MRI machine
SCAN

Standardized Centralized Alzheimer’s & Related Dementias Neuroimaging (SCAN)

The goal of SCAN is to enable standardized PET and MRI data collection from across the Alzheimer’s Disease Research Centers (ADRC) Program so that it can be combined and shared with researchers around the world via the NACC Data Platform. The National Institute on Aging (NIA) provides SCAN’s funding.

The SCAN initiative is a collaboration between:

Berkeley University of California
Lawrence Berkeley National Laboratory
University of Michigan
Mayo Clinic
UC Davis
National Alzheimer's Coordinating Center
Laboratory of Neuro Imaging
National Institutes of Health

Submit SCAN Data

THE SCAN INITIATIVE ONLY ACCEPTS SCAN-COMPLIANT DATA
Images that don't meet SCAN protocol are still accepted by NACC. Learn more.

Submit SCAN-Compliant data to LONI

Please carefully review the SCAN PET manual and the SCAN MRI manual to ensure that your data is compliant with the SCAN protocol and for uploading instructions.

Only SCAN-compliant data should be submitted to the Laboratory of Neuro Imaging (LONI). Non-approved data (with or without approved data) will be quarantined. Images collected before 2021 do not meet SCAN-compliance criteria.

Submit non–SCAN-compliant data directly to NACC

SCAN does not accept data that is not prospectively collected and SCAN-compliant.

Any data that that is 'heterogenous' or non-SCAN-compliant should be submitted to NACC.

About

Overview

The Standardized Centralized Alzheimer’s & Related Dementias Neuroimaging (SCAN) initiative is a multi-institutional project that was funded as a U24 grant (AG067418) by the National Institute on Aging (NIA) in May 2020 with the goal of standardizing the acquisition, curation, and analysis of PET and MR images acquired through the NIA Alzheimer’s Disease Research Center (ADRC) Program. The National Alzheimer’s Coordinating Center (NACC) Data Platform enriches the SCAN dataset by linking with the longitudinal Uniform Data Set and other data modalities at NACC.

ADRCs upload SCAN-compliant images to a portal hosted by the Laboratory of Neuro Imaging (LONI) at the University of Southern California where they are de-identified and defaced by the Aging and Dementia Imaging Research (ADIR) laboratory at Mayo Clinic. The PET and MRI laboratories at the University of Michigan and the Aging and Dementia Research (ADIR) Laboratory at Mayo Clinic then process for quality assurance and harmonization. Following this, the PET laboratory at UC Berkeley and the MRI laboratories at Mayo Clinic and UC Davis analyze the images to produce MRI volumes and PET Standardized Uptake Value Ratio (SUVR) data.

Recently, SCAN methods have been applied to the ADRC Consortium for Clarity in ADRD Research Through Imaging (CLARiTI).

A schematic of data flow. The caption describes this schematic.

Why is SCAN needed?

For many years, researchers at the NIA-funded ADRCs have been collecting different types of PET and MR images. This “heterogenous” or “legacy” data was collected using a variety of different acquisition methods such as T1-weighted imaging, diffusion imaging, or resting state functional MRI. Because of this, image data could not be easily combined across ADRCs, resulting in lost opportunities for scientific collaboration. The goal of SCAN is to standardize PET and MRI data collection from across the ADRC Program so that it can be combined and shared with researchers around the world via the NACC Data Platform.

Data Sharing

The NACC Data Platform makes harmonized images and numerical summaries (e.g., Standardized Uptake Value Ratio ‘SUVRs’ and volumes) available to ADRCs and approved researchers around the world through the following mechanisms:

ADRC Portals: ADRCs can access and download SCAN data for their participants

  • SCAN QC Dashboards: ADRCs can track and audit their image submission’s quality control (QC) status and other summary information in real-time.

  • All SCAN Variables: Numerical values (SUVRs and volumes) will be accessible to ADRCs via the ADRC Portals for all their participants.

NACC Data Front Door: Researchers anywhere can access SCAN data for free

  • SCAN Public Dashboard: The SCAN Public Dashboard provides researchers with up-to-date information on the number of participants with SCAN-compliant PET and MR images and the total number of images submitted by each ADRC to SCAN.

  • Quick Access File Data Request System: Researchers can request SCAN data collected from all participating ADRCs, including summary, QC, and analysis (volumes and SUVRs) data. Starting in Fall 2024, researchers will also be able to access defaced SCAN images via this data request system.

