Polarization Maps Research Articles

Magneto-optical polarization texturing

Left and right circularly polarized transverse electromagnetic waves propagate at slightly different speeds in a magnetic material leading to a polarization rotation by an amount proportional to the projection of the magnetic field along the direction of the wave propagation. We show how this magneto-optical effect can serve as a vectorial polarization shaper if the input mode is either a radially-polarized or an azimuthally-polarized Laguerre-Gaussian (LG) mode. The specific polarization map of the output field can be achieved by choosing appropriately the magnetic material and/or its geometry. We show further that when the LG beam waist is comparable to the wavelength (i.e. w 0 ≈ λ ) the fields are no longer purely transverse but acquire an additional longitudinal (axial) component. We demonstrate how this modifies the polarization texturing.

Digital Infographic Creation in Design Education: A Participatory Learning Algorithm Measuring Location‐Based Spatial Impact

AbstractDesign education includes many pursuits that deal with creativity, thinking and visual communication techniques in the learning process. This study aims to create a participatory learning algorithm based on a location, while measuring the spatial impact through an emergent situation. The exemplified issue is determined as fire that emerged due to climate change, which has become a significant agenda of the 21st century in most countries. The scope of the study is based on the creation of an algorithm for participatory learning techniques by using social media to create digital infographics in a workshop redefining Mugla, an affected place after the fire. The workshop context is designed to reveal the interaction between humankind and its natural environment, including nature, topography, animals, aids and all actors affected after the fire, while students are involved in research practices on participatory learning, using the diary method as a pedagogical research tool. The outputs of the participatory learning algorithm examine the informative part of the produced digital infographics with ethnomethodology and the visual part with descriptive analysis as a hybrid methodology taking data materials from social media. Cumulative results that reflect the location‐based spatial impact are measured with a coding system of frequencies and a time‐series data of polar mapping. We propose that such a participatory learning algorithm can improve students' visual communication, design creation, visualisation, expression of ideas and organisation of knowledge skills with the discipline of working together to make multilayered spatial readings.

EXPERIMENTAL VALIDATION OF THE USE OF POLARISATION TOMOGRAPHY OF POLYCRYSTALLINE COMPONENT OF BLOOD FILMS IN THE DIFFERENTIAL DIAGNOSTICS OF THE SEVERITY OF THE COURSE OF ABDOMINAL SEPSIS

Introduction. Assessment of the severity of enteric insufficiency in abdominal sepsis requires improvement, as a differentiated approach to the treatment of such patients depends on it. Therefore, the use of polarization tomography of the polycrystalline component of blood films is one of the promising directions for diagnosing the severity of the course of abdominal sepsis. Aim. To investigate in an experiment the method of polarization tomography of the polycrystalline component of blood films as a diagnostic criterion for determining the severity of the course of abdominal sepsis. Materials and methods. We modelled mild, moderate and severe peritonitis on 80 white non-linear rats of both sexes, weighing from 180 to 220 g, according to the methodology developed in the clinic. Samples of blood films from rats with different severity of peritonitis were used as objects of research using polarization tomography of the polycrystalline component of blood films and determination of distributions of phase parameters in pixels of a digital image. Results. The conducted experimental studies showed that the system of polarization mapping of the polycrystalline component of the blood films of laboratory rats clearly determines the degree of intoxication depending on the severity of abdominal sepsis, which is visualized by obtaining an album of maps of distributions of phase values of digital microscopic image points. The most diagnostically sensitive statistical criteria for differentiation of phase maps of microscopic images of blood films of rats from control group 1 and experimental groups 2-4 were found, which contributed to the determination of relationships between the distributions of statistical parameters of the 1st-4th orders, which characterize the phase maps depending on the severity of peritonitis. Conclusions. The transformation of the statistical structure of linear birefringence polarization tomograms of the blood of rats is associated with necrotic degradation (anemia) of optically anisotropic hemoglobin structures, as well as with a decrease in the number of optically active erythrocytes in the blood of rats changed as a result of abdominal sepsis, depending on the severity of its course. The balanced accuracy of differentiation of rats of the control and experimental groups, the intergroup differentiation of the course of abdominal sepsis depending on the degree of severity testify to the presence of the diagnostic ability of the polarization tomography method.

