47 results on '"Zand, T."'
Search Results
2. Intimal Responses to Shear Stress, Hypercholesterolemia, and Hypertension : Studies in the Rat Aorta
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Majno, C., Zand, T., Nunnari, J. J., Kowala, M. C., Joris, I., Simionescu, Nicolae, editor, and Simionescu, Maya, editor
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- 1988
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Catalog
3. Fast Linear and Parabolic Radon Transforms via Chirp Z-Transform
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Zand, T., primary and Gholami, A., additional
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- 2017
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4. Total-variation Based Seismic Imaging with Bregmanized Operator Splitting Algorithm
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Zand, T., primary, Gholami, A., additional, and Sacchi, M.D., additional
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- 2015
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5. Occupational and patient exposure as well as image quality for full spine examinations with the EOS imaging system
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Damet, J., primary, Fournier, P., additional, Monnin, P., additional, Sans-Merce, M., additional, Ceroni, D., additional, Zand, T., additional, Verdun, F. R., additional, and Baechler, S., additional
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- 2014
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6. The RalGEF-Ral Effector Signaling Network: The Road Less Traveled for Anti-Ras Drug Discovery
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Neel, N. F., primary, Martin, T. D., additional, Stratford, J. K., additional, Zand, T. P., additional, Reiner, D. J., additional, and Der, C. J., additional
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- 2011
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7. BolinOS - e-learning tools as an extension of open-source medical content online publication
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Zand, T, primary, Billet, J, additional, and Lovis, C, additional
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- 2005
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8. Online radiological examination: open-source tool for federal certification
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Billet J, Zand T, Lovis C, none, primary
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- 2005
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9. Prise en charge radiologique des fractures de rate chez l’enfant : US ET/OU CT
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Sayegh Martin, Y., primary, Merlini, L., additional, Anooshiravani, M., additional, Zand, T., additional, Maarouf, M., additional, and Hanquinet, S., additional
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- 2004
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10. Lymphangiomes kystiques retroperitoneaux : a propos de 4 observations
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Maarouf, M., primary, Sayegh Martin, Y., additional, Anooshiravani, M., additional, Merlini, L., additional, Zand, T., additional, and Hanquinet, S., additional
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- 2004
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11. Description d'un système d'authoring multimédia collaboratif pour plate-forme mobile
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Tschopp, M, primary, Billet, J, additional, Zand, T, additional, and Geissbühler, A, additional
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- 2004
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12. MULTI-INSTRUMENT X-RAY OBSERVATIONS OF THERMONUCLEAR BURSTS WITH SHORT RECURRENCE TIMES
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Zand, t
- Abstract
Type I X-ray bursts from low-mass X-ray binaries result from a thermonuclear runaway in the material accreted onto the neutron star. Although typical recurrence times are a few hours, consistent with theoretical ignition model predictions, there are also observations of bursts occurring as promptly as 10 minutes or less after the previous event. We present a comprehensive assessment of this phenomenon using a catalog of 3387 bursts observed with the BeppoSAX/WFCs and RXTE/PCA X-ray instruments. This catalog contains 136 bursts with recurrence times of less than 1 hr, that come in multiples of up to four events, from 15 sources. Short recurrence times are not observed from the so-called ultra-compact binaries, indicating that hydrogen-burning processes play a crucial role. As far as the neutron star spin frequency is known, these sources all spin fast at over 500 Hz; the rotationally induced mixing may explain burst recurrence times of the order of 10 minutes. Short recurrence time bursts generally occur at all mass accretion rates where normal bursts are observed, but for individual sources the short recurrence times may be restricted to a smaller interval of accretion rate. The fraction of such bursts is roughly 30%. We also report the shortest known recurrence time of 3.8 minutes. more...
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- 2010
13. ROSSI X-RAY TIMING EXPLORER AND BeppoSAX OBSERVATIONS OF THE TRANSIENT X-RAY PULSAR XTE J1859+083
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Zand, t and Levine, M
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We present observations of the 9.8 s X-ray pulsar XTE J1859+083 made with the All Sky Monitor (ASM) and Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer, and the Wide Field Camera (WFC) on board BeppoSAX. The ASM data cover a 12 year time interval and show that an extended outburst occurred between approximately MJD 50,250 and 50,460 (1996 June 16 to 1997 January 12). The ASM data excluding this outburst interval suggest a possible modulation with a period of 60.65 +- 0.08 days. Eighteen sets of PCA observations were obtained over an approximately one month interval in 1999. The flux variability measured with the PCA appears consistent with the possible period found with the ASM. The PCA measurements of the pulse period showed it to decrease nonmonotonically and then to increase significantly. Doppler shifts due to orbital motion rather than accretion torques appear to be better able to explain the pulse period changes. Observations with the WFC during the extended outburst give a position that is consistent with a previously determined PCA error box, but which has a significantly smaller error. The transient nature of XTE J1859+083 and the length of its pulse period are consistent with it being a Be/neutron star binary. The possible 60.65 day orbital period would be of the expected length for a Be star system with a 9.8 s pulse period. more...
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- 2009
14. The Orbit of the Eclipsing X-Ray Pulsar EXO 1722-363
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J, Thomas W., Tomsick, John A., Zand, t, Rothschild, Richard E., and Walter, Roland
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With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray measurements of the heavily obscured X-ray pulsar EXO 1722-363 (IGR J17252-3616), we carried out a pulse-timing analysis to significantly improve the accuracy of the orbital parameters. The binary system is characterized by ax sin i = 101 +- 3 lt-s and Porb = 9.7403 +- 0.0004 days (90% confidence), with the precision of the orbital period obtained by connecting data sets separated by more than 7 yr (272 orbital cycles). The orbit is consistent with circular, and e < 0.19 at the 90% confidence level. The orbital solution also shows that a torque reversal occurred sometime between 1998 November and 2006 February. The mass function is 11.7 +- 1.2 M and confirms that this source is a high-mass X-ray binary (HMXB) system. Using previous eclipse time measurements by Corbet et al. and our orbital solution, combined with the assumption that the primary underfills its Roche lobe, we find that i > 61deg at the 99% confidence level, the radius of the primary is between 21 and 37 R, and its mass is less than about 22 M. The acceptable range of radius and mass shows that the primary is probably a supergiant of spectral type B0 I-B5 I. Photometric measurements of its likely counterpart are consistent with the spectral type and luminosity if the distance to the system is between 5.3 and 8.7 kpc. Spectral analysis of the pulsar as a function of orbital phase reveals an evolution of the hydrogen column density suggestive of dense filaments of gas in the downstream wake of the pulsar, with higher levels of absorption seen at orbital phases 0.5-1.0, as well as a variable Fe Ka line. more...
