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Researchers use dynamic PET imaging with target-selective tracer molecules to probe molecular processes. Kinetic models have been developed to describe these processes. The models are typically fitted to the measured PET data with the assumption that the brain is in a steady-state condition for the duration of the scan. The end results are quantitative parameters that characterize the molecular processes. The most common kinetic modeling endpoints are estimates of volume of distribution or the binding potential of a tracer. If the steady state is violated during the scanning period, the standard kinetic models may not apply. To address this issue, time-variant kinetic models have been developed for the characterization of dynamic PET data acquired while significant changes (e.g., short-lived neurotransmitter changes) are occurring in brain processes. These models are intended to extract a transient signal from data. This work in the PET field dates back at least to the 1990s. As interest has grown in imaging nonsteady events, development and refinement of time-variant models has accelerated. These new models, which we classify as belonging to the first, second, or third generation according to their innovation, have used the latest progress in mathematics, image processing, artificial intelligence, and statistics to improve the sensitivity and performance of the earliest practical time-variant models to detect and describe nonsteady phenomena. This review provides a detailed overview of the history of time-variant models in PET. It puts key advancements in the field into historical and scientific context. The sum total of the methods is an ongoing attempt to better understand the nature and implications of neurotransmitter fluctuations and other brief neurochemical phenomena.

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On October 24 and 25, SophosAI presents ideas on how to use models large and small—and defend against malignant ones.

Make the most of your Sophos Firewall.

Sophos X-Ops unveils five-year investigation tracking China-based groups targeting perimeter devices

Decades of obsolete and unpatched hardware and software endanger us all

What our incident responders know from five years of fighting an octopus

Thirty-five years after the first great cat-and-mouse infosecurity story, here we are again

On beyond “Detect and Respond” and “Secure by Design”

Sophos X-Ops unveils five-year investigation tracking China-based groups targeting perimeter devices

The Internet is full of cats—and in this case, malware-delivering fake cat websites used for very targeted search engine optimization.

Last month, Sophos X-Ops reported several MDR cases where threat actors exploited a vulnerability in Veeam backup servers. We continue to track the activities of this threat cluster, which recently included deployment of a new ransomware. The vulnerability, CVE-2024-40711, was used as part of a threat activity cluster we named STAC 5881. Attacks leveraged compromised […]

Felicia Grasso
Dec 1, 2020; 19:1986-1996
Research

Jessica Y. Franco
Dec 1, 2020; 19:1936-1951
Research

Wenhe Zhu
Dec 29, 2020; 0:RA120.002353v1-mcp.RA120.002353
Research

Tricia Rowlison
Dec 1, 2020; 19:2090-2103
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Simone Kurz
Dec 29, 2020; 0:RA120.002266v1-mcp.RA120.002266
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Toma Keser
Dec 29, 2020; 0:RA120.002433v1-mcp.RA120.002433
Research

Yadong Yu
Dec 1, 2020; 19:1997-2014
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Xiao-Ting Wen
Dec 17, 2020; 0:RA120.002119v1-mcp.RA120.002119
Research