126 research outputs found
Evaluation of ultrasound sensors for transcranial photoacoustic sensing and imaging
Biomedical photoacoustic (PA) imaging is typically used to exploit
absorption-based contrast in soft tissue at depths of several centimeters. When
it is applied to measuring PA waves generated in the brain, the acoustic
properties of the skull bone cause not only strong attenuation but also a
distortion of the wavefront, which diminishes image resolution and contrast.
This effect is directly proportional to bone thickness. As a result,
transcranial PA imaging in humans has been challenging to demonstrate. We
measured the acoustic constraints imposed by the human skull to design an
ultrasound sensor suitable for transcranial PA imaging and sensing. We imaged
the phantoms using a planar Fabry-Perot sensor and employed a range of
piezoelectric and optical ultrasound sensors to measure the frequency dependent
acoustic transmission through human cranial bone. Transcranial PA images show
typical frequency and thickness dependent attenuation and aberration effects
associated with acoustic propagation through bone. The skull insertion loss
measurements showed significant transmission at low frequencies. In comparison
to conventional piezoelectric sensors, the performance of plano-concave optical
resonator (PCOR) ultrasound sensors was found to be highly suitable for
transcranial PA measurements. They possess high acoustic sensitivity at a low
acoustic frequency range that coincides with the transmission window of human
skull bone. PCOR sensors showed low noise equivalent pressures and flat
frequency response which enabled them to outperform conventional piezoelectric
transducers in transcranial PA sensing experiments. Transcranial PA sensing and
imaging requires ultrasound sensors with high sensitivity at low acoustic
frequencies, and a broad and ideally uniform frequency response. We designed
and fabricated PCOR sensors and demonstrated their suitability for transcranial
PA sensing
An AI Chatbot for Explaining Deep Reinforcement Learning Decisions of Service-oriented Systems
Deep Reinforcement Learning (Deep RL) is increasingly used to cope with the
open-world assumption in service-oriented systems. Deep RL was successfully
applied to problems such as dynamic service composition, job scheduling, and
offloading, as well as service adaptation. While Deep RL offers many benefits,
understanding the decision-making of Deep RL is challenging because its learned
decision-making policy essentially appears as a black box. Yet, understanding
the decision-making of Deep RL is key to help service developers perform
debugging, support service providers to comply with relevant legal frameworks,
and facilitate service users to build trust. We introduce Chat4XAI to
facilitate the understanding of the decision-making of Deep RL by providing
natural-language explanations. Compared with visual explanations, the reported
benefits of natural-language explanations include better understandability for
non-technical users, increased user acceptance and trust, as well as more
efficient explanations. Chat4XAI leverages modern AI chatbot technology and
dedicated prompt engineering. Compared to earlier work on natural-language
explanations using classical software-based dialogue systems, using an AI
chatbot eliminates the need for eliciting and defining potential questions and
answers up-front. We prototypically realize Chat4XAI using OpenAI's ChatGPT API
and evaluate the fidelity and stability of its explanations using an adaptive
service exemplar.Comment: To be published at 21st Int'l Conference on Service-Oriented
Computing (ICSOC 2023), Rome, Italy, November 28-December 1, 2023, ser. LNCS,
F. Monti, S. Rinderle-Ma, A. Ruiz Cortes, Z. Zheng, M. Mecella, Eds.,
Springer, 202
Photoacoustic pump-probe tomography of fluorophores in vivo using interleaved image acquisition for motion suppression
In fluorophores, the excited state lifetime can be modulated using pump-probe
excitation. By generating photoacoustic (PA) signals using simultaneous and
time-delayed pump and probe excitation pulses at fluences below the maximum
permissible exposure, a modulation of the signal amplitude is observed in
fluorophores but not in endogenous chromophores. This provides a highly
specific contrast mechanism that can be used to recover the location of the
fluorophore using difference imaging. The practical challenges in applying
this method to in vivo PA tomography include the typically low concentrations
of fluorescent contrast agents, and tissue motion. The former results in
smaller PA signal amplitudes compared to those measured in blood, while the
latter gives rise to difference image artefacts that compromise the
unambiguous and potentially noise-limited detection of fluorescent contrast
agents. To address this limitation, a method based on interleaved pump-probe
image acquisition was developed. It relies on fast switching between
simultaneous and time-delayed pump-probe excitation to acquire PA difference