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- 2007
15. Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae
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Kaneko, Yuki, Ramirez, Enrico, Granot, Jonathan, Kouveliotou, Chryssa, Woosley, Stan E., Patel, Sandeep K., Rol, Evert, M, Jean J., Zand, t, van, Alexander J., Horst, der, M, Ralph A., and Strom, Richard more...
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We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425, 030329, 031203, and 060218) that were spectroscopically found to be associated with Type Ic supernovae and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolution and estimate the total energy budget based on broadband observations. The observational inventory for these events has become rich enough to allow estimates of their energy content in relativistic and subrelativistic form. The result is a global portrait of the effects of the physical processes responsible for producing long-soft GRBs. In particular, we find that the values of the energy released in mildly relativistic outflows appears to have a significantly smaller scatter than those found in highly relativistic ejecta. This is consistent with a picture in which the energy released inside the progenitor star is roughly standard, while the fraction of that energy that ends up in highly relativistic ejecta outside the star can vary dramatically between different events. more...
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- 2007
16. Orbital Parameters for the X-Ray Pulsar IGR J16393-4643
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J, Thomas W., Tomsick, John A., Rothschild, Richard E., Zand, t, and Walter, Roland
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With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray measurements of the heavily obscured X-ray pulsar IGR J16393-4643, we carried out a pulse timing analysis to determine the orbital parameters. Assuming a circular orbit, we phase-connected data spanning over 1.5 yr. The most likely orbital solution has a projected semimajor axis of 43 +- 2 lt-s and an orbital period of 3.6875 +- 0.0006 days. This implies a mass function of 6.5 +- 1.1 M and confirms that this INTEGRAL source is a high-mass X-ray binary (HMXB) system. By including eccentricity in the orbital model, we find e < 0.25 at the 2 s level. The 3.7 day orbital period and the previously known ~910 s pulse period place the system in the region of the Corbet diagram populated by supergiant wind accretors, and the low eccentricity is also consistent with this type of system. Finally, it should be noted that although the 3.7 day solution is the most likely one, we cannot completely rule out two other solutions with orbital periods of 50.2 and 8.1 days. more...
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- 2006
17. Long Type I X-Ray Bursts and Neutron Star Interior Physics
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Cumming, Andrew, Macbeth, Jared, Zand, t, and Page, Dany
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Two types of long-duration type I X-ray bursts have been discovered by long-term monitoring observations of accreting neutron stars: superbursts and ``intermediate duration'' bursts. We investigate the sensitivity of their ignition conditions to the interior thermal properties of the neutron star. First, we compare the observed superburst light curves to cooling models. Our fits require ignition column depths in the range (0.5-3) x 1012 g cm-2 and an energy release [?]2 x 1017 ergs g-1. The implied carbon fraction is XC > 10%, constraining models of rp-process hydrogen burning. Neutrino emission and inwards conduction of heat lead to a characteristic surface fluence of 1042 ergs, in good agreement with observations. Next, we compare ignition models to observations of superbursts. Consistent with our light-curve fits, carbon fractions XC [?] 0.2 are needed to avoid stable burning at the lowest rates for which superbursts have been observed. Unstable carbon ignition at the observed depths requires crust temperatures [?]6 x 108 K, which implies that neutrino emission from the interior is inefficient, and the crust has a poor thermal conductivity. In particular, we cannot match observed superburst properties when Cooper pair neutrino emission from the crust is included. We conclude that an extra ingredient, for example additional heating of the accumulating fuel layer, is required to explain the observed properties of superbursts. If Cooper pair emission is less efficient than currently thought, the observed ignition depths for superbursts imply that the crust is a poor conductor, and the core neutrino emission is not more efficient than modified Urca. The observed properties of helium bursts support these conclusions, requiring inefficient crust conductivity and core neutrino emission. more...
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- 2006
18. Probing the Environment in Gamma-Ray Bursts: The Case of an X-Ray Precursor, Afterglow Late Onset, and Wind Versus Constant Density Profile in GRB 011121 and GRB 011211
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Pasquale, De and Zand, t
- Abstract
In this paper we present BeppoSAX and XMM-Newton observations of two long gamma-ray bursts (GRBs), the X-ray-rich event of 2001 December 11 (GRB 011211) and the hard and very bright event of 2001 November 21 (GRB 011121). In both events we find evidence of a late X-ray burst taking place several minutes after the prompt emission. In the November burst the spectrum of the X-ray burst is much softer than that of the preceding prompt phase and consistent with the spectrum of the afterglow at 1 day. In addition, the tail of the X-ray burst and the light curve of the afterglow at 1 day are connected by a single power law [?](t - t0)img1.gif, when t0 corresponds with the onset of the X-ray burst. These evidences suggest that the late X-ray burst represents the onset of the afterglow. A similar conclusion is drawn for the December burst. The temporal and spectral behavior of the X-ray and optical afterglows indicate that the fireball evolution in the December burst takes place in an interstellar medium (ISM) environment. In contrast, in the November burst the wind case is revealed by an X-ray decay slower than that observed in the optical (dX = 1.29 +- 0.04 vs. dO = 1.66 +- 0.06). The wind profile should change into a constant-density profile at large radii in order to reconcile late-time radio data with a jet. Two other results are obtained for this burst. An X-ray burst precedes the much harder GRB by about 30 s. Contrary to the prediction of simple models of precursor activity for collapsars, the precursor's spectrum is not consistent with a blackbody. Finally, a substantial absorption column [NH = (7 +- 2) x 1022 cm-2] is detected during the early part of the prompt emission. This is much greater than that of the wind, and it is thus likely associated with the region surrounding the burst. more...
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- 2005
19. The Prompt X-Ray Emission of GRB 011211: Possible Evidence of a Transient Absorption Feature
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Zand, t
- Abstract
We report observation results of the prompt X- and gamma-ray emission from GRB 011211. This event was detected with the Gamma-Ray Burst Monitor and one of the wide-field cameras aboard the BeppoSAX satellite. The optical counterpart of the gamma-ray burst was soon identified and its redshift determined (z = 2.140), while the X-ray afterglow emission was detected with the XMM-Newton satellite. Evidence of soft X-ray emission lines was reported by Reeves and colleagues but not confirmed by other authors. In investigating the spectral evolution of the prompt emission, we find the possible evidence of a transient absorption feature at 6.9img1.gif keV during the rise of the primary event. The significance of the feature is derived with nonparametric tests and numerical simulations, finding a chance probability that ranges from 3 x 10-3 down to 4 x 10-4. The feature shows a Gaussian profile and an equivalent width of 1.2img2.gif keV. We discuss our results and their possible interpretation. more...
