N. Debernardi

Microcalcifications in Early Intimal Lesions of Atherosclerotic Human Coronary Arteries

Although calcium (Ca) precipitation may play a pathogenic role in atherosclerosis, information on temporal patterns of microcalcifications in human coronary arteries, their relation to expression of calcification-regulating proteins, and colocalization with iron (Fe) and zinc (Zn) is scarce. Human coronary arteries were analyzed post mortem with a proton microprobe for element concentrations and stained (immuno)histochemically for morphological and calcification-regulating proteins. Microcalcifications were occasionally observed in preatheroma type I atherosclerotic intimal lesions. Their abundance increased in type II, III, and IV lesions. Moreover, their appearance preceded increased expression of calcification-regulating proteins, such as osteocalcin and bone morphogenetic protein-2. In contrast, their presence coincided with increased expression of uncarboxylated matrix Gla protein (MGP), whereas the content of carboxylated MGP was increased in type III and IV lesions, indicating delayed posttranslational conversion of biologically inactive into active MGP. Ca/phosphorus ratios of the microcalcifications varied from 1.6 to 3.0, including amorphous Ca phosphates. Approximately 75% of microcalcifications colocalized with the accumulation of Fe and Zn. We conclude that Ca microprecipitation occurs in the early stages of atherosclerosis, inferring a pathogenic role in the sequel of events, resulting in overt atherosclerotic lesions. Microcalcifications may be caused by local events triggering the precipitation of Ca rather than by increased expression of calcification-regulating proteins. The high degree of colocalization with Fe and Zn suggests a mutual relationship between these trace elements and early deposition of Ca salts.

Atherosclerosis : contrast-enhanced MR imaging of vessel wall in rabbit model-comparison of gadofosveset and gadopentetate dimeglumine

PURPOSE To investigate the potential of gadofosveset for contrast material-enhanced magnetic resonance (MR) imaging of plaque in a rabbit model of atherosclerosis. MATERIALS AND METHODS All experiments were approved by the animal ethics committee. Thirty-one New Zealand White rabbits were included in one of four study groups: animals with atherosclerosis imaged with gadofosveset (n = 10) or gadopentetate dimeglumine (n = 7) and control animals imaged with gadofosveset (n = 7) or gadopentetate dimeglumine (n = 7). Aortic atherosclerosis was induced through endothelial denudation combined with a cholesterol-enriched diet. Control rabbits underwent a sham surgical procedure and received a regular diet. After 8 weeks, pre- and postcontrast T1-weighted MR images of the aortic vessel wall were acquired. Relative signal enhancement was determined with dedicated software. Statistical analysis was performed by using a generalized linear mixed model. Immunohistochemical staining with CD31 and albumin was used to assess microvessel density and the albumin content of the vascular wall. Group differences were analyzed by using a chi(2) test. Gadofosveset spatial distribution and content within the vessel wall were determined with proton-induced x-ray emission (PIXE) analysis. RESULTS Postcontrast signal enhancement was significantly greater for atherosclerotic than for control animals imaged with gadofosveset (P = .022). Gadopentetate dimeglumine could not enable discrimination between normal and atherosclerotic vessel walls (P = .428). PIXE analysis showed higher amounts of gadopentetate dimeglumine than gadofosveset in both atherosclerotic and normal rabbit aortas. Immunohistochemical staining revealed the presence of albumin and increased microvessel density in the vascular walls of atherosclerotic rabbits. CONCLUSION These results suggest that gadofosveset can be used to differentiate between atherosclerotic and normal rabbit vessel walls. SUPPLEMENTAL MATERIAL http://radiology.rsnajnls.org/cgi/content/full/250/3/682/DC1.

Optimization of the current extracted from an ultracold ion source

Photoionization of trapped atoms is a recent technique for creating ion beams with low transverse temperature. The temporal behavior of the current that can be extracted from such an ultracold ion source is measured when operating in the pulsed mode. A number of experimental parameters are varied to find the conditions under which the time-averaged current is maximized. A dynamic model of the source is developed that agrees quite well with the experimental observations. The radiation pressure exerted by the excitation laser beam is found to substantially increase the extracted current. For a source volume with a typical root-mean-square radius of 20µm, a maximum peak current of 88pA is observed, limited by the available ionization laser power of 46mW. The optimum time-averaged current is 13pA at a 36% duty cycle. Particle-tracking simulations show that stochastic heating strongly reduces the brightness of the ion beam at higher current for the experimental conditions.