Real-time three-dimensional transthoracic echocardiographic segmental volume analysis: a quantitative and objective tool for assessing regional left ventricle wall motion in patients with ischemic heart disease

Abstract Background Evaluation of regional left ventricle function using two-dimensional echocardiography (2DE) in patients with ischemic heart disease has limitations due to its low objectivity and qualitative nature. In addition, 2DE is limited because multiple acoustic windows are used to obtain the image, whereas three-dimensional echocardiography (3DE) uses a single window. This study aims to demonstrate the clinical utility of 3DE segmental volume analysis for evaluating regional wall motion abnormality (RWMA). Methods This retrospective study included 33 patients with ischemic heart disease and single-vessel territory RWMA confirmed on coronary angiography. RWMA was visually assessed using 2DE, generating 17-segment bull's-eye polar maps, and 3DE. In the 3DE study, two independent observers analyzed segmental volumes and segmental volume ejection fractions (SVEFs) using QLAB 3D quantification software. The optimal SVEF cutoff value differentiating normal from abnormal was determined using receiver operating curve analysis. The accuracy of 3DE in predicting culprit coronary arteries was compared with that of 2DE using Cohen κ coefficients, which also were used for interobserver and intraobserver variability assessments. Results Mean 3DE SVEFs were significantly lower in segments showing RWMA on 2DE. The optimal SVEF cutoff value was 44%, with sensitivity of 75.0% and specificity of 73.9% (area under the curve, 0.801; 95% CI, 0.763–0.838; P < 0.001). The reliability of 3DE-derived bull's-eye predictions of culprit coronary arteries was 81.8% (κ = 0.672; 95% CI, 0.555–0.789; P < 0.001). Interobserver and intraobserver variabilities were 97.0% (κ = 0.947; 95% CI, 0.894–1.00; P < 0.001) and 93.9% (κ = 0.897; 95% CI, 0.827–0.967; P < 0.001), respectively. Conclusions The 3DE segmental volume analysis effectively quantified regional left ventricle function and aligned well with 2DE and coronary angiography findings in predicting culprit coronary arteries. Thus, 3DE segmental volume analysis can serve as a quantitative and objective tool for RWMA assessment in patients with ischemic heart disease.

Validation of the SIMIND simulation code using the myocardial phantom HL

Introduction. Monte Carlo simulation codes simulating medical imaging nuclear detectors (SIMIND) are notable tools used to model nuclear medicine experiments.This study aimed to confirm the usability of SIMIND as an alternative method for nuclear medicine experiments with a cardiac phantom HL, simulating human body structures, by comparing the actual experiment data.Methods. A cardiac phantom HL that simulates myocardial scintigraphy using123I-meta-iodobenzylguanidine was developed, and single-photon emission computed tomography/computed tomography imaging was performed using Discovery NM/CT 670 scanner. Aside from the main-energy window(159 keV ± 10%), additional windows were set on the low(137.5 keV ± 4% ) and high(180.5 keV ± 3%)-energy sides. The simulations were performed under the same conditions as the actual experiments. Regions of interest (ROIs) were set in each organ part of the experiments and simulated data, and a polar map for the myocardial part was developed. The mean, maximum (max), and minimum (min) counts within each ROI, as well as the relative errors of each segment in the polar map, were calculated to evaluate the accuracy of the simulation.Results. Overall, the results were favorable with relative errors of <10% except in some areas based on the data from the main-energy window and postreconstruction. On the other hand, relative errors of >10% were found in both the low and high subenergy windows. The smallest error occurred when assessing using mean values within the ROIs. The relative error was high at the cardiac base in the polar map evaluation; however, it remained <10% from the mid to apical heart sections.Conclusion. SIMIND is considered an alternative method for nuclear medicine experiments using a myocardial phantom HL that closely resembles human body structures. However, caution is warranted as accuracy may decrease under specific conditions.

