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Functional MRI (fMRI)
Primer for Radiologist
Sangam Kanekar, M.D.
Depts. of Radiology and Neurology
.
Penn State Milton S Hershey
Medical Center and
College of Medicine
Conflict of Interest Statement
Neither I nor my immediate family members have a financial relationship with a
commercial organization that may have a direct or indirect interest in the
content.
Abstract
Purpose:
1. To discuss the principles and physics of BOLD fMRI technique
2. To illustrate with examples fMRI application in the clinical practice particularly in the neurodegenerative disease and
for presurgical planning.
3. To understand the challenges and limitations of fMRI.
Approach:
Functional magnetic resonance imaging (fMRI) is an advanced imaging technique which helps us to visualize the neuronal
activity of the human brain. The fMRI has been used extensively for investigating various brain functions, including vision,
motor, language, and cognition. One of the primary indications for fMRI is evaluation of eloquent areas of the brain in
relation to a focal parenchymal brain lesion such as neoplasm or arterial venous malformation. fMRI is also used to
localize language centers, visual pathways and in analyzing the episodic, semantic and working memory. fMRI has gained
significant importance over a decade due to collateral advances in the noninvasive-/micro-neurosurgical techniques.
Increasing indications are also seen in the evaluation of epilepsy and dementia patients, making it even more important
for radiologist to understand and when indicated to incorporate this high end modality technique in our practice.
Findings
We classify this exhibit into five parts. Part I explains the various fMRI techniques, with detail physiology, and principle of
BOLD imaging. Part II of the exhibit explains in details the various commonly employed tasks which include: a) Visual, b)
Auditory, c) Motor (finger tapping, foot movement, and leg movements) d) Speech language (word generation, verb
generation and sentence composition) and e) Memory testing. Part III illustrates in short the normal relevant cortical
brain anatomy, Part IV discuss and explain with examples the application of fMRI in various (neurology and neurosurgery)
clinical patients. Part V of the exhibit discusses the challenges and limitations of fMRI.
Summary / Conclusion
1. Functional MRI is a very powerful method to map brain functions with relatively high spatial and temporal resolution.
2. We illustrate with examples the application and limitations of this technique for various neurology and neurosurgical
conditions.
3. For participants, this exhibit will be core learning module to understand the principles and basic physics of BOLD fMRI
technique and; how to perform and interpret the fMRI.
Part I: explains the various fMRI techniques, with detail physiology, and principle of BOLD
imaging.
Physiology, and Principle of BOLD Imaging
Two main principles
1
basic principle of fMRI
Regional Cerebral Blood Flow Could Reflect Neuronal
Activity
1890, experiments of Roy and Sherrington at Cambridge University
Synaptic
signaling
metabolic
signaling
Vascular response
BOLD signal
2
difference in the magnetic properties of oxyhemoglobin and
deoxyhemoglobin (dHb).
1
Part I
↑ Neuronal Activity
↑ O2 extraction
↑ Deoxyhemoglobin
(T2* dark signal)
Cerebral
blood flow
Oxyhemoglobin
(T2* bright signal)
increase in the ratio of O-Hb to D-Hb.
↑ BOLD Signal
Blood Oxygenation Level Dependent (BOLD)
signal: As the neuronal activity in the specific
region of brain tissue increases with a
particular task, there is an increase in the
local increase in energy and oxygen
consumption in functional brain areas, which
is followed by an increase of regional
cerebral blood volume (rCBV) and regional
cerebral blood flow (rCBF).
Since increased neuronal activity results in an
increase in blood flow beyond the exact
demand, more oxygenated hemoglobin
appears in the venous capillaries. This shifts
the relation between oxygenated and
deoxygenated hemoglobin
neural activity   blood flow   oxyhemoglobin   T2*   fMR signal
2
Part I
Magnetic susceptibility of OxyHb (diamagnetic) is some what EQUAL to
tissue, therefore field is uniform, therefore MRI signal is high.
Magnetic susceptibility of deOxyHb (paramagnetic) is >>> to tissue,
therefore field is non-uniform, therefore MRI signal is low.
Rest
Activation
Origins of the BOLD effect in fMRI.