  • Cohort Selection Tool: Coming in 2025! A new self-service tool coming to NACC allowing researchers to perform cohort selection, data visualization, and provide access to raw data at NACC directly.

Data Front Door overview

Raw images are stored at the Laboratory of Neuro Imaging (LONI). ADRCs and researchers interested in accessing the raw images will be able request them via LONI in the near future. NACC will provide updates on the availability of raw images as progress is made by SCAN, LONI, and NACC to ensure raw image data is de-identified before it is made available to the public.

SCAN Protocols

Prospective image files that meet SCAN acquisition protocols, regardless of the funding source, are submitted to LONI as part of this project. Existing images, and prospective images that don’t meet SCAN protocol, are instead submitted directly to NACC.
SCAN has a set of required acquisition schemes for PET and MR data. This includes required PET protocols for acquiring amyloid, tau, and fludeoxyglucose-18 (FDG) PET scans, and required MRI sequences for structural T1 and Fluid Attenuated Inversion Recovery (FLAIR) scans. Additional MRI sequences are optional. Analyzed data available to investigators will include:

  • Regional measures of amyloid, tau, and FDG tracer uptake

  • Brain volumes

  • White matter hyperintensities

  • Cerebral infarction

  • Fractional anisotropy, cerebral blood flow, and functional connectivity (depending on the availability of advanced MRI sequences)

Current SCAN protocols are focused on widely accepted and applied biomarkers generally, but not exclusively, related to characterizing research participants in the A/T/N framework. To continue to support collaborative research, SCAN will base future directions on the needs and goals of the ADRC program. These may include other MRI techniques or PET tracers as best practices for their acquisition and analysis become available.

SCAN Dashboard

This dashboard tracks the number of Standardized Centralized Alzheimer’s and Related Dementias Neuroimaging (SCAN)-compliant MR/PET images and the number of participants that images have been submitted for by each Alzheimer’s Disease Research Center (ADRC) to the Laboratory of Neuro Imaging (LONI) for the SCAN Initiative.
Due to delays caused by the defacing process, these counts may differ slightly from the total number of submitted images.

New to the SCAN Dashboards?

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Please note: Only ADRC members with data access privileges can view the ADRC-Specific SCAN QC Dashboards. Learn how to get access in the SCAN Dashboard Quick Guide.

Resources for ADRCs

How to Participate

  • Acquire Images

    Alzheimer’s Disease Research Centers participating in SCAN should refer to the MRI and PET checklist and manuals linked below for detailed SCAN image acquisition protocols.

    SCAN will troubleshoot prospectively with ADRCs to advise on making data SCAN compliant. Contact SCAN.

    Current SCAN Protocols

    MRI

    MRI Checklist and Manual

    All longitudinal scans must be performed on the same MRI scanner.

    Each MRI scanner must be certified and approved by SCAN. MR scanners that are now certified for ADNI 3 can be certified for SCAN using a phantom scan. MR scanners that have not been certified for ADNI 3 (or SCAN) must be certified using a human volunteer scan. This must be permissible using a local IRB – i.e. SCAN does not plan to create a central IRB nor will SCAN manage local IRB administrative proceedures.

    The Standard MRI protocol (using SCAN-specific parameters) is required. Your remaining scan time can be used for your site specific sequences.

    There are 2 options for SCAN MR – each site can choose which they prefer.

    Option 1: Site only required to do 2 primary SCAN sequences: T1 & FLAIR
    • The first 10 minutes of exam belongs to NIA/SCAN — this is when the SCAN T1 & FLAIR would be done

    • Remainder of exam is unique to site

    • SCAN would only collect and analyze T1 and FLAIR

    Option 2: Site may do full SCAN protocol (which mirrors ADNI)

    PET

    PET Checklist and Manual

    All longitudinal scans must be performed on the same PET scanner.

    Each PET scanner must be certified and approved by SCAN. ADNI approved PET scanners will not need to be re-certified.

