About

Arion Chatziioannou is a Professor in the Department of Pharmacology at the University of California, Los Angeles. He holds the Crump Chair in Medical Engineering and serves as an Associate Director at the Crump Institute for Molecular Imaging. His research focuses on molecular and medical pharmacology, with involvement in the Cancer Molecular Imaging, Molecular Pharmacology GPB Home Area, and the Physics & Biology in Medicine GPB Home Area. He is a faculty member at the Crump Institute for Molecular Imaging and is engaged in advancing medical imaging technologies and molecular imaging research. His laboratory is located at UCLA's Center for Health Sciences, and he is actively involved in the academic and research community through his roles and collaborations.

Research topics

• Optics
• Physics
• Computer Science
• Computer hardware
• Materials science
• Optoelectronics

Selected publications

• Preclinical evaluation of high-resolution CT, 18F-FDG, and 18F-NaF PET imaging for longitudinal monitoring of atherosclerosis

  European Journal of Nuclear Medicine and Molecular Imaging · 2025-04-27 · 3 citations

  articleOpen access

  Abstract Rationale Detection of atherosclerosis is essential to the management and prevention of life-threatening cardiovascular events. Although non-invasive imaging modalities, such as 18 F-sodium fluoride ( 18 F-NaF), 18 F-fluorodeoxyglucose ( 18 F-FDG) PET, and CT, visualize distinct hallmarks of atherosclerosis, there has yet to be a singular multi-cohort interrogation of their strengths and limitations. Thus, we focused on identifying the optimal approach for visualizing atherosclerosis at different stages of disease progression. Methods In this study, 6-week-old, male, ApoE deficient mice ( Apoe −/− ) were placed on a high cholesterol diet for 12–20 weeks to induce calcific atherosclerotic disease. Age-matched, male, wildtype (WT) C57BL/6 mice fed with regular chow served as the control group. Mice were imaged at 12, 15, 18, and 20 weeks after starting their respective diets. To follow the progression of calcified atherosclerotic lesions, at each time point, in vivo , 18 F-NaF microPET/CT images were acquired 1 h and 3 h post tracer i.v. injection. In a separate cohort, in vivo 18 F-FDG PET/CT images were acquired at 3 and 5 h post tracer i.v. injection to follow inflammation as a result of progressive atherosclerotic lesion formation. High-resolution microCT images were acquired for all mice to visualize aorta calcification. After each imaging session, a subset ( n = 3) was euthanized from each group and histological analysis of the aorta was performed to confirm disease progression. Results In this comparative study, within the same cohort, 18 F-NaF PET detected atherosclerotic calcification earlier than microCT. At both 1 and 3 h post-injection (p.i.), calcified lesions were clearly detected by 18 F-NaF with a six-fold higher signal in Apoe -/- compared to WT mice. Interestingly, 18 F-NaF signal peaked at week 18, whereas aortic CT signal progressively increased with a 13-, 16-, and 29-fold at 15, 18, and 20 weeks, respectively. 18 F-FDG arortic accumulation at weeks 12 and 15, were significantly greater in Apoe −/− mice than WT control when images were acquired at 5 h but not at 3 h p.i.. In contrast to histological analysis, at ≥ 16 weeks where inflammation is significantly elevated, 18 F-FDG was equivalent in Apoe −/− and WT control mice and significantly reduced with disease progression. Conclusions Our results show that 18 F-NaF PET and 18 F-FDG PET are sensitive imaging modalities for the early detection of atherosclerotic lesions. However, both 18 F-NaF PET and high-resolution microCT prove to be effective methods for monitoring late-stage and progressive disease.

  PublisherOA PDFDOI

• Multipurpose Transparent Nanocomposites for Gamma Spectroscopy, Pulse Shape Discrimination, Thermal Neutron Detection, Radiation Shielding, and High Refractive Index Applications

