About

Youngho Seo, PhD, is a Professor in Residence and Director of Nuclear Imaging Physics in the Department of Radiology and Biomedical Imaging at the University of California, San Francisco (UCSF). He also holds positions in the Department of Radiation Oncology at UCSF, is a Faculty Affiliate at the Bakar Computational Health Sciences Institute, and is a Program Member of Pediatric Malignancies and Prostate Cancer programs at the Helen Diller Family Comprehensive Cancer Center. Additionally, he serves as a Professor in Residence in the Department of Nuclear Engineering at the University of California, Berkeley, and is a Physicist Faculty Scientist at Lawrence Berkeley National Laboratory. Dr. Seo's educational background includes a bachelor's degree in Physics from Korea Advanced Institute of Science and Technology (KAIST), where he investigated radiation effects on electronics by cosmic ray. He earned two master's degrees—one in Physics from the University of Alabama in Huntsville, focusing on space plasma physics, and another from UCLA with a dissertation on a dark matter experiment using dual-phase xenon. He completed his PhD in Physics at UCLA, followed by postdoctoral training in experimental neutrino physics. He joined UCSF in 2003, initially training in medical imaging physics, and became a faculty member in 2006. His primary research focus is on the use of quantitative SPECT/CT, PET/CT, and PET/MR molecular imaging tools for a broad range of research areas, including small animal imaging, instrumentation development, and physics analysis of clinical research data. Dr. Seo leads a group of physicists and engineers working in radionuclide and x-ray imaging instrumentation and physics, directing the UCSF Physics Research Laboratory. His work encompasses hardware development such as energy-resolving detectors and novel imaging technologies, as well as software development including model-based image reconstruction and machine learning-based image analytics. His application focus includes neuroblastoma, neuroendocrine tumors, small volume imaging, dynamic imaging of the heart and brain, prostate and liver cancers, and neuropsychiatric disorders. He also directs preclinical and clinical research efforts, including animal imaging, molecular probes, and regulatory compliance. Dr. Seo has received numerous honors and awards, including the Mentored Quantitative Research Career Development Award from the National Cancer Institute, the Frost & Sullivan Technology Innovation of the Year Award, the Distinguished Investigator Award from the Academy for Radiology & Biomedical Imaging Research, and the Alexander R. Margulis Award for Scientific Excellence from the Radiological Society of North America. He is a full member of the American Association of Physicists in Medicine, a diplomate of the American Board of Science in Nuclear Medicine, a senior member of IEEE, and a member of the Society of Nuclear Medicine and Molecular Imaging.

Research topics

• Medicine
• Internal medicine
• Cancer research
• Virology
• Biology
• Pathology
• Nuclear medicine
• Oncology
• Radiology
• Pharmacology
• Immunology

Selected publications

• Mitochondrial Imaging Detects Early Cardiac Changes Following Cancer Immunotherapy

  Clinical Cancer Research · 2026-05-13

  articleOpen access

  PURPOSE: Advances in cancer therapy have improved survival but increased the risk of treatment-related cardiotoxicity, which remains difficult to detect early with existing biomarkers. [¹⁸F]F-AraG is a PET tracer that targets cells with active mitochondrial biogenesis, including cardiomyocytes and activated T cells, and may enable concurrent assessment of cardiac involvement and therapy-associated immune activity. This study evaluated whether [¹⁸F]F-AraG PET can serve as an early imaging biomarker of cardiac effects across different cancer therapies. METHODS: Twenty-six healthy subjects underwent [¹⁸F]F-AraG PET to establish baseline myocardial uptake. Seven patients with stage III melanoma and ten with advanced non-small cell lung cancer were imaged before and after immunotherapy. Myocardial uptake (SUVmax, SUVmean, SUVtotal) was quantified in the left (LV) and right (RV) ventricles, with LV regional uptake analyzed using a 17-segment model. Myocardial uptake was examined in relation to abnormal cardiac status in a subset of patients with available electrocardiogram (ECG) data. Associations between cardiac uptake, mitochondrial content, and PGC-1α expression were evaluated. RESULTS: Healthy myocardium demonstrated consistent and spatially uniform [¹⁸F]F-AraG uptake across age and sex, with higher uptake in the LV than RV. Conventional therapy was associated with increased global myocardial uptake, whereas immunotherapy was associated with additional heterogeneous and focal myocardial uptake. Altered myocardial uptake patterns were observed in patients with ECG abnormalities. CONCLUSIONS: [¹⁸F]F-AraG PET detects therapy-associated changes in myocardial tracer uptake following cancer treatment. These findings support its potential utility as a noninvasive imaging approach for early evaluation of cardiac effects in patients receiving cancer therapies.

