Transcript Temporal Aspects of Visual Extinction

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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How does an X-ray work?
 An overhead project transmits visible light
through object to screen
– Different materials have different opacity to
light
 Acetate plastic is transparent
 Some plastics translucent
 Ink is opaque
 X-ray camera send X-rays through object
to film plate.
– Different materials have different opacity to Xrays
 Air is transparent
 Soft tissue translucent
 Bones are relatively opaque
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 X-Rays are ‘ionizing radiation’ –
exposure can lead to cancer.
 Dose must be carefully monitored.
Ionizing Radiation
Breaks Bonds
 MRI uses radio waves.
 signal s are in the same range as
FM radio and TV (30-300MHz).
 Dose must be monitored as
extreme levels can warm you up.
Non-Ionizing Radiation
Heating
Electromagnetic radiation
Excites Electrons
Excites Nuclei
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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 patient’s 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
patient’s 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
CT scan
CT - scan
Enhancement
Dense
bone
Air
Bright
Infarct
Dark
Subacute
Bleed
Bright
No
Fat
Dark
Tumor
Dark
Yes
Water
Dark
MS plaque
Dark
Acute
Brain
Gray
Dark
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Static: CT
Infarct
Hemorrhage
Tumor
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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
T1-MRI
T2-MRI
dense
bone
bright
dark
air
dark
dark
fat
bright
bright
water
dark
bright
brain
gm=gray,
wm=white
medium
T1-MRI T2-MRI
Infarct
Bleed
Tumor
dark
bright1
dark
bright
bright1
bright
MS
plaque
dark
bright
1. Unless very fresh or very old.
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Static: MRI
Infarct
T1
T2
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Static: MRI
Bleed
T1
Low relative
contrast –
hard to see
on T2
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 subject’s 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 >13 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 <3 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_Neurosciences/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
Dn
nn
Dn
nn
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.
NN
Example: Blue eyes.
N
C
C
Nr
Nr
Nr
Nr
rr
C
C
A
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X-Linked Inheritance
 Females have two Xchromosomes, males have
one.
 All boys inherited their Xchromosome from their
mother.
 Boys vulnerable to
recessive mutations on the
X-chromosome.
 Example: Red-green color
blindness.
C
N
Xx
xy
xy
xx
Xy
Xx
N
N
A
C
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Plunnett square
 For traits that are determined by a single gene, you easy to compute
odds of a gene being expressed.
 Example: In cats: long hair (l) is recessive, Short hair (S) is dominant.
 Consider the kittens from two cats – a long hair (l l) and a homozygous
short hair (SS).
– All the kittens will have the short hair trait
– All the kittens will we heterozygous (S l):
all are carriers for long hair.
l
l
S
Sl
Sl
S
Sl
Sl
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Plunnett square
 Consider the kittens from two cats – a long hair (l l) and a
heterozygous short hair (Sl).
– 50% of the kittens will be long hairs (l l)
– 50% of the kittens will be heterozygous short hairs (S l)
l
l
S
Sl
Sl
l
ll
ll
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Plunnett square
 Consider the kittens from two cats – a long hair (l l) and a
heterozygous short hair (SS).
– 50% of the kittens will be long hairs (l l)
– 50% of the kittens will be heterozygous short hairs (S l)
l
l
S
Sl
Sl
l
ll
ll
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Plunnett square
 Consider kittens from two heterozygous short hair (Sl) cats.
– 25% of the kittens will be homozygous short hairs (S S)
– 50% of the kittens will be heterozygous short hairs (S l)
– 25% of the kittens will be long hairs (l l)
S
l
S
SS Sl
l
Sl
ll
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Plunnett square – Sex linked
 X chromosome has far more genes than Y. Virtually all sex linked genes
are on the X chromosome. Males have one X, while females have two.
 Consider color vision – normal (N) vision is dominant, color blindness ©
is recessive.
 If the mother is a carrier, half of her boys will express the gene, half of
her daughters will be carriers:
N
N
NN N
c
Nc
c
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Electrical stimulation, TMS
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Guided electrode implant
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Aneurysms
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