MRI Brain — Dedicated Protocol for Alzheimer's Disease (AD)
MRI Brain — Dedicated Protocol for Alzheimer's Disease (AD)
MRIninja Knowledge Base | Child Protocol Page Parent page: Brain MRI — Generic Standard Protocol Version 1.0 — May 2026
1. Executive Summary
Alzheimer's disease represents a fundamentally different imaging challenge from any structural brain pathology covered in the master protocol page. The generic brain MRI protocol is designed to detect focal lesions — tumours, infarcts, demyelination, haemorrhage. AD, by contrast, is a diffuse neurodegenerative disease whose MRI signature is not a lesion but a pattern: the progressive, regionally selective loss of cerebral cortex and hippocampal volume, evolving over years, embedded in an ageing brain with multiple co-pathologies. Reading a brain MRI for AD requires a fundamentally different interpretive framework, dedicated quantitative or semi-quantitative volumetry, and a different set of sequences than those used for routine neurological indications.
MRI in the AD diagnostic pathway serves three distinct functions: (1) exclusion of alternative causes of dementia — this function is fulfilled by the master protocol; (2) pattern recognition of AD-typical neurodegeneration (medial temporal lobe atrophy, posterior cortical predominance) — this requires dedicated coronal planes and volumetric sequences; (3) biomarker-level characterisation — quantitative hippocampal volumetry, amyloid-sensitive SWI, and white matter change grading that support the ATN (Amyloid/Tau/Neurodegeneration) biomarker framework [1].
The clinical context has changed substantially with regulatory approval of anti-amyloid immunotherapy (lecanemab FDA 2023, donanemab FDA 2024) [2, 3]. These treatments require MRI safety monitoring for amyloid-related imaging abnormalities (ARIA) — a new category of MRI indication that demands specific SWI/GRE sequences, specific ARIA grading terminology, and specific follow-up protocols that do not exist in the generic brain MRI protocol.
Prerequisite: the reader is assumed to be familiar with the Brain MRI Generic Standard Protocol on MRIninja, which covers universal safety, preparation, positioning, and standard sequence design.
1.1 Added Value Over the Generic Protocol
The dedicated AD protocol adds:
- Coronal 3D high-resolution T1 optimised for hippocampal volumetry (MPRAGE/BRAVO at 1 mm isotropic or better, replacing 2D T1 from the generic protocol)
- Visual rating scale application (MTA scale, GCA scale, PA scale) — systematic regional atrophy assessment requiring specific plane and resolution
- SWI dedicated for microhaemorrhage and cortical superficial siderosis — ARIA monitoring in patients on anti-amyloid therapy
- FLAIR optimised for white matter hyperintensity (WMH) grading (Fazekas scale) — a co-pathology with direct diagnostic and prognostic implications
- DWI interpretation specific to Creutzfeldt-Jakob disease exclusion — CJD is the most dangerous AD mimic and requires DWI to be read with the cortical ribbon sign in mind
- ARIA grading framework (ARIA-E and ARIA-H monitoring protocol) for patients on lecanemab or donanemab
The dedicated protocol removes or deprioritises: gadolinium contrast (rarely indicated in typical AD assessment); post-contrast T1 (not a routine AD sequence unless ARIA-E assessment is needed); standard T2 TSE axial (replaced by the coronal 3D T1 as the primary morphometric sequence).
1.2 Limits of the Dedicated Protocol
MRI cannot diagnose AD with certainty — amyloid and tau PET provide direct molecular biomarkers that MRI cannot replicate. Structural MRI detects the neurodegeneration ("N") biomarker of the ATN framework but does not directly detect amyloid ("A") or tau ("T"). A normal structural MRI does not exclude AD, particularly in early or atypical presentations (logopenic variant, posterior cortical atrophy, frontal variant). For these presentations, amyloid PET or CSF biomarkers (Aβ42/40 ratio, p-tau181, total tau) are the definitive diagnostic tools. MRI in these contexts serves to exclude alternative diagnoses and to provide the atrophy pattern that supports the molecular diagnosis.
2. Clinical Context and Pre-Test Information
2.1 Clinical Presentation Relevant to MRI
The typical AD patient referred for dedicated brain MRI presents with: progressive episodic memory loss over ≥ 6 months; age ≥ 60 years (early-onset AD peaks at 50–65); preserved daily function early then declining; neuropsychological testing showing hippocampal-pattern memory impairment. However, atypical presentations are increasingly recognised:
Posterior cortical atrophy (PCA): visuospatial dysfunction, alexia, apraxia — often misdiagnosed as ocular disease for months. MRI shows predominantly posterior (parieto-occipital, posterior temporal) cortical atrophy with relative sparing of the hippocampus.
Logopenic variant primary progressive aphasia (LvPPA): word-finding difficulties, slow speech — predominantly left temporal-parietal atrophy.
Frontal variant AD (bvAD): disinhibition, apathy — frontal and anterior temporal atrophy, mimicking FTD.
These variants require specific regional atrophy assessment that the standard coronal-hippocampal view does not adequately cover. The radiologist must know the clinical syndrome before reading the MRI.
In patients starting or already on anti-amyloid therapy (lecanemab, donanemab): the primary MRI question changes completely — from diagnosis to ARIA safety monitoring. These patients require SWI and T2-FLAIR specifically to detect ARIA-E (vasogenic oedema/effusion, appearing as FLAIR white matter or gyral signal, and fluid in sulci or meninges) and ARIA-H (microhaemorrhages or cortical superficial siderosis on SWI/GRE) [4, 5].
