Functional MRI

Last revised by Harry Whitehead on 9 Nov 2021

Functional magnetic resonance imaging (fMRI) is a technique used to obtain functional information by visualizing cortical activity. fMRI detects subtle alteration in blood flow in response to stimuli or actions. It is used in two broad ways:

  1. clinical practice
    • typically in presurgical patients 
  2. research 
    • often cohort of patients (often normals)
    • aimed at elucidating novel neural networks

fMRI is technically-challenging to perform as the techniques used to visualize cortical activity (most commonly BOLD imaging) rely on minute changes in a low signal-to-noise ratio (SNR) environment. 

  • 1.5 T or higher field strength MRI
  • excellent quality assurance
  • appropriate software
  • appropriate paradigms and ability to deliver visual and auditory stimuli and record motor response
  • co-operative patients

Two testing designs are employed most commonly:

Block design uses repeated blocks of activity (paradigm) separated by blocks of inactivity or alternative activity. This is by far the most frequently used study design in clinical fMRI.

Event-related design involves individual events rather than blocks, and can be randomly distributed during the study. 

The activity performed or stimulus received by the patient is termed a paradigm, and each is designed to elicit a specific cortical response. Numerous paradigms have been developed of various complexity. In the clinical setting four paradigms (with modifications according to the clinical situation) suffice for most indications. 

  • visual paradigm
  • motor paradigm
  • speech paradigm
  • memory paradigm

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Cases and figures

  • Figure 1: motor paradigm
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  • Figure 2: language paradigm
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  • Figure 3: fMRI block design
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  • Case 1: low grade astrocytoma
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