2026 - Thesis - Accelerate 3D Brain Mapping

Alzheimer's Disease, warp


Readings


1. Comparison between Conventional Structural MRI and Quantitative Susceptibility Mapping (QSM MRI)

Property Conventional Structural MRI (e.g., T1/T2) Quantitative Susceptibility Mapping (QSM MRI)
Signal origin Measures proton relaxation properties (T1 and T2 relaxation times) following RF excitation. Measures phase shifts induced by local variations in the proton Larmor precession frequency.
Primary contrast mechanism Differences in longitudinal and transverse relaxation of hydrogen protons. Local magnetic field perturbations caused by tissue magnetic susceptibility.
What it depicts Macroscopic anatomical structures (e.g., gray matter–white matter boundaries, cortical thickness). The absolute magnetic susceptibility (χ) distribution of tissue.
Physical nature Qualitative or semi-quantitative signal intensity (relative brightness or darkness). Quantitative physical parameter expressed in parts per million (ppm).
Biophysical interpretability Indirect and non-specific; contrast reflects multiple tissue properties simultaneously. Directly linked to underlying biophysical sources of magnetism in tissue.
Sensitivity to pathology Sensitive to gross structural changes such as atrophy or lesions, but largely insensitive to early molecular pathology. Highly sensitive to paramagnetic substances (e.g., iron deposition) and diamagnetic components (e.g., calcification or protein aggregates).


2. Model Structures

- Comparison of Contributions under Medical Saliency Perspective (ADNI, Amyloid Mapping)
- The core model is a voxel-wise mapping fθ: X → Y, where learning implicitly assigns region-aware
saliency weights over 3D brain structures to disentangle amyloid-related signals from QSM inputs.
Medical Fact / Aspect Modeling Requirement
Amyloid deposition is regionally distributed (e.g., cortex, hippocampus) Must incorporate region-level context
Dense 2D feature descriptors per pixel Limited usefulness for 3D brain modeling
Designed for 2D images Not suitable for volumetric data
Local implicit saliency (pixel-level peaks) Only partially useful
No anatomical structure modeling Not useful for medical interpretation
Local neighborhood only Insufficient for global brain structure
No region-level context Not useful for AD modeling
Local feature correspondence Moderately useful
Image matching / retrieval objective Poor fit for medical regression tasks
No disentanglement of mixed signals Not useful
Not scalable to 3D brain volumes Not usable
Local feature inspiration only Minor contribution
Pixel importance (local saliency) Weak interpretability
3D voxel-based representation Highly useful for brain modeling
Native 3D modeling Fully aligned with volumetric data
Region-aware implicit saliency Critical for amyloid prediction
Encodes spatial brain structure Essential for medical interpretation
Captures 3D spatial dependencies Essential
Supports region-level aggregation Highly useful
Voxel-wise mapping function fθ(X) Core modeling requirement
3D regression / field prediction Strong fit for ADNI task
Implicit signal separation via structure Useful
Efficient volumetric processing Highly useful
Direct voxel-wise amyloid prediction Major contribution
Region-aware voxel importance Critical for interpretability


3. Medical Principles for Amyloid Prediction

Medical Fact Modeling Requirement
Amyloid deposition is regionally distributed (e.g., cortex, hippocampus) Must incorporate region-level context
QSM signals are mixed (iron + amyloid) Must perform signal disentanglement
PET provides voxel-wise ground truth Must support voxel-wise prediction
Alzheimer’s disease progression is network-level Must capture cross-voxel dependencies