2.2 Pre-Test Information the Radiologist and Technologist Must Know
| Item | Clinical relevance for the AD protocol |
|---|---|
| Neuropsychological test results (MMSE, MoCA, CDR) | Calibrates expected atrophy severity; CDR 0.5 → mild impairment, CDR 2–3 → severe |
| Amyloid PET or CSF Aβ42/40 result | If amyloid-negative, AD is less likely; redirects to other dementias |
| Clinical syndrome (typical amnestic vs PCA vs LvPPA vs frontal) | Determines the primary atrophy region to assess |
| Anti-amyloid therapy status (lecanemab, donanemab) | Triggers ARIA monitoring protocol — mandatory SWI; specific ARIA-E FLAIR |
| APOE ε4 genotype | ARIA-H risk is higher in ε4 carriers; affects ARIA threshold for treatment modification |
| Prior brain MRI date | Essential for comparison; progression rate is diagnostically valuable |
| Relevant vascular risk factors | Affects WMH burden interpretation (Fazekas grade) |
| Relevant comorbidities (renal failure, hepatic failure) | Gadolinium — rare indication in AD; standard preparation rules apply |
2.3 Differential Diagnosis Landscape
The dedicated AD protocol must be designed to distinguish AD from:
- Vascular cognitive impairment (VCI): subcortical ischaemic dementia with white matter hyperintensities, lacunes, strategic infarcts — differentiated by WMH pattern and hippocampal sparing until late
- Lewy body dementia (DLB): parietal > medial temporal atrophy; visual hallucinations; DaTscan abnormal — MRI less specific; dopaminergic imaging is the key discriminator
- Frontotemporal dementia (FTD/bvFTD/semantic variant): frontal and anterior temporal atrophy predominance; knife-blade cortical thinning; TDP-43 or tau pathology
- Creutzfeldt-Jakob disease (CJD): rapid progression (weeks); cortical ribbon sign on DWI (restricted diffusion in cortex and basal ganglia); prion disease — DWI is the critical sequence
- Normal pressure hydrocephalus (NPH): triad of gait, continence, cognition; dilated ventricles disproportionate to sulcal atrophy; Evans index > 0.3
- Cerebral amyloid angiopathy (CAA): cortical microbleeds (posterior predominance), cortical superficial siderosis on SWI — overlaps with AD (amyloid angiopathy and AD co-occur in 30–50%)
3. Indications, Appropriateness and Imaging Pathway
3.1 When the Dedicated Protocol Is Indicated
The dedicated AD protocol is indicated when:
- First-time dementia workup in a patient with cognitive symptoms meeting MCI or dementia criteria
- Follow-up of a known MCI patient to assess atrophy progression
- Pre-treatment baseline before anti-amyloid immunotherapy initiation (mandatory)
- ARIA monitoring during anti-amyloid immunotherapy (every 2–4 weeks for the first 14 infusions per FDA label monitoring protocols [4, 5])
- Atypical dementia syndrome requiring pattern atrophy assessment (PCA, LvPPA, frontal variant)
- Biomarker imaging for clinical trial eligibility
The ACR Appropriateness Criteria [6] list MRI brain as "usually appropriate" for initial evaluation of dementia. The Society for Nuclear Medicine (SNMMI) and the Alzheimer's Association guidelines [1] endorse structural MRI as the first-line imaging investigation.
3.2 When the Generic Master Protocol Is Sufficient
The generic brain MRI protocol is sufficient when: the clinical question is exclusion of a treatable cause of cognitive decline (tumour, hydrocephalus, subdural haematoma, encephalitis) rather than AD-specific characterisation. In emergency or acute settings, the generic protocol adequately excludes these reversible causes.
3.3 When Further Sub-Specialised Protocols Are Required
- Amyloid PET (florbetapir, flutemetamol, florbetaben): when AD diagnosis requires confirmation of amyloid burden; when biomarker-level diagnosis is needed for treatment eligibility; when structural MRI is atypical and the syndrome is uncertain
- FDG-PET: superior to MRI for dementia subtype classification in complex cases; parietotemporal hypometabolism in AD; frontal hypometabolism in bvFTD
- DaTscan/I-123-ioflupane SPECT: DLB vs AD when visual hallucinations and parkinsonism are features
- Post-amyloid therapy ARIA follow-up sub-protocol: if ARIA develops, a more frequent monitoring protocol with specific SWI parameter adjustment may be required
3.4 Red Flags Modifying Urgency or Protocol
| Clinical red flag | Protocol or pathway adjustment |
|---|---|
| Rapid cognitive decline (weeks rather than months) | Priority DWI for CJD cortical ribbon sign; add DWI as first sequence |
| Focal neurological deficit + cognitive decline | Generic protocol first to exclude structural lesion; then AD protocol if structural cause excluded |
| Active anti-amyloid therapy + headache or vision changes | Emergency ARIA protocol: FLAIR + SWI within 24 hours |
| ARIA grade ≥ 2 on monitoring MRI | Clinical consultation before next infusion; modify monitoring frequency |
| New seizure in known AD patient on anti-amyloid therapy | Urgent MRI within 24 hours for ARIA-E |
| Age < 60 with cognitive symptoms | Early-onset AD or genetic AD — add comprehensive atrophy protocol; consider genetic counselling pathway |
4. Dedicated Protocol Design
4.1 Protocol Delta vs the Master Protocol
| Element | Master generic protocol | Dedicated AD protocol | Rationale |
|---|---|---|---|
| 3D T1 (MPRAGE/BRAVO) | 1 mm isotropic standard | ≤ 1 mm isotropic, maintained across follow-up | Reproducible hippocampal volumetry; Visual rating application |
| T2 TSE axial | Standard axial T2 | Retained for WMH and structural assessment | No modification; complement to FLAIR |
| FLAIR | Standard 2D or 3D FLAIR | 3D FLAIR mandatory (per ARIA monitoring guidelines [4, 5]); FLAIR used for Fazekas WMH grading | ARIA-E appears as FLAIR-bright; Fazekas requires full-brain FLAIR |
| DWI | Standard | DWI mandatory with high-b variant (b=1000–1500); cortical ribbon sign assessment | CJD exclusion is mandatory in any dementia workup |
| SWI | Not routine in generic protocol | SWI mandatory | ARIA-H monitoring; microbleed count; CAA pattern; cortical superficial siderosis |
| Gadolinium | Conditional in generic | Not routinely indicated for structural AD assessment; indicated for ARIA-E characterisation when FLAIR is ambiguous | AD structural assessment is non-contrast; ARIA-E may need contrast clarification |
| Coronal plane (T1) | Optional in generic | Coronal reformat from 3D T1 mandatory for hippocampal and parahippocampal assessment | MTA scale requires coronal plane perpendicular to hippocampal long axis |
| Coverage | Standard brain | Full brain including temporal poles | Anterior temporal atrophy important in semantic variant FTD differential |
4.2 Mandatory Dedicated Sequences
| # | Sequence | Plane | Status | Disease-specific purpose |
|---|---|---|---|---|
| 1 | 3D T1-weighted (MPRAGE/BRAVO/TFE) ≤ 1 mm isotropic | Sagittal acquisition; coronal reformat | Mandatory | Hippocampal volume; MTA scale; GCA scale; atrophy pattern |
| 2 | 3D FLAIR | Axial acquisition | Mandatory (modern protocol) | WMH burden (Fazekas); ARIA-E detection; periventricular vs subcortical WMH distribution |
| 3 | DWI (b=0/1000) + ADC | Axial | Mandatory | CJD cortical ribbon exclusion; DWI restriction in CJD vs AD |