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- 2004
20. Discovery of X-Ray Burst Oscillations from a Neutron Star X-Ray Transient in the Globular Cluster NGC 6440
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Zand, t
- Abstract
We report the discovery of millisecond oscillations in an X-ray burst from the X-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440. Oscillations at a frequency of 409.7 +- 0.3 Hz were present in one of 15 X-ray bursts observed with the Proportional Counter Array on the Rossi X-Ray Timing Explorer during the outburst that occurred in 2001. The burst was relatively dim and had the second longest duration and decay time. The average peak luminosity of two bursts showing radius expansion is (3.6 +- 0.4) x 1038 ergs s-1, consistent with the Eddington luminosity for a 1.4 M and 10 km radius neutron star burning hydrogen-poor matter. We speculate that the dichotomy observed between sources with burst oscillations at once versus twice the frequency difference of kHz quasiperiodic oscillations in the persistent emission may be related to the magnetic field geometry of the neutron stars. more...
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- 2003
21. A Comparative Study of the X-Ray Afterglow Properties of Optically Bright and Dark Gamma-Ray Bursts
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Pasquale, De and Zand, t
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We have examined the complete set of X-ray afterglow observations of dark and optically bright gamma-ray bursts (GRBs) performed by BeppoSAX through 2001 February. X-ray afterglows are detected in ~90% of the cases. We do not find significant differences in the X-ray spectral shape, in particular no increased X-ray absorption in GRBs without optical transient (dark GRBs) compared to GRBs with optical transient (OTGRBs). Rather, we find that the 1.6-10 keV flux of OTGRBs is on average about 5 times larger than that of the dark GRBs. A Kolmogorov-Smirnov test shows that this difference is significant at 99.8% probability. Under the assumption that dark and OTGRBs have similar spectra, this could suggest that the first are uncaught in the optical band because they are just faint sources. In order to test this hypothesis, we have determined the optical-to-X-ray flux ratios of the sample. OTGRBs show a remarkably narrow distribution of flux ratios, which corresponds to an average optical-to-X-ray spectral indeximg1.gifimg2.gif = 0.794 +- 0.054. We find that, while 75% of dark GRBs have flux ratio upper limits still consistent with those of OT GRBs, the remaining 25% are 4-10 times weaker in optical than in X-rays. The significance of this result is [?]2.6 s. If this subpopulation of dark GRBs were constituted by objects assimilable to OTGRBs, they should have shown optical fluxes higher than upper limits actually found. We discuss the possible causes of their behavior, including a possible occurrence in high-density clouds or origin at very high redshift and a connection with ancient, Population III stars. more...
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- 2003
22. The Bright Gamma-Ray Burst of 2000 February 10: A Case Study of an Optically Dark Gamma-Ray Burst
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Zand, t
- Abstract
The gamma-ray burst GRB 000210 had the highest gamma-ray peak flux of any event localized by BeppoSAX as yet, but it did not have a detected optical afterglow, despite prompt and deep searches down to Rlim [?] 23.5. It is therefore one of the events recently classified as dark GRBs, whose origin is still unclear. Chandra observations allowed us to localize the X-ray afterglow of GRB 000210 to within [?]1'', and a radio transient was detected with the Very Large Array. The precise X-ray and radio positions allowed us to identify the likely host galaxy of this burst and to measure its redshift, z = 0.846. The probability that this galaxy is a field object is [?]1.6 x 10-2. The X-ray spectrum of the afterglow shows significant absorption in excess of the Galactic one corresponding, at the redshift of the galaxy, to NH = (5 +- 1) x 1021 cm-2. The amount of dust needed to absorb the optical flux of this object is consistent with the above H I column density, given a dust-to-gas ratio similar to that of our Galaxy. We do not find evidence for a partially ionized absorber expected if the absorption takes place in a giant molecular cloud. We therefore conclude that either the gas is local to the GRB but is condensed in small-scale high-density (n [?] 109 cm-3) clouds, or the GRB is located in a dusty, gas-rich region of the Galaxy. Finally, we examine the hypothesis that GRB 000210 lies at z [?] 5 (and therefore that the optical flux is extinguished by Lya forest clouds), but we conclude that the X-ray-absorbing medium would have to be substantially thicker from that observed in GRBs with optical afterglows. more...
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- 2002
23. Discovery of Millisecond Variability in the Neutron Star X-Ray Transient SAX J1750.8-2900
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Zand, t
- Abstract
We report the discovery of millisecond oscillations in the X-ray emission from the X-ray transient SAX J1750.8-2900. Millisecond quasiperiodic oscillations were present in the persistent emission with frequencies ranging from 543 to 1017 Hz. Oscillations at a frequency of 600.75 Hz were present in the brightest X-ray burst observed. We derive an upper limit on the source distance of 6.3 +- 0.7 kpc from this X-ray burst. more...
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- 2002
24. Very Low Luminosities from the Accretion-driven Millisecond X-Ray Pulsar SAX J1808.4-3658 during Quiescence
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Wijnands, Rudy, Kuiper, Lucien, in, Jean, Zand, t, Dotani, Tadayasu, van, Michiel, Klis, der, and Heise, John
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We have observed the millisecond X-ray pulsar SAX J1808.4-3658 on three occasions during its 2000 outburst with the BeppoSAX satellite. The source was highly variable and erratic during this outburst, and by coincidence we obtained data only during times when the source had very low luminosities. During our observations, we detected four faint sources. The source closest to the position of SAX J1808.4-3658 is still ~1.'6 away. This source can be identified with SAX J1808.4-3658 only if we assume that the BeppoSAX positional reconstruction is not completely understood. We also reanalyzed a BeppoSAX observation taken in 1999 March by Stella et al. when the source was in quiescence and during which the source was thought to have been detected. Based on the similarities (position and luminosity) of this source with the above-mentioned source ~1.'6 away from SAX J1808.4-3658, it is possible that they are the same source. If this source is not the millisecond pulsar, then during all BeppoSAX observations of SAX J1808.4-3658 (the 2000 outburst ones and the 1999 quiescent one), the millisecond pulsar was not detected. A reanalysis of the ASCA quiescent data of SAX J1808.4-3658 recently performed by Dotani, Asai, & Wijnands confirms that during this observation the source was securely detected in quiescence. We discuss our results for SAX J1808.4-3658 in the context of the quiescent properties of low-mass X-ray binary transients. more...
