introduction to neuroimaging dr mohamed el safwany, md
TRANSCRIPT
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Introduction to Neuroimaging
Dr Mohamed El Safwany, MD.
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Intended Learning Outcomes
The student should be able to recognize an introduction to neuroimaging.
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Neuroimaging ModalitiesRadiography (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 (MRS)
• Functional MR (fMRI)
Nuclear Medicine
• Positron Emission Tomography (PET)
“Duplex”
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Radiography (X-Ray)
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Radiography (X-Ray)
Disorders of spine:• Trauma• Degenerative Disorders• Post-opeerative
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Fluoroscopy (Real-Time X-Ray)
Fluoro-guided procedures:• Angiography• Myelography
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Fluoroscopy (Real-Time X-Ray)
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Fluoroscopy (Real-Time X-Ray)Digital Subtraction Angiography
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Fluoroscopy (Real-Time X-Ray)Digital Subtraction Angiography
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Fluoroscopy (Real-Time X-Ray)
Myelography
Lumbar or cervical puncture
Inject contrast intrathecally with fluoroscopic guidance
Follow-up with post-myelo CT (CT myelogram)
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Ultrasound
carotid
US transducer
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Ultrasound
• Carotid stenosis• Vasospasm - Transcranial Doppler (TCD)• Infant brain imaging (open fontanelle = acoustic window)
• Noninvasive, well-tolerated, readily available, low cost• Quantitates blood velocity • Reveals morphology (stability) of atheromatous plaques
• Severe stenosis may appear occluded• Limited coverage, difficult through air/bone• Operator dependent
Indications:
Advantages:
Disadvantages:
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Ultrasound – Gray Scale
Gray-scale image of carotid artery
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Ultrasound – Gray Scale
Gray-scale image of carotid artery
Plaque in ICA
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Ultrasound - Color Doppler
Peak Systolic Velocity (cm/sec) ICA Stenosis (% diameter)
125 – 225 50 – 70
225 – 350 70 – 90
>350 >90
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Computed Tomography (CT)
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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 = “hyper-attenuating” or
“hyper-dense”
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Computed Tomography
Typical HU Values:
Air –1000Fat –100 to –40Water 0Other fluids (e.g. CSF) 0–20White matter 20–35Gray matter 30–40Blood clot 55–75Calcification >150Bone 1000Metallic foreign body>1000
Brain
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Computed Tomography
“Soft Tissue Window” “Bone Window”
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Computed Tomography
Scan axially……stack and re-slice
in any plane“2D Recons”
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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)
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Skull and skull base, vertebrae
Fractures
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Ventricles
Hydrocephalus
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Intracranial masses, mass effects
Solid mass Cystic mass
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Intracranial masses, mass effects
L hemisphere swelling Generalized swelling
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Acute Hemorrhage
Intraparenchymal Subarachnoid Subdural Epidural
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Acute Ischemia
Loss of gray-white distinction and swelling in known arterial territory
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Calcification
Hyperparathyroidism
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1. Rapid IV contrast bolus
2. Dynamic scanning during arterial phase
3. Advanced 2D and 3D Reconstructions: 2D multi-planar (sagittal, coronal) Volume–rendered 3D recons
CT Angiography
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CT Angiography - HeadCircle of Willis
Aneurysms
Vascular Malformations
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CT Angiography - Neck
Carotid
bifurcations
Vertebral arteries
Aortic arch
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• Atherosclerosis
• Thromboembolism
• Vascular dissection
• Aneurysms
• Vascular malformations
• Penetrating trauma
CT Angiography - Indications
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CT Perfusion CBV
CBF
MTT
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Hemodynamic Parameters Derived From Concentration-Time Curves
Artery
VeinBolus arrival
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Hemodynamic Parameter Maps
Transit Time (sec)
Blood Flow (mL/min/g)
Blood Volume (mL/g)
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• Spinal CT immediately following conventional
myelogram
• Cross-sectional view of spinal canal along with spinal
cord and nerve roots
• Assess spinal stenosis/nerve root compression
(e.g. disc herniation, vertebral fracture,
neoplasm)
CT Myelography
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CT Myelography
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CT Myelography
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Magnetic Resonance (MR)
Hydrogen proton in water or fat
MRI
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COMPUTER
Magnetic Resonance Imaging
magnetic field
RF
Transmitter Receiver
RF = Radio Frequency energy Received
signal
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“T1-weighted” “T2-weighted” w/ fat
suppression
Magnetic Resonance
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Magnetic Resonance
Arachnoid Cyst
T2T1
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NORMAL CYTOTOXIC EDEMA (Acute Ischemia)
Diffusion
MR Signal
Diffusion MR Imaging
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Magnetic ResonanceImaging Diffusion
Highly sensitive to acute ischemia—
+ within a few hours!
No other imaging is more sensitive to acute ischemia
although perfusion imaging
reveals hypoperfused tissue
at risk for ischemia
Acute left MCA infarction
DWI
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Magnetic Resonance Angiography
Axial “source” images… …reformatted to “maximum intensity projections” (MIP)
Multiple projections allow 3D-like displayNo need for IV contrast!
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MRA Perfusion MR
Magnetic Resonance Angiography with Perfusion MR
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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)
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1. CT: Iodine-based
Iodine is highly attenuating of X-ray beam (bright on CT)
MRI: Gadolinium-based
Gadolinium is a paramagnetic metal that hastens T1 relaxation of nearby water protons (bright on T1-weighted images)
2. Tissue that gets brighter with IV contrast is said to “enhance” (Brightness, in and of itself, is not enhancement!)
3. Enhancement reflects the vascularity of tissue, but…
The blood-brain barrier keeps IV contrast out of the brain!
Enhancement implies BBB is absent or dysfunctional
Remember: Some brain anatomy lives outside the BBB
IV Contrast in Neuroimaging
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EnhancementT1 T1+C
Hemorrhagic melanoma metastasis
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Question
State three different orientations of the brain?
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Assignments
5 Students will be selected for assignments.
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Suggested Readings
Sutton’s Radiology
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Thanks