| 4 | SWI or T2* GRE | Axial | Mandatory | ARIA-H microbleed count; CAA pattern; cortical superficial siderosis |
| 5 | T2 TSE | Axial | Mandatory | Structural lesion exclusion; hippocampal T2 signal; vascular lesions |
| 6 | Coronal reformat from 3D T1 | Coronal (perpendicular to hippocampal long axis) | Mandatory | MTA visual rating; hippocampal height measurement |
4.3 Conditional and Advanced Sequences
| Sequence | When to add | Plane | Added value |
|---|---|---|---|
| Post-contrast FLAIR (1–3 min post Gd) | ARIA-E suspicion; ambiguous FLAIR white matter change on lecanemab/donanemab; suspected encephalitis | Axial | Confirm enhancement in sulci/meninges for ARIA-E; leptomeningeal enhancement pattern |
| Post-contrast T1 (standard) | Atypical dementia; suspected tumour or encephalitis; first-time presentation with rapid progression | Axial | Meningeal/cortical enhancement; exclude inflammatory/infectious cause |
| ASL perfusion (pCASL) | Research setting; atypical syndrome; FDG-PET unavailable | Axial | Parietotemporal hypoperfusion pattern in AD; frontal pattern in bvFTD — expert practice, not standard |
| Quantitative hippocampal volumetry (automated) | When available (post-processing); clinical trial; treatment monitoring | 3D from MPRAGE | Quantitative volume vs age-matched normative database; more sensitive than visual rating |
| MR spectroscopy (NAA/Cr, mI/Cr) | Research; equivocal MCI vs normal — very limited clinical utility | MRS: posterior cingulate, hippocampus | NAA reduction + myo-inositol elevation in AD — limited routine clinical adoption |
| DWIBS / high-b DWI (b=1500) | Suspected CJD with typical rapid progression | Axial | Cortical ribbon and basal ganglia restriction in CJD more conspicuous at high b-value |
4.4 Disease-Specific Sequence Rationale
4.4 Rationale per Disease-Specific Sequence
3D T1 isotropic — Hippocampal Volumetry
The 3D T1-weighted acquisition (MPRAGE, BRAVO, or TFE at ≤ 1 mm isotropic) is the foundational sequence for AD-specific structural assessment. The generic brain MRI T1 sequence serves primarily for contrast enhancement and anatomy; for AD, its primary purpose is hippocampal volume assessment — enabling both visual rating (MTA scale) and, in equipped centres, automated volumetry.
For visual rating, the coronal reformat must be perpendicular to the long axis of the hippocampus (described in Section 4.5). The MTA score is assessed on these true coronal sections at the level of the mamillary bodies — only this specific angulation provides the correct view of hippocampal height and width required for the validated scale.
The 3D isotropic acquisition is mandatory (not optional) for AD assessment because: (a) it enables retrospective reformatting in any plane including the coronal-oblique hippocampal plane; (b) it provides reproducible volumetry for follow-up comparison; (c) 2D coronal T1 sequences, while useful for visual rating, do not provide the full-brain atrophy pattern assessment nor the volumetric data needed for trial-grade or treatment-grade monitoring.
SWI — ARIA-H and Microbleed Assessment
SWI in AD differs from its generic use (haemorrhage, cavernoma) in two disease-specific ways:
First, ARIA-H monitoring: lecanemab and donanemab cause ARIA-H (microhaemorrhages and cortical superficial siderosis) as a treatment side effect mediated by amyloid clearance from vessel walls. ARIA-H appears on SWI as new focal dark spots (< 10 mm = microbleed; linear cortical dark signal = superficial siderosis). The ARIA grading system [4] defines:
- ARIA-H grade 0: no new microbleeds or superficial siderosis
- ARIA-H grade 1: 1–4 new microbleeds
- ARIA-H grade 2: 5–9 new microbleeds
- ARIA-H grade 3: 10+ new microbleeds or > 2 sulci with superficial siderosis
Serial comparison between ARIA-H monitoring MRIs requires identical SWI parameters (TE, slice thickness, B0 field) — even minor parameter changes alter microbleed count and confound the ARIA safety assessment.
Second, CAA pattern vs ARIA-H: cerebral amyloid angiopathy (frequent co-pathology in AD) produces posterior-predominant cortical/juxtacortical microbleeds that are indistinguishable from ARIA-H on SWI. The distinction (prior CAA microbleeds from new ARIA-H) requires careful comparison with the mandatory pre-treatment baseline SWI — any centre starting anti-amyloid therapy must document the pre-treatment microbleed count and pattern as the reference for subsequent monitoring.
3D FLAIR — ARIA-E and WMH Assessment
ARIA-E (vasogenic oedema/effusion) appears on FLAIR as:
- Subcortical or deep white matter FLAIR hyperintensity (new or expanding)
- Gyral FLAIR signal in the cortex (cortical oedema)
- Sulcal FLAIR hyperintensity (meningeal effusion)
- T2 hyperintensity on T2 TSE in the same distribution
The FLAIR in AD serves dual function: ARIA-E detection and Fazekas WMH grading. These serve different clinical purposes and require different interpretive approaches. The ARIA-E detection requires direct comparison with the pre-treatment baseline FLAIR; the Fazekas WMH assessment is a standalone rating.
ARIA-E grading [4]:
- Mild: FLAIR hyperintensity in 1 region, ≤ 5 cm in any dimension
- Moderate: 2 regions, or > 5 cm in 1 region
- Severe: 3+ regions, or > 10 cm in any region; sulcal involvement
3D FLAIR is preferred over 2D for ARIA monitoring because: isotropic voxels enable the detection of small gyral ARIA-E lesions that fall between 2D slices; the absence of inter-slice gaps eliminates the coverage blind spots that are clinically critical in ARIA monitoring; sulcal ARIA-E (meningeal effusion) is better depicted on 3D isotropic.
DWI — Cortical Ribbon Sign (CJD Exclusion)
In any dementia workup, DWI is mandatory to exclude CJD. The cortical ribbon sign — bilateral restricted diffusion along cortical ribbons in multiple lobes — is pathognomonic for sporadic CJD and is invisible on T2/FLAIR in the early stages when DWI is already strongly positive. This sign differs from the restricted diffusion of acute infarcts (vascular territory, matches vessels, unilateral) and from diffuse cortical DWI signal in hypoxic-ischaemic injury (follows ischaemic pattern, clinical context).
In AD, DWI is negative — no cortical restriction, no basal ganglia restriction. Any cortical DWI restriction in a patient referred for AD evaluation mandates urgent CJD pathway activation.
4.5 Dedicated Planes, FOV, Resolution and Coverage
Coronal-oblique plane for hippocampal assessment: the coronal reformat from the 3D T1 must be prescribed perpendicular to the long axis of the hippocampus. The hippocampal long axis runs approximately from anterolateral (head) to posteromedial (tail). On the axial 3D T1 at the level of the temporal horns, the hippocampus appears as a C-shaped structure; the long axis is oriented approximately 15–25° oblique to the standard coronal plane. The coronal-oblique sections perpendicular to this axis provide the validated plane for the MTA scale — at the level of the mammillary bodies, showing the hippocampal height (the distance from the floor of the temporal horn to the superior surface of the hippocampus).