While arterial blood is similar in its
magnetic properties to tissue,
deoxygenated
blood
is
paramagnetic and so induces
inhomogeneities
within
the
magnetic field in tissue.
These cause the MRI signal to decay
faster.
As the oxygenation increases
MR (BOLD) signal increases
Due to more OxyHb signals from
activated regions of cortex increase
as the tissue becomes more
magnetically uniform.
Part I
MRI T2* Signal
Activation
Activation
Activation 20 seconds
Rest 20 seconds
Repeat 8 times
Rest
Activation
Rest
Activation
Rest
The most commonly used paradigms are “blocked” designs, in which the subject repeatedly
performs a task for a specified time, resting for a similar time between repetitions (i.e.,
alternating “task” and “control” blocks). This repetition is required for statistical processing to
detect the small signal changes that characterize the BOLD response, on the order of 1 to 5% at
1.5 tesla (T) or 2 to 10% at 3.0 T, against a background of physiologic noise. Discussion of detail
post-processing technique is beyond scope of this exhibit.
Part II illustrates in short the normal relevant cortical brain anatomy, Part IV discuss and explain
with examples the application of fMRI in various (neurology and neurosurgery) clinical patients.
CORTICAL ANATOMY
There are four major areas very successfully analyzed by fMRI: the primary motor cortex, the
primary sensory cortex, the premotor cortex, and the supplementary motor area (SMA). The
motor and sensory gyri often referred to as one larger area termed the primary sensorimotor
cortex
THE PRIMARY SENSORIMOTOR CORTEX
To identify and differentiate the sensory and motor cortex it is important to identify the central
sulcus. Gyrus anterior to the CS is motor while posterior is sensory gyrus. Central sulcus also
marks the posterior limit of the frontal lobe and the sensory gyrus marks the start of the parietal
lobe. The motor gyrus is somatotopically mapped; different body regions are distinctly
represented in cortical space in a common.
= postcentral gyrus (sensory)
= precentral gyrus (motor)
= central sulcus
= precentral sulcus
= postcentral sulcus
THE CENTRAL SULCUS
Part II
How to identify central sulcus ?
•
•
•
superior frontal sulcus - pre CS sign the posterior end of the superior frontal sulcus joins the
precentral sulcus in 85%
sigmoidal Hook sign-- Hook like configuration of the posterior surface of the precentral gyrus
the “hook” corresponds to the motor hand area. The “hook” is well seen on CT (89%) and
MRI (98%).
pars bracket sign--The paired pars marginalis form a “bracket” to each side of the
interhemispheric fissure at or behind the central sulcus (96%).
Superior frontal
sulcus
Precentral
sulcus
Ʊ
Part II
THE CENTRAL SULCUS
How to identify central sulcus ?
• Bifid post-CS sign-- the post-CS is bifid (85%). The bifid post-CS encloses the lateral end of the
pars marginalis (88%).
• Thin postcentral gyrus sign-- the postcentral gyrus is thinner than the precentral gyrus (98%).
• Intraparital sulcus-post-CS intersection--in axial MRI/CT, the intraparietal sulcus intersects the
post-CS (99%).
• Midline sulcus sign--the most prominent convexity sulcus that reaches the midline
interhemispheric fissure is the CS (70%).
Thin postcentral gyrus sign
Postcentral sulcus
Midline sulcus sign
intraparietal sulcus
Part II
Precentral sulcus
Precentral gyrus
Postcentral gyrus
Central sulcus
Central sulcus
Precuneus
Postcentral sulcus
Paracentral lobule
Supramarginal
gyrus
Postcentral sulcus
It is of vital importance to understand and memorize few of the important anatomical
land marks of the brain. Without knowing eloquent areas of the brain especially which
take part in motor, sensory, memory and visual cortex (sulci, gyri) it will be impossible
to understand and interpret fMRI. We illustrate here the most important sulci and gyri,
which are very essential for day to day reading of fMRI. We have discussed these
eloquent areas first on the structural imaging and then try to identify them along with
various paradigm on fMRI.
