Quantitative dual-isotope preclinical SPECT/CT imaging and biodistribution of the mercury-197m/g theranostic pair with [197m/gHg]HgCl2 and a [197m/gHg]Hg-tetrathiol complex as a platform for radiopharmaceutical development
Bibliographic record
Abstract
Abstract Background Mercury-197m ( 197m Hg, t 1/2 = 23.8 h) and mercury-197g ( 197g Hg, t 1/2 = 64.14 h) possess favorable nuclear properties for imaging and targeted therapy, but the development of suitable chelators for mercury-based radiopharmaceuticals remains underexplored. Additionally, accurate imaging and quantification of mercury isotopes, particularly in dual-isotope formats, require tools that account for their complex decay schemes. Phantom imaging studies are essential for validating spatial resolution, quantitative accuracy, and isotope-specific calibration prior to in vivo application. In this study, we investigated the commercially available ligand H 4 Tetrathiol for chelation of [ 197m/g Hg]Hg 2+ and developed a robust imaging and quantification pipeline to support the use of these nuclear isomers in preclinical imaging. Results Radiolabeling of H 4 Tetrathiol yielded exceptionally efficient complexation, achieving the lowest ligand-to-metal ratio reported for radio-mercury. The resulting [ 197m/g Hg]Hg 2+ -complex demonstrated high in vitro stability in the presence of serum proteins, glutathione, and competing biologically relevant metal ions, though it exhibited kinetic lability when challenged with excess HgCl₂. In vivo biodistribution studies in mice showed a distinct pharmacokinetic profile from unchelated [ 197m/g Hg]HgCl₂, suggesting in vivo complex stability. Phantom imaging studies with a high sensitivity collimator demonstrated submillimeter resolution (≥ 1.1 mm) for both 197g Hg and 197m Hg, with decay behavior consistent with known half-lives. To facilitate accurate quantification, we developed HgQuant , a Python-based tool for isotope-specific calibration, Bateman decay correction, and automated dual-isotope analysis. This tool enabled reproducible, time-resolved quantification in both phantom and in vivo settings. Conclusions These results establish Tetrathiol as a promising scaffold for mercury-based theranostics, offering efficient radiolabeling and in vivo stability. The integration of high-resolution imaging and HgQuant -based quantification of each isomer establishes a comprehensive framework for advancing [ 197m/g Hg]Hg radiopharmaceutical development.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".