    The following tracers and imaging protocols are all compatible with SCAN:

     Suggested Target Dose ± 10%Minimum injectable doseAcquisition start-stop time post-injection (min)
    TracermCiMBqmCiMBq
    Amyloid Tracers
    PIB15555830040–60 or 50–70, 40–70
    Florbetapir10370622550–70
    Florbetaben8295518590–110
    NAV46948.13006.524040–70, 50–70
    TAU Tracers
    Flortaucipir10370622580–100
    MK62405185415070–90 or 90–110, 70–110
    PI26205185415030–60, 45–75, 60–90, 45–90
    GTP17260518560–90
    Glucose metabolism tracer
    FDG5185415030–45, 30–60

    NOTE: The SCAN MR protocol is the same as the Alzheimer’s Disease Neuroimaging Initiative (ADNI) protocol. The current protocol is ADNI 4. See this set of ADNI MR protocols created for various vendor/model/operating system options.

  • Upload Images

    Submit SCAN-Compliant data to LONI

    Please carefully review the SCAN PET manual and the SCAN MRI manual to ensure that your data is compliant with the SCAN protocol and for uploading instructions.

    Only SCAN-compliant data should be submitted to the Laboratory of Neuro Imaging (LONI). Non-approved data (with or without approved data) will be quarantined. Images collected before 2021 do not meet SCAN-compliance criteria.

    Submit non–SCAN-compliant data directly to NACC

    SCAN does not accept data that is not prospectively collected and SCAN-compliant.

    Any data that that is 'heterogenous' or non-SCAN-compliant should be submitted to NACC.

  • Track and audit image submissions

    Sites are responsible for auditing their submissions and making sure that the information is correct using the SCAN QC Dashboards.

    Each ADRC can access their ADRC-specific SCAN QC Dashboards via the SCAN Public Dashboard.

    • These enable sites to track the QC status of their MRI and PET submissions, allowing them to rapidly address errors. They also serve as an auditable record of all SCAN MRI data submitted to SCAN by a given ADRC and are downloadable as a csv file.

    • NOTE: The ADRC-specific SCAN QC Dashboards are only available to ADRC staff with data access privileges. Please refer to the SCAN Dashboard Quick Access Guide for details.

  • Access your SCAN data and analysis results

    All SCAN variables will soon be available via ADRC Portals. We anticipate this data being available by June 2024.

    In the meantime, ADRCs may access analysis results by submitting a data request via NACC’s Quick Access File Data Request System.

    NOTE: Analysis results are calculated after defacing and QC has been performed on MR and PET images. Sites should expect a delay from when images are submitted to when analysis results are available.

Resources for Researchers

Researchers around the world can access Standardized Centralized Alzheimer’s Disease and Related Dementias Neuroimaging (SCAN) initiative harmonized images and numerical summaries (e.g. Standardized uptake value ratio ‘SUVRs’ and volumes) via the National Alzheimer’s Coordinating Center (NACC) Data Platform through NACC’s Data Front Door.

NACC's Data Front Door

Free access is available via the following mechanisms:

SCAN Public Dashboard

Up-to-date information about the number of participants with SCAN-compliant MR/PET images and the total number of images submitted by each Alzheimer’s Disease Research Center (ADRC) to SCAN.

View the SCAN Dashboard

Quick Access File Data Request System

Researchers can request SCAN numerical data collected from all participating ADRCs, including summary, QC, and analysis (volumes, cortical thickness, surface area, and SUVRs) data. Starting in Fall 2024, researchers will also be able to access defaced SCAN images via this data request system.

Request SCAN data at NACC

Raw Image Availability

Images are currently stored at the Laboratory of Neuro Imaging (LONI). These images are not yet available but will be soon.

Cohort Selection Tool:

Coming in 2025! A new self-service tool coming to NACC allowing researchers to perform cohort selection, data visualization, and provide access to raw data at NACC directly.

Data Resources

Meet the Team


Standardized Centralized Alzheimer’s and Related Dementias Neuroimaging (SCAN) Initiative Team

MRI Team

  • Clifford Jack, MD - Mayo Clinic (Principal Investigator)

  • Charles DeCarli, MD

  • Chadwick Ward

  • Pauline Maillard

  • Christopher Schwarz

  • Denise Reyes

  • Bret Borowski

  • John Moore-Weiss

  • Leonard Matoush

  • Robert Reid

  • Anne Effron

  • Gregory Preboske

  • Jeffrey Gunter

  • Matthew Senjem

  • Colin Hortman

  • Kejal Kantarci

  • Oliver Martinez

PET Team

  • William Jagust, MD - UC Berkeley (Principal Investigator)

