71 research outputs found
Bi-Plane X-ray coronary 3D reconstruction for flow velocity assessment
In coronary angiography the coronary blood flow velocity can be assessed by tracking a contrast agent in an image sequence. The contrast agent flow velocity is used to estimate the functional behavior of the coronary arteries using TIMI frame count (TFC). In this paper we descibe the 3D reconstruction algorithm used in our method towards the automation of TFC. The method creates a two dimensional map of the contrast agent in which the opacification of the vessel centerline is plotted against time. This map is used to find the velocity of the contrast agent and subsequently the TFC. The vessel centerline is obtained using the Fast Marching Method to find the minimum cost path between\ud
the catheter point and the end of the vessel. The determination of the start and endpoint is estimated using a 3D model reconstructed from bi-plane 2D image\ud
data. The final reconstructed coronary model only includes the segments matching our error criterion
Estimation of x-ray parameters in digital coronary angiography for compensation of myocardial perfusion measurements
Moving from laboratory to real life conditions: Influence on the assessment of variability and stability of gait
The availability of wearable sensors allows shifting gait analysis from the traditional laboratory settings, to daily life conditions. However, limited knowledge is available about whether alterations associated to different testing environment (e.g. indoor or outdoor) and walking protocols (e.g. free or controlled), result from actual differences in the motor behaviour of the tested subjects or from the sensitivity to these changes of the indexes adopted for the assessment. In this context, it was hypothesized that testing environment and walking protocols would not modify motor control stability in the gait of young healthy adults, who have a mature and structured gait pattern, but rather the variability of their motor pattern.
To test this hypothesis, data from trunk and shank inertial sensors were collected from 19 young healthy participants during four walking tasks in different environments (indoor and outdoor) and in both controlled (i.e. following a predefined straight path) and free conditions. Results confirmed what hypothesized: variability indexes (Standard deviation, Coefficient of variation and Poincaré plots) were significantly influenced by both environment and walking conditions. Stability indexes (Harmonic ratio, Short term Lyapunov exponents, Recurrence quantification analysis and Sample entropy), on the contrary, did not highlight any change in the motor control.
In conclusion, this study highlighted an influence of environment and testing condition on the assessment of specific characteristics of gait (i.e. variability and stability). In particular, for young healthy adults, both environment and testing conditions affect gait variability indexes, whereas neither affect gait stability indexes
Two-level system with a thermally fluctuating transfer matrix element: Application to the problem of DNA charge transfer
Charge transfer along the base-pair stack in DNA is modeled in terms of
thermally-assisted tunneling between adjacent base pairs. Central to our
approach is the notion that tunneling between fluctuating pairs is rate-limited
by the requirement of their optimal alignment. We focus on this aspect of the
process by modeling two adjacent base pairs in terms of a classical damped
oscillator subject to thermal fluctuations as described by a Fokker-Planck
equation. We find that the process is characterized by two time scales, a
result that is in accord with experimental findings.Comment: original file is revtex4, 10 pages, three eps figure
Mesoscopic models for DNA stretching under force: new results and comparison to experiments
Single molecule experiments on B-DNA stretching have revealed one or two
structural transitions, when increasing the external force. They are
characterized by a sudden increase of DNA contour length and a decrease of the
bending rigidity. It has been proposed that the first transition, at forces of
60--80 pN, is a transition from B to S-DNA, viewed as a stretched duplex DNA,
while the second one, at stronger forces, is a strand peeling resulting in
single stranded DNAs (ssDNA), similar to thermal denaturation. But due to
experimental conditions these two transitions can overlap, for instance for
poly(dA-dT). We derive analytical formula using a coupled discrete worm like
chain-Ising model. Our model takes into account bending rigidity, discreteness
of the chain, linear and non-linear (for ssDNA) bond stretching. In the limit
of zero force, this model simplifies into a coupled model already developed by
us for studying thermal DNA melting, establishing a connexion with previous
fitting parameter values for denaturation profiles. We find that: (i) ssDNA is
fitted, using an analytical formula, over a nanoNewton range with only three
free parameters, the contour length, the bending modulus and the monomer size;
(ii) a surprisingly good fit on this force range is possible only by choosing a
monomer size of 0.2 nm, almost 4 times smaller than the ssDNA nucleobase
length; (iii) mesoscopic models are not able to fit B to ssDNA (or S to ss)
transitions; (iv) an analytical formula for fitting B to S transitions is
