Introduction to Introduction to Neuroimaging Neuroimaging

Aaron S. Field, MD, PhDAaron S. Field, MD, PhDAssistant Professor of RadiologyAssistant Professor of Radiology

Neuroradiology SectionNeuroradiology Section

University of Wisconsin–MadisonUniversity of Wisconsin–Madison

Updated 10/3/06

Neuroimaging ModalitiesNeuroimaging Modalities• Radiography (X-Ray)Radiography (X-Ray)

• Fluoroscopy (guided procedures)Fluoroscopy (guided procedures)

• AngiographyAngiography

• DiagnosticDiagnostic

• InterventionalInterventional

• MyelographyMyelography

• Ultrasound (US)Ultrasound (US)

• Gray-Scale Gray-Scale

• Color DopplerColor Doppler

• Computed Tomography (CT)Computed Tomography (CT)

• CT Angiography (CTA)CT Angiography (CTA)

• Perfusion CT Perfusion CT

• CT MyelographyCT Myelography

•Magnetic Resonance (MR)Magnetic Resonance (MR)

• MR Angiography/Venography MR Angiography/Venography (MRA/MRV)(MRA/MRV)

• Diffusion and Diffusion Tensor MRDiffusion and Diffusion Tensor MR

• Perfusion MRPerfusion MR

• MR SpectroscopyMR Spectroscopy

• Functional MR (fMRI)Functional MR (fMRI)

•Nuclear MedicineNuclear Medicine

•SPECTSPECT

•PETPET

““Duplex”Duplex”

Radiography (X-Ray)Radiography (X-Ray)

Radiography (X-Ray)Radiography (X-Ray)

Primarily used for spine:Primarily used for spine:• TraumaTrauma• Degenerative DzDegenerative Dz• Post-opPost-op

Fluoroscopy (Real-Time X-Ray)Fluoroscopy (Real-Time X-Ray)

Fluoro-guided procedures:Fluoro-guided procedures:• AngiographyAngiography• MyelographyMyelography

Fluoroscopy (Real-Time X-Ray)Fluoroscopy (Real-Time X-Ray)Digital Subtraction AngiographyDigital Subtraction Angiography

Fluoroscopy (Real-Time X-Ray)Fluoroscopy (Real-Time X-Ray)Digital Subtraction AngiographyDigital Subtraction Angiography

• Aneurysms, vascular malformations and fistulaeAneurysms, vascular malformations and fistulae• Vessel stenosis, thrombosis, dissection, pseudoaneurysmVessel stenosis, thrombosis, dissection, pseudoaneurysm• Stenting, embolization, thrombolysis (mechanical and pharmacologic) Stenting, embolization, thrombolysis (mechanical and pharmacologic)

• Ability to interveneAbility to intervene• Time-resolved blood flow dynamics (arterial, capillary, venous phases)Time-resolved blood flow dynamics (arterial, capillary, venous phases)• High spatial resolutionHigh spatial resolution

• Invasive, risk of vascular injury and strokeInvasive, risk of vascular injury and stroke• Iodinated contrast and ionizing radiationIodinated contrast and ionizing radiation

Indications:Indications:

Advantages:Advantages:

Disadvantages:Disadvantages:

Digital Subtraction AngiographyDigital Subtraction Angiography

Fluoroscopy (Real-Time X-Ray)Fluoroscopy (Real-Time X-Ray)

MyelographyMyelography

Lumbar/cervical punctureLumbar/cervical puncture

Inject contrast intrathecally Inject contrast intrathecally with fluoroscopic guidancewith fluoroscopic guidance

Follow-up with post-myelo CT Follow-up with post-myelo CT (CT myelogram)(CT myelogram)

MyelographyMyelography

• Spinal stenosis, nerve root compressionSpinal stenosis, nerve root compression• CSF leakCSF leak

• Excellent CSF/soft-tissue/bone/metal contrastExcellent CSF/soft-tissue/bone/metal contrast• Defines extent of subarachnoid space, identifies spinal blockDefines extent of subarachnoid space, identifies spinal block• Dynamic imaging possible (e.g. weight bearing, flexion/extension)Dynamic imaging possible (e.g. weight bearing, flexion/extension)

• Invasive, complications (CSF leak, headache, contrast reaction, Invasive, complications (CSF leak, headache, contrast reaction,

etc.)etc.)• Ionizing radiation and iodinated contrastIonizing radiation and iodinated contrast• Limited coverageLimited coverage