Coverage: full brain coverage is mandatory — from the vertex to the skull base including the temporal poles. The temporal poles (anterior temporal cortex) are the site of early atrophy in semantic variant FTD (a differential) and must be within the field of view.
Slice thickness for visual rating: 1 mm isotropic from 3D T1 enables reformatting at any thickness. For visual rating (MTA scale), the coronal sections displayed at 1 mm are optimal; some centres use 1.5 mm for visual rating to reduce noise-related pseudo-thinning.
SWI coverage and resolution: for ARIA monitoring, SWI must cover the full brain at ≤ 2 mm slice thickness. The detection of cortical superficial siderosis requires 1.5–2 mm coverage to resolve the thin cortical signal. The standard SWI protocol from the MRIninja SWI sequence page applies, with the specific requirement that the parameters be identically reproduced at every monitoring MRI.
4.6 Contrast Strategy Specific to AD
Routine structural AD MRI does not require gadolinium. The diagnostic signatures of AD (hippocampal atrophy, white matter hyperintensities) are visible on non-contrast sequences. Contrast provides no additional value for hippocampal volumetry, MTA rating, or Fazekas WMH grading.
Gadolinium is indicated in the AD context for:
- ARIA-E with ambiguous FLAIR appearance — post-contrast FLAIR (meningeal enhancement confirms effusion) and post-contrast T1 (cortical enhancement in severe ARIA-E)
- Atypical rapid dementia where CNS vasculitis, autoimmune encephalitis, or neoplastic leptomeningeal disease must be excluded
- First-time dementia presentation with fever or CSF pleocytosis (encephalitis protocol)
STIR post-gadolinium is contraindicated as in all MRIninja protocols.
4.7 Sequence Matching, Reproducibility and Follow-Up
For AD monitoring (whether clinical follow-up or ARIA monitoring), identical acquisition parameters must be maintained at every examination:
For ARIA monitoring (anti-amyloid therapy), the FDA-approved labels for lecanemab [4] and donanemab [3] specify MRI monitoring at: baseline (before treatment); weeks 4–8 (after first infusions); then every 2–4 weeks during the early infusion period. The monitoring MRI must use the same scanner (or equivalent field strength), the same SWI and FLAIR parameters, and must be compared directly to the pre-treatment baseline.
For longitudinal atrophy monitoring (clinical progression or trial), the MPRAGE/BRAVO must be acquired at the same field strength, with the same TR/TI/TE and flip angle, to ensure that automated volumetry tools (FreeSurfer, Clinica) produce reproducible hippocampal volume measurements across timepoints. A change in MPRAGE parameters between baseline and follow-up invalidates automated volumetric comparison.
5. MRI Semiotics — Disease-Specific Imaging Findings
5.1 Direct Signs
Medial temporal lobe atrophy (MTA): the hallmark of typical AD. On coronal-oblique T1:
- Widening of the choroidal fissure (the space between the hippocampus and the thalamus superiorly)
- Widening of the temporal horn of the lateral ventricle
- Reduction in hippocampal height (from temporal horn floor to hippocampal superior surface)
- Parahippocampal gyrus atrophy (the cortex medial to the collateral sulcus)
- Entorhinal cortex thinning (most anterior portion of the parahippocampal gyrus)
Critically: the entorhinal cortex shows the earliest atrophy in AD (preceding clinical symptoms by years), but is the most difficult to assess visually on standard clinical MRI. It requires sub-millimetre resolution to accurately measure. For clinical purposes, hippocampal height and the MTA scale are the validated visual tools.
Posterior cortical atrophy: in typical AD and especially in PCA variant, the parietal and posterior temporal cortices show thinning that is visible on 3D T1 as:
- Widening of the posterior-superior temporal sulcus
- Reduction in parietal lobe volume
- Thinning of the precuneus and posterior cingulate cortex
- Posterior > anterior distribution of sulcal widening
Generalised cortical atrophy (GCA): widespread cortical volume loss affecting all lobes, assessed on coronal and axial planes. Graded by the GCA scale (see Section 5.4).
Posterior atrophy (PA) score: specifically addresses posterior cortical atrophy pattern — assessed on axial T1 at the level of the parieto-occipital sulcus.
5.2 Indirect and Secondary Signs
White matter hyperintensities (WMH / leukoaraiosis): assessed by the Fazekas scale on FLAIR. WMH are a co-pathology (cerebral small vessel disease) frequently coexisting with AD. The Fazekas score (0–3 for periventricular WMH and deep WMH separately) provides the vascular burden co-assessment. High Fazekas scores (grade 3 deep WMH) suggest mixed dementia (AD + vascular) and affect prognosis and treatment decisions. Important: WMH do not distinguish AD from VCI alone — the pattern and distribution (periventricular caps vs deep irregular lesions) provide additional differential information.
Ventricular enlargement: enlargement of the temporal horns is a surrogate for medial temporal atrophy and can be assessed on axial T2 or FLAIR in addition to the coronal T1. Hippocampal atrophy leads to temporal horn dilatation and eventually to third ventricular widening as thalamic atrophy progresses.
Corpus callosum atrophy: the splenium (posterior) and body of the corpus callosum thin in parallel with posterior cortical atrophy. Sagittal T1 sections show this clearly. Significant callosal atrophy indicates more advanced or posterior-predominant disease.
Vascular lesions (lacunes, microbleeds): visible on T2 and SWI. Lacunes in the basal ganglia and white matter indicate concomitant small vessel disease. Microbleeds (SWI) may represent comorbid CAA — particularly if posterior-predominant (cortical/juxtacortical in the occipital and parietal lobes).
5.3 Severity, Extent and Activity Assessment
AD is a progressive neurodegenerative disease — there is no "activity" in the inflammatory sense. The severity is assessed by the degree of atrophy:
Mild (MCI stage): subtle MTA (MTA 1–2); posterior cortical sulcal widening; minimal WMH Moderate (early dementia): MTA 2–3; generalised cortical atrophy; progressive temporal horn enlargement Severe (late dementia): MTA 4; severe generalised atrophy; marked third and lateral ventricular enlargement; callosal thinning
The rate of progression (hippocampal volume loss approximately 3–6% per year in AD, vs 1–2% in normal ageing) is the most useful metric for tracking disease progression and distinguishing AD from normal ageing atrophy.
