Chapter 20 Diagnostic Techniques l Chris Rorden University

Chapter 20 Diagnostic Techniques l Chris Rorden University of South Carolina Norman J. Arnold School of Public Health Department of Communication Sciences and Disorders University of South Carolina 1

Brain Imaging l Static : ‘Anatomical’ – identify brain structures – l Was the frontal cortex damaged by the stroke? Dynamic: Identify brain function – Does the frontal cortex show normal metabolism? 2

Static: X-Ray l l X-ray tube projects through head Detector plate measures transmission of X-rays – – l l 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 3

How does an X-ray work? l An overhead project transmits visible light through object to screen – Different materials have different opacity to light l l 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 l l l Air is transparent Soft tissue translucent Bones are relatively opaque 4

l l X-Rays are ‘ionizing radiation’ – exposure can lead to cancer. Dose must be carefully monitored. Ionizing Radiation Breaks Bonds l MRI uses radio waves. signal s are in the same range as FM radio and TV (30 -300 MHz). Dose must be monitored as extreme levels can warm you up. Non-Ionizing Radiation Heating Electromagnetic radiation Excites Electrons Excites Nuclei 5

Static: Cerebral Angiography l l l 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 6

Static: CT Computerized Tomography (CT) or Computerized Axial Tomography (CAT) l Looks at radiographic pictures taken in series across brain l May be enhanced by use of compounds injected l Excellent for distinguishing relationships and shifts and lesions l 7

Static: CT l l l 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) 8

Static: CT l l l 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” 9

Static: CT Disadvantages of CT Advantages of CT l Uses X-rays (radiation!) l Very quick l Cannot detect acute l Good spatial resolution ischemic stroke compared to metabolic imaging l Poor spatial resolution l Newer CTs can scan perfusion compared to MRI l Is widely available (cheap compared to MRI) 10

Static: CT l 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 t. PA always get a CT before administration to rule out hemorrhage 11

Static: CT Abnormal Normal CT scan Enhancement CT - scan Dense bone Air Bright Fat Dark Infarct Dark Subacute Bleed Bright No Tumor Dark Yes Water Dark MS plaque Dark Acute Brain Gray Dark 12

Static: CT Infarct Hemorrhage Tumor 13

CT scans are improving 14

Static: MRI l Magnetic Resonance Imaging – – Not radiographic, analyzes response to radiofrequency signal Visualizes structures 15

MRI l Different types of MRI scan – – T 1 (anatomical): fast to acquire, excellent structural detail (e. g. white and gray matter). T 2 (pathological): slower to acquire, therefore usually lower resolution than T 1. Excellent for finding lesions. T 2 16

Static: MRI Abnormal Normal Tumor MS plaque bright 1 dark bright T 2 -MRI dense bone bright dark fat bright dark bright brain Bleed dark T 1 -MRI water Infarct T 1 -MRI T 2 -MRI air gm=gray, wm=white medium bright 1. Unless very fresh or very old. 17

Static: MRI l Infarct T 1 T 2 18

Static: MRI l Bleed T 1 Low relative contrast – hard to see on T 2 19

Static: MRI l Tumor T 1 T 2 20

Static: MRI l Multiple-Sclerosis T 1 T 2 21

Dynamic: PET Positron Emission Tomography (PET) l Measures uptake of radioactively-tagged tracer. Often tracer is glucose to determine which tissues have highest energy use during activity l l. 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? 22

Dynamic: PET – Clinical uses l l 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 T 2 MRI 23

Dynamic: PET – Clinical uses l l l 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. 24

Dynamic: PET – Disadvantages l l 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 25

PET scans are improving 26

Dynamic: f. MRI l l l Take rapid MRI scans that are sensitive to blood-oxygen level (T 2* 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 T 2* f. MRI scan Scans entire brain every 3 sec 27

Dynamic: f. MRI We can use f. MRI to examine recovery from brain injury and guide neurosurgery. l We can also use f. MRI to discover how the healthy brain functions. l Analysis of a series of f. MRI scans Shown on top of T 1 scan 28

Sodium Amytal Infusion l 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 29

Electroencephalography (EEG) l l 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 30

Measuring electrical activity When neurons fire, they create electical dipoles. l Neurons aligned perpendicular to cortical surface. l - + 31

EEG l 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 l Useful for measuring sleep l http: //www. brown. edu/Departments/Clinical_Neurosciences/louis/eegfreq. html 32

Electromyography (EMG) l l l 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 33

Additional Procedures l Dichotic listening – – – l 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 34

Neurosurgical Procedures l l l Cortical mapping through craniotomy Stereotactic Surgery (subcortical mapping) Cordotomy – l Carotid Endarterectomy – l sectioning of lateral spinothalamic tract to relieve pain when medication is not effective 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 35

Seizures l 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) 36

Types of Seizures l Partial-Focal – – l Partial-Complex – – l Lesions in temporal lobe structures Automatic irrational behavior for which there is not memory Petit Mal Seizures – – l Single area with a cortical or subcortical lesion Seizure spreads from one body part action recruiting additional movement 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 37

Seizures l For epilepsy – – l 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 38

Dominant Inheritance l l 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 A N 39

Recessive Inheritance For children to express trait, both parents must be have at least one copy of the gene. l In this example, both parents are ‘carriers’ – they have only a single copy. NN l Example: Blue eyes. l N C C Nr Nr rr C C A 40

X-Linked Inheritance l l 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 41

Plunnett square l l l 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 S l S l 42

Plunnett square l 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 S l l l l 43

Plunnett square l 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 S l l l l 44

Plunnett square l 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 S l l l 45

Plunnett square – Sex linked l l l 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 N c c 46

Electrical stimulation, TMS 47

Guided electrode implant 48

49

Aneurysms 50