Part II
Central sulcus
Precentral sulcus
Central sulcus
Superior parietal gyrus
Postcentral sulcus
Superior Temporal gyrus
Superior Temporal sulcus
Middle Temporal gyrus
Inferior Temporal gyrus
Part II
Paracentral lobule
Cingulate gyrus
Marginal ramus of
Cingulate sulcus
Central sulcus
Marginal ramus of
Cingulate sulcus
Precentral gyrus
Gyrus rectus
Subcallosal gyrus
Cingulate sulcus
Part II
Superior Frontal gyrus
Superior Frontal sulcus
Middle Frontal gyrus
Postcentral gyrus
Paracentral lobule
Central Sulcus
Precentral sulcus
Supramarginal gyrus
Cingulate gyrus
Heschl’s gyrus
Precentral gyrus
Parahippocampal gyrus
Entorhinal area
Amygdala
Superior
Middle
Inferior
Temporal gyrus
Part II
MOTOR HOMUNCULUS
SENSORY HOMUNCULUS
SUPPLEMENTARY MOTOR AREA (SMA)
Part II
• The SMA is located in the superior frontal gyrus just medial to
the superior frontal sulcus.
• The SMA can be roughly divided into three parts: anterior,
middle and posterior. Anterior portion (pre-SMA), more active
on fMRI during language tasks, and a posterior portion, more
active on fMRI during motor tasks. A centralized region of the
SMA that is active during both language and motor tasks.
• The motor portion of the SMA is, like the primary motor gyrus,
also somatotopically arranged. The SMA is broadly responsible
for motor planning and activates temporally before the primary
motor gyrus.
• The SMA has been shown to be involved in temporal planning
and organization of motor movements before execution, in
addition to sequencing multiple movements.
The SMA is found in the posterior aspect of the superior frontal
gyrus in the region of cortex medial to the precentral sulcus.
Anterior to the paracentral lobule (foot motor).
activation of the SMA during finger
tapping:
Part III
Motor Pathway
Superior Frontal Gyrus
Superior Frontal Sulcus
Precentral Sulcus
Precentral Gyrus
Central Sulcus
Postcentral Gyrus
Centrum Semiovale.
Corona Radiata
Internal capsule
Starts with the upper motor neurons in the primary motor cortex. Axons from these neurons
traverse the centrum semi ovale to the corona radiata. The tracts continue through the posterior
limb of the internal capsule They then continue caudally via the cerebellar peduncles (midbrain)
and basilar pons Finally the fibers enter the medullary pyramids, and then decussate to become
the lateral corticospinal tract in the spinal cord.
Part II
The Primary Visual Cortex
Visual processing areas (V1, V2, V3, V4, V5/MT, V6, intraparietal sulcus regions) each
have a complete retinotopic map of visual space, & each is largely dependent on the
primary visual cortex for its activation.
Extrastriate cortical areas project to temporal & parietal cortical association areas.
Parieto-occipital sulcus
Upper retinal Q
17
Calcarine fissure
18
18
Lower retinal Q
17 Primary visual cortex
Inferior fibers (Meyer's loop) ==below the calcarine fissure
superior and central tracts ==above the calcarine fissure
The Primary Visual Cortex
Cingulate sulcus
Subparietal sulcus
Calcarine sulcus
Lingual Gyrus
Part II
COMMON PARADIGMS
Part III
fMRI localization depends on the paradigm used to elicit the activation. Specific motor tasks
should be selected based on the location of the lesion.
fMRI may be performed using
TWO TYPES OF PARADIGMS
BLOCK DESIGNS
EVENT-RELATED PARADIGMS
stimulus ON and OFF
•
•
•
stimuli are presented in alternating short runs •
(“blocks”) of several seconds’ duration, and the
MRI signals are then compared for the two types
of blocks.
•
Example of motor task would have the patient
resting for 5 images and finger tapping for 5
images. This alternating cycle of rest and task •
would repeat 5 or 6 times and last approximately
5 minutes
Example for visual-stimulation task to localize
primary visual areas, a subject might view a
bright flickering checkerboard for 20 seconds,
followed by a dark screen for 20 seconds, with
these blocks repeated several times; eight pairs
of blocks
In an event-related design the patient
performs one event (eg, a finger tap), which
is followed by rest.
