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Chapter 20 Diagnostic Techniques

Chris RordenUniversity of South CarolinaNorman J. Arnold School of Public HealthDepartment of Communication Sciences and DisordersUniversity 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 X-rays

Air is transparent Soft tissue translucent Bones are relatively opaque

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Electromagnetic radiation

X-Rays are ‘ionizing radiation’ – exposure can lead to cancer.

Dose must be carefully monitored.

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.

Ioni

zing

Rad

iatio

nB

reak

s B

onds

Non

-Ion

izin

g R

adia

tion

Hea

ting

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  CT - scan

Dense bone

Bright

Air Dark

Fat Dark

Water Dark

Brain Gray

  CT scan Enhancement

Infarct Dark Subacute

Bleed Bright No

Tumor Dark Yes

MS plaque Dark Acute

Normal

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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

  T1-MRI T2-MRI

Infarct dark bright

Bleed bright1 bright1

Tumor dark bright

MS plaque dark bright

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

1. Unless very fresh or very old.

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Static: MRI

Infarct

T1 T2

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Static: MRI

Bleed

T1 T2Low relative

contrast – hard to see on 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

A N

A NA N

Dn nn

nnDn nnDn

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

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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

C AN C

Nr Nr

NrNN rrNr

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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

A CN N

Xx xy

xxxy XxXy

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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.

S

S

l l

S l

S l

S l

S l

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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)

S

l

l l

S l

l l

S l

l l

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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)

S

l

l l

S l

l l

S l

l l

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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 l

S S

S l

S l

l l

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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

c

N

N N

N c

N

c

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Electrical stimulation, TMS

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Guided electrode implant

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Aneurysms