derived in the strong force approximation and for long DNAs, which is in
excellent agreement with exact transfer matrix calculations; (v) this formula
fits perfectly well poly(dG-dC) and -DNA force-extension curves with
consistent parameter values; (vi) a coherent picture, where S to ssDNA
transitions are much more sensitive to base-pair sequence than the B to S one,
emerges.Comment: 14 pages, 9 figure
Tight-binding parameters for charge transfer along DNA
We systematically examine all the tight-binding parameters pertinent to
charge transfer along DNA. The molecular structure of the four DNA bases
(adenine, thymine, cytosine, and guanine) is investigated by using the linear
combination of atomic orbitals method with a recently introduced
parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are
discussed and then used for calculating the corresponding wavefunctions of the
two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO
and LUMO energies of the bases are in good agreement with available
experimental values. Our results are then used for estimating the complete set
of charge transfer parameters between neighboring bases and also between
successive base-pairs, considering all possible combinations between them, for
both electrons and holes. The calculated microscopic quantities can be used in
mesoscopic theoretical models of electron or hole transfer along the DNA double
helix, as they provide the necessary parameters for a tight-binding
phenomenological description based on the molecular overlap. We find that
usually the hopping parameters for holes are higher in magnitude compared to
the ones for electrons, which probably indicates that hole transport along DNA
is more favorable than electron transport. Our findings are also compared with
existing calculations from first principles.Comment: 15 pages, 3 figures, 7 table
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Three-dimensional densitometric reconstruction and visualization of stenosed coronary artery segments
Global surveillance of cancer survival 1995-2009: analysis of individual data for 25,676,887 patients from 279 population-based registries in 67 countries (CONCORD-2)
BACKGROUND:
Worldwide data for cancer survival are scarce. We aimed to initiate worldwide surveillance of cancer survival by central analysis of population-based registry data, as a metric of the effectiveness of health systems, and to inform global policy on cancer control.
METHODS:
Individual tumour records were submitted by 279 population-based cancer registries in 67 countries for 25·7 million adults (age 15-99 years) and 75,000 children (age 0-14 years) diagnosed with cancer during 1995-2009 and followed up to Dec 31, 2009, or later. We looked at cancers of the stomach, colon, rectum, liver, lung, breast (women), cervix, ovary, and prostate in adults, and adult and childhood leukaemia. Standardised quality control procedures were applied; errors were corrected by the registry concerned. We estimated 5-year net survival, adjusted for background mortality in every country or region by age (single year), sex, and calendar year, and by race or ethnic origin in some countries. Estimates were age-standardised with the International Cancer Survival Standard weights.
FINDINGS:
5-year survival from colon, rectal, and breast cancers has increased steadily in most developed countries. For patients diagnosed during 2005-09, survival for colon and rectal cancer reached 60% or more in 22 countries around the world; for breast cancer, 5-year survival rose to 85% or higher in 17 countries worldwide. Liver and lung cancer remain lethal in all nations: for both cancers, 5-year survival is below 20% everywhere in Europe, in the range 15-19% in North America, and as low as 7-9% in Mongolia and Thailand. Striking rises in 5-year survival from prostate cancer have occurred in many countries: survival rose by 10-20% between 1995-99 and 2005-09 in 22 countries in South America, Asia, and Europe, but survival still varies widely around the world, from less than 60% in Bulgaria and Thailand to 95% or more in Brazil, Puerto Rico, and the USA. For cervical cancer, national estimates of 5-year survival range from less than 50% to more than 70%; regional variations are much wider, and improvements between 1995-99 and 2005-09 have generally been slight. For women diagnosed with ovarian cancer in 2005-09, 5-year survival was 40% or higher only in Ecuador, the USA, and 17 countries in Asia and Europe. 5-year survival for stomach cancer in 2005-09 was high (54-58%) in Japan and South Korea, compared with less than 40% in other countries. By contrast, 5-year survival from adult leukaemia in Japan and South Korea (18-23%) is lower than in most other countries. 5-year survival from childhood acute lymphoblastic leukaemia is less than 60% in several countries, but as high as 90% in Canada and four European countries, which suggests major deficiencies in the management of a largely curable disease.
INTERPRETATION:
International comparison of survival trends reveals very wide differences that are likely to be attributable to differences in access to early diagnosis and optimum treatment. Continuous worldwide surveillance of cancer survival should become an indispensable source of information for cancer patients and researchers and a stimulus for politicians to improve health policy and health-care systems
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