It records the event-related potentials
(ERPs) in electrophysiological studies.
This type of design requires many
repetitions because the change from
baseline for any one event is small and
therefore takes longer time
Part III
COMMON PARADIGMS
Number of the paradigms performed varies from institution and clinical question. Since the
cooperation of the patient is a must it may not be practical of doing all the paradigms. In case of
preoperative planning paradigm may be tailed depending on the location of the lesion. Few of
the commonly performed paradigm include:
MOTOR
•
•
•
•
•
•
•
Bilateral Complex Finger
•
Tapping
Unilateral Sequential Finger •
•
Tapping
Lip Puckering and Tongue •
•
Movement
•
Unilateral Foot/Ankle
•
Movement
Passive hand stimulation •
•
Motor Task
•
•
•
•
SPEECH AND LANGUAGE
MEMORY
VISION
Auditory Responsive Naming Task
Temporal Phase
Semantic Decision Task (Visual)
Mapped Visual Field
Text reading vs. non-linguistic symbols
Visual Field
Rhyming
Eccentricity
Silent Word Generation
Polar Angle
Simple object naming
(Rotating Wedges)
Passive Listening
The Visual Language Comprehension Task
Silent Verb Generation Task
Word Listening Task
Noun-verb semantic association task
•
•
Novel vs Familiar
Face-Name
Memory
Encoding/Retrieval
Task
Visual Memory
Paradigm
The most common MRI sequence used in BOLD fMRI is a T2* gradient-echo sequence using single-shot echo
planar imaging(EPI), which allows whole-brain data collection in a few seconds or less.
This high speed comes at the expense of spatial resolution, which is substantially lower than for a conventional
MRI scan.
Another drawback to EPI is distortion and signal loss in the frontotemporal regions secondary to the sensitivity of
EPI to magnetic susceptibility differences.
Motor and Premotor
Part III
Paradigm: Bilateral Complex Finger Tapping.
Bilateral Complex Finger Tapping Paradigm
description: bilateral simultaneous complex
finger tapping. Subjects tap fingers bilaterally
in the sequential order of 1, 3, 5, 2, and 4.
important aspect of he task is the sequencing
of the finger movements, rather than location.
Activation patterns: robust activation in the
bilateral sensorimotor cortex, bilateral SMA,
bilateral basal ganglia, bilateral thalami, and
bilateral superior cerebellum. Additional areas
of activation are oftentimes noted in the
bilateral premotor regions.
Paradigm: Unilateral Sequential Finger
Tapping. For the sequential finger tapping task,
the patient is asked to tap their thumb to each
finger of their hand in a sequential manner at
a self-paced rate on a “go” command and to
continue tapping until a ”stop” command is
presented.
RIGHT finger tapping will
activate the LEFT precentral
gyrus while LEFT finger tapping
will activate the RIGHT
precentral gyrus.
Right hand tapping
Alternating Right and Left hand tapping
Left hand tapping
An alternating finger tapping paradigm
demonstrates the contralateral relationship the
cerebellar and cerebral hemispheres have in
motor control.
Activation patterns: robust activation in the bilateral sensorimotor cortex, bilateral
SMA, bilateral basal ganglia, bilateral thalami, and bilateral superior cerebellum.
Additional areas of activation are oftentimes noted in the bilateral premotor regions.
Unilateral Foot/Ankle Movement
Part III
Another way in which fMRI contributes significantly to motor gyrus localization is in the foot
motor region. The foot motor region is located most medially just over the interhemispheric
fissure.
Left foot tapping
Paradigm: Patient is asked to dorsiflex and
plantar flex the foot and ankle in a smooth,
steady manner at a self-paced rate on a “go”
command and to continue tapping until a
”stop” command is presented.
Right foot tapping
Activation patterns: Robust activity results in
premotor and primary sensori-motor activation
(about the superior termination of the central sulcus
and in the paracentral lobule) + SMA activation is
seen. Secondary somatosensory activation may also
be observed. Premotor cortex and cerebellar
activation is variable.