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- 2002
25. BeppoSAX Measurements of the Bright Gamma-Ray Burst 010222
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Zand, t
- Abstract
We analyze the BeppoSAX measurements of the prompt and afterglow emission of the g-ray burst GRB 010222. Among 45 GRBs detected with the Wide Field Cameras on BeppoSAX, the 40-700 keV fluence of (9.3 +- 0.3) x 10-5 ergs cm-2 is only surpassed by GRB 990123. In terms of the isotropic 20-2000 keV energy output of 7.8 x 1053 ergs, it ranks third of all GRBs with measured distances. Since this burst is so bright, the data provide complete and valuable coverage up to 65 hr after the event, except for a gap between 3.5 and 8.0 hr. The 2-10 keV flux history shows clear signs of a break, which is consistent with a break seen in the optical, and provides supporting evidence for the achromatic nature of the break. An explanation for the break in the context of a collimated expansion is not straightforward. Rather, a model is favored whereby the fireball is braked to the nonrelativistic regime quickly (within a fraction of day) by a dense (~106 cm-3) circumburst medium. This implies that, after a mild beaming correction, GRB 010222 may be the most energetic burst observed thus far. The X-ray decay index after the break is 1.33 +- 0.04, the spectral index 0.97 +- 0.05. The decay is, with unprecedented accuracy, identical to that observed in the optical. more...
- Published
- 2001
26. X-Ray Afterglow Detection of the Short Gamma-Ray Burst GRB 991014
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Zand, t
- Abstract
GRB 991014 is one of the shortest gamma-ray bursts detected so far with the Wide Field Cameras aboard BeppoSAX, in both gamma rays and X-rays. The duration is 9.6 s in 2-28 keV and 3.2 s in 40 to 700 keV (as measured between the times when 5% and 95% of the burst photons have been accumulated). We have refined the InterPlanetary Network annulus of the burst; we present the detection of the X-ray afterglow of GRB 991014 within this refined annulus and discuss X-ray and gamma-ray observations of the prompt and afterglow emission. Except for the briefness of the prompt event, no other unusual aspects were found in the prompt and afterglow observations as compared to such measurements in previous gamma-ray bursts. more...
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- 2000
27. Prompt and Afterglow Emission from the X-Ray-Rich GRB 981226 Observed with BeppoSAX
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Fiume, Dal and Zand, t
- Abstract
We discuss observations of the prompt X- and g-ray emission and X-ray afterglow from GRB 981226. This event has the weakest gamma-ray peak flux detected with the BeppoSAX Gamma-Ray Burst Monitor. It shows an isolated X-ray precursor and the highest X-ray to gamma-ray fluence ratio measured thus far with the BeppoSAX Wide Field Cameras. The event was followed up with the BeppoSAX Narrow Field Instruments, and the X-ray afterglow was detected up to 10 keV. The afterglow flux is observed to rise from a level below the sensitivity of the MECS/LECS telescopes up to a peak flux of (5 +- 1) x 10-13 ergs cm-2 s-1 in the 2-10 keV energy band. This rise is followed by a decline according to a power law with an index of 1.31img1.gif. We discuss these results in the light of the current GRB models. more...
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- 2000
28. BeppoSAX Observations of GRB 980425: Detection of the Prompt Event and Monitoring of the Error Box
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Zand, t, Fiume, Dal, and Sordo, Del
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We present BeppoSAX follow-up observations of GRB 980425 obtained with the Narrow Field Instruments (NFI) in 1998 April, May, and November. The first NFI observation has detected within the 8' radius error box of the gamma-ray burst (GRB) an X-ray source positionally consistent with the supernova 1998bw, which exploded within a day of GRB 980425, and a fainter X-ray source, not consistent with the position of the supernova. The former source is detected in the following NFI pointings and exhibits a decline of a factor of 2 in six months. If it is associated with SN 1998bw, this is the first detection of X-ray emission from a Type I supernova above 2 keV. The latter source exhibits only marginally significant variability. The X-ray spectra and variability of the supernova are compared with thermal and nonthermal models of supernova high-energy emission. Based on the BeppoSAX data, it is not possible to establish firmly which of the two detected sources is the GRB X-ray counterpart, although probability considerations favor the supernova. more...
- Published
- 2000
29. Integrating the BeppoSAX Gamma-Ray Burst Monitor into the Third Interplanetary Network
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Fiume, Dal and Zand, t
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We have added the BeppoSAX Gamma-Ray Burst Monitor to the third Interplanetary Network (IPN3) of burst detectors. We analyze 16 bursts whose positions are known to good accuracy from measurements at other wavelengths. We show that there is excellent agreement between the Ulysses/BeppoSAX triangulation annuli and the known positions of these events and that these annuli can in many cases provide useful constraints on the positions of bursts detected by the BeppoSAX Wide-Field Camera and Narrow-Field Instruments. more...
- Published
- 2000
30. The X-Ray, Optical, and Infrared Counterpart to GRB 980703
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Paradijs, van and Zand, t
- Abstract
We report on X-ray, optical, and infrared follow-up observations of GRB 980703. We detect a previously unknown X-ray source in the GRB error box; assuming a power-law decline, we find for its decay index a < -0.91 (3 s). We invoke host-galaxy extinction to match the observed spectral slope with the slope expected from "fireball" models. We find no evidence for a spectral break in the infrared to X-ray spectral range on 1998 July 4.4, and determine a lower limit of the cooling break frequency, nc > 1.3 x 1017 Hz. For this epoch we obtain an extinction of AV = 1.50 +- 0.11. From the X-ray data we estimate the optical extinction to be AV = 20.2+12.3-7.3, inconsistent with the former value. Our optical spectra confirm the redshift of z = 0.966. We compare the afterglow of GRB 980703 with that of GRB 970508 and find that the fraction of the energy in the magnetic field, [?]B < 6 x 10-5, is much lower in the case of GRB 980703, as a consequence of the high frequency of the cooling break. more...
