Chapter 20 Diagnostic Techniques

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Chapter 20 Diagnostic Techniques

• Chris Rorden
• University of South Carolina
• Norman J. Arnold School of Public Health
• Department of Communication Sciences and
  Disorders
• University of South Carolina

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Brain Imaging

• Static Anatomical identify brain structures
• Was the frontal cortex damaged by the stroke?
• Dynamic Identify brain function
• Does the frontal cortex show normal metabolism?

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Static X-Ray

• X-ray tube projects through head
• Detector plate measures transmission of X-rays
• Bone relatively opaque to X-rays
• Soft tissue relatively transparent
• Useful for Angiography, looking for broken bones
• Poor for questions about grey vs white matter

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Static Cerebral Angiography

• Identifies arterial disease, aneurysms and AV
  malformations
• Radiopaque substance released into blood and
  followed through system
• Digital subtraction computer development to
  improve contrast in pictures

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Static CT

• Computerized Tomography (CT) or Computerized
  Axial Tomography (CAT)
• Looks at radiographic pictures taken in series
  across brain
• May be enhanced by use of compounds injected
• Excellent for distinguishing relationships and
  shifts and lesions

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Static CT

• Imaging technique that relies on X-rays
• Widely available
• Most (if not all) hospitals have CT
• Many clinics also have CT scanners
• CT shows body structures (bone and soft tissue)
  does not show function (metabolism)

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Static CT

• Is based on absorption of x-rays as they pass
  through the different parts of a patients body
• Depending on the amount absorbed in a particular
  tissue such as muscle or lung, a different amount
  of x-rays pass through and exit the body
• The amount of x-rays absorbed contributes to the
  radiation dose to the patient
• During conventional x-ray imaging, the exiting
  x-rays interact with a detection device (x-ray
  film or other image receptor) and provide a 2
  dimensional image of the tissues within the
  patients body an x-ray produced photograph
  called a radiograph.
• CT uses the same principle but uses a rotating
  x-ray device and detectors to make a slice

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Static CT

• Advantages of CT
• Very quick
• Good spatial resolution compared to metabolic
  imaging
• Newer CTs can scan perfusion
• Is widely available (cheap compared to MRI)

• Disadvantages of CT
• Uses X-rays (radiation!)
• Cannot detect acute ischemic stroke
• Poor spatial resolution compared to MRI

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Static CT

• What is CT used for?
• CT is mainly used for bone scans (broken bones!),
  chest x-rays, and stroke imaging
• CT is very quick (1-5 minutes) and is optimal for
  detection of cerebral hemorrhage
• Usually does not detect acute ischemic stroke
• Patients who receive tPA always get a CT before
  administration to rule out hemorrhage

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Static CT

• Abnormal

Normal
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Static CT
Hemorrhage
Tumor

• Infarct

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CT scans are improving
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Static MRI

• Magnetic Resonance Imaging
• Not radiographic, analyzes response to
  radiofrequency signal
• Visualizes structures

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MRI

• Different types of MRI scan
• T1 (anatomical) fast to acquire, excellent
  structural detail (e.g. white and gray matter).
• T2 (pathological) slower to acquire, therefore
  usually lower resolution than T1. Excellent for
  finding lesions.

T1
T2
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Static MRI
Abnormal
Normal
1. Unless very fresh or very old.
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Static MRI

• Infarct

T1
T2
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Static MRI

• Bleed

Low relative contrast hard to see on T2
T1
T2
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Static MRI

• Tumor

T1
T2
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Static MRI

• Multiple-Sclerosis

T1
T2
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Dynamic PET

• Positron Emission Tomography (PET)
• Measures uptake of radioactively-tagged tracer.
  Often tracer is glucose to determine which
  tissues have highest energy use during activity

• PET is similar to CT scans
• CT scans measure X-ray transmission which parts
  of the body block X-rays
• PET scans measure X-ray emissions where is the
  tracer uptake?

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Dynamic PET Clinical uses

• Tumor detection (increased metabolism)
• Decreased metabolism in the brain
• Can help distinguish between Alzheimer's disease,
  blood flow shortages, depression, or some other
  reason for dementia
• PET can localize the origin of seizure activity,
  guiding neurosurgery

PET
T2 MRI
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Dynamic PET Clinical uses

• PET can tell if muscle tremor is Parkinson's
  disease or another of the "Movement" disorders.
• PET can look at brain tumor and reveal if it's
  benign or malignant. It is also widely used when
  recurrence is suspected to show whether
  structural change is tumor re-growth or merely
  scar tissue.
• PET can "map" the areas of the brain responsible
  for movement, speech, and other critical
  functions. This is a remarkable guide for
  surgeons who are performing delicate operations
  on different areas of the brain.

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Dynamic PET Disadvantages

• Poor spatial resolution (compared to MRI)
• Can be used for functional imaging but because of
  spatial resolution very few researchers still use
  PET
• Much more expensive than CT
• Takes a long time. Therefore
• Not optimal for persons with acute condition
  needing immediate medical management
• Not for persons who have difficulty laying still
  for extended period of time

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PET scans are improving
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Dynamic fMRI

• Take rapid MRI scans that are sensitive to
  blood-oxygen level (T2 weighted images).
• Used to determine which parts of the brain are
  activated by different types of physical
  sensation or activity.
• By collecting repeated MRI scans while a subject
  is processing a specific task, it is possible
  to identify what regions of the subjects brain
  receive increased blood flow

T2 fMRI scan Scans entire brain every 3 sec
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Dynamic fMRI

• We can use fMRI to examine recovery from brain
  injury and guide neurosurgery.
• We can also use fMRI to discover how the healthy
  brain functions.