Indications:Indications:

Advantages:Advantages:

Disadvantages:Disadvantages:

UltrasoundUltrasound

carotidcarotid

US US transducertransducer

UltrasoundUltrasound

• Carotid stenosisCarotid stenosis• Vasospasm - Transcranial Doppler (TCD)Vasospasm - Transcranial Doppler (TCD)• Infant brain imaging (open fontanelle = acoustic window)Infant brain imaging (open fontanelle = acoustic window)

• Noninvasive, well-tolerated, readily available, low costNoninvasive, well-tolerated, readily available, low cost• Quantitates blood velocity Quantitates blood velocity • Reveals morphology of atheromatous plaquesReveals morphology of atheromatous plaques

• Severe stenosis may appear occludedSevere stenosis may appear occluded• Limited coverage, difficult through air/boneLimited coverage, difficult through air/bone• Operator dependentOperator dependent

Indications:Indications:

Advantages:Advantages:

Disadvantages:Disadvantages:

Ultrasound – Gray ScaleUltrasound – Gray Scale

Gray-scale image of carotid arteryGray-scale image of carotid artery

Ultrasound – Gray ScaleUltrasound – Gray Scale

Gray-scale image of carotid arteryGray-scale image of carotid artery

Plaque in ICAPlaque in ICA

Ultrasound - Color DopplerUltrasound - Color Doppler

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

125 – 225125 – 225 50 – 7050 – 70

225 – 350225 – 350 70 – 9070 – 90

>350>350 >90 >90

Computed Tomography (CT)Computed Tomography (CT)

Computed TomographyComputed Tomography

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

ray beam ray beam attenuationattenuation (essentially(essentially

densitydensity)) inin

Hounsfield Units (HU)Hounsfield Units (HU)

HUHUwaterwater = 0 = 0

Bright = Bright = “hyperattenuating”“hyperattenuating” or or

“hyperdense”“hyperdense”

Computed TomographyComputed Tomography

Typical HU Values:Typical HU Values:

AirAir –1000–1000

FatFat –100 to –40–100 to –40

WaterWater 00

Watery fluid Watery fluid (e.g. CSF)(e.g. CSF) 0–200–20

White matterWhite matter 20–3520–35

Gray matterGray matter 30–4030–40

Blood clotBlood clot 55–7555–75

CalcificationCalcification >150>150

BoneBone 10001000

Metallic foreign bodyMetallic foreign body>1000>1000

BrainBrain

CT IndicationsCT Indications• Skull and skull base, vertebraeSkull and skull base, vertebrae

(trauma, bone lesions)(trauma, bone lesions)

• VentriclesVentricles

(hydrocephalus, shunt placement)(hydrocephalus, shunt placement)

• Intracranial masses, mass effectsIntracranial masses, mass effects

(headache, N/V, visual symptoms, etc.)(headache, N/V, visual symptoms, etc.)

• Hemorrhage, ischemiaHemorrhage, ischemia

(stroke, mental status change)(stroke, mental status change)

• CalcificationCalcification

(lesion characterization)(lesion characterization)

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed TomographyParenchymaParenchyma

Attenuation: High or Low?Attenuation: High or Low?

High:High:

1.1. Blood, calciumBlood, calcium

2.2. Less fluid, more tissueLess fluid, more tissue

Low:Low:

1.1. Fat, air Fat, air

2.2. More fluid, less tissueMore fluid, less tissue

AirAir –1000–1000

FatFat –100 to –40–100 to –40

WaterWater 00

Watery fluidWatery fluid 0–200–20

White matterWhite matter 20–3520–35

Gray matterGray matter 30–4030–40

Blood clotBlood clot 55–7555–75

CalcificationCalcification >150>150

BoneBone 10001000

Metallic foreign bodyMetallic foreign body >1000>1000

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Cytotoxic EdemaCytotoxic Edema Vasogenic EdemaVasogenic EdemaCellular swellingCellular swelling

Gray-white margin lostGray-white margin lostLeaky capillariesLeaky capillariesGray is sparedGray is spared

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Computed TomographyComputed Tomography

Scan axially…Scan axially………stack and reslice stack and reslice

in any planein any plane

1.1. Rapid IV contrast bolusRapid IV contrast bolus

2.2. Dynamic scanning during Dynamic scanning during arterial phasearterial phase Neck: arch to skull baseNeck: arch to skull base Head: circle of WillisHead: circle of Willis

