Curs 2 Neuroimagistica

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NEUROIMAGISTICA

CURS



Brain Imaging

Static : „Anatomical‟ – identify brainstructures

Was the frontal cortex damaged by thestroke?

Dynamic: Identify brain function

Does the frontal cortex show normalmetabolism?



Neuroimaging Modalities• Radiography (X-Ray)

• Fluoroscopy (guided procedures)

• Angiography

• Diagnostic

• Interventional

• Myelography

• Ultrasound (US)

• Gray-Scale

• Color Doppler

• Computed Tomography (CT)

• CT Angiography (CTA)

• Perfusion CT

• CT Myelography

•Magnetic Resonance (MR)

• MR Angiography/Venography(MRA/MRV)

• Diffusion and Diffusion Tensor MR

• Perfusion MR

• MR Spectroscopy

• Functional MR (fMRI)

•Nuclear Medicine

•SPECT

•PET

―Duplex‖



Radiography (X-Ray)



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 brokenbones

Poor for questions about grey vs white matter



Radiography (X-Ray)

Primarily used for spine:

• Trauma

• Degenerative Dz

• Post-op



Fluoroscopy (Real-Time X-Ray)

Fluoro-guided procedures:

• Angiography

• Myelography



Static: Cerebral Angiography

Identifies arterialdisease, aneurysmsand AV malformations

Radiopaque substancereleased into blood andfollowed throughsystem

Digital subtraction:computer developmentto improve contrast inpictures




Digital Subtraction Angiography




Myelography

Lumbar/cervical puncture

Inject contrast intrathecallywith fluoroscopic guidance

Follow-up with post-myelo CT

(CT myelogram)



Ultrasound

carotid

UStransducer



Static: CT

Computerized Tomography (CT) orComputerized Axial Tomography (CAT)

Looks at radiographic pictures taken inseries across brain

May be enhanced by use of compounds

injected

Excellent for distinguishing relationshipsand shifts and lesions



Ultrasound – Gray Scale

Gray-scale image of carotid artery



Ultrasound – Gray Scale

Gray-scale image of carotid artery

Plaque in ICA



Ultrasound - Color Doppler

Peak Systolic Velocity (cm/sec) ICA Stenosis (% diameter)

125 – 225 50 – 70

225 – 350 70 – 90

>350 >90



Static: CT

Imaging technique thatrelies 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)



CT or CAT scan(Computed Tomography)



Computed Tomography (CT)



Computed Tomography

A CT image is a pixel-by-pixel map of

X-ray beam attenuation

(essentially density) in

Hounsfield Units (HU)

HUwater = 0

Bright = ―hyperattenuating‖ or

―hyperdense‖



Computed Tomography

Typical HU Values:

Air –1000

Fat –100 to –40

Water 0

Watery fluid (e.g. CSF) 0–20

White matter 20–35

Gray matter 30–40

Blood clot 55–75Calcification >150

Bone 1000

Metallic foreign body >1000

Brain





Computed Tomography



Computed Tomography



Computed Tomography



Computed Tomography



Computed Tomography

Scan axially…

…stack and reslice

in any plane



1. Rapid IV contrast bolus

2. Dynamic scanning during arterial phase

Neck: arch to skull base

Head: circle of Willis

3. Advanced 2D and 3D Reconstructions:

2D multi-planar (sagittal, coronal)

Volume–rendered 3D recons

CT Angiography



CT Angiography - Neck

Carotid

bifurcations

Vertebralarteries

Aortic arch

CT A i h H d



CT Angiography - HeadCircle of Willis

Aneurysms

Vascular Malformations



CT Angiography

3D Volume Rendering



CT Angiography

3D Volume Rendering



CT Perfusion CBV

CBF

MTT



Rapid Imaging During 1st Pass of Contrast Bolus

Anterior cerebral artery

Superior sagittal sinus

Arterial

phase:

Venousphase:



Perfusion Parameters Derived FromConcentration-Time Curves

Artery

VeinBolus

arrival



Perfusion Parameter Maps

Transit Time Blood FlowBlood

Volume



48 YO W/ CONFUSION,

IMPAIRED COGNITION AND

LEG WEAKNESS

Dense MCA branch?