  Advanced Functional Materials · 2025-11-28

  articleOpen access

  Abstract Materials exist that are useful for gamma scintillation, radiation shielding, neutron‐gamma pulse shape discrimination (PSD), thermal neutron detection, or high refractive index applications. While certain materials have exhibited optimal performance for each of these applications, none achieve multiple functions. This work presents a tunable, multipurpose nanocomposite system that may be used for all these applications, with enhanced performance. A sample containing 20 wt.% hafnium oxide nanoparticles and 20 wt.% 9,9‐dimethyl‐9 H ‐fluorene has a gamma light yield of 9782 Ph/MeV. The energy resolution of the hafnium K α escape peak is 9.4% at 607 keV, and the energy resolution of the deconvoluted photopeak is 4.9% at 662 keV. A 5.4 cm thick nanocomposite loaded with 80 wt.% hafnium oxide nanoparticles offers the same stopping power as 4.9 cm of leaded glass at an incident photon energy of 10 MeV, while being transparent and nontoxic. A nanocomposite containing 40 wt.% hafnium oxide nanoparticles, 1 wt.% gadolinium oxide nanoparticles, 2‐(4‐ tert ‐butylphenyl)‐5‐(4‐biphenylyl)‐1,3,4‐oxadiazole, and 1,4‐bis(5‐phenyl‐2‐oxazolyl)benzene can detect high‐energy gamma rays, fast neutrons, and thermal neutrons in a single material. A zirconium oxide nanocomposite sheet has a high refractive index of 1.656.

  PublisherOA PDFDOI

• Retrospective Cardiac Gating with A Prototype Small-Animal X-ray Computed Tomograph

  Journal of Visualized Experiments · 2025-02-21 · 2 citations

  articleOpen access

  The CrumpCAT is a prototype small-animal X-ray computed tomography (CT) scanner developed at our research institution. The CMOS detector with a maximum frame rate of 29 Hz and similar Tungsten X-ray sources with energies ranging from 50 kVp to 80 kVp are widely used across commercially available preclinical X-ray CT instruments. This makes the described work highly relevant to other institutions, despite the generally perceived wisdom that these detectors are not suitable for gating the high heart rates of mice (~600 beats/min). The scanner features medium- (200 µm) and high- (125 µm) resolution imaging, fluoroscopy, retrospective respiratory gating, and retrospective cardiac gating, with iterative or filtered-back projection image reconstruction. Among these features, cardiac gating is the most useful feature for studying cardiac functions in vivo, as it effectively eliminates image blurring caused by respiratory and cardiac motion. Here, we describe our method for preclinical intrinsic retrospective cardiac-gated CT imaging, aimed at advancing research on in vivo cardiac function and structure analysis. The cardiac-gating method acquires a large number of projections at the shortest practical exposure time (~20 ms) and then retrospectively extracts respiratory and cardiac signals from temporal changes in raw projection sequences. These signals are used to reject projections belonging to the high motion rate inspiration phase of the respiratory cycle and to divide the remaining projections into 12 groups, each corresponding to one phase of the cardiac cycle. Each group is reconstructed independently using an iterative method to produce a volumetric image for each cardiac phase, resulting in a four-dimensional (4D) dataset. These phase images can be analyzed either collectively or individually, allowing for detailed assessment of cardiac function. We demonstrated the effectiveness of both approaches of the prototype scanner's cardiac-gating feature through representative in vivo imaging results.

  PublisherOA PDFDOI

• Robust calibration of a dynamic model for a high-resolution microCT scanner

  2025-02-14 · 1 citations

  articleSenior author

  High-resolution microCT scanners, like the prototype HiCT at our institution, require accurate calibration of their physical projection model. The high magnification used to attain high-resolution amplifies mechanical imperfections like gantry wobbling, bracket sagging and component thermal expansion. Projection models with constant parameters fail to represent the moving system and are not suitable for high quality image reconstruction. Furthermore, variable and non-reproducible environmental conditions render even well-calibrated models inapplicable to every situation. To address these two problems, we developed: (i) a dynamic projection model whose parameters vary as a function of gantry angle, and (ii) a customized recalibration process that modifies an initial reference calibration adapting it to every scan. Both calibrations (initial and customized) use sets of Tungsten beads and a wire that are present in all data acquisitions. A conjugate gradient optimization algorithm minimizes the distance between the model-projected beads and wire with their actual projections on the detector. Approximately 500k iterations (initial) or 5k (recalibration) are required to achieve the desired accuracy i.e., where 99% of calibration data is projected within one detector pixel. With the combined dynamic model and custom recalibration, images of constant quality are produced, regardless of environmental conditions. Qualitatively, no doubling was observed on sample images and the 10% Modulation Transfer Function value on scans acquired in various conditions (scanner cold, warm and hot) was 17.6±1.1 lp/mm. The calibration method with its dynamic model and custom recalibration was able to compensate for changing–and non-reproduceable–environmental conditions. The optimization step that calibrates the model operates globally to simultaneously find the best model parameters and position of the beads. In that sense, it is completely self-calibrating.