Lip Puckering/Tongue Movement
Paradigm: For lip-puckering, patients are asked
to pucker their lips repeatedly on a visually
presented, or auditory, “go” command. Tongue
movement task, patients are asked to wiggle
their tongue back and forth in a closed mouth
Subcentral Lobule
Activation patterns: activation about the
lateral central sulcus in the expected
somatotopic location for lower face sensorimotor cortex. Secondary somatosensory,
premotor cortex, and SMA activation are also
observed. Tongue movement will activate
similar areas, but with primary sensori-motor
cortex located along the homunculus
Lip movement
Part III
LANGUAGE TASK
Part III
Introduction: Language is a collection of highly skilled interconnected process in which
multiple areas of the brain take part for a distinct function.
Many linguistic and nonlinguistic tasks require neural systems that process auditory or
visual sensory information. For example: Word production begins with retrieval of a
concept from a store of semantic knowledge (semantic processing), followed by
activation of a sound-based representation of the target word (phonological
processing). thus there is considerable overlap in the brain regions activated by
production and comprehension tasks.
The main goal of fMRI language mapping for presurgical planning is to: a) cerebral hemispheric
language LATERALIZATION (dominance) and b) the spatial PROXIMITY OF ELOQUENT LANGUAGE
REGIONS to potentially brain lesions such as brain tumors.
THEREFORE
The paradigms designed for language mapping should elicit activation in the
speech productive areas in the frontal lobe as well as the receptive language
areas in the temporal and parietal lobes.
LANGUAGE TASK
Part III
Depending on the case, site of the lesion or pathology/disorder suspected any of the following
paradigm is selected:
Paradigm used to study language function
•
•
•
•
•
•
•
•
•
•
•
Auditory Responsive Naming Task
Semantic Decision Task (Visual)
Text reading vs. non-linguistic symbols
Rhyming
Silent Word Generation
Simple object naming
Passive Listening
The Visual Language Comprehension Task
Silent Verb Generation Task
Word Listening Task
Noun-verb semantic association task
LANGUAGE TASK
The choice of the paradigms that are administered depends mainly on the location of the lesion
and the patient’s neurological deficits. They are usually categorized into three groups:
EXPRESSIVE
RECEPTIVE
elicit activation mainly in the
speech production areas.
**Silent Word Generation,
Silent Verb Generation, and
Simple Object Naming are
among the most used and cited
verbal fluency paradigms in
fMRI
paradigms is designed to
identify mainly receptive
language regions in the
temporal and parietal
lobe, Wernicke’s area (the
posterior aspect of the left
STG)
**Sentence reading or
the dorsolateral prefrontal cortex listening comprehension
(DLPFC), inferior frontal gyrus (IFG),
variably within cingulate language
regions, supplementary motor area
(SMA), premotor and motor regions
and occasionally the parietal,
temporal, and/or occipital cortex
depending on whether auditory or
visual stimuli are used.
entire language network including
Broca’s area (BA, left IFG), Wernicke’s
area (WA, posterior left STG) & right
hemispheric homologues, DLPFC,
ITG, middle temporal gyrus (MTG),
angular (AG) and supramarginal
gyrus (SMG), other parietal language
cortices and SMA
SEMANTIC PARADIGMS
intended to activate both
key
expressive
and
receptive
language
cortices, including Broca’s
and Wernicke’s.
**a noun to verb
association
(e.g.dogbarking), a word category
association (e.g. applefruit),
and
Sentence
completion
the
dominant
cerebral
hemisphere within the IFG,
posterior
temporal,
and
inferior parietal speech areas.
Silent Word Generation
Paradigm: This task visually presents letter
during the activation state and a nonsense
symbol during the control condition. During
letter presentation, patients are instructed to
think of as many words as possible that begin
with the letter presented on the screen.
Activation
patterns:
the
dorso-lateral
prefrontal cortex, inferior frontal gyrus,
variably within cingulate language regions,
SMA, premotor and motor regions. Posterior
language cortex may also activate to this task.
Small amounts of activity can be seen in the
ventral occipito-temporal cortex.