  • Bob Koeppe

  • Susan Landau

  • Suzanne Baker

  • Tessa Harrison

  • Trevor Chadwick

LONI Team

  • Arthur Toga

  • Karen Crawford

NACC Team

  • Sarah Biber

  • Bud Kukull

  • Brittany Hale

  • Brendan Smith

  • Zach Stark

  • Jessica Culhane

Collaborators

Berkeley University of California
Lawrence Berkeley National Laboratory
University of Michigan
Mayo Clinic
UC Davis
National Alzheimer's Coordinating Center
Laboratory of Neuro Imaging
National Institutes of Health

SCAN Updates

  • PET Summary and Analysis Data Availability

    In January 2024, SCAN PET summary and analysis (SUVRs) data was returned to ADRCs that have contributed to SCAN. Sites were sent a summary report of the PET data each site has uploaded to SCAN, in addition to the PET numerical data analysis report which contains the derived outputs of the PET image data after it has passed through the SCAN PET QC pipeline, which includes QC of the incoming images as well as QC inspection of the products of the analytic pipelines.

    The PET data file contained the following:
    • PET summary and QC data

    • PET SUVRs

    Documentation, such as the SCAN PET Researcher’s Data Dictionary, Methods, and other documentation can be found here.

    NOTE: Due to the processing time needed to perform defacing, QC, and analysis on submitted data, not all data that has been submitted and/or passed through QC has analysis data associated with it.

  • MRI Summary and Analysis Data Availability

    In March 2024, SCAN MRI summary and analysis (analysis) data was returned to ADRCs that have contributed MRI data to SCAN. Sites were sent a summary report of the MRI data each site has uploaded to SCAN, in addition to the MRI volumetric analysis report which contains the derived outputs of the MRI image data after it has passed through the SCAN MRI QC pipeline.

    The MRI data file contained the following:
    • MRI summary and QC data

    • MRI brain volumes, cortical thickness, and surface area data

    About the SCAN analysis process

    The SCAN MR analysis team performs standard processing of all MR images that have passed QC using FreeSurfer to provide standard readouts. These include the parcellations of regional brain volumes, cortical thickness and surface area for 31 bilateral gray matter regions from the Desikan-Killiany atlas.

    NOTE: Due to the processing time needed to perform defacing, QC, and analysis on submitted data, not all data that has been submitted and/or passed through QC has analysis data associated with it.

    Documentation, such as the SCAN MRI Researcher’s Data Dictionary, Methods, and other documentation can be found here.

  • The LONI uploader includes a new verification step

    Beginning July 29, 2023 the LONI imaging data submission interface will require that sites enter both the PTID and the NACCID for a given participant to submit their MRI/PET data to SCAN. This change was introduced to ensure NACCID and data fidelity for the SCAN initiative. As shared in our ADRC-wide communication on March 17, 2023, ADRCs are currently only able to submit SCAN data for participants with existing NACCIDs. More details about this temporary limitation and next steps can be found in the What is the current process for submitting MRI/PET images? section of this page.

    How to correctly submit your data via the new LONI uploader

    • Sites must enter both identifiers into the Subject ID text field using the convention PTID+NACCID, where PTID and NACCID are separated by the + character.

      • If the given PTID and NACCID pair match the record present in the NACC database, the upload process will be allowed to continue.

      • If not, then the user will receive an error message indicating that the PTID and NACCID combination are not valid, and the upload will not be allowed to continue.

    • Users who do not follow the PTID+NACCID convention will see a message describing the expected formatting of the Subject ID.

    How do I find the NACCIDs for my participants?

    To access your site’s PTID and NACCID pairs, please work with your site’s data manager to utilize the PTID to NACCID Map tool available via the NACC portal.

Frequently asked questions

General FAQs

  • What are the SCAN Dashboards?

    About the SCAN Public Dashboard

    The SCAN Public Dashboard tracks the number of participants with SCAN-compliant MRI and PET images and the total number of images submitted by each Alzheimer’s Disease Research Center (ADRC) to SCAN. This resource is meant to provide ADRCs and researchers with up-to-date information on the number of standard images that are available for analysis. View a demo of the SCAN Public Dashboard.

