Download CT Angiography

Introduction to
Neuroimaging
Aaron S. Field, MD, PhD
Assistant Professor of Radiology
Neuroradiology Section
University of Wisconsin–Madison
Updated 10/3/06
Neuroimaging Modalities
• Radiography (X-Ray)
• Fluoroscopy (guided procedures)
• Angiography
• Interventional
• Functional MR (fMRI)
• Ultrasound (US)
•Nuclear Medicine
• Gray-Scale
“Duplex”
• Computed Tomography (CT)
• CT Angiography (CTA)
• CT Myelography
• Perfusion MR
• MR Spectroscopy
• Myelography
• Perfusion CT
• MR Angiography/Venography
(MRA/MRV)
• Diffusion and Diffusion Tensor MR
• Diagnostic
• Color Doppler
•Magnetic Resonance (MR)
•SPECT
•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)
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 resolution
Disadvantages:
•
•
Invasive, risk of vascular injury and stroke
Iodinated contrast and ionizing radiation
Fluoroscopy (Real-Time X-Ray)
Myelography
Lumbar/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
Advantages:
•
•
•
Excellent CSF/soft-tissue/bone/metal contrast
Defines extent of subarachnoid space, identifies spinal block
Dynamic imaging possible (e.g. weight bearing, flexion/extension)
Disadvantages:
•
•
•
Invasive, complications (CSF leak, headache, contrast reaction, etc.)
Ionizing radiation and iodinated contrast
Limited coverage
Ultrasound
US
transducer
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 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
X-ray beam attenuation
(essentially density) in
Hounsfield Units (HU)
HUwater = 0
Bright = “hyperattenuating” or
“hyperdense”
Computed Tomography
Typical HU Values:
Brain
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
55–75
Calcification
>150
Bone
1000
Metallic foreign body >1000
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)
Computed Tomography
Computed Tomography
Computed Tomography
Computed Tomography
Computed Tomography
Computed Tomography
Computed Tomography
Computed Tomography
Parenchyma
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
Watery fluid
White matter
Gray matter
–1000
–100 to –40
0
0–20
20–35
30–40
Blood clot
Calcification
Bone
Metallic foreign body
55–75
>150
1000
>1000
Computed Tomography
Computed Tomography
Computed Tomography
Computed Tomography
Cytotoxic Edema
Vasogenic Edema
Cellular swelling
Gray-white margin lost
Leaky capillaries
Gray is spared
Computed Tomography
Computed Tomography
Computed Tomography
Computed Tomography
Computed Tomography
Scan axially…
…stack and reslice
in any plane
CT Angiography
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
• Atherosclerosis
• Thromboembolism
• Vascular dissection
• Aneurysms
• Vascular malformations
• Penetrating trauma
CT Angiography - Neck
Carotid
bifurcations
Aortic arch
Vertebral
arteries
CT Angiography - Head
Circle of Willis
Vascular Malformations
Aneurysms
CT Angiography
3D Volume Rendering
CT Angiography
3D Volume Rendering
CT Perfusion
CBF
MTT
CBV
Rapid Imaging During 1st Pass of Contrast Bolus
Arterial
phase:
Anterior cerebral artery
Venous
phase:
Superior sagittal sinus
Perfusion Parameters Derived From
Concentration-Time Curves
Bolus
arrival
Vein
Artery
Perfusion Parameter Maps
Transit Time
Blood Flow
Blood
Volume
CTA + Perfusion Example 1
48 YO W/ CONFUSION,
IMPAIRED COGNITION AND
LEG WEAKNESS
Dense MCA branch?
CTA
CTP
CBF
MTT
56.8
8.2
13.3
CBV
2.7
1.4
3.5
ULCERATED PLAQUE
CT Myelography
• Spinal CT following conventional myelogram
• Cross-sectional view of spinal canal along with
spinal cord and nerve roots
• Assess spinal stenosis/nerve root compression
(spondylosis/spondylolisthesis, disc herniation,
trauma, pathologic fracture, neoplasm)
CT Myelography
CT Myelography
Magnetic Resonance (MR)
Hydrogen proton
in H20
MRI
Magnetic Resonance
Transmitter
Receiver
RF
RF = Radio Frequency
B0
COMPUTER
The Magnet is Never Off!