Simple object naming
Part III
Paradigm: The active tasks consist of
presenting simple objects that the subject
names silently, at a rate of approximately one
object every 3 seconds. The control task
utilizes a nonsense symbol for visual fixation
and to minimize elementary visual cortical
activation
Activation patterns: activity within the inferior
frontal gyrus (frontal operculum), dorsal lateral
prefrontal cortex, or premotor cortex, SMA, ventral
occipito-temporal cortex (VOTC), and to a variable
extent within the posterior temporo-parietal
language cortex. The task will also variably cause
activation of posterior temporal or temporo-parietal
opercular cortex, corresponding to language relevant
cortex.
The Visual Language Comprehension
Task
Part III
Silent Verb Generation Task
Patient generates verbs related to visually
presented written nouns. Delivered via LCD
Advantages of this task include robust
projector and mirror setup as visual stimuli.
language lateralization of both frontal and
temporal language regions and the ability to
measure behavioral data related to task
performance.
A visual language comprehension task is useful
for clinical questions regarding language
localization in Broca’s area (inferior frontal
lobes) and Wernicke’s area (posterior superior
temporal sulci) and hippocampal structures.
Eye movement areas (precentral sulci, medial
frontal lobes, intraparietal sulci), unilateral
thumb movement (finger switch in dominant
hand), working memory (middle frontal gyri)
and primary and associative visual areas
(occipital areas) are also mapped.
receptive
speech areas
in
frontal
regions
VISION
Part III
Vision - Temporal Phase Mapped Visual Field
Visual Field Eccentricity (Expanding Rings) and
Polar Angle (Rotating Wedges):Neurons
responding preferentially to visual stimulation
at different locations in the visual field are
activated at different times during each of the
stimulus sequences. Corresponding differences
in the temporal phase of the fMRI responses
thus indicate the eccentricity and polar angle
represented by each brain voxel.
Used to efficiently map visually
responsive brain areas that are
retinotopically organized
Expanding Rings
Rotating Wedges
Memory
Part III
• Neuropsychological testing reveals that generally the left medial temporal lobe
(MTL) is most involved in verbal memory functions whereas the right mediates
visuospatial memory. Therefore evaluating the functional areas are very important
before the epilepsy surgery especially that part of the temporal lobe or lobes will
be sacrificed leading to the functional loss.
• fMRI is uniquely suited to investigate the functional anatomy of memory, and is
thus poised to contribute a more direct metric of functional adequacy of the
epileptogenic tissue.
• Evaluation of these areas are also of primary interest in the various
neurodegenrative disorders such as Alzheimer disease. The hippocampus and
entorhinal cortex have long been recognized as structures showing early damage in
the pathologic progression of these disorders. Besides measurement of
hippocampal volume and entorhinal cortex thickness, functional evaluation of
these areas have been very useful tool to understand the pathophysiology and
possibly the long term outcome of these disorders (MCI and Alzheimer disease).
Part III
Memory
Novel vs Familiar Face-Name
Memory Encoding/Retrieval Task
Paradigm Sixty novel and two familiar facename pairs, drawn from The AR Face Database
4 , are presented within a block design. Faces
are balanced for age, race and gender.
Behavioral responses are monitored via a fiber
optic button box within the scanner.
Activation patterns: Prefrontal cortex, parietal
and medial temporal lobes
Visual Memory Paradigm
Paradigm The subsequent active blocks
(retrieval) are lists of colored object pictures
that contain one or two pictures from the first
list that was to be remembered. The objects
are identified as in (YES) or not (NO) in the first
list by a manual finger switch response using
the dominant hand.
Activation
patterns:
robust
memory
localization in both mesiotemporal and
dorsolateral prefrontal cortex regions and the
ability to measure behavioral data of task
performance. visual activation in the occipital
lobes
Part IV: CLINICAL APPLICATIONS
Case: Brain tumor surgery right frontal tumor treated with temodar. FMRI evaluating motor
tract.