Confusion of extragalactic sources in the far-infrared: A baseline assessment of the performance of PRIMAger in intensity and polarization

Aims. Because of their limited angular resolution, far-infrared telescopes are usually affected by the confusion phenomenon. Since several galaxies can be located in the same instrumental beam, only the brightest objects emerge from the fluctuations caused by fainter sources. The PRobe far-Infrared Mission for Astrophysics imager (PRIMAger) will observe the mid- and far-infrared (25–235 μm) sky both in intensity and polarization. We aim to provide predictions of the confusion level and its consequences for future surveys. Methods. We produced simulated PRIMAger maps affected only by the confusion noise using the simulated infrared extragalactic sky (SIDES) semi-empirical simulation. We then estimated the confusion limit in these maps and extracted the sources using a basic blind extractor. By comparing the input galaxy catalog and the extracted source catalog, we derived various performance metrics as completeness, purity, and the accuracy of various measurements (e.g., the flux density in intensity and polarization or the polarization angle). Results. In intensity maps, we predict that the confusion limit increases rapidly with increasing wavelength (from 21 μJy at 25 μm to 46 mJy at 235 μm). The confusion limit in polarization maps is more than two orders of magnitude lower (from 0.03 mJy at 96 μm to 0.25 mJy at 235 μm). Both in intensity and polarization maps, the measured (polarized) flux density is dominated by the brightest galaxy in the beam, but other objects also contribute in intensity maps at longer wavelengths (∼30% at 235 μm). We also show that galaxy clustering has a mild impact on confusion in intensity maps (up to 25%), while it is negligible in polarization maps. In intensity maps, a basic blind extraction will be sufficient to detect galaxies at the knee of the luminosity function up to z ∼ 3 and 1011 M⊙ main-sequence galaxies up to z ∼ 5. In polarization for the most conservative sensitivity forecast (payload requirements), ∼200 galaxies can be detected up to z = 1.5 in two 1500 h surveys covering 1 deg2 and 10 deg2. For a conservative sensitivity estimate, we expect ∼8000 detections up to z = 2.5, opening a totally new window on the high-z dust polarization. Finally, we show that intensity surveys at short wavelengths and polarization surveys at long wavelengths tend to reach confusion at similar depth. There is thus a strong synergy between them.

Forgotten treasures in the HST/FOC UV imaging polarimetric archives of active galactic nuclei

Context. The active galactic nucleus within M87, a giant elliptical galaxy, is responsible for one of the closest kiloparsec-scale relativistic jets to Earth. It is thus a perfect target for spatially resolved observations. Aims. This one-sided jet has been extensively observed at almost all wavelengths, with almost all techniques. Among many other discoveries, it was found that the optical emission is more concentrated in the knots and along the center line of the jet, in comparison to, for example, the radio emission. A remaining question relates to what we can learn from its polarized counterpart. Methods. We unearthed unpublished polarization maps taken with the Faint Object Camera (FOC) aboard the Hubble Space Telescope (HST), obtained between 1995 and 1999. At a rate of one observation per year, we can follow the evolution of the polarized flux knots in the jet. We can thus constrain the timescale of variation in the magnetic field up to a spatial resolution of one tenth of an arcsecond (∼11.5 pc). Results. After coherently reducing the five observations using the same methodology presented in the first paper of this series, the analysis of polarized maps from POS 1 (base of the jet) and POS 3 (end of the jet) reveals significant temporal and spatial dynamics in the jet’s magnetic field morphology. Despite minimal changes in the overall intensity structure, notable fluctuations in polarization degrees and angles are detected across various knots and inter-knot regions. In addition, the emission and polarization characteristics of M87’s jet differ significantly between POS1 and POS3. POS1 shows a more collimated jet with strong variability in polarization, while POS3 reveals a thicker structure, a quasi-absence of variability, and complex magnetic field interactions. This suggests that the jet may have coaxial structures with distinct kinetic properties. Theoretical models like the jet-in-jet scenario, featuring double-helical magnetic flux ropes, help to explain these observations and indicate a strong density contrast and higher speeds in the inner jet. Conclusions. Our temporal analysis demonstrates the importance of high-spatial-resolution polarization mapping in understanding jets’ polarization properties and overall dynamics, especially if such maps are taken at different wavelengths (ultraviolet and radio).

Simultaneous Infrared Observations of the Jovian Auroral Ionosphere and Thermosphere.