5.4 Validated Classification and Grading Systems
MTA Scale (Scheltens Scale) [7]:
| Score | Description |
|---|---|
| 0 | No atrophy |
| 1 | Only widening of the choroidal fissure |
| 2 | Also widening of temporal horn of lateral ventricle |
| 3 | Moderate loss of hippocampal volume (decrease of height) |
| 4 | Severe hippocampal volume loss |
Scoring is applied bilaterally. Age-adjusted threshold: MTA ≥ 2 abnormal for age < 75; MTA ≥ 3 abnormal for age ≥ 75. This age correction is clinically critical — applying a non-age-adjusted threshold overdiagnoses AD in the elderly [7].
Inter-reader reliability: κ approximately 0.7 (good to very good) in trained readers; reliability decreases for intermediate scores (MTA 1–2).
GCA Scale (Global Cortical Atrophy) [8]: grades generalised cortical atrophy on axial T1 or FLAIR:
- GCA 0: no atrophy
- GCA 1: mild (sulcal widening, no gyral involvement)
- GCA 2: moderate (gyral volume loss but gyri still present)
- GCA 3: end-stage (knife-blade gyri)
PA Scale (Posterior Atrophy) [9]: rated on axial T1 at the parieto-occipital sulcus level:
- PA 0: no atrophy
- PA 1: mild (sulcal widening)
- PA 2: moderate (gyral loss)
- PA 3: severe (complete posterior lobe volume loss)
PA ≥ 2 with relative MTA sparing suggests PCA variant or DLB rather than typical AD.
Fazekas Scale [10] for WMH on FLAIR:
- Score 0–3 for periventricular WMH (PWMH): 0=absent; 1=caps/pencil-thin lining; 2=smooth halos; 3=irregular WMH extending into deep WM
- Score 0–3 for deep WMH (DWMH): 0=absent; 1=punctate foci; 2=confluent beginning foci; 3=large confluent areas
Fazekas ≥ 3 (PWMH or DWMH) indicates significant cerebrovascular disease that requires separate clinical management consideration.
ARIA Grading (anti-amyloid therapy monitoring) [4]: as described in Section 4.4.
5.5 Differential Diagnosis on MRI
| Differential | Key MRI features for it | Key MRI features against AD | Decisive sequence or sign |
|---|---|---|---|
| Normal ageing | MTA 0–1; GCA 0–1; no posterior atrophy | Normal for age on all scales; no hippocampal atrophy | Age-adjusted MTA scale |
| Hippocampal sclerosis (ageing) | Bilateral hippocampal T2 signal increase; hippocampal atrophy without white matter change | T2-bright hippocampus > pure volume loss; often more asymmetric | T2 TSE coronal — hippocampal signal |
| Semantic variant FTD (svPPA) | Anterior temporal > posterior; asymmetric left temporal atrophy; temporal poles; knife-blade | Posterior > anterior; no knife-blade; posterior cingulate involvement | 3D T1 coronal — temporal pole assessment |
| bvFTD | Frontal and anterior temporal predominance; relatively preserved hippocampi; MTA ≤ 1 | AD: MTA ≥ 2; posterior > frontal | GCA + PA + MTA pattern combined |
| DLB | Posterior atrophy like PCA-AD; but MTA relatively preserved; requires DaTscan | AD: marked MTA; no DaTscan abnormality expected | DaTscan SPECT (outside MRI scope) |
| VCI | WMH-predominant; lacunes; microbleeds; relatively preserved hippocampi | AD: MTA >> WMH; no lacunar pattern required | Fazekas scale; MTA comparison |
| CJD | Rapid progression; cortical ribbon DWI restriction; basal ganglia DWI restriction; no significant atrophy | AD: DWI negative; slow progression | DWI — cortical ribbon sign pathognomonic for CJD |
| NPH | Dilated ventricles out of proportion to sulcal atrophy; Evans index > 0.3; tight high-convexity sulci; cingulate sulcus sign | AD: proportionate sulcal widening; no tight-sulcus sign | Evans index; sulcal pattern on FLAIR |
5.6 Mimickers, Pseudolesions and Normal Variants
Age-related hippocampal atrophy: normal hippocampal volume decreases approximately 1–2% per year after age 60. The MTA scale accounts for this with age-adjusted thresholds. Applying non-age-adjusted thresholds produces false-positive AD diagnoses in elderly patients.
Hippocampal T2 signal increase (mesial temporal sclerosis pattern): in patients with prior seizure history or in ageing hippocampal sclerosis, T2-bright signal increase within the hippocampus simulates — and coexists with — atrophy. This must be distinguished from pure AD atrophy: in mesial temporal sclerosis, the T2 signal increase is the primary finding; in AD, volume loss predominates with normal or minimally altered T2 signal.
Dilated perivascular spaces (DPVS): large DPVS in the midbrain and basal ganglia can appear as T2-bright foci simulating lacunes. They follow CSF signal on FLAIR (dark) whereas true lacunes show FLAIR-bright rims. This distinction is relevant in the AD context because large DPVS are increasingly recognised as a marker of amyloid angiopathy and early neurodegeneration [11].
Developmental abnormalities: hippocampal variants (sulcal remnant, malrotation) produce apparent asymmetric atrophy or abnormal shape that must be distinguished from true hippocampal atrophy. The hippocampal malrotation (HIMAL) appears as incomplete inversion with preserved volume — identifiable on coronal T1 by the typical morphological features (flat and round shape, abnormal sulcal pattern) without volume loss.
6. Reporting Framework Specific to This Pathology
6.1 Structured Reporting Template
Indication: cognitive symptoms [duration, clinical severity: MCI/dementia]; clinical syndrome [typical amnestic / PCA / logopenic / frontal variant]; prior MRI [date]; anti-amyloid therapy status [agent, cumulative infusions, prior ARIA events].
Technique: 3D T1-weighted MPRAGE ≤ 1 mm isotropic; 3D FLAIR; T2 TSE axial; DWI b=0/1000 with ADC; SWI; coronal reformat from 3D T1 perpendicular to hippocampal long axis; [gadolinium if administered: agent, dose, indication].
Comparison: [prior MRI date, field strength, institution; available for volumetric comparison: yes/no].
