167 research outputs found
Characterization Of Local And Global Statistics In Three Kinds Of Medical Images, And An Example Of Their Role In A Clinical Judgment
Use of Equivalent Relative Utility (ERU) to Evaluate Artificial Intelligence-Enabled Rule-Out Devices
We investigated the use of equivalent relative utility (ERU) to evaluate the
effectiveness of artificial intelligence (AI)-enabled rule-out devices that use
AI to identify and autonomously remove non-cancer patient images from
radiologist review in screening mammography.We reviewed two performance metrics
that can be used to compare the diagnostic performance between the
radiologist-with-rule-out-device and radiologist-without-device workflows:
positive/negative predictive values (PPV/NPV) and equivalent relative utility
(ERU). To demonstrate the use of the two evaluation metrics, we applied both
methods to a recent US-based study that reported an improved performance of the
radiologist-with-device workflow compared to the one without the device by
retrospectively applying their AI algorithm to a large mammography dataset. We
further applied the ERU method to a European study utilizing their reported
recall rates and cancer detection rates at different thresholds of their AI
algorithm to compare the potential utility among different thresholds. For the
study using US data, neither the PPV/NPV nor the ERU method can conclude a
significant improvement in diagnostic performance for any of the algorithm
thresholds reported. For the study using European data, ERU values at lower AI
thresholds are found to be higher than that at a higher threshold because more
false-negative cases would be ruled-out at higher threshold, reducing the
overall diagnostic performance. Both PPV/NPV and ERU methods can be used to
compare the diagnostic performance between the radiologist-with-device workflow
and that without. One limitation of the ERU method is the need to measure the
baseline, standard-of-care relative utility (RU) value for mammography
screening in the US. Once the baseline value is known, the ERU method can be
applied to large US datasets without knowing the true prevalence of the
dataset
DEMIST: A deep-learning-based task-specific denoising approach for myocardial perfusion SPECT
There is an important need for methods to process myocardial perfusion
imaging (MPI) SPECT images acquired at lower radiation dose and/or acquisition
time such that the processed images improve observer performance on the
clinical task of detecting perfusion defects. To address this need, we build
upon concepts from model-observer theory and our understanding of the human
visual system to propose a Detection task-specific deep-learning-based approach
for denoising MPI SPECT images (DEMIST). The approach, while performing
denoising, is designed to preserve features that influence observer performance
on detection tasks. We objectively evaluated DEMIST on the task of detecting
perfusion defects using a retrospective study with anonymized clinical data in
patients who underwent MPI studies across two scanners (N = 338). The
evaluation was performed at low-dose levels of 6.25%, 12.5% and 25% and using
an anthropomorphic channelized Hotelling observer. Performance was quantified
using area under the receiver operating characteristics curve (AUC). Images
denoised with DEMIST yielded significantly higher AUC compared to corresponding
low-dose images and images denoised with a commonly used task-agnostic DL-based
denoising method. Similar results were observed with stratified analysis based
on patient sex and defect type. Additionally, DEMIST improved visual fidelity
of the low-dose images as quantified using root mean squared error and
structural similarity index metric. A mathematical analysis revealed that
DEMIST preserved features that assist in detection tasks while improving the
noise properties, resulting in improved observer performance. The results
provide strong evidence for further clinical evaluation of DEMIST to denoise
low-count images in MPI SPECT
Homologous and heterologous desensitization of guanylyl cyclase-B signaling in GH3 somatolactotropes
The guanylyl cyclases, GC-A and GC-B, are selective receptors for atrial and C-type natriuretic peptides (ANP and CNP, respectively). In the anterior pituitary, CNP and GC-B are major regulators of cGMP production in gonadotropes and yet mouse models of disrupted CNP and GC-B indicate a potential role in growth hormone secretion. In the current study, we investigate the molecular and pharmacological properties of the CNP/GC-B system in somatotrope lineage cells. Primary rat pituitary and GH3 somatolactotropes expressed functional GC-A and GC-B receptors that had similar EC50 properties in terms of cGMP production. Interestingly, GC-B signaling underwent rapid homologous desensitization in a protein phosphatase 2A (PP2A)-dependent manner. Chronic exposure to either CNP or ANP caused a significant down-regulation of both GC-A- and GC-B-dependent cGMP accumulation in a ligand-specific manner. However, this down-regulation was not accompanied by alterations in the sub-cellular localization of these receptors. Heterologous desensitization of GC-B signaling occurred in GH3 cells following exposure to either sphingosine-1-phosphate or thyrotrophin-releasing hormone (TRH). This heterologous desensitization was protein kinase C (PKC)-dependent, as pre-treatment with GF109203X prevented the effect of TRH on CNP/GC-B signaling. Collectively, these data indicate common and distinct properties of particulate guanylyl cyclase receptors in somatotropes and reveal that independent mechanisms of homologous and heterologous desensitization occur involving either PP2A or PKC. Guanylyl cyclase receptors thus represent potential novel therapeutic targets for treating growth-hormone-associated disorders
The XMM Cluster Survey: X-ray analysis methodology
The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters
using all publicly available data in the XMM-Newton Science Archive. Its main
aims are to measure cosmological parameters and trace the evolution of X-ray
scaling relations. In this paper we describe the data processing methodology
applied to the 5,776 XMM observations used to construct the current XCS source
catalogue. A total of 3,675 > 4-sigma cluster candidates with > 50
background-subtracted X-ray counts are extracted from a total non-overlapping
area suitable for cluster searching of 410 deg^2. Of these, 993 candidates are
detected with > 300 background-subtracted X-ray photon counts, and we
demonstrate that robust temperature measurements can be obtained down to this
count limit. We describe in detail the automated pipelines used to perform the
spectral and surface brightness fitting for these candidates, as well as to
estimate redshifts from the X-ray data alone. A total of 587 (122) X-ray
temperatures to a typical accuracy of < 40 (< 10) per cent have been measured
to date. We also present the methodology adopted for determining the selection
function of the survey, and show that the extended source detection algorithm
is robust to a range of cluster morphologies by inserting mock clusters derived
from hydrodynamical simulations into real XMM images. These tests show that the
simple isothermal beta-profiles is sufficient to capture the essential details
of the cluster population detected in the archival XMM observations. The
redshift follow-up of the XCS cluster sample is presented in a companion paper,
together with a first data release of 503 optically-confirmed clusters.Comment: MNRAS accepted, 45 pages, 38 figures. Our companion paper describing
our optical analysis methodology and presenting a first set of confirmed
clusters has now been submitted to MNRA
Natriuretic peptide activation of extracellular regulated kinase 1/2 (ERK1/2) pathway by particulate guanylyl cyclases in GH3 somatolactotropes.