signals in quick succession, and to minimise the effects of tissue motion. The
feasibility of this method is demonstrated in tissue phantoms and in initial
experiments in vivo
A User Study on Explainable Online Reinforcement Learning for Adaptive Systems
Online reinforcement learning (RL) is increasingly used for realizing
adaptive systems in the presence of design time uncertainty. Online RL
facilitates learning from actual operational data and thereby leverages
feedback only available at runtime. However, Online RL requires the definition
of an effective and correct reward function, which quantifies the feedback to
the RL algorithm and thereby guides learning. With Deep RL gaining interest,
the learned knowledge is no longer explicitly represented, but is represented
as a neural network. For a human, it becomes practically impossible to relate
the parametrization of the neural network to concrete RL decisions. Deep RL
thus essentially appears as a black box, which severely limits the debugging of
adaptive systems. We previously introduced the explainable RL technique
XRL-DINE, which provides visual insights into why certain decisions were made
at important time points. Here, we introduce an empirical user study involving
54 software engineers from academia and industry to assess (1) the performance
of software engineers when performing different tasks using XRL-DINE and (2)
the perceived usefulness and ease of use of XRL-DINE.Comment: arXiv admin note: substantial text overlap with arXiv:2210.0593
Evaluation of Absorbing Chromophores Used in Tissue Phantoms for Quantitative Photoacoustic Spectroscopy and Imaging
Effect of microstructures on the electron-phonon interaction in the disordered metals PdAg
Using the weak-localization method, we have measured the electron-phonon
scattering times in PdAg thick films prepared by DC-
and RF-sputtering deposition techniques. In both series of samples, we find an
anomalous temperature and disorder dependence,
where is the electron elastic mean free path. This anomalous behavior
cannot be explained in terms of the current concepts for the electron-phonon
interaction in impure conductors. Our result also reveals that the strength of
the electron-phonon coupling is much stronger in the DC than RF sputtered
films, suggesting that the electron-phonon interaction not only is sensitive to
the total level of disorder but also is sensitive to the microscopic quality of
the disorder.Comment: accepted for publication in Phys. Rev.
Automatic sound speed selection in photoacoustic image reconstruction using an autofocus approach
a clinical study protocol
Introduction The approved analgesic and anti-inflammatory drugs ibuprofen and
indometacin block the small GTPase RhoA, a key enzyme that impedes axonal
sprouting after axonal damage. Inhibition of the Rho pathway in a central
nervous system-effective manner requires higher dosages compared with orthodox
cyclooxygenase-blocking effects. Preclinical studies on spinal cord injury
(SCI) imply improved motor recovery after ibuprofen/indometacin-mediated Rho
inhibition. This has been reassessed by a meta-analysis of the underlying
experimental evidence, which indicates an overall effect size of 20.2%
regarding motor outcome achieved after ibuprofen/indometacin treatment
compared with vehicle controls. In addition, ibuprofen/indometacin may also
limit sickness behaviour, non-neurogenic systemic inflammatory response
syndrome (SIRS), neuropathic pain and heterotopic ossifications after SCI.
Consequently, ‘small molecule’-mediated Rho inhibition after acute SCI
warrants clinical investigation. Methods and analysis Protocol of an
investigator-initiated clinical open-label pilot trial on high-dose ibuprofen
treatment after acute traumatic, motor-complete SCI. A sample of n=12 patients
will be enrolled in two cohorts treated with 2400 mg/day ibuprofen for 4 or 12
weeks, respectively. The primary safety end point is an occurrence of serious
adverse events, primarily gastroduodenal bleedings. Secondary end points are
pharmacokinetics, feasibility and preliminary effects on neurological
recovery, neuropathic pain and heterotopic ossifications. The primary safety
analysis is based on the incidence of severe gastrointestinal bleedings.
Additional analyses will be mainly descriptive and casuistic. Ethics and
dissemination The clinical trial protocol was approved by the responsible
German state Ethics Board, and the Federal Institute for Drugs and Medical
Devices. The study complies with the Declaration of Helsinki, the principles
of Good Clinical Practice and all further applicable regulations. This safety
and pharmacokinetics trial informs the planning of a subsequent randomised
controlled trial. Regardless of the result of the primary and secondary
outcome assessments, the clinical trial will be reported as a publication in a
peer-reviewed journal. Trial registration number NCT02096913; Pre-results
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