CTA + Perfusion Example 1

CBF MTTCTP



8.2

56.8

13.3

3.5

CBF MTT

CBV

1.4

2.7

CTP



CT Myelography



CT Myelography



Static: CT

Is based on absorption of x-rays as they pass throughthe 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-rayspass through and exit the body

The amount of x-rays absorbed contributes to theradiation dose to the patient

During conventional x-ray imaging, the exiting x-raysinteract with a detection device (x-ray film or otherimage 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 “ ”



Static: CT Advantages of CT Very quick

Good spatial resolutioncompared to metabolic

imaging Newer CTs can scan

perfusion

Is widely available (cheap

compared to MRI)

Disadvantages of CT

Uses X-rays (radiation!)

Cannot detect acuteischemic stroke

Poor spatial resolutioncompared to MRI



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



Static: CT

AbnormalCT -

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

C t d T h



Computed Tomography

Parenchyma

Attenuation: High or Low?

High:

1. Blood, calcium

2. Less fluid, more tissue

Low:

1. Fat, air

2. More fluid, less tissue

Air –1000

Fat –100 to –40

Water 0

Watery fluid 0–20White matter 20–35

Gray matter 30–40

Blood clot 55–75

Calcification >150

Bone 1000

Metallic foreign body >1000



Static: CT

Infarct

Hemorrhage Tumor



CT scans are improving



Static: MRI

Magnetic Resonance Imaging

Not radiographic, analyzes response to

radiofrequency signal Visualizes structures

A T h i MRI



Assessment Techniques MRI.

M ti R (MR)



Magnetic Resonance (MR)

Hydrogen protonin H20

MRI

M ti R



COMPUTER

Magnetic Resonance

B0

RF

Transmitter Receiver

RF = Radio Frequency



First Recorded Use of MRIThe first use of MRI on a human happened on July 3, 1977 at 4:45am.Dr Damadian and his post-graduate assistants, Doctors LawrenceMinkoff and Michael Goldsmith, made a MRI image of Larry Minkoff’schest. This scan was done using the very first MRI machine, known asIndomitable. The first scans of patients with cancer occurred in 1978.Indomitable can now be found in the Smithsonian Institute as a pieceof pioneering medical history.

Dr Damadian and his assistants, Dr

Minkoff and Goldsmith standing next tothe Indomitable

The first ever Magnetic ResonanceImage. This is an image of DrMinkoff’s Chest taken on July 3, 1977at 4:45am



Principles of MRIMRI revolves around the fact that the human body is primarilycomposed of fat and water. Both of which contain hydrogen atoms. Thehuman body is roughly 63% hydrogen.

MRI also uses the fact that the nuclei of some atoms behave like amagnet. Whilst there is no magnetic field external to our body thehydrogen atoms are not lined up in any particular order. When these

atoms are subjected to a strong magnetic field, such as one created byan MRI machine, the nuclei align the axis of spin either with or againstthe direction of the magnetic field.

In picture A the atoms have noexternal magnetic field acting uponit, therefore the alignment of theatoms is not uniform.In picture B however there is anexternal magnetic force acting uponthe atoms causing them to line upuniformly either along or againstthe magnetic axis of B

0



Principles of MRI (continued)When the magnetic field applied is turned off, the atoms will return totheir un-uniform state again. In doing this they release a certain radiofrequency photon emission. These emissions are what’s collected andcan be turned into an image by a computer.

Simplified diagram of the components of anMRI system.



Transmit Receive

rf

coil

rf

coil

main

magnetmain

magnet

gradientShimming

ControlComputer

The Magnet is Never Off!