Simultaneous observations of and in Jupiter's northern infrared aurora were conducted on 02 June 2017 using Keck-NIRSPEC to produce polar projection maps of radiance, rotational temperature, column density, and radiance. The temperature variations within the auroral region are K, generally consistent with previous studies, albeit with some structural differences. Known auroral heating sources including particle precipitation, Joule heating, and ion drag have been examined by studying the correlations between each derived quantity, yet no single dominant mechanism can be identified as the main driver for the energetics in Jupiter's northern auroral region. It appears that a complex interaction exists between the heating driven by various mechanisms and the cooling from the thermostat effect. Comparisons between the temperature and the line-of-sight ion velocity in the reference frame of (a) the planetary rotation and (b) the neutral atmosphere further suggest that the local thermodynamic equilibrium effect may play an important role in thermospheric heating at Jupiter. Along with previously reported heating events that occurred in both the lower and upper atmosphere, it is speculated that the heating source may originate from an altitude above Jupiter's stratosphere but below the peak altitude of overtone and quadrupole emissions.

Semi-supervised rotation measure deconvolution and its application to MeerKAT observations of galaxy clusters

Context. Faraday rotation contains information about the magnetic field structure along the line of sight and is an important instrument in the study of cosmic magnetism. Traditional Faraday spectrum deconvolution methods such as RMCLEAN face challenges in resolving complex Faraday dispersion functions and handling large datasets. Aims. We developed a deep learning deconvolution model to enhance the accuracy and efficiency of extracting Faraday rotation measures from radio astronomical data, specifically targeting data from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). Methods. We used semi-supervised learning, where the model simultaneously recreates the data and minimizes the difference between the output and the true signal of synthetic data. Performance comparisons with RMCLEAN were conducted on simulated as well as real data for the galaxy cluster Abell 3376. Results. Our semi-supervised model is able to recover the Faraday dispersion for extended rotation measure (RM) components, while accounting for bandwidth depolarization, resulting in a higher sensitivity for high-RM signals, given the spectral configuration of MGCLS. Applied to observations of Abell 3376, we find detailed magnetic field structures in the radio relics, and several active galactic nuclei. We also applied our model to MeerKAT data of Abell 85, Abell 168, Abell 194, Abell 3186, and Abell 3667. Conclusions. We have demonstrated the potential of deep learning for improving RM synthesis deconvolution, providing accurate reconstructions at a high computational efficiency. In addition to validating our data against existing polarization maps, we find new and refined features in diffuse sources imaged with MeerKAT.

Forgotten treasures in the HST/FOC UV imaging polarimetric archives of active galactic nuclei

Context. The Mrk 463 system is known to host two powerful sources that are separated by about 4 kpc, which were both identified as active galactic nuclei (AGN). This makes the Mrk 463 system a unique laboratory for studying the geometry and dynamics of galaxy merging and its relation to AGN duty cycles. Aims. The eastern nucleus, Mrk 463E, is the brighter of the two and thus a prime target for a polarimetric study. It is classified as a Seyfert 2 galaxy, meaning that high polarization degrees from scattering off electrons and dust in the polar winds are expected. Methods. In the continuity of our series of papers, we reduced archived and previously unpublished polarization observations obtained with the Faint Object Camera on board the Hubble Space Telescope to obtain a high-resolution near-ultraviolet polarization map of the Mrk 463E nuclei. We coupled this map to near-infrared and X-ray observations to obtain a clear picture of the geometric arrangement of matter around the core of Mrk 463E. Results. We found that the nucleus location is farther south of the optical peak flux than previously estimated. The strongly polarized conical wind has a half-opening angle of ∼15° and displays three main periods of mass ejection. Its polarization allowed us to estimate the AGN inclination toward the observer (∼55°). Finally, our maps revealed a streamer connecting Mrk 463E and Mrk 463W, with a tentative detection of a large kiloparsec-scale ordered magnetic field connecting both galaxies. Conclusions. This unpublished observation finally offered more than the original proposal asked for and allowed us to derive tight geometric and dynamical constraints for Mrk 463E. High-resolution radio maps and infrared polarimetry are now necessary to further study the jet and the newly discovered streamer.

