38,651 research outputs found
Deep learning analysis of the myocardium in coronary CT angiography for identification of patients with functionally significant coronary artery stenosis
In patients with coronary artery stenoses of intermediate severity, the
functional significance needs to be determined. Fractional flow reserve (FFR)
measurement, performed during invasive coronary angiography (ICA), is most
often used in clinical practice. To reduce the number of ICA procedures, we
present a method for automatic identification of patients with functionally
significant coronary artery stenoses, employing deep learning analysis of the
left ventricle (LV) myocardium in rest coronary CT angiography (CCTA). The
study includes consecutively acquired CCTA scans of 166 patients with FFR
measurements. To identify patients with a functionally significant coronary
artery stenosis, analysis is performed in several stages. First, the LV
myocardium is segmented using a multiscale convolutional neural network (CNN).
To characterize the segmented LV myocardium, it is subsequently encoded using
unsupervised convolutional autoencoder (CAE). Thereafter, patients are
classified according to the presence of functionally significant stenosis using
an SVM classifier based on the extracted and clustered encodings. Quantitative
evaluation of LV myocardium segmentation in 20 images resulted in an average
Dice coefficient of 0.91 and an average mean absolute distance between the
segmented and reference LV boundaries of 0.7 mm. Classification of patients was
evaluated in the remaining 126 CCTA scans in 50 10-fold cross-validation
experiments and resulted in an area under the receiver operating characteristic
curve of 0.74 +- 0.02. At sensitivity levels 0.60, 0.70 and 0.80, the
corresponding specificity was 0.77, 0.71 and 0.59, respectively. The results
demonstrate that automatic analysis of the LV myocardium in a single CCTA scan
acquired at rest, without assessment of the anatomy of the coronary arteries,
can be used to identify patients with functionally significant coronary artery
stenosis.Comment: This paper was submitted in April 2017 and accepted in November 2017
for publication in Medical Image Analysis. Please cite as: Zreik et al.,
Medical Image Analysis, 2018, vol. 44, pp. 72-8
Automatic Synchronization of Multi-User Photo Galleries
In this paper we address the issue of photo galleries synchronization, where
pictures related to the same event are collected by different users. Existing
solutions to address the problem are usually based on unrealistic assumptions,
like time consistency across photo galleries, and often heavily rely on
heuristics, limiting therefore the applicability to real-world scenarios. We
propose a solution that achieves better generalization performance for the
synchronization task compared to the available literature. The method is
characterized by three stages: at first, deep convolutional neural network
features are used to assess the visual similarity among the photos; then, pairs
of similar photos are detected across different galleries and used to construct
a graph; eventually, a probabilistic graphical model is used to estimate the
temporal offset of each pair of galleries, by traversing the minimum spanning
tree extracted from this graph. The experimental evaluation is conducted on
four publicly available datasets covering different types of events,
demonstrating the strength of our proposed method. A thorough discussion of the
obtained results is provided for a critical assessment of the quality in
synchronization.Comment: ACCEPTED to IEEE Transactions on Multimedi
Clustering properties of a type-selected volume-limited sample of galaxies in the CFHTLS
(abridged) We present an investigation of the clustering of i'AB<24.5
galaxies in the redshift interval 0.2<z<1.2. Using 100,000 precise photometric
redshifts in the four ultra-deep fields of the Canada-France Legacy Survey, we
construct a set of volume-limited galaxy catalogues. We study the dependence of
the amplitude and slope of the galaxy correlation function on absolute B-band
rest-frame luminosity, redshift and best-fitting spectral type. We find: 1. The
comoving correlation length for all galaxies decreases steadily from z~0.3 to
z~1. 2. At all redshifts and luminosities, galaxies with redder rest-frame
colours have clustering amplitudes between two and three times higher than
bluer ones. 3. For bright red and blue galaxies, the clustering amplitude is
invariant with redshift. 4. At z~0.5, less luminous galaxies have higher
clustering amplitudes of around 6 h-1 Mpc. 5. The relative bias between
galaxies with red and blue rest-frame colours increases gradually towards
fainter absolute magnitudes. One of the principal implications of these results
is that although the full galaxy population traces the underlying dark matter
distribution quite well (and is therefore quite weakly biased), redder, older
galaxies have clustering lengths which are almost invariant with redshift, and
by z~1 are quite strongly biased.Comment: 16 pages, 18 figures, accepted for publication in Astronomy and
Astrophysic
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