- Published
- 1999
31. Occupational and patient exposure as well as image quality for full spine examinations with the EOS imaging system
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Zand, T. [Department of Radiology, Division of paediatric radiology, University Hospitals of Geneva, Geneva 1205 (Switzerland)]
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- 2014
- Full Text
- View/download PDF
32. Unraveling the Structure and Function of Melanin through Synthesis.
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Cao W, Zhou X, McCallum NC, Hu Z, Ni QZ, Kapoor U, Heil CM, Cay KS, Zand T, Mantanona AJ, Jayaraman A, Dhinojwala A, Deheyn DD, Shawkey MD, Burkart MD, Rinehart JD, and Gianneschi NC
- Subjects
- Electron Spin Resonance Spectroscopy, Indoles chemistry, Indoles metabolism, Magnetic Resonance Spectroscopy, Melanins biosynthesis, Molecular Conformation, Polymers chemistry, Polymers metabolism, Melanins chemistry
- Abstract
Melanin is ubiquitous in living organisms across different biological kingdoms of life, making it an important, natural biomaterial. Its presence in nature from microorganisms to higher animals and plants is attributed to the many functions of melanin, including pigmentation, radical scavenging, radiation protection, and thermal regulation. Generally, melanin is classified into five types-eumelanin, pheomelanin, neuromelanin, allomelanin, and pyomelanin-based on the various chemical precursors used in their biosynthesis. Despite its long history of study, the exact chemical makeup of melanin remains unclear, and it moreover has an inherent diversity and complexity of chemical structure, likely including many functions and properties that remain to be identified. Synthetic mimics have begun to play a broader role in unraveling structure and function relationships of natural melanins. In the past decade, polydopamine, which has served as the conventional form of synthetic eumelanin, has dominated the literature on melanin-based materials, while the synthetic analogues of other melanins have received far less attention. In this perspective, we will discuss the synthesis of melanin materials with a special focus beyond polydopamine. We will emphasize efforts to elucidate biosynthetic pathways and structural characterization approaches that can be harnessed to interrogate specific structure-function relationships, including electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. We believe that this timely Perspective will introduce this class of biopolymer to the broader chemistry community, where we hope to stimulate new opportunities in novel, melanin-based poly-functional synthetic materials. more...
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- 2021
- Full Text
- View/download PDF
33. The Seatbelt Syndrome-Do We Have a Chance?: A Report of 3 Cases With Review of Literature.
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Eberhardt CS, Zand T, Ceroni D, Wildhaber BE, and La Scala G
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- Abdominal Injuries diagnostic imaging, Abdominal Injuries surgery, Child, Fatal Outcome, Female, Humans, Male, Spinal Cord Injuries diagnostic imaging, Spinal Cord Injuries surgery, Syndrome, Tomography, X-Ray Computed, Abdominal Injuries etiology, Accidents, Traffic, Seat Belts adverse effects, Spinal Cord Injuries etiology
- Abstract
The seatbelt syndrome represents an injury pattern seen after motor vehicle accidents. It is secondary to either the misplacement of seatbelts over the abdomen or the misuse of the restraint systems. This syndrome is infrequent in the pediatric population and occurs mostly in school-aged children because recommended lap-shoulder belts and booster seats are often not used in this age group, so that the seatbelt lies over the abdomen. Sudden deceleration bends the child around the lap belt causing injuries to the viscera, head, and spine (Chance fracture), often associated with paraplegia. Because not all patients have an abdominal seatbelt sign, this syndrome can easily not be recognized with potentially life-threatening consequences.We report on 3 patients with the seatbelt syndrome and review the literature regarding prevalence, diagnosis, treatment, and prognosis of the different injuries and discuss the diagnostic challenges of intestinal lesions and their management.Following this accident pattern, in hemodynamically stable patients with a normal abdominal computed tomography scan, close surveillance is warranted to rule out intestinal lesions manifesting with progressive peritoneal irritation. In hemodynamically unstable patients, or if there is evidence of free air on the computed tomography scan, emergency abdominal exploration is required. more...
- Published
- 2016
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34. Clinical outcomes of patients with nondiagnostic biopsy during cryoablation of small renal masses.
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Babaian KN, Okhunov Z, Juncal S, Ordon M, Lusch A, Zand T, Andreoni C, and Landman J
- Subjects
- Aged, Biopsy, Carcinoma, Renal Cell pathology, Female, Humans, Kidney Neoplasms pathology, Male, Middle Aged, Retrospective Studies, Treatment Outcome, Carcinoma, Renal Cell surgery, Cryosurgery, Kidney Neoplasms surgery, Nephrectomy methods
- Abstract
Objective: To compare the outcomes of patients with biopsy-proven renal cell carcinoma (RCC), benign tumors (BTs), and nondiagnostic (ND) biopsies after renal cryoablation (RC)., Methods: We retrospectively reviewed medical records of 114 patients who underwent RC between 2003 and 2013. Patients were stratified according to biopsy histopathology results-RCC, BT, and ND biopsy. We recorded patient demographics and tumor features and examined oncologic outcomes among the 3 groups., Results: RC was performed in 114 patients with 117 tumors. Seventy-two tumors (61.5%) were RCC, 18 (15.4%) were BTs (oncocytoma or angiomyolipoma), and 27 (23.1%) were ND. Patient characteristics and tumor features were similar among the 3 groups. The median follow-up was 26.5, 26.0, and 22.0 months in the RCC, BT, and ND biopsy groups, respectively (P = .18). Residual disease occurred in the RCC (1.4%) and ND biopsy (7.4%) groups, but not in the BT group (P = .19). All 9 patients (12.5%) who developed recurrent disease had biopsy-proven RCC. The 2- and 5-year recurrence-free survival rates (RFS) for patients with biopsy-proven RCC were 90.2% and 81.2%, respectively. Because no patient in the BT and ND biopsy groups had a recurrence, their RFS was 100%., Conclusion: No patient with a BT or ND biopsy developed a local recurrence with short-term follow-up, whereas a recurrence developed in 12.5% of biopsy-proven RCC tumors. RFS for patients with biopsy-proven RCC was worse than the other 2 biopsy groups, although not statistically significant. Long-term follow-up in a larger cohort of patients is needed to further evaluate these preliminary findings., (Copyright © 2015 Elsevier Inc. All rights reserved.) more...
- Published
- 2015
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35. Lung volume assessments in normal and surfactant depleted lungs: agreement between bedside techniques and CT imaging.