The Magnet is Never Off!

i i



Copyright 2007

Imaging Equipment Common causes of accidents

• Mechanical failures with radiology systems

• MR environment problems



Copyright 2007

Radiology Systems

Accidents result from Heavy use

Abuse

Poor/inadequate maintenance



Copyright 2007

Mechanical Failures

Carriage supports

Table

Foot rest

Falling parts

Impacts

Collisions (failure of

anti-collision sensors



Copyright 2007

MR Environment Problems

Projectile effect

Torque

Burns

Image artifacts

Accessory devicemalfunctions



Copyright 2007

Projectile Effect

MR systemO cylinder 2



Copyright 2007

Projectiles we have seen:

• Oxygen cylinders• Chairs

• IV poles

•

Ladder • Scissors

• Infusion pumps

•

Oscilloscope• Pens

• Pillows• Pulse oximeters

• Laundry Carts

•Sandbag

• Stethoscopes

• Hand tools

•

Floor buffer • Hair clips



Copyright 2007

Torque Problems

Magnetic implants

Aneurysm clips

Tiny magnetic particlesor fragments

Greater risk with high-field-strength systems

(1.0 T)



Copyright 2007

Burns Coiled or looped devices

Pulse-oximeter sensors

ECG electrodes

Implantable infusion pumps Nitroglycerin patches

Metal-containing tissue expanders

Pacing electrodes Contact with bore walls or RF coils



Copyright 2007

Device Malfunctions

Reference: Kaut-Roth, C. MRI Safety [online]. 1996. Available from

Internet: http://www.t2star.com/safety_1/MR_Safety.pdf .

Note increase in the

T-wave or ST-segment amplitude.

Static Field Effectson ECG

http://www.t2star.com/safety_1/MR_Safety.pdf

http://www.t2star.com/safety_1/MR_Safety.pdf



Copyright 2007

Device Malfunctions

Pacemakers and other implanted devices

Electric motors

Electronic circuits

Magnetically attached device

ECG waveforms

Analog gauges/meters

Magnetic Resonance



Magnetic ResonanceExcited protons relax back to equilibrium

Relaxation rates depend on

local molecular environment

T1

T2

Magnetic Resonance



T1 T2(w/ fat suppression)

Magnetic Resonance

Magnetic Resonance



Magnetic Resonance

Tissue contrast in MR may be based on:

• Proton density

• Water/fat/protein content

• Metabolic compounds (MR Spectroscopy)

e.g. Choline, creatine, N-acetylaspartate, lactate

• Magnetic properties of specific molecules

e.g. Hemoglobin

• Diffusion of water

• Perfusion (capillary blood flow)

• Bulk flow (large vessels, CSF)

Magnetic Resonance



Magnetic Resonance

T1-Hyperintense (bright)

“Fat and the 4 M’s”

Fat (unless deliberately suppressed)

Methemoglobin (subacute hematoma)

Mineral deposition (Ca, Mg, Mn, etc.)

Melanin (melanoma)

“Mush” (highly proteinaceous fluid)

Contrast material (gadolinium)

T1-Hypointense (dark)Water, paucity of mobile protons (air, cortical bone)

High flow (e.g. arterial “flow voids”)

Magnetic Resonance



Magnetic Resonance

T2-Hyperintense (bright)

Water

T2 bright = more water and/or less tissue (“T2 = H20”)

e.g. fluid collections, edema, demyelination, gliosis,

some tumors, et al… (non-specific!!)

Fat (but usually suppressed by design)

T2-Hypointense (dark)Some blood products (subacute hematoma)

Mineral deposition (Ca, Mg, Mn, etc.)

Paucity of water or mobile protons (air, cortical bone)

High flow (e.g. arterial “flow voids”)

Magnetic Resonance



T1 T2(w/ fat suppression)

Magnetic Resonance

Magnetic Resonance



Magnetic Resonance

Magnetic Resonance



Magnetic Resonance

Magnetic Resonance



Magnetic Resonance

Magnetic Resonance



Magnetic Resonance

Fat Suppression

Magnetic Resonance



Magnetic Resonance

Fluid Suppression

T2-weighted T2-weighted FLuidAttenuated Inversion

R ecovery (FLAIR )

