Table 2.

Summary of methodological barriers for the harmonization of multicentric neuroimaging protocols in the context of ND reported in the survey and actions proposed to address them

Neuroimaging modality	Perceived barriers	Actions to address barriers
MRI	•Unclear recommendations for acquisition and analyses details for multivendor protocols using state-of-the-art equipment •Unclear quality control guidelines and reference values in the context of different markers •Unclear recommendations for retrospective harmonization of existing data acquired with different protocols	•Harmonize multivendor state-of-the-art acquisition and quality assurance. In particular three-dimensional anatomic and quantitative tissue mapping (e.g., susceptibility, tissue relaxation, myelin, and so forth), advanced structural (diffusion), and functional (resting state) connectivity •Quantify reproducibility for different markers •Standardize quality assurance for different markers. Evaluate optimal markers for different ND types, stages, and experimental designs (cross-sectional or longitudinal) •Standardization of retrospective MRI data harmonization strategies
PET-SPECT	•Lack of harmonization for analysis tools and quantification (FDG-PET, amyloid PET, tau PET, and dopaminergic PET/SPECT) •Lack of standardization across amyloid PET tracers •Lack of public normative reference data, especially healthy volunteers •Lack of PET-SPECT comparisons (dopaminergic tracers)	•Harmonize multivendor image reconstruction parameters and quantification •Develop public databases of normal and ND patients (uniform with respect to acquisition and quantification) •Create centralized analysis platforms for widely available markers lacking standardization of analysis such as FDG and dopaminergic markers
EEG	•Lack of standardization of spectral source EEG analysis and high-resolution recordings •Lack of quality assurance standardization (ocular motion and cardiac artifacts) •Lack of clarity of the limits and opportunities of EEG biomarkers for NDs	•Harmonize multivendor state-of-the-art acquisition and quality assurance EEG protocols •Harmonize biomarker extraction using spectral or time-domain analysis: resting state (eyes open/closed) and event related (oddball, and so forth) •Quantify test-retest reliability from multivendor EEG data •Evaluate best biomarkers for different NDs and experimental designs (cross-sectional, longitudinal)

Abbreviations: EEG, electroencephalography; MRI, magnetic resonance imaging; ND, neurodegenerative diseases; PET, positron emission tomography; SPECT, single-photon emission computed tomography.