Findings:
Medial temporal lobe (bilateral): MTA score R __ / L __ (0–4); [age-adjusted normal/abnormal for age __] Temporal horn dilatation: mild/moderate/severe Entorhinal cortex: visually preserved/thinned
Hippocampal signal (T2): normal / increased (R/L/bilateral)
Posterior cortical atrophy: PA score: __ (0–3) Precuneus/posterior cingulate atrophy: absent/mild/moderate/severe Parieto-occipital sulcal widening: absent/present
Generalised cortical atrophy: GCA score: __ (0–3); distribution: generalised / predominantly frontal / predominantly temporal-parietal
White matter hyperintensities (FLAIR): Fazekas PWMH: __ / 3; Fazekas DWMH: __ / 3 Distribution: periventricular caps / subcortical punctate / deep confluent
Lacunes: absent / present (location, number)
Microbleeds (SWI): Count: __ ; distribution: lobar/posterior-predominant (CAA pattern) / deep/mixed Cortical superficial siderosis: absent / present (lobar: __ sulci involved)
DWI: no cortical or basal ganglia restricted diffusion / [positive: describe cortical ribbon sign if present]
Vascular structures: normal / incidental finding
Comparison with prior MRI [date]: [stable / interval progression: specify which regions and rating changes]
Impression: [MRI findings are / are not] consistent with AD-pattern neurodegeneration: medial temporal lobe atrophy [MTA R/L, age-adjusted: normal/abnormal]; [posterior cortical predominance suggesting PCA variant / typical amnestic pattern / frontal variant atrophy];
WMH burden: Fazekas total [score] — mild/moderate/severe cerebrovascular co-pathology;
Microbleed pattern [if present]: [posterior-predominant/lobar pattern consistent with / atypical for CAA; ARIA-H grade __ per treatment monitoring criteria];
No evidence of CJD cortical ribbon sign on DWI.
Alternative/confounding diagnoses: [absent / features of: NPH pattern / FTD pattern / VCI pattern — specify].
ARIA monitoring statement (if patient is on anti-amyloid therapy): ARIA-E: absent / present [severity: mild/moderate/severe; location; change from baseline] ARIA-H: [new microbleeds: N; total count: N]; grade __ per ARIA-H scale; [change from prior: N new lesions]
Limitations: [comparison study not available; DWI not performed; different scanner from baseline — automated volumetry unreliable].
Recommendations: [repeat in __ months; amyloid PET if biomarker confirmation needed; treatment continuation recommended/requires clinical review based on ARIA grade].
6.2 Mandatory Disease-Specific Reporting Checklist
- [ ] MTA score bilaterally with age-adjusted interpretation
- [ ] PA score for posterior cortical atrophy
- [ ] GCA score for global atrophy
- [ ] Fazekas PWMH and DWMH separately
- [ ] Lacune count and location
- [ ] Microbleed count and distribution pattern (lobar/deep/mixed)
- [ ] Cortical superficial siderosis: present/absent
- [ ] DWI: cortical ribbon sign explicitly excluded
- [ ] ARIA-E: present/absent (FLAIR — mandatory in patients on anti-amyloid therapy)
- [ ] ARIA-H grade (SWI — mandatory in patients on anti-amyloid therapy)
- [ ] Hippocampal T2 signal: normal / increased
- [ ] Atrophy pattern: typical AD vs atypical (posterior/frontal/temporal dominant)
- [ ] Comparison with prior: which elements changed
6.3 Critical Findings and Communication
| Finding | Communication requirement |
|---|---|
| Cortical ribbon sign on DWI (suspected CJD) | Urgent communication to referring clinician and neurologist; prion disease pathway activation |
| ARIA-E moderate-severe (> 5 cm or multi-lobar) on anti-amyloid therapy | Same-day communication to treating neurologist; treatment modification decision required |
| ARIA-H grade 3 (≥ 10 microbleeds or > 2 sulci siderosis) | Communication to treating neurologist before next infusion |
| New large cortical infarct or haemorrhage | Standard stroke communication pathway |
| NPH pattern not previously recognised | Communication to clinician — potentially treatable reversible cause |
6.4 Common Reporting Errors
| Error | Clinical consequence | Prevention |
|---|---|---|
| Applying MTA score without age correction | Overdiagnosis of AD in elderly patients (MTA 2 is normal for age ≥ 75) | Use Scheltens age-adjusted thresholds: < 75 yrs: abnormal ≥ 2; ≥ 75 yrs: abnormal ≥ 3 |
| Not performing DWI with cortical ribbon sign assessment | CJD diagnosis missed; patient treated as AD; catastrophic outcome | DWI is mandatory in every dementia workup |
| Grading ARIA-H without pre-treatment baseline comparison | Cannot distinguish new ARIA-H from pre-existing CAA microbleeds; treatment modification decisions incorrect | Always require pre-treatment baseline SWI before anti-amyloid therapy |
| Reporting "atrophy consistent with age" without applying rating scales | Non-actionable report; no treatment planning information | Apply MTA, GCA, PA, Fazekas — quantify what you see |
| Missing posterior predominance in PCA variant | Misclassifying PCA as typical AD; incorrect treatment and prognosis discussion | PA score applies specifically to posterior cortical assessment |
| Omitting ARIA statement in patients on anti-amyloid therapy | Treatment continuation without safety data; ARIA progression not detected | Add explicit ARIA-E and ARIA-H statement to every MRI report in patients on lecanemab/donanemab |
| WMH Fazekas not graded | Vascular burden unknown; mixed dementia not recognised | Fazekas PWMH and DWMH are mandatory output in every dementia report |
7. Technical Pitfalls and Disease-Specific Optimisation
7.1 Technical Pitfalls Specific to AD
MPRAGE parameter changes between baseline and follow-up: small changes in TR, TI, flip angle, or scanner upgrade between baseline and follow-up MPRAGE acquisitions produce apparent hippocampal volume differences of 2–5% that are artefactual. Automated volumetry tools (FreeSurfer, Clinica) are partially sensitive to acquisition parameter changes. Always document MPRAGE parameters in the report; flag any change from the baseline acquisition; consider re-establishing a new volumetric baseline after a parameter change.
3T vs 1.5T MPRAGE comparison for longitudinal follow-up: comparing hippocampal volumes from 1.5T and 3T MPRAGE acquisitions — or from different vendors — is not valid for absolute volumetry. The hippocampal volume at 3T is systematically approximately 5–8% different from 1.5T due to differences in tissue contrast. If the scanner changes between baseline and follow-up, automated volumetric comparison is unreliable and the report must state this explicitly.
FLAIR artefact from gadolinium at wrong timing: post-contrast FLAIR in the 10–25 minute window produces sulcal bright signal (gadolinium in CSF) that simulates ARIA-E or leptomeningeal enhancement. In patients who have received contrast for another indication before the dementia MRI, this can simulate ARIA-E. Always document contrast administration timing; acquire FLAIR before gadolinium or at > 30 minutes post-injection (as documented in the FLAIR sequence page on MRIninja).
SWI phase convention for microbleed vs calcification: as documented in the SWI sequence page, the phase sign convention varies between vendors. Iron/microbleeds are dark on both phase and magnitude; calcium is bright on phase and dark on magnitude. In the temporal lobes, small physiological calcium deposits (choroid plexus calcification extending into hippocampal fissure) may simulate microbleeds on magnitude. Always review phase images for equivocal dark foci — calcium will appear bright on phase; haemosiderin will appear dark on both.