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Albu G, Petak F, Zand T, Hallbäck M, Wallin M, and Habre W
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- Animals, Bronchoalveolar Lavage, Capnography, Helium, Lung diagnostic imaging, Peak Expiratory Flow Rate, Rabbits, Respiration, Artificial, Lung metabolism, Lung physiopathology, Lung Volume Measurements methods, Point-of-Care Systems, Pulmonary Surfactants metabolism, Tomography, Spiral Computed methods
- Abstract
Background: Bedside assessment of lung volume in clinical practice is crucial to adapt ventilation strategy. We compared bedside measures of lung volume by helium multiple-breath washout technique (EELVMBW,He) and effective lung volume based on capnodynamics (ELV) to those assessed from spiral chest CT scans (EELVCT) under different PEEP levels in control and surfactant-depleted lungs., Methods: Lung volume was assessed in anaesthetized mechanically ventilated rabbits successively by measuring i) ELV by analyzing CO2 elimination traces during the application of periods of 5 consecutive alterations in inspiratory/expiratory ratio (1:2 to 1.5:1), ii) measuring EELVMBW,He by using helium as a tracer gas, and iii) EELVCT from CT scan images by computing the normalized lung density. All measurements were performed at PEEP of 0, 3 and 9 cmH2O in random order under control condition and following surfactant depletion by whole lung lavage., Results: Variables obtained with all techniques followed sensitively the lung volume changes with PEEP. Excellent correlation and close agreement was observed between EELVMBW,He and EELVCT (r = 0.93, p < 0.0001). ELV overestimated EELVMBW,He and EELVCT in normal lungs, whereas this difference was not evidenced following surfactant depletion. These findings resulted in somewhat diminished but still significant correlations between ELV and EELVCT (r = 0.58, p < 0.001) or EELVMBW,He (0.76, p < 0.001) and moderate agreements., Conclusions: Lung volume assessed with bedside techniques allow the monitoring of the changes in the lung aeration with PEEP both in normal lungs and in a model of acute lung injury. Under stable pulmonary haemodynamic condition, ELV allows continuous lung volume monitoring, whereas EELVMBW,He offers a more accurate estimation, but intermittently. more...
- Published
- 2014
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36. Spontaneous tibiotalar arthrodesis as a complication of acute tibial osteomyelitis due to Panton-Valentine leukocidin-producing Staphylococcus aureus: a case report.
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Ceroni D, de la Llana RA, Zand T, Lamah L, Dominguez D, De Coulon G, and Dubois-Ferrière V
- Abstract
Introduction: Strains of Panton-Valentine leukocidin-producing Staphylococcus aureus producing a new pattern of disease have emerged worldwide. Infection with these bacteria typically presents as a life-threatening infection of soft tissues and bones, and may cause potentially devastating consequences., Case Presentation: We report a case of osteoarticular infection caused by Panton-Valentine leukocidin-producing Staphylococcus aureus. A 12-year-old Caucasian girl presented with acute osteomyelitis of the tibia associated with toxic shock syndrome, which was complicated by an unexpected spontaneous ankle arthrodesis., Conclusions: Osteoarticular infections due to Panton-Valentine leukocidin-producing Staphylococcus aureus appear to be severe, and are characterized by their tendency to evolve towards serious complications. This case highlights the need for early and aggressive surgical procedures in conjunction with appropriate antimicrobial therapy and regular long-term follow-up. more...
- Published
- 2012
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37. Sinus pericranii: a scalp mass in a 6-month-old boy.
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Kanavaki A, Dhouib A, Zand T, Anooshiravani M, and Hanquinet S
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- Humans, Infant, Male, Magnetic Resonance Imaging, Scalp blood supply, Sinus Pericranii diagnostic imaging, Sinus Pericranii pathology, Ultrasonography, Doppler, Color
- Abstract
'Sinus pericranii' is an abnormal communication between the extracranial veins and the dural venous sinuses (usually the superior sagittal and the transverse sinuses). It is a rare childhood abnormality. We report a case of a 6-month-old boy presenting with a scalp swelling in the left parietal region. Ultrasound with color Doppler and MRI showed a dilated epicranial vein that communicated with the superior sagittal sinus. This anomalous venous connection is known as sinus pericranii. We describe the imaging findings, associated abnormalities and management of this rare vascular abnormality., (Copyright © 2012 S. Karger AG, Basel.) more...
- Published
- 2012
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38. Communication in the diagnostic mammography suite: implications for practice and training.
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Sasson JP, Zand T, and Lown BA
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- Female, Humans, Internship and Residency, Male, Surveys and Questionnaires, Attitude of Health Personnel, Communication, Mammography, Physician-Patient Relations, Practice Patterns, Physicians' statistics & numerical data, Radiology education
- Abstract
Rationale and Objectives: The diagnostic mammography suite is a microcosm of challenging physician-patient communication in radiology. Little has been written about communication practices in the diagnostic mammography suite, the effect of this communication on both physicians and patients, and implications for radiology training programs. We surveyed radiology residents and staff about communication training, practices, and experiences communicating directly with patients in the diagnostic mammography suite., Materials and Methods: We asked the membership of the Association of Program Directors in Radiology to disseminate surveys to radiology residents and staff radiologists in their institutions. We analyzed response frequencies and correlations., Results: We received responses from 142 residents and 120 staff radiologists. More than half of staff respondents spoke personally with every patient who had an abnormal diagnostic mammogram; 37% felt they had inadequate time to do so. Most residents and staff highly rated their own communication skills and confidence in ability to explain results and respond to patients' emotions, but experienced stress doing so. A majority of respondents reported no formal communication skills education after medical school. Twenty-nine percent of staff respondents regularly observed residents' communication with patients and 39% of residents reported receiving feedback about their communication. Residents' opportunities to observe staff communicate with a patient and to receive feedback on their own patient interactions were correlated with self-rated communication skill and confidence in ability to respond to patients' emotions (P < .05)., Conclusions: Radiologists engage in challenging and stressful patient communication interactions. There is a paucity of educational curricula on interpersonal and communication skills in radiology. This has implications for both patient and physician satisfaction and patient outcomes. more...
- Published
- 2008
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39. Lipid deposition in rat aortas with intraluminal hemispherical plug stenosis. A morphological and biophysical study.