ABCMB: deep delensing assisted likelihood-free inference from CMB polarization maps

ABCMB: deep delensing assisted likelihood-free inference from CMB polarization maps

Physical prior-guided deep fusion network with shading cues for shape from polarization

Shape from polarization (SfP) is a powerful passive three-dimensional imaging technique that enables the reconstruction of surface normal with dense textural details. However, existing deep learning-based SfP methods only focus on the polarization prior, which makes it difficult to accurately reconstruct targets with rich texture details under complicated scenes. Aiming to improve the reconstruction accuracy, we utilize the surface normal estimated from shading cues and the innovatively proposed specular confidence as shading prior to provide additional feature information. Furthermore, to efficiently combine the polarization and shading priors, a novel deep fusion network named SfPSNet is proposed for the information extraction and the reconstruction of surface normal. SfPSNet is implemented based on a dual-branch architecture to handle different physical priors. A feature correction module is specifically designed to mutually rectify the defects in channel-wise and spatial-wise dimensions, respectively. In addition, a feature fusion module is proposed to fuse the feature maps of polarization and shading priors based on an efficient cross-attention mechanism. Our experimental results show that the fusion of polarization and shading priors can significantly improve the reconstruction quality of surface normal, especially for objects or scenes illuminated by complex lighting sources. As a result, SfPSNet shows state-of-the-art performance compared with existing deep learning-based SfP methods benefiting from its efficiency in extracting and fusing information from different priors.

Toric polar maps and characteristic classes

Toric polar maps and characteristic classes

Abstract 4144700: Short Term Effect of His bundle pacing on Myocardial Fatty Acid Metabolism, Perfusion and Function.

Background: Long term right ventricular apex pacing has been reported to affect myocardial metabolism and perfusion to lead to impaired left ventricular function. However, there is little information available on the effect on fatty acid metabolism, myocardial perfusion and function in RV septal or His bundle pacing. Methods and Results: We studied 94 patients (mean age 77±11 years, male 40%, AV block 71%) admitted for pacemaker implantation in our prospective cohort study, excluding patients with coronary artery disease who had past histories of coronary arterial revascularization and severe stenosis in coronary CT or coronary angiography. Forty-five patients had right ventricular apex pacing (RVA; n=10) or right ventricular septal pacing (RVS; n=35), 17 had selective or non-selective His bundle pacing (HIS) and, as a control, 32 had right atrial pacing (RA). The patients underwent 123I-β-methyl-P-iodophenyl-pentadecanoic acid (BMIPP) SPECT imaging and Tc-99m- methoxyisobutylisonitrile (MIBI) SPECT imaging between 3 months and 1 year after implantation. The uptakes of both tracers were displayed on a polar map, which was divided into 17 segments. Regional tracer activity at each segment was quantified as %uptake. Left ventricular ejection fraction (LVEF) was also obtained in MIBI imaging. There were no significant differences in baseline characteristics such as age, gender, or underlying heart disease between the four groups. LVEF in MIBI rest imaging in RVA group was significantly lower than RA group (58.3±2.1% vs 64.9±1.2%, p=0.013), while there was no significant difference in LVEF among RVS, HIS and RA groups, with non-significantly (p=0.25) lower LVEF in RVS (62.5±1.1%) than HIS (65.3±1.6%) groups. The average of BMIPP %uptake in 17 segments significantly correlated with LVEF (r=-0.259, p=0.01). BMIPP and MIBI (stress and rest) %uptake were significantly lower in RVA group and RVS group than RA group in the septal or anterolateral area. Especially, BMIPP %uptake in RVA group was significantly lower at the broad area. On the other hand, BMIPP and MIBI (stress and rest) %uptake in HIS group were almost similar to those in RA group. Conclusion: His bundle pacing, but not RV septal pacing, maintains myocardial metabolism, perfusion and function.

