333 research outputs found
Eye Tracker Accuracy: Quantitative Evaluation of the Invisible Eye Center Location
Purpose. We present a new method to evaluate the accuracy of an eye tracker
based eye localization system. Measuring the accuracy of an eye tracker's
primary intention, the estimated point of gaze, is usually done with volunteers
and a set of fixation points used as ground truth. However, verifying the
accuracy of the location estimate of a volunteer's eye center in 3D space is
not easily possible. This is because the eye center is an intangible point
hidden by the iris. Methods. We evaluate the eye location accuracy by using an
eye phantom instead of eyes of volunteers. For this, we developed a testing
stage with a realistic artificial eye and a corresponding kinematic model,
which we trained with {\mu}CT data. This enables us to precisely evaluate the
eye location estimate of an eye tracker. Results. We show that the proposed
testing stage with the corresponding kinematic model is suitable for such a
validation. Further, we evaluate a particular eye tracker based navigation
system and show that this system is able to successfully determine the eye
center with sub-millimeter accuracy. Conclusions. We show the suitability of
the evaluated eye tracker for eye interventions, using the proposed testing
stage and the corresponding kinematic model. The results further enable
specific enhancement of the navigation system to potentially get even better
results
Pathology Segmentation using Distributional Differences to Images of Healthy Origin
Fully supervised segmentation methods require a large training cohort of
already segmented images, providing information at the pixel level of each
image. We present a method to automatically segment and model pathologies in
medical images, trained solely on data labelled on the image level as either
healthy or containing a visual defect. We base our method on CycleGAN, an
image-to-image translation technique, to translate images between the domains
of healthy and pathological images. We extend the core idea with two key
contributions. Implementing the generators as residual generators allows us to
explicitly model the segmentation of the pathology. Realizing the translation
from the healthy to the pathological domain using a variational autoencoder
allows us to specify one representation of the pathology, as this
transformation is otherwise not unique. Our model hence not only allows us to
create pixelwise semantic segmentations, it is also able to create inpaintings
for the segmentations to render the pathological image healthy. Furthermore, we
can draw new unseen pathology samples from this model based on the distribution
in the data. We show quantitatively, that our method is able to segment
pathologies with a surprising accuracy being only slightly inferior to a
state-of-the-art fully supervised method, although the latter has per-pixel
rather than per-image training information. Moreover, we show qualitative
results of both the segmentations and inpaintings. Our findings motivate
further research into weakly-supervised segmentation using image level
annotations, allowing for faster and cheaper acquisition of training data
without a large sacrifice in segmentation accuracy
ACCURATUM: improved calcium volume scoring using a mesh-based algorithm—a phantom study
To overcome the limitations of the classical volume scoring method for quantifying coronary calcifications, including accuracy, variability between examinations, and dependency on plaque density and acquisition parameters, a mesh-based volume measurement method has been developed. It was evaluated and compared with the classical volume scoring method for accuracy, i.e., the normalized volume (measured volume/ground-truthed volume), and for variability between examinations (standard deviation of accuracy). A cardiac computed-tomography (CT) phantom containing various cylindrical calcifications was scanned using different tube voltages and reconstruction kernels, at various positions and orientations on the CT table and using different slice thicknesses. Mean accuracy for all plaques was significantly higher (p < 0.0001) for the proposed method (1.220 ± 0.507) than for the classical volume score (1.896 ± 1.095). In contrast to the classical volume score, plaque density (p = 0.84), reconstruction kernel (p = 0.19), and tube voltage (p = 0.27) had no impact on the accuracy of the developed method. In conclusion, the method presented herein is more accurate than classical calcium scoring and is less dependent on tube voltage, reconstruction kernel, and plaque densit
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