7.2 Sequence-Specific Disease Pitfalls
MTA visual scoring at wrong coronal level: MTA must be scored at the level of the mammillary bodies (mid-hippocampal body level). Scoring at the hippocampal head (anterior) overestimates the MTA score because the head normally appears wider and less deep; scoring at the tail (posterior) also produces inaccurate readings. The mammillary body level is identifiable as the level where the rounded mammillary bodies are visible on the same coronal slice as the mid-body of the hippocampus.
FLAIR overgrading of WMH due to slice-thickness effects: 5 mm 2D FLAIR slices produce partial volume averaging at the periventricular margin, leading to overgrading of Fazekas PWMH (caps appear thicker). 3D FLAIR at 1 mm isotropic more accurately represents WMH volume. If transitioning from 2D to 3D FLAIR for serial WMH assessment, the Fazekas scores are not directly comparable — establish a new baseline.
DWI b-value underestimating cortical ribbon sign: at b=1000, the cortical ribbon sign in CJD may be subtle in early disease. A higher b-value (b=1500) with calculated b=1000 equivalent provides better cortical restriction contrast. If clinical suspicion for CJD is moderate-to-high, add b=1500 to the DWI acquisition.
7.3 When the Exam Is Non-Diagnostic for This Question
The dedicated AD protocol fails to answer the clinical question when:
- The patient has a contraindication to MRI (pacemaker, metallic implant) — switch to FDG-PET or CT volumetry as partial substitutes
- Head motion renders the 3D T1 non-interpretable — visual rating is possible from T2 TSE coronal if available; re-scan with motion-robust protocol (PROMO/MUSE acquisition) or under sedation if clinically urgent
- Prior craniotomy or large metallic clip produces susceptibility artefact affecting the medial temporal lobe — assess contralateral side only; supplement with FDG-PET or amyloid PET
- The atrophy pattern is atypical and does not clearly discriminate AD from FTD — refer for amyloid PET and tau PET
8. MRI Technologist Pearls Specific to AD
8.1 Disease-Specific Positioning and Coil Tricks
As discussed in the Brain MRI master protocol page, standard head coil and supine positioning apply. For AD-specific assessment, one additional check: verify that the 3D T1 is acquired with the head in a symmetric, non-rotated position — asymmetric head rotation produces left-right asymmetric grey matter thickness estimates in automated volumetry that can simulate asymmetric atrophy. A minor head rotation (5°) produces apparent cortical thickness asymmetry of up to 8% in automated pipelines.
8.2 Sequence Order Logic in the AD Dedicated Protocol
- 3D T1 (MPRAGE) ← first; motion-sensitive but most critical; fresh patient, minimal fatigue
- 3D FLAIR ← second; long acquisition; required before contrast
- T2 TSE axial ← structural complement; relatively fast
- DWI ← CJD exclusion; independent clinical urgency
- SWI ← microbleed/ARIA-H; before contrast
- Gadolinium (only if ARIA monitoring requires FLAIR comparison or if atypical presentation)
- Post-contrast FLAIR ← if ARIA-E characterisation needed; at 3–5 minutes post-injection
8.3 Fast Salvage Version of the Dedicated Protocol
| Priority | Sequence | Time (3T) | What it answers for AD |
|---|---|---|---|
| 1 | 3D T1 MPRAGE 1 mm isotropic | 4–6 min | MTA score; GCA; PA; hippocampal volumetry |
| 2 | 3D FLAIR | 4–6 min | WMH Fazekas; ARIA-E detection |
| 3 | DWI | 2–3 min | CJD cortical ribbon sign exclusion |
| 4 | SWI | 3–4 min | Microbleed count; ARIA-H; CAA pattern |
This 13–19 minute protocol provides all four mandatory AD-specific sequences. Adequate for both diagnosis and ARIA monitoring. T2 TSE can be omitted in the salvage protocol if the primary question is AD pattern assessment rather than structural lesion exclusion.
8.4 Disease-Specific Avoidable Errors
| Error | Consequence | Prevention |
|---|---|---|
| 3D T1 acquired with different parameters than prior examination | Automated volumetry comparison invalid; apparent volume change is artefactual | Document MPRAGE parameters in every report; flag changes from baseline; never upgrade protocol mid-monitoring cycle without establishing new baseline |
| SWI protocol changed between anti-amyloid therapy MRIs | ARIA-H microbleed count unreliable; wrong ARIA-H grade; treatment decisions based on artefactual change | Lock SWI parameters (TE, flip angle, slice thickness) for the duration of treatment monitoring |
| Coronal reformat for MTA not perpendicular to hippocampal long axis | MTA score systematically incorrect — appears oblique to true hippocampal height | Plan coronal reformat from axial view at temporal horn level; verify hippocampus appears as a round cross-section (not oblique) at the mammillary body level |
| DWI omitted because "patient has known AD" | CJD cortical ribbon sign missed in a rapidly progressing patient misclassified as AD | DWI is mandatory in every dementia workup regardless of pre-test diagnosis |
9. Quality Control Checklist for the AD Dedicated Protocol
- [ ] 3D T1 ≤ 1 mm isotropic: voxel dimensions documented in report; identical to prior examination (or new baseline declared)
- [ ] Coronal reformat from 3D T1 available at mammillary body level, perpendicular to hippocampal long axis
- [ ] 3D FLAIR: full brain coverage, no inter-slice gaps
- [ ] DWI: cortical and basal ganglia signal explicitly reviewed for cortical ribbon sign
- [ ] SWI: TE and slice thickness documented; identical to prior ARIA monitoring MRI (if applicable)
- [ ] MTA score applied bilaterally with age-adjusted interpretation documented
- [ ] GCA score applied
- [ ] PA score applied
- [ ] Fazekas PWMH and DWMH graded separately
- [ ] Microbleed count and distribution pattern documented
- [ ] Cortical superficial siderosis: explicitly addressed
- [ ] ARIA-E statement included (for patients on anti-amyloid therapy)
- [ ] ARIA-H grade stated (for patients on anti-amyloid therapy)
- [ ] Comparison with prior imaging explicitly addressed
10. Advanced Technical Parameters Specific to AD
Advanced technical reference
10.1 3D T1-Weighted (MPRAGE) for Hippocampal Volumetry
The MPRAGE (or BRAVO/TFE at 3T) for AD-dedicated volumetry must meet specific parameters to ensure compatibility with automated segmentation tools (FreeSurfer, FSL-FIRST, Clinica). The ADNI (Alzheimer's Disease Neuroimaging Initiative) protocol [12] — the globally standardised protocol for AD clinical trials — provides the reference parameters:
| Parameter | ADNI-standard (1.5T) | ADNI-standard (3T) | Rationale |
|---|---|---|---|
| Sequence type | 3D MP-RAGE | 3D MP-RAGE | Inversion-prepared GRE |
| TR | 2300 ms | 2300 ms | |
| TI | 900 ms | 900 ms | Grey-white contrast optimisation |
| TE | 2.98 ms | 2.98 ms | Minimum |
| Flip angle | 8° | 8° | |
| Voxel size | 1.0 × 1.0 × 1.0 mm | 1.0 × 1.0 × 1.0 mm | Isotropic for volumetry |
| Bandwidth | 200 Hz/px | 200 Hz/px | |
| Fat suppression | None | None | |
| Orientation | Sagittal | Sagittal | Standard for cortical surface |
Why ADNI parameters: the ADNI protocol was established to enable cross-site and cross-vendor volumetric comparison. Automated tools (FreeSurfer, Clinica/CAT12) have been validated against ADNI acquisitions. Deviating from ADNI parameters — particularly TI, flip angle, and voxel size — produces systematic differences in hippocampal volume estimates that invalidate normative database comparison.
