorological data: (1) the time series R 570 /R 630 (ratio between RDA at 570 nm and 630 nm) of varves in Lake Silvaplana and May to October temperatures at nearby station of Sils correlate highly significantly (calibration period AD 1864 – 1951, r = 0.74, p < 0.01 for 5ptsmoothed series; RMSE is 0.28 ̊C, RE = 0.41 and CE = 0.38), and (2) the minimum reflectance within the 690nm band (min690) data correlate with May to October (calibration period AD 1864 – 1951, r = 0.68, p < 0.01 for 5pt-smoothed series; RMSE = 0.22 ̊C, RE = 0.5, CE = 0.31). Both proxy series (min690nm and R 570 /R 630 values) are internally highly consistent (r = 0.8, p < 0.001). In proglacial Lake Silvaplana the largest amount of sediment is transported by glacial meltwater. The melting season spans approximately from May to October, which gives us a good understanding of the geophysical processes explaining the correlations between lithoclastic proxies and the meteorological data. The reconstructions were extended back to AD 1580 and show a broad corresponddence with fully independent reconstructions from tree rings and documentary data.

High-resolution paleoclimatology of the last millennium: a review of current status and future prospects

This review of late-Holocene palaeoclimatology represents the results from a PAGES/CLIVAR Intersection Panel meeting that took place in June 2006. The review is in three parts: the principal high-resolution proxy disciplines (trees, corals, ice cores and documentary evidence), emphasizing current issues in their use for climate reconstruction; the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual-to-decadal timescale Northern Hemisphere surface temperatures and other climate variables, such as large-scale circulation indices; and the forcing histories used in climate model simulations of the past millennium. We discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo-proxies derived from climate model runs, where the `answer' is known. The article concludes with a list of recommendations. First, more raw proxy data are required from the diverse disciplines and from more locations, as well as replication, for all proxy sources, of the basic raw measurements to improve absolute dating, and to better distinguish the proxy climate signal from noise. Second, more effort is required to improve the understanding of what individual proxies respond to, supported by more site measurements and process studies. These activities should also be mindful of the correlation structure of instrumental data, indicating which adjacent proxy records ought to be in agreement and which not. Third, large-scale climate reconstructions should be attempted using a wide variety of techniques, emphasizing those for which quantified errors can be estimated at specified timescales. Fourth, a greater use of climate model simulations is needed to guide the choice of reconstruction techniques (the pseudo-proxy concept) and possibly help determine where, given limited resources, future sampling should be concentrated.