36 research outputs found
Color Intensity Projections: A simple way to display changes in astronomical images
To detect changes in repeated astronomical images of the same field of view
(FOV), a common practice is to stroboscopically switch between the images.
Using this method, objects that are changing in location or intensity between
images are easier to see because they are constantly changing. A novel display
method, called arrival time color intensity projections (CIPs), is presented
that combines any number of grayscale images into a single color image on a
pixel by pixel basis. Any values that are unchanged over the grayscale images
look the same in the color image. However, pixels that change over the
grayscale image have a color saturation that increases with the amount of
change and a hue that corresponds to the timing of the changes. Thus objects
moving in the grayscale images change from red to green to blue as they move
across the color image. Consequently, moving objects are easier to detect and
assess on the color image than on the grayscale images. A sequence of images of
a comet plunging into the sun taken by the SOHO satellite (NASA/ESA) and Hubble
Space Telescope images of a trans-Neptunian object (TNO) are used to
demonstrate the method.Comment: 9 pages, 2 figures. Accepted for publication in Publications of the
Astronomical Society of the Pacific. The quality of figure 1 been improved
from the previous posted versio
A robust and reliable method for detecting signals of interest in multiexponential decays
The concept of rejecting the null hypothesis for definitively detecting a
signal was extended to relaxation spectrum space for multiexponential
reconstruction. The novel test was applied to the problem of detecting the
myelin signal, which is believed to have a time constant below 40ms, in T2
decays from MRI's of the human brain. It was demonstrated that the test allowed
the detection of a signal in a relaxation spectrum using only the information
in the data, thus avoiding any potentially unreliable prior information. The
test was implemented both explicitly and implicitly for simulated T2
measurements. For the explicit implementation, the null hypothesis was that a
relaxation spectrum existed that had no signal below 40ms and that was
consistent with the T2 decay. The confidence level by which the null hypothesis
could be rejected gave the confidence level that there was signal below the
40ms time constant. The explicit implementation assessed the test's performance
with and without prior information where the prior information was the
nonnegative relaxation spectrum assumption. The test was also implemented
implicitly with a data conserving multiexponential reconstruction algorithm
that used left invertible matrices and that has been published previously. The
implicit and explicit implementations demonstrated similar characteristics in
detecting the myelin signal in both the simulated and experimental T2 decays,
providing additional evidence to support the close link between the two tests.
[Full abstract in paper]Comment: 23 pages with 8 figure
Accelerating regional atrophy rates in the progression from normal aging to Alzheimer’s disease
We investigated progression of atrophy in vivo, in Alzheimer’s disease (AD), and mild cognitive impairment (MCI). We included 64 patients with AD, 44 with MCI and 34 controls with serial MRI examinations (interval 1.8 ± 0.7 years). A nonlinear registration algorithm (fluid) was used to calculate atrophy rates in six regions: frontal, medial temporal, temporal (extramedial), parietal, occipital lobes and insular cortex. In MCI, the highest atrophy rate was observed in the medial temporal lobe, comparable with AD. AD patients showed even higher atrophy rates in the extramedial temporal lobe. Additionally, atrophy rates in frontal, parietal and occipital lobes were increased. Cox proportional hazard models showed that all regional atrophy rates predicted conversion to AD. Hazard ratios varied between 2.6 (95% confidence interval (CI) = 1.1–6.2) for occipital atrophy and 15.8 (95% CI = 3.5–71.8) for medial temporal lobe atrophy. In conclusion, atrophy spreads through the brain with development of AD. MCI is marked by temporal lobe atrophy. In AD, atrophy rate in the extramedial temporal lobe was even higher. Moreover, atrophy rates also accelerated in parietal, frontal, insular and occipital lobes. Finally, in nondemented elderly, medial temporal lobe atrophy was most predictive of progression to AD, demonstrating the involvement of this region in the development of AD