Magnetic Resonance



Magnetic Resonance

Fluid Suppression

T2-weighted T2-weighted FLuidAttenuated Inversion

R ecovery (FLAIR )

Magnetic Resonance



Magnetic Resonance

Magnetic Resonance



Magnetic Resonance

T2 T2*

Accentuating blood/calcium

Magnetic Resonance



Magnetic Resonance

FIESTA

CN-5CN-8

CN-7

Cranial nerves

High spatial resolution, high tissue-CSF contrast (T2 weighting)

Diffusion MR Imaging



NORMAL CYTOTOXICEDEMA

Diffusion

MR Signal

Diffusion MR Imaging

Magnetic Resonance



Magnetic Resonance

Imaging Diffusion

Highly sensitive toacute ischemia—

+ within a few hours!

No other imaging ismore sensitive toacute ischemia!

Magnetic Resonance Angiography



Contiguous axial―source‖ images…

…reformatted to ―maximumintensity projections‖ (MIP)

Multiple projections allow3D-like display




MR Venogram

Superior sagittal sinus thrombosis




MRA Perfusion MR

with Perfusion MR

IV Contrast in Neuroimaging



1. CT: Iodine-based (I is highly attenuating of X-ray beam)

MRI: Gadolinium-based (Gd is a paramagnetic metal thathastens T1 relaxation of nearby water protons)

2. Normal blood-brain barrier keeps contrast out of brain!

Enhancement implies BBB either leaky or non-existentRemember: Some structures live outside the BBB!

IV Contrast in Neuroimaging



1. Vessels 2. Meninges

pachy = dura

lepto = pia-arachnoid

3. Circumventricular organs

(structures outside BBB)

Pineal gland

Pituitary gland

Choroid plexus

4. Disrupted/leaky BBB

Some tumors

Inflammation

Infarction

Enhancement:

IV C t t Y N ?



IV Contrast: Yes or No?

Congenital malformations

Trauma

R/O stroke

R/O hemorrhage Hydrocephalus

Dementia

Epilepsy

Neoplasm

Infection

Vascular disease

Inflammatory disease

w/o contrast with contrast

Always best to provide detailed indication!

Radiologist will protocol exam accordingly

MR vs. CT



Advantages:

• Simpler, cheaper, more accessible

• Tolerated by claustrophobics

• No absolute contraindications

• Fewer pitfalls in interpretation

• Better than MR for bone detail

Disadvantages:

• Ionizing radiation

• IV contrast complications

• Need recons for multi-planar

• Limited range of tissue contrasts

CT MR Advantages:

• Much broader palette of tissue contrasts(including functional and molecular) yieldsgreater anatomic detail and morecomprehensive analysis of pathology

• No ionizing radiation

• Direct multi-planar imaging

• IV contrast better tolerated

Disadvantages:

• Higher cost, limited access

• Difficult for unstable patients

• Several absolute contraindications (cardiac

pacer, some aneurysm clips, etc.)• Claustrophobics may need sedation

• Image interpretation more challenging

• Lacks bone detail



MRI

Different types of MRI scan

T1 (anatomical): fast to acquire, excellent structuraldetail (e.g. white and gray matter).

T2 (pathological): slower to acquire, therefore usuallylower resolution than T1. Excellent for finding lesions.

T1 T2



Static: MRI

T1-

MRI

T2-

MRI

Infarct dark bright

Bleed bright1 bright1

Tumor dark bright

MS

plaque dark bright

Abnormal NormalT1-MRIT2-

MRI

dense

bonebright dark

air dark dark

fat bright bright

water dark bright

brain gm=gray,

wm=whitemedium

1. Unless very fresh or very old.



Static: MRI

Infarct

T1

T2



Static: MRI

Bleed

T1

T2

Low relative

contrast –

hard to

see on T2



Static: MRI

Tumor

T1

T2



Static: MRI

Multiple-Sclerosis

T1

T2

Positron Emission Tomography



Positron Emission Tomography(PET)



Physics of PET

Cherry, S. R. & Phelps, M. E. (1996) Imaging brain function with positron emission tomography. In A. W. Toga &

J. C. Maxxiotta (Eds.), Brain Mapping: The Methods (pp. 191-221). Toronto, ON: Academic Press.

PET images - radioactive



PET images radioactiveisotopes

O15 WaterFDG or

F18 fluorodeoxyglucose



Dynamic: PET

Positron Emission Tomography (PET) Measures uptake of radioactively-tagged

tracer. Often tracer is glucose to determine

which tissues have highest energy useduring 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?