  PublisherOA PDFDOI

• Figure S9 from Treatment of Prostate Cancer with CD46-targeted <sup>225</sup>Ac Alpha Particle Radioimmunotherapy

  2025-11-25

  articleOpen access

  <p>Figure S9: Histology evaluation of the healthy tissues for long-term (117 days) toxicity analysis. Hematoxylin and Eosin (H&E) staining of spleen, liver, lungs, heart, and bone samples show no toxicity at 0.25 µCi or 0.5 µCi doses of [225Ac]DOTA-YS5. Scale bar: 20 µm</p>

  PublisherDOI

• Mitochondrial Imaging Detects Early Cardiac Responses to Cancer Immunotherapy

  medRxiv · 2025-10-17

  preprintOpen access

  Advances in cancer therapy have improved survival but introduced substantial cardiac risk. Mitochondrial dysfunction underlies cardiotoxicity from conventional therapy, while T cell infiltration drives immunotherapy-related myocarditis. Early detection remains challenging, as current biomarkers and imaging lack sensitivity. Here, we show that [ 18 F]F-AraG, a mitochondrial PET tracer that images both activated T cells and cardiomyocytes, may provide an early biomarker of cardiac involvement across different cancer therapies. Healthy cardiac uptake was clearly detectable, consistent across age and sex, and spatially uniform. In patients with cancer, conventional therapy increased cardiac uptake, while immune checkpoint inhibitors induced further increases and regional heterogeneity suggestive of T cell infiltration. Abnormal [ 18 F]F-AraG cardiac uptake patterns were observed alongside ECG abnormalities. These findings establish [ 18 F]F-AraG PET as a first-in-class imaging tool for simultaneous assessment of early anti-tumor immunity and cancer therapy-related cardiac effects.

  PublisherOA PDFDOI

• Broad-Energy Gamma-Ray Imaging of Radiopharmaceuticals Using a Collimated Compton Camera

  2025-11-01

  article

  Accurate imaging of radiopharmaceuticals across a broad photon energy spectrum is critical in nuclear medicine for diagnosis, dosimetry, and for monitoring cancer treatment. This is specially true for targeted radionuclide therapy, where direct imaging and quantification are vital to leverage the therapeutic potential of this approach. Over the past decades, Single Photon Emission Computed Tomography (SPECT) has become the leading imaging modality for gammaray emitting radionuclides. However, its limited sensitivity and narrow energy range pose a significant challenge for imaging emerging therapeutic radiopharmaceuticals. A high-sensitivity imaging solution capable of handling both low- and high-energy gamma rays is still an unmet need in the clinic. In this work, we propose as a solution a collimated Compton camera consisting of a 3D-positioning gamma-ray tracking detector system combined with a parallel-hole collimator capable of performing Compton imaging for high-energy gamma rays and SPECT imaging for lowenergy gamma rays. Using this concept, we performed simultaneous imaging in the 30-300 KeV range using SPECT, in the 300-400 keV range using a combination of SPECT and Compton, and above 400 keV exclusively using Compton imaging. We measured the Compton and SPECT sensitivities of 64(8) cps MBq at 440 keV and 62(8) cps MBq at 218 keV, respectively, for only a single detector head. A practical application in nuclear medicine is for imaging of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">225</sup> Ac, a promising alpha emitter for tumor treatment that also emits gamma rays across a wide energy range. We demonstrate broad-energy imaging of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">225</sup> Ac and its daughters in point sources and a mouse phantom. Our concept could offer a versatile imaging solution for most of the relevant therapy and diagnose radionuclides.