3.3. Advanced 2D and 3D Reconstructions:Advanced 2D and 3D Reconstructions: 2D multi-planar (sagittal, coronal)2D multi-planar (sagittal, coronal) Volume–rendered 3D reconsVolume–rendered 3D recons

CT AngiographyCT Angiography

• AtherosclerosisAtherosclerosis

• ThromboembolismThromboembolism

• Vascular dissectionVascular dissection

• AneurysmsAneurysms

• Vascular malformationsVascular malformations

• Penetrating traumaPenetrating trauma

CT AngiographyCT Angiography

CT Angiography - NeckCT Angiography - Neck

CarotidCarotid

bifurcationsbifurcations

Vertebral Vertebral arteriesarteries

Aortic archAortic arch

CT Angiography - HeadCT Angiography - HeadCircle of WillisCircle of Willis

AneurysmsAneurysms

Vascular MalformationsVascular Malformations

CT AngiographyCT Angiography3D Volume Rendering3D Volume Rendering

CT AngiographyCT Angiography3D Volume Rendering3D Volume Rendering

CT PerfusionCT Perfusion CBV

CBF

MTT

Rapid Imaging During 1Rapid Imaging During 1stst Pass of Contrast Bolus Pass of Contrast Bolus

Anterior cerebral arteryAnterior cerebral artery

Superior sagittal sinusSuperior sagittal sinus

Arterial Arterial phase:phase:

Venous Venous phase:phase:

Perfusion Parameters Derived From Perfusion Parameters Derived From Concentration-Time CurvesConcentration-Time Curves

Artery

VeinBolus arrival

Perfusion Parameter MapsPerfusion Parameter Maps

Transit TimeTransit Time Blood FlowBlood FlowBlood Blood

VolumeVolume

48 YO W/ CONFUSION,IMPAIRED COGNITION AND

LEG WEAKNESS

Dense MCA branch?Dense MCA branch?

CTA + Perfusion Example 1CTA + Perfusion Example 1

CTACTA

8.2

56.8

13.3

3.5

CBF MTT

CBV

1.4

2.7

CTP

ULCERATED PLAQUE

• Spinal CT following conventional myelogramSpinal CT following conventional myelogram

• Cross-sectional view of spinal canal along with Cross-sectional view of spinal canal along with

spinal cord and nerve rootsspinal cord and nerve roots

• Assess spinal stenosis/nerve root compression Assess spinal stenosis/nerve root compression

(spondylosis/spondylolisthesis, disc herniation, (spondylosis/spondylolisthesis, disc herniation,

trauma, pathologic fracture, neoplasm)trauma, pathologic fracture, neoplasm)

CT MyelographyCT Myelography

CT MyelographyCT Myelography

CT MyelographyCT Myelography

Magnetic Resonance (MR)Magnetic Resonance (MR)

Hydrogen proton Hydrogen proton in Hin H2200

MRIMRI

COMPUTERCOMPUTER

Magnetic ResonanceMagnetic Resonance

BB00

RFRF

TransmitterTransmitter ReceiverReceiver

RF = Radio FrequencyRF = Radio Frequency

The Magnet is Never Off!The Magnet is Never Off!

Magnetic Resonance Magnetic Resonance SafetySafety

Typically safe*:Typically safe*:• Orthopedic hardwareOrthopedic hardware

• Surgical clips, staples, sutures Surgical clips, staples, sutures (older devices must be checked!)(older devices must be checked!)

• Intravascular stents/filtersIntravascular stents/filters

* This is an incomplete list and there are many exceptions to every “rule”* This is an incomplete list and there are many exceptions to every “rule” When in doubt, check it out!When in doubt, check it out!

Typically unsafe*:Typically unsafe*:• Cardiac pacemakers Cardiac pacemakers

(and other electrical devices)(and other electrical devices)

• Some older aneurysm clipsSome older aneurysm clips

• Metal fragments in orbit Metal fragments in orbit (1 case report)(1 case report)

• Oxygen tanks, carts, chairs, stools, Oxygen tanks, carts, chairs, stools, IV poles, gurneys, etc.IV poles, gurneys, etc.

• Some cosmetics, tattoos, jewelry, Some cosmetics, tattoos, jewelry, hairpins, etc.hairpins, etc.

• Pager, watch, wallet, ID badge, Pager, watch, wallet, ID badge, pen, keys, pocketknife, etc.pen, keys, pocketknife, etc.