4. Coding


5. Alzheimer’s Disease Neuroimaging Initiative (ADNI)

  • A large-scale longitudinal multi-center study initiated in 2004. The dataset includes 3D brain MRI and PET images with associated diagnostic labels and clinical metadata, and is publicly available via the ADNI Image and Data Archive under a data use agreement
  • ADNI Database
  • The essence of Alzheimer’s disease (AD) is the breakdown of neuronal connections caused by the deposition of amyloid plaques at the microscopic level, PATHFINDER (bioRxiv 2025) addresses how to precisely reconstruct damaged neurons, QSM/MRI Framework (Arxiv 2503) addresses how to quantify plaque burden in vivo using imaging
  • Data alignment: Microscopic data (PATHFINDER) and MRI data (ADNI) differ in spatial scale by several orders of magnitude. Instead of directly feeding them into the same model, you need to learn their representation mapping, 3D U-Net or A Medical GAN
  • Python + PyTorch (deep learning) + ANTs (image registration) + MEDI (QSM reconstruction)
  • Based on 3D deep learning, Spatial Mapping Reconstruction from QSM magnetic signals to Amyloid pathological signals is achieved, Why:
    • PET scan: Can directly visualize amyloid plaques in the brain, but it is expensive, involves radiation, and is not available in many hospitals
    • QSM MRI (Input): A newer MRI technique, highly sensitive to magnetic materials in the brain (such as iron deposits and plaques). It is inexpensive and safe
    • Thesis task: Use AI to find patterns between QSM signals and PET plaque distribution.


ADNI Cohort
│
├── QSM MRI (in vivo)
│     ├── QSM reconstruction & normalization
│     ├── Spatial registration to PET space
│     └── 3D volume cropping / resampling
│
├── Amyloid PET (reference standard)
│     ├── ADNI-standard preprocessing
│     ├── Intensity normalization
│     └── Co-registration with QSM
│
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3D QSM Volume
│
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Encoder: BrainIAC-Pretrained 3D Vision Transformer
│   (global contextual representation learning)
│
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Latent Cross-Modal Representation
│
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Alignment Module
│   (Conditional Diffusion or GAN-based refinement)
│
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Decoder
│
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Predicted Amyloid Burden Map
(continuous voxel-wise 3D estimate)
│
â–Ľ
Loss Optimization
│   ├── Structural Similarity (SSIM)
│   ├── Perceptual Loss (VGG-based)
│   └── Intensity Consistency Loss
│
â–Ľ
Voxel-wise Quantification of Cerebral Amyloid Plaque Burden


Overview of the ADNI Dataset

Item Description
Study Name Alzheimer’s Disease Neuroimaging Initiative (ADNI)
Start Year 2004
Current Phase ADNI4
Phases ADNI1, ADNIGO, ADNI2, ADNI3, ADNI4
Study Type Longitudinal, multi-center, multi-modal
Primary Goal Early detection and progression modeling of Alzheimer’s disease
Access IDA portal (login + Data Use Agreement required)


Participant Identifiers and Longitudinal Indexing

Field Description Usage
PTID Participant ID (format: XXX_S_XXXXX) Primary key across all tables
RID Numeric subject ID derived from PTID Easier joins and indexing
VISDATE / EXAMDATE / SCANDATE Visit / exam / scan date Temporal alignment for longitudinal analysis
Phase Indicator ADNI1 / GO / 2 / 3 / 4 Cohort and protocol stratification


Diagnostic Group Distribution

Group Description Number of Subjects
CN Cognitively Normal 1,272
SMC Significant Memory Concern 97
EMCI Early Mild Cognitive Impairment 315
LMCI Late Mild Cognitive Impairment 180
MCI (total) EMCI + LMCI 1,006
AD Alzheimer’s Disease 523
Total Patients All non-CN subjects 141


Neuroimaging Data (Raw and Processed)

Modality Access Path Format Dimensionality Typical Use
Structural MRI Advanced Image Search DICOM / NIfTI 3D Brain atrophy analysis, 3D CNN
Functional MRI Advanced Image Search NIfTI 4D Functional connectivity
Amyloid PET Advanced Image Search DICOM / NIfTI 3D Amyloid burden estimation
FDG-PET Advanced Image Search DICOM / NIfTI 3D Glucose metabolism analysis
Pathology Slides Advanced Image Search Whole-slide images 2D/3D Neuropathological validation


Brain Signals (Why Median + MAD)

Property Meaning Impact
Non-stationary The mean varies across time and sessions Mean and standard deviation become unstable
Heavy-tailed distribution Strong artifacts or high-amplitude spikes Standard deviation is inflated by outliers
Weak signal + mixed noise High-frequency oscillations + low-frequency drift Large mean variation, clear skewness
Inter-channel variation Each sensor has different sensitivity Requires independent per-channel normalization


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