A review of the neurological imaging techniques in dementia diagnosis

By Pooja Toshniwal PahariaAug 28 2023Reviewed by Lily Ramsey, LLM

In a recent review published by Molecular Psychiatry, researchers reviewed existing data on the contribution of neuroimaging modalities such as magnetic resonance imaging (MRI) and positron emission tomography imaging (PET) in dementia diagnosis.

Study: The use of neuroimaging techniques in the early and differential diagnosis of dementia. Image Credit: KaliAntye/Shutterstock.com

Background

Dementia has resulted in disability, cognitive impairment, and mortality worldwide. It necessitates early detection and precise treatment for prevalent kinds such as Vascular dementia, Alzheimer's disease (AD), Frontotemporal dementia (FTD), and Lewy Body Dementia (LBD).

Molecular and structural imaging assists in understanding the etiology of neurodegenerative-type dementias, allowing for better clinical care and therapies.

About the review

In the present review, researchers presented the role of neuroimaging in dementia diagnosis.

Magnetic resonance imaging to assess neurodegeneration

Structural magnetic resonance imaging is an important diagnostic technique for dementia based on atrophy, white matter abnormalities, and cerebrovascular illness.

It can aid in the identification of disorders such as space-occupying lesions, stroke, and normal-pressure hydrocephalus, and the differentiation of dementia from other illnesses. In Alzheimer's disease, temporal lobe atrophy is widespread, with localized alterations in the hippocampus.

Volumetric MRI measures pathological alterations with techniques such as voxel-based morphometry and cortical thickness evaluation.

Volumetric MRI alterations, on the other hand, are insensitive in early prodromal dementia phases and generally correspond with established neurodegenerative processes. Serial MRI has been utilized to enhance dementia differential diagnosis and is frequently employed as a secondary outcome measure in treatment studies.

Diffusion tensor imaging (DTI) is an MRI method that evaluates the direction and integrity of white matter pathways in the brain by evaluating factors related to water molecule diffusion. DTI data is also employed in analytical approaches like tractography. Recent MRI investigations have revealed physiologically plausible variations between dementia subtypes and predicted the transition from MCI to dementia.

Blood flow may be measured using injectable contrast agents or arterial spin labelling (ASL) in functional MRI, and variations in blood flow correlate with FDG-PET results.

Magnetic resonance spectroscopy, magnetoencephalography, and neurite orientation dispersion and density imaging (NODDI) are examples of MR-based advances in neuroimaging.

F-FLUORODEOXYGLUCOSE (FDG) PET imaging in identifying neurodegenerative diseases

FDG-PET, which measures the local brain metabolic rate of glucose consumption, is commonly used to diagnose Alzheimer's disease and other kinds of dementia. It has a high specificity in identifying approximately half of the individuals with behavioral variant FTD (bvFTD) who are undetectable by MRI, allowing the exclusion of psychiatric and other neurodegenerative illnesses.

Hypometabolism on FDG-PET can be found at least 10 years before symptoms start in hereditary types of FTD, and the severity of symptoms corresponds with more broad regions of hypometabolism on FDG-PET. However, FDG-PET should be utilized along with a history and other available examinations.

Neuroimaging is a well-established neurodegenerative marker, including brain dopamine transporter imaging, cardiac sympathetic nerve imaging (MIBG), and single-photon emission computed tomography (SPECT).

Amyloid PET is a significant imaging technique in the initial and particular diagnosis of Alzheimer's disease, notably in the diagnosis of young-onset Alzheimer's disease, and it distinguishes it from other dementias.

However, it has a few limitations, including the fact that it is not correlated with symptomatic onset or disease severity, that it cannot predict dementia onset, and that more research is required for older individuals due to the prevalence of amyloid pathology among a large fraction of the older and cognitively unimpaired population.

Tau protein PET imaging, which uses ligand molecules that bind with neurofibrillary tangles, has been authorized by the Food and Drug Administration (FDA) for in vivo tau evaluation in persons with Alzheimer's disease.

It may not, however, be appropriate for non-AD tauopathies. Apart from amyloid and tau protein, other important PET ligands include ¹¹C-UCBJ, ¹⁸F-SynVesT-1, and ¹¹C -PK11195.

Conclusions

Overall, the review findings emphasized the significance of neuroimaging in dementia diagnosis, with structural MRI being frequently employed in routine clinical practices. However, its sensitivity for early diagnosis and differential identification of dementia subgroups is quite poor.

FDG-PET imaging has high specificity and sensitivity for FTD and AD, but PET with tau and amyloid protein ligands can enhance the differentiation of Alzheimer's disease-related and non- Alzheimer's disease dementias, including identification at prodromal phases.

Dopaminergic-type imaging can help in diagnosing LBD, although there are currently no validated tracers for TAR DNA-binding protein 43 (TDP-43) or alpha-synuclein imaging.

Experts agree on three approaches for clinical dementia diagnosis: Amyloid protein PET or cerebrospinal fluid (CSF) examination in the case of suspected AD; FDG-PET if the first workup reveals non- Alzheimer's disease dementia; and [(123)I]N-omega-fluoropropyl-2beta-carbomethoxy-3beta-{4-iodophenyl}nortropane ([(123)I]FP-CIT)  SPECT imaging or MIBG in cases of cognitive deficits associated with movement-related conditions.

Neuroimaging of the brain is increasingly being utilized to stratify clinical trial participants and assess treatment response in studies of disease-modifying pharmaceutical agents.

The amyloid/tau/neurodegeneration (ATN) framework for Alzheimer's disease diagnosis, which specifies the existence of Alzheimer's disease pathology in the preclinical as well as prodromal phases, is critical to applying disease-modifying drugs (DMDs) in clinical care.