  PublisherDOI

• High-Energy Imaging Capability of a State-of-the-Art Full-Ring CZT SPECT/CT

  2025-11-01

  articleSenior author

  A full-ring CZT-based single photon emission computed tomography (SPECT) is the current state-of-the-art for SPECT imaging. This modern clinical SPECT (e.g., StarGuide, GE HealthCare) is offered as SPECT/CT with 12 small rectangular CZT detector modules, allowing multiple degrees of freedom to focus and contour the imaging object. While this advance is a significant improvement from conventional NaI-based systems, there is a fundamental challenge to completely take over all applications of SPECT, i.e., lack of high energy photon imaging capability required for imaging radionuclides with high-energy photon emissions (e.g., <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{131} \mathrm{I}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{225} \text{Ac}$</tex>). This deficiency comes from the fact that it is not easily feasible to change collimators between scans. As a close academic-industry collaborative research effort, we have evaluated strategies to overcome this challenge by redesigning collimator geometries using validated Monte Carlo simulation tools and advanced image reconstructions. The validation step for the Monte Carlo simulation was performed using experimental data. First, we performed a NEMA body phantom scans with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{177} \text{Lu}$</tex>, and confirmed the imaging performance for both the low (113 keV) and high energy (208 keV) peaks of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{177} \text{Lu}$</tex> by both simulation and experimental data. Then, we tested if the current configuration of the collimator and detector shielding was able to image <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{131} \mathrm{I}$</tex> (364 keV) and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{213} \text{Bi}$</tex> of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{225} \text{Ac}$</tex> decay (440 keV), which showed expected artifacts from septal and shielding penetrations. Using the validated simulation tool, we also designed a high-energy collimator that can offer the imaging capability for these radionuclides (i.e., <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{131} \mathrm{I}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{225} \text{Ac}$</tex>) assuming that there is a mechanism to adopt a second set of collimators for the imaging system. Our results indicate that the option of using two sets of collimators can provide the full imaging capability of existing SPECT applications including <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{131} \mathrm{I}$</tex> imaging and potentially <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{225} \text{Ac}$</tex> imaging.

  PublisherDOI

• High Sensitivity In-Vivo ²²⁵ Ac Imaging of Mice with a Compton Camera

  2025-11-01

  article

  Targeted alpha therapy with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">225</sup>Ac is a promising modality for cancer treatment, as recently shown in pre-clinical and clinical trials. Achieving a precise understanding of the biokinetics of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">225</sup>Ac radiopharmaceuticals is critical to leverage their potential in the clinic. Although this is typically achieved via gamma-ray imaging experiments, such imaging is very challenging for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">225</sup>Ac due to the extremely low injected activities (<37 kBq), the unfavorable gamma-ray branching ratios (<26%), and the complicated decay chain. Standard SPECT with collimation struggles to achieve quality images and accurate quantification in pre-clinical experiments. In this work, we propose Compton imaging as an alternative solution for this problem. We leverage a commercial CZT Compton camera to achieve in-vivo imaging of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">225</sup>Ac in mice at therapeutic activities below the microcurie. We compared the sensitivity of a single-head Compton imaging system with that of a standard collimated gamma camera to be 4.7 times greater for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">213</sup>Bi and 7.5 for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">221</sup>Fr. We successfully imaged <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">225</sup>Ac daughter biodistributions of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">221</sup>Fr and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">213</sup>Bi in a mouse in vivo with only 30 minutes scan time and a single bed position. Performance can be further improved by using more detector heads and via system optimization. Comparison between in-vivo and ex-vivo will be presented and discussed.