  PublisherDOI

• In-Situ Activity Measurements of Microliter Droplets Using Cerenkov Radiation

  2025-11-01

  articleSenior author

  Development and validation of new imaging and therapeutic radiopharmaceuticals takes years of research due to the complexity, cost and limited throughput of conventional radiochemistry. To address this limitation, we devised a high-throughput radiochemistry system for rapid development of radiotracers for imaging and radiotherapeutics for cancer therapy. The core of the system is a silicon wafer that contains a 4×4 array of 3mm diameter microdroplet reaction sites allowing simultaneous droplet-based radiosynthesis. A critical requirement for these systems is that the activity of the droplets must be repeatedly measured to monitor the efficacy of each radiosynthesis step. Previously, we presented at this conference a method to rapidly measure radioactivity for positron imaging isotopes. Quantification of radioactivity in droplets is complicated by variations in overall positron energy deposition depending on the stage of synthesis, including the volume of the droplet. We showed that we could determine the activity in the droplets but required measuring both the intrinsic but weak Cerenkov light produced by positrons inside droplets and measuring the stronger scintillation light generated above the reaction sites from positrons that exit the droplets and interact in a scintillator. In this work, we demonstrate a simpler method to determine the droplet activity using only Cerenkov light by introducing a custom made “converter” layer covering the droplets that allows collection of Cerenkov light from the positrons that is less dependent of the droplet volume and geometry. Here we seek to determine the sensitivity and efficacy of this method to measure the activity in the droplets via Monte Carlo simulations of positrons emanating from arrays of droplets. We also present preliminary data from a 3D printed plastic converter place over radioactive droplets.

  PublisherDOI

• Kinetic Trajectories of Glucose Uptake in Single Cancer Cells Reveal a Drug-Induced Cell-State Change Within Hours of Drug Treatment

  The Journal of Physical Chemistry B · 2024-08-08

  articleOpen access

  The development of drug resistance is a nearly universal phenomenon in patients with glioblastoma multiforme (GBM) brain tumors. Upon treatment, GBM cancer cells may initially undergo a drug-induced cell-state change to a drug-tolerant, slow-cycling state. The kinetics of that process are not well understood, in part due to the heterogeneity of GBM tumors and tumor models, which can confound the interpretation of kinetic data. Here, we resolve drug-adaptation kinetics in a patient-derived in vitro GBM tumor model characterized by the epithelial growth factor receptor (EGFR) variant(v)III oncogene treated with an EGFR inhibitor. We use radiolabeled 18F-fluorodeoxyglucose (FDG) to monitor the glucose uptake trajectories of single GBM cancer cells over a 12 h period of drug treatment. Autocorrelation analysis of the single-cell glucose uptake trajectories reveals evidence of a drug-induced cell-state change from a high- to low-glycolytic phenotype after 5–7 h of drug treatment. Information theoretic analysis of a bulk transcriptome kinetic series of the GBM tumor model delineated the underlying molecular mechanisms driving the cellular state change, including a shift from a stem-like mesenchymal state to a more differentiated, slow-cycling astrocyte-like state. Our results demonstrate that complex drug-induced cancer cell-state changes of cancer cells can be captured via measurements of single cell metabolic trajectories and reveal the extremely facile nature of drug adaptation.

  PublisherOA PDFDOI

• Exploring Automated Contouring Across Institutional Boundaries: A Deep Learning Approach with Mouse Micro-CT Datasets.

  PubMed · 2024-05-29

  articleOpen access

  Image-guided mouse irradiation is essential to understand interventions involving radiation prior to human studies. Our objective is to employ Swin UNEt Transformers (Swin UNETR) to segment native micro-CT and contrast-enhanced micro-CT scans and benchmark the results against 3D no-new-Net (nnU-Net). Swin UNETR reformulates mouse organ segmentation as a sequence-to-sequence prediction task, using a hierarchical Swin Transformer encoder to extract features at 5 resolution levels, and connects to a Fully Convolutional Neural Network (FCNN)-based decoder via skip connections. The models were trained and evaluated on open datasets, with data separation based on individual mice. Further evaluation on an external mouse dataset acquired on a different micro-CT with lower kVp and higher imaging noise was also employed to assess model robustness and generalizability. Results indicate that Swin UNETR consistently outperforms nnU-Net and AIMOS in terms of average dice similarity coefficient (DSC) and Hausdorff distance (HD95p), except in two mice of intestine contouring. This superior performance is especially evident in the external dataset, confirming the model's robustness to variations in imaging conditions, including noise and quality, thereby positioning Swin UNETR as a highly generalizable and efficient tool for automated contouring in pre-clinical workflows.