MRI Safety Test:MRI Safety Test:

Will it: Move? Torque? Get hot? Pass a current? Malfunction? Will it: Move? Torque? Get hot? Pass a current? Malfunction? Become a projectile? Get stuck in scanner? Become a projectile? Get stuck in scanner?

Magnetic ResonanceMagnetic ResonanceExcited protons Excited protons relax relax back to equilibriumback to equilibrium

Relaxation rates depend onRelaxation rates depend on local molecular environmentlocal molecular environment

T1T1

T2T2

T1T1 T2 T2 (w/ fat suppression)(w/ fat suppression)

Magnetic ResonanceMagnetic Resonance

Magnetic ResonanceMagnetic Resonance

Tissue contrast in MR may be based Tissue contrast in MR may be based on:on:• Proton densityProton density

• Water/fat/protein contentWater/fat/protein content

• Metabolic compounds (MR Spectroscopy)Metabolic compounds (MR Spectroscopy)

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

• Magnetic properties of specific moleculesMagnetic properties of specific molecules

e.g.e.g. HemoglobinHemoglobin

• Diffusion of waterDiffusion of water

• Perfusion (capillary blood flow)Perfusion (capillary blood flow)

• Bulk flow (large vessels, CSF)Bulk flow (large vessels, CSF)

Magnetic ResonanceMagnetic ResonanceT1-HyperintenseT1-Hyperintense (bright) (bright)

““FatFat and the and the 4 M’s4 M’s””

Fat Fat (unless deliberately suppressed)(unless deliberately suppressed)

MMethemoglobin (subacute hematoma)ethemoglobin (subacute hematoma)

MMineral deposition (Ca, Mg, Mn, etc.)ineral deposition (Ca, Mg, Mn, etc.)

MMelanin (melanoma)elanin (melanoma)

““MMush” (highly proteinaceous fluid)ush” (highly proteinaceous fluid)

Contrast material (gadolinium)Contrast material (gadolinium)

T1-HypointenseT1-Hypointense (dark) (dark)Water, paucity of mobile protons (air, cortical bone)Water, paucity of mobile protons (air, cortical bone)

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

Magnetic ResonanceMagnetic ResonanceT2-HyperintenseT2-Hyperintense (bright) (bright)

Water Water

T2 bright = more water and/or less tissue T2 bright = more water and/or less tissue (“T2 = H(“T2 = H220”)0”)

e.g. fluid collections, edema, demyelination, gliosis, e.g. fluid collections, edema, demyelination, gliosis, some tumors, et al…some tumors, et al… (non-specific!!)(non-specific!!)

FatFat (but usually (but usually suppressedsuppressed by design) by design)

T2-HypointenseT2-Hypointense (dark) (dark)Some blood products (subacute hematoma)Some blood products (subacute hematoma)

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

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

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

T1T1 T2 T2 (w/ fat suppression)(w/ fat suppression)

Magnetic ResonanceMagnetic Resonance

Magnetic ResonanceMagnetic Resonance

Magnetic ResonanceMagnetic Resonance

Magnetic ResonanceMagnetic Resonance

Magnetic ResonanceMagnetic ResonanceFat SuppressionFat Suppression

Magnetic ResonanceMagnetic ResonanceFluid SuppressionFluid Suppression

T2-weightedT2-weighted T2-weightedT2-weighted FLFLuiduid AAttenuatedttenuated IInversion nversion

RRecovery (ecovery (FLAIRFLAIR))

Magnetic ResonanceMagnetic ResonanceFluid SuppressionFluid Suppression

T2-weightedT2-weighted T2-weightedT2-weighted FLFLuiduid AAttenuatedttenuated IInversion nversion

RRecovery (ecovery (FLAIRFLAIR))

Magnetic ResonanceMagnetic Resonance

Magnetic ResonanceMagnetic Resonance

T2T2 T2*T2*

Accentuating blood/calciumAccentuating blood/calcium

Magnetic ResonanceMagnetic Resonance

FIESTAFIESTA

CN-5CN-8

CN-7

Cranial nervesCranial nerves

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

NORMALNORMAL CYTOTOXIC CYTOTOXIC EDEMAEDEMA

Diffusion Diffusion

MR Signal MR Signal

Diffusion MR ImagingDiffusion MR Imaging

Magnetic ResonanceMagnetic ResonanceImaging DiffusionImaging Diffusion

Highly sensitive to Highly sensitive to acute ischemia—acute ischemia—

+ within a few hours!+ within a few hours!