Analysis of a series of fMRI scans Shown on top
of T1 scan
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Sodium Amytal Infusion

• Wada Test
• Intracarotid injection decreases function in one
  hemisphere for 2-10 min.
• Can test function of remaining hemisphere
  separate from one receiving drug.
• Used early in epilepsy cases

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Electroencephalography (EEG)

• Measuring electrical potentials from electrodes
  placed on the scalp
• Can make comparisons of activity in various parts
  of the brain
• Comparison of different wave patterns to
  represent different physiological functioning
• Compares function over time

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Measuring electrical activity

• When neurons fire, they create electical dipoles.
• Neurons aligned perpendicular to cortical surface.

-

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EEG

• With EEG we measure rhythms of the brain
• Alpha 7-13 Hz mostly posterior. It is brought
  out by closing the eyes and by relaxation, and
  abolished by thinking. It is the major rhythm
  seen in normal relaxed adults
• Beta gt13 Hz most evident frontally. It is
  accentuated by sedatives. It is the dominant
  rhythm in people who are alert or anxious or who
  have their eyes open
• Theta 3.5-7.5 Hz and is classed as "slow"
  activity. It is abnormal in awake adults but is
  perfectly normal in children upto 13 years and in
  sleep
• Delta lt3 Hz. It tends to be the highest in
  amplitude. It is quite normal and is the dominant
  rhythm in infants up to one year and in stages 3
  and 4 of sleep
• Useful for measuring sleep
• http//www.brown.edu/Departments/Clinical_Neurosci
  ences/louis/eegfreq.html

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Electromyography (EMG)

• Measure electrical activity at the level of the
  muscle
• Can determine if muscle is receiving electrical
  stimulation
• Helpful in spinal injury cases and myoneural
  problems

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Additional Procedures

• Dichotic listening
• Assesses cerebral dominance
• Individuals usually understand speech better with
  right ear as fibers cross to left hemisphere
  which is dominant for speech
• Two words presented simultaneously - one to each
  ear - Person reports which word was processed
• Lumbar Puncture
• Spinal Tap to determine the presence of
  infections in cerebrospinal fluid
• Fluid removed from lumbar subarachnoid space

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Neurosurgical Procedures

• Cortical mapping through craniotomy
• Stereotactic Surgery (subcortical mapping)
• Cordotomy
• sectioning of lateral spinothalamic tract to
  relieve pain when medication is not effective
• Carotid Endarterectomy
• Removal of sclerotic plaque from the internal
  carotid artery to increase blood flow
• Aneurysm Clipping
• Metal lip is used to obliterate the bulge to
  reduce possibility of rupture

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Seizures

• Instability of electrical activity in the brain
• 70-75 occur before age 20.
• Some are not recurrent
• Recurrent seizures Epilepsy
• Can be secondary to head injury, metabolic
  abnormalities, tumors, infarcts, infections, and
  physiological disturbances. (Some etiologies are
  unknown)

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Types of Seizures

• Partial-Focal
• Single area with a cortical or subcortical lesion
• Seizure spreads from one body part action
  recruiting additional movement
• Partial-Complex
• Lesions in temporal lobe structures
• Automatic irrational behavior for which there is
  not memory
• Petit Mal Seizures
• Between ages 3 and 12 usually disappear after age
  30
• Staring, chewing clinking, and myoclonic jerks
• Grand Mal (Tonic Clonic) Seizures
• Loss of consciousness with tonic convulsion

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Seizures

• For epilepsy
• Anti-epileptic drugs available
• Neurosurgery to remove origin
• What to Do When a Person Has a Seizure
• Do not hold the person down or try to stop
  movements
• Keep objects or furniture away from area to
  prevent injury
• Do not put anything in the mouth
• Turn head to side to avoid choking on food
• Call for assistance and observe symptoms. Time if
  possible

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Dominant Inheritance

• For children to express trait, one parent must
  have at least one copy of the gene.
• In this example, the father has the gene.
• You will express this gene, regardless of whether
  you have one or two copies.
• Example Brown eyes

A
N
nn
Dn
nn
Dn
nn
Dn
A
N
A
N
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Recessive Inheritance

• For children to express trait, both parents must
  be have at least one copy of the gene.
• In this example, both parents are carriers
  they have only a single copy.
• Example Blue eyes.

C
C
Nr
Nr
rr
Nr
Nr
NN
C
A
N
C
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X-Linked Inheritance

• Females have two X-chromosomes, males have one.
• All boys inherited their X-chromosome from their
  mother.
• Boys vulnerable to recessive mutations on the
  X-chromosome.
• Example Red-green color blindness.

C
N
Xx
xy
xx
xy
Xy
Xx
A
C
N
N
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Electrical stimulation, TMS
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Guided electrode implant
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Aneurysms