  PublisherOA PDF

• Robust Automated Mouse Micro-CT Segmentation Using Swin UNEt TRansformers

  Bioengineering · 2024-12-11 · 2 citations

  articleOpen access

  Image-guided mouse irradiation is essential to understand interventions involving radiation prior to human studies. Our objective is to employ Swin UNEt TRansformers (Swin UNETR) to segment native micro-CT and contrast-enhanced micro-CT scans and benchmark the results against 3D no-new-Net (nnU-Net). Swin UNETR reformulates mouse organ segmentation as a sequence-to-sequence prediction task using a hierarchical Swin Transformer encoder to extract features at five resolution levels, and it connects to a Fully Convolutional Neural Network (FCNN)-based decoder via skip connections. The models were trained and evaluated on open datasets, with data separation based on individual mice. Further evaluation on an external mouse dataset acquired on a different micro-CT with lower kVp and higher imaging noise was also employed to assess model robustness and generalizability. The results indicate that Swin UNETR consistently outperforms nnU-Net and AIMOS in terms of the average dice similarity coefficient (DSC) and the Hausdorff distance (HD95p), except in two mice for intestine contouring. This superior performance is especially evident in the external dataset, confirming the model's robustness to variations in imaging conditions, including noise and quality, and thereby positioning Swin UNETR as a highly generalizable and efficient tool for automated contouring in pre-clinical workflows.

  PublisherDOI

• Supplementary Tables 1-2 from Integrated Microfluidic and Imaging Platform for a Kinase Activity Radioassay to Analyze Minute Patient Cancer Samples

  2023-03-30

  supplementary-materialsOpen access

  Supplementary Tables 1-2 from Integrated Microfluidic and Imaging Platform for a Kinase Activity Radioassay to Analyze Minute Patient Cancer Samples

  PublisherOA PDFDOI

• Simulation Study of Fast, High-Z, High-Transparency Nanocomposite Organic Scintillators for use in Timing Radiation Detectors

  2023-11-04

  articleSenior author

  Organic scintillators traditionally had limited use for x-ray and gamma ray detection because of their low stopping power. In addition, because of the near absence of photoelectric interactions they lack spectroscopy capabilities. Recent advances in material engineering have made it possible to efficiently embed high atomic number elements within plastic while retaining high transparency to light. These nanocomposite materials hold the promise of combining the fast rise and decay times of organic scintillators with the higher density, efficiency and photofraction of traditional inorganic scintillators. Furthermore, such nanocomposites are easily scalable to significant volumes without the difficulties involved with growing large inorganic crystals. Here we examine in simulation the expected response to gamma radiation of several new nanocomposite scintillators under development at UCLA. Three high-Z composites are studied: CdxZn1-xS/ZnS (CZS) which is a self-luminescent quantum dot (QD) and HfO2 and YbF3 which are non-luminescent high-Z compounds. The response of these nanocomposites loaded in plastic at several weight percentages are compared to common organic and inorganic scintillators: NE102 and LYSO. The coincidence timing response (CTR) will depend on the measured rise (τr) and decay (τd) times of these scintillators as well as the light yield (LY) and collection efficiency (ε) of a photo detector. Here we report on the photofraction and efficiency as determined through simulation and discuss our plan to measure CTR for these scintillators.

  PublisherDOI

Recent grants

• NIH Grant R01EB001458

  NIH · $1.3M · 2008

• Integrate high Z and low Z compound semiconductors for 60 keV spectrometry

  NSF · $385k · 2018–2022

• Cancer Molecular Imaging, Nanotechnology, and Theranostics (CMINT)

  NIH · $65.6M · 1996–2030

Frequent coauthors

• Nam T. Vu

  50 shared

• David Prout

  39 shared

• Robert W. Silverman

  Institute for Molecular Medicine

  39 shared

• Michael E. Phelps

  33 shared

• Hsian‐Rong Tseng

  University of California, Los Angeles

  32 shared

• Richard Taschereau

  University of California, Los Angeles

  30 shared

• Simon R. Cherry

  University of California, Davis

  26 shared

• Zheng Gu

  Shenzhen Bay Laboratory

  23 shared