  PublisherDOI

• Figure S10 from Treatment of Prostate Cancer with CD46-targeted &lt;sup&gt;225&lt;/sup&gt;Ac Alpha Particle Radioimmunotherapy

  2025-11-25

  articleOpen access

  &lt;p&gt;Figure S10: Tumor volumes, overall survival, and body weights for the saline and fractionated dose (0.125 µCi x 3) injections in 22Rv1 xenografts. Results show delayed tumor growth and improved survival without the significant toxicity from fractionated dose treatment (n=10).&lt;/p&gt;

  PublisherDOI

• Dynamic PET imaging predicts broadly neutralizing antibody distribution and HIV prevention efficacy

  medRxiv · 2025-11-28

  preprintOpen access

  Abstract HIV continues to impose a significant global burden despite success of effective antiretroviral therapy and pre-exposure prophylaxis (PrEP), due to stigma, access, and continuity of treatment that impact real-world effectiveness. Broadly neutralizing antibodies (bNAbs) are novel monoclonal antibody therapeutics being studied for long-acting ART and PrEP, and part of curative HIV regimens. Clinical translation for dose optimization remains a major challenge for the development of these therapeutics. Further, methods to characterize tissue levels of these agents are limited and often impractical due to the need for invasive tissue biopsies. Here we demonstrate the ability of serial whole body positron emission tomography (PET) imaging, following microdosing of the bNAb VRC01 in people without HIV, coupled with physiological-based pharmacokinetic (PBPK) modeling, to accurately predict therapeutic plasma, tissue exposure and prevention efficacy in two major VRC01 prevention trials. Based on our PBPK model, we determined a &gt;51-fold anorectal tissue VRC01 level:inhibitory concentration (IC 80 ) target would achieve 90% prevention efficacy compared to &gt;200 based on plasma levels in the primary trial analysis. Thus, these PET-PBPK approaches are promising for noninvasive determination of bNAb penetration more closely linked with concentrations needed to prevent virus acquisition, and may be leveraged to improve efficient development of bNAbs.

  PublisherOA PDFDOI

• Clinical Translation of Antibody Positron Emission Tomography for Cancer Imaging

  Clinical Cancer Research · 2025-12-02

  article1st authorCorresponding

  Hepatocellular carcinoma (HCC) lacks precise and noninvasive diagnostic tools. To address this, a new positron emission tomography (PET) radiotracer, [68Ga]Ga-XH-06, was developed. It uses an antibody fragment to target glypican-3 (GPC3), a highly specific biomarker, successfully visualizing GPC3 expressions in patients with HCC, potentially meeting an important unmet need. See related article by Lin et al., p. 550.

  PublisherDOI

• EVALUATING THE FEASIBILITY OF COMPTON IMAGING FOR AC-225 IN TARGETED ALPHA THERAPY

  International Journal of Particle Therapy · 2025-11-25

  articleOpen access
  PublisherDOI

Recent grants

• Dynamic cardiac SPECT

  NIH · $2.4M · 2017–2022

• Pretherapy 124I-MIBG Dosimetry for Planning 131I-MIBG Neuroblastoma Therapy

  NIH · $1.9M · 2011–2019

• NIH Grant R01EB012965

  NIH · $2.2M · 2017

• NIH Grant S10OD012301

  NIH · $1.2M · 2017

• Preclinical Dark-Field/Phase-Contrast Scanner Using X-ray Biprisms

  NIH · $225k · 2018–2020

Frequent coauthors

• Henry F. VanBrocklin

  University of California, San Francisco

  318 shared

• Robert R. Flavell

  294 shared

• David M. Wilson

  223 shared

• Jiang He

  214 shared

• Li Zhang

  University of Michigan–Ann Arbor

  213 shared

• Emily Chan

  211 shared

• Bin Liu

  208 shared

• Anil P. Bidkar

  203 shared

Awards & honors

• Mentored Quantitative Research Career Development Award, Nat…
• Frost & Sullivan Technology Innovation of the Year Award, Pr…
• Distinguished Investigator Award, Academy for Radiology & Bi…
• Alexander R. Margulis Award for Scientific Excellence, Radio…