    Information included in the Dashboard:
    • Links to each center's ADRC-specific SCAN QC Dashboard

    • Total number of MRI and PET participants for whom the site has submitted data to SCAN

    • Total number of standard MRI exams and series submitted to SCAN that are available for analysis

    • Total number of PET scans (amyloid or tau) submitted to SCAN that are available for analysis

    Information NOT included in the Dashboard:
    • SCAN analysis data for ADRCs

    • SCAN analysis data for Researchers: ADRD researchers around the world may access this data via NACC's Quick Access File beginning in late 2023.

    • ADRC-specific PET and MRI data: The MRI and PET summary and QC status information is available through the ADRC-specific SCAN QC dashboards

    • Data for participants without existing NACCIDs: For the time being LONI will only be accepting data submissions for participants who have existing NACCIDs


    About the ADRC-specific SCAN QC Dashboards

    Each ADRC can access their ADRC-specific SCAN QC dashboards via the SCAN Public Dashboard located above. The ADRC-specific SCAN QC dashboards will:

    • Enable them to track the QC status of their MRI and PET submissions, allowing them to rapidly address errors.

    • Serve as an auditable record of all SCAN MRI data submitted to SCAN by a given ADRC, downloadable as a csv file.

    IMPORTANT NOTE: The ADRC-specific SCAN QC Dashboards are only available to ADRC members.

    Information that will be included in the ADRC-specific SCAN dashboards includes:
  • All PET summary and QC data submitted by each ADRC including:

    • NACCIDs

    • PTIDs

    • PET study date and time

    • Image UID & Scanner model

    • PET radiotracer used

    • Whether the scan passed QC or not

    • QC comments (why the scan failed QC, if failed)

  • All MRI summary and QC data submitted by each ADRC including:

    • NACCIDs

    • PTIDs

    • MRI study date and time

    • Image UID & Scanner model

    • Series date and time

    • Series number

    • Series type

    • Study comments: Visual artifacts, etc.

    • Release for Analysis: Whether the series was released for analysis or not based on QC and protocol checks

  • What is the current process for submitting MRI/PET images?

    As of March 17, 2023, sites will only be able to submit SCAN MRI and PET images to LONI for participants that already have a NACCID. This change will prevent errors (i.e., duplicate NACC IDs for participants, etc.) from being introduced into the database and the need for future SCAN data audits. See Changes to the LONI Uploader section for more information.

    Please note that this is a temporary change. Sites are encouraged to continue collecting SCAN data on all of their participants but will not be able to submit data for participants without existing NACC IDs until a new process for assigning NACCIDs to SCAN participants is put in place. NACC hopes to provide further updates to ADRCs on this new process soon.

    What about non-SCAN compliant MRI/PET images that are submitted to NACC?

    As of March 17, 2023, sites will only be able to submit non-standard (non-SCAN compliant) MRI and PET images to NACC for participants that already have pre-existing NACCIDs.

    Please do not submit non-standard MRI and PET images to SCAN as the SCAN initiative only collects SCAN-compliant MRI and PET images.

    Existing MRI and PET images collected before January 1, 2021, and prospective images that don't meet SCAN protocol are still accepted by NACC.

    Learn more about submitting this data to NACC here.
  • How are MR/PET image submissions being tracked?

    SCAN-compliant MRI/PET images submitted to LONI as part of the SCAN initiative:

    • SCAN Public Dashboard:The Public SCAN Dashboard tracks the number of SCAN-compliant MRI/PET images and the number of participants that images have been submitted for by each ADRC to SCAN.

    • ADRC-Specific SCAN QC Dashboards As part of the ADRC Portals, each ADRC will have access to their ADRC-specific SCAN QC dashboards that will a) enable them to track the summary and QC status of their MRI and PET submissions, allowing them to rapidly address errors, and b) serve as an auditable record of all SCAN MRI data submitted to LONI/NACC by a given ADRC, downloadable as a csv file.

    • The NACC monthly reports for each ADRC do not include the MRI/PET images submitted to LONI for the SCAN project in the image counts. We will not be adding SCAN images to these static monthly reports because we are in the process of modernizing the NACC Data Platform and complete SCAN-compliant image counts will be available through the SCAN dashboards.

    Non-SCAN compliant MRI/PET images submitted to NACC:

    • NACC is currently in discussion with NIA and the Imaging Steering Committee to determine how legacy MRI and PET images will be tracked and reported at NACC as we transition to our modern Data Platform and ADRC portals.