Asymmetric measures of polar Chebyshev chaotic map for discrete/dimensional emotion recognition using PPG

Human emotion recognition is a challenge in both medical and non-medical fields. While there are several physiological signals available for detecting emotions, the Photoplethysmogram (PPG) signal has been disregarded, despite its non-invasive nature and ease of recording using common devices like smartphones. This study addresses the research question: How can we effectively analyze PPG signals to enhance emotion recognition? To tackle this question, we employed novel nonlinear measures based on the polar form of the Chebyshev chaotic map to analyze the dynamic behavior of PPG signals. What makes this research unique is the use of the polar form of the Chebyshev chaotic map for biosignal analysis, specifically in quantifying the map’s asymmetry using multiple indices. Our main goal is to improve our understanding of the nonlinear characteristics of PPG signals and gain new insights into their dynamic properties. While previous research has explored PPG-based emotion recognition, our study stands out by utilizing the Chebyshev chaotic map to characterize PPG signals. We evaluated the effectiveness of these features in discrete and dimensional emotion recognition tasks, using the Database for Emotion Analysis using Physiological signals (DEAP) as a benchmark. Our experimental results showed a maximum accuracy of 94.49% for discrete emotion recognition and 85.59% for dimensional emotion recognition. Experiments were also conducted on another public dataset to further validate the efficacy of the proposed approach. The significance of our study lies in providing new insights into the nonlinear characteristics of PPG signals and enhancing emotion recognition capabilities, thereby contributing to both the fields of emotional analysis and biomedical engineering.

Blood Plasma Film Multifractal Scanning in COVID-19 Consequences Diagnostics.

A 3D phase scanning method was applied to study blood plasma facies, generating layered polarization maps of the object field. The most sensitive parameters to changes in birefringence distribution were identified. Multifractal analysis using wavelet transforms and fractal dimension spectra provided specific insights into the scale self-similarity of the polarization maps. The multifractal spectra of ellipticity distributions were algorithmically derived, revealing that the third- and fourth-order statistical moments were most sensitive to changes in the supramolecular networks of the facies. These findings were successfully applied to differentiate post-COVID-19 effects with high accuracy.

Arctic and Southern Ocean polar sea level maps and along-tracks from multi-mission satellite altimetry from 2011 to 2021

Polar sea surface height observation by radar altimeters requires missions with high-latitude orbit and specific processing to observe the sea-ice-covered region within fractures in the ice. Here, we combine sea surface height estimates from different radar satellites over the ice-free and ice-covered polar oceans to create cross-calibrated along-tracks and gridded products over the Arctic Ocean (2011–2021) and the Southern Ocean (2013–2021). The sea surface height from our regional polar products is in great agreement with tide gauges and bottom pressure recorders at monthly timescales in seasonally to year-round ice-covered regions. Thanks to the use of several missions and the mapping strategy, our multi-mission products have a greater resolution than mono-mission products. Part of the sea level variability of the Arctic Ocean product is related to the Arctic Oscillation atmospheric circulation. At long term, the Arctic altimetry sea level is coherent with in-situ steric height evolution in the Beaufort gyre, and negative sea level trends over the 10-year period are observed in the East Siberian slope region, which may be related to the local freshwater decrease observed by other studies. Our regional polar sea level products are limited by current understanding of the sea-ice lead measurements, and homogenization of these polar products with global sea level products needs to be tackled.

Controllable reverse energy flow in the focus of tightly focused hybrid vector beams.

We demonstrate analytically and numerically that the reverse energy flow is able to appear around the optical axis in the focal region of tightly focused hybrid vector beams. Theoretically, we derive and obtain the general expression of the longitudinal component of the Poynting vector in the focal plane for hybrid vector beams having circular polarization mapping tracks on the Poincaré sphere under xy basis vectors. Following from the obtained expression and the numerical simulation results, the on-axis and near-axis reverse energy flow behaviors are proved. We also reveal that the relative phase of xy basis vectors can be adopted to conveniently control the reverse energy flow. Furthermore, we show that the concerned hybrid vector beams can meanwhile induce the nonzero transverse energy flow in the focal plane, while the previously reported cases with locally linear polarization states cannot. More strikingly, further simulation results indicate that one can observe the reverse energy flow phenomena for the hybrid vector beams under circular and elliptical polarization basis vectors. The results provide a fresh method for achieving and controlling the reverse energy flow.

A Novel Approach to Identifying Hibernating Myocardium Using Radiomics-Based Machine Learning.