LEFT FOOT TAPPING
LEFT FOOT TAPPING: There are large clusters of activation localized predominately around the right paracentral region including the
motor and sensory strips in the expected superomedial location within the homunculus. Comparatively smaller clusters are detected in the
right supramarginal gyrus. There are small clusters in the left cerebellum. LEFT FINGER TAPPING: There are significant activation
clusters localized in the right paracentral region including the motor strip and supplementary motor area at the midline. There are small
activation clusters detected in the cerebellum. While the bulk of the right paracentral activation is well posterior to the tumor, at the more
superior slices, there is some motor activation detected that approaches the posterior border of the tumor, though these are comparatively
small.
LEFT FINGER TAPPING:
1/2
Word generation
Verb generation
WORD
GENERATION:
Significant
activation clusters are detected almost
exclusively in the left cerebral hemisphere
with the major cluster localized along the left
inferior frontal gyri, rostral temporal gyri,
left supplementary motor area and posterior
premotor region of the left hemisphere. Some
activation clusters are also detected in the
left parietal region and in the occipital lobes
bilaterally and the right cerebellum. VERB
GENERATION: Results were similar to the
word generation task, all of the activity is
localized in the left cerebral hemisphere.
There are activation clusters localized at the
posterior
border
of
the
tumor
SENTENCE COMPLETION: There are
several significant activation clusters
localized in the left cerebral hemisphere with
large clusters detected in the right cerebral
hemisphere. These clusters are localized
predominantly in the left frontal operculum
and bilateral parietal cortex. Small
activation clusters are also detected posterior
to tumor in the precentral gyrus, bilateral
superior temporal gyri and right cerebellum.
Sentence completion:
2/2
N block
Case: H/O traumatic head
injury, function deficit and
phonophobia
Visual task
Word listening
No significant
deficit seen on
fMRI
WORD LISTENING TASK: Demonstrates large cluster of activity in the left superior temporal lobe including the Hessel's gyrus, the left inferior frontal
lobe near the operculum and also posterior portion of the left superior temporal lobe. Also large cluster of activity is seen in the right superior temporal
lobe centered around the Hessel's gyrus activity; More activity is seen in the left cerebral hemisphere likely due to activation and language areas in the
inferior frontal and posterior superior temporal lobe. VISUAL TASK: Demonstrates prominent activity in the bilateral occipital lobes in the expected
location of the visual areas. N-BACK TEST: Demonstrates large cluster of activity in the bilateral pre frontal region and the anterior cingulate gyrus.
Also cluster of activity seen in the bilateral inferior parietal lobes left more than right.
Part IV
Left finger tapping
Left foot tapping
Lip movement
Case: H/O Right fronto-temporal lobe neoplastic lesion. fMRI prior to
surgical resection.
1/2
Part IV
Word generation
Sentence completion
No sensorimotor functions are seen in close proximity to the lesion.
Therefore this lesion can be resected without any major sensory-motor
deficit.
2/2
Part V: of the exhibit discusses the challenges and limitations of fMRI.
Part V
• Functional MRI has several inherent disadvantages and pitfalls that are important to
understand.
• Remember that BOLD fMRI detects only changes, rather than the absolute level, of brain
activity and that it does so indirectly through neurovascular coupling.
• The importance of variations in the blood levels of everyday substances (such as caffeine,
nicotine, and glucose), or of hormones (such as estrogen), all of which are likely to affect the
BOLD signal, is not well documented.
• There is often reduced signal intensity and geometric distortion in the frontal and temporal
regions or in the vicinity of surgical changes, blood products, and so forth, secondary to
magnetic susceptibility effects, potentially leading to false-negatives.
Parallel acquisition techniques have been developed that not only reduce image
acquisition time but also reduce susceptibility artifacts, improving signal detection in
basal frontal and mesial temporal regions and benefitting studies involving memory,
emotion, and executive function. Decreasing voxel size can decrease distortion in
hippocampus and amygdala.
BUT
• The use of fast imaging reduces the spatial resolution to a few millimeters
• The temporal resolution is poor and is limited by the nature of the hemodynamic
response.
CONCLUSION
fMRI provides an accurate and
painless method for mapping of
critical functions and likely has a much
larger role to play in the management
of clinical patients for diverse
disorders.
THANK YOU
a Penn State presentation
.
Questions and suggestions to: [email protected]