Neurorad 1 intro

Introduction to
Neuroimaging
Aaron S. Field, MD, PhD
Assistant Professor of Radiology
Neuroradiology Section
University of Wisconsin–Madison

Updated 7/17/07


Neuroimaging Modalities
Magnetic Resonance (MR)

Radiography (X-Ray)
Fluoroscopy (guided procedures)
• Angiography
• Diagnostic
• Interventional
• Myelography
Ultrasound (US)
• Gray-Scale
• Color Doppler

“Duplex”

Computed Tomography (CT)
• CT Angiography (CTA)
• Perfusion CT
• CT Myelography

•

MR Angiography/Venography
(MRA/MRV)

•

Diffusion and Diffusion Tensor
MR

•

Perfusion MR

•

MR Spectroscopy (MRS)

•

Functional MR (fMRI)

Nuclear Medicine
•

Single Photon Emission
Computed Tomography (SPECT)

•

Positron Emission Tomography

(PET)


Radiography (X-Ray)


Radiography (X-Ray)
Primarily used for spine:
• Trauma
• Degenerative Dz
• Post-op


Fluoroscopy (Real-Time X-Ray)
Fluoro-guided procedures:
• Angiography
• Myelography


Fluoroscopy (Real-Time X-Ray)


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


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

Digital Subtraction Angiography
Indications:
•
•
•

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

Advantages:
•
•
•

Ability to intervene
Time-resolved blood flow dynamics (arterial, capillary, venous phases)
High spatial and temporal resolution

Disadvantages:
•
•

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


Fluoroscopy (Real-Time X-Ray)
Myelography
Lumbar or cervical puncture

Inject contrast intrathecally
with fluoroscopic guidance
Follow-up with post-myelo CT
(CT myelogram)


Myelography
Indications:
•
•
•

Spinal stenosis, nerve root compression
CSF leak
MRI inadequate or contraindicated

Advantages:
•

Defines extent of subarachnoid space, identifies spinal block

Disadvantages:
•
•
•

Invasive, complications (CSF leak, headache, contrast reaction,
etc.)
Ionizing radiation and iodinated contrast
Limited coverage

Ultrasound

US
transduce
r

carotid


Ultrasound
Indications:
•
•
•

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

Advantages:
•
•
•

Noninvasive, well-tolerated, readily available, low cost
Quantitates blood velocity
Reveals morphology (stability) of atheromatous plaques

Disadvantages:
•
•
•

Severe stenosis may appear occluded
Limited coverage, difficult through air/bone
Operator dependent


Ultrasound – Gray Scale

Gray-scale image of carotid artery


Ultrasound – Gray Scale

Plaque in ICA
Gray-scale image of carotid artery


Ultrasound - Color Doppler

Peak Systolic Velocity (cm/sec)
125 – 225
225 – 350
>350

ICA Stenosis (% diameter)
50 – 70

70 – 90
>90


Computed Tomography (CT)


Computed Tomography
A CT image is a pixel-by-pixel map of Xray beam attenuation
(essentially
density) in
Hounsfield Units (HU)
HUwater = 0
Bright = “hyper-attenuating” or
“hyper-dense”


Computed Tomography
Typical HU Values:
Air
Fat
Water
Other fluids

–1000
–100 to –40
0
(e.g. CSF)

White matter

Brain
Gray matter
Blood clot
Calcification

0–20
20–35
30–40
55–75
>150
1000

Bone
Metallic foreign body

>1000


Computed Tomography
Attenuation: High or Low?
High:

Low:

1. Blood, calcium

1. Fat, air

2. Less fluid / more tissue

2. More fluid / less tissue

Air
Fat
Water
Other fluids
White matter
Gray matter
Blood clot
Calcification
Bone
Metallic foreign body

–1000
–100 to –40
0
0–20
20–35
30–40
55–75
>150
1000
>1000



Computed Tomography

“Soft Tissue Window” “Bone Window”

Computed Tomography


Computed Tomography

Scan axially…

“2D Recons”

…stack and re-slice
in any plane


CT Indications
• Skull and skull base, vertebrae
(trauma, bone lesions)

• Ventricles
(hydrocephalus, shunt placement)

• Intracranial masses, mass effects
(headache, N/V, visual symptoms, etc.)

• Hemorrhage, ischemia
(stroke, mental status change)

• Calcification
(lesion characterization)