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Zand T, Hoffman AH, Savilonis BJ, Underwood JM, Nunnari JJ, Majno G, and Joris I
- Subjects
- Animals, Aortic Valve Stenosis pathology, Biophysics methods, Disease Models, Animal, Hypercholesterolemia metabolism, Hypercholesterolemia pathology, Male, Perfusion, Rats, Rats, Wistar, Rheology, Stress, Mechanical, Aorta metabolism, Aortic Valve Stenosis metabolism, Lipid Metabolism
- Abstract
A new method was devised to create a stenosis in the rat abdominal aorta. To restrict blood flow, a hemispherical plug was inserted into the aorta through a renal artery. This type of intrinsic (intraluminal) stenosis minimizes possible intramural effects associated with external compression or ligation which severely deform the arterial wall. In the aorta of hypercholesterolemic rats, lipid deposits were distributed in crescent-shaped patches proximal and distal to the plug, whereas lipid deposition in the opposite aortic wall was inhibited. Based on enlarged physical scale models used to study the flow field, the regions of lipid deposition were found to coincide with regions of low shear stress, stagnation, and recirculation. Shear stress was elevated at the wall opposite the plug. These results show that when confounding mural effects are minimized, lipid deposition is promoted in regions of low shear stress with recirculation and inhibited in regions of elevated shear stress. more...
- Published
- 1999
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40. Lipid deposition and intimal stress and strain. A study in rats with aortic stenosis.
- Author
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Zand T, Majno G, Nunnari JJ, Hoffman AH, Savilonis BJ, MacWilliams B, and Joris I
- Subjects
- Animals, Aortic Valve Stenosis pathology, Aortic Valve Stenosis physiopathology, Hypercholesterolemia metabolism, Hypercholesterolemia physiopathology, Male, Rats, Rats, Inbred Strains, Regional Blood Flow, Stress, Mechanical, Aorta metabolism, Aortic Valve Stenosis metabolism, Lipid Metabolism
- Abstract
These experiments were designed to study the topography of lipid deposition in the stenotic aorta of hypercholesterolemic rats, and to correlate it with flow conditions and intimal stresses and strains studied in a scale biophysical model and in a computer model. A 69% +/- 5% stenosis was produced with a U-shaped metal clip. One month to 8 months later, the aorta was studied en face by light microscopy after fixation and lipid staining. The intima in the throat of the stenosis was almost completely free of lipid, whereas symmetric lipid deposits occurred as bands just above and especially just below the stenosis; elsewhere lipid deposits appeared to be random. The flow data obtained from the scale model showed that the intima in the throat of the stenosis was subjected to an increase of as much as 20 times in shear stress, whereas the lipid deposits just above and just below the stenosis were associated with asymmetric flow conditions: the proximal area corresponded to a region of rapidly increasing shear stress, the distal area to a region of low to normal shear stress and separated flow. A finite element computer model based on the aortic deformations indicated that the endothelium at the inlet and outlet of the stenosis is subjected to a symmetric pattern of elevated stresses and strains. These results indicate that 1) the pattern of lipid deposition can not be adequately explained by a hypothesis based solely on flow conditions, and 2) lipid deposits can develop in areas of increased fluid shear stress, decreased fluid shear stress, and increased intimal strains. more...
- Published
- 1991
41. The significance of endothelial stomata and stigmata in the rat aorta. An electron microscopic study.
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Majno G, Underwood JM, Zand T, and Joris I
- Subjects
- Animals, Endothelium physiology, Intercellular Junctions metabolism, Microscopy, Electron, Permeability, Rats, Silver, Aorta anatomy & histology, Endothelium cytology
- Abstract
Perfusion of arteries with dilute silver nitrate produces in the endothelium (a) a pattern of pericellular black lines, which we earlier interpreted as a marker of the physiological electrolyte pathway (Zand et al. 1982), and (b) focal black deposits on or between the cells, either ring-shaped (stomata) or solid (stigmata). The purpose of this study was to clarify the nature and significance of these controversial structures. A glutaraldehyde-fixed normal rat aorta was perfused with silver nitrate; 17 typical stomata and stigmata were photographed en face, then studied on ultrathin serial sections. When seen en face, they fell into three groups: (I) 4 stomata in endothelial cells; (II) 6 stigmata in endothelial cells; (III) 7 stigmata on intercellular junctions. By electron microscopy, (I) all the stomata in endothelial cells corresponded to myoendothelial herniae. (II) Of the 6 stigmata in endothelial cells, 4 corresponded again to myoendothelial herniae, 2 corresponded to blebs (it seemed likely that these blebs had existed in vivo, but the possibility of a fixation artefact could not be excluded). (III) Of the 7 stigmata on intercellular junctions, one corresponded to the diapedesis of a mononuclear cell; the other 6 did not correspond to visible endothelial changes and are best interpreted as points of normally higher permeability. We conclude that stomata and stigmata (under the conditions of our experiments) can be explained in at least 4 different ways, depending in part on their location (in cells, on junctions). These ancient terms therefore remain useful for descriptive purposes, as long as it is realized that their significance in any given case must be determined by electron microscopic study. more...
- Published
- 1985
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42. Hydrodynamic injury of the endothelium in acute aortic stenosis.
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Joris I, Zand T, and Majno G
- Subjects
- Animals, Aorta, Abdominal pathology, Aortic Valve Stenosis physiopathology, Blood Pressure, Contrast Media administration & dosage, Endothelium pathology, Horseradish Peroxidase administration & dosage, Male, Microscopy, Electron, Rats, Rats, Inbred Strains, Silver Nitrate administration & dosage, Stress, Mechanical, Aorta, Abdominal ultrastructure, Aortic Valve Stenosis pathology, Endothelium ultrastructure, Hemodynamics
- Abstract
The acute effects of increased shear stress on the endothelium were studied by reducing the lumen of the rat aorta to 20-25% of normal by means of metal clips. Intimal damage in the stenotic area was assessed by light microscopy after perfusion with AgNo3 and study of the endothelium en face. Most of the endothelium was lost within 3 minutes; the extent of the damage was not increased after 1 hour. Electron-microscopic examination showed that some endothelial cells became permeable to tracers (thorium dioxide and horseradish peroxidase); platelets adhered to the exposed internal elastic membrane. Focal endothelial changes were represented by myelin figures of various kinds arising from the luminal surface and by "cellular ulcers," superficial erosions of the endothelial cells accompanied by localized cytoplasmic changes. These "ulcers" occurred more frequently over the nucleus and near junctions; they have not been described in other forms of arterial injury. more...