Vendor equivalents: Siemens MPRAGE; GE BRAVO; Philips 3D TFE; Canon MP-RAGE equivalent.
Advanced technical reference
10.2 SWI for ARIA-H Monitoring
For ARIA monitoring specifically, SWI parameters must be optimised for microbleed sensitivity and then maintained unchanged throughout the monitoring period:
| Parameter | 1.5T | 3T | Rationale |
|---|---|---|---|
| Sequence | 3D flow-compensated GRE | 3D flow-compensated GRE | Standard SWI |
| TE | 35–45 ms | 20–30 ms | T2* optimal for brain; scales with B0 |
| Flip angle | 15–20° | 15–20° | |
| Voxel size | ≤ 1 × 1 × 2 mm | ≤ 0.7 × 0.7 × 1.5 mm | Microbleed detection threshold |
| Slice thickness | 2 mm | 1.5–2 mm | Cortical superficial siderosis requires ≤ 2 mm |
| mIP slab | 10–15 mm | 10–15 mm | Venous network display |
| Phase mask multiplication | N=4 | N=4 | Standard |
Critical for ARIA monitoring: the ARIA-H grading scale counts microbleeds and assesses siderosis extent. Any change in TE or slice thickness between baseline and monitoring MRI can produce spurious new "microbleeds" (artefacts from different T2* weighting at different TE) or missed siderosis (insufficient z-resolution). The monitoring protocol must lock these parameters from the pre-treatment baseline.
Section 10 Dedicated Bibliography
Jack CR Jr, et al. The Alzheimer's Disease Neuroimaging Initiative (ADNI): MRI methods. J Magn Reson Imaging. 2008;27(4):685–691. PMID: 18302232. DOI: 10.1002/jmri.21049. (Technical / Foundational) ADNI MRI protocol; defines the MPRAGE parameters for AD volumetric imaging that enable cross-site comparison and normative database compatibility.
Sperling RA, et al. Amyloid-related imaging abnormalities in patients treated with aducanumab: an overview of key imaging findings. Alzheimers Res Ther. 2021;13(1):17. PMID: 33436007. DOI: 10.1186/s13195-020-00767-3. (Technical / Foundational) ARIA SWI technical requirements and ARIA grading; parameters for ARIA-H and ARIA-E monitoring in anti-amyloid therapy.
11. Evidence Gaps and Ongoing Debate Specific to AD
MRI vs amyloid PET for early AD diagnosis: structural MRI (hippocampal atrophy) has limited sensitivity for preclinical AD (amyloid-positive with normal cognition) because neurodegeneration lags amyloid deposition by years. The added value of amyloid PET vs MRI for early diagnosis is substantial and well-documented, but amyloid PET availability remains limited outside specialised centres. The optimal first-line investigation (MRI vs CSF biomarkers vs amyloid PET) in the new anti-amyloid therapy era is under active debate.
Automated volumetry in clinical practice: FreeSurfer and similar tools provide quantitative hippocampal volume referenced to normative databases. Their clinical utility over visual MTA rating has been debated: automated tools have higher sensitivity for subtle atrophy but require consistent acquisition parameters, are expensive in time and infrastructure, and have not been shown to change clinical management in routine practice compared with trained visual rating. Automated volumetry is standard in clinical trials; its role in routine clinical AD diagnosis varies by centre.
ASL perfusion as a surrogate for FDG-PET: ASL perfusion (pCASL) shows parietotemporal hypoperfusion patterns in AD analogous to the FDG-PET hypometabolism that is a validated AD biomarker. The clinical utility of ASL over structural MRI for routine AD diagnosis is not established — ASL is noisier, less reproducible across centres, and not validated against the ATN framework. It remains an area of active research rather than clinical implementation.
ARIA threshold for treatment modification: the FDA labels for lecanemab and donanemab define ARIA-H and ARIA-E grading thresholds at which treatment should be held, modified, or discontinued. These thresholds (e.g., ARIA-E severe = hold treatment; ARIA-H grade 3 = hold treatment) are based on safety data from pivotal trials but represent early-era decisions with limited long-term outcome data. The optimal management of intermediate ARIA (grade 1–2) is still evolving.
Inter-reader reliability of visual rating scales: the MTA scale has κ approximately 0.7 in trained readers — acceptable but not excellent. Non-expert readers (general radiologists not trained in dementia imaging) have substantially lower reliability. The implication: visual rating must be performed by trained readers applying the age-adjusted thresholds. AI-assisted automated rating of the MTA scale is under validation but not yet standardised.
DWI for CJD: b-value optimisation: the optimal b-value for cortical ribbon sign detection in CJD is debated. Some studies support b=1500 over b=1000 for cortical detection; others show equivalent performance. No consensus b-value for CJD-targeted DWI has been universally adopted. Expert practice at specialist centres typically includes b=0/1000/1500 for suspected CJD.
12. Evidence-Based References
A. Guidelines / Consensus / Society Recommendations
B. Systematic Reviews / Meta-analyses
(No dedicated systematic review specifically addresses the combined AD dedicated MRI protocol as a whole; individual elements are addressed in prospective studies below.)
C. Important Prospective / Original Studies
D. Technical MRI Papers
End of document — MRI Brain Dedicated Protocol for Alzheimer's Disease — MRIninja v1.0 — May 2026 Prerequisite page: Brain MRI Generic Standard Protocol (MRIninja master page) Related child pages: Brain MRI for FTD · Brain MRI for Lewy Body Dementia · Brain MRI for CJD · ARIA Monitoring Protocol for Anti-Amyloid Therapy
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