arXiv subjects

Narendra Rathod

Publications and source records attributed to Narendra Rathod.

5 recordsLinked to original sources

arXiv2026

Voxel-wise Bayesian Estimation for Multi-Population Positronium Lifetime Imaging

Positronium lifetime imaging (PLI) provides local annihilation environment data beyond conventional activity imaging. Existing approaches, however, often estimate lifetime parameters over predefined regions, neglecting multiple lifetime populations within the same location. We present a 3D, population-specific Bayesian framework for fast voxel-wise PLI. A partial system matrix describes the spatial probability of detected events, while measured lifetimes provide soft assignments to slow, fast, and noise populations. These event responsibilities are used to estimate a decay-rate posterior independently for each voxel, preserving local lifetime variation and statistical uncertainty. In simulations, our formulation recovered spatially varying slow-population decay rates and a common fast-population rate, whereas a single-population model produced systematic bias. Slow-population two-standard-deviation coverage ranged from 93.8% to 98.1%. Experimental validation using 124I triple-coincidence data from a Siemens Biograph Vision Quadra scanner produced separate slow- and fast-population maps for aluminum, nickel, copper, and quartz. The long-lived quartz component matched ortho-positronium, while the fast population showed material-dependent differences among metals. Fast-population coverage was lower (69.1%), indicating underestimated uncertainty. The method is highly efficient, requiring only seconds to minutes per population on a single CPU core. This framework provides fast, population-specific PLI with Bayesian uncertainty quantification, making spatially resolved statistical inference feasible and practical for volumetric applications.

stat.AP↗

arXiv2025

First Positronium Lifetime Imaging using $^{52}$Mn and $^{55}$Co with a plastic-based PET scanner

Positronium Lifetime Imaging (PLI) extends positron emission tomography by using the lifetime of positronium atoms as a probe of tissue molecular architecture. In this work, we report the first PLI measurements performed with $^{52}$Mn and $^{55}$Co using the modular J-PET. Four samples were studied in each experiment: two Certified Reference Materials (polycarbonate and fused silica) and two human tissues (cardiac myxoma and adipose). The selection of PLI events was based on the registration of two 511~keV annihilation photons and one prompt gamma in triple coincidence. From the resulting lifetime spectra we extracted the mean ortho-positronium lifetime $\tau_{\text{oPs}}$ and the mean positron lifetime $\Delta T_{\text{mean}}$ for each sample. The measured values of $\tau_{\text{oPs}}$ in polycarbonate using both isotopes matches well with the certified reference values. Furthermore, $^{55}$Co reproduced identical results for fused-silica measurements at their respective uncertainty levels. In contrast, measurements with $^{52}$Mn in fused silica show a minor deviation, which could be caused by the Parafilm spacer. In myxoma and adipose tissue, the reduced $\tau_{\text{oPs}}$ values are mainly linked to the long storage history of the samples rather than to the choice of isotope. Comparing peak-to-background ratios and spectral purity, $^{55}$Co provides cleaner PLI data under the same experimental conditions. Although $^{52}$Mn offers a longer half-life and a multi gamma cascade enhancing $\beta^{+}$ + $\gamma$ coincidences, but at the expense of higher background. In this study, we demonstrate that the applied selection criteria on the data measured with the modular J-PET can be used for PLI studies even with radionuclides with complex decay patterns.

physics.med-ph↗

arXiv2025

First Positronium Lifetime Imaging with Scandium-44 on a Long Axial Field-of-view PET/CT

Purpose: 44Sc has been successfully produced, synthesized, labeled and first-in-human studies were conducted some years ago. The decay properties of 44Sc, together with being close to a clinical implementation, make it an ideal candidate for in vivo positronium lifetime measurements. In this study, we investigate the count statistics for ortho-positronium (oPs) measurements with 44Sc. Method: A NEMA image quality phantom was filled with 41.7 MBq of 44Sc dissolved in water and scanned on a commercial long-axial field-of-view PET/CT. Three-photon events were identified using a prototype feature of the scanner and dedicated software. The lifetime of oPs was determined in the phantom spheres and in 4x4x4 mm^3 voxels. Results: All measured oPs lifetimes are compatible, within the uncertainties, with the literature values for water. The oPs lifetime is 2.65+-0.50, 1.39+-0.20 and 1.76+-0.18 ns in the three smallest spheres of the phantom and 1.79+-0.57 ns for a single voxel in the central region of the largest sphere. The relative standard deviation in the background regions of the time difference distributions, i.e., for time differences smaller than -2.7 ns, is above 20% - even for voxels inside the phantom spheres. Conclusions: Despite the favorable physical properties of 44Sc, the count statistics of three-photon events remains a challenge. The high prompt-photon energy causes a significant amount of random three-photon coincidences with the given methodology and, therefore, increases the statistical uncertainties on the measured oPs lifetime.

physics.med-ph↗

arXiv2025

Particle spectra in the integrated hydrokinetic model at RHIC Beam-Energy-Scan energies

We study light-hadron production in Au+Au collisions at $\sqrt{s_{NN}} = 7.7-39$ GeV using an extended Integrated HydroKinetic Model (iHKMe). Focusing on transverse momentum spectra, we investigate the sensitivity to key model parameters, particularly the thermalization timescale. We consider two distinct equations of state: one featuring a crossover and the other a first-order phase transition. In both cases, thermalization begins shortly before full nuclear overlap and lasts approximately 1~fm/$c$ across all energies. Both equations of state provide a similarly good description of the soft particle momentum spectra once the other parameters are slightly adjusted. The most pronounced differences arise at the lower RHIC BES energy of $\sqrt{s_{NN}} = 7.7$~GeV, particularly in proton and kaon yields, reflecting their sensitivity to the freeze-out parameters.

nucl-th↗

arXiv2025

Positronium Lifetime Imaging with the Biograph Vision Quadra using 124I

Purpose: Measuring the ortho-positronium (oPs) lifetime in human tissue bears the potential of adding clinically relevant information about the tissue microenvironment to conventional positron emission tomography (PET). Through phantom measurements, we investigate the voxel-wise measurement of oPs lifetime using a commercial long-axial field-of-view (LAFOV) PET scanner. Methods: We prepared four samples with mixtures of Amberlite XAD4, a porous polymeric adsorbent, and water and added between 1.12 MBq and 1.44 MBq of $^{124}$I. The samples were scanned in two different setups: once with a couple of centimeters between each sample (15 minutes scan time) and once with all samples taped together (40 minutes scan time). For each scan, we determine the oPs lifetime for the full samples and at the voxel level. The voxel sizes under consideration are $10.0^3$ mm$^3$, $7.1^3$ mm$^3$ and $4.0^3$ mm$^3$. Results: Amberlite XAD4 allows the preparation of samples with distinct oPs lifetime. Using a Bayesian fitting procedure, the oPs lifetimes in the whole samples are $2.52 \pm 0.03$ ns, $2.37\pm 0.03$ ns, $2.27\pm0.04$ ns and $1.82\pm 0.02$ ns, respectively. The voxel-wise oPs lifetime fits showed that even with $4.0^3$ mm$^3$ voxels the samples are clearly distinguishable and a central voxels have good count statistics. However, the situation with the samples close together remains challenging with respect to the spatial distinction of regions with different oPs lifetimes. Conclusion: Our study shows that positronium lifetime imaging on a commercial LAFOV PET/CT should be feasible under clinical conditions using $^{124}$I.

physics.med-ph↗