Dynamic: PET – Clinical uses

Tumor detection (increased metabolism) Decreased metabolism in the brain

Can help distinguish between Alzheimer's disease, bloodflow shortages, depression, or some other reason fordementia

PET can localize the origin of seizure activity, guidingneurosurgery

PET

T2 MRI



Dynamic: PET – Clinical uses

PET can tell if muscle tremor is Parkinson'sdisease 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 whenrecurrence is suspected to show whetherstructural change is tumor re-growth or merelyscar tissue.

PET can "map" the areas of the brainresponsible for movement, speech, and othercritical functions. This is a remarkable guide forsurgeons who are performing delicate

operations on different areas of the brain.



Dynamic: PET – Disadvantages

Poor spatial resolution (compared to MRI)

Can be used for functional imaging but becauseof spatial resolution very few researchers stilluse PET

Much more expensive than CT

Takes a long time. Therefore:

Not optimal for persons with acute condition needingimmediate medical management

Not for persons who have difficulty laying still forextended period of time



PET scans are improving

f



Dynamic: fMRI

Take rapid MRI scans that are sensitive to blood-oxygen level (T2* weighted images).

Used to determine which parts of the brain areactivated 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 identifywhat regions of the subject‟s brain receive increased

blood flow T2* fMRI scan

Scans entire brain every 3 sec

D i fMRI



Dynamic: fMRI

We can use fMRI to examine recoveryfrom brain injury and guide neurosurgery.

We can also use fMRI to discover how thehealthy brain functions.

Analysis of a series of fMRIscans

Shown on top of T1 scan

S di A t l I f i



Sodium Amytal Infusion

Wada Test

Intracarotid injection decreases

function in one hemisphere for2-10 min.

Can test function of remaininghemisphere separate from one

receiving drug. Used early in epilepsy cases

El t h l h (EEG)



Electroencephalography (EEG)

Measuring electricalpotentials from electrodesplaced on the scalp

Can make comparisons of activity in various parts of the brain

Comparison of different

wave patterns to representdifferent physiologicalfunctioning

Compares function over

time

M i l t i l ti it



Measuring electrical activity

When neurons fire, they createelectical dipoles.

Neurons aligned perpendicular tocortical surface.

+

-

Event-Related Potential



Event Related Potential(ERP)

128 Channel Cap

M t h l h (MEG)



Magnetoencephalography (MEG)

151 Channel MEG

MRI MEG



MRI vs MEG

EEG



EEG With EEG we measure rhythms of the brain:

Alpha 7-13 Hz: mostly posterior. It is brought out by closing theeyes and by relaxation, and abolished by thinking. It is the majorrhythm seen in normal relaxed adults

Beta >13 Hz: most evident frontally. It is accentuated bysedatives. 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 andin sleep

Delta <3 Hz. It tends to be the highest in amplitude. It is quitenormal and is the dominant rhythm in infants up to one year andin stages 3 and 4 of sleep

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

El t h (EMG)



Electromyography (EMG)

Measure electrical activity at the level of themuscle

Can determine if muscle is receiving electricalstimulation

Helpful in spinal injury cases and myoneuralproblems

Additi l P d



Additional Procedures

Dichotic listening Assesses cerebral dominance

Individuals usually understand

speech better with right ear asfibers cross to left hemisphere whichis dominant for speech

Two words presentedsimultaneously - one to each ear -

Person reports which word wasprocessed

Lumbar Puncture Spinal Tap to determine the

presence of infections in

El t i l ti l ti TMS



Electrical stimulation, TMS

G ided elect ode implant



Guided electrode implant

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