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This study evaluates limitations when moving from tau-negative to tau-positive classifications and aims to quantify confidence levels for tau PET abnormality thresholds across different tracers. Methods: Using HEAD study data (485 participants) with head-to-head scans, Uniτ gray zones were characterized with T+ defined via Uniτ exceeding mean+3 SD of ages under 28, and TVR+ probability from logistic regression; gray zones were set between liberal T+ and probability cutoffs. Results and conclusions report tracer-consistent Uniτ thresholds and enhanced certainty during the negative-positive transition.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":35,"@type":76,"position":81},"https://docshare.wps.com/document/healthcare/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/defining-tau-pet-positivity-grey-zones-for-mk6240-and-flortaucipir-quantification/459403/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/defining-tau-pet-positivity-grey-zones-for-mk6240-and-flortaucipir-quantification/459403.png","ImageObject",300,407,{"name":92,"@type":93},"Rowan","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-11-07","2026-09-30",true,{"@type":102,"interactionType":103,"userInteractionCount":19},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"Why are tau PET positivity thresholds challenging to use?","Question",{"text":112,"@type":113},"Tau PET measures are inherently continuous, so dichotomized thresholds can introduce conceptual and analytical idiosyncrasies during classification.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How were tau positivity (T+) and visual reads (TVR+) defined?",{"text":117,"@type":113},"T+ was defined as Uniτ values above the mean plus 3 SD in participants under 28 years. Two physicians then performed visual assessment, and TVR+ agreement reflected clear tau pathology; TVR+ probabilities were modeled with logistic regression.",{"name":119,"@type":110,"acceptedAnswer":120},"What did the study find about the Uniτ gray zone across tracers?",{"text":121,"@type":113},"The Uniτ gray zone was consistent between MK6240 and Flortaucipir, with differences limited to the decimal range, and higher TVR+ probabilities corresponded to higher Uniτ values.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},459403,1790755855,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":34,"category_name":35,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":19,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":14,"language":139,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":140,"faqs":141,"seo_title":142,"seo_description":67,"update_tm":129,"read_time":24,"preview_page_count":4},1099514067415,"https://ap-avatar.wpscdn.com/avatar/100002539d78ffe74a7?x-image-process=image/resize,m_fixed,w_180,h_180&k=1779092875211072502","DOI: 10. 1002/alz70856_106847  \nBIOMARKERS  \nPOSTER PRESENTATION  \nNEUROIMAGING  \nDefining tau PET positivity grey zones for MK6240 and Flortaucipir quantification  \nGuilherme Povala1  Bruna Bellaver 1 MarinaScop Medeiros 1  Livia Amaral 1 Carolina Soares 1  Dana L Tudorascu 1  \nGuilherme Bauer-Negrini 1  Emma Ruppert 1 Firoza Z Lussier 1  Pamela C. L. Ferreira 1   \nQuentin Finn2  Joseph C. Masdeu2   \nHwamee Oh3  Juan Fortea4  David N. Soleimani-Meigooni5  Val J Lowe6 Brian A. Gordon7  Belen Pascual2  Pedro Rosa-Neto8  Suzanne L. Baker9 Tharick A Pascoal 1  \n1 University of Pittsburgh, Pittsburgh, PA, USA  \n2 Houston Methodist Research Institute, Houston, TX, USA  \n3 Brown University, Providence, RI, USA  \n4Sant Pau Memory Unit, Hospital de la Santa Creu i Sant Pau, Biomedical Research Institute Sant Pau, Barcelona, Spain  \n5 University of California, San Francisco, San Francisco, CA, USA  \n6 Mayo Clinic, Rochester, MN, USA  \n7Washington University in St. Louis, St. Louis, MO, USA  \n8 McGill University, Montreal, QC, Canada  \n9 Lawrence Berkeley National Laboratory, Berkeley, CA, USA  \nCorrespondence  \nGuilherme Povala, University of Pittsburgh, Pittsburgh, PA, USA.  \n[Email:](Email: gup11@pitt.edu)[ gup11@pitt.edu](Email: gup11@pitt.edu)  \nAbstract  \nBackground: Tau PET measures are inherently continuous and applying dichotomized thresholds introduces conceptual and analytical idiosyncrasies. Understanding the limitations in the transition from tau-negative to tau-positive classifications is crucial for the effective use of these thresholds. This study aims to determine the confidence levels of tau PET thresholds of abnormality for different tau PET tracers by characterizing their “gray zone” using the universal tau PET scale (Uniτ, www. unitau. app).  \nMethod: We evaluated 485 individuals across the aging and AD spectrum from the HEAD study, with head-to-head scans for MK6240 and Flortaucipir. Uniτ estimates were derived from the Meta-Temporal ROI. Tau positivity (T+) was defined as Uniτ values exceeding the mean plus 3 SD of individuals younger than 28 years (n = 24). Two physicians independently performed a visual assessment of tau positivity for each tracer, with agreement indicating clear tau pathology (TVR+). Logistic regression was used to estimate the probability of TVR+ across Uniτ values for each tracer (n = 189, CU elderly Aβ-and CI Aβ+). Individuals were classified as negative, positive, or within a “gray zone” between the most liberal T+ threshold and varying TVR+ probability thresholds (50%, 75%, 90%, 95%, and 99%).  \nResult: The Uniτ gray zone, defined as a function of TVR+ probabilities, demonstrated consistency between the two tracers, with differences observed only in the decimal range. The most liberal Uniτ threshold for T+ was 11.0 for both MK6240 and Flortaucipir, closely matching the 50% TVR+ probability threshold (11. 1 for MK6240  \nThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.  \n© 2025 The Alzheimer’s Association. Alzheimer’s & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer’s Association.  \nAlzheimer’s Dement. 2025;21(Suppl. 2):e106847.  \n[https://doi.org/10.1002/alz70856_106847](https://doi.org/10.1002/alz70856_106847)  \nwi[leyonlinelibrary.com/journal/alz](leyonlinelibrary.com/journal/alz)  \n1of2  \nBIOMARKERS  \nand 11.7 for Flortaucipir). Higher TVR+ probabilities corresponded to increased Uniτ values with MK6240 and Flortaucipir showing near-identical values between the tracers: 14.2 and 14.8 for 75%, 17.3 and 17.9 for 90%, 19.4 and 19.9 for 95%, and 24.1 and 24.6 for 99%, respectively (Figure 1). In total, 26 participants fell within the gray zone for MK6240, compared to 47 participants for Flortaucipir.  \nConclusion: These findings highlight the potential of Uniτ to provide a standardized approach for assessing tau positivit","cbCaicq7hhzj2lfq","https://ap.wps.com/l/cbCaicq7hhzj2lfq","pdf",599175,"English","# Abstract\n## Background\n## Method\n## Result\n## Conclusion","[{\"question\":\"Why are tau PET positivity thresholds challenging to use?\",\"answer\":\"Tau PET measures are inherently continuous, so dichotomized thresholds can introduce conceptual and analytical idiosyncrasies during classification.\"},{\"question\":\"How were tau positivity (T+) and visual reads (TVR+) defined?\",\"answer\":\"T+ was defined as Uniτ values above the mean plus 3 SD in participants under 28 years. Two physicians then performed visual assessment, and TVR+ agreement reflected clear tau pathology; TVR+ probabilities were modeled with logistic regression.\"},{\"question\":\"What did the study find about the Uniτ gray zone across tracers?\",\"answer\":\"The Uniτ gray zone was consistent between MK6240 and Flortaucipir, with differences limited to the decimal range, and higher TVR+ probabilities corresponded to higher Uniτ values.\"}]","Defining tau PET positivity grey zones for MK6240 and Flortaucipir quantification | PDF"]