Measurement of the temperature of an ultracold ion source using time-dependent electric fields

We report on a measurement of the characteristic temperature of an ultracold rubidium ion source, in which a cloud of laser-cooled atoms is converted to ions by photo-ionization. Extracted ion pulses are focused on a detector with a pulsed-field technique. The resulting experimental spot sizes are compared to particle-tracking simulations, from which an effective source temperature T = (3 ± 2) mK and the corresponding transversal reduced emittance er = 1.4 × 10−8 m rad eV are determined. Space charge effects that may affect the measurement are also discussed.

Time-dependent manipulation of ultracold ion bunches

The combination of an ultracold ion source based on photoionization of a laser-cooled gas and time-dependent acceleration fields enables precise manipulation of ion beams. We demonstrate reduction in the longitudinal energy spread and transverse (de)focusing of the beam by applying time-dependent acceleration voltages. In addition, we show how time-dependent acceleration fields can be used to control both the sign and strength of the spherical aberrations. The experimental results are in close agreement with detailed charged particle tracking simulations and can be explained in terms of a simple analytical model.

Microcalcifications in atherosclerotic lesion of apolipoprotein E‐deficient mouse

Evidence is accumulating that calcium‐rich microdeposits in the vascular wall might play a crucial role in the onset and progression of atherosclerosis. Here we investigated an atherosclerotic lesion of the carotid artery in an established murine model, i.e. the apolipoprotein E‐deficient (APOE−/−) mouse to identify (i) the presence of microcalcifications, if any, (ii) the elemental composition of microcalcifications with special reference to calcium/phosphorus mass ratio and (iii) co‐localization of increased concentrations of iron and zinc with microcalcifications. Atherosclerosis was induced by a flow‐divider placed around the carotid artery resulting in low and high shear‐stress regions. Element composition was assessed with a proton microprobe. Microcalcifications, predominantly present in the thickened intima of the low shear‐stress region, were surrounded by areas with normal calcium levels, indicating that calcium‐precipitation is a local event. The diameter of intimal microcalcifications varied from 6 to 70 μm. Calcium/phosphorus ratios of microcalcifications varied from 0.3 to 4.8, mainly corresponding to the ratio of amorphous calcium‐phosphate. Increased iron and zinc concentrations commonly co‐localized with microcalcifications. Our findings indicate that the atherosclerotic process in the murine carotid artery is associated with locally accumulated calcium, iron and zinc. The calcium‐rich deposits resemble amorphous calcium phosphate rather than pure hydroxyapatite. We propose that the APOE−/− mouse, in which atherosclerosis was evoked by a flow‐divider, offers a useful model to investigate the pathophysiological significance of accumulation of elements such as calcium, iron and zinc.

Performance predictions for a laser-intensified thermal beam for use in high-resolution focused-ion-beam instruments

Photoionization of a laser-cooled and compressed atomic beam from a high-flux thermal source can be used to create a high-brightness ion beam for use in focused-ion-beam instruments. Here we show using calculations and Doppler cooling simulations that an atomic rubidium beam with an equivalent brightness of 2.1 × 107 A/(m2 sr eV) can be created using a compact 5 cm long two-dimensional magneto-optical compressor. If this can be conserved during the photoionization process, this leads to an ion beam brightness an order of magnitude higher than produced by a liquid metal ion source. The source is also capable of producing a flux of 6.2 × 109 s-1 that results in a substantial beam current of 1 nA once fully ionized.

An Ultracold Electron Source for Ultrafast Electron Diffraction Experiments

We create ultrashort, ultracold electron bunches by accelerating electrons which are created by near-threshold photoionization of a cloud of laser-cooled atoms. With these bunches we can perform diffraction experiments of crystals of macromolecules.