    • Your monthly report should currently reflect the correct number of legacy MRI and PET images that have been submitted to by your site to NACC.

    • There were previously some errors in these counts due to a bug. However, we believe all errors with counts of images at NACC have now been corrected. If you experience an error, please reach out to nacchelp@uw.edu.

  • How will MR/PET image submissions be tracked in the future?
    As NACC completes its transition onto our new modern data platform, we will launch the following resources:

    ADRC Portals

    The ADRC Portals will provide ADRCs with self-service access to view, download, and audit their real-time data. These portals will replace inefficient static monthly reports with modern real-time ADRC-specific data portals (ADRC Portals), fulfilling an emergent request from ADRCs to have better access to their data submissions.

    The ADRC Portals will provide ADRCs with access to six core data/metadata types:

    • UDS

    • Neuropathology

    • Non-standard MRI/PET

    • Standard MRI/PET

    • Biospecimen (NCRAD) and Genetic/genomic (NIAGADS)

    • Participant Diversity Metrics

    NACC is currently working to build the ADRC Portals within NACC's new Data Platform (powered by Flywheel). Flywheel will support the need to make this data accessible only to designated ADRC representatives, requiring management by ADRC personnel and the technology platform to allow access control for appropriate viewers. NACC is using user centered design to develop dashboards to adapt the Flywheel interface to the ADRC programs' unique needs.

    Data Portal overview
    Overview of the ADRC Data Portals that will allow for each center to have self-service access to their patient UDS, neuropathology, non-standard MRI/PET, diversity metrics, ADRC standard MRI/PET, and specimen/marker/genetic metadata.

    NACC's new Data Platform

    The NACC Data Platform (NACC DP) that will integrate a host of existing and new standardized and longitudinal data streams from across the ADRC Program as well as metadata and analysis from partner organizations and initiatives, with all data streams linked by NACC Identifiers (NACC IDs). The NACC DP will include a variety of data search and access interfaces including the Data Front Door, ADRC Data Portals, and the NIA Portal.

    These systems have been designed with an eye towards needing a modern tools that will not only accommodate our existing long-standing data streams such as the Uniform Data Set (UDS), neuropathology reports, and non-standard MRI/PET but that will also scale to accommodate and share innovative new data streams such as standardized imaging data, digital neuropathology, and digital biomarkers, and that can integrate complementary metadata and analysis data for standardized MRI/PET imaging (SCAN/LONI), genetic/genomic (NIAGADS) and biomarker (NCRAD) data from other ADRD data repositories, with all data streams linked by NACC unique identifiers (NACC IDs).

    The transition to this new data platform will begin by giving access to ADRC portals in which each center will be able to access their data and view dashboards allowing them to track their contributions to the ADRC program. NACC will increasingly add functionality to these portals, ultimately replacing old processes like emailed monthly reports.

  • How are identifiers used for SCAN data?

    When submitting MRI/PET images to SCAN via the LONI uploader, you are currently asked to enter the Subject ID or PTID. This number is different from the NACCID as described below:

    • Subject ID or PTID: this is the ADRC-managed participant ID, or "local ID". Formats vary by ADRC.

    • NACCID: this is the NACC-managed participant ID. It is a string with the prefix 'NACC' followed by 6 digits.

    • ADCID: this is the NACC-managed center ID. This is a two-digit number.

    Each PTID and ADCID pair maps to a unique NACCID.

  • How will ADRCs contributing data to SCAN be acknowledged?

    NACC will build off the current NACC Data Use Agreement (DUA) policy to provide researchers with a comprehensive list of ADRCs and other related grants who have contributed their data to SCAN. All researchers and person(s) requesting data from NACC (including SCAN data in the future) must accept the NACC DUA policy.

    The current NACC DUA policy requires authors to include the following statement acknowledging the NACC grant and Center support in presentations and the acknowledgments section of manuscripts:

    The NACC database is funded by NIA/NIH Grant U24 AG072122. NACC data are contributed by the NIA-funded ADRCs: P30 AG...., etc.

    If your site is involved in the SCAN initiative and you have additional grants or updates to include in the acknowledgements, please reach out to naccmail@uw.edu.

  • FAQs for ADRCs participating in SCAN