What is the purpose and use of functional magnetic resonance imaging (fMRI) in diagnosing and managing neurological and psychiatric disorders?

Functional MRI (fMRI) in Neurological and Psychiatric Disorders

Functional MRI remains a research tool and is not recommended for routine clinical diagnosis or management of neurological and psychiatric disorders, despite showing promising findings in multiple conditions. 1

Current Clinical Status

The American College of Radiology explicitly states across multiple appropriateness criteria that there is insufficient evidence to support the routine clinical use of fMRI at the individual patient level for:

• Head trauma and traumatic brain injury 1
• Frontotemporal dementia 1
• Creutzfeldt-Jakob disease 1
• Parkinson's disease and other movement disorders 1

Limited Clinical Applications

Presurgical Epilepsy Evaluation

fMRI has established utility only in presurgical planning for drug-resistant epilepsy, specifically for:

• Language lateralization: Demonstrates 89% concordance with intracarotid amobarbital procedure (IAP) for right temporal lobe epilepsy and 85% for left temporal lobe epilepsy 1
• Predicting postsurgical language deficits: Strong left frontal activation predicts postresection decline 1
• Memory lateralization: Shows moderate correlation (r = 0.31; P = .007) between hippocampal fMRI laterality index and IAP memory laterality index, though conflicting data exists 1

fMRI can be considered as a replacement for IAP for language lateralization in temporal lobectomy candidates 1, particularly valuable in MRI-negative epilepsy where prognosis for seizure-free outcomes is worse 1

Technical Principles

fMRI uses blood oxygen level-dependent (BOLD) technique to indirectly detect brain activity through hemodynamic responses 1:

• Neuronal activity stimulates increased glucose and oxygen delivery
• Decreased paramagnetic deoxyhemoglobin is detected on dynamic T2*-weighted images
• Can be performed during specific tasks (task-based) or at rest (resting-state) 1

Research Findings Without Clinical Application

Traumatic Brain Injury

• Task-based fMRI shows variable BOLD signal changes (increases may represent compensatory neuronal recruitment; decreases may represent performance deficits) 1
• Resting-state fMRI demonstrates reduced connectivity correlating with cognitive performance and post-concussive symptoms at 6 months 1
• Increased connectivity in brain regions with elevated tau burden may reflect compensatory processes 1

Frontotemporal Dementia

• Brain activation significantly decreased in frontal and parietal lobes compared to Alzheimer's disease 1
• Resting-state fMRI shows alterations in structural and functional connectivity in presymptomatic FTD 1

Seizure Disorders Beyond Presurgical Planning

• fMRI demonstrates promise in MRI-negative epilepsy for identifying epileptogenic zones 1
• Model paradigms show potential for noninvasively predicting memory decline 1

Critical Limitations

Pathophysiological Concerns

The fundamental limitation is that neurovascular coupling can be regionally altered by pathological conditions or drugs, meaning fMRI responses may not truly reflect neural activity 2, 3:

• Mild TBI may induce decoupling between neuronal activity and blood flow 1
• fMRI detects neural activity only indirectly through slow hemodynamic variations 2

Individual Patient Assessment

All research findings are demonstrated at the group level and cannot be reliably applied to individual patient assessment 1, which is why guidelines consistently recommend against routine clinical use 1

Preferred Clinical Alternatives

For routine clinical diagnosis and management:

• Structural MRI remains the first-line imaging modality for most neurological conditions 1, 4, 5
• FDG-PET is preferred over fMRI for differentiating neurodegenerative dementias 1
• Ioflupane SPECT is superior for differentiating Parkinsonian syndromes from essential tremor 1

Future Directions

Simultaneous EEG-fMRI recordings show promise for:

• Detecting cortical areas involved in epileptic activity 2
• Studying eloquent cortical areas for neurosurgery planning 2
• Evaluating functional connectivity in uncooperative or unconscious patients 2

However, these applications require further validation before clinical implementation 2, 3, 6