71 research outputs found
Cube-Cut: Vertebral Body Segmentation in MRI-Data through Cubic-Shaped Divergences
In this article, we present a graph-based method using a cubic template for
volumetric segmentation of vertebrae in magnetic resonance imaging (MRI)
acquisitions. The user can define the degree of deviation from a regular cube
via a smoothness value Delta. The Cube-Cut algorithm generates a directed graph
with two terminal nodes (s-t-network), where the nodes of the graph correspond
to a cubic-shaped subset of the image's voxels. The weightings of the graph's
terminal edges, which connect every node with a virtual source s or a virtual
sink t, represent the affinity of a voxel to the vertebra (source) and to the
background (sink). Furthermore, a set of infinite weighted and non-terminal
edges implements the smoothness term. After graph construction, a minimal
s-t-cut is calculated within polynomial computation time, which splits the
nodes into two disjoint units. Subsequently, the segmentation result is
determined out of the source-set. A quantitative evaluation of a C++
implementation of the algorithm resulted in an average Dice Similarity
Coefficient (DSC) of 81.33% and a running time of less than a minute.Comment: 23 figures, 2 tables, 43 references, PLoS ONE 9(4): e9338
Saliency Map Verbalization: Comparing Feature Importance Representations from Model-free and Instruction-based Methods
Saliency maps can explain a neural model's predictions by identifying
important input features. They are difficult to interpret for laypeople,
especially for instances with many features. In order to make them more
accessible, we formalize the underexplored task of translating saliency maps
into natural language and compare methods that address two key challenges of
this approach -- what and how to verbalize. In both automatic and human
evaluation setups, using token-level attributions from text classification
tasks, we compare two novel methods (search-based and instruction-based
verbalizations) against conventional feature importance representations
(heatmap visualizations and extractive rationales), measuring simulatability,
faithfulness, helpfulness and ease of understanding. Instructing GPT-3.5 to
generate saliency map verbalizations yields plausible explanations which
include associations, abstractive summarization and commonsense reasoning,
achieving by far the highest human ratings, but they are not faithfully
capturing numeric information and are inconsistent in their interpretation of
the task. In comparison, our search-based, model-free verbalization approach
efficiently completes templated verbalizations, is faithful by design, but
falls short in helpfulness and simulatability. Our results suggest that
saliency map verbalization makes feature attribution explanations more
comprehensible and less cognitively challenging to humans than conventional
representations.Comment: ACL 2023 Workshop on Natural Language Reasoning and Structured
Explanations (NLRSE
Detection of Beat Cepheids in M33 and Their Use as a Probe of the M33 Metallicity Distribution
Our analysis of the Deep CFHT M33 variability survey database has uncovered 5
Beat Cepheids (BCs) that are pulsating in the fundamental and first overtone
modes. With {\it only} the help of stellar pulsation theory and of
mass--luminosity (M-L) relations, derived from evolutionary tracks, we can
accurately determine the metallicities Z of these stars. The [O/H] metallicity
gradient of -0.16 dex/kpc that is inferred from the M33 galacto-centric
distances of these Cepheids and from their 'pulsation' metallicities is in
excellent agreement with the standard spectroscopic metallicity gradients that
are determined from H II regions, early B supergiant stars and planetary
nebulae. Beat Cepheids can thus provide an additional, independent probe of
galactic metallicity distributions.Comment: 5 pages, 2 fig
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