No other imaging is No other imaging is more sensitive to more sensitive to acute ischemia!acute ischemia!

Magnetic Resonance AngiographyMagnetic Resonance Angiography

Contiguous axial Contiguous axial “source” images…“source” images…

……reformatted to “maximum reformatted to “maximum intensity projections” intensity projections” (MIP)(MIP)

Multiple projections allow Multiple projections allow 3D-like display3D-like display

MR VenogramMR Venogram

Superior sagittal sinus thrombosisSuperior sagittal sinus thrombosis

Magnetic Resonance AngiographyMagnetic Resonance Angiography

MRA MRA Perfusion MR Perfusion MR

Magnetic Resonance Angiography Magnetic Resonance Angiography with Perfusion MRwith Perfusion MR

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

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

2.2. Normal blood-brain barrier Normal blood-brain barrier keeps contrast outkeeps contrast out of brain! of brain!

Enhancement implies BBB either leaky or non-existentEnhancement implies BBB either leaky or non-existent

Remember: Some structures live outside the BBB!Remember: Some structures live outside the BBB!

IV Contrast in NeuroimagingIV Contrast in Neuroimaging

1.1. VesselsVessels

2.2. MeningesMeninges

pachy = durapachy = dura

lepto = pia-arachnoidlepto = pia-arachnoid

3.3. Circumventricular organsCircumventricular organs (structures outside BBB)(structures outside BBB)

Pineal glandPineal gland

Pituitary glandPituitary gland

Choroid plexusChoroid plexus

4.4. Disrupted/leaky BBBDisrupted/leaky BBB

Some tumorsSome tumors

InflammationInflammation

InfarctionInfarction

IV Contrast in NeuroimagingIV Contrast in Neuroimaging

Enhancement:Enhancement:

IV Contrast: Yes or No?IV Contrast: Yes or No?

• Congenital malformationsCongenital malformations• TraumaTrauma• R/O strokeR/O stroke• R/O hemorrhageR/O hemorrhage• HydrocephalusHydrocephalus• DementiaDementia• EpilepsyEpilepsy

• NeoplasmNeoplasm• Infection Infection • Vascular diseaseVascular disease• Inflammatory diseaseInflammatory disease

w/o contrastw/o contrast with contrastwith contrast

Always best to provide detailed indication!Always best to provide detailed indication!

Radiologist will protocol exam accordinglyRadiologist will protocol exam accordingly

MR vs. CTMR vs. CT

Advantages:Advantages:

• Simpler, cheaper, more accessibleSimpler, cheaper, more accessible

• Tolerated by claustrophobicsTolerated by claustrophobics

• No absolute contraindicationsNo absolute contraindications

• Fewer pitfalls in interpretationFewer pitfalls in interpretation

• Better than MR for bone detailBetter than MR for bone detail

Disadvantages:Disadvantages:

• Ionizing radiationIonizing radiation

• IV contrast complicationsIV contrast complications

• Need recons for multi-planarNeed recons for multi-planar

• Limited range of tissue contrastsLimited range of tissue contrasts

CTCT MRMRAdvantages:Advantages:

• Much broader palette of tissue contrasts Much broader palette of tissue contrasts (including functional and molecular) yields (including functional and molecular) yields greater anatomic detail and more greater anatomic detail and more comprehensive analysis of pathologycomprehensive analysis of pathology

• No ionizing radiationNo ionizing radiation

• Direct multi-planar imagingDirect multi-planar imaging

• IV contrast better toleratedIV contrast better tolerated

Disadvantages:Disadvantages:

• Higher cost, limited accessHigher cost, limited access

• Difficult for unstable patientsDifficult for unstable patients

• Several absolute contraindications (cardiac Several absolute contraindications (cardiac pacer, some aneurysm clips, etc.)pacer, some aneurysm clips, etc.)

• Claustrophobics may need sedationClaustrophobics may need sedation

• Image interpretation more challengingImage interpretation more challenging

• Lacks bone detailLacks bone detail

Introduction to Introduction to Neuroimaging Neuroimaging

Aaron S. Field, MD, PhDAaron S. Field, MD, PhDAssistant Professor of RadiologyAssistant Professor of Radiology

Neuroradiology SectionNeuroradiology Section

University of Wisconsin–MadisonUniversity of Wisconsin–Madison