Background To assess the feasibility of a machine learning (ML) approach using radiomics features of perfusion defects on rest myocardial perfusion imaging (MPI) to detect the presence of hibernating myocardium. Methodology Data of patients who underwent 99mTc-sestamibi MPI and 18F-FDG PET/CT for myocardial viability assessment were retrieved. Rest MPI data were processed on ECToolbox, and polar maps were saved using theNFile PMap tool. The reference standard for defining hibernating myocardium was the presence of mismatched perfusion-metabolism defect with impaired myocardial contractility at rest. Perfusion defects on the polar maps were delineated with regions of interest (ROIs) after spatial resampling and intensity discretization. Replicable random sampling allocated 80% (257) of the perfusion defects of the patients from January 2017 to September 2022 to the training set and the remaining 20% (64) to the validation set. An independent dataset of perfusion defects from 29 consecutive patients from October 2022 to January 2023 was used as the testing set for model evaluation. One hundred ten first and second-order texture features were extracted for each ROI. After feature normalization and imputation, 14 best-ranked features were selected using a multistep feature selection process including the Logistic Regression and Fast Correlation-Based Filter. Thirteen supervised ML algorithms were trained with stratified five-fold cross-validation on the training set and validated on the validation set. The ML algorithms with a Log Loss of <0.688 and <0.672 in the cross-validation and validation steps were evaluated on the testing set. Performance matrices of the algorithms assessed included area under the curve (AUC), classification accuracy (CA), F1 score, precision, recall, and specificity. To provide transparency and interpretability, SHapley Additive exPlanations (SHAP) values were assessed and depicted as beeswarm plots. Results Two hundred thirty-nine patients (214 males; mean age 56 ± 11 years) were enrolled in the study. There were 371 perfusion defects (321 in the training and validation sets; 50 in the testing set). Based on the reference standard, 168 perfusion defects had hibernating myocardium (139 in the training and validation sets; 29 in the testing set). On cross-validation, six ML algorithms with Log Loss <0.688 had AUC >0.800. On validation, 10 ML algorithms had a Log Loss value <0.672, among which six had AUC >0.800. On model evaluation of the selected models on the unseen testing set, nine ML models had AUC >0.800 with Gradient Boosting Random Forest (xgboost) [GB RF (xgboost)] achieving the highest AUC of 0.860 and could detect the presence of hibernating myocardium in 21/29 (72.4%) perfusion defects with a precision of 87.5% (21/24), specificity 85.7% (18/21), CA 78.0% (39/50) and F1 Score 0.792. Four models depicted a clear pattern of model interpretability based on the beeswarm SHAP plots. These were GB RF (xgboost), GB (scikit-learn), GB (xgboost), and Random Forest. Conclusion Our study demonstrates the potential of ML in detecting hibernating myocardium using radiomics features extracted from perfusion defects on rest MPI images. This proof-of-concept underscores the notion that radiomics features capture nuanced information beyond what is perceptible to the human eye, offering promising avenues for improved myocardial viability assessment.

Characterization of myocardial perfusion imaging systems - an extension of quality metrics

PurposeThe aim of this study was to evaluate the performance of myocardial perfusion imaging (MPI) systems in detecting perfusion defects (PDs). The defect perfusion index (DPI) was introduced to extend and further advance the current MPI quality metrics. MethodsAn anthropomorphic phantom simulating normal and pathological myocardial perfusion conditions was imaged by various NaI-crystal detector systems with and without corrections for scatter (SC) and attenuation (AC) (Symbia, Symbia + SC, Symbia IQ + SCAC, Symbia IQ), and cadmium-zinc-telluride detector systems without corrections (DSPECT, D530c). The extent of PD and the summed score (SS) were obtained by comparing polar maps with ad hoc normal databases created for each MPI system by using phantom polar maps with normal perfusion. The segmental uptake (SU) and the global uniformity (GU) were evaluated. The DPI was calculated on segments included in the PD to minimize attenuation artifacts outside the PD. The 17 segmental model was used. ResultsThe highest level of uniformity of polar map was obtained for Symbia IQ + SCAC. D530c showed the highest extent of PD and dependence of the extent on the PD position. It showed in general the lowest SU values and the highest GU due to attenuation artifacts. Nevertheless, D530c outperforms other MPI systems in terms of PD detection, showing the highest DPI value. DSPECT system showed the lowest SS value, and DPI values comparable to NaI-crystal detector systems. ConclusionThe DPI can be evaluated to investigate the intrinsic ability of MPI systems to detect PDs, whatever the quantitative post-processing software used.