The natriuretic peptides, Atrial-, B-type and C-type natriuretric peptides (ANP, BNP, CNP), are regulators of many endocrine tissues and exert their effects predominantly through the activation of their specific guanylyl cyclase receptors (GC-A and GC-B) to generate cGMP. Whereas cGMP-independent signalling has been reported in response to natriuretic peptides, this is mediated via either the clearance receptor (Npr-C) or a renal-specific NPR-Bi isoform, which both lack intrinsic guanylyl cyclase activity. Here, we report evidence of GC-B-dependent cGMP-independent signalling in pituitary GH3 cells. Stimulation of GH3 cells with CNP resulted in a rapid and sustained enhancement of ERK1/2 phosphorylation (P-ERK1/2), an effect that was not mimicked by dibutryl-cGMP. Furthermore, CNP-stimulated P-ERK1/2 occurred at concentrations below that required for cGMP accumulation. The effect of CNP on P-ERK1/2 was sensitive to pharmacological blockade of MEK (U0126) and Src kinases (PP2). Silencing of the GC-B1 and GC-B2 splice variants of the GC-B receptor by using targeted short interfering RNAs completely blocked the CNP effects on P-ERK1/2. CNP failed to alter GH3 cell proliferation or cell cycle distribution but caused a concentration-dependent increase in the activity of the human glycoprotein Îą-subunit promoter (ÎąGSU) in a MEK-dependent manner. Finally, CNP also activated the p38 and JNK MAPK pathways in GH3 cells. These findings reveal an additional mechanism of GC-B signalling and suggest additional biological roles for CNP in its target tissues
GRB 050117: Simultaneous Gamma-ray and X-ray Observations with the Swift Satellite
The Swift Gamma-Ray Burst Explorer performed its first autonomous, X-ray
follow-up to a newly detected GRB on 2005 January 17, within 193 seconds of the
burst trigger by the Swift Burst Alert Telescope. While the burst was still in
progress, the X-ray Telescope obtained a position and an image for an
un-catalogued X-ray source; simultaneous with the gamma-ray observation. The
XRT observed flux during the prompt emission was 1.1 x 10^{-8} ergs cm^{-2}
s^{-1} in the 0.5-10 keV energy band. The emission in the X-ray band decreased
by three orders of magnitude within 700 seconds, following the prompt emission.
This is found to be consistent with the gamma-ray decay when extrapolated into
the XRT energy band. During the following 6.3 hours, the XRT observed the
afterglow in an automated sequence for an additional 947 seconds, until the
burst became fully obscured by the Earth limb. A faint, extremely slowly
decaying afterglow, alpha=-0.21. The X-ray position
triggered many follow-up observations: no optical afterglow could be confirmed,
although a candidate was identified 3 arcsecs from the XRT position.Comment: 27 pages, 6 figures. Accepted for publication in Ap
Paramedic assessment of pain in the cognitively impaired adult patient
<p>Abstract</p> <p>Background</p> <p>Paramedics are often a first point of contact for people experiencing pain in the community. Wherever possible the patient's self report of pain should be sought to guide the assessment and management of this complaint. Communication difficulty or disability such as cognitive impairment associated with dementia may limit the patient's ability to report their pain experience, and this has the potential to affect the quality of care. The primary objective of this study was to systematically locate evidence relating to the use of pain assessment tools that have been validated for use with cognitively impaired adults and to identify those that have been recommended for use by paramedics.</p> <p>Methods</p> <p>A systematic search of health databases for evidence relating to the use of pain assessment tools that have been validated for use with cognitively impaired adults was undertaken using specific search criteria. An extended search included position statements and clinical practice guidelines developed by health agencies to identify evidence-based recommendations regarding pain assessment in older adults.</p> <p>Results</p> <p>Two systematic reviews met study inclusion criteria. Weaknesses in tools evaluated by these studies limited their application in assessing pain in the population of interest. Only one tool was designed to assess pain in acute care settings. No tools were located that are designed for paramedic use.</p> <p>Conclusion</p> <p>The reviews of pain assessment tools found that the majority were developed to assess chronic pain in aged care, hospital or hospice settings. An analysis of the characteristics of these pain assessment tools identified attributes that may limit their use in paramedic practice. One tool - the Abbey Pain Scale - may have application in paramedic assessment of pain, but clinical evaluation is required to validate this tool in the paramedic practice setting. Further research is recommended to evaluate the Abbey Pain Scale and to evaluate the effectiveness of paramedic pain management practice in older adults to ensure that the care of all patients is unaffected by age or disability.</p
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