- Published
- 1982
43. Endothelium and "silver lines". An electron microscopic study.
- Author
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Zand T, Underwood JM, Nunnari JJ, Majno G, and Joris I
- Subjects
- Animals, Aorta ultrastructure, Basement Membrane ultrastructure, Biological Transport, Electrolytes metabolism, Intercellular Junctions ultrastructure, Microscopy, Electron, Rats, Silver, Staining and Labeling, Endothelium ultrastructure
- Abstract
The significance of endothelial "silver lines" was studied by TEM in rat aortas after perfusion with glutaraldehyde followed by silver nitrate. Standard TEM technique proved unsatisfactory (coarse silver granules, imprecise localization, artefacts). Exposure of the silver-treated aortas to photographic fixer markedly improved the image of the deposits leaving fine, stable, uniform "residual granules" about 100 A in diameter. Most of these granules were localized along the intercellular junctions; they also tended to pool in the basement membrane beneath each junction. This image suggests that the Ag+ ions pass through the junction, and react with its contents as well as with the basement membrane beyond it. A scheme is proposed to explain the reaction of Ag+ ions with anions and negatively charged radicals within the junction. It is concluded that the "silver lines" represent not only a histochemical effect, but also the visualization of a transendothelial electrolyte pathway. more...
- Published
- 1982
- Full Text
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44. Atherosclerosis: new horizons.
- Author
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Majno G, Joris I, and Zand T
- Subjects
- Animals, Arteriosclerosis metabolism, Biological Transport, Endothelium pathology, Humans, Inflammation pathology, Lipid Metabolism, Muscle, Smooth, Vascular pathology, Platelet-Derived Growth Factor physiology, Thrombosis pathology, Arteriosclerosis pathology
- Published
- 1985
- Full Text
- View/download PDF
45. Endothelial adaptations in aortic stenosis. Correlation with flow parameters.
- Author
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Zand T, Nunnari JJ, Hoffman AH, Savilonis BJ, MacWilliams B, Majno G, and Joris I
- Subjects
- Actins metabolism, Animals, Aortic Valve Stenosis metabolism, Aortic Valve Stenosis pathology, Endothelium, Vascular metabolism, Endothelium, Vascular ultrastructure, Male, Microscopy, Electron, Models, Cardiovascular, Rats, Rats, Inbred Strains, Regional Blood Flow, Adaptation, Physiological, Aortic Valve Stenosis physiopathology, Endothelium, Vascular physiopathology
- Abstract
A 69 +/- 5% stenosis was produced in the rat aorta, with the purpose of correlating endothelial changes with local flow patterns and with levels of shear stress; the hydrodynamic data were obtained from a scaled-up model of the stenosed aorta. In the throat of the stenosis, where shear stress values were 15-25 times normal, the endothelium was stripped off within 1 hour. It regenerated at half the rate of controls but modulated into a cell type that could withstand the increased shear stress. Adaptations included changes in cell orientation, number, length, width, thickness, stress fibers, and anchoring structures, as well as changes in the length, argyrophilia, and permeability of the junctions. Areas of either elongated or "polygonal" cells consistently developed at the same sites in relation to the stenosis, but the hydrodynamic data showed that they did not always correspond (as had been anticipated) to high and low shear, respectively. It is concluded that endothelial cell shape in the living artery must be determined by some other factor(s) in addition to shear stress. more...
- Published
- 1988
46. Quantitation of oil red O staining of the aorta in hypercholesterolemic rats.
- Author
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Nunnari JJ, Zand T, Joris I, and Majno G
- Subjects
- Animals, Aorta analysis, Coloring Agents, Lipids analysis, Rats, Rats, Inbred Strains, Aorta pathology, Azo Compounds, Histocytochemistry methods, Hypercholesterolemia pathology
- Abstract
A technique is described which provides morphologic and quantitative data on the amount of oil red O (ORO) staining in thoracic aortas of rats fed a high cholesterol diet. Samples are stained with ORO, the dye is extracted, and the concentration of ORO in the extract is measured colorimetrically. Wistar rats fed ad libitum either standard chow (control group: n = 15) or chow supplemented with 4% cholesterol, 1% cholic acid, and 0.5% thiouracil (CCT group: n = 23) were maintained on these diets for 1, 3, 6, 9, or 12 months. Plasma cholesterol levels averaged overall 87 and 737 mg/dl for the control and CCT groups, respectively. Animals were killed under anesthesia by perfusion fixation with formalin or glutaraldehyde, and samples of thoracic aorta were stained with ORO. After microscopic study en face and measurement of surface area, the ORO was extracted in chloroform-methanol (2:1). Concentrations of ORO (microM) were determined from a standard curve and expressed as microM/mm2 of aorta. Aortas of CCT animals showed progressive diet- and time-dependent increases in the amount of ORO staining compared to controls. We conclude that this method yields reliable quantitative data applicable to studying atherosclerosis in small animals. more...
- Published
- 1989
- Full Text
- View/download PDF
47. Studies on the pathogenesis of atherosclerosis. I. Adhesion and emigration of mononuclear cells in the aorta of hypercholesterolemic rats.
- Author
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Joris I, Zand T, Nunnari JJ, Krolikowski FJ, and Majno G
- Subjects
- Animals, Cell Adhesion, Cell Movement, Lipids blood, Male, Rats, Rats, Inbred Strains, Aorta ultrastructure, Arteriosclerosis etiology, Hypercholesterolemia pathology, Monocytes ultrastructure
- Abstract
In rats with diet-induced hypercholesterolemia, two concomitant changes began to occur within 1 week and persisted for 1 year: an increase in total plasma cholesterol and an increase in the number of mononuclear cells adhering to the aortic intima (up to values 50 times normal). Adherent cells were approximately 90% monocytes and approximately 10% lymphocytes. Adhesion was focal, with some preference for ostia of aortic branches; it was followed by migration into the subendothelial space. The subendothelial monocytes/macrophages progressively became foam cells, thus giving rise to microscopic "fatty streaks." Ultimately, typical atherosclerotic plaques were formed. Four possible mechanisms of increased cell adhesion are suggested. Endothelial changes were mild; myelin figures arising from the endothelial surface were seen by electron microscopy. Endothelial denudation was never observed, neither in light-microscopic preparations stained with AgNO3 nor by ultrastructure. Platelet participation was minimal. It is concluded that in this model atherosclerotic plaques are initiated by mononuclear cell adhesion and emigration; endothelial denudation is not a necessary step in their pathogenesis. more...
- Published
- 1983
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