arXiv subjects

Efstathios Stiliaris

Publications and source records attributed to Efstathios Stiliaris.

6 recordsLinked to original sources

arXiv2026

Development and Performance of an Instrumentation Laboratory for Infrared Medical Imaging

We present an experimental setup and methodology designed to facilitate high-precision thermal measurements required for infrared medical tomography. The approach which is best suited for the study of specialized hardware phantoms comprises a controlled environmental enclosure, infrared detection, internal thermal reference elements, and a comprehensive data acquisition counting chain and protocol. Temporal and spatial corrections applied to sequential thermal images and panoramic projections reduce measurement fluctuations resulting in measurement uncertainty to approximately 25~mK. The capability to resolve weak surface temperature variations, well below 0.1~K, meets the requirement of medical imaging sensitivity. The methodology was validated using wax phantoms with elevated-temperature sources ($ΔT$ = 1.5 to 10~K). Reconstructed 3D thermal tomographic images of hot spots embedded in hardware phantoms are found to be in quantitative agreement with thermocouple measurements and $μCT$ derived source positions. The results demonstrate that the proposed setup and methodology enable high-precision thermal measurements and establish the feasibility of detecting surface temperature variations below 0.1 K, consistent with low-temperature localized internal contrasts ($ΔT =$ 1-3 K) at subsurface depths of a few centimeters, relevant to biological tissue.

physics.med-ph↗

arXiv2026

Standardized Images and Evaluation Metrics for Tomography

Advances in instrumentation and computation have enabled increasingly sophisticated tomographic reconstruction methods. However, existing evaluation practices -- often based on simple phantoms and global image metrics -- are limited in their ability to differentiate among modern high-fidelity reconstructions. A standardized, quantitative framework capable of revealing subtle yet meaningful differences is therefore required. We introduce such a framework, built upon two core components. The first is a set of four standardized reference images -- Source, Detector, Ideal, and Realistic -- each derived from physical modeling and representing a distinct stage in the imaging and reconstruction chain. The second is a suite of diagnostic and quantitative tools that remain sensitive in regimes where conventional metrics (e.g., SSIM, PSNR, NMSE, CC) tend to saturate. These include pixel-wise $χ^2$ and difference maps, their quantitative characterization, spectral decomposition of intensity distributions, and Region-of-Interest (RoI)-based metrics. Application of this framework to MLEM and RISE-1 reconstructions using software phantoms demonstrates its ability to expose discrepancies that might elude detection by conventional global metrics. While developed in the context of SPECT, the methodology generalizes to other tomographic modalities, providing a reproducible, interpretable, and physically grounded basis for evaluating reconstruction fidelity in the high-performance regime.

physics.med-ph↗

arXiv2020

Attributing Uncertainties in the Identification of Hotspots in SPECT Imaging

In SPECT imaging, the identification and detection of a lesion rely either on visual inspection of the reconstructed tomographic images or post-processing image analysis methods. Both approaches do not provide the capability to attribute a quantifiable uncertainty to this identification. We present a framework which allows the quantification of this uncertainty and the assignment of a level of confidence to the detection of hotspots. Based on the "Reconstructed Image from Simulations Ensemble" (RISE), an image reconstruction method, the presented scheme uses the set of projection measurements to derive the parameters defining the uptake of radioactivity, the position and the size of a hotspot, and as well as their associated uncertainties. The capabilities of the proposed method are demonstrated with projection data from GATE phantom simulations.

eess.IV↗

arXiv2020

Decoding the QCD critical behaviour in A+A collisions

In a systematic search for the QCD critical point in nuclear collisions, at the CERN SPS, it was found that intermittency measurements in the freeze-out state of central Si+Si collisions, at the maximum SPS energy, provide us with an indication of sizeable critical fluctuations. Also, rather recently, a weaker effect was traced in preliminary data of the Ar+Sc reaction for 10-20% most central collisions at (approximately) the same energy. However, the uncertainties in the analysis and the limitations of the experimental event statistics make the interpretation of the above measurements (NA49, NA61/SHINE) rather inconclusive, inviting for a further, phenomenological investigation with complementary tools and theoretical ideas. To this end, in the present work, we employ intermittency techniques within a model-independent analysis scheme (AMIAS), a novel method from Data Science [arXiv:1205.6505], in order to produce unbiased results for the parameters of the power-laws and in particular for the associated power-law exponent (intermittency index) $ϕ_2$. Using data-sets at different peripheralities, we also study the dependence of the $ϕ_2$-value on the number of wounded nucleons, in order to uncover the approach to the critical point. With these findings and the help of Ising-QCD partition function, the interpretation of SPS intermittency measurements and their links to the critical region, are discussed.

nucl-th↗

arXiv2019

Examining an Image Reconstruction Method in Infrared Emission Tomography

We present and evaluate the application of the "Reconstructed Image from Simulations Ensemble" (RISE), a novel tomographic image reconstruction method, in infrared tomography. We demonstrate that established methods of photon emission tomography, widely used with penetrating ionizing radiation, are applicable to infrared radiation. RISE, the method of choice, employs statistical physics concepts and utilizes Monte Carlo techniques to construct the imaged object from its infrared planar projections. The validity of the InfraRed Emission Tomographic (IRET) method is demonstrated, and the efficacy of RISE is evaluated with A) simulated data and B) experimental sets of infrared projections obtained from a thermal phantom with an infrared camera. For the simulation studies presented, the reconstructed images obtained with RISE and the well - known Algebraic Reconstruction Technique (ART) and Maximum Likelihood Expectation Maximization (MLEM) method were evaluated using well-established metrics.

physics.med-ph↗

arXiv2018

A Novel Analysis Method for Emission Tomography

We present a novel analysis method for image reconstruction in emission tomography. The method, named Reconstructed Image from Simulations Ensemble (RISE), utilizes statistical physics concepts and Monte Carlo techniques to extract the parameters of a physical model representing the imaged object from its planar projections. Its capabilities are demonstrated and evaluated by reconstructing tomographic images from sets of simulated SPECT projections. The RISE results compare favourably to those derived from the well - known Maximum Likelihood Expectation Maximization (MLEM) method, the Algebraic Reconstruction Technique (ART) and the Filtered Back Projection (FBP).

physics.med-ph↗