Magnetic Resonance Safety
MRI Safety Test:
Will it: Move? Torque? Get hot? Pass a current? Malfunction?
Become a projectile? Get stuck in scanner?
Typically safe*:
Typically unsafe*:
•
Orthopedic hardware
•
•
Surgical clips, staples, sutures
(older devices must be checked!) •
•
Intravascular stents/filters
Cardiac pacemakers
(and other electrical devices)
Some older aneurysm clips
•
Metal fragments in orbit
(1 case report)
•
Oxygen tanks, carts, chairs, stools,
IV poles, gurneys, etc.
•
Some cosmetics, tattoos, jewelry,
hairpins, etc.
•
Pager, watch, wallet, ID badge,
pen, keys, pocketknife, etc.
* This is an incomplete list and there are many exceptions to every “rule”
When in doubt, check it out!
Magnetic Resonance
Excited protons relax back to equilibrium
T2
T1
Relaxation rates depend on
local molecular environment
Magnetic Resonance
T1
T2
(w/ fat suppression)
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
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
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
Fat Suppression
Magnetic Resonance
Fluid Suppression
T2-weighted
T2-weighted FLuid
Attenuated Inversion
Recovery (FLAIR)
Magnetic Resonance
Fluid Suppression
T2-weighted
T2-weighted FLuid
Attenuated Inversion
Recovery (FLAIR)
Magnetic Resonance
Magnetic Resonance
Accentuating blood/calcium
T2
T2*
Magnetic Resonance
Cranial nerves
CN-7
CN-5
CN-8
FIESTA
High spatial resolution, high tissue-CSF contrast (T2 weighting)
Diffusion MR Imaging
NORMAL
CYTOTOXIC
EDEMA
Diffusion 
MR Signal 
Magnetic Resonance
Imaging Diffusion
Highly sensitive to
acute ischemia—
+ within a few hours!
No other imaging is
more sensitive to
acute ischemia!
Magnetic Resonance Angiography
Contiguous axial
“source” images…
…reformatted to “maximum
intensity projections” (MIP)
Multiple projections allow
3D-like display
Magnetic Resonance Angiography
MR Venogram
Superior sagittal sinus thrombosis
Magnetic Resonance Angiography
with Perfusion MR
MRA
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 that
hastens T1 relaxation of nearby water protons)
2. Normal blood-brain barrier keeps contrast out of brain!
Enhancement implies BBB either leaky or non-existent
Remember: Some structures live outside the BBB!
IV Contrast in Neuroimaging
Enhancement:
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
IV Contrast: Yes or No?
w/o contrast
•
•
•
•
•
•
•
Congenital malformations
Trauma
R/O stroke
R/O hemorrhage
Hydrocephalus
Dementia
Epilepsy
with contrast
•
•
•
•
Neoplasm
Infection
Vascular disease
Inflammatory disease
Always best to provide detailed indication!
Radiologist will protocol exam accordingly
MR vs. CT
CT
MR
Advantages:
Advantages:
• Simpler, cheaper, more accessible
• No absolute contraindications
• Much broader palette of tissue contrasts
(including functional and molecular) yields
greater anatomic detail and more
comprehensive analysis of pathology
• Fewer pitfalls in interpretation
• No ionizing radiation
• Better than MR for bone detail
• Direct multi-planar imaging
Disadvantages:
• IV contrast better tolerated
• Ionizing radiation
Disadvantages:
• IV contrast complications
• Higher cost, limited access
• Need recons for multi-planar
• Difficult for unstable patients
• Limited range of tissue contrasts
• Several absolute contraindications (cardiac
pacer, some aneurysm clips, etc.)
• Tolerated by claustrophobics
• Claustrophobics may need sedation
• Image interpretation more challenging
• Lacks bone detail
Introduction to
Neuroimaging
Aaron S. Field, MD, PhD
Assistant Professor of Radiology